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

heat flow and age of the gulf of oman we present the results of twenty heat flow stations in the gulf of oman which are used to infer the first reliable age estimates for the basin a mean surface heat flux of 42 6 3 6 mw m 2 exhibits no significant regional variation after correction for thick and rapidly deposited sediments this yields an age of 70 to 100 ma according to oceanic thermal models this age is also consistent with the sediment corrected basement depths of 5 5 6 0 km and with formation during the cretaceous quiet zone the latter can explain the absence of magnetic sea floor spreading lineations heat flow measurements are also used to confirm the presence of gas hyrdate layers the measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from bright spots seen on seismic reflection profiles

structure of the makran subduction zone from wide angle and reflection seismic data abstract makran is one of the largest accretionary wedges on the globe formed by the convergence between the eurasian and the arabian plates it is characterised by an extremely high sediment input of 7 km and a shallow subduction angle we present seismic velocity models from four wide angle seismic lines that image the wedge sediments and the subducted oceanic crust three strike lines show complex but rather one dimensional structures where the observed seismic phases have been studied with the reflectivity method a 160 km long dip line was surveyed coincident with a mcs line collected by cambridge university in 1986 prestack depth migration of this data with the new wide angle velocities shows improved images compared to earlier results interpretation of the wide angle and the mcs data indicates that a decollement is developed along a bright reflector within the turbiditic sequence more than 3 km of sediment bypasses the first accretionary ridges underthrusting and is transported to greater depth this might help to explain the sparse earthquake activity associated with subduction here in the strike lines low velocity layers occur landward of the deformation front in zones where active thrusting or underplating takes place the oceanic crust is characterised by a strong velocity contrast between layer ii and layer iii

very high temperature moderate pressure metamorphism in the new russia gneiss complex northeastern adirondack highlands metamorphic aureole to the marcy anorthosite discussion alcock and muller 1999 assert four inferences regarding grenville gneisses near new russia n y named new russia gneiss complex by them and the adjacent ca 1130 ma marcy anorthosite massif these four inferences follow 1 metamorphism and anatexis of the new russia complex were due to contact effects in the thermal aureole of the ca 1130 ma marcy anorthosite 2 pressure estimates in the gneiss suggest anorthosite emplacement pressures of 750 mpa 3 heat from intrusion of the marcy anorthosite and coeval anorthosite mangerite charnockite granite amcg plutons caused regional granulite facies metamorphism of the adirondack highlands and 4 the marcy anorthosite massif which commonly is only mildly deformed in its core is a postkinematic intrusion thus implying that the adirondacks experienced no post marcy ottawan orogenesis at ca 1090 1030 ma we consider all four assertions to be seriously flawed and we address these and related issues beginning with inference 4 above which is critical to their entire argument alcock and muller ignore or misrepresent two critical pieces of widely reported data based upon field relations and u pb zircon geochronology in addition their own most recent geochronological results contradict the model that they propose these critical issues are discussed below under three separate headings 1 alcock and muller cite the existence of only younger undeformed or mildly deformed granites following the ca 1150 1130 ma amcg plutonism of the adirondack highlands this ignores the existence of the well established hawkeye granitic suite of the highlands that is closely related to buddington s 1939 younger hornblende granite and has been dated six samples from across the region by u pb zircon at 1095 13 ma chiarenzelli and mclelland 1991 mclelland et al 1996 in press the hawkeye suite commonly exhibits intense ductile strain fig d1 and therefore predates high grade granulite facies t 700 850 c metamorphism and penetrative deformation of the ottawan orogeny ca 1090 1030 ma the age of which has

ternary feldspar thermometry in granulites from the oaxacan complex mexico coexisting feldspars from across 2 000 km2 of the granulite facies oaxacan complex southern mexico exhibit variable amounts of solid solution from nearly binary ab an and ab or to substantially ternary ab an or reintegrated analyses of 21 coarsely exsolved perthite af plagioclase pl pairs yield af or30 63 ab30 56an2 15 and pl or1 2ab70 84an11 28 these data have been used to test existing two feldspar geothermometers for this extended composition range

extraction and carbon isotope analysis of co2 from scapolite in deep crustal granulites and xenoliths abstract carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust co 2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75 c thus partial yields of co 2 from scapolite are sufficient for accurate carbon isotopic analysis isotopic compositions of coexisting scapolite and calcite in high grade calc silicate gneisses and marbles and consideration of the crystal chemical environment of co 3 in the scapolite structure indicate little fractionation of 13 c 12 c between scapolite and calcite 0 1 1 2 at equilibrium conditions of 650 800 c the carbon isotope composition of co 2 extracted from scapolite in twenty nine samples of regional granulite facies gneisses amphibolites calc silicate gneisses and crustal xenoliths yield values of 13 c that range from 10 to 1 pdb high grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study as the former are isotopically enriched and the latter isotopically depleted in 13 c 12 c relative to the range of isotopic compositions determined here the 13 c values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences 10 1 to 4 0 may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths the values of 13 c for scapolite in mafic xenoliths and some granulite facies orthogneisses 8 2 to 1 2 are consistent with crystallization of the scapolite from a mafic melt or derivation of co 2 from mafic melts emplaced in the lower crust or upper mantle the values of 13 c for scapolites from calc silicate gneisses and calc silicate xenoliths 10 0 to 2 9 may result from depletion of 13 c 12 c as a result of decarbonation of calcite bearing protoliths during prograde metamorphism

climate change and the episodicity of sediment flux of small california rivers abstract we studied the streamflow and sediment flux characteristics of the 20 largest streams entering the pacific ocean along the central and southern california coast extending for 750 km from monterey bay to just south of the u s mexico border drainage basins ranged in area from 120 to 10 800 km2 with headwater elevations ranging from 460 to 3770 m annual streamflow ranged from 0 to a maximum of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 1 times 10 9 end document m3 yr for the santa clara river in 1969 with a

young high temperature granulites from the base of the crust in central mexico characterization of the lower continental crust is essential to understanding processes of crustal formation and evolution many workers have concluded that the lower crust is composed of granulite facies rocks see for example refs 1 2 but many exposed granulite facies terranes seem to have mid crustal rather than lower crustal origins3 5 here we present new data from direct samples of the lower continental crust in the form of metapelitic rock fragments brought to the surface by quaternary volcanism in central mexico these xenoliths contain exsolved ternary feldspars that record extremely high minimum metamorphic temperatures of 950 1 100 c the highest yet known to be preserved in deep seated metamorphic rocks the metamorphism seems to be the result of underplating by basaltic magma and to be regional in extent our barometry on these samples demonstrates that granulite facies metamorphic rocks are present in the lower crust and provides important constraints on tectonic models and interpretations of geophysical data chemical and text lira i evidence suggest that the xenoliths were not able to cool to below 850 900 c before being entrained in their host magmas indicating that the granulite facies metamorphism occurred no more than 30 myr ago

origin of granulite terranes and the formation of the lowermost continental crust differences in composition and pressures of equilibration between exposed regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust as had been thought but rather middle and lower middle crustal levels application of well calibrated barometers indicate that exposed granulites record equilibration pressures of 0 6 to 0 8 gigapascal 20 to 30 kilometers depth of burial whereas granulite xenoliths which also tend to be more mafic record pressures of at least 1 0 to 1 5 gigapascals 35 to 50 kilometers depth of burial thickening of the crust by the crystallization of mafic magmas at the crust mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep seated mafic crust represented by many xenolith suites

internal deformation and compaction of the makran accretionary wedge the makran accretionary wedge is one of the largest on earth a 7 km thick column of sands and quartzolithic turbidites are incorporated into this wedge in a series of deformed thrust sheets we present the results of prestack depth migration and focusing error analysis migration velocity analysis performed on a profile across the makran wedge the depth section shows the deformation style of the accreted sediments and the migration velocities allow us to estimate porosity variations in the sediments the thrust sheets show evidence of fault propagation folding with a long wavelength of deformation 12 km and secondary thrusting in the kink bands of the folds such that the central part of each thrust sheet is elevated to form an additional ridge this deformation style and the 15 steep surface slope of the first ridge suggest a high degree of consolidation porosities were calculated from the seismic migration velocities and the ratio of fluid pressure to lithostatic pressure was estimated for 5 locations along the profile rather than being undercompacted and overpressured as in most accretionary wedges the sedimentary input is normally compacted exponential porosity decay throughout almost the whole wedge however a slight increase in porosity and at depth with respect to the normal compaction curve indicates that the turbiditic sequence might be overpressured landward of the deformation front

co2transfer between the upper mantle and the atmosphere temporary storage in the lower continental crust the co2 atmospheric content has shown large variations over geological times high contents up to one order of magnitude more than present day values ultimately correspond to discrete episodes of mantle degassing either juvenile or subduction related carbon recycling a number of arguments e g the continuous volume increase of carbonate bearing sediments with time suggest that throughout the earth s history juvenile co2 has formed a major contribution to the global carbon budget of the earth the absence of a direct relationship between major volcanic episodes and the average co2 atmospheric content suggests that volcanoes might not be the only way by which mantle co2 is transported to the surface it is proposed that large quantities of juvenile co2 could temporarily be stored in the lower continental crust during major episodes of granulite formation these are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of co2 bearing mantle derived magmas most of the co2 migrates through the crust during post metamorphic evolution and isostatic restoration of the normal continental thickness however large quantities of co2 can still be present in some areas notably as high density fluids enclosed in minerals

compatibility of geobarometers in the system cao feo al_ 2 o_ 3 sio_ 2 tio_ 2 cfast implications for garnet mixing models in the system cao feo al 2 o 3 sio 2 tio 2 several barometers have been experimentally calibrated hese include alm 3 ru 3 jim sil qtz grail 2 alm gr 6 ru 6 ilm 3 an 3 qtz grips 2 alm gr 3 fa 3 an fag 3 an gr 2 ky qtz gasp 2 fs fa qtz ffq and gr qtz an 2 wo wags because grips grail and gasp form a linearly dependent set they provide a stringent test for the accuracy of a x models for grossular almandine solid solutions the ganguly and saxena garnet solution model yields a calculated position for gasp two kb above a best fit to the available experimental reversals using these reactions to constrain mixing parameters for grossular almandine garnets on a ca fe 2 1 cation basis yields w h cafe 6240 j w h fcca 23800 j and w s cafe w s feca 11 4 j k model 1 or w h cafe 628 j wh feca 17080 j model 2 using the measured pyrope grossular value for w s 6 216 j k grips can be further

petrology and geochemistry of granulite xenoliths from central hoggar algeria implications for the lower crust granulitic xenoliths enclosed in neogene alkali basalts from the atakor and adrar n addjer volcanic massifs in central hoggar southern algeria include mafic metaigneous and felsic metasedimentary rocks the main mineral phases of metaigneous xenoliths are plagioclase and pyroxenes whereas quartz feldspars sillimanite garnet and sapphirine occur in metasedimentary granulites the metaigneous xenoliths represent a magmatic sequence of cumulitic and non cumulitic rocks which resembles gabbroic bodies associated with anorthosites and has calc alkaline affinities similar types and distributions of granulitic xenoliths are widespread and are probably characteristic of the lower crust in general suggesting its homogeneity on a large scale but heterogencity on a local scale

composition and smnd isotopic data of the lower crust beneath san luis potosi central mexico evidence from a granulite facies xenolith suite quaternary volcanics from san luis potosi slp in central mexico sampled a xenolith suite comprising uppermantle nodules spinell lherzolites hornblende pyroxenites spinel pyroxenites and lower crustal xenoliths the latter consist of granulite facies mafic to intermediate metaigneous rocks and high grade metasediments precursors of the metaigneous suite range from gabbroic to tonalitic compositions whole rock ree patterns permit classification of metaigneous rocks into cumulates and fractionated melts mafic xenoliths consist of plagioclase clinopyroxene orthopyroxene garnet amphibole apatite rutile scapolite garnet has reacted extensively with clinopyroxene forming corona textures of secondary plagioclase orthopyroxene and amphibole intermediate xenoliths are garnet free and quartz bearing all samples display similar ca al zoning patterns documented in orthopyroxene clinopyroxene and plagioclase which are along with the presence of coronas around garnet interpreted as representing partial re equilibration stages from 940 60 c and 7 11 kbar down to lower temperatures and pressures there is no indication of a secondary heating event in these xenoliths sm nd isotopic compositions of the spinel lherzolites indicate a heterogeneous composition of the mantle segment beneath slp similar sr and nd isotopic signatures reveal that the hornblende pyroxenites are high pressure cumulates linked to the host basanites four mainly intermediate metaigneous granulites from a single vent which are free of secondary amphibole and two spinel pyroxenites regarded as the most primitive member of the metaigneous suite define a regression line in a sm nd isochron diagram yielding an age value of 1248 69 ma and an initial nd value of 2 3 metaigneous xenoliths containing secondary amphibole plot significantly above the regression line which is probably due to the introduction of externally derived nd during amphibole formation under retrograde p t conditions discussing the geological significance of the calculated age value there are some arguments for interpreting this age as representing the intrusion age of the magmatic precursors this gives evidence for formation of lower crust of basic to intermediate compositions during the mid proterozoic now situated beneath slp

armalcolite in crustal paragneiss xenoliths central mexico aluminous armalcolite has been found in two sillimanite bearing xenoliths that were recently exhumed from the lower crust of central mexico the ranges of compositions are fe5 1s 0 66mgo ls 0 2salo ls 0 ls v6 66 o lofe6 6o o o6titt4 l s6 os and fefi1o o s1 mgo ls 0 29alo 16 0 19v6 62 0 06fe6 1o o s1 ti1 19 1 71 os the occurrence of armalcolite is unusual in crustal paragneisses because most terrestrial armalcolite occurs in volcanic rocks that are derived from partial melting in the earth s mantle textures suggest that armalcolite is a late product formed by the reaction rutile ilmenitess armalcolitess during rapid transport of the xenoliths to the surface phase equilibria in the system mgo feo fe203 ti02 which indicate that armalcolite is stable in the crust at 900 1200 c are consistent with this interpretation thermodynamic properties are estimated for oxides in the system mgo feo fe203ti02 to constrain activity composition relations for armalcolite and conditions of formation activity coefficients calculated for armalcolite range from 0 27 to 1 36 depending on the ilmenite model used at temperatures between 1000 and 1300 c depth of formation of armalcolite in the crust is not well constrained thermodynamic calculations at 800 1200 c for the compositions observed indicate that the armalcolite in one xenolith would have been in equilibrium with rutile at values of 102 between the hematite magnetite buffer hm and the fayalite magnetite quartz fmq buffer and that armalcolite in the other xenolith would have been in equilibrium with rutile and ilmenite at values of 102 between fmq and two log units below the fmq buffer

comparison of measured and bsr derived heat flow values makran accretionary prism pakistan abstract during the german research cruise so 124 on rv sonne fall 1997 on the makran accretionary wedge off pakistan geophysical investigations were carried out to study the thermal regime at a gas hydrate bearing sediment in a tectonically deformed accretionary wedge on a transect perpendicular to the strike of the deformation front 42 heat flow measurements were carried out accompanied by seismic reflection experiments the investigations start in the south in the abyssal plain and cover the continental slope up to 2300 m water depth the aim of this study is to compare the bsr derived heat flow denoted as estimated heat flow with the values from measurements at the seafloor this requires the calculation of sediment physical properties at depth using empirical relationships between velocity and porosity the value measured and corrected for sedimentation of 47 mw m 2 south of the deformation front is slightly higher than values reported by hutchison et al earth planetary sci lett 56 1981 252 262 in all basins the estimated heatflow is significantly higher than the measured values as a result temperatures at the bsr extrapolated from seafloor measurements are 5 6 k lower than those taken from gas hydrate stability considerations as an overall trend the estimated as well as the measured heat flow show a small decrease from the deformation front to the northward thickening prism a similar observation was made at other accretionary wedges and described by wang et al j geophys res 98 b3 1993 4121 4142 and ferguson et al j geophys res 98 b6 1993 9975 9984 within the slope basins heat flow values show little variation indicating predominantly conductive heat transport fluid flow might occur at the bounding faults where we have little control the effect of rapid sedimentation on the dynamic behavior of the bsr might also have a significant influence on the estimated heat flow values our data set shows clearly that detailed seismic surveys and good control of the subsurface velocity are absolute necessities for the comparison of measured and bsr derived heat flow values however the uncertainty of the velocity porosity relationship together with a high and only approximately established sedimentation rate represent crucial but missing constraints which can be gained only by drilling

an indian ocean tsunami triggered remotely by an onshore earthquake in balochistan pakistan this paper describes and documents instrumentally recorded tsunami waves that are interpreted as secondary effects of a 7 7 magnitude earthquake in southern pakistan on 24 september 2013 the tsunami waves were almost unnoticed because the wave heights were low and the tsunami occurred at low tide the historical record of tsunami events within the arabian sea northern indian ocean is fragmentary large tsunamigenic earthquakes are known to be generated in the makran subduction zone the area that forms the boundary of the arabian and eurasian plates submarine sliding is reported along the owen fracture zone which marks the boundary between the arabian and indian plates hence the tsunami hazard potential within the arabian sea is enigmatic our analysis is based on sea level oscillations recorded at various tide gauge stations along the coastlines of oman pakistan and iran as well as eyewitness accounts of the event in oman our results indicate that the waves were in the range of 1 m or less in height they were first recorded along the eastern coast of oman and propagated toward the west we suggest that the waves must have been triggered by a submarine slide on the makran margin cascading effects resulting in large submarine slope failures within the arabian sea are more frequent than postulated the hazard potential is underestimated as such secondary effects of distant ruptures onshore were previously not taken into account

adirondack highlands northwest lowlands boundary a multiply folded intrusive contact with fold associated mylonitization the boundary between the adirondack highlands and the northwest lowlands near harrisville new york is a multiply folded intrusive contact between metamorphosed sedimentary rocks of the lowlands and metamorphosed intrusive rocks of the diana complex in the highlands this is shown by detailed geologic mapping and analysis of stratigraphy and minor structural features regionally developed protomylonitic foliation in the diana complex is an axial plane foliation formed during isoclinal folding of dry quartz syenite at granulite facies metamorphic grade lack of major post intrusive fault displacement along the diana complex northwest lowlands boundary is demonstrated by correlation of xenoliths in the diana complex with immediately adjacent metamorphosed sedimentary rock units of the northwest lowlands and by continuity of major folds across the boundary a stratigraphic succession consisting of seven rock units has been recognized in northwest lowlands rocks of the harrisville area rocks in these units include from oldest to youngest 1 garnet sillimanite cordierite gneiss 2 rusty pelitic gneiss with biotite gneiss pyroxene amphibolite and quartzite 3 graphitic calcite marble 4 siliceous marble 5 rusty calc silicate rocks 6 diopside gneiss and 7 calc silicate granulite four phases of folding are evident in these stratigraphic units but only the last three phases affect intrusive quartz syenite gneisses of the diana complex first phase isoclinal folds in bedding have a pervasive axial plane foliation which is the regional foliation associated regional lineations are parallel to first phase fold axes foliation and lineation formed during the first phase of folding were deformed by second phase isoclinal folds which have a weak to strong axial plane foliation or slip cleavage quartz syenite of the diana complex intruded folded metamorphosed sedimentary rocks early during second phase folding and was itself isoclinally folded somewhat later during the second phase isoclinal folding of quartz syenite gneiss is associated with development of protomylonitic to mylonitic axial plane foliation which is most intense in the northwest border zone of the diana complex due to lithic contrast with rocks northwest of the border third phase folds are isoclinal to open and are locally characterized by axial plane slip cleavage or fracture cleavage the axial surfaces of folds associated with the first three phases of deformation have a general northeasterly trend and northwesterly dip but their axes have varied plunges two dimensional heart and anchor and hook patterns are a product of interference of second and third phase folds fourth phase deformation resulted in northwest trending open folds with locally developed axial plane slip or fracture cleavage interference of third and fourth phase folds is manifest in dome and basin patterns that are elongate to the northeast and overturned to the southeast similar to dome and basin patterns throughout the northwest lowlands late stage ductile shearing produced very fine grained thin mylonite and ultramylonite in shear zones that transect the preexisting protomylonite foliation in quartz syenite gneiss later brittle deformation resulted in closely spaced fractures quartz and epidote veins and local minor faults however no evidence for major faulting has been observed along this part of the adirondack highlands northwest lowlands boundary

feldspar thermometry in ultrahigh temperature metamorphic rocks evidence of crustal metamorphism attaining 1100 c in the archean napier complex east antarctica ultrahigh metamorphic temperatures attained in the mid to lower crust have been assessed by examining the mineral chemistry of ternary feldspars with relatively coarse exsolution lamellae from the archean napier complex east antarctica chemical compositions of re integrated perthitic mesoperthitic and antiperthitic feldspars are calculated from the modal proportions and the chemical analyses of host and lamellar domains formed through exsolution based on ternary feldspar solvus models re integrated compositions of feldspars from a variety of rock types yield the minimum equilibrium temperatures ranging from 1000 to 1110 c 0 8 gpa these data confirm the suggestion that the regional thermal conditions of the napier complex reached or exceeded 1100 c as feldspar is one of the common constituents of the crustal rocks this approach could be applicable to a wide variety of rocks in which feldspar represents exsolution textures

long term tectonic control on holocene shelf sedimentation offshore la jolla california a high resolution compressed high intensity radar pulse chirp survey reveals shore parallel variations in the holocene sediment thickness offshore la jolla california sediment thicknesses decrease from 20 m in the south near scripps canyon to zero in the north approaching torrey pines in addition to the south to north variation in sediment thickness the transgressive surface observed in seismic lines shoals from scripps canyon to the north despite these dramatic shore parallel subsurface changes the nearshore bathymetry exhibits little to no change along strike a left jog i e a constraining bend along the rose canyon fault causes local uplift in the region and appears to explain the northward shoaling of the transgressive surface the decrease in relief on the transgressive surface away from the left jog and the holocene sediment thickness variation this tectonic deformation is shore parallel and thus the accommodation can be separated into its tectonic and eustatic components

the role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments northwest adirondacks field and petrologic studies along the adirondack lowlands highlands boundary near harrisville ny indicate that heat from the synmetamorphic intrusion of the diana syenite complex intrusion temperature of 1 050 c played a major role in the local metamorphic thermal regime and was responsible for extensive partial melting of adjacent metasedimentary units major paragneiss of engel and engel metamorphic temperatures inferred from two feldspar and spinel quartz assemblages decrease from 850 950 c along the diana metasediment contact to 650 700 c 2 3 km away from the contact metamorphic pressures are 7 0 5 kb as determined from coexisting plagioclase garnet sillimanite quartz kyanite sillimanite and garnet rutile ilmenite sillimanite quartz grail in the paragneiss migmatites consisting of quartz microcline perthite sodic plagioclase leucosomes are generally concordant with the melanosome consisting of biotite sillimanite garnet spinel plagioclase corundum cordierite qualitatively the amount of partial melt and occurrences of corundum bearing assemblages decrease away from the diana contact activity of h2o inferred from coexisting biotite sillimanite quartz garnet k feldspar ranges from 0 01 to 0 17 and is five to ten times lower in corundum bearing rocks

silicic magma formation in overthickened crust melting of charnockite and leucogranite at 15 20 and 25 kbar 50 60 vol accompanied by settling of residualof crustal source rocks at depths 50 km 2 production of syenite crystals would lead to a magma of restricted compositional rangemagma by partial melting of quartzofeldspathic rocks at pressures with a heavy rare earth element depleted pattern overall the granitic 15 kbar melting experiments at 15 20 and 25 kbar were melt composition obtained in the experiments divers from that ofperformed on archaean biotite bearing charnockite of opx bearing a type granite however at degrees of melting below

quantification of gas bubble emissions from submarine hydrocarbon seeps at the makran continental margin offshore pakistan 1 evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 khz echosounder records flares was obtained at the convergent makran continental margin the hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column dives with the remotely operated vehicle quest 4000 m revealed that several individual bubble vents contributed to one hydroacoustic anomaly analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume we found that a low volume flux flare 1 at 575 mbsl 90 ml min caused a weak hydroacoustic signal in echograms whereas high volume fluxes flare 2 at 1027 mbsl 1590 ml min flare 5 c at 2870 mbsl 760 ml min caused strong anomalies the total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies an order of magnitude estimate further considers the temporal variability of some of the flares assuming a constant flux over time and allows a large range of uncertainty inherent to the method our results on the fate of bubbles and the order of magnitude estimate suggest that all of the 40 32 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean

interaction between accretionary thrust faulting and slope sedimentation at the frontal makran accretionary prism and its implications for hydrocarbon fluid seepage 1 using high resolution seismic profiles and other geophysical data collected during r v meteor cruise m74 2 we investigate the distribution patterns of shallow sediments their structure and deformation processes and their role in the migration accumulation and seepage of hydrocarbon rich fluids here we show that rapid syn kinematic sedimentation at the frontal makran accretionary prism provides a mechanism by which emerging imbricated thrust packets override the footwall at the seafloor without significant mass wasting and destruction of fault related anticline in the hanging wall these anticlines may rise high above the seafloor to form plate boundary parallel ridges and distinguish from simple thrust blocks seen at convergent margins elsewhere with the fast burial of many thrust faults by the syn kinematic sediments anticlinal growth structures form in these syn kinematic sediments by continuous thrust activity the anticlinal structures preserved within the cores of the ridges or formed from these syn kinematic sediments act as structural traps for migrating hydrocarbon rich fluids above which fluid escape structures are generated leading to seafloor seeps most of the discovered hydrocarbon seeps around sixth ridge are sourced from these traps despite the compressional environment and the rapid syn kinematic sedimentation rates shallow subsurface of the frontal makran is a normally pressured regime in which the buoyancy of hydrocarbons may account for the fluid migration in this important respect the makran accretionary prism differs from many other convergent margins and accretionary prisms where fluid flow is largely driven by tectonically induced overpressure

evidence for a thick free gas layer beneath the bottom simulating reflector in the makran accretionary prism abstract seismic reflection data from the makran continental margin indicate the presence of a strong and widespread bottom simulating reflector bsr we apply a nonlinear full waveform inversion technique to multichannel reflection data from this area to investigate the detailed velocity structure and hence the origin of the bsr our result shows an abrupt decrease in the compressional wave velocity from 2 2 to 1 3 km s at a depth of 500 m below the sea bed the low velocity zone is unusually thick 200 350 m and may contain large quantities of free gas similar to some of the recently drilled blake ridge sites of odp leg 164 the voluminous free gas may have been generated by the dissociation of gas hydrates as a consequence of the upward movement of the base of gas hydrate stability field relative to the sediment column due to uplift and sedimentation in the accretionary wedge

origin of rhyolitic lavas in the mesa central mexico by crustal melting related to extension the emplacement of a voluminous sequence of rhyolitic lava flows and domes characterizes oligocene volcanism in the mesa central mc of mexico its dominant effusive style of emplacement contrasts deeply with the predominantly explosive volcanism of the sierra madre occidental volcanic province toward the west whole rock geochemical major and trace elements and sr nd isotopic data of the mc oligocene rhyolitic lavas document a marked change in magma composition at around 30 ma allowing us to distinguish between a lower and an upper sequence lavas from the lower sequence are geochemically similar to the high k rhyolitic rocks of the eastern sierra madre occidental major and trace element variations are characteristic of mantle derived magmas evolving through fractional crystallization the initial 87 sr 86 sr and e nd values are nearly constant 0 70644 0 70770 and 1 2 to 2 1 respectively and indicate some contribution from crustal material lavas from the upper sequence are high silica peraluminous rhyolites with strong enrichment in fluorine and in some incompatible lithophile elements rb la sm yb y th u nb ta and strong depletion in the feldspar compatible elements sr ba eu initial 87 sr 86 sr ratios of the upper sequence lavas are high and variable 0 70812 0 72190 and decrease as silica content increases whereas the e nd values are relatively constant 1 4 to 2 8 the trace element behavior indicates an origin by variable degrees of non modal partial melting of granulitic low crustal rocks and chemical disequilibrium during melting processes the high and variable sr isotopic ratios could also be related to isotope disequilibrium melting processes if the isotopic heterogeneities between individual mineral phases were preserved during heating of the source rocks the changes in geochemical compositions are related to the onset of crustal extension at high strain rates documented for the mc crustal extension promoted crustal melting at high melting rates high melt segregation rates rapid ascent of low viscosity fluorine rich magmas and inhibited melt stagnation in magma chambers such conditions favored the effusive volcanic style and support the possibility of melting under disequilibrium conditions

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

geochemistry of exposed granulite facies terrains and lower crustal xenoliths in mexico the trace element compositions of 13 samples from exposed granulite facies terrains and 17 granulitic lower crustal xenoliths were determined using an inductively coupled plasma mass spectrometer to constrain the composition and evolution of the mexican lower crust most xenoliths found are pyroxeneplagioclase orthogneisses although quartzo feldspathic paragneisses form up to 50 of the xenolith population in some areas lithologies in the exposed terrains consist of pelitic and carbonate rich paragneisses charnockites and less abundant basic intermediate and felsic orthogneisses both xenoliths and exposed granulites generally have low abundances of incompatible elements such as k rb th and u the xenoliths however often have lower abundances of these elements than the exposed granulites high k rb ratios coupled with an inverse correlation between k2o and k rb indicate that most samples from the mexican lower crust are depleted in both k and rb furthermore th u ratios similar to upper crustal materials and high la th ratios suggest depletion in both th and u relative to average crustal material removal of a melt phase either after the crystallization of cumulates or following a partial melting event can explain many of the chemical features observed and may be responsible for the elemental depletions some samples however appear to have been unaffected during their residence in the lower crust and chemically resemble their presumed protoliths available geobarometric data suggest that xenoliths equilibrated near the crust mantle boundary 10 kbar and represent the lowermost crust while the exposed granulites equilibrated at shallower crustal levels 7 kbar thus the differences observed between the xenoliths and exposed granulites indicate that there may be chemical and lithologic zonation in the mexican lower crust the lowermost crust in mexico consists of crystallized basaltic liquids cumulates and or residue after the removal of a partial melt as well as garnet rich metasediments

the mud volcanoes of pakistan marine geologic investigations on the arabian sea by bundesanstalt fur geowissenschaften und rohstoffe bgr in 1995 and 1998 and land expeditions in 1998 and 1999 to the coastal regions of the makran desert pakistan have extended the knowledge of the aerial distribution of mud volcanoes these structures rise from under compacted formations within the regional accretionary prism which is built by the subduction of the oceanic crust of the arabian sea and its km thick sedimentary load the occurrence of mud volcanoes is limited to the abyssal plain near the accretionary front to the coastal region of the makran desert and to a region in the interior of the desert to the south to southeast of the so called hinglay synform the location of mud volcanoes in pakistan is clearly tied to fault systems mud volcanoes are conspicuously absent on the lower slope of the accretionary prism where thick gas hydrate layers have developed the presence of large gas plumes emerging from the seafloor landward of the gas hydrate stability zone at water depths of less than 800 m points to a redirection of fluids from depth which might explain the absence of mud volcanoes along the lower slope

cryptoperthites and cooling rate in a layered syenite pluton a chemical and tem study alkali feldspars in the klokken layered syenite south greenland are optically either coarse turbid deuteric patch perthites or clear unaltered fine braid microor cryptoperthites irregular clear volumes can be found in most turbid grains electron microscopy shows that all clear crystals or volumes are cryptoperthites in which the periodicity of the exsolution lamellae increases systematically with distance from the roof of the intrusion from 40 nm to 300nm they are composed of low albite and diagonally associated maximum microcline a secondary coarsening is responsible for optically visible braid microperthites the layered series consists of interleaved granular syenites and coarser grained laminated syenites with mineral layering microprobe analyses show a downward decrease in ca and ba in the granular syenite feldspars consistent with chilling from the roof inwards most laminated syenite feldspars contain 1 an increasing to 5 in mafic layers the periodicity of the exsolution lamellae in the laminated syenite feldspars is consistently up to twice that in adjacent granular syenites periodicity is not influenced by ab or or an content but high an feldspars have continuous zig zag intergrowths while others are more lozengeshaped lamellar periodicities largely reflect cooling rate in the pluton cooling times in the exsolution interval were probably about 103 104 years at the top of the series whereas existing experimental data suggest that the periodicities would be reached in a few days or years the periodicities at the top of the granular series are only slightly greater than experimentally determined initial wavelengths for spinodal decomposition suggesting that little or no coarsening occurred despite the long cooling times coarsening did occur lower in the pile framework ordering and twinning must slow or stop coarsening the difference in periodicity between the granular and laminated syenite series may be caused by differences in amount of water incorporated in the feldspar structure from the magma the exsolution of this water at low temperatures could be the cause of the deuteric unmixed patch perthites small volumes of cryptoperthite which have escaped deuteric unmixing may be common in igneous rocks in general and may be useful relative indicators of cooling rate

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

holocene sand beaches of southern california enso forcing and coastal processes on millennial scales abstract a proxy record of sand beach accretion for the past 10 000 years has been assembled from radiocarbon dates on the pismo clam tivela stultorum in archaeological sites along the southern california coast when this record is compared with numerous climate proxies it appears that el nino southern oscillation enso controls on wave climate and sediment flux have acted upon regional geomorphology at different sea levels to either accrete or erode the holocene beaches of southern california tivela dates from the santa maria coast indicate that perennial sand beaches built by 9000 years ago in response to abundant riverine sediment contained by the natural groin at point sal wave sheltering by the massive headland of point buchon and early holocene el nino events on the western santa barbara coast sand beaches were forming by 7000 years ago in response to high sand fluxes from the santa ynez mountains to the many small littoral catchments possibly aided by high local rates of uplift decline of these sand beach habitats 5000 4000 years ago coincides with increased el nino driven wave energy in accord with slowing in sea level rise ca 6000 years ago sand beaches were most widespread in the period 6000 5000 years ago on estero bay the western santa barbara coast and west of point dume however tivela dates first appear 5000 years ago in the oceanside and silver strand littoral cells of the san diego region this lag coincides with the middle holocene shift to a more variable climate and modern periodicity in el nino events that increased sediment supply to the southern coast the ontogeny of the littoral cells provides timelines for modeling coastal evolution with implications for sand beach ecology prehistoric human coastal adaptations and coastal planning for future climate change

seismic and tectono metamorphic characters of the lower continental crust in phanerozoic areas a consequence of post thickening extension deep seismic profiles of phanerozoic continental crust commonly show a highly reflective lower crust rheological considerations suggest that the seismic fabric of the lower crust can be attributed to the tectonic transposition of various petrological heterogeneities in the main flow plane the variscan provinces of western europe have been affected during phanerozoic times by several extensional and compressional events the geometrical relationships between seismic and geological structures indicate that the layering of the lower crust was acquired during the late carboniferous to permian when the thickened variscan crust was affected by gravitational collapse petrological and geochronological analyses of deep crustal rocks xenoliths and exposed sections indicate that the lower crust has recorded a major high t medium p granulite facies metamorphism during the late variscan extension whereas on the surface upper carboniferous to permian basins were being deposited a similar scenario characterizes other phanerozoic orogenic belts in the caledonian provinces of the british islands the lower crust is seismically reflective it has undergone medium p granulitic metamorphism during the deposition of devonian sedimentary basins at the end of the caledonian orogeny in the same way collapse of the mesozoic belt in the western part of north america is responsible during the cenozoic for pervasive crustal extension whose consequence is a seismic layering of the lower crust accompanied by a low p granulite grade metamorphic event while in the mid and upper crusts low angle ductile normal faults give rise to the basin and range province therefore it is proposed that there is a genetic relationship between 1 post thickening crustal extension 2 low to medium p granulite facies metamorphism of the lower crust and 3 seismic layering of the lower crust

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

highstand fans in the california borderland comment and reply comment covault et al 2007 1 is a timely article that provides an important bridge between coastal processes basin deposition and the essential role that sea level stillstands have on the depositional budgets of basin sediments their study is also in agreement with the findings from the

origin of gneisses in the aureole of the san gabriel anorthosite complex and implications for the proterozoic crustal evolution of southern california granulite facies gneisses along the southwestern margin of the san gabriel anorthosite complex include compositionally banded locally migmatitic felsic gneisses and mafic granulites with rare interlayered augen gneiss and garnet hypersthene spinel aluminous gneiss previous workers accepted a 1 4 ga age for these granulites and a 1 2 ga age for the adjacent anorthosite complex and hence that this proterozoic basement is allochthonous with respect to the southwestern united states part of the north american craton solvus geothermometry in felsic and mafic granulites yields minimum metamorphic temperatures of 900 950 c and new u pb zircon data yield a minimum metamorphic age of 1186 ma coincident with that of the adjacent anorthosite we reinterpret these rocks as a 1190 ma anorthosite complex and its granulite grade thermal aureole geochemical data suggest that the anorthosite complex intruded early proterozoic rocks correlative with the mojave crustal province representing the north american craton exposed to the northeast we conclude that these proterozoic basement rocks represent the southwestern margin of the north american craton and not an exotic terrane accreted in mesozoic or tertiary time

paleoproterozoic ultrahigh temperature granulite facies metamorphism in the sulu orogen eastern china evidence from zircon and monazite in the pelitic granulite abstract because of their essential information for constraining the timescales of high temperature processes zircon and monazite are the two most important minerals for understanding crustal processes zircon and monazite are common accessory minerals in pelitic granulites sulu orogen eastern china the pelitic granulites have a peak mineral assemblage of garnet sillimanite antiperthite plagioclase quartz rutile biotite zircons from the granulite have low th u ratios

a cenozoic uplift history of mexico and its surroundings from longitudinal river profiles geodynamic models of mantle convection predict that mexico and western north america share a history of dynamic support we calculate admittance between gravity and topography which indicates that the elastic thickness of the plate in mexico is 11 km and in western north america it is 12 km admittance at wavelengths 500 km in these regions suggests that topography is partly supported by subcrustal processes these results corroborate estimates of residual topography from isostatic calculations and suggest that the amount of north american topography supported by the mantle may exceed 1 km the cenozoic history of magmatism sedimentary flux thermochronometric denudation estimates and uplifted marine terraces imply that north american lithosphere was uplifted and eroded during the last 30 ma we jointly invert 533 mexican and north american longitudinal river profiles to reconstruct a continent scale rock uplift rate history uplift rate is permitted to vary in space and time erosional parameters are calibrated using incision rate data in southwest mexico and the colorado plateau calculated rock uplift rates were 0 15 0 2 mm yr between 25 and10 ma central mexico experienced the highest uplift rates central and southern mexico continued to uplift at 0 1 mm yr until recent times this uplift history is corroborated by independent constraints we predict clastic flux to the gulf of mexico and compare it to independent estimates we tentatively suggest that the loop between uplift erosion and deposition can be closed here mexico s staged uplift history suggests that its dynamic support has changed during the last 30 ma

petrogenesis of syenite granite suites from the bryansky complex transbaikalia russia implications for the origin of a type granitoid magmas abstract two syenite granite suites metaluminous and peralkaline that form the bryansky complex in transbaikalia russia have been studied with the aim to constrain the existing models of a type granitoid magma generation the bryansky complex is a large intrusive body of about 1600 km2 emplaced in the central part of the mongolian transbaikalian granitoid belt which extends for more than 2000 km and is 200 300 km wide the belt comprises about 350 a type granitoid plutons and numerous volcanic fields u pb and rb sr isotope dating revealed that all the intrusive rocks of the complex and closely associated comendites were emplaced within a narrow time span 279 285 ma the isotope characteristics are rather similar for all main rock types the metaluminous suite has a 87sr 86sr t value of 0 7050 0 001 end t from 1 9 to 3 0 and the peralkaline suite has 87sr 86sr t 0 7053 0 0008 end t 2 1 and 2 4 comendites and trachyandesites have similar end t values from 2 2 to 3 5 but a slightly higher 87sr 86sr t value of 0 7062 0 0002 the systematic change in chemical and mineralogical composition from syenitic to granitic rocks in both suites and the similar isotopic ratios suggest that the granites were formed by fractional crystallization of the syenite magmas several lines of evidence suggest that metaluminous syenite is the parental magma for the whole bryansky complex study of melt inclusions in quartz phenocrysts from the peralkaline granite and in pyroxene from the nordmarkite indicates that fractional crystallization has resulted in significant f enrichment in the granitic magma up to 1 5 1 7 wt the syenite magmas crystallized at rather high temperature 940 c whereas the near liquidus temperature of the peralkaline granite was lower 760 790 c very high homogenization temperatures of the melt inclusions in quartz phenocrysts from comendites 1000 1100 c suggest that the alkali rich silicic magma formed at a depth of 50 60 km far exceeding the normal crust thickness the sr nd isotope data advocate the main role of mantle derived material in the source region from which the alkali rich syenitic and granitic magmas were produced

application of the two feldspar geothermometer to ultrahigh temperature uht rocks in the khondalite belt north china craton and its implications the paleoproterozoic khondalite belt in the north china craton preserves evidence for ultrahigh temperature uht crustal metamorphism associated with the collision of the yinshan and ordos blocks here we apply two feldspar geothermometry to uht granulites from two localities newly reported in this study tuguishan and xuwujia and another two localities from previous studies dajing tuguiwula and dongpo in the khondalite belt the presence of abundant perthite mesoperthite in these rocks reflects post peak slow cooling the minimum estimated peak metamorphic temperatures are 832 998 819 952 844 1037 and 966 1019 c computed at 8 kbar for the dajing tuguiwula dongpo tuguishan and xuwujia areas respectively these results confirm the previous report of extreme metamorphism at dajing tuguiwula and dongpo and reveal similar conditions in the new localities reported here suggesting that uht metamorphism is widespread in the khondalite belt of the north china craton our study demonstrates that uht metamorphism can be recognized using the two feldspar geothermometry in rocks that do not possess other key uht assemblages

terrestrial source to deep sea sink sediment budgets at high and low sea levels insights from tectonically active southern california sediment routing from terrestrial source areas to the deep sea influences landscapes and seascapes and supply and filling of sedimentary basins however a comprehensive assessment of land to deep sea sediment budgets over millennia with significant climate change is lacking we provide source to sink sediment budgets using cosmogenic radionuclide derived terrestrial denudation rates and submarine fan deposition rates through sea level fluctuations since oxygen isotope stage 3 younger than 40 ka in tectonically active spatially restricted sediment routing systems of southern california we show that source area denudation and deep sea deposition are balanced during a period of generally falling and low sea level 40 13 ka but that deep sea deposition exceeds terrestrial denudation during the subsequent period of rising and high sea level younger than 13 ka this additional supply of sediment is likely owed to enhanced dispersal of sediment across the shelf caused by seacliff erosion during postglacial shoreline transgression and initiation of submarine mass wasting during periods of both low and high sea level land and deep sea sediment fluxes do not show orders of magnitude imbalances that might be expected in the wake of major sea level changes thus sediment routing processes in a globally significant class of small tectonically active systems might be fundamentally different from those of larger systems that drain entire orogens in which sediment storage in coastal plains and wide continental shelves can exceed millions of years furthermore in such small systems depositional changes offshore can reflect onshore changes when viewed over time scales of several thousand years to more than 10 k y

ultra high temperature metamorphism of metapelitic granulites from kondapalle eastern ghats belt implications for the indo antarctic correlation a suite of quartz and corundum bearing metapelitic granulites intruded by layered gabbronorite pyroxenite anorthosite at kondapalle eastern ghats belt preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions in the quartz bearing associations the reactions are a biotite sillimanite quartz garnet liquid b garnet sillimanite spinel magnetite quartz c fe2tio4 o2 ferrian ilmenite magnetite d reversal of reaction b e fe2o3 rich ilmenite plagioclase quartz fe2o3 poor ilmenite garnet o2 reactions in the corundum bearing associations are f spinel biotite sillimanite garnet liquid g biotite sillimanite garnet ti rich spinel corundum liquid h biotite sillimanite garnet corundum liquid i fe2tio4 feal2o4 o2 ferrian ilmenite fe3o4 al2o3 in ilmenite j garnet corundum spinel sillimanite to examine the paragenetic evolution of the metapelitic granulites a petrogenetic grid for the kfmash system at high temperatures and pressures involving quartz and corundum was constructed the sequence of inferred reactions documents an anticlockwise heating cooling path reintegrated compositions of spinel with 10 mol fe2tio4 and feldspars indicate ultra high temperature uht of metamorphism 1000 c comparable with the liquidus temperature of the enclosing magmatic rocks crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying uht metamorphism occurred in the lower crust 8 kbar reported u pb cooling ages of monazite and allanite from a late pegmatite suggest the uht metamorphism to be older than 1600 ma the deduced p t history and the absence of grenvillian high grade metamorphism in the study area provide important constraints on the configuration of east gondwana in particular on the continuation of the napier rayner terrane boundary into the eastern ghats belt