zircon lu hf isotopic compositions of metaluminous and peralkaline a type granitic plutons of the emeishan large igneous province sw china constraints on the mantle source abstract permian a type granitoids of the emeishan large igneous province elip in the panxi region sw china are predominantly peralkaline and metaluminous in composition in situ zircon hf isotopic compositions along with whole rock trace element and nd isotopic data are used to examine the probable source characteristics of these a type granitic plutons zircons from the baima and taihe peralkaline plutons have weighted average ehf t values of 8 7 0 4 and 9 2 1 0 whereas the woshui and huangcao metaluminous plutons have differing ehf t values 8 6 0 2 and 5 8 0 3 respectively previous studies have suggested that the plutons were derived by differentiation e g fractionation or partial melting of mafic magmas from an enriched mantle source similar to oceanic island basalt with little or no contribution from the crust end t 1 3 to 3 2 zr nb 0 9 14 4 rb nb 0 1 8 4 and th ta t values of the woshui and baima plutons indicates that spatially and temporally associated peralkaline and metaluminous a type granitic rocks can originate from the same mantle source without crustal assimilation

carbonate factories a conundrum in sedimentary geology abstract describing characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums intricate and difficult problems having only conjectural answers that have occupied geologists for more than two centuries depositional features including components rock textures lithofacies platform types and architecture all vary in space and time as do the results of diagenetic processes on those primary features approaches to the study of carbonate rocks have become progressively more analytical one focus has evolved from efforts to build reference models for specific phanerozoic windows to scrutinize the effect of climate and long term oscillations of the ocean atmosphere system in influencing the mineralogy of carbonate components this paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate producing organisms during the mesozoic cenozoic while striving to minimize the uniformitarian bias our approach integrates estimates of changes in ca2 concentration in seawater and atmospheric co2 with biological evolution and ecological requirements of characteristic carbonate producing marine communities the underlying rationale for our approach is the fact that co2 is basic to both carbonates and organic matter and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification gross photosynthesis and hypercalcification are dependent largely upon sunlight while net primary production and e g subsequent burial of organic matter typically requires sources of new nutrients n p and trace elements our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle while identifying uncertainties that deserve further research with metazoan consumer diversity reduced by the end permian extinctions excess photosynthesis by phytoplankton and microbial assemblages in surface waters induced by moderately high co2 and temperature during the early mesozoic supported proliferation of non tissular metazoans e g sponges and heterotrophic bacteria at the sea floor metabolic activity by those microbes especially sulfate reduction resulted in abundant biologically induced geochemical carbonate precipitation on and within the sea floor for example with the opening of tethyan seaways during the triassic massive sponge microbe boundstones the benthic automicrite factory formed steep massive and thick progradational slopes and locally mud mounds as tectonic processes created shallow epicontinental seas photosynthesis drove lime mud precipitation in the illuminated zone of the water column the resulting neritic lime mud component of the shallow water carbonate factory became predominant during the jurassic paralleling the increase in atmospheric pco2 while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans phytoplankton and zooplankton with atmospheric pco2 declining through the cretaceous the potential habitats for neritic lime mud precipitation declined at the same time peak oceanic ca2 concentrations promoted biotically controlled calcification by the skeletal factory with changes produced by extinctions and turnovers at the cretaceous tertiary boundary adaptations to decreasing ca2 and pco2 coupled with increasing global temperature gradients i e high latitude and deep water cooling and strategies that efficiently linked photosynthesis and calcification promoted successive changes of the dominant skeletal factory through the cenozoic larger benthic foraminifers protist protist symbiosis during the paleogene red algae during the miocene and modern coral reefs metazoan protist symbiosis since late miocene

depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

permian rifting related fayalite syenite in the panxi region sw china abstract within the panxi rift of the permian emeishan large igneous province elip sw china a 20 km 2 quartz bearing fayalite syenitic pluton intrudes the 260 ma baima igneous complex bic the fayalite syenite is dated using shrimp zircon u pb techniques at 252 2 5 ma the panxi fayalite syenite is mainly composed of alkali feldspar ferroan augite fayalite quartz and fe ti oxides and contains 61 8 63 7 wt sio 2 5 0 7 3 wt fe 2 o 3 t and 9 9 12 1 wt total alkalis belonging to an a type variety of ferroan alkalic metaluminous granitoids the fayalite syenite displays positive eu anomalies eu eu 0 9 8 9 and is enriched in lree la yb n 6 6 11 5 the nd values and 87 sr 86 sr initial ratios of the fayalite syenite range from 1 3 to 1 9 and from 0 7035 to 0 7068 respectively the fayalite syenite and the bic had the same mantle source however the 8 myr age gap between them suggests the fayalite syenite formed by remelting of underplated mafic magmas injected into the crust during elip magmatism the ages of the fayalite syenite and bic are coincident with two permian mass extinction events and suggest that elip may have influenced both

derivation of the 1 0 0 9 ga ferro potassic a type granitoids of southern norway by extreme differentiation from basic magmas major and trace elements sr and nd isotopic data as well as mineral compositions are presented for a selection of the 1 0 0 9 ferro potassic a type granitoids bessefjellet rustfjellet verhuskjerringi valle holum svofjell handeland tveit aseral lyngdal gabbronorites that occur close to the mandal ustaoset line mul of southern norway these hornblende biotite granitoids hbg define an extensive differentiation trend ranging from gabbronorites 50 wt sio 2 to granites 77 wt sio2 this trend is interpreted as resulting from extreme fractional crystallization of several basaltic magma batches with similar major and trace elements compositions at 930 ma the hbg suite displays a narrower range in isr 0 7027 0 7056 than in end t 1 97 down to 4 90 suggesting some assimilation of a rb depleted lower crust afc process or and source variability an age of 929 47 ma is given by a rb sr isochron on the holum granite sri 0 7046 0 0006 mswd 1 7 geothermobarometers indicate a low pressure of emplacement 1 3 2 7 kbar and an oxygen fugacity close to nno high liquidus temperatures are given by the apatite saturation thermometer 1005 1054 c and are in agreement with results from other studies the basaltic parent magmas of the hbg suite are partial melts of an hydrous mafic potassic source lying either in the lithospheric upper mantle or in the mafic lower crust derived from it this contrasts with the 930 ma anorthosite mangerite charnockite suite amc suite of the rogaland province for which a depleted lower crustal anhydrous gabbronoritic source has been indicated the present data imply the penecontemporaneous melting of two contrasting sources in southern norway the source duality could result from an increasing degree of metamorphism amphibolite to granulite from east to west an horizontal stratification of the lower crust or from the stratification of the lithosphere melting of the lower crust or upper mantle it may also indicate that the amc and hbg suites formed in two distinct crustal segments the linear alignment of the hbg suite along the mandal ustaoset shear zone suggests that a linear uprise of the asthenosphere following a lithospheric delamination under this structure could be the vector of the mantle heat 2003 elsevier science b v all rights reserved

episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

elemental and sr nd isotope geochemistry of two neoproterozoic mangerite suites in se brazil implications for the origin of the mangerite charnockite granite series abstract neoproterozoic 625 ma mangerites are the dominant rock type in a 100 km long belt of deformed tabular bodies in the socorro guaxupe nappe sgn a high grade terrane southwest of the sao francisco craton southeastern brazil the mangerites form two suites sao pedro de caldas shows a wide compositional variation and abundant felsic rocks mangerite hornblende granite leucogranite initial 87 sr 86 sr of 0 707 and initial e nd of 4 to 5 divinol ndia is dominated by more mafic mangerites with minor charnockite granite and diorite and has initial 87 sr 86 sr of 0 710 and initial e nd of 10 to 12 the probable sources of the sao pedro de caldas mangerites were granulites depleted by previous melting events in radiogenic elements and the light rare earth element primary melts of sao pedro de caldas were generated at 950 c p 10 kbar from a biotite free and k feldspar bearing source with plagioclase as an important residual phase the amount of melting was low as required by low mg enrichment in nb and ta relative to potential sources and high nb ta and was probably controlled by exhaustion of k feldspar in the source contribution from infracrustal mafic melts cannot be ruled out and would help explain the weakly negative e nd and high nb but is not essential the divinol ndia rocks depart from typical within plate mangerites towards more mafic rocks with orogenic signatures e g higher mg sr ca lower zr radiogenic isotope data require sources with greater crustal residence time than those envisioned for sao pedro de caldas elemental data require that these sources were more depleted e g higher k rb granulites with these characteristics are exposed in the northern portion of the sgn these were probably melted at slightly higher temperatures than the sao pedro de caldas suite 970 c before a sufficient amount of melt was generated and the magmas could leave their sources in this case k feldspar was exhausted and plagioclase in amounts exceeding those of the granite minimum was dissolved

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

dynamics of tethyan carbonate platforms tethyan carbonate platforms are relatively short lived depositional systems which were born developed died and sometime resurrected in a tectonically active area in contrast with pericratonic platforms which are generally huge in size hundreds of kilometers across and show wide facies belts very gentle slopes ramps and transitional boundaries tethyan carbonate platforms are smaller tens of kilometers and have steep slopes generally faulted boundaries and abrupt facies changes it appears clear that the overall control on these two contrasting systems is the geodynamic milieu relatively stable in the first case where eustatic oscillations and long term subsidence are probably the main dictators quite dynamic and aggressive in the second one where carbonate platforms developed through the entire geodynamic spectrum rifting transtension transpression and collision of the wilson cycle primary controls on tethyan carbonate platforms appear to be tectonics most important and eustatic sea level oscillations which determine their emplacement growth and decay their overall shape and architecture are a function of these factors secondary factors affecting tethyan carbonate platform evolution are physiography oceanographic conditions and biology as a function of geologic time especially across the mesozoic tertiary boundary facies and facies distribution and to a lesser extent their shape are controlled by thesemore variables less

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

petrogenesis of early permian olivine bearing cumulates and associated basalt dykes from bocca di tenda northern corsica implications for post collisional variscan evolution abstract the early permian gabbroic sequence of bocca di tenda northern corsica intrudes a plutonic suite made of hornblende granitoids and is crosscut by basalt dykes with chilled margins the gabbroic sequence includes olivine gabbronorite cumulates that consist mainly of euhedral olivine fo78 72 and plagioclase an68 61 and poikilitic clinopyroxene mg 0 85 0 80 orthopyroxene and ti pargasite pyroxenes from the olivine gabbronorites have 18 o values of 6 3 to 6 7 which are evidence for the involvement of a crustal component in the petrogenesis of these rocks the basalts have mg values of 57 to 53 and chondrite normalised patterns characterised by a steady decrease from lree to hree relative to modern n morb they show also moderate enrichment of nb and ta over zr and hf which are in turn slightly enriched over y and hree the olivine gabbronorites and basalts show overlapping nd isotopic compositions initial nd of 2 4 to 1 4 and of 3 0 to 1 5 respectively and have clinopyroxenes with nearly parallel incompatible trace element patterns thus revealing that these two rock types formed by melts with similar compositions most likely the primary melts of bocca di tenda gabbroic sequence were slightly enriched in most incompatible elements and nd isotopic compositions relative to modern n morb

petrology and geochemistry of syn to post collisional metaluminous a type granites a major and trace element and nd sr pb o isotope study from the proterozoic damara belt namibia abstract leucocratic a type granites of the proterozoic damara orogen namibia are a distinctive groups of rocks based on their mineralogical chemical and isotopic characteristics a type granites can be distinguished from the leucocratic s type granites on the basis of fe rich amphibole and biotite and higher abundances of zr nb y and lree but lower values of 87 sr 86 sr 500 ma and 18 o in the a type granites in comparison with a type granites described in the literature the damaran a type granites are enriched in cao al2o3 mgo feo ba sr and eu but depleted in ga and zn low k rb rb sr rb ba and sr ba ratios indicate that these melts are not fractionation products of calc alkaline source rocks and therefore these chemical criteria are interpreted as a feature of the source rocks i e undepleted metatonalites the a type granites have high calculated zircon and monazite saturation temperatures mostly in excess of 800 c and it is concluded that these granites represent high temperature partial melts the relationship between major and trace element data and isotopic composition demonstrates that the a type granites originate from several sources and have undergone different processes the lack of evidence for shallow crustal contamination e g lack of country rock xenoliths the low viscosities of the melts as inferred from their high calculated temperature and their high nd concentrations relative to the country rocks suggest that the isotopic characteristics were acquired from an enriched mantle initial sr isotopic compositions vary over a narrow range 0 70486 0 70928 but the initial nd isotopic compositions vary considerably with initial end values between 0 03 and 6 35 this wide range in the nd isotope values is probably the result of interaction of mantle derived magmas with crustal rocks a type granites at baukwab have negatively correlated initial end values and 207 pb 204 pb and 206 pb 204 pb ratios indicating interaction of mantle derived magmas low initial end low 207 pb 204 pb and 206 pb 204 pb with continental crust high initial end high 207 pb 204 pb and 206 pb 204 pb a type granites from albrechtstal and oetmoed have positively correlated pb isotope ratios and show also positive correlations between nd isotopes and pb isotopes suggesting interaction of at least two different source materials the relationship between nd isotopes and nd concentrations precludes simple assimilation instead mixing of different sources seems to be more realistic for the a type granites from oetmoed oxygen isotopes are negatively correlated with sr isotopes indicating that the crustal end member has high 18 o values and rather low initial 87 sr 86 sr ratios whereas a hypothetical mantle component has lower 18 o values but higher initial 87 sr 86 sr ratios the chemical and isotope data suggest that the damaran a type granites were generated by a variety of processes including partial melting of mantle derived tonalitic sources limited crystal fractionation and interaction of these magmas with crustal material these data indicate that the damaran a type suites mark episodes of continental growth during which mantle material although limited in extent is added to the crust

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

petrogenetic relationships between peralkaline rhyolite dykes and mafic rocks in the post variscan gabbroic complex from bocca di tenda northern corsica france the lower permian complex from bocca di tenda corsica island france consists of a gabbroic sequence crosscut by chilled dykes ranging in composition from basalt to trachyandesite and peralkaline rhyolite the gabbroic sequence is mostly composed of olivine gabbronorites quartz gabbronorites diorites locally displaying high ilmenite amounts and hornblende rich tonalites the quartz gabbronorites diorites and the hornblende rich tonalites have similar initial end values 0 9 to 1 1 and record a fractional crystallization process driven by separation of plagioclase pyroxene and ilmenite the olivine gabbronorites have slightly higher initial end than the quartz gabbronorites diorites and the hornblende rich tonalites thereby documenting that the early evolution of the melts that gave rise to the gabbroic sequence was controlled by concomitant fractional crystallization and crustal assimilation the trachyandesite dykes are rare and rich in dark mica the selected trachyandesite has initial end of 0 4 which is slightly lower than the end of the basalt dykes the basalt and the trachyandesite dykes are most likely genetically related through a process of fractional crystallization controlled by segregation of plagioclase clinopyroxene and minor ilmenite and assimilation of crustal material the peralkaline rhyolites have initial end values ranging from 0 3 to 0 3 whole rock chemical variations and trace element compositions of na amphibole arfvedsonite indicate that the peralkaline rhyolite dykes record a process of fractional crystallization mainly controlled by separation of alkali feldspar and minor ilmenite and arfvedsonite a plausible petrogenetic hypothesis for the genesis of the peralkaline rhyolite melts implies a protracted process of fractional crystallization from the trachyandesitic melts this fractionation process would be initially ruled by separation of plagioclase dark mica and minor ilmenite an alternative hypothesis for the origin of the peralkaline rhyolite melts implies partial melting of nearly coeval amphibole rich mafic intrusives which formed by crustally contaminated mantle derived melts the genesis of the peralkaline rhyolites is in any case correlated with mantle derived melts that experienced extensive crustal contamination

oxfordian ramp system la manga formation in the bardas blancas area mendoza province neuquen basin argentina facies and depositional sequences abstract the outcrops of the oxfordian la manga formation at bardas blancas neuquen basin west central argentina allow the recognition of six different depositional facies a to f on the basis of sedimentological analysis taphonomic attributes and microfacies studies these depositional facies correspond to outer ramp a middle ramp b inner ramp oolitic shoal c inner ramp margin patch reef d lagoon deposits e and a paleokarst surface f outer ramp deposits which are not completely represented consist of greyish carbonate beds where the fabric of the shell beds gryphaeids reflects the action of waves and currents middle ramp deposits consist of a packstone grainstone lithofacies indicating the importance of storm processes and is dominated by ooids intraclasts pelecypods echinoderms and gastropods which accumulated on a middle ramp storm dominated shoreface trace fossils belong to the skolithos and cruziana ichnofacies characterizing the upper lower and middle shoreface setting respectively the inner ramp deposits consist of oolitic grainstones and subordinate packstones shoal with a small sponge bioherm at the base different types of ooids peloids and coated grains are abundant as well as skeletal fragments of molluscs echinoderms and corals lithofacies and microfacies studies suggest a high energy and shallow water depositional setting the inner ramp margin deposits consist of reef core facies fore and back reef facies characterized by a scleractinian community of relatively low generic diversity the rich associated fauna consists of bivalves echinoids serpulids bryozoans dasycladacean algae and cyanophytes as well as foraminifers and ostracods the growth forms of the corals are indicative of shallow well illuminated water both the back and fore reef deposits suggest intensive reworking by storm waves or currents the lagoon deposits consist of bioclastic and peloidal wackestones as well as bioclastic intraclastic packstones which accumulated on a lagoon under intermittently agitated water in a shallow subtidal to intertidal settings a stratiform breccia with both matrix and clasts supported fabrics is interpreted as paleokarst the clasts are derived from the rocks of oolitic shoal and inner ramp margin patch reef the six depositional facies are included into a major organizational framework of three third order depositional sequences ds 1 ds 2 ds 3 mainly represented by transgressive and highstand systems tracts stages with sequence boundaries of regional importance the general depositional evolution is here related to the slow subsidence experienced during the oxfordian earliest kimmeridgian time related to tectonic inversion in the neuquen basin a four step architectural and sedimentary schematic model of the response of the platform to sea level changes is proposed

origin and timing of the post variscan gabbro granite complex of porto western corsica the post variscan complex of porto consists of metaluminous to slightly peraluminous a type biotite granites mingled with gabbro dioritic rocks and late dykes with basaltic to trachyandesitic composition u pb zircon dating by la icp ms on two mafic intrusive samples constrains the time of the gabbro granite crystallisation at 281 3 ma and 283 2 ma hornblende 40ar 39ar ages from a late trachyandesite dyke date the dyking event at 280 2 ma which is within error the u pb zircon ages of the intrusives biotite granites show variable major and trace element compositions and similar initial end 0 3 to 0 9 whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that the granites are genetically linked essentially through fractional crystallisation of feldspars and minor allanite on the basis of whole rock chemistry e g initial end 4 9 to 1 7 and trace element clinopyroxene compositions we have ascertained that the mafic intrusives and basic dykes formed from isotopically depleted mantle source derived melts with similar trace element signature these basic melts experienced slightly different evolutionary histories controlled by fractional crystallisation and crustal contamination mainly by the acid magma that gave rise to the associated biotite granites but also by the enclosing older variscan granitoids u pb zircon data suggest that the porto complex was affected by hydrothermal fluid circulation at 259 9 ma

hydrogen and oxygen isotope geochemistry of a type granites in the continental margins of eastern china hydrogen and oxygen isotope studies of both whole rock and mineral separates were carried out for five representative atype granites in eastern china from north to south the whole rock d d and d 18 o values vary from 2145 to 282 and from 21 2 to 5 0 for nianzishan pluton from 2135 to 2110 and from 1 6 to 6 7 for shanhaiguan pluton and from 2145 to 2111 and from 1 5 to 9 1 for laoshan massif respectively the highest whole rock dd and d 18 o values are observed in suzhou pluton and range from 281 to 259 and from 3 5 to 9 2 respectively homogeneous d d and d 18 o values are found in kuiqi massif ranging from 2113 to 299 and from 5 6 to 8 5 respectively the results show that the large variabilities in the hydrogen and oxygen isotope ratios are mainly related to the diverse processes of magma evolution such as magma degassing fractional crystallization as well as post magmatic alteration by local meteoric water under subsolidus conditions the initial d d and d 18 o values of the a type granites in eastern china are constrained to be about 250 5 and 7 5 1 0 respectively this is consistent with mantle like protoliths for granitoid rocks and thus precludes the possibility that the a type granites is derived from the anatexis of the 18 o rich upper crust however recycling of crustal materials by earlier subduction cannot be excluded in the processes of generating the a type granitic magmas the variation in the ddepletion of the granites with latitude implies that the paleogeographic localities of the a type granites have not changed significantly since the mesozoic q 2000 elsevier science b v all rights reserved

anorogenic magmatism chemical evolution of the mount el sibai a type complex egypt and implications for the origin of within plate felsic magmas the mount el sibai alkaline granitic complex eastern egypt forms an elongate body which was emplaced at the extension of a nw trending shear zone within voluminous calc alkaline pan african host rocks the complex is hypersolvus in nature and is composed of perthite quartz alkali amphibole fe rich biotite and accessory zircon apatite fluorite aenigmatite and ilmenite data on mineral chemistry show that the amphibole ranges in composition from hastingsite to pure end member arfvedsonite and the biotite is largely titaniferous annite geochemically the complex is highly evolved in composition with 72 78 wt sio 2 and di values of 85 98 is enriched in rb 48 291 ppm nb 28 237 ppm y 47 269 ppm zr 58 618 ppm ga 17 41 ppm and the ree 176 437 ppm and depleted in al mg ca sr and eu the complex exhibits a wide trace element compositional range the ree patterns are uniform parallel to sub parallel fractionated la yb n 4 7 lree enriched over hree and show prominent negative eu anomalies the albitized facies of this complex shows the highest concentrations of large ion lithophile lil and high field strength hfs elements the complex exhibits mineralogical and chemical traits typical of within plate a type granites mount el sibai is interpreted to have been developed during a phase of cooling relaxation crustal attenuation and fracturing of the newly formed pan african crust results of geochemical modelling indicate that the magma may have formed by a large degree of batch partial melting f 0 65 of pan african calc alkaline rocks which had been metasomatized metasomatism of source rocks may have been caused by a na f rich fluid phase compositionally similar to that which produced the albitized facies the volatile flux may have caused fenitization type reactions along fissures and re activated pan african fractures prior to anatexis and is considered to have played a role as an important agent of heat transfer temperature necessary for crustal anatexis is likely to have been produced as a result of shear heating caused by a rapid change in the direction of plate motions beneath eastern egypt during early palaeozoic times the confining pressure must have been released by fissuring of the crust magma ascent may have been facilitated by reactivation of pre existing faults and shear zones this model may have wider implications for the generation of within plate felsic magmas in other regions

evolution of the corsica sardinia batholith and late orogenic shearing of the variscides the corsica sardinia batholith formed in the late carboniferous permian along the northern gondwana margin one or more of the following processes may have raised the variscan geotherm enhancing melting of the crust and uppermost mantle such as i break off and detachment of the rheic oceanic slab ii mantle delamination due to gravitational re equilibration of thickened crust iii shear heating iv advection of mantle derived melts and v concentration of heat producing elements in this paper we present a simple one dimensional thermal model to explain the origin of the batholith in a geodynamic setting consistent with intraplate shearing between gondwana and cadomian avalonian blocks input parameters and boundary and initial conditions of the model crust are derived from a careful re examination of large petrological geochronological and structural datasets all parameters are varied within a range of geologically realistic values to reproduce thermal histories related to different tectonic processes and the reliability of models is quantitatively evaluated by comparing the simulated geotherms with a large dataset of pressure temperature time p t t constraints the best fit to p t t constraints is obtained for i break off in the late devonian early carboniferous ii decreasing exhumation rates from 340 to 280 ma and iii transpression at high average strain rates mostly coeval with the peak of high t low p metamorphism

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

isotopic geochemistry zircon u pb ages and hf isotopes of a type granites from the xitian w sn deposit se china constraints on petrogenesis and tectonic significance abstract zircon u pb geochronological geochemical and petrological analyses have been carried out on the xitian granite emplaced in the middle part of shi hang zone which is closely related to the economically important xitian tungsten tin deposit in hunan province southeast china la icp ms zircon u pb dating of two representative samples yielded weighted means 206 pb 238 u age of 151 7 1 2 ma and 151 8 1 4 ma these granites are comprised mainly of k feldspar quartz plagioclase fe rich biotite and minor fluorite and are characterized by enrichments in rb th rees total ree 159 351 ppm and hfses e g zr and y but depletions in ba sr p eu and ti they are metaluminous to weakly peraluminous and show a clear a type granite geochemical signature with high sio 2 73 44 78 45 wt total alkalis na 2 o k 2 o 2 89 8 98 wt fe 2 o 3 mgo ratios and low p 2 o 5 cao mgo and tio 2 contents in situ zircon hf isotope analysis suggests their e hf t values ranging from 7 43 to 14 69 sr nd isotope data show their e nd t values in the range of 9 2 to 7 3 with corresponding t dm2 ages of 1 72 1 56 ga these characteristics indicate that the xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle derived materials combined with previous geochemical and isotopic data it is derived that mantle crust interaction was gradually enhanced from the early to late stages of magmatism the ore forming materials and fluids of the xitian w sn deposit are mainly produced by the early yanshanian granitic magmatism which is also responsible for the late jurassic ca 152 ma a type granitic rocks that host the w sn polymetallic deposits distributed along the shi hang zone implying a significant mesozoic extensional event in southeast china likely caused by the subduction of the paleo pacific plate

hf isotopes in zircon reveal contrasting sources and crystallization histories for alkaline to peralkaline granites of temora southeastern australia peralkaline granites exhibit the hallmark features of a type igneous rocks but strongly differentiated chemistry and intense hydrothermal alteration camouflage their ultimate origins we present the first in situ hf isotope data from zircons of peralkaline granites aimed at clarifying the protoliths of these plutons and their genetic relationship to associated metaluminous weakly peraluminous granites this study used rocks of the devonian narraburra complex in southeastern australia and found that correlations between hf isotopes and trace element ratios reveal fundamentally different origins for the nonperalkaline and peralkaline granites the latter have a depleted mantle like ancestry whereas a weakly peraluminous rock formed from melts of older arc crust that were modified by interaction with juvenile probably alkaline magmas juxtaposition of crust and mantle derived magmas reflects the high heat flow and lithosphere scale faults associated with continental extension and explains the diversity of a type granites

growth dynamics and ecology of upper jurassic mounds with comparisons to mid palaeozoic mounds the mid palaeozoic including the late jurassic was a time of both widespread coral reef growth and pronounced mound formation a comparison of mound features and their general setting highlights despite all differences general similarities in overall growth dynamics mound formation was frequently driven by discontinuous patterns particularly by background sedimentation in many examples episodes of mound stabilisation by early lithification growth of microbolite crusts and winnowing of fines was followed by growth episodes of benthic fauna under reduced to negligible background sedimentation this pattern of variable sedimentation and organic buildups may have occurred in different orders and magnitudes inducing a fractal pattern in some mound complexes a composite approach in estimating growth rates of mounds demonstrates that highfrequency oscillations necessary for growth of most mounds might have ranged from a few thousand years to 4th and 5th order milankovich cycles that were superimposed by autocyclic factors d 2001 elsevier science b v all rights reserved

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

endorheic exorheic transitions of the rio grande and east african rifts this research was supported by nsf ear 1516680 and spanish government project mite cgl2014 59516

alkali pyroxenes and amphiboles a window on rare earth elements and other high field strength elements behavior through the magmatic hydrothermal transition of peralkaline granitic systems peralkaline granites and pegmatites are a prime repository of ree and hfse critical raw materials although it is accepted that magmatic processes are fundamental in concentrating these metals the role of hydrothermal fluids in concentrating and fractionating these elements remains unclear this paper investigates the global reproducibility of the magmatic hydrothermal evolution of alkaline silica saturated systems using alkali pyroxene and amphiboles from six alkaline complexes these minerals contain significant amounts of ree and other hfse and pyroxene is stable throughout the magmatic and hydrothermal stages amphibole consists of mostly unzoned arfvedsonite leakeite and katophorite while pyroxene is always aegirine two types of aegirine were defined in all complexes type i aegirine is zoned its core is enriched in ca ree zr hf sc and sn and the rims in na fe3 and contains secondary rare metal bearing minerals and fluid inclusions type ii aegirine replaces amphibole and is oscillatory zoned we interpret the amphiboles and ree rich cores of type i aegirine to have grown during the magmatic stage whereas the rims of ree poorer type i and ii aegirine are formed during the hydrothermal stage during magmatic crystallization ree intake into amphiboles and pyroxene as well as lree hree fractionation were favored by their crystallographic properties and by competition among them and other minerals during subsequent hydrothermal stages ree and other hfse were remobilized locally reconcentrated and fractionated in mineral pseudomorphs and secondary pyroxene these observations point out the importance of studying rock forming minerals such as pyroxenes and amphiboles to unravel geological events controlled by common processes globally

rock strength along a fluvial transect of the colorado plateau quantifying a fundamental control on geomorphology a b s t r a c t bedrock strength is a key parameter that influences slope stability landscape erosion and fluvial incision yet it is often ignored or indirectly constrained in studies of landscape evolution as with the k erodibility parameter in stream power models empirical datasets of rock strength suited to address geomorphic questions are rare in part because of the difficulty in measuring those rocks at earth s surface that are heterolithic weak or poorly exposed here we present a large dataset of measured bedrock strength organized by rock units exposed along the length of the trunk green colorado river through the iconic colorado plateau of the western u s measurements include field compressive tests fracture spacing and selby rock mass strength at 168 localities as well as 672 individual tensile strength tests in the laboratory tensile strength results are compared to geomorphic metrics of unit stream power river gradient and channel and valley bottom width through the arid colorado plateau where the influence of bedrock is intuitive but unquantified our dataset reveals logical trends between tensile and compressive strength as well as between strength rock type and age in bedrock reaches of the fluvial transect there is a positive rank correlation and a strong power law correlation between reach averaged rock strength and unit stream power as well as a linear relation between tensile strength and river gradient expected relations between fracture spacing and topography are masked partly by the massive yet weak sandstones in the dataset to constrain values for weak rock types such as shale we utilize the inverse power law scaling between tensile strength and valley bottom width to estimate their effective tensile strength results suggest that tensile strength varies to at least an order of magnitude smaller values than evident with directly testable rocks in this landscape and values for erodibility k in numerical simulations may be informed by this dataset in terms of landscape evolution these results support the finding that equilibrium adjustment to bedrock strength not differential uplift or transient incision is the first order control on large scale fluvial geomorphology in the colorado plateau this has broad implications for the interpretation of topography in terms of tectonic drivers

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

drainage systems and the development of normal faults an example from pleasant valley nevada abstract drainage systems in regions of active extension contain information about fault zone structure and development and particularly about the lateral growth of individual fault segments that is difficult to obtain by more conventional means such as the dating of sedimentary material we investigate drainage fault interaction in pleasant valley nevada where a large normal faulting earthquake occurred in 1915 we find geomorphological evidence for a propagation increase in length of several km at both ends of one of the 1915 fault segments at one end we estimate the propagation rate to be about 50 m per earthquake this estimate is uncertain but is within the range predicted by theoretical models of fault growth drainage along the axes of half graben in this region may be influenced by the spacing of tilted fault blocks the highest valleys are also the narrowest whether the axial streams succeed in reaching lower neighbouring sinks depends on whether sedimentation rates are able to keep basins filled to the levels of the basement highs that separate half graben of opposite polarity a knowledge of modern drainage fault interactions may help predict drainage systems and the position of potential syn rift reservoir sediments in older extensional terrains where fault configurations but not facies distributions are known from seismic reflection surveys

an earth moon silicon isotope model to track silicic magma origins abstract a comparison between terrestrial and lunar igneous rocks reveals that si isotope compositions become slightly though significantly enriched in heavy isotopes from basalts to granites and anorthosites as a function of the rock sio 2 concentration and or tectosilicate content this is interpreted as the result of a global igneous differentiation process that leads to an increased amount of tectosilicates in the rocks this relationship of increasing degree of melt polymerization with increasingly heavy silicon isotope composition is particularly apparent in lunar rocks the terrestrial trend however is more scattered given the sensitivity of si isotopes to water rock interactions it is likely that the more erratic terrestrial trend reveals the involvement of water that does not occur on the moon hence si isotopes appear to reflect the occurrence of low temperature water rock interaction products like clay minerals in the source of peraluminous leucogranites conversely the heavy silicon isotope composition of some andesites possibly trace the input of fluids involved in subduction zones and or interaction of the oceanic crust with isotopically heavy seawater before subduction

postcollisional granites in the south tien shan variscan collisional belt kyrgyzstan abstract two major types of the potassium rich postcollisional granites of permian age were studied in the south tien shan variscan collisional belt the first type metaluminous granites of the jangart complex are located along the southeastern boundary of this belt with the precambrian tarim block the plagioclase rims on k feldspar megacrysts rapakivi texture extremely high feot feot mgo ratio indications of the low h2o and o2 fugacities high concentrations of the incompatible elements especially light rare earth elements lree ba nb along with heightened contents of the compatible elements especially ni cr and moderately initial 87sr 86sr ratio sr0 0 7075 make those granites similar to other rapakivi granites the second type peraluminous granites of the inylchek complex is located along the northwestern boundary of the belt with the caledonian kazakh microcontinent those granites are rich in f b li rb cs sn ta and heavy rare earth elements hree but are poor in ba sr ni and cr and are characterized by the relatively high initial 87sr 86sr ratio sr0 0 7098 li mica granites are distributed widely among them the granites of a transitional type uchkoshkon complex occupy an intermediate geographic position between major granite types the initial sr isotopic composition of the transitional granites varies widely sr0 from 0 7080 to 0 7256 the variation in chemical composition of the coeval postcollisional granites across the collisional belt together with the variability of initial sr isotopic ratios of the transitional granites are thought to indicate basement heterogeneity this heterogeneity in turn is probably related to thrusting of the tarim block under south tien shan during the collision

dynamic ridges and valleys in a strike slip environment strike slip faults have long been known for characteristic near fault landforms such as offset rivers and strike parallel valleys in this study we use a landscape evolution model to investigate the longer term catchment wide landscape response to horizontal fault motion our results show that strike slip faulting induces a persistent state of disequilibrium in the modeled landscapes brought about by river lengthening along the fault alternating with abrupt shortening due to stream capture the models also predict that in some cases ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion we find that ridge migration happens when slip rate is slow enough and or soil creep and river incision are efficient enough that the landscape can respond to the disequilibrium brought about by strike slip motion regional rock uplift relative to baselevel also plays a role as topographic relief is required for ridge migration in models with faster horizontal slip rates stronger rocks or less efficient hillslope transport ridge mobility is limited or arrested despite the continuance of river lengthening and capture in these cases prominent steep fault facing facets form along well developed fault valleys comparison of landscapes adjacent to fast slipping 30 mm yr and slower slipping 1 mm yr or less strike slip faults in california usa reveals features that are consistent with model predictions our results highlight a potential suite of geomorphic signatures that can be used as indicators of horizontal crustal motion and geomorphic processes in strike slip settings even after river capture has diminished or erased apparent offset along the fault

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

petrogenesis and tectonic implications of late mesoproterozoic a1 and a2 type felsic lavas from the huili group southwestern yangtze block this paper presents new la icp ms zircon u pb chronology whole rock geochemical and zircon hf isotopic data for the felsic lavas of the huili group from the southwestern yangtze block la icp ms zircon u pb dating shows that these rocks were emplaced in late mesoproterozoic time 1028 to 1019 ma relative to typical i type and s type granitoids all the samples are characterized by low sr and eu and high high field strength element contents high t feo mgo enriched rare earth element compositions and negative eu anomalies indicating that they share the geochemical signatures of a type granitoid they can be further divided into two groups group i and group ii group i are a 1 type felsic rocks and were produced by fractional crystallization of alkaline basaltic magmas the group ii felsic lavas belong to the a 2 type and were derived by partial melting of a crustal source with mixing of mantle derived magmas both group i and group ii felsic lavas may erupt in a continental back arc setting the coexistence of a 1 and a 2 type rocks in the southwestern yangtze block suggests that they can occur in the same tectonic setting

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

palaeoceanographic and palaeoclimatic reorganization around the middle late jurassic transition abstract a middle to upper jurassic succession of submarine hardgrounds overlain by nodular limestones is exposed in the jura mountains and in the helvetic of the swiss alps these sediments were accumulated along the northern shelf of the east west trending tethys seaway submarine hardgrounds and nodular limestones were also formed on the brianconnais high today outcropping in the middle penninic nappe pile of the alps hardgrounds record strong and persistent current activity along the northern tethys shelf and on the brianconnais high during the callovian and early oxfordian the transition from hardgrounds to nodular limestones corresponds to a major reorganization of tethys oceanography the change occurred in plicatilis ammonite zone middle oxfordian carbon isotope stratigraphy calibrated against an ammonite dated reference section in the french subalpine basin serves as a correlation tool between ammonite dated sections and successions with poor biostratigraphic resolution correlation demonstrates that the end of hardground formation was synchronous over wide parts of the northern tethys the change in shelf sedimentation coincides with a positive carbon isotope excursion with an amplitude of 1 5 the change in c isotope stratigraphy indicates that observed reorganization of current patterns along the northern tethys shelf was coupled with global change in oceanography and climate we propose that the change in northern tethys sedimentation was caused by opening of new seaways at a time of progressive collapse of pangaea

petrogenesis of the linxi granitoids northern inner mongolia of china constraints on basaltic underplating five representative granitoid plutons in the linxi area northern inner mongolia of china divided into two suites are mainly granodiorite and syenogranite and correspond to i and a type granites respectively zircon u pb dating yields an age of 230 ma but most ages range from 149 ma to 111 ma for intrusion of the five plutons suite 1 granitoids show lower sio2 66 1 72 51 and k2o higher al2o3 cao mgo feo and tio2 higher sr ba and eu and lower sm gd nb y and yb than suite 2 granitoids 71 73 78 14 sio2 modeling of major and trace elements shows that fractional crystallization of hornblende and lesser amounts of feldspars for suite 1 and plagioclase and alkali feldspar for suite 2 with overprint of magmatic hydrothermal fluids can explain the geochemical variations the linxi granitoids have initial end t values varying between 5 60 and 2 89 and initial 87 sr 86 sr t ratios ranging from 0 701764 to 0 707654 geochronology of inherited zircons coupled with the nd sr isotopic comparison between granitoids late jurassic basalts and proterozoic gneisses indicates that the linxi granitoids derive from a mixed source of dominantly underplated material or mafic magma with various amounts of the proterozoic gneiss basaltic underplating provides both material and heat to produce the late jurassic to early cretaceous granitoids variation of end t and 87 sr 86 sr t with age suggests involvement in the melting of increasingly greater amounts of the old lower crustal rock our refined equation yields less scattered nd isotope depleted mantle model ages the least fractionated granitoids from each suite have low ca sr rb sr rb ba and k ba ratios and hence represent parental magmas suite 1 parent magma is produced by dehydration melting or derives principally from the fluid metasomatized mantle melting of the underplated tholeiites and their differentiated products generates suite 2 parent magma d 2005 elsevier b v all rights reserved

extensional fault propagation folding and base level change as controls on growth strata geometries abstract outcrop and analogue modelling studies indicate that upward widening zones of distributed deformation often monoclinal folds form above blind normal faults and are particularly common features at the depositional surface during the early stages of rifting with increasing displacement strain such folds are cut by faults as they propagate upwards into the cover we use a kinematic model of fault propagation folding above a blind extensional fault together with a sedimentary model of coarse grained clastic deposition to investigate growth strata geometries associated with fault tip monoclines in particular we consider coarse grained deltaic deposition where sedimentary geometries are markedly different from the simple sub horizontal fill to the top sedimentation used in most growth strata models for a given fault dip and slip rate growth strata geometries are strongly influenced by the fault propagation to slip ratio p s and the width of the zone of distributed deformation however base level changes also act as fundamental controls on sequence development the results of a number of experiments compare favourably to well documented examples of growth strata this study highlights the importance of integrating structural and stratigraphic studies in interpreting both fault fold kinematics and the controls on stratigraphy kinematic studies need to address the depositional geometry of stratal surfaces whereas sequence stratigraphic interpretation of stratal patterns must deconvolve tectonic rotation and translation from depositional architecture

devonian a type granitic magmatism on the northern margin of the north china craton shrimp u pb zircon dating and hf isotopes of the hongshan granite at chifeng inner mongolia china abstract we report first data for the devonian hongshan a type granite along the northern margin of the precambrian north china craton the granite is rich in silica sio2 76 07 77 62 wt and alkalis na2o k2o 8 45 8 78 wt but poor in calcium cao 0 28 0 70 wt and magnesium mgo 0 08 0 20 wt chondrite normalized ree patterns for the samples from the hongshan granite show significant negative eu anomalies eu eu 0 13 0 19 they contain high rb ga y nb and zn but low ba and sr contents and in the multi element spider diagrams normalized to primitive mantle they show a similar pattern to that of a type granites such as negative ba nb ta sr p and ti anomalies geochemical plots also show an affinity with a type granites and suggest a post orogenic setting a2 type granite shrimp u pb zircon dating yielded a concordant weighted mean 206pb 238u age of 387 4 ma which defines a devonian magmatic event the zircons have negative ehf t of 8 4 to 11 5 and give old hf model ages of tdm2 2548 2820 ma mean 2667 ma most 176hf 177hf and ehf values display hf isotope evolutional line of the lower continental crust these results suggest that the hongshan granite originated from melting of archaean lower crust beneath the north china craton in a post orogenic extensional setting during the devonian

geochronological geochemical and sr nd hf isotopic constraints on the petrogenesis of late cretaceous a type granites from the sibumasu block southern myanmar se asia abstract the late cretaceous to paleogene granitoids occur widespread in the sibumasu block within myanmar se asia which show a close association with tin tungsten mineralization however the precise timing petrogenesis and tectonic significance of these granitoids are poorly constrained so far in this study we present a detailed study on geochronology elemental and sr nd hf isotopic geochemistry for the hermyingyi and taungphila granites in southern myanmar with the aim of determining their petrogenesis and tectonic implications la icp ms u pb dating of zircon grains from the two granites yield ages of 69 70 ma indicating a late cretaceous magmatic event these granitic rocks are weakly peraluminous and belong to the high k calc alkaline series they are both characterized by high sio2 k2o na2o feot feot mgo and ga al ratios and low al2o3 cao mgo p2o5 and tio2 contents enriched in rb th u and y but depleted in ba sr p and eu suggesting an a type granite affinity moreover they display prominent tetrad ree patterns and non charac trace element behavior which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration the granites belong to a2 type and probably formed at a high temperature and anhydrous condition they have zircon ehf t values from 12 4 to 10 0 and whole rock end t values from 11 3 to 10 6 with paleoproterozoic tdm2 ages 1741 1922 ma for both hf and nd isotopes geochemical and isotopic data suggest that these a type granites were derived from partial melting of the paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions without significant input of mantle derived magma and followed by subsequent fractional crystallization by integrating all available data for the regional tectonic evolution in se asia and adjacent regions we attribute the formation of the late cretaceous a type granites to a back arc extension in the hinterland behind the subduction zone which is induced by the rollback of the flat neo tethyan subducting slab around ca 70 ma

interaction between basic and acid magmas during the latest stages of the post collisional variscan evolution clues from the gabbro granite association of ota corsica sardinia batholith abstract the intrusive association of ota post variscan corsica sardinia batholith consists of mafic rocks and granites displaying mingling relations the mafic rocks are olivine gabbros to quartz diorites and the granites are subsolvus and characterised by biotite as the only mafic phase minor amounts of amphibole bearing granodiorites to granites develop along the contacts between mafic rocks and granites the rather high initial e nd 4 5 of the most primitive mafic sample indicates that parental basic melts had an extensive contribution from a depleted mantle source in the mafic rocks the decrease of initial e nd to 2 1 is associated with an increase of th and u concentrations in clinopyroxene thus indicating that the ota basic melts underwent a process of crustal contamination associated biotite granites have low initial e nd 0 4 and high th and u concentrations the chemical evolution of ota basic melts most likely occurred through fractional crystallisation and concomitant contamination with the acid magma that gave rise to associated biotite granites the incompatible element signature of late stage anhedral amphibole from variably evolved mafic rocks is similar thus suggesting that the whole ota mafic sequence recorded the contamination process possibly by percolation within the gabbroic crystal mush of a melt contaminated by the acid magma hybridisation between basic and acid magmas is also documented by contact amphibole bearing granitoids in particular major and trace element zoning of amphibole from granodiorites reveals that such a hybridisation was associated with reactions between crystals from the basic magma amphibole and clinopyroxene and the acid melt the occurrence of chemically homogeneous amphiboles in associated granites suggests that contact hybridisation comprised also a process of gradient induced chemical diffusion

oxfordian reef architecture of the la manga formation neuquen basin mendoza province argentina abstract the neuquen back arc basin is located on the west margin of the south american platform between latitudes 36 and 40 s the basin is famous for its continuous sedimentary record from the late triassic to cenozoic comprising continental and marine clastic carbonate and evaporitic deposits up to 2 600 m in thickness the stratigraphical and paleontological studies of the outcrops of the la manga formation argentina located near the bardas blancas region mendoza province 35 s and 69 o allow the reconstruction of the sedimentary environments of an oxfordian carbonate ramp where outer ramp middle ramp inner ramp oolitic shoal inner ramp margin patch reef lagoon and paleokarst were differentiated the reefs consist of back reef facies and in situ framework of coral boundstones that was formed at the top of shallowing upward succession coral reefs were analyzed by defining coral colonies shapes paleontological content coral diversity and taphonomy studies in some studied sections abundant fragments of gryphaeids encrusting bryozoans and isolated sponges provided a suitable substrate for coral colonization however other sections show an increase in the proportions of ooids peloidal and coral intraclasts the core reef facies is composed of white grey unstratified and low diversity scleractinian coral limestone dominated by robust and thinly branching corals with cerioid phocoid growths and massive coral colonies with meandroid thamnasteroid growth forms the assemblage is characterized by actinastraea sp australoseris sp thamnasteria sp and garateastrea sp internal facies organization and different types of coral colonies allow to recognize the development of varying framework as well as intercolony areas a superstratal growth fabric characterizes the coral assemblage on the basis of coral growth fabric branche and domal types the reef of la manga formation is considered a typical mixstones the intercolony areas consist of biomicrites and biomicrorudites containing abundant coral fragments parautochthonous gryphaeids and another bivalves ctenostreon sp gastropods harpagodes sp natica sp echinoderms test and spines plegiocidaris sp miliolids cayeuxia sp acicularia sp salpingoporella sp intraclasts ooids peloids and coated grains the domal growth forms are probably more protected against biological and physical destruction meanwhile delicate branching growth forms with very open and fragile framework were more affected and fragmented due to wave action and bioerosion the reef fabric shows different intervals of truncation as consequence of erosion resulting from coral destruction by storm waves or currents the maximum flooding surface separates oolitic shoal facies below from the aggradational and progradational coralline limestones facies above subsequent sea level fall and karstification 148 ma affected reef and oolitic facies

modes of extensional faulting controlled by surface processes we investigate the feedbacks between surface processes and tectonics in an extensional setting by coupling a 2 d geodynamical model with a landscape evolution law focusing on the evolution of a single normal fault we show that surface processes significantly enhance the amount of horizontal extension a fault can accommodate before being abandoned in favor of a new fault in simulations with very slow erosion rates a 15 km thick brittle layer extends via a succession of crosscutting short lived faults heave 10 km using simple scaling arguments we quantify the effect of surface mass removal on the force balance acting on a growing normal fault this leads us to propose that the major range bounding normal faults observed in many continental rifts owe their large offsets to erosional and depositional processes

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

bayesian noise reduction in arabia somalia and nubia arabia finite rotations since 20 ma implications for nubia somalia relative motion knowledge of nubia somalia relative motion since the early neogene is of particular importance in the earth sciences because it i impacts on inferences on african dynamic topography and ii allows us to link plate kinematics within the indian realm with those within the atlantic basin the contemporary nubia somalia motion is well known from geodetic observations precise estimates of the past 3 2 myr average motion are also available from paleo magnetic observations however little is known of the nubia somalia motion prior to 3 2 ma chiefly because the southwest indian ridge spread slowly posing a challenge to precisely identify magnetic lineations this also makes the few observations available particularly prone to noise here we reconstruct nubia somalia relative motions since 20 ma from the alternative plate circuit nubia arabia somalia we resort to trans dimensional hierarchical bayesian inference which has proved effective in reducing finite rotation noise to unravel the arabia somalia and arabia nubia motions we combine the resulting kinematics to reconstruct the nubia somalia relative motion since 20 ma we verify the validity of the approach by comparing our reconstruction with the available record for the past 3 2 myr obtained through antarctica results indicate that prior to 11 ma the total motion between nubia and somalia was faster than today furthermore it featured a significant strike slip component along the nubia somalia boundary it is only since 11 ma that nubia diverges away from somalia at slower rates comparable to the present day one kinematic changes of some 20 might have occurred in the period leading to the present day but plate motion steadiness is also warranted within the uncertainties

felsic a type basic plume induced early palaeozoic bimodal magmatism in the maures massif southeastern france the maures massif forms an important piece of the southernmost part of the variscan belt of western europe this massif exhibits high grade bimodal felsic basic volcanic complexes a distinctive lithological feature documented elsewhere in similar domains of the european variscides and referred to the cambro ordovician extensional episode two major alkalic and tholeiitic compositional groups and subordinate transitional metabasites have been identified occurring at several distinct horizons or in bimodal complexes this chemical diversity is interpreted in terms of variable degrees of partial melting of progressively depleted mantle source s which experienced melting at different depths from garnet to spinel stability domains during a progressive mantle upwelling associated with intracontinental rifting this setting is reinforced by the presence of metabasites with compositions similar to continental flood basalts showing slightly humped ree patterns and interpreted as resulting from the melting of a partially depleted source at a relatively low degree of melting in the garnet spinel transition zone the metafelsites from the tholeiitic bimodal complex exhibit the distinctive major and trace element characteristics of a type rhyolites their elemental variations are consistent with fractional crystallization of major and accessory phases but some discontinuous ree profiles result from a hydrothermal fractionation mechanism the modelling of common anhydrous fractionating assemblages suggests that these a type compositions may be derived from the associated tholeiites by extensive degrees of fractionation 90 with some continental crust involvement or by anhydrous partial melting 30 of an underplated mafic parent of tholeiitic composition the bimodal character of the late cambrian maures magmatism together with the chemistry of the various metabasites and metafelsites suggests plume induced intracontinental magmatic activity resulting in lithospheric thinning prior to the onset of rifting and break up of the palaeozoic continental lithosphere at this northern margin of gondwana

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

evolution of a callovian oxfordian carbonate margin in the neuquen basin of west central argentina facies architecture depositional sequences and global sea level changes abstract this paper reviews a detailed stratigraphic and sedimentologic study of a carbonate complex developed on the foreland side of the neuquen embayment a protected shallow water epicratonic site behind the active edge of the south american plate superb outcrops at the core of basement involved andean structures expose the shelf to basin transition and reveal with clarity the external and the internal architecture of the depositional sequences and component system tracts platform carbonates are largely represented by ooid and mainly rhodoid grainstones with associated patches of coral framestone the deeper platform and slope facies are composed of oncoidal and skeletal micritic limestones with scattered coral sponge algal build ups the overall composition and facies pattern bears resemblance to other late jurassic carbonate complexes form europe and with the smackover formation from the gulf coast basin of north america analysis based on mapping of the stratal patterns and facies associations in outcrops allowed the recognition of four depositional sequences timing provided by ammonite biochronology suggests that eustatic fluctuations were a major factor influencing the carbonate margin architecture and regulated episodes of condensed sedimentation shifts of the depositional belts and development of stratigraphic discontinuities the onset and the end of carbonate sedimentation were associated with episodes of marine retreat and accumulation of evaporites and eolian fluvial deposits at basin centre locations however most of the marine fluctuations recorded within the carbonate complex were insufficient to expose the shelf break type 2 and accordingly lowstand system tracts are poorly represented on the shelf the transgressive system tracts are represented by thin grain supported carbonate blankets these taper out downslope into omission surfaces or are replaced by patches of small sponge buildups highstand system tract organization changes through time reflecting changes in productivity and accomodation presumably tied to second order sea level changes callovian highstand accumulation featured a catch up carbonate system and produced a thin aggradational ramp configuration whereas conditions during middle late oxfordian allowed a keep up system and produced outbuilding depositional geometries with steeper slopes

coeval potassic and sodic calc alkaline series in the post collisional hercynian tanncherfi intrusive complex northeastern morocco geochemical isotopic and geochronological evidence abstract the post collisional late hercynian tanncherfi intrusive complex tic is part of a widespread intrusive episode in the moroccan meseta the complex contains a wide range of rock types from monzogabbros to monzogranites two distinct magmatic series are recognized 1 a potassic shoshonitic series consisting of monzogabbros quartz monzonites and monzogranites and 2 a sodic granodioritic series represented by quartz monzodiorites and granodiorites all the tanncherfi plutonic rocks display similar spider diagram profiles with lile and lree enrichment and nb ta ti depletion which are typical of subduction related magmas combined major trace element compositions and sr nd isotopic results indicate that the two series have been derived from a lile and lree enriched continental lithospheric mantle source under different partial melting and or depth conditions intrusion of the tanncherfi rocks was not temporally related to subduction and the enrichment of their source is likely to be linked to preceding subduction events the two series evolved by fractional crystallization of clinopyroxene plagioclase hornblende biotite k feldspar and accessories fe ti oxide minerals titanite apatite and zircon for the potassic series while the sodic series combined fractional crystallization with assimilation of felsic magmas with lower sr isotopic ratio than the more mafic term of the series the quartz monzodiorite the intrusion of the potassic magmas 344 6 ma marks a major change in the tectonic regime of eastern meseta these magmas intruded during post thickening uplift and extension both probably favored by convective thinning of the lithosphere this model provides a reasonable mechanism for the genesis of other hercynian intrusive complexes in morocco

mid triassic felsic igneous rocks from the southern lancangjiang zone sw china petrogenesis and implications for the evolution of paleo tethys abstract the southern lancangjiang magmatic belt is an important component of the triassic san jiang igneous zone in southwestern china and is mainly composed of the lincang lc batholith and a mesozoic volcanic belt that contains abundant rhyolites our new la icp ms zircon u pb results together with previous shrimp and la icp ms ages define two emplacement ages for the lincang batholith at 230 ma and 220 ma corresponding to the eruption times of volcanic rocks of the manghuai and xiaodingxi formations respectively most of the 230 ma lc granites possess high a cnk values 1 1 and display strongly peraluminous characteristics similar to s type granite whereas the manghuai formation mhf rhyolites show an affinity to a type granite especially their elevated feot feot mgo and ga al ratios both of the granitic and volcanic rocks have strongly fractionated ree patterns la yb n 2 66 33 2 and 13 1 19 7 respectively and have conspicuous negative eu anomalies eu eu 0 06 0 65 and 0 52 0 74 respectively with a similar depletion in hfse nb zr hf p ba and sr the sr nd isotopic data and t dm2 model ages suggest that the lc granitic magma had a dominantly crustal source whereas the mhf rhyolites were derived from mixing between middle upper crustal rocks similar to the source of the lc granitic magma with a small volume of mantle derived melt in combination with regional studies our new geochemical data and geochronological results show that the mid triassic magmatism was generated in a post collisional tectonic setting the spatial distribution pattern of the mesozoic igneous rocks along the lancangjiang zone favors a slab breakoff model which resulted in post collisional extension and asthenospheric upwelling that induced large scale partial melting of the middle lower crust to produce voluminous amounts of felsic magma therefore the occurrence of the mid triassic post collisional magmatism clearly indicates that the final continent continent arc collision between the gondwana derived sibumasu and indochina blocks of paleo tethys was completed by the early mid triassic

sequence stratigraphy of the mesozoic domeyko basin northern chile the domeyko basin of northern chile records late triassic to early cretaceous mixed carbonate and siliciclastic marine deposition along the western margin of gondwana sequence stratigraphical analysis has identified five long term sequences of 11 17 ma duration comparison of the relative sea level fluctuations interpreted from the domeyko basin succession with those documented from other similar aged south american marginal basins and northern hemisphere basins allows the distinction of regional from global events relative sea level fall in the early pliensbachian early aalenian and early valanginian and rises in the early hettangian early and late toarcian early and late bajocian late bathonian and early oxfordian of the domeyko basin appear time equivalent to similar events in other southern and northern hemisphere basins and are thus interpreted to be products of global sea level cycles long term relative sea level falls in the early bathonian late oxfordian early valanginian and rise in the late kimmeridgian are interpreted to be tectonically driven continental scale changes in sediment accommodation space the domeyko basin succession thus appears to have been dominantly controlled by global sea level fluctuations during the early to mid jurassic and by continental scale but not global fluctuations during the mid jurassic to mid cretaceous interpreted to have been driven by the fragmentation of gondwana

importance of late magmatic and hydrothermal fluids on the sm nd isotope mineral systematics of hypersolvus granites abstract despite the significant impact of the sm nd radiometric system in various fields of isotope geochemistry very few attempts have been made to use it at the mineral scale in granite studies this approach has been used on two granites from the anorogenic province of corsica se france two statistically acceptable alignments were obtained in an isochron diagram for the hypersolvus fayalite bearing granite of mantelluccio alkali feldspar amphibole inclusion free zircon fluorite and fergusonite give an age of 331 10 ma whereas allanite whole rock amphibole and inclusion free zircon yield a significantly younger age at 291 13 ma the latter is validated by a zircon u pb age of 283 1 ma as the magmatic emplacement date of the granite the other alignment giving a 50 ma older age can be interpreted either as being inherited or more likely as the result of hydrothermal convection interacting with the country rocks at the end of granite crystallization the sm nd systematics of epidote records a second fluid rock event which probably occurred at least 200 ma after the emplacement of the granite extremely low 143 nd 144 nd ratio indicates that the epidote crystallized from a fluid that carried lanthanides in the crust over a distance of at least 1 km zircons with inclusions have a lower initial 143 nd 144 nd ratio than inclusion free zircons this feature is attributed to apatite and or zircon core inheritance through contamination during the ascent of the granitic melt in the crust two isochrons have been also obtained for the hypersolvus peralkaline granite of evisa amphibole fluorite sphene and fergusonite yield an age of 259 6 ma whereas the whole rock alkali feldspar and metamict zircon give an age at 209 14 ma in this case the former value is roughly in agreement with a possibly slightly rejuvenated whole rock rb sr date of 249 3 ma suggesting that it documents the magmatic crystallization age of the granite sm nd isotope systematics of the alkali feldspar metamict zircon and possibly allanite were re equilibrated during an important hydrothermal event that affected western europe in early jurassic times in both examples however it appears that the whole rock nd isotopic signatures were not strongly affected by the various fluid rock events indicating that they can still be used for petrogenetic investigations in contrast these results show that like k ar and rb sr the sm nd systematics of minerals with weak resistance to post magmatic processes can be used to trace and date hydrothermal events

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

genesis and timing of mo mineralization in the mada ring complex north central nigeria insights from whole rock geochemistry nd sr isotopes zircon u pb hf isotopes and molybdenite re os systematics the genesis and timing of molybdenum mo mineralization in the mada ring complex north central nigeria have been constrained using a combination of whole rock elemental geochemistry nd sr isotopes zircon u pb hf isotopes and molybdenite re os geochronological data the mada ring complex is one of fifty three within plate alkaline ring complexes with economically significant sn and nb production from largely alluvial placer deposits in north central nigeria molybdenum mineralization in the ring complex is dominantly disseminated with minor stockwork veins hosted within biotite granite integrated zircon u pb and molybdenite re os geochronology constrain initial magma emplacement to between 152 and 151 1 ma and the mo mineralization event to 150 1 ma the granites associated with mo mineralization are highly silicic and display elevated whole rock concentrations of nb zr y and ree except eu as well as high 87rb 86sr ratios but low concentrations of sr ba cao mgo and tio2 consistent with highly differentiated a type granites they yield moderately negative whole rock end t 5 87 to 5 47 and zircon ehf t 4 97 to 10 06 suggesting that their parental magmas were largely derived from the lower crust with a contribution from the upper mantle magmatic oxygen fugacity o2 of the a type granites log fmq 1 16 constrained from zircon compositions is lower than values reported from typical within plate porphyry molybdenum deposits log fmq 2 to 3 however compared to regional sn nb mineralized a type granites the mada a type granites have higher o2 and ce4 ce3 but are less differentiated

geochemistry zircon ages and whole rock nd isotopic systematics for palaeoproterozoic a type granitoids in the northern part of the delhi belt rajasthan nw india implications for late palaeoproterozoic crustal evolution of the aravalli craton determination of zircon ages as well as geochemical and sm nd isotope systematics of granitoids in the khetri copper belt of the aravalli mountains nw india constrain the late palaeoproterozoic crustal evolution of the aravalli craton the plutons are typical a type within plate granites derived from melts generated in an extensional tectonic environment they display ree and multi element patterns characterized by steep lree enriched and almost flat hree profiles and distinct negative anomalies for sr p and ti initial e nd values range from 1 3 to 6 2 and correspond to crustal sources with mean crustal residence ages of 2 5 to 2 1 ga a lower mafic crustal anatectic origin is envisaged for these granitoids and the heterogeneous e nd t values are inferred to have been acquired from the magma source region zircon pb pb evaporation and u pb ages indicate widespread rift related a type magmatism at 1711 1660 ma in the northern delhi belt and also suggest a discrete older magmatic event at around 1800 ma the emplacement ages of the compositionally distinct a type granitoid plutons and virtually coeval granulite metamorphism and exhumation in another segment of the aravalli mountains further signify that part of the aravalli crust evolved during a widespread extensional event in late palaeoproterozoic time

zircon oxygen isotopic constraint on the sources of late mesozoic a type granites in eastern china abstract a type granites are usually derived from partial melting of the lower crust and or the upper mantle within extensional settings but their exact sources for specific plutons are required to unravel a systematic laser fluorination analysis of oxygen isotopes was carried out for five well documented late mesozoic a type granites in eastern china zircon from 41 samples was separated and 109 aliquots of fresh zircon were analyzed along with whole rock powder and quartz from the same samples hydrothermally altered whole rock samples show scattered 18 o values of 2 3 to 7 4 with a total variation up to 9 7 in contrast zircon 18 o values vary only from 3 1 to 5 4 with a range of 2 3 most available zircon 18 o values of a type granites are lower than normal mantle zircon values of 5 3 0 6 2sd and high temperature equilibrium fractionations are well preserved between quartz and zircon in most cases the above lines of evidence suggest that the low 18 o zircons in a type granites were crystallized from low 18 o magmas because low 18 o magmas cannot be derived entirely from the mantle reworking and or recycling of crustal igneous rocks are involved for their petrogenesis the low 18 o zircons in this study thus offer evidence for a dominantly crustal origin of the late mesozoic a type granites in eastern china

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

early palaeozoic crustal melting in an extensional setting petrological and sm nd evidence from the izera granite gneisses polish sudetes the izera block in the west sudetes which is composed of granites gneisses and transitional granite gneisses and minor mica schists is one of the largest outcrops of early palaeozoic ca 500 ma metagranitoid rocks in the basement units of the variscides of central europe the izera granites show s type features magmatic cordierite relict garnet and sillimanite lack of mafic enclaves and absence of coexisting tonalites and diorites the paucity of pegmatites indicates that the granitic magma was relatively dry the s type character of these granites is further supported by their peraluminous character a cnk 1 0 1 63 high content of normative corundum up to 3 5 and relatively high 87sr 86sr initial ratio the chemical variation of these rocks was controlled by the fractional crystallization of plagioclase cao sr eu eu biotite and cordierite al2o3 mgo feo zircon zr hf and monazite ree initial end values range from 5 2 to 6 9 mean 5 9 sd 0 6 these largely negative end values imply that the granitic magmas emplaced ca 500 ma were extracted from a source reservoir that was strongly enriched in lree i e with low sm nd ratio on a time integrated basis the relatively consistent depleted mantle model ages 1 730 2 175 ma mean 1 890 ma is in agreement with the earlier reported presence of ca 2 1 ga old inherited pb component in zircon from the closely related rumburk granite this points to an old early proterozoic crustal residence age of the inferred metasedimentary protoliths of the izera granitoids with only minor contribution to their protoliths of juvenile components of late proterozoic early palaeozoic age although the izera granites show some trace element features reminiscent of syn collisional or post collisional granitoids they more likely belong to the broad anorogenic class our data corroborate some previous interpretations that granite generation was connected with the early palaeozoic rifting of the passive margin of the saxothuringian block well documented in the region by bimodal volcanic suites of similar age kaczawa unit eastern and southern envelope of the karkonosze izera block in this scenario granite magmatism and bimodal volcanism would represent two broadly concomitant effects of a single major event of lithospheric break up at the northern edge of gondwana

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

permian peralkaline peraluminous and metaluminous a type granites in the panxi district sw china their relationship to the emeishan mantle plume abstract numerous permian granitic intrusions plutons in the panxi region sw china are spatially and temporally associated with the emeishan large igneous province elip granites from the 260 ma panzhihua and taihe plutons are peralkaline asi 0 76 1 12 na k al 0 78 1 2 and have high fe values 0 92 0 99 with negative eu anomalies eu eu 0 22 0 98 contrasted with the peralkaline plutons syenites from the 260 ma woshui pluton are metaluminous asi 0 84 1 0 na k al 0 91 1 01 and have moderately high fe 0 79 0 81 and positive eu anomalies eu eu 0 82 1 91 both the peralkaline and metaluminous rocks have mantle isotopic signatures end t 1 3 3 2 and were derived from the elip mantle plume source the peralkaline rocks were likely derived by fractional crystallization of the temporally spatially and chemically associated layered mafic intrusions which host giant magmatic fe ti v oxide deposits the metaluminous granitic rocks although spatially related to the peralkaline granites and layered gabbros were likely generated by partial melting of underplated mafic rocks granites from the 251 ma ailanghe pluton are peraluminous asi 0 97 1 29 and have high fe 0 82 0 91 values and negative eu anomalies eu eu 0 10 0 37 their crustal isotopic signature end t 5 7 to 6 7 indicates possible derivation from melting of yangtze block basement rocks the ailanghe pluton is contemporaneous with other a type granites in the region supporting the view that elip magmatism was sporadic for at least 9 million years the coexistence of three chemically exclusive a type granites in the elip suggests that a variety of a type granites can be generated in the same tectonic setting

the serra da graciosa a type granites and syenites southern brazil part 2 petrographic and mineralogical evolution of the alkaline and aluminous associations abstract the serra da graciosa granites and syenites comprise five distinct plutons in the brasiliano pan african graciosa a type province southern brazil six petrographic series can be identified in these plutons 1 alkaline series 1 composed of amphibole bearing alkali feldspar syenites with varied mafic mineralogy and quartz contents from alkali feldspar syenites with calcic amphibole clinopyroxene olivine and allanite to alkali feldspar quartz syenites with sodic calcic amphibole and chevkinite perrierite and to alkali feldspar granites with sodic amphibole 2 alkaline series 2 characterized by amphibole bearing alkali feldspar granites with limited modal variations but amphibole compositions also varying from calcic to sodic 3 alkaline series 3 of limited occurrence which includes alkali feldspar syenites with olivine and clinopyroxene and no amphibole 4 aluminous series 1 of widespread occurrence with various petrographic facies of biotite granites with amphibole 5 aluminous series 2 characterized by alkali feldspar granites with biotite and only minor amphibole 6 monzodiorites typically with biotite calcic amphibole and augitic clinopyroxene partially mingled with granitic magmas the mafic minerals present are in general fe rich with correspondingly low mg and al contents in alkaline series 1 amphiboles crystallized in progressively more oxidizing and alkaline conditions while in alkaline series 2 the initial conditions were somewhat more oxidizing and shifted to reducing in the final stages in aluminous series 1 and aluminous series 2 amphiboles are calcic and comparatively homogeneous the amphiboles in the monzodioritic rocks while also homogeneous are more mg rich and show compositions quite distinct from the calcic varieties in the other associations and this is also the case for clinopyroxene mg in biotite decreases from the monzodioritic rocks to aluminous series 1 and further to aluminous series 2 contrasting evolution of the various associations suggests that several coeval magmatic series are present in the serra da graciosa granites

alkali calcic and alkaline post orogenic po granite magmatism petrologic constraints and geodynamic settings abstract the end of an orogenic wilson cycle corresponds to amalgamation of terranes into a pangaea and is marked by widespread magmatism dominated by granitoids the post collision event starts with magmatic processes still influenced by subducted crustal materials the dominantly calc alkaline suites show a shift from normal to high k to very high k associations source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle affected by dehydration melting and generating more and more k and lile rich magmas in the vicinity of intra crustal magma chambers anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves the post collision event ends with emplacement of bimodal post orogenic po suites along transcurrent fault zones two suites are defined i the alkali calcic monzonite monzogranite syenogranite alkali feldspar granite association characterised by biotite plagioclase fractionation and moderate lile hfse enrichments and ii the alkaline monzonite syenite alkali feldspar granite association characterised by amphibole alkali feldspar fractionation and displaying two evolutionary trends one peralkaline with sodic mafic mineralogy and higher enrichments in hfse than in lile and the other aluminous biotite bearing marked by hfse depletion relative to lile due to accessory mineral precipitation alkali calcic and alkaline suites differ essentially in the amounts of water present within intra crustal magma chambers promoting crystallisation of various mineral assemblages the ultimate enriched and not depleted mantle source is identical for the two po suites the more primitive lile and hfse rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere present rock compositions are a mixture of major mantle contribution and various crustal components carried by f rich aqueous fluids circulating within convective cells created around magma chambers in favourable areas po suites pre date a new orogenic wilson cycle

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

a climate signal in exhumation patterns revealed by porphyry copper deposits porphyry copper deposits are emplaced at a fixed crustal depth in convergent tectonic settings the age and distribution of deposits exposed at the surface suggest that mountain exhumation is influenced by precipitation rates

the depth of pelagic deposits in the tethyan jurassic and the use of corals an example from the apennines abstract assessing the palaeobathymery of pelagic deposits is rather speculative as proof through lithology or fossils significant for depth estimates is sparse this is unfortunate as the bathymetric history of pelagic successions allows to conceive the evolution of continental margins and oceanic basins discoveries in coral biology bring an unexpected impact on basin analysis evidence strongly suggests that pennular corals fossil and modern constitute a zooxanthellate group with an outstanding specialization in colonizing deeper parts of the marine photic zone this adaptation includes light amplification by autofluorescent pigmented cells and particular feeding witnessed by peculiar gastric ducts and skeletal features such corals occur in the umbria marche and sabina apennines on top of late jurassic submarine highs and at basin margins values of palaeodepth relative to pelagic deposits are provided by corals and other environmental data because depth reconstruction involves classical tethyan facies such as ammonitico rosso aptychus limestone and radiolarian cherts we must note that these results do not meet with actualistic models relying on carbonate dissolution for estimating depth deposits viewed as bathyal to abyssal could also have accumulated within or just below the photic zone thus a new insight opens on mesozoic bathymetries regarding vast areas middle east to caribbean and on subjects ranging from platform drowning to regional extension styles

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

detailed oxygen and carbon isotope stratigraphy of the oxfordian in central poland a collection of 73 belemnites and brachiopods from detailed stratigraphically documented sections in the polish jura chain of central poland representing almost the whole oxfordian stage was studied for oxygen and carbon isotopes the 18o and 13c v pdb values range from 3 6 to 0 5 and from 1 6 to 2 for belemnite rostra and from 2 5 to 0 4 and from 1 6 to 4 3 for brachiopod shells respectively the 13c temporal trends of belemnite rostra and brachiopod shells show a constant isotopic difference ca 2 5 3 which is interpreted as a vital effect of belemnites or as a result of different life environments 18o values are similar in both groups of fossils the 18o values in the lower and middle oxfordian oscillate around 0 and decrease in the upper oxfordian this decrease results mainly from diagenetic overprint as proved by the cathodoluminescence studies the lower and middle oxfordian 18o derived temperatures were constant in consequence of significant ocean depth for this reason there are no established links with distribution of ammonite faunas the 13c temporal trend displays a gentle slope through the oxfordian and reaches maximum values at the turn of the plicatilis transversarium zones of the middle oxfordian which is commonly considered as a global event it can be related to the sea level highstand and growth crisis of carbonate platforms the decrease in 13c values starting in the upper middle oxfordian is interpreted to be due to the acceleration of carbonate sedimentation rate during this time period

petrogenesis of the 1 43 ga sherman batholith se wyoming usa a reduced rapakivi type anorogenic granite the 1 43 ga sherman batholith southeastern wyoming usa origin that are found throughout the proterozoic anorogenic granite provinces of the southwestern usa adirshows extreme a type petrochemical characteristics compared with other mid proterozoic granite batholiths of north america it ondacks eastern canada southern greenland and the fennoscandian shield anderson 1983 phanerozoic consists of 1 the sherman granite a coarse grained biotite hornblende granite that locally contains fayalite and pyroxenes 2 examples include paleozoic granites of southeastern australia collins et al 1982 and of corsica poitrasson et the lincoln granite a medium grained biotite granite 3 a porphyritic biotite hornblende granite that probably formed by interaction al 1995 and the mesozoic nigerian younger granites jacobsen et al 1958 and the white mountain magma of granitic and mafic magmas and 4 iron enriched mafic dikes and pods the ilmenite series metaluminous sherman granite series foland allen 1991 anorogenic granite refers to plutons that are not associated with compressional exhibits extreme values of feo feo mgo and is rich in structures and that were emplaced long after any known k ree nb and y it crystallized at temperatures exceeding orogenic event anorogenic or a type granites loiselle 900 c and a pressure of 2 5 kbar with water activity of 0 7 wones 1979 are characterized by low h2o and o2 and dlog fo2 of 0 1 to 0 5 the lincoln granite which is fugacities along with high feo feo mgo k2o peraluminous and has less extreme a type geochemical characteristics na2o and k2o contents a type granites typically are rich crystallized at temperatures as low as 750 c and dlog fo2 of in incompatible elements including rare earth elements around 0 5 units above fmq fayalite magnetite quartz the ree zr nb and ta but poor in co sc cr ni ba rocks of the sherman batholith are chemically equivalent to lavas sr and eu minimum magma liquidus temperatures are from the yellowstone hotspot like the yellowstone magmas the 900 1000 c clemens et al 1986 creaser white sherman batholith probably originated by partial melting of under1991 some workers suggest these rocks are derived plated mantle derived mafic rocks from melting of tonalitic or more felsic crust anderson cullers 1978 collins et al 1982 clemens et al 1986 creaser et al 1991 whereas others relate the granites

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur