highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

low grade metamorphism of mafic rocks through most of this past century metamorphic petrologists in the united states have paid their greatest attention to high grade rocks especially those which constitute the core zones of exhumed mountain belts the pioneering studies of the 50 s through the 80 s those which applied the principles of thermodynamics to metamorphic rocks focused almost exclusively on high temperature systems for which equilibrium processes could be demonstrated by the 1980 s metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks of course low grade metamorphic rocks here defined as those which form at pressures and temperatures up to and including the greenschist facies had been well known and described as well initially through the efforts of alpine and circum pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts and that they underlay large portions of accreted terranes many of oceanic origins but until the mid 80 s much of the effort in studying low grade rocks for a comprehensive review of the literature to that point see frey 1987 had been concentrated on mudstones volcanoclastic rocks and associated lithologies common to continental mountain belts and arcs in the mid 80 s results of the deep sea drilling project dsdp rather dramatically mitigated a shift in the study of low grade metamorphic rocks

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

geochronological and geochemical constraints on aolunhua porphyry mo cu deposit northeast china and its tectonic significance abstract the aolunhua porphyry mo cu deposit is located in the northern margin of the north china craton ncc and belongs to the northern part of the xilamulun metallogenic belt more than 90 of the mineralization occurs within the aolunhua monzogranite porphyry a small part is hosted within quartz veins that crosscut late permian strata the syenogranite occurring as dikes and cutting through the aolunhua monzogranite porphyry is radially distributed in the mining district zircon u pb ages show that the aolunhua monzogranite porphyry and the post ore syenogranite have concordant 206pb 238u ages of 138 7 1 2 ma and 131 4 2 8 ma respectively based on analyses of major trace elements and hf isotopes the aolunhua porphyry is characterized by high sr low y with high la yb and sr y ratios typical of adakitic granites whereas the post ore syenogranite has lower sr and higher y values showing apparently negative eu anomalies eu 0 26 to 0 31 the hf isotopic composition of the aolunhua porphyry ehf t 3 6 to 9 2 and the post ore syenogranite ehf t 3 6 to 8 7 indicates that both juvenile crustal sources and depleted mantle contributed to their origin the regional geological setting together with the discrepancy of geochemistry between the aolunhua porphyry and the post ore syenogranite probably indicates that they formed in different tectonic regimes the aolunhua porphyry is derived from partial melting of the thickened crust due to underplating of the basaltic magma under the transformation tectonic regime while the post ore syenogranite comes from the crustal root melting during the lithospheric delamination stage under the lithosphere thinning regime of northeast china

inversion styles in the songliao basin northeast china and estimation of the degree of inversion abstract two inversion patterns fault reactivated and cover folded inversions are recognized in the songliao basin of northeastern china mild inversion with a reactivated fault showing normal separation in all synrift beds moderate partial inversion and total inversion are the common styles of fault reactivated inversion the magnitude of extension by rifting as well as orientation of the synrift faults in relation to the compressional direction during inversion significantly controlled the inversion structures the same amount of shortening may produce a moderate inversion style where the normal slip during the rifting was large but a total inversion in which the initial normal slip was small the cover folded inversions in the songliao basin have either no normal faults or have one or more normal faults that occurred prior to inversion and remained dormant during the inversion the geometry of cover folded inversion may be controlled by deep faults in the basement a graben like basement fault assemblage can result in an antiformal geometry while a horst like basement fault assemblage may control a synformal cover folded inversion an inversion with antiformal geometry of the sedimentary sequences is the major style in the songliao basin a new method of estimating the degree of fault inversion is discussed the degree of fault inversion is the ratio between reverse slip during inversion and normal slip during extension both measured along the fault it can be estimated in most fault reactivated inversions where the top of the basement or the floor of the synrift deposits does not fold during the inversion the horizontal inversion ratio represents the relative amount of shortening and extension of a structure or basin it can be used to analyse the degree of inversion of complex structures or basins however both fault inversion and horizontal inversion ratios are primarily influenced by the amount of extension if undergoing same amount of shortening a structure with a small amount of extension may have a much greater inversion ratio than one with a large amount of extension

asynchronizing paleo pacific slab rollback beneath se china insights from the episodic late mesozoic volcanism abstract extensive late mesozoic igneous rocks in se china have been widely considered to be generated under the paleo pacific tectonic regime previous studies suggested a fundamental oceanward younging trend for the igneous rocks further implying a nw ward paleo pacific subduction model with gradual slab rollback new la icp ms zircon u pb dating results show that early stage of the late mesozoic volcanic sequences also known as the lower volcanic series in fujian province was formed in three episodes 160 148 ma for the changlin formation 145 130 ma for the nanyuan formation and 130 127 ma for the xiaoxi formation among which the second episode made the volcanism climax thus the entire lower volcanic series in fujian were formed earlier than those in zhejiang 140 118 ma displaying a ne ward younging trend parallel to the potential subduction belt besides in situ hf isotope analyses on dated zircons yield an ehf t range of 19 2 to 1 7 for the lower volcanic series in fujian the majority of the studied volcanic rocks have more radiogenic hf than that of the metamorphic basement requiring the involvement of juvenile components in their origin moreover the zircon ehf t value increases with time in each single area as well as the igneous rocks elsewhere in se china except for the changlin formation which shows very opposite isotopic varying trend increasing zircon ehf t values imply an increasing material contribution of contemporaneous underplated mantle derived magmas which was plausibly induced by gradual crustal decompression as well as the ne ward younging trend of the lower volcanic series it is also identified that the juvenile material contribution in the igneous petrogenesis gradually took place in the same direction along the coastal area thus here we propose an asynchronizing paleo pacific slab rollback model during 150 120 ma to account for the episodic magmatism and crustal extension in se china on the contrary decreasing zircon ehf t values of the changlin formation volcanics indicate that they were formed under enhanced crustal compression probably induced by slab advance on the other hand the upper volcanic series in fujian were formed during 110 88 ma coevally to those in zhejiang with more depleted zircon hf isotopic compositions than the lower volcanic series as well indicating that the entire coastal se china was under the back arc tectonic setting during that time

resolving bathymetric components of the upper shoreface on a wave dominated coast abstract the bathymetric components of a wave and storm dominated shoreface were examined as a key to understanding the controlling effects of hydrodynamic processes and geological factors that maintain the shoreface results of empirical orthogonal function analysis applied to bathymetric data from the upper shoreface of long island s south shore between fire island inlet and montauk point show that this area can be divided morphologically into a headland section and a barrier island section the headland section is characterized by well organized well correlated bathymetry in contrast to the barrier island section which has more complex and less organized less correlated bathymetry the first three spatial eigenfunctions modes account for nearly 90 of the variance among the headland shoreface bathymetry data whereas the first three eigenfunctions of the barrier island section account for 82 of the variance among the data the headland shoreface is steeper than the barrier island shoreface and is dominated by a primary nearshore bar mode which accounts for 70 of the variance among the shoreface bathymetry data for this section secondary bathymetric components of the headland shoreface account for less than 20 of the remaining variance the bathymetry of the barrier island shoreface is dominated by a terrace mode this mode accounts for only 54 of the variance among the bathymetric data however and secondary bathymetric components account for more than 27 of the remaining variance underlying factors determining the differences in shoreface bathymetry between the barrier island and headland sections of the study area include topographic control by the outwash plain backing much of the headland section and proximity to sediment source the factor directly responsible for differences in bathymetric components however is the relative difference in dissipative conditions between the two sections with respect to incident wave energy both sections have an outer dissipative domain and a more resonant inner domain however the barrier island section is twice as dissipative as the headland section

regional trends in water chemistry smackover formation southwest arkansas geochemical and physical controls we present results on regional geochemical analyses of formation waters from jurassic carbonate strata of the upper smackover formation from the southwest arkansas shelf gulf coast basin these formation waters have been noted in earlier studies for their exceptional salinities and abnormally br rich composition our detailed and regionally extensive database shows that chemical heterogeneities occur on a relatively small scale and have spatial relations to faults which may act as pathways for fluid migration from deeper and hotter portions of the stratigraphic section one of the most pronounced heterogeneities in water chemistry is an h 2 s rich anomaly in the center of the shelf enrichments in h 2 s are accompanied by large increases in alkali elements li k and b and b which could be produced by higher temperature diagenesis of clay minerals and feldspars in deeper seated siliciclastic strata bromide enrichments in all smackover formation waters are apparent from relations between br and cl contents as well as br and divalent cation carpenter function values as suggested by earlier studies of these waters evaporatively concentrated seawater expelled from associated thick monomineralic evaporite sections may be an important source of br cl and na whereas ca mg and sr concentrations have been modified by carbonate mineral recrystallization and dolomitization mineral equilibria exert significant controls on concentrations of ca mg sr and so 4 in these brines br enrichment likely was produced by halite recrystallization in fluids already enriched in br from seawater evaporation elevated cl br ratios occur in regional association with lower salinity water near t e south arkansas fault system consistent with halite dissolution during meteoric water recharge thus despite relatively uniform reservoir lithology and simple structural setting processes on small spatial scales have resulted in significant heterogeneity in water chemistry within a small area of the gulf coast sedimentary basin although movement of fluids along these fault systems is not demonstrated in our study the regional trends in geochemistry are strongly suggestive of their important role in controlling chemical heterogeneities in smackover formation waters

wave energy saturation on a natural beach of variable slope time series of flow were measured across the inner surf zone during a storm these data were used to quantify the dependence of wave height transformed from measured flow and velocity on local slope and depth similar to previous studies as incident waves broke and propagated into the surf zone wave energy became saturated and wave height was strongly dependent on depth however the ratio of rms wave height to local depth rms was found not to be constant but to vary between 0 29 and 0 55 rms increased with local slope and was independent of deepwater wave steepness thus the surf zone similarity parameter the ratio of slope to the square root of steepness did not adequately parameterize rms

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

characterization of hydrated silicate bearing outcrops in tyrrhena terra mars implications to the alteration history of mars abstract the tyrrhena terra region of mars is studied with the imaging spectrometers omega observatoire pour la mineralogie l eau les glaces et l activite onboard mars express and crism compact reconnaissance infrared spectrometer for mars onboard mars reconnaissance orbiter through the observation of tens of craters that impacted into this part of the martian highlands the 175 detections of hydrated silicates are reported mainly associated with ejecta blankets crater walls and rims and central up lifts sizes of craters where hydrated silicates are detected are highly variable diameters range from less than 1 km to 42 km we report the presence of zeolites and phyllosilicates like prehnite mg chlorite mg rich smectites and mixed layer chlorites smectites and chlorite vermiculite from comparison of hyperspectral infrared observations with laboratory spectra these minerals are associated with fresh craters post dating any aqueous activity they likely represent ancient hydrated terrains excavated by the crater forming impacts and hence reveal the composition of the altered noachian crust although crater related hydrothermal activity may have played a minor role for the largest craters 20 km in diameter most detected minerals formed over relatively high temperatures 100 300 c likely due to aqueous alteration of the noachian crust by regional low grade metamorphism from the noachian thermal gradient and or by extended hydrothermal systems associated with noachian volcanism and ancient large impact craters this is in contrast with some other phyllosilicate bearing regions like mawrth vallis where smectites kaolinites and hydrated silica were mainly identified pointing to a predominance of surface shallow sub surface alteration and where excavation by impacts played only a minor role smooth plains containing hydrated silicates are observed at the boundary between the noachian altered crust dissected by fluvial valleys and the hesperian unaltered volcanic plains these plains may correspond to alluvial deposition of eroded material the highlands of tyrrhena terra are therefore particularly well suited for investigating the diversity of hydrated minerals in ancient martian terrains

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

age constraints on late mesozoic lithospheric extension and origin of bimodal volcanic rocks from the hailar basin ne china abstract following the amalgamation of the late mesoproterozoic carboniferous central asian orogenic belt with the siberian and north china cratons ne china underwent late mesozoic lithospheric extension and widespread formation of volcano sedimentary basins we report u pb zircon ages and geochemical data for mafic and felsic volcanic rocks from the hailar basin located about 1000 km north of beijing zircon populations of six felsic rock samples analyzed by laser ablation icp ms yielded similar u pb age spectra ranging from 158 to 125 ma the youngest zircon ages are interpreted as time of magma eruption and the xenocrystic zircon age spectra as evidence for a protracted melting of lower crust due to the underplating of mantle derived magmas during lithospheric extension the volcanic assemblage has a bimodal composition comprising geochemically evolved trachybasalts and felsic volcanic rocks of i and subordinate a type compositions the mafic volcanic rocks have negative nb anomalies high th nb and ce pb ratios low initial e nd values of 0 4 to 3 4 and radiogenic pb and sr isotopes all interpreted as evidence for the melting of passively upwelling asthenosphere and lithospheric mantle previously modified by plate subduction the xenocrystic zircon ages and chemical isotopic data of the felsic rocks support an origin from juvenile crustal protoliths the data of i type felsic rocks are consistent with the melting of underplated mafic protoliths and those of the a type rhyolites support the melting of a crustal source with a composition similar to the i type felsites with apatite controlling their nb anomaly the evidence for the persistent melting of a subduction modified mantle in ne china is in agreement with a model of an extending coupled upper mantle crust system due to a retreating paleo pacific trench

reaction pathways and reaction progress for the smectite to chlorite transformation evidence from hydrothermally altered metabasites the transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite smectite mixed layering sequence or an equilibrated discontinuous sequence involving smectite corrensite chlorite here analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving i a continuous mixed layer chlorite smectite series ii a discontinuous smectite corrensite chlorite series and iii a direct smectite to chlorite transition such contrasting pathways are not in accord with an equilibrium mineral reaction series suggesting that these pathways record kinetically controlled reaction progress in the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization and not to differences in thermal gradients or clay grain size this suggests a kinetic effect linked to variation in fluid rock ratios and or a contrast between advective or diffusive fluid transport the mode of fluid transport provides a means by which the rates of dissolution nucleation growth can control the reaction style and the reaction progress of the smectite to chlorite transition slow rates of growth are linked to the first reaction pathway involving mixed layering while increasing rates of growth relative to nucleation promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition representative of the third pathway

using nonlinear forecasting to learn the magnitude and phasing of time varying sediment suspension in the surf zone the time dependent response of sediment suspension to flow velocity was explored by modeling field measurements collected in the surf zone during a large storm linear and nonlinear models were created and tested using flow velocity as input and suspended sediment concentration as output a sequence of past velocities velocity history as well as velocity from the same instant as the suspended sediment concentration was used as input this velocity history length was allowed to vary the models also allowed for a lag between input instantaneous velocity or end of velocity sequence and output suspended sediment concentration predictions of concentration from instantaneous velocity or instantaneous velocity raised to a power up to 8 using linear models were poor correlation coefficients between predicted and observed concentrations were less than 0 10 allowing a lag between velocity and concentration improved linear models correlation coefficient of 0 30 with optimum lag time increasing with elevation above the seabed from 1 5 s at 13 cm to 8 5 s at 60 cm these lags are largely due to the time for an observed flow event to effect the bed and mix sediment upward using a velocity history further improved linear models correlation coefficient of 0 43 the best linear model used 12 5 s of velocity history approximately one wave period to predict concentration nonlinear models gave better predictions than linear models and as with linear models nonlinear models using a velocity history performed better than models using only instantaneous velocity as input including a lag time between the velocity and concentration also improved the predictions the best model correlation coefficient of 0 58 used 3 s approximately a quarter wave period of the cross shore velocity squared starting at 4 5 s before the observed concentration to predict concentration using a velocity history increases the performance of the models by specifying a more complete description of the dynamical forcing of the flow including accelerations and wave phase and shape responsible for sediment suspension incorporating such a velocity history and a lag time into the formulation of the forcing for time dependent models for sediment suspension in the surf zone will greatly increase our ability to predict suspended sediment transport

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

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

crustal structure beneath ne china imaged by necessarray receiver function data abstract we analyzed tens of thousands of receiver function data recorded by 185 broadband seismic stations to study the crustal structure beneath the northeast china moho depth and average crustal v p v s ratio were measured at each station using the h grid searching technique for stations located above unconsolidated sediments we applied the h method to remove strong shallow reverberations and generate subsurface receiver functions that allow for effective h analysis the measurements show that the songliao basin has a relatively thin crust 31 km and the moho depth increases significantly from southeast 27 km to northwest 35 km the northwestward tilting of the songliao basin may suggest that it was initiated by lithospheric flexure due to the load of the great xing an range in the jurassic before the large scale extension in the cretaceous moho depth varies from 26 7 km to 42 3 km across the study area with the shallowest and deepest moho being located at the eastern flank of the songliao basin and the great xing an range respectively the moho depth correlates well with the surface topography in the western part but not the central and eastern parts of the study area the residual topography computed based on the airy s isostasy model indicates that the high topography at the eastern flank of the songliao basin the changbaishan volcanic center and the southern end of the great xing an range is likely dynamically supported by the upper mantle

nearshore bars and the break point hypothesis abstract the set of hypotheses calling for bar formation at the break point was tested with field data during two different experiments waves were measured across the surf zone coincident with the development of a nearshore bar we use a criterion based on the wave height to depth ratio to determine the offshore limit of the inner surf zone during the first experiment the bar became better developed and migrated offshore while remaining well within the inner surf zone during the second experiment the surf zone was narrower and we cannot rule out the possibility of break point processes contributing to bar development we conclude that bars are not necessarily coupled with the break point and can become better developed and migrate offshore while being in the inner surf zone landward from initial wave breaking in the outer surf zone

infragravity waves over a natural barred profile measurements of cross shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run up spectrum of leaky mode or high mode edge waves as in earlier studies the spectra compared closely however for some frequencies the energy of the measured spectrum exceeded the energy of the synthetic spectrum suggesting that the run up spectrum was not white but had dominating frequencies utilizing cross shore flow data and synthetic spectra from a number of cross shore locations an equivalent run up spectrum was calculated for each day on the first day of the storm the equivalent run up spectrum indicated a dominant wave that had a node in velocity reasonably close to the bar crest later during the storm when the bar had migrated farther offshore there was no evidence for a dominant motion having a velocity node at the bar crest the structure of the equivalent run up spectrum compared well with spectra of direct measurements of run up obtained several hundred meters away we have no clear evidence in support of the theory that infragravity waves might form or force the offshore migration of a bar to confirm this finding longer records obtained synoptically over a developing bar are required the dominant wave observed early in the storm was consistent with symond and bowen s 1984 theoretical prediction of resonant amplification of discrete frequencies over a barred profile

early jurassic mafic magmatism in the lesser xing an zhangguangcai range ne china and its tectonic implications constraints from zircon u pb chronology and geochemistry abstract la icp ms zircon u pb dating and geochemical data have been obtained from five representative mafic ultramafic intrusions in the lesser xing an zhangguangcai range ne china with the aim of improving our understanding of the mesozoic tectonic evolution in the region and in particular determining the time of initiation of the circum pacific tectonic system the selected zircons exhibit striped absorption in cathodoluminescence cl images and have high th u ratios 0 20 3 16 indicating a magmatic origin the zircon u pb dates indicate that most of these magmatic zircons other than a few relics that were captured and entrained in the magma formed in the late early jurassic 186 182 ma and not as previously supposed in the middle caledonian the five mafic ultramafic plutons are composed of olivine gabbro hornblendite gabbro hornblende gabbro and gabbro diorite the olivine gabbro and hornblendite display cumulate textures implying that fractional crystallization of olivine and plagioclase took place during magma evolution these mafic ultramafic igneous rocks have sio2 37 3 55 7 mgo 3 05 13 3 al2o3 11 8 23 8 mg 42 69 mg 100mg mg fe2 total and eu 0 88 1 32 and they display three types of rare earth element ree distribution patterns right slipped flat patterns or dome like the trace element spider diagrams show that the rocks are enriched in large ion lithophile elements liles such as ba k and sr and depleted in high field strength elements hfses such as nb ta zr and hf the zircons have ehf 186 182 ma 2 7 to 12 0 and tdm1 366 732 ma the geochemical data indicate that the early jurassic mafic magma originated in an extensional environment from the partial melting of a depleted mantle wedge that had been metasomatized by fluids released from a fossil subducted slab these data combined with information on the spatial variation of coeval igneous rocks indicate that the formation of the early jurassic mafic ultramafic rocks in the lesser xing an zhangguangcai range was related to the subduction of the paleo pacific plate beneath the eurasian continent and this event would mark the beginning of the circum pacific tectonic system

clay mineral and zeolite diagenesis in the toa baja well puerto rico several diagenetic reactions typical of volcaniclastic sediments have been identified in the toa baja well the zeolites heulandite and less commonly analcite present in the upper half of the drilled section give way to laumontite at depth a decrease with depth in the expandability of mixed layer chlorite smectite was observed corrensite was detected over the depth range 1 676 2 286 m temperatures implied by the depth ranges of diagenetic and indicator minerals are consistent with a paleothermal gradient of about 30 50c km assuming little or no erosion of section

spatial and temporal distributions of the late mesozoic volcanic successions and their controlling effects on the changling fault depression of the songliao basin northeast china volcanic successions including their spatial temporal tectonic and geochemical attributes were identified based on well data 2d and 3d seismic data u pb isotopic ages and major and trace element data from the changling fault depression of the songliao basin in northeastern china three eruption cycles developed in the changling fault depression k1h huoshiling formation 124 118 ma k1yc1 first member of the yingcheng formation 115 106 ma and k1yc3 third member of the yingcheng formation 106 102 ma these three eruption cycles comprised seven eruption stages the volcanic successions in every eruption cycle were bimodal and evolved from basic to acidic the magma of the basic and intermediate rocks in these cycles was derived from partial melting of the asthenosphere in k1yc1 and k1yc3 partial melting of the newly formed basic rocks in the lower crust formed the high sio2 acidic magma in addition fractional crystallization of basic magma formed the small scale intermediate acidic m

formation of the giant chalukou porphyry mo deposit in northern great xing an range ne china partial melting of the juvenile lower crust in intra plate extensional environment abstract the chalukou porphyry mo deposit 2 46 mt 0 087 mo located in the northern great xing an range ne china is the largest mo deposit discovered in china so far the host rocks consist of aplite porphyry granite porphyry and quartz porphyry and are intruded into lower ordovician intermediate felsic volcanic sedimentary rocks and pre ore monzogranite and are cut by post ore feldspar porphyry diorite porphyry and quartz monzonite porphyry here we present the zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data for the pre ore syn ore and post ore intrusive rocks the chalukou ore forming porphyries intruded during 147 148 ma and have high silica alkali rich metaluminous to slightly peraluminous compositions and are oxidized they are enriched in large ion lithophile elements e g k rb u and th light ree and depleted in high field strength elements e g nb p and ti depletions in eu ba sr nb ta p and ti suggest that they have experienced strong fractional crystallization of plagioclase biotite hornblende and accessory minerals the pre ore monzogranite 172 ma also belongs to the high k calc alkaline series highly fractionated ree patterns la yb n 19 6 21 7 high values of sr y 54 69 and la yb 29 32 are adakite like geochemical features the post ore rocks 141 128 ma have similar geochemical characteristics with ore forming porphyries except that quartz monzonite porphyry shows no ba sr negative anomaly all intrusive rocks have relative low initial 87sr 86sr 0 705413 0 707889 and end t values 1 28 to 0 92 positive ehf t values 2 4 to 10 1 and young two stage nd and hf model ages tdm2 nd 863 977 ma tdm2 hf 552 976 ma these geochemical and isotopic data are interpreted to demonstrate that the ore forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra plate extensional setting the pre ore monzogranite formed by partial melting of thickened lower crust in a collisional setting caused by closure of mongol okhotsk ocean the post ore feldspar porphyry shares a similar magma source with ore forming porphyry but the quartz monzonite porphyry has a relatively deeper magma source region and has not experienced as much fractional crystallization the transformation from middle jurassic compression to late jurassic extension created favorable conditions for the generation and emplacement of the ore forming magma the juvenile lower crust provided the main source of molybdenum for chalukou deposit enrichment of mo by fractional crystallization played an important role in concentrating mo during formation of the chalukou mo deposit the age 147 ma high fluorine and associated pb zn deposits are all different from other major porphyry mo deposits in ne china chalukou is a new mineral deposit type in the great xing an range

origins of large volume rhyolitic volcanism in the antarctic peninsula and patagonia by crustal melting voluminous rhyolitic volcanism along the palaeo pacific margin of gondwana was marked by three principal episodes of magmatism the first of these v1 is essentially coincident with the main episode of karoo ferrar magmatism at 184 ma a younger v2 episode occurred at 168 ma and a third episode v3 occurred in the interval 157 153 ma we evaluate the origin of v1 and v2 rhyolites from the antarctic peninsula using major and trace element and isotopic sr nd o data an isotopically uniform 87sr 86sri 0 707 endi 3 andesite dacite magma was generated as a result of anatexis of grenvillian age hydrous mafic lower crust linked to earlier arc related underplating the lower crustal partial melts would have mixed with fractionated components of the mafic underplate followed by subsequent storage and homogenization early jurassic v1 rocks of the southern antarctic peninsula are interpreted as melts of upper crustal paragneiss which have mixed with the isotopically uniform magma in upper crustal magma chambers the v2 rhyolites are the result of assimilation fractional crystallization of the isotopically uniform magma this occurred in upper crustal magma chambers involving assimilants with similar isotopic composition to that of the magma a continental margin setting was crucial in developing hydrous readily fusible lower crust lower crustal anatexis was in response to mafic underplating associated with the discovery shona bouvet group of plumes thought to be responsible for the karoo magmatic province the progression old to young of volcanism from ne to sw in patagonia and south to north in the antarctic peninsula is consistent with migration away from the mantle plumes towards the proto pacific margin of gondwana during rifting and break up

zeolite to prehnite pumpellyite facies metamorphism of the late proterozoic zig zag dal basalt formation eastern north greenland abstract the zig zag dal basalt formation 1300 m maximum thickness of late proterozoic age exposed in eastern north greenland has been variably affected by low temperature metamorphism resulting in the development of calc silicate and mafic phyllosilicate bearing assemblages relatively fresh flows sometimes preserving primary olivine calcic plagioclase augite and pigeonite and showing randomly mixedlayer chlorite smectite are sandwiched between flows showing not only more extensive alteration but also higher temperature assemblages accordingly in these flows the primary igneous phases are replaced with the exception of augite and prehnite and pumpellyite along with rare zeolites are sporadically developed while regular mixed layer chlorite smectite and or true chlorite predominate temperatures have been estimated on the presence absence of various secondary minerals and also using the chlorite geothermometer and are indicative of progressive metamorphism in the range from below 125 c to approximately 200 c i e in the zeolite facies to lowermost prehnite pumpellyite facies range no depth dependent temperature related zonation of secondary mineral phases as seen in other thick altered basalt successions has been identified in the zig zag dal basalts however instead alteration appears to have been influenced by the physical character of the flows themselves including flow thickness degree of vesicularity and the presence or absence of jointing all of which appear to have exerted an influence over access of fluid this relation between flow character and intensity of alteration suggests that fluid flow through the zig zag dal basalts must have been predominantly lateral rather than vertical

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

silver base metal epithermal vein and listwaenite types of deposit crnac rogozna mts kosovo part i ore mineral geochemistry and sulfur isotope study abstract pb zn ag vein and listwaenite types of mineralization in crnac deposit western vardar zone were deposited within several stages i the pre ore stage comprises pyrite arsenopyrite pyrrhotite quartz kaolinite and is followed by magnetite pyrite ii the syn ore stage is composed of galena sphalerite tetrahedrite and stefanite and iii the post ore stage is composed of carbonates pyrite arsenopyrite and minor galena the vein type mineralization is hosted by jurassic amphibolites and veins terminate within overlying serpentinites mineralized listwaenites are developed along the serpentinite amphibolite interface the reserves are estimated to 1 7 mt of ore containing in average 7 6 lead 2 9 zinc and 102 g t silver sulfides from the pre and syn mineralization assemblage of the vein and listwaenite types of mineralization from the crnac pb zn ag deposit have been analyzed using microprobe crush leachates and sulfur isotopes the pre ore assemblage precipitated under high sulfur fugacities f s 2 10 8 10 6 bar from temperatures ranging between 350 c and 380 c most likely water rock reactions boiling and or increase of ph caused an increase of 34 s of pyrite toward upper levels within the deposit the decomposition of pre ore pyrrhotite to a pyrite magnetite mixture occurred at a fugacity of sulfur from f s 2 8 7 10 10 to 9 6 10 9 bar and fugacity of oxygen from f o 2 2 4 10 30 to 3 1 10 28 bars indicating a contribution of an oxidizing fluid i e meteoric water during pre ore stages of hydrothermal activity the crystallization temperatures obtained by the sphalerite galena isotope geothermometer range from 230 to 310 c the 34 s values of pre and syn ore sulfides pyrite galena sphalerite 34 s 0 3 5 9 point to magmatic sulfur values of 34 s of galena and sphalerite are decreasing upwards due to precipitation of early formed sulfide minerals post ore assemblage precipitated at temperature below 190 c based on data presented above we assume two fluid sources i a magmatic source supported by sulfur isotopic compositions within pre and syn ore minerals and a high mol of fluorine found within pre and syn ore leachates and ii a meteoric source deduced by coincident pyrite magnetite intergrowth sulfur isotopic trends within syn ore minerals and decrease of crystallization temperatures from the pre ore stage 380 350 c towards the syn ore 310 215 c and post ore stages

geochemical constraints on the origin of bimodal magmatism at the okinawa trough an incipient back arc basin abstract the magmatism at the axial zone of the middle okinawa trough a young continental back arc basin comprises a bimodal basaltic rhyolitic suite accompanied by minor intermediate rocks we report major and trace element and sr nd isotopie data for the intermediate to silicic suites to provide constraints on their petrogenesis the rhyolites recovered as lava and pumice fall into three geochemical groups type 1 2 and 3 rhyolites type 1 rhyolites have 87sr 86sr 0 7040 0 7042 and 143nd 144nd 0 5128 0 5129 identical to those of associated basalts and are characterized by highly fractionated ree patterns petrogenesis of type 1 rhyolites is explicable in terms of fractional crystallization of the associated basalt in contrast type 2 rhyolites and andesite have slightly higher 87sr 86sr 0 7044 0 7047 but similar 143nd 144nd 0 5128 compared to those of the basalts the compositions of type 2 rhyolite and andesite can be explained by assimilation and fractional crystallization afc processes of the basalt magma quantitative analysis suggests assimilation fractional crystallization ma mc ratios of 0 05 hybrid andesite generated by mixing of evolved basalt and type 1 rhyolite is also present we emphasize that mechanical extension in this part of the okinawa trough involves gabbro ic lower crust that resulted from fractionation of mantle derived basaltic magmas type 3 rhyolite occurs only as pumice which makes its derivation questionable this rhyolite has major and trace element compositions and sr nd isotopie ratios which suggests that it may be derived from volcanic activity on the southern ryukyu volcanic front and arrived in the okinawa trough by drifting on the kuroshio current

transition from the zeolite to prehnite pumpellyite facies in the karmutsen metabasites vancouver island british columbia

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

the morphodynamic effects of incident wave groupiness and tide range on an energetic beach abstract the roles played by daily tide range and incident wave groupiness in affecting the short term morphodynamic responses of an energetic beach are examined demodulation of original tide and wave time series from the moderate energy narrabeen beach australia resulted in new time series of daily tide range and a daily grouping factor which expresses the relative amplitude of the alternation between groups of high and low waves using these new time series together with time series of daily beach state and changing breaker conditions statistical analyses were performed aimed at determining the contributions made by tide and groupiness in explaining time varying beach state additional to those made by time varying wave conditions eigenvector analyses of monthly surveyed beach and surf zone profiles provided a set of time series on modes of profile configuration change which were also analyzed to determine the relative effects of waves and tide range on profile shape both tide range and groupiness are significant determinants of beach state the six beach states are reflective low tide terrace transverse bar and rip rhythmic bar and beach longshore bar trough and dissipative wright and short 1984 provided that wave conditions are within the appropriate range to favor beach states at the reflective end of the sequence spring tides will tend to favor the low tide terrace over the transverse bar and rip state higher tide ranges are also associated with more subdued bar trough topography the more accentuated bar trough profiles are developed when tide range is minimal overall higher relative incident wave groupiness favors the more dissipative states incident wave groupiness is the dominant factor determining whether the low tide terrace state or transverse bar and rip state prevails provided incident wave steepnesses permit one or the other of these states groupiness is also important in discriminating between the transverse bar and rip and rhythmic bar and beach states

vertical structure of mean cross shore currents across a barred surf zone mean cross shore currents observed across a barred surf zone are compared to model predictions the model is based on a simplified momentum balance with a turbulent boundary layer at the bed turbulent exchange is parameterized by an eddy viscosity formulation with the eddy viscosity a independent of time and the vertical coordinate mean currents result from gradients due to wave breaking and shoaling and the presence of a mean setup of the free surface descriptions of the wave field are provided by the wave transformation model of thornton and guza 1983 the wave transformation model adequately reproduces the observed wave heights across the surf zone the mean current model successfully reproduces the observed cross shore flows both observations and predictions show predominantly offshore flow with onshore flow restricted to a relatively thin surface layer successful application of the mean flow model requires an eddy viscosity which varies horizontally across the surf zone attempts are made to parameterize this variation with some success the data does not discriminate between alternative parameterizations proposed the overall variability in eddy viscosity suggested by the model fitting should be resolvable by field measurements of the turbulent stresses consistent shortcomings of the parameterizations and the overall modeling effort suggest avenues for further development and data collection

timing and processes of late mesozoic mid lower crustal extension in continental ne asia and implications for the tectonic setting of the destruction of the north china craton mainly constrained by zircon u pb ages from metamorphic core complexes abstract late mesozoic large scale crustal extension occurred across the northeastern section of continental asia and metamorphic core complexes mccs are the major features in this region this paper presents new zircon u pb and ar ar ages of biotite and hornblende for pre or syn mylonitized and post kinematic unmylonitized intrusions from these mccs and attempts to determine the timing of initiation duration and termination of the mid lower crustal ductile extension by integrating with geochronological data from previous studies these mccs have similar 40 ar 39 ar biotite and hornblende ages 130 to 110 ma mainly from 130 to 120 ma which are interpreted as the cooling ages and represent the timing of the late stage formation of the mccs zircon u pb ages for syn to post kinematic intrusions from some mccs suggest that the mid lower crustal extension probably initiated at ca 150 145 ma with a peak occurring 145 130 ma and continued to 130 120 ma which is older than that suggested by 40 ar 39 ar ages by 10 20 ma the early ductile extension most likely initiated in mongolia and northern china during the late jurassic 150 145 ma at a deeper level then propagated southwards 140 130 ma and finally developed throughout the entire continental ne asia 130 120 ma based on the timing and processes of the extension a geodynamic model and tectonic setting of the destruction of the north china craton ncc are proposed

retrograde fluid infiltration in the high grade modum complex south norway evidence for age source and ree mobility the high grade metamorphic basement of the modum complex south norway exhibits retrogradation and alteration due to late stage fluid infiltration extensive alteration zones of albite and calcite rich veining occur especiallywithin and around numerous metagabbros the gabbros intruded at 1224 15ma are now partly altered to amphibolites due to the subsequent high grade metamorphism two generations of albite rich rocks have been recognized 1 a fine grained foliated type 2 a coarse grained crosscutting type both types show a typical greenschist facies mineralassemblage albite actinolite chlorite talc the calcite veins dykesrepresent a younger generation of veins than both albite rich types u pb data for spheneof type 1 yielded an age of 1080 3 ma determining a point on the retrogradep t t path of the modum complex increasing albitisation of themetagabbros leads to a decrease in 143nd 144nd oand an increase in 87sr 86 o albite and calcite rich samples show negative nd and positive sr suggesting that fluids which interacted with the metagabbros originated from a crustal reservoir the nd and sr isotopic data show disequilibrium at the microscale as well as at the macroscale negative sm nd model ages of the albite rich rocks demonstrate that rare earth elements rees were mobile and fractionated during albitisation

zeolite to prehnite pumpellyite facies metamorphism in the toa baja drill hole puerto rico secondary mineral assemblages in eocene volcanic and volcaniclastic rocks of the toa baja drill hole progressively change as a function of depth four metamorphic zones are delineated with increasing depth caclinoptilolite heulandite laumontite prehnite purnpellyite zone the deepest belongs to the prehnite pumpellyite facies whereas the three zones at shallower depths 2350 m belong to the zeolite facies ca clinoptilolite and heulandite exhibit continuous solid solution with varying si al 2 9 5 2 and ca ca na k ratios 0 45 0 89 pumpellyites are characterized by extensive variation in the fe fe al mg ratio 0 29 0 74 and extreme fe enrichment in the laumontite zone temperatures estimated from mineral assemblages and fades transitions suggest that the north coast basin puerto rico has been subject to a metamorphic field gradient of 50 to 70 c km

age constraints on late mesozoic lithospheric extension and origin of felsic volcanism in the songliao basin ne china abstractlate mesozoic lithospheric extension in ne asia resulted in the development of a large extensional province and widespread formation of volcanosedimentary basins songliao basin is the biggest in that region situated between the siberian and sino korean north china cratons the songliao basin contains voluminous volcanic rocks as a major part of the basin fill volcanic successions form a significant but unexposed part of the late mesozoic magmatic province in ne china here we report zircon u pb ages and geochemical data for felsic volcanic rocks from the songliao basin zircon populations of two types of rhyolites with distinct i and a type affinities analyzed by laser ablation inductively coupled plasma mass spectrometry yielded similar u pb ages of 114 2 and 113 2 ma respectively whole rock nd and zircon hf isotope data of the felsic rocks indicate an origin from newly formed crustal protoliths the i type dacites and rhyolites show geochemical signatures with subduction related af

late mesozoic calc alkaline volcanism of post orogenic extension in the northern da hinggan mountains northeastern china abstract late mesozoic calc alkaline volcanism in the northern da hinggan mountains ndhm ne china exhibits geochemical and sr nd isotopic characteristics similar to those of cenozoic calc alkaline volcanism in the basin and range province usa whole rock k ar dating results show that these volcanic sequences were erupted during 138 116 ma composed of basaltic andesites trachyandesites group 1 hornblende andesites trachytes group 2 and rhyolite lavas group 3 they are characterized by low mgo contents 4 20 lile lree enrichment and significant nb ta depletion as well as a little depleted to slightly enriched nd and weakly enriched sr isotopic ratios group 1 initial 87sr 86sr 0 70502 0 70572 nd t 0 78 to 0 91 group 2 initial 87sr 86sr 0 70497 0 70518 nd t 0 86 to 1 26 group 3 initial 87sr 86sr 0 70510 0 70635 nd t 0 41 to 0 25 the systematic variations in major and trace elements homogeneous sr nd isotope data and temporal consistency among three volcanic groups indicate that they were derived from a similar mantle source metasomatized by fluids related to the closure of the paleo asian and or mongolia okhotsk oceans and were produced through different degrees of fractional crystallization of the primary melts group 1 basaltic rocks were formed through removal of olivine and pyroxene of the primary melts while group 2 trachytes which contain the lowest lree contents e g la 24 28 ppm and relatively less enriched sr and higher nd isotope ratios were generated after removal of a few percent of lree rich minerals such as hornblende clinopyroxene and apatite of melts like group 1 group 3 rhyolite lavas exhibiting the highest abundances of strongly incompatible elements such as rb and k moderate lree contents e g la 28 53 ppm as well as apparently negative eu and sr anomalies represent the final crystallized products following a plagioclase predominant fractionation of melts like group 2 the low mgo contents and evolved affinities of the volcanic rocks imply that beneath the ndhm there existed many crustal magma reservoirs throughout the eruption episodes in which mantle derived primary melts had experienced intense differentiation these facts in combination with the contemporaneous basin and range tectonic regime suggest that the extensive calc alkaline volcanism in the ndhm was attributed to post orogenic diffuse extension rather than either an upwelling mantle plume or mesozoic oceanic plate subduction

early jurassic extensional basin formation in the daqing shan segment of the yinshan belt northern north china block inner mongolia abstract structural and stratigraphic studies of the western daqing shan segment of the yinshan belt have recognized an early jurassic extensional episode supported by several lines of evidence first normal faults cut the lowermost jurassic sequence and are overlapped by younger lower jurassic rocks second lower jurassic rocks include growth strata in small scale graben at the base of the jurassic basin third rapid lateral facies changes are mapped from boulder conglomerates along the basin bounding faults to lacustrine and meandering fluvial rocks in the basin center fourth paleodrainage systems provided sediment input from three sides of the basin two transverse and one axial finally there is a strongly asymmetric distribution of coarse proximal and fine distal facies within the basin the early jurassic extensional episode was responsible for formation of an east trending half graben basin in the western daqing shan in which at least 1800 m of syn extensional nonmarine sediments accumulated and are preserved previous studies in the triassic and jurassic of other parts of northwest and north central china have concluded that the early mesozoic was a time of continental amalgamation and contractile deformation the recognition of an early jurassic extensional episode along the northern margin of the north china block is problematic in this context at least superficially we propose two possible explanations for the early jurassic extension transtension associated with strike slip tectonics or gravitational collapse of a pre existing late paleozoic early mesozoic contractile orogenic belt the first possibility transtensional deformation is problematic because specific strike slip faults have not been identified that could control extension in the western daqing shan however several lines of evidence allow the possibility of such a driving mechanism including documented early jurassic transtensional systems in the southwestern north china block several candidate strike slip faults along the china mongolia border region structural discontinuity between the daqing shan and southern mongolia and along strike changes in structural style within the yinshan belt the second possibility orogenic collapse is similarly difficult to establish because of the limited amount of data concerning the regional distribution and orientation of pre jurassic contractile structures and early jurassic extensional structures however documented late paleozoic triassic contractile deformation as well as the close temporal and spatial association and parallelism between early jurassic extensional structures and older contractile structures in the western daqing shan requires consideration of gravitational collapse as a driving mechanism for early jurassic extension in the yinshan belt

a system for measuring bottom profile waves and currents in the high energy nearshore environment abstract a new data acquisition system capable of measuring waves currents and the nearshore profile in breaking waves as high as 5 m has been developed and successfully field tested components of the mechanical system are a sled carrying a vertical mast a double drum winch placed landward of the beach and a line that runs from one drum of the winch around three blocks which are the corners of a right triangle to the other drum of the winch the sled is attached to the shore normal side of the triangular line arrangement and is pulled offshore by one drum of the winch and onshore by the other the profile is measured as the sled is towed along the shore normal transect using an infrared rangefinder mounted landward of the winch and optical prisms mounted on top of the sled s mast a pressure sensor and two axis electromagnetic current meter are mounted on the frame of the sled these data are encoded on the sled and telemetered to a receiving recording station onshore preliminary results suggest that near bottom offshore flowing currents during periods of high energy swell are important in forcing changes to the configuration of the nearshore profile

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

cenozoic episodic volcanism and continental rifting in northeast china and possible link to japan sea development as revealed from k ar geochronology abstract cenozoic volcanic rocks in northeast china comprise part of the volcanic belt of the western circum pacific rim and represent one of the presently active tectono magmatic regions of the world over 590 volcanoes with erupted basalts covering an area of 50 000 km 2 are exposed in the songliao graben and particularly on its flanks k ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire cenozoic corresponding to the tectono magmatic interactions particularly between the india eurasia and pacific plates the volcanism initiated in the songliao graben in late cretaceous 86 ma and migrated flankward since 28 ma the magmatic propagation shows three major stages intimately associated with the evolution of japan sea and related to the geodynamic forcing of the india eurasia collision prior to japan sea rifting volcanic eruptions were restricted to the songliao basin during japan sea opening volcanism migrated into the lateral belts after cessation of japan sea opening at 15 ma volcanism with greatest intensity occurred on both flanks particularly along the yi yi fault system around 14 13 ma and subsequently the fu mi fault between 11 and 7 ma continuing this trend of migration eruptions scattered further away from the songliao basin in the last 4 5 ma we suggest that the cenozoic volcanic belt in northeast china and the japan sea backarc basin are competitive parts in the eastern marginal magmatic system of the eurasian plate the early stage of the volcanism in the songliao basin may have resulted from mantle upwelling beneath the songliao bohai basin belt rifting of the ne faults and relatively weak intensity of volcanism in northeast china during japan sea opening could be attributable to the lithospheric breakup in the japan sea and spreading of japan sea the subsequent strong volcanism in northeast china after cessation of the japan sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin the diversified volcanism in scattered localities during the quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly a magmatically waning phase of the limited source in eastern china

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

carbon and oxygen stable isotopes in the toa baja well puerto rico implications for burial diagenesis and hydrocarbon generation this is the publisher s version also available electronically from http onlinelibrary wiley com

40ar 39ar and k ar dating on the volcanic rocks in the songliao basin ne china constraints on stratigraphy and basin dynamics precise 40ar 39ar and k ar ages were determined on sanidine and whole rock separates of volcanic rocks in the songliao basin sb the volcanism is characterized by a series of continual and episodic eruptions in the late jurassic 147 157 ma and early cretaceous 113 136 ma a fairly accurate chronostratigraphic column was first established based on those data the volcanic activities happened synchronously with closure of the mongolia okhotsk ocean north to the sb structures of the volcanogenic successions are s dipping or se dipping fault blocks coupled with n dipping or nw dipping major detachment systems distribution of the volcanics revealed by high resolution seismic reflections is neither restricted within nor in agreement with the framework of the overlying sedimentary sequence striking nne this new evidence fits the overlap model proposed in the present paper that formation of the volcanic successions in the sb is related to the subduction of the mongolia okhotsk plate under the mongolia north china block during the jurassic and early cretaceous whereas the overlying sedimentary sequence unconformably on the volcanics is tectonically controlled by the oblique subduction of the pacific plate under the eurasian plate since late aptian in addition the coal bearing epiclastic sediments intercalating the volcanics were deposited at the subduction quiescence episodes when extensional collapse occurred

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

the smectite to chlorite transition in the chipilapa geothermal system el salvador clay mineralogical x ray diffraction and electron microprobe studies have been carried out on separated 2 m fractions from cutting and core material from three wells in the chipilapa geothermal system in el salvador the data indicate that the smectite to chlorite transition is prevalent but a secondary smectite to illite transition is also present at depths approximately 750 m smectite with very minor chlorite mixed layers approximately 15 is dominant and has a composition midway between a di and tri smectite at 750 m there is a very clear distinction and sharp transition into discrete chlorite with very minor smectite mixed layers approximately 10 corrensite is recorded only as a rare and minor phase smectite occurs in abundance at temperatures up to 200 c and the transition from a smectitedominant to chlorite dominant assemblage takes place over a narrow temperature range 150 to 200 c the stability range of smectite is very similar to that recorded in other geothermal systems whereas the smectite to chlorite transition differs greatly from that recorded in other systems the transition does not involve continuous chlorite smectite mixed layering but a marked step it is the sharpest and most discontinuous stepped sequence of this mineralogical transition recorded

zircon rock partition coefficients of rees y th u nb and ta in granitic rocks uses for provenance and mineral exploration purposes abstract the trace element composition of magmatic zircon is highly variable even within the same grain and its study is complicated by the abundance of microinclusions metamict portions and strong compositional zoning among other factors to contribute to the understanding of the geochemistry of trace elements in zircon we determined the rare earth y nb ta th and u contents in zircon grains by laser ablation inductively coupled plasma mass spectrometry la icp ms with the use of cathodoluminescence and backscattered mev images zircon rock partition coefficients were determined in nine different types of granitoids and compared with experimental and natural data the obtained data are comparable with those reported by other authors by using the partition coefficient we estimated the composition of the host granitoids based on the zircon grain composition which was interpreted as evidence that the patterns of the trace elements in zircon grains are controlled by the liquid composition at the moment of crystallization a new set of partition coefficients for rees y nb ta th and u is suggested for provenance and exploratory studies la 0 8 ce 1 7 pr 2 1 nd 3 4 sm 9 8 eu 7 9 gd 24 tb 37 dy 69 ho 117 er 167 tm 281 yb 379 lu 437 nb 1 6 ta 2 9 th 27 u 177 and y 109 trace element diagrams eu eu vs yb nb vs th and y 200 lu 10 nb vs nb ce are proposed for discriminating zircon from different types of granitoids particularly for a type i type and shoshonitic rocks the trace element patterns of zircon are useful as a tool for mineral exploration studies because they often reproduce the patterns of mineralized granites

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

geologic implications of the oxygen isotope profile of the toa baja drill hole puerto rico the whole rock o isotopic compositions of volcanic and volcaniclastic samples from the toa baja drill hole demonstrate that low temperature 200 c processes have strongly enriched the island arc materials in 18o subsequent to eruption processes such as subaerial weathering alteration during transport and deposition in volcaniclastic aprons submarine weathering burial diagenesis and prograde regional metamorphism through the beginning of the prehnite pumpellyite facies have raised average whole rock 18o values by 4 for basalt and andesite lava flows and by 8 for volcaniclastic sandstones these o isotopic disturbances were probably caused by oxygen exchange with regionally circulating seawater under rather high water rock conditions the processes associated with ageing of volcanic and volcaniclastic materials in the oceanic environment are probably more important to the global budgets of the oxygen isotopes than has been assumed in the past integration of these results into global models for the oxygen isotopes awaits analysis of more varied oceanic terranes to determine the generality of the o isotopic conclusions preferred here and to more carefully evaluate the relative sizes of volcanic volcaniclastic and oceanic oxygen reservoirs and their variabilities in time

vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach greenwood b and osborne p d 1990 vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach coastal eng 14 543 580 eulerian measurements of the horizontal cross shore velocity field in the lowermost meter of the water column in association with measurements of waves and the mean elevation of the water surface across a nontidal low relief barred surf zone reveal a spatially coherent patterns of the timeaveraged first second and third moments of the velocity field which vary temporally in direct response to the incident waves b large asymmetries in the flow field with offshore directed mean flows upto 0 20 m s a and onshore directed velocity skewness the third moment normalized by the standard deviation upto 0 60 c mean flows decrease and oscillatory flows measured by the standard deviation of the velocity field increase towards the water surface d a fourth order polynomial provides the best fit to the cross shore set up reflecting the influence of variable energy dissipation due to topographic controls on wave breaking e significant linear correlations exist between the cross shore mean velocities and the maximum set up of the still water surface near to the shoreline upto 82 of the observed variability in the former can be accounted for by linear regressions f set up is highly correlated with the incident wave height 86 of the observed variability in the former can be accounted for by a linear regression g gradients in the mean water surface are significantly less than those predicted by a linear function of beach slope as originally proposed by bowen et al even using an appropriate breaking criterion 0 4 0 6 for the spilling breakers recorded cross shore circulation over the low relief barred nearshore slope is predominantly two dimensional over the outer bar in this case study the near bed mean flow is an undertow responding to the balance between the wave generated depth dependent momentum flux directed onshore the stress induced by the onshore mass transport under waves and wind and the hydraulic pressure gradient induced by set up of the mean water level

on predicting infragravity energy in the surf zone flow data were obtained in the surf zone across a barred profile during a storm rms cross shore velocities due to waves in the infragravity band wave periods greater than 20 s had maxima in excess of 0 5 m s over the bar crest for comparison to measured spectra synthetic spectra of cross shore flow were computed using measured nearshore profiles the synthetic spectra were calculated assuming a white runup spectrum of mode 4 edge waves of unit amplitude although the results would be essentially the same for standing waves or any edge wave mode above 2 the structure in the infragravity band of these synthetic spectra corresponded reasonably well with the structure of the measured spectra total variances of measured cross shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra these nondimensional variances were independent of distance offshore and increased with the square of the breaker height thus cross shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions

geochronology and geochemistry of the wunugetushan porphyry cu mo deposit in ne china and their geological significance abstract the wunugetushan porphyry cu mo deposit is located in the manzhouli district of ne china on the southern margin of the mesozoic mongol okhotsk orogenic belt concentric rings of hydrothermal alteration and cu mo mineralization surround an early middle jurassic monzogranitic porphyry the cu mo mineralization is clearly related to the quartz potassic and quartz sericite alteration molybdenite re os and groundmass 40 ar 39 ar of the host porphyry dates indicate that the ore formation and porphyry emplacement occurred at 177 6 4 5 ma and 179 0 1 9 ma respectively geochemically the host porphyry of the deposit is characterized by strong lree hree fractionation enrichment in lile ba rb u th and pb and depletion of hfse nb ta ti and hree the sr nd pb isotopic compositions of the porphyry display an varied initial 87 sr 86 sr i ratio a positive e nd t values and high 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t ratios these data indicate that the magmatic source of the host porphyry comprised two end members lithospheric mantle metasomatized by fluids derived from the subducted slab and continental crust we infer that the primitive magma of the host porphyry was derived from crust mantle transition zone based on regional geology and geochemistry of the host porphyry the wunugetushan deposit is suggested to form in a continental collision environment after closure of the mongol okhotsk ocean

dynamic process analysis for the initiation and movement of the donghekou landslide debris flow triggered by the wenchuan earthquake the donghekou landslide debris flow was a remarkable geological disaster triggered by the wenchuan earthquake in 2008 the dynamic process of a rapid landslide debris flow is very complicated and can be divided into two aspects the slope dynamic response of the earthquake and the mass movement and accumulation process a numerical method combined with a finite difference method fdm and discrete element method dem for simulation of landslide debris flow under seismic loading is presented the fdm and dem are coupled through the critical sliding surface initiation time and velocity the dynamic response of the slope is simulated by the finite difference method and critical sliding surface is determined using the earthquake response spectrum method the landslide initiation time and the velocity are determined by time history analysis the mass movement and accumulation process is simulated using the discrete element method simulation results demonstrate that the maximum amplification coefficient of dynamic acceleration for the donghekou slope is approximately 3 909 the initiation time of landslide is approximately 6 0 s and the average initial velocity of the sliding mass is approximately 0 85 m s the failure of the slope is the result of elevation orientated amplification effect and the sliding mass triggered with a small initial velocity the numerical simulated result of the maximum sliding velocity is approximately 66 35 m s and the mass is disintegrated rapidly because of collision and free fall the landslide velocity decreases when the flowing mass reaches a lower slope angle and gradually comes to a stop and the total travel distance is approximately 2400 m c 2013 elsevier ltd all rights reserved

early cretaceous adakitic lavas and a type rhyolites in the songliao basin ne china implications for the mechanism of lithospheric extension abstract there is a broad consensus that the extensive late mesozoic igneous rocks in ne china were generated in an extensional setting however the timing and mechanism of the lithospheric extension remain controversial to address this we carried out an integrated study involving la icp ms zircon u pb dating and geochemical analyses major elements trace elements and hf isotopes for the early cretaceous adakitic lavas and a type rhyolites of the songliao basin the adakitic lavas are andesites and dacites the u pb dating of zircons from the adakitic lavas and a type rhyolites yielded ages between 115 and 102 ma geochemically the adakitic lavas are characterized by high sr contents 515 1610 ppm and low y 0 98 17 58 ppm and heavy rare earth element hree contents and they therefore have high sr y 51 112 ratios they also exhibit high mg values 36 57 and high contents of mgo 0 56 3 53 wt cr 15 7 87 3 ppm and ni 6 7 44 7 ppm that are comparable with those of high mg adakitic rocks the a type rhyolites show an affinity with aluminous a type magmatic rocks and they are metaluminous to peraluminous a cnk 0 98 1 35 enriched in alkalis ga zr nb and y depleted in sr and p and exhibit fractionated ree patterns with negative eu anomalies eu eu 0 05 0 77 all the primary zircons from the adakitic lavas and a type rhyolites have positive ehf t values of 3 6 to 12 1 and juvenile two stage model tdm2 ages of 934 392 ma the adakitic lavas probably resulted from the partial melting of a delaminated region of the lower continental crust with the magmas subsequently interacting with mantle materials upon ascent while the a type rhyolites were probably generated by the partial melting of a dehydrated charnockitic middle lower crust the data suggest that the adakitic lavas and the a type rhyolites formed in an extensional environment related to the rollback of the subducting paleo pacific plate the upwelling of asthenospheric mantle and local delamination of the lithosphere which were induced by rollback of the subducting paleo pacific plate extended from the great xing an range southeastward through the songliao basin to eastern heilongjiang and jilin provinces giving rise to the southeastward migration of lithospheric extension and extension related volcanism after ca 140 ma

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

albitized microcline grains of post depositional and probable detrital origins in brottum formation sandstones upper proterozoic sparagmite region of southern norway untwinned albite ab 99 4 an 0 4 or 0 2 grains forming during diagenesis and very low grade metamorphism are common in sandstones of the brottum formation upper proterozoic in the sparagmite region of southern norway these untwinned albite grains are usually clouded by vacuoles and tiny inclusions which are mostly made of carbonaceous material although some albite grains also contain some combination of carbonates quartz phengite chlorite pyrite halite and anatase the presence of microcline grains replaced partly by albite indicates that the albite grains are pseudomorphs after microcline chessboard albite which occurs in the brottum formation is suggested to be detrital in origin

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method