petrogenesis and tectonic implications of early paleozoic granitic magmatism in the jiamusi massif ne china geochronological geochemical and hf isotopic evidence abstract this paper reports geochronological whole rock geochemical and zircon hf isotopic data for the early paleozoic granitic rocks in the jiamusi massif in the eastern segment of the central asian orogenic belt caob in order to investigate their precise geochronological framework petrogenesis sources and tectonic setting la icp ms zircon u pb age data indicate that the syenogranite monzogranite and granodiorite were emplaced during the period of 530 484 ma geochemically these granitoids have high sio2 64 66 79 17 and k2o 3 08 7 33 low mgo 0 14 2 63 and cao 0 37 3 87 with a cnk and eu values of 0 89 1 10 and 0 16 1 77 respectively these rocks are characterized by enrichment in rb and nd and depletion in nb ta p and ti in addition in situ hf isotopic analyses of zircons from the granitic rocks reveal that they have ehf t 5 8 to 2 3 with two stage hf model ages tdm2 varying from 1 3 ga to 2 4 ga indicating that they probably originated from the partial melting of a dominantly old paleo mesoproterozoic crustal source additionally these granites have variable major and trace element concentrations magmatic zircons from these rocks record consistent homogeneous u pb ages but have heterogeneous ehf t values reflecting that they resulted from fractional crystallization and crustal assimilation based on these geochemical data combined with regional geological investigations we propose that the early paleozoic granitic magmatism in the study area occurred in a post collisional extensional setting which was probably related to the collapse of a thickened crust

the distribution of the mid to lower crustal low velocity zone beneath the northeastern tibetan plateau revealed from ambient noise tomography we collected continuous seismic data recorded between 2007 and 2010 by 208 broadband stations from the chinese provincial digital seismic networks a seismic collaborative experiment of northern tibet and the northeastern tibet seismic experiment cross correlations of vertical component records are computed to extract the rayleigh wave empirical green s functions group and phase velocities are then constructed from the empirical green s functions in 8 to 50 s period at periods 25 s more than 10 lower velocities are imaged beneath the qaidam basin and high velocities are observed beneath the nonbasin regions at periods 30 s up to 10 lower velocities are imaged in the qiangtang and songpan ganze terranes from these group and phase velocity maps a three dimensional 3 d vsv model of the crust is derived the model shows that the qiangtang and songpan ganze terranes have a very thick crust with a prominent low velocity zone lvz in the middle crust the lvz thins out in the vicinity of the eastern kunlun mountains providing a new constraint on the mode of deformation across the tibetan plateau the northwestern qilian orogen where receiver functions reveal a moho deeper than the surrounding areas also features a relatively weak midcrustal lvz which we interpret as an intracrustal response associated with the shortening between the north china craton and the tibetan plateau

a review of antarctic granulite facies rocks abstract precambrian granulite facies rocks occur in significant proportion in the east antarctic precambrian shield ages of metamorphic and deformational events range from 2500 m y to about 500 m y but some rocks are much older notably the approximately 3500 m y ages for crust formation in enderby land mineral assemblages over most of the area are typical of the hornblende granulite facies and sparse temperature pressure estimates indicate metamorphism at 700 800 c and 5 8 kbar at reduced water pressures a terrane of exceptional interest is the napier complex of enderby land where sapphirine quartz garnet sillimanite orthopyroxene osumilite and inverted pigeonite are associated with pyroxene granulite facies rocks metamorphic conditions are estimated to have reached 900 980 c 7 9 kbar and ph2o

shear velocity structure radial anisotropy and dynamics of the tibetan crust geophysical and geological data suggest that tibetan middle crust is a partially molten mechanically weak layer but it is debated whether this low viscosity layer is present beneath the entire plateau what its properties are how it deforms and what role it has played in the plateau s evolution broad band seismic surface waves yield resolution in the entire depth range of the tibetan crust and can be used to constrain its shear wave velocity structure indicative of crustal composition temperature and partial melting and radial anisotropy indicative of the patterns of deformation we measured love and rayleigh wave phase velocity curves in broad period ranges up to 7 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds of interstation measurements made with cross correlation and waveform inversion methods shear velocity profiles were then determined by extensive series of non linear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy shear wave speeds within the tibetan middle crust are anomalously low and also show strong lateral variations across the plateau the lowest mid crustal shear speeds are found in the north and west of the plateau 3 1 3 2 km s 1 within a pronounced low velocity zone in southeastern tibet crustal shear wave speeds increase gradually towards southeast whereas in the north the change across the kunlun fault is relatively sharp the lateral variations of shear speeds within the crust are indicative of those in temperature a mid crustal temperature of 800 c reported previously can account for the low shear velocities across lhasa in the north the temperature is higher and exceeds the solidus resulting in partial melting that we estimate at 3 6 per cent strong radial anisotropy is required by the data in western central tibet 5 per cent but not in northeastern tibet the amplitude of radial anisotropy in the crust does not correlate with isotropic average shear speed and by inference with crustal rock viscosity or with surface elevation instead radial anisotropy is related to the deformation pattern and is the strongest in regions experiencing extension crustal flattening as noted previously the growth of tibet by the addition of indian crustal rocks into its crust from the south is reflected in the higher crustal seismic velocities and thus lower temperatures in the southern compared to northern parts of the plateau more recently added rocks having had less time to undergo radioactive heating within the thickened tibetan crust gravity driven flattening the basic cause of extension and normal faulting in the southern western and central tibet is evidenced by pervasive radial anisotropy in the middle crust beneath the regions undergoing extension the overall eastward flow of the crust is directed by the boundaries and motions of the lithospheric blocks that surround tibet

constraints on the origin of archean trondhjemites based on phase relationships of nuk gneiss with h2o at 15 kbar we report the t x h2o phase relations for the trondhjemitic nuk gneiss which comprises the principal component of the second phase of archean 3 0 2 8 by igneous activity in the godthab region of southwestern greenland a pressure of 15 kbar was chosen to place constraints on possible protoliths for trondhjemitic melts at lower crustal depths under h2o saturated conditions a melting interval of 135 c separates the solidus at 610 c from the liquidus at 745 c h2o saturation at 15 kbar occurs at approximately 15 5 wt h2o the h2o undersaturated liquidus extends along a curved path from 745 c at 15 5 wt h2o to 1100 c at 2 h2o lower h2o contents were not investigated at low h2o contents 7 mafic residues consisting of some combination of hb ga ep and bi are possible and could correspond to amphibolitic source rocks at lower melt h2o contents 5 possible residues consist of na pl qz ga and could correspond to an earlier generation of tonalitic trondhjemitic rocks however such residues would not impart the highly fractionated ree patterns characteristic of archean trondhjemites if a first generation of tonalitic trondhjemitic melts was generated by higher pressure partial fusion of eclogite and emplaced at 55 km depth it would crystallize to an assemblage consisting almost entirely of na pl qz with highly fractionated ree patterns these rocks in turn could be partially melted to yield a second generation of trondhjemites which would inherit the highly fractionated ree patterns because neigher pl nor qz is capable of significantly fractionating hree from lree

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

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

petrogenesis of mafic dykes and high mg adakitic enclaves in the late mesozoic fangshan low mg adakitic pluton north china craton abstract late mesozoic mafic dykes high mg adakitic enclaves and the low mg adakitic host from the fangshan pluton provide important insights into the process of crust mantle interaction the mafic dykes 134 2 ma have a wide range of total alkali na 2 o k 2 o 3 41 7 11 wt mgo 2 6 6 5 wt ni 60 1 541 7 ppm and cr 138 2 749 5 ppm contents and high mg values 57 6 72 0 they are enriched in lrees and liles rb ba k and depleted in hrees and hfses nb ta zr hf suggesting a garnet bearing enriched mantle source the host granodiorites 136 2 ma have low mg adakitic geochemical compositions they belong to the of high k calc alkaline series with low mgo contents 1 4 3 0 wt and mg values 41 9 48 1 they exhibit extremely high sr and low y and yb contents and are strongly enriched in lrees resulting in high sr y and la yb n ratios the low mg adakitic granodoirites were probably generated by partial melting of thickened eclogitic lower continental crust lcc the enclaves 136 2 ma with a strong affinity to the mafic dyke show high mg adakitic geochemical characteristics they are alkaline series with relatively low sio 2 52 2 59 6 wt and high mgo mg 44 7 57 2 contents they contain high sr ni and cr low y and yb and have very high sr y and la yb n ratios with depletion in hfses nb ta zr hf ti but without eu and sr negative anomalies numerical simulation indicates that the high mg adakitic enclaves were likely produced by mixing of low mg adakitic melt with mantle derived magma we propose that the underplating of the mantle derived magma might have triggered partial melting of the thickened lcc and resulted in the mixing between them in the early cretaceous

peralkaline granitoid magmatism in the mongolian transbaikalian belt evolution petrogenesis and tectonic significance article i nfo the central asian orogenic belt caob is well known for its massive generation of juvenile crust in the phanerozoic in eastern caob voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanics were emplaced in three stages from early permian to late mesozoic 295 270 ma 230 190 ma and 150 120 ma they occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area among them the 2500 km long mongolian transbaikalian belt mtb is the most spectacular and it comprises more than 350 granite syenite plutons and stocks with numerous co genetic volcanic fields the three stages of granitoids have similar chemical compositions but show temporal variation in nd isotopic composition initial end t values range from 1t o 5 for the early permian 0 to 4 for the early mesozoic and 2t o 3 5 for the late mesozoic granitoids the negative end t values observed in the mtb are not typical of the caob granitoids which are generally characterized by positive values however several pieces of evidence suggest that the mtb peralkaline and alkali feldspar granitoids were produced from enriched mantle derived sources the evidence includes 1 felsic and mafic rocks formed in the same stage have similar initial nd sr isotopic ratios and sm nd model ages tdm 2 the granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces but no correlation is found in chemical compositions between the granitoids and country rocks 3 the abundant syenites are considered to be cogenetic or in some cases parental to the granites experimental and isotope data argue for the derivation of syenites from an enriched mantle source thus the granites and comendites are regarded as mantle derived 4 a study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000 1100 c for the magma generation this suggests that the silicic magma was generated in an unusually high temperature condition which is likely produced by basaltic magma that underplated the lower crust the generation of voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanic rocks represents an important addition of juvenile crustal mass to the earth s continental crust during a time span of about 150 ma from late paleozoic to late mesozoic

petrogenesis of the kuangshancun and hongshan intrusive complexes from the handan xingtai district implications for iron mineralization associated with mesozoic magmatism in the north china craton abstract the handan xingtai district in eastern china exposes numerous late mesozoic intrusions among these the kuangshancun intrusive complex is one of the major ore related intrusions whereas the hongshan complex is barren although both intrusions display similar geochemical characteristics the kuangshancun complex consists of diorite and monzonite with zircon la icp ms u pb age of 133 7 1 ma the hongshan complex mainly consists of syenite and shows zircon u pb age of 134 5 1 ma the mineral chemistry of plagioclase from both complexes reveals normal zoning consistent with the fractional crystallization process rocks of the kuangshancun complex show sio 2 in the range of 58 92 63 84 wt na 2 o of 4 63 8 81 wt and al 2 o 3 of 16 14 18 18 wt together high sr y 14 54 and high la n yb n 8 30 16 18 ratios they show enrichment in lree and depletion in hree and hfse with no remarkable eu anomalies similar to the features of adakites the whole rock initial 87 sr 86 sr ratios range from 0 706661 to 0 706722 and e nd t 134 ma between 15 26 and 15 12 which are consistent with zircon 176 hf 177 hf ratios of 0 281940 0 282059 and e hf t values of 27 0 to 22 7 samples of the hongshan complex show sio 2 in the range of 56 57 68 16 wt high sr y 19 112 and high la n yb n 11 39 16 82 ratios the zircon e hf t values are in the range of 15 9 to 12 8 and e nd t 134 ma is between 9 82 and 8 62 the kuangshancun complex was derived through partial melting of an enriched lithospheric mantle contaminated by lower continental crust components the hongshan complex was also derived from the em i like mantle source however the calculated zircon ce 4 ce 3 and eu eu ratios indicate that the source magma of the kuangshancun complex were characterized by higher oxygen fugacity as compared to that the hongshan complex the high oxidation states and high water contents are considered as possible key factors that led to the iron mineralization in the kuangshancun and other intrusions in the handan xingtai district

tracing magma mixing and crystal melt segregation in the genesis of syenite with mafic enclaves evidence from in situ zircon hf o and apatite sr nd isotopes abstract alkaline rocks contain essential information on post collisional intraplate extensional magmatic processes within the continental lithosphere the erhulai syenitic pluton in the liaodong peninsula north china craton consists of quartz syenite mafic enclaves and porphyritic k feldspar granite field observations and zircon u pb dating reveal that the quartz syenite and the hosted mafic enclaves were coeval with identical emplacement ages of 129 126 ma and slightly older than the porphyritic k feldspar granite ca 123 ma the mafic enclaves have relatively low sio2 and high mgo contents up to 3 0 and lack ba or eu anomalies whole rock analyses of the mafic enclaves and accessory minerals in the enclaves show relatively low initial 87sr 86sr ratios 0 7056 to 0 7078 and variable end t 11 2 to 2 0 and ehf t 15 8 to 5 5 values large proportion of zircons from the mafic enclaves possess mantle like 18o values these geochemical features suggest an enriched mantle source with the addition of crustal material the quartz syenites have relatively high sio2 and low cao and mgo contents as well as significantly positive k ba and eu anomalies all the quartz syenites show variable 87sr 86sr i ratios 0 7073 to 0 7081 and end t values 10 4 to 8 6 for the whole rocks and apatites ehf t values of 12 4 to 3 6 for the zircons and zircon 18o values of 4 4 to 7 0 mainly greater than 5 3 all these features can be isotopically produced by the partial melting of ancient crustal material with the involvement of mantle derived magma crystal fractionation process such as k feldspar crystallization and accumulation played an important role in the formation of the quartz syenite the porphyritic k feldspar granites possess relatively evolved geochemical compositions with high silica contents sio2 69 wt and remarkable negative ba and eu anomalies which are chemically complementary to the quartz syenite a crystal mush model was employed to establish the genetic link between the porphyritic k feldspar granite and the quartz syenite with the granite representing the interstitial melt extracted from the crystal mush and the quartz syenite representing the residual accumulation of crystals the variable isotopic compositions of the quartz syenite and the porphyritic granite were mainly the result of extensive interaction of isotopes between mantle and crust derived magmas during magma mixing in situ analyses of the sr nd hf and o isotopes of accessory minerals coupled with field observations and whole rock geochemical data for the erhulai syenitic pluton indicate a complex multi stage magmatic process involving magma mixing crystal melt segregation and wall rock assimilation our study also shows that in situ isotopic analyses of accessory minerals provide unique information on and are powerful geochemical tracers of mantle crust interactions and magmatic processes

prograde metamorphism decompressional partial melting and subsequent melt fractional crystallization in the weihai migmatitic gneisses sulu uhp terrane eastern china abstract in order to decipher fluid melt activity during subduction and subsequent exhumation of felsic continental crust we carried out a combined study of zircon internal structure zircon u pb age zircon trace element composition and whole rock geochemistry on migmatitic gneisses from the weihai region in the sulu ultra high pressure uhp metamorphic terrane eastern china the weihai migmatitic gneisses are composed of intercalated compositional layers of melanosome and plagioclase pl rich leucosome and k feldspar kfs rich pegmatite veins whole rock geochemistry suggests that mgo fe2o3t cao tio2 p2o5 rare earth elements ree and large ion lithophile elements hfse are nearly completely retained in the melanosome whereas significant amounts of lile e g rb ba k sr pb and u are partitioned into the pl rich leucosome and the kfs rich pegmatite veins the kfs rich pegmatite vein has much higher k2o u pb and rb but lower cao and na2o contents than those of the pl rich leucosome layer protolith magmatic zircon domains with an upper intercept age of about 780 ma are common in the cores of zircon grains from the melanosome and the pl rich leucosome layers indicating that the protolith of the migmatitic gneiss is mid neoproterozoic magmatic rock metamorphic zircons with concordant ages ranging from 243 to 256 ma occur as overgrowth mantles on the protolith magmatic zircon cores they are characterized by remarkably flat heavy rare earth element hree patterns without obviously negative eu anomalies and have low y and th contents low th u and high hf y ratios indicating a prograde metamorphism in the hp eclogite facies during subduction recrystallized rims of zircons 228 2 ma in the pl rich leucosome layer are similar to magmatic zircons in terms of their hree enriched patterns with negative eu anomalies high y and low th contents and low hf y and th u ratios this indicates that the gneiss has experienced decompressional partial melting and the pl rich leucosome layers were formed by fractional crystallization of the primary melt during the early stage hot exhumation zircon grains 219 2 ma in the kfs rich veins are characterized by aqueous fluid melt related signatures with strongly hree enriched patterns high u pb and low th contents and low th u and high lu hf ratios indicating that the pegmatite vein was formed by crystallization of residual aqueous melt after the crystallization of pl rich leucosome layers during later stage cooling during exhumation our results suggest that the migmatitic gneiss successively recorded information concerning the protolith prograde hp metamorphism during subduction fractional crystallization of primary melt and crystallization of the residual melt during exhumation

petrogenesis of the late yanshanian mantle derived intrusions in southeastern china response to the geodynamics of paleo pacific plate subduction abstract several late yanshanian syenitic and gabbroic rocks from the coastal area of southeastern se china have been studied to determine zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings the systematic la icp ms zircon u pb dating results indicate that they can be divided into two main stages the early stage 141 118 ma and the late stage 98 86 ma which temporally correspond to the regional lower and upper volcanic series respectively the early stage syenitic and gabbroic rocks are accompanied by vast rhyolitic and dacitic volcanic rocks with minor granites their parental magma was derived from an enriched mantle metasomatized by subducted sedimentary materials the late stage syenitic rocks mainly occur as the central intrusion of the caldera with ages close to the accompanied volcanics forming a caldera related volcanic intrusive ring complex they were produced by magma mixing between depleted asthenosphere melts and subduction related enriched mantle melts it is suggested that the late yanshanian tectonic settings of se china transformed from a compressional environment to an extensional environment corresponding to the transformation from forward to rollback subduction of the paleo pacific plate at approximately 110 ma

the system tonalite h_2o at 15 kbar and the genesis of calc alkaline magmas experimental phase relations and well characterized mineral and melt compositions have been determined for a sierra nevada tonalite andesite with 2 5 to 10 wt h 2o added at 15 kbar and 850 to 1100 c all results are from experiments conducted in au capsules minimal fe loss to capsule at oxygen fugacities measured to be near ni nio with increasing water content the liquidus mineral changes from clinopyroxene at 3 wt h20 to garnet followed within 50 c by clinopyroxene at 3 to 9 wt h 2o to hornblende at water contents greater than 9 wt microprobe analyses of glasses quenched from within the tonalite melting interval show an enrichment in ca relative to mg fe where fe represents total fe as fe 2 with increasing sio 2 instead of the typical calcalkaline trend of approximately constant ca mg fe from basalt through rhyolite the results document the importance of garnet and clinopyroxene in andesitic to dacitic compositions at deep crustal to uppermost mantle pressures and they indicate that it is not possible to directly produce magmas of calc alkaline composition at 15 kbar and the investigated range of water contents by either 1 partial melting of tonalitic to gabbroic eclogitic lower crust or 2 crystal fractionation from melts of andesitic to basaltic composition melting or fractionation at lower pressures or with lower water contents may produce calc alkaline liquids as plagioclase replaces garnet as the major al bearing phase cale alkaline rocks showing evidence of garnet liquid equilibration in their ree patterns must also have undergone lower pressure fractionation in order to explain their major element compositions

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

geochemistry and zircon u pb ages of adakitic rocks from the dulan area of the north qaidam uhp terrane north tibet constraints on the timing and nature of regional tectonothermal events associated with collisional orogeny abstract geochemistry and u pb ages of leucosomes and tonalites in a high pressure granulite unit of the dulan area have been determined to constrain the tectonothermal evolution related to collision and thickening of lower crust in the north qaidam mountains nqd leucosomes and tonalites show a marked chemical resemblance to adakites 1 high la yb and sr y and low y and hree 2 high al 2 o 3 and low mg values with obvious positive eu anomalies and 3 slightly positive e nd t values zircon u pb analysis of leucosomes and tonalites yielded 206 pb 238 u ages of 428 437 ma and 436 437 ma respectively which constrain the emplacement ages of the adakitic rocks petrological geochronological and geochemical characters indicate that the adakitic rocks may have been derived from partial melting of a thickened mafic lower crust 50 km suggesting a dominating source regime of synchronous high pressure mafic granulites contemporary magmatism in other units of the nqd shows evidence of a widespread tectonothermal event during early silurian 420 450 ma that includes metamorphism magmatism and anatexis related to collision and thickening of lower crust

thermal maturity source rock potential and kinetics of hydrocarbon generation in permian shales from the damodar valley basin eastern india abstract this study investigates the source rock characteristics of permian shales from the jharia sub basin of damodar valley in eastern india borehole shales from the raniganj barren measure and barakar formations were subjected to bulk and quantitative pyrolysis carbon isotope measurements mineral identification and organic petrography the results obtained were used to predict the abundance source and maturity of kerogen along with kinetic parameters for its thermal breakdown into simpler hydrocarbons the shales are characterized by a high toc 3 4 mature to post mature heterogeneous type ii iii kerogen raniganj and barren measure shales are in mature late oil generation stage rr raniganj 0 99 1 22 rr barren measure 1 1 1 41 vitrinite is the dominant maceral in these shales barakar shows a post mature kerogen in gas generation stage rr barakar 1 11 2 0 and consist mainly of inertinite and vitrinite the 13corg value of kerogen concentrate from barren measure shale indicates a lacustrine marine origin 24 6 30 84 vs vpdb and that of raniganj and barakar 22 72 25 03 vs vpdb show the organic provenance to be continental the 13c ratio of thermo labile hydrocarbons c1 c3 in barren measure suggests a thermogenic source discrete bulk kinetic parameters indicate that raniganj has lower activation energies e 42 62 kcal mol compared to barren measure and barakar e 44 68 kcal mol temperature for onset 10 middle 50 and end 90 of kerogen transformation is least for raniganj followed by barren measure and barakar mineral content is dominated by quartz 42 63 siderite 9 15 and clay 14 29 permian shales in particular the barren measure as inferred from the results of our study demonstrate excellent properties of a potential shale gas system

phase equilibria and compositions of fe mg al minerals and melts in water saturated peraluminous granitic systems phase assemblages and phase compositions were studied experimentally in water saturated biotite bearing peraluminous granitic melts as a function of alumina excess and temperature the runs were performed at 2 and 5 kbars under nno buffer biotite was stable only in composition containing 5 of normative corundum it coexisted with cordierite and hercynite at 2 kbars and with hercynite at 5 kbars in composition containing 10 of normative corundum biotite was not observed abundant cordierite and hercynite were the only fe mg al minerals these relationships show that at constant pressure the amount of cordierite increases with increasing excess of alumina simultaneously the stability of biotite decreases due to preferential partitioning of mg into cordierite and fe into biotite besides the distribution of fe mg and al among the coexisting solid phases solubility of these elements in the melts is given below 900 c melts are poor in iron and magnesium and correspond in terms of these elements to leucogranites it is suggested that the leucogranitic magmas such as parental magmas of european hercynian and himalayan leucogranites must have been formed through highly efficient separation of partial melt from restite in which ferromagnesian components are concentrated peraluminous granites rich in ferromagnesian minerals originate supposedly from restite bearing magmas

granitoid magmas preserved as melt inclusions in high grade metamorphic rock this review presents a compositional database of primary anatectic granitoid magmas entirely based on melt inclusions mi in high grade metamorphic rocks although mi are well known to igneous petrologists and have been extensively studied in intrusive and extrusive rocks mi in crustal rocks that have undergone anatexis migmatites and granulites are a novel subject of research they are generally trapped along the heating path by peritectic phases produced by incongruent melting reactions primary mi in high grade metamorphic rocks are small commonly 5 10 m in diameter and their most common mineral host is peritectic garnet in most cases inclusions have crystallized into a cryptocrystalline aggregate and contain a granitoid phase assemblage nanogranitoid inclusions with quartz k feldspar plagioclase and one or two mica depending on the particular circumstances after their experimental remelting under high confining pressure nanogranitoid mi can be analyzed combining several techniques emp la icp ms nanosims raman the trapped melt is granitic and metaluminous to peraluminous and sometimes granodioritic tonalitic and trondhjemitic in composition in agreement with the different formula 1 conditions of melting and protolith composition and overlap the composition of experimental glasses produced at similar conditions being trapped along the up temperature trajectory as opposed to classic mi in igneous rocks formed during down temperature magma crystallization fundamental information provided by nanogranitoid mi is the pristine composition of the natural primary anatectic melt for the specific rock under investigation so far 600 nanogranitoid mi coming from several occurrences from different geologic and geodynamic settings and ages have been characterized although the compiled mi database should be expanded to other potential sources of crustal magmas mi data collected so far can be already used as natural starting point compositions to track the processes involved in formation and evolution of granitoid magmas 1 embed mml math 1 gif

partial melt in the upper middle crust of the northwest himalaya revealed by rayleigh wave dispersion article i nfo seismic shear wave velocities are sensitive to the partial melts that should be present in the himalayan orogen if low viscosity channel flow is active at the present day we analyzed regional earthquakes in the western himalaya and tibet recorded on 16 broadband seismometers deployed across the nw indian himalaya from the indian platform to the karakoram range we used a multiple filter technique to calculate the group velocity dispersion of fundamental mode rayleigh waves and then inverted the dispersion records to obtain separate one dimensional shear wave velocity models for five geologic provinces the tibetan plateau ladakh arc complex indus tsangpo suture zone tethyan himalaya and himalayan thrust belt our velocity models show a low velocity layer lvl with 7 17 velocity reduction centered at 30 km depth and apparently continuous from the tethyan himalaya to the tibetan plateau this lvl shows good spatial correspondence with observations of low resistivity from magnetotelluric studies along the same profile of the possible explanations for low velocity and low resistivity in the mid crust only the presence of melts or aqueous fluids or both satisfactorily explains both sets of observations elevated heat flow observed in the nw himalaya implies that if aqueous fluids are present in the mid crust then the mid crust is well above its solidus comparison of our results with laboratory measurements and theoretical models suggests 3 7 melt is present in a channel in the upper middle crust of the nw himalaya at the present day and the physical conditions to enable active channel flow may be present

zircon shrimp u pb ages and in situ hf isotopic analysis for the mesozoic intrusions in south taihang north china craton evidence for hybridization between mantle derived magmas and crustal components abstract the north china craton ncc was stabilized in paleo proterozoic times and the eastern part of it was remobilized in the mesozoic as is indicated by the presence of voluminous mesozoic magmas in eastern ncc in particular the lithospheric mantle beneath eastern ncc was significantly thinned during the intense mesozoic tectono magmatic activity which makes the ncc different from most other ancient cratons the mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the ncc from craton to a tectonically active region the south taihang magmatic complex lies in the western part of the mesozoic magmatic zone in the ncc the complex falls into three main plutonic rocks the hongshan syenite the xishu gabbroic diorite monzonite and the wu an monzonitic rocks zircon u pb dating reveals that the three plutonic rocks were emplaced contemporaneously at 132 ma in situ hf isotopic analyses for the dated zircons indicate that the hongshan syenites show homogeneous hf t values 10 to 13 which are slightly lower than those 9 0 for the enriched subcontinental lithospheric mantle sclm as revealed by zircons from mafic rocks that originated from melting of sclm this suggests that the parental magma to the syenites was likely derived from melting of the enriched sclm and contaminated slightly by old lower continental crustal material during ascent the xishu and wu an gabbroic diorites to monzonitic rocks however show significantly varied hf isotopic compositions with hf t 9 2 to 16 and 15 5 to 24 respectively the wide range of hf t values for a single sample suggests that the xishu and wu an plutons formed through a process of hybridization between enriched mantle derived mafic magma and crustal components in variable proportions this is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons the wu an monzonitic rocks show lower hf t values than the xishu gabbroic diorite monzonite suggesting more incorporation of crustal components in the source the sudden surge of magmatic activity in the south taihang orogen took place as a result of lithospheric extension that caused partial fusion of the enriched portions of sclm generating voluminous mafic magmas underplating of the mafic magmas in the lower crust consequently caused partial melting of the old basement rocks to produce granitic melts which was followed by mixing between the mafic and granitic magmas

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

palaeoenvironmental conditions during deposition of the upper cretaceous oil shale sequences in the songliao basin ne china implications from geochemical analysis abstract excellent hydrocarbon source rocks oil shales containing type i organic matter om were deposited in the continental songliao rift basin during the late cretaceous a major contribution of aquatic organisms dinoflagellates green algae botryococcus and minor input from macrophytes and land plants to om accumulation is indicated by n alkane distribution steroid composition and 13 c values of individual biomarkers microbial communities included heterotrophic bacteria cyanobacteria and chemoautotrophic bacteria as well as purple and green sulfur bacteria the presence of methanotrophic bacteria is indicated by 13 c depleted methyl hopane the sediments were deposited in a eutrophic alkaline palaeolake highly reducing saline bottom water conditions and a stratified water column existed during om accumulation of the qingshankou formation and member 1 of the nenjiang formation this is indicated by low pristane phytane gammacerane index and mttc ratios and the presence of carotane and aryl isoprenoids however an abrupt change in environmental conditions during deposition of member 2 of the nenjiang formation is indicated by significant changes in salinity and redox sensitive biomarker ratios a freshwater environment and suboxic conditions in the deep water prevailed during this period higher input of terrigenous om occurred during deposition of the upper nenjiang formation good oil to source rock correlation was obtained using biomarker fingerprints of oil stained sandstone from the quantou formation and oil shales from the qingshankou formation based on the extent of isomerisation of c 31 hopanes the oil was most probably derived from oil shales of the qingshankou formation in deeper parts of the basin

multiple breakdown and chemical equilibrium of silicic clinopyroxene under extreme metamorphic conditions in the kontum massif central vietnam clinopyroxene in ultrahigh temperature mafic granulites from the kontum massif in central vietnam records multiple metamorphic stages manifested as exsolution textures quartz rods and orthopyroxene hornblende plagioclase needles and as symplectitic intergrowths involving clinopyroxene plagioclase these textures suggest a metamorphic evolution characterized by decompression and subsequent cooling from eclogite facies to amphibolite facies conditions through ultrahigh temperature conditions quartz rods in clinopyroxene and clinopyroxene plagioclase symplectites were formed under eclogite conditions prior to ultrahigh temperature metamorphism the orthopyroxene hornblende plagioclase needles in clinopyroxene are regarded as cooling products after ultrahightemperature metamorphism recalculated compositions of precursor clinopyroxene show supersilicic composition during the metamorphic evolution the chemical composition varies from silicic ca eskola rich via sodic jadeite rich to aluminous ca tschermak rich compositions presence of supersilicic clinopyroxene suggests that the granulite decompressed from possible ultrahigh pressure conditions ca 800 900 c at 2 3 gpa preceding the ultrahigh temperature stage 1050 c at 1 3 gpa which provide strong constraints on the tectonic evolution of the indochina region and it also provides insights on crustal exhumation at a continental collision zone another significant aspect of this study is that the breakdown textures of clinopyroxene and its chemical variations may provide important information in establishing pre and post peak evolution especially for extremely high temperature or high pressure metamorphic rocks

geochronological and geochemical constraints on the petrogenesis of the early paleoproterozoic potassic granite in the lushan area southern margin of the north china craton abstract we conducted a geochronological and geochemical study on the paleoproterozoic potassic granites in the lushan area southern margin of the north china craton ncc to understand the tectonic regime of the ncc at 2 2 2 1 ga this rock suite formed at 2194 29 ma the rocks are rich in sio2 76 10 77 73 wt and k2o 5 94 6 90 wt with high k2o na2o contents from 7 56 wt to 8 48 wt but poor in cao 0 10 0 28 wt p2o5 0 02 0 05 wt and mgo 0 01 0 30 wt mg 1 08 27 3 indicating they experienced fractional crystallization major element compositions suggest the potassic granites share an affinity with high k calc alkaline granite even though the lushan potassic granitic rocks have high a cnk ratios 1 11 1 25 which can reach peraluminous feature the very low p2o5 contents and negative correlation of p2o5 and sio2 ruling out they are s type granites different from peralkaline a type granites the lushan potassic granites have variable zr concentrations 160 344 ppm 226 ppm on average and 10 000 ga al ratios 1 76 3 00 together with high zircon saturation temperatures tzr 826 885 c indicating they are fractionated aluminous a type granites enriched lree la yb n 9 72 81 8 negative eu anomalies and low sr y with no correlations in sr y and sr zr versus cao suggest the possible presence of ca rich plagioclase and absence of garnet in the residual magmatic zircon grains have variable ehf t values 2 4 to 7 3 with zircon two stage hf model ages tdmc varying from 2848 ma to 2306 ma mostly around ca 2 5 ga and are plotted in the evolution line of crustal felsic rock we propose that the rocks mainly formed by partial melting of ca 2 50 ga tonalitic granodioritic crust as a result of upwelling mantle derived magmas which provided thermal flux and source materials in an intra continent rifting the ca 2 2 ga magmatism suggests that intra continental rifting occurred at 2 35 1 97 ga at least in the southern margin of the ncc after its final cratonization in the late neoarchean

phase relationships of gabbro tonalite granite water at 15 kbar with applications to differentiation and anatexis phase relationships have been determined at 15 kbar with variable h 2o contents for three rocks a gabbro a tonalite and a muscovite granite representing the compositional trend of the calc alkaline rock series experiments were conducted in 0 5 in piston cylinder apparatus using ag pd or pt capsules the results obtained are acceptable representations of the phase relationships for elucidation of petrological processes selected runs with 5 h 2o were completed using au capsules to overcome the problem of iron loss up to the temperature limit of au for reliable electron microprobe analyses of glass garnet clinopyroxene amphibole and plagioclase no glasses could be analyzed in the gabbro the data provide k d values as a function of temperature for pairs of coexisting minerals and liquid the chemical variations are used to evaluate 1 the fractionation trends in hydrous magmas at 55 km in thickened continental crust or uppermost mantle and 2 the products of anatexis of the thickened crust at this depth fractionation of hydrous basalt or anatexis of gabbro and tonalite or their metamorphosed equivalents appears to produce liquids diverging from the calc alkaline trend anatexis of granite produces a liquid less siliceous than itself with some chemical characteristics of syenite

geochronology petrogenesis and tectonic implications of the newly discovered cu ni sulfide mineralized yueyawan gabbroic complex kalatag district northwestern eastern tianshan nw china abstract the early permian cu ni sulfide bearing mafic ultramafic intrusions from north xinjiang in nw china help to provide constraints on the late paleozoic crustal growth in the central asian orogenic belt caob and improve the understanding of the genesis of magmatic sulfide mineralization in orogenic settings and the identification of future prospecting targets the cu ni sulfide mineralized yueyawan gabbroic complex in kalatag represents a new breakthrough for cu ni prospecting in covered areas in the northwestern part of the eastern tianshan orogenic belt north xinjiang rocks from this intrusion have similar la icp ms zircon u pb ages 282 4 1 1 281 3 1 2 ma to other mafic ultramafic intrusions containing magmatic sulfide mineralization in north xinjiang these early permian gabbroic intrusions are thus important targets for cu ni mineralization exploration in this region the rocks of the yueyawan gabbroic complex are a ca 1 km2 elongated nw trending crescent shaped at the junction of two e w and nw se trending faults the intrusion has the morphology of a conduit tube the rocks include troctolite olivine gabbro hornblende gabbro and gabbro and the cu ni sulfides occur as steeply dipping 65 70 lenses with disseminated textures in the contact zone between the olivine gabbro and hornblende gabbro indicating that sulfide precipitation was coeval with the crystallization of the magmas giving rise to these rocks the rocks investigated in this study are gabbroic in composition they are characterized by moderate concentrations of sio2 44 8 48 8 wt and low to moderate concentrations of mgo 1 69 13 4 wt mg values of 39 6 73 3 ni and cr furthermore the rocks have high positive ehf t values 13 1 to 15 9 and flat rare earth element patterns la yb n 2 01 2 89 with marked positive eu anomalies high ti zr ratios 70 164 and low ce pb 3 65 14 83 and nb ta values 9 16 indicating very restricted amounts 5 10 of crustal assimilation this complex was likely derived from 10 to 20 partial melting as evidenced by the low sm yb values of 1 48 2 02 and la sm values of 1 61 2 23 of weakly slab melt metasomatized as evidenced by the low ba nb and ba zr ratios subcontinental lithospheric mantle with 2 garnet and 2 spinel lherzolite at depths greater than 85 km in a post collisional extensional source that contained sufficient ni and cu for the saturation and segregation of immiscible sulfides to concentrate the metals the magma underwent sulfide saturation and segregation together with olivine fractionation as evidenced by ni and tfe2o3 increase and sio2 cao and zr decrease with increasing mgo content in the conduit type intrusion therefore regional fault structures ore bearing rock types and geochemical ratios that reflect high degrees of partial melting are features of the cu ni mineralized gabbroic rocks in adjacent areas that help support exploration

generation of post collisional normal calc alkaline and adakitic granites in the tongbai orogen central china abstract post collisional granites are generally generated by partial melting of continental crust during orogenic extension the occurrence of normal calc alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension which has been debated yet in this paper we present a comprehensive study of zircon u pb ages hf o isotopes as well as whole rock major and trace elements and sr nd isotopes for tongbai and jigongshan post collisional granitic plutons in the tongbai orogen zircon u pb dating yields intrusion ages of ca 140 and 135 ma for the tongbai and jigongshan plutons respectively suggesting they are post collisional granites these granites are high k calc alkaline series metaluminous to weakly peraluminous with a cnk ratios of 0 85 1 08 the tongbai gneissic granites are normal calc alkaline granite having variable sio2 61 93 76 74 wt and sr y 2 9 38 9 and la yb n 1 7 30 1 ratios with variably negative eu anomalies 0 41 0 92 they have relatively high initial sr isotope ratios of 0 707571 to 0 710317 and low end t 15 74 to 11 09 and ehf t 17 6 to 16 9 values their nd and hf model ages range from 2 2 to 1 8 ga and 2 3 to 2 2 ga on the contrary the jigongshan granites show higher sio2 66 56 72 11 wt and sr y 30 1 182 0 and la yb n 27 4 91 4 ratios with insignificant eu anomalies 0 73 1 00 belonging to adakitic granite they have isr 0 707843 0 708366 end t 19 83 to 17 59 and ehf t 26 0 to 23 5 their nd and hf model ages vary from ca 2 5 to 2 4 ga and ca 2 8 to 2 6 ga the tongbai and jigongshan granites are characterized by mantle like zircon 18o values 5 17 5 46 these geochemical features suggest that the tongbai and jigongshan granites were derived from partial melting of paleoproterozoic and archean continental crust respectively fractional crystallization affected the geochemical compositions of the tongbai gneissic granites while the compositions of the jigongshan granites were mainly controlled by partial melting the adakitic signatures of the jigongshan granites were either inherited from their source or ascribed to more garnet in their residues the voluminous post collisional granites might form by the collapse of the thickened tongbai orogenic root the normal tongbai gneissic granites occurred slightly earlier than the jigongshan adakitic granites in the tongbai orogen suggesting that it is not a mandate to sign the tectonic transition from adakitic to normal calc alkaline granites in post collisional settings therefore this study provides another example supporting the burst of voluminous post collisional granites with different compositions as a consequence of the collapse of the thickened orogenic roots of collisional orogens

petrogenesis and geochronology of precambrian granitoid gneisses in western liaoning province constraints on neoarchean to early paleoproterozoic crustal evolution of the north china craton abstract the north chaoyang fuxin yixian granite greenstone belt ncfy ggb at the northern margin of the eastern continental block of the north china craton is composed chiefly of metamorphic volcanic and volcano sedimentary rocks and granitoid gneisses the magmatic precursors of these granitoid gneisses are diorites tonalites trondhjemites granodiorites and monzogranites these granitoid gneisses can be divided into two groups a high mg group hmg and a low mg group lmg according to their contrasting geochemical characteristics petrogenetic studies indicate that the hmg magmas were derived from partial melting of a subducted oceanic slab which was contaminated by mantle peridotites during their ascent whereas the lmg magmas were generated from the partial melting of lower continental crust composed chiefly of metamorphosed basaltic and pelitic rocks la icpms zircon u pb dating reveals that granitoid gneisses in the hmg and low k granitoid gneisses in the lmg were emplaced at 2511 2521 ma but that the high k granitoid gneisses in the lmg formed later at ca 2495 ma these neoarchean to early paleoproterozoic granitoid gneisses intrusive into the metamorphic volcanic assemblages of the yixian fuxin greenstone belt indicate that the ncfy ggb was developed at a neoarchean to early paleoproterozoic andean type active continental margin

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

characterisation of oil and potential source rocks in the northeastern song hong basin vietnam indications of a lacustrine coal sourced petroleum system oil discovered in the b10 stb 1x well in the northeastern song hong basin vietnam has typical lacustrine coaly geochemical features indicating the existence of a principally lacustrine sourced petroleum system with minor contributions from a coal source the presence of lacustrine source rocks in the basin is indicated by distinct high amplitude seismic reflectors in undrilled half grabens and outcrops of oligocene immature mudstones and humic coals at dong ho and on bach long vi island the mudstones from dong ho generally have a toc content of 8 17 wt and hi values 500 mg hc g toc the organic matter is principally composed of fluorescing amorphous organic matter and liptodetrinite alginite with botryococcus morphology is present the organic matter corresponds to type i kerogen the bach long vi island mudstones contain 2 7 wt toc and have hi values from 200 700 mg hc g toc the organic matter is largely similar to that in the dong ho mudstones but in addition may contain some marine organic material the b10 stb 1x oil shows features common to both the dong ho and bach long vi island mudstones but was probably principally generated from a source similar to the dong ho mudstones with contributions from higher land plant organic matter a prominent activation energy peak dominates the activation energy distributions of the mudstones and upon artificial maturation hydrous pyrolysis the mudstones show extensive hydrocarbon generation over a narrow temperature range hydrocarbon expulsion has been estimated to occur at a vitrinite reflectance of 0 75 ro the source of the b10 stb 1x oil may be located in the thuy nguyen graben and maturity modelling shows that the lacustrine mudstones will be thermally mature in this graben

pyroxene exsolution in granulites from fyfe hills enderby land antarctica evidence for 1000 degrees c metamorphic temperatures in archean continental crust reply

petrogenesis of the archean tonalite trondhjemite granodiorite ttg and granites in the lushan area southern margin of the north china craton implications for crustal accretion and transformation abstract tonalite trondhjemite granodiorite ttg assemblages and abundant high k calc alkaline magmatism are considered to be closely related to craton stabilization and usually record a tectonic transition three episodes of granitic magmatism are identified in the lushan area at the southern margin of the north china craton ncc on the basis of new la icp ms zircon u pb ages and whole rock geochemical data they are ttg gneisses sodic potassic granite spg suite and potassic granite dated at 2840 ma 2760 ma and 2570 ma respectively the ttg gneisses have high sio 2 variable mg cr and ni contents with high la yb n and sr y ratios suggesting that the parental magmas were derived by partial melting of subducted oceanic crust they show no obvious correlations between sr y and dy yb or la yb n and dy yb and all have negative nb and ta but positive zr and hf anomalies and variable dy yb nb ta zr hf and zr sm ratios suggesting melting of a deep source 45 km with rutile eclogite and garnet amphibolite in the residue the ttg samples have positive hf t values 2 6 to 7 0 with the youngest t dm c 2896 ma close to the crystallization age indicating that they were produced by partial melting of juvenile crustal materials in an arc setting rocks of the spg suite have high sio 2 contents variable na 2 o k 2 o ratios 0 41 10 91 and low y and yb contents with high sr y ratios indicating an affinity to i type granites they display depleted and concave upward ree patterns between middle and heavy rees and higher zr sm than ttg gneisses possibly resulting from amphibole removal by fractional crystallization or as a residual phase during melting meanwhile the rocks have a large variation of dy yb without obvious correlations between sr y and dy yb and la yb n and dy yb in combination with variable but uniformly low y contents therefore we suggest that the spg samples were derived from partial melting with garnet in the residue magmatic zircons have hf t values from 4 3 to 4 2 with t dm c ages from 3200 ma to 2877 ma indicative of older mafic lower crustal sources the rocks formed within a short time interval with the ttg and their emplacement was accompanied by regional granulite and amphibolite metamorphism implying that they may also have formed in an arc setting the potassic granite has high sio 2 74 79 wt and k 2 o na 2 o 9 22 wt contents with a low 10 000ga al 1 89 ratio and t zr 670 c magmatic zircons have a narrow range of hf t values 2 0 to 4 1 with t dm c ages 2942 2692 ma older than the formation age but consistent with the formation age ca 2760 ma of the lushan spg suite the potassic granite has a hf isotope composition identical to that of the spg suite and is enriched in lree and depleted in y with a positive eu anomaly suggesting that the spg suite is the main source one zircon yielded an inherited age of 2837 36 ma consistent with the age of the ttg gneisses indicating that the gneisses could also be the source of the potassic granite the two types of source rocks indicate a shallow crust depth hence the heat required for partial melting of granodioritic rocks to form the potassic granite could have been provided by the upwelling of mantle or mantle derived melts in an extensional setting therefore the ttg gneisses spg suite and potassic granite in the lushan area record a tectonic transition from a compressive to an extensional setting in the southern margin of the ncc between 2 85 and 2 50 ga

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

geochronology and geochemistry of the neoarchean lulong complex in the eastern hebei province north china craton implications on regional crustal evolution abstract the lulong complex exposed in the southeastern part of the eastern hebei province in the north china craton ncc is mainly composed of meta basalt biotite plagioclase gneiss migmatite amphibolite and granitoids mineral assemblages indicate the rocks in this complex underwent upper amphibolite facies metamorphism zircon u pb and lu hf data constrain that both protolith of the biotite plagioclase gneiss and the homogeneous domain of the migmatite formed at 2 53 ga and were mainly derived from the reworking of 2 8 2 7 ga crustal source the similar mineral association zircon u th pb systematics and geochemical features suggest that their protolith should be dominated by felsic volcanic sequences with limited contributions from older crust the protolith of the amphibolite gabbro or diabase was metamorphosed at 2477 20 ma geochemistry and zircon lu hf systems indicate that these meta mafic rocks originated from an enriched subcontinental lithospheric mantle source the granitoids exposed in the lulong area yield zircon u pb ages of 2507 21 ma to 2473 38 ma and record 2 5 ga regional metamorphic event the initial zircon 176hf 177hf ratios of the granite are in the range of 0 280640 0 281678 and suggest a complicated source where as those from the granodiorite indicate melting of juvenile crustal materials geochemically the felsic meta volcanics of the lulong complex are comparable to rhyodacite dacite with calc alkaline affinities the granitoids suite comprises 2 47 ga peraluminous granite felsic dikes and 2 51 ga metaluminous granodiorite all these felsic intrusions are characterized by moderate differentiation of ree patterns and low sr y ratios

geochronological and geochemical constraints on the petrogenesis of the 2 6 2 5 ga amphibolites low and high al ttgs in the wangwushan area southern north china craton implications for the neoarchean crustal evolution abstract the crustal evolutionary processes of the north china craton ncc during the late neoarchean ca 2 6 2 5 ga are still under large debate the systematic investigations of widespread ca 2 6 2 5 ga meta volcanic basalts and ttg assemblages can provide a better understanding of tectonic evolution at this period the wangwushan neoarchean amphibolites high and low al ttgs in southern ncc were formed at 2 57 2 52 ga the amphibolites are tholeiitic in composition they have whole rock end t values of 2 8 4 0 tdm1 3 7 2 6 ga and zircon ehf t values of 1 2 7 2 tdm1 2 81 2 57 ga indicative of a depleted mantle source with involvement of older crustal materials their compositional spectrum accords with those in island arc field or straddles the boundary between morb and island arc fields suggesting significant contributions from subduction zone derived fluids during magma formation the high al ttgs contain high mg cr and ni contents and la yb n and sr y ratios together with positive whole rock end t values 0 6 5 2 tdm2 2 95 2 48 ga indicating that they derived from partial melting of a subducted oceanic slab with older crustal materials their geochemical features are corresponding to slab melt identification criterion in an arc setting and illustrate a deep source 45 km with garnet amphibolite in the residue without rutile the low al ttgs show low mg and la yb n ratios negative eu anomalies relatively flat hree and y patterns their zircon ehf t 2 2 8 8 and 1 3 6 9 and whole rock end t values ca 2 23 are positive all the evidences support that the low al ttgs derived from a low degree partial melting of basaltic crust with the residue lack of garnet consistent with a shallower depth about

multi proxy approach on the hydrocarbon generation perspective of barjora basin india abstract barjora basin in india is a small basin characterized by a high organic richness of early mature nature the present study aims to find the source of organic matter om and hydrocarbon generation potential of barjora basin systematically collected coal and shale samples from r ii seam of the basin were used for proximate and ultimate analyses rock eval pyrolysis along with total organic carbon toc content organo micropetrographic framework thermal maturity carbon isotopic signature biomarker composition functional group studies and estimation of relative aliphaticity and aromaticity through fourier transform infrared spectroscopy ftir the novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon 13c biomarker signatures thermal maturity parameters organo micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin a dominant terrestrial om input in barjora basin is indicated by the toc to total nitrogen ratio c n 13c and biomarker compositions high gelification index gi tissue preservation index tpi and carbon preference index cpi values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity in addition large liptinite content tpi and gi designate short transportation of the om before burial leading to organic richness of the barjora basin moreover high liptinite content type ii iii admixed kerogen input s2 s3 ratio tpi and index for hydrocarbon generation ihg signify higher potential of the basin for hydrocarbon generation

lateral variations in the crustal structure of the indo eurasian collision zone we thank michael ritzwoller and two anonymous reviewers for constructive comments that have helped improve the manuscript the majority of the seismic data used in this study were downloaded from iris dmc data for the ngri stations in india were provided by s s rai and zahid ra provided the pmd pakistan data kajal borah provided the ambient noise cross correlations for the uttaranchal network figures were prepared using generic mapping tools gmt software wessel and smith 1998 we thank robert herrmann for making the computer programs in seismology freely available

early cretaceous granitoids and their implications for the collapse of the dabie orogen eastern china shrimp zircon u pb dating and geochemistry abstract two stages of early cretaceous post orogenic granitoids are recognized in the dabie orogen eastern china which recorded processes of extensional collapse of the orogen the early stage granitoids 132 ma are foliated hornblende quartz monzonites and porphyritic monzogranites they are of high k calc alkaline series and metaluminous to weakly peraluminous with high k 2 o and low mgo contents mg values 32 0 46 0 they contain high sr low y and heavy rare earth elements hree and have high sr y and la yb n ratios without clear negative eu sr and ti anomalies the early stage deformed granitoids have adakitic geochemical compositions and are equilibrated with residues rich in garnet and poor in anorthite rich plagioclase and thus indicate the existence of an over thickened 50 km crustal root beneath the orogen at 132 ma the later stage granitoids 128 ma are undeformed fine grained monzogranites fine grained k feldspar granites and coarse grained k feldspar granite porphyry they belong to a peraluminous and high k calc alkaline to shoshonite series and display a flat hree pattern and have strong negative eu sr and ti anomalies with low sr y and la yb n ratios the late stage granitoids are equilibrated with residues rich in anorthite rich plagioclase hornblende ilmenite titanite and poor in garnet indicating that the crust of the dabie orogen became thinner

preserved near ultrahigh pressure melt from continental crust subducted to mantle depths remnants of hydrous melt formed at mantle depths have been identified and characterized within high pressure leucogranulites of the orlica snieznik dome bohemian massif central europe they occur as nanogranites in garnet formed via partial melting of granitoids during the variscan orogeny melt composition and h2o content have been investigated in situ after experimental re homogenization of the nanogranites and are consistent with melts produced experimentally from crustal lithologies at mantle depths this is the first geochemical study of melt inclusions from natural crustal rocks equilibrated close to the stability field of coesite shedding light on how continental crust melts during deep subduction whereas decompressional melting is commonly invoked for deeply subducted crustal lithologies melting occurred near or at the metamorphic peak pressure in the orlica snieznik granulites melting of deeply subducted crustal rocks significantly modifies the rheology and thus promotes fast exhumation this process has a critical influence on the geodynamic evolution of subduction collision orogens as well as crustal differentiation at depth

isotopic signals from callovian kimmeridgian middle upper jurassic belemnites and bulk organic carbon staffin bay isle of skye scotland abstract the stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the middle to late jurassic interval the belemnite samples collected from the staffin bay and staffin shale formations from the isle of skye scotland yielded oxygen isotope values consistent with callovian kimmeridgian palaeotemperatures of 6 7 20 6 c the carbon isotope data comprise one of the first moderately high resolution investigations of the relationship between terrestrial 13 c org predominantly fossil wood debris and marine 13 c carb belemnites as derived from a geologically coeval record the staffin bay data reveal a broad early to mid oxfordian positive carbon isotope excursion the excursion maximum occurs in the cordatum zone british boreal ammonite zonation although high values persist into the tenuiserratum zone the correspondence between the marine and terrestrial records indicates a strong coupling of the ocean atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time the mid oxfordian negative carbon isotope excursions identified in published tethyan records and commonly attributed to methane release are not recorded in the staffin bay data which may suggest that the tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re evaluated supplementary material isotopic and geochemical data are available at http www geolsoc org uk sup18339

geochronology and geochemistry of 2 5 to 2 4 ga granitic plutons from the southern margin of the north china craton implications for a tectonic transition from arc to post collisional setting abstract the xutai and lujiagou plutons exposed in the songshan jishan area in the southern margin of the north china craton ncc are studied to constrain the tectonic regime of the ncc between 2 5 and 2 4 ga the xutai pluton dated at 2509 33 ma mainly consists of tonalite and monzogranite with a calc alkaline affinity rittmann index

crustal structure and deformation beneath eastern and northeastern tibet revealed by p wave receiver functions abstract the present day tibetan crust records the shallow response of the cenozoic continental collision between the indian and eurasian plates an analysis of the deep crustal structure beneath eastern and northeastern tibet is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the tibetan plateau we herein provide detailed images of the crustal structure of eastern and northeastern tibet and the adjacent sichuan basin using teleseismic p wave receiver function p rf data from a nw se trending linear seismic array our p rf imaging result reveals distinct structural features of the study region including marked lateral variations in the depth to basement beneath the songpan ganzi block and the sichuan basin a seismically slow mid lower crust beneath the songpan ganzi block and a low velocity anomaly just above the moho around the easternmost kunlun fault area and obvious moho offsets near the boundaries of tectonics blocks these structural features may reflect various crustal responses within the continental interior to the india eurasia collision at the plate margin the rigid crust of the sichuan basin might have wedged into the tibetan crust in the longmenshan area which probably facilitated crustal thickening and enabled channelized mid lower crustal flow in the songpan ganzi block to the west being a pre existing tectonic boundary the kunlun fault could have acted as a focus of heating and hot mantle upwelling associated with the deep processes of the indian plate underthrusting and subduction possibly resulting in localized weakening and modification of the lower crust around this fault area the observed significant differences in the crustal structure of eastern and northeastern tibet suggest that crustal shortening in this region may have been absorbed by not only vertical thickening in the interiors of the tectonic blocks but also complex local deformation along the boundary zones

petrogenesis of two granites from the nilgiri and madurai blocks southwestern india implications for charnockite calc alkaline granite and charnockite alkali a type granite link in high grade terrains abstract igneous charnockites share some of the characteristics of calc alkaline and alkali a type granites and together constitute important rock types in many high grade terrains the neoproterozoic kalpatta and munnar biotite hornblende granites intrude the upper amphibolite to granulite facies terrain of southwestern india geochemical characteristics of the kalpatta granite are similar to high k calc alkaline magnesian granitoids whereas those of the munnar granite are similar to alkali ferroan granitoids within the constraints imposed by the high temperature k rich nature of the magmas comparison with experimental studies on various granitoid source compositions and trace and rare earth element modeling the distinctive features of both granites reflect a source rock of charnockitic nature in this context the northern kerala nkm and cardamom hill cm charnockite massifs occurring near the granites were considered as probable source rock compositions both the nkm and cm charnockites consists of an intermediate low sio2 type and silicic high sio2 type with the intermediate type showing similarities to high ba sr granitoids with low k2o na2o ratios and the silicic type showing similarities to high ba sr granitoids with high k2o na2o ratios the proposed petrogenetic model involves partial melting of the intermediate nkm charnockite forming the kalpatta calc alkaline granite in contrast the munnar alkali a type granite was the product of melting followed by fractional crystallization of the intermediate cm charnockite it is suggested that granitoids that formed by melting of intermediate type charnockites show high k calc alkaline magnesian geochemical characteristics whereas those formed by intermediate type charnockite melting fractional crystallization show alkali ferroan geochemical characteristics

crustal anatexis during the influx of mantle volatiles abstract many data show that large masses of silicic magma can be formed by crustal anatexis under the influence of volatiles possibly enriched in primary water derived from a mantle source in the present paper a model of crustal anatexis accompanied by a limited influx of volatiles is suggested the water influx is not excessive no independent fluid water phase appearing in the magma convective diffusion is assumed to be the dominant mechanism of volatile transport within the silicic melt this mechanism increases the volatile flux by several orders of magnitude compared with the diffusion flux in a non convecting system a high convective flux may be generated only at specific stages of magma chamber formation in this paper a mathematical formulation of the conditions favouring this type of anatexis is given the most plausible source of deep seated water bearing volatiles beneath large silicic crust derived magma masses are mantle derived magmas which maintain vigorous convection it is shown that convective diffusion influx of volatiles from a lower layer of mafic magma into an upper layer of silicic magma leads to a quasi equilibrium situation transient two liquid eguilibrium watson 1976 in this situation the distribution coefficient of water between adjacent silicic and mafic magmas is proportional to the ratio of water solubilities in these magmas and amounts to about 1 4 by mass the silicic magma overlying the mafic magma can contain up to 6 wt water which is particularly true of the latest stages of cryatallization of the mafic magma when its water content rises and diffusion of water across the mafic silicic melt boundary becomes more efficient on the basis of our results the different stages of formation of a silicic magma are discussed the geological consequences are analyzed and some new regularities in the interpretation of geological and petrological data relevant to granitoid petrogenesis are proposed

petrogenesis of an alkali syenite granite rhyolite suite in the yanshan fold and thrust belt eastern north china craton geochronological geochemical and nd sr hf isotopic evidence for lithospheric thinning the yanshan fold and thrust belt in eastern china has been intruded by a series of alkalic igneous rocks ranging in composition from granite and rhyolite to syenite and trachyte laser ablation inductively coupled plasma mass spectrometry u pb analyses of zircon from three alkaline suites yield early cretaceous ages of 130 117ma three groups of rocks have been identified based on their mineralogical geochemical and sr nd hf isotope characteristics the alkali granites and rhyolites are ferroan and have low al2o3 mgo cao sr ba and eu concentrations and high sio2 total fe2o3 k2o nb ga ta th and heavy rare earth element abundances and ga al ratios geochemical data and sr ndand zircon hf isotopic compositions sr sr i1 4 0 7050 0 7164 end t 1 4 8 4 to 13 6 and ehf t 1 4 5 7 to 16 8 indicate that they were probably generated by shallow dehydration melting of biotiteor hornblende bearing granitoid crustal source rocks and then mixed with contemporaneous magma from a mantle and or lower crustal source ferroan syenites have distinct geochemical features from those of the alkaline granites and rhyolites suggesting that they were produced by clinopyroxene and plagioclase fractionation of melt derived from an enriched mantle source mixed with lower and upper crustal derived magmas the magnesian syenites and trachytes have sr ndand zircon hf isotopic compositions that are distinct from those of the ferroan syenites they were mainly derived from partial melting of lower crustal materials mixed with enriched mantle derived alkali basaltic magma the emplacement of an alkali syenite granite rhyolite suite coeval with the formation of metamorphic core complexes and pull apart basins in eastern china indicates they formed in an extensional setting possibly as a result of lithospheric thinning

tio2 exsolution from garnet by open system precipitation evidence from crystallographic and shape preferred orientation of rutile inclusions we investigated rutile needles with a clear shape preferred orientation in garnet from ultra high pressure metapelites from the kimi complex of the greek rhodope by electron microprobe electron backscatter diffraction and tem techniques a definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that rt 001 is either parallel to grt or describes cones with opening angle 27 6 around grt each rt 001 small circle representing a cone on the pole figure displays six maxima in the density plots this evidence together with microchemical observations in tem when compared to various possible mechanisms of formation corroborates a precipitate origin a review of exchange vectors for ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system it requires that components are exchanged between the garnet interior and the rock matrix by solid state diffusion a process we refer to as open system precipitation osp the kinetically most feasible reaction of this type will dominate the overall process the perhaps most efficient reaction involves internal oxidation of fe2 to fe3 and transfer from the dodecahedral to the octahedral site just vacated by text ti 4 6 text m 2 3 text tial left text alsi 2 right text o 1 2 6 text m 2 2 5 text tialsi 3 text o 1 2 10 text m 2 3 0 text al 1 8 text fe 0 2 text si 3 text o 1 2 text m 2 2 text e 1 2 text tio 2 osp is likely to occur at conditions where the transition of natural systems to open system behaviour becomes apparent as in the granulite and high temperature eclogite facies

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

vapour absent melting from 10 to 20 kbar of crustal rocks that contain multiple hydrous phases implications for anatexis in the deep to very deep continental crust and active continental margins

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

the eocene bimodal piranshahr massif of the sanandaj sirjan zone nw iran a marker of the end of the collision in the zagros orogen abstract the bimodal piranshahr massif is composed of coeval but geochemically unrelated mafic 40 7 0 2 ma zircon u pb sensitive high resolution ion microprobe shrimp age and a type felsic rocks 41 0 5 ma rb sr and 41 3 0 8 ma zircon u pb shrimp age the mafic rocks consist of two geochemical types of gabbros that derived from different magmas the more abundant gabbros are moderately alkaline have ratios of large ion lithophile elements to ree and high field strength elements to ree similar to those of intraplate mantle magmas 87 sr 86 sr 41 ma 0 7036 and e nd 41 ma 7 2 the less abundant gabbros have calc alkaline affinities 87 sr 86 sr 41 ma 0 7043 and e nd 41 ma 4 78 felsic rocks are metaluminous a2 type annite fayalite hedenbergite hypersolvus leucocratic coarse grained agpaitic syenites pulaskites and granites with 87 sr 86 sr 41 ma 0 7048 and e nd 41 ma 3 6 4 5 syenites pulaskites and granites are genetically related pulaskites probably represent alkali enriched water rich residual melts from which an f rich vapour phase was later separated granites were probably generated during open system processes in which f rich hydrous alkaline fluids released from the syenites acted upon pre existing felsic rocks the c 41 ma age of the post collisional piranshahr massif indicates that the related collision probably occurred at 50 60 ma i e late palaeocene or early eocene thus resolving a much debated question

process of lithospheric delamination beneath the lhasa qiangtang collision orogen constraints from the geochronology and geochemistry of late cretaceous volcanic rocks in the lhasa terrane central tibet abstract the geochemistry of post collisional granitoids can be used to reconstruct crustal thickness and constrain deep geodynamic processes two series of volcanic rocks of the jiangba formation in the xiongmei area central tibet record the process of lithospheric delamination in the lhasa qiangtang collisional orogen the andesites and dacites crystallized at c 87 and 85 ma respectively and have positive zircon ehf t values 2 7 5 4 and 2 7 7 1 respectively they have calc alkaline compositions with relatively high mg 100 molar mg2 mg2 fe2 39 66 sr contents and sr y and la yb n ratios subscript n signifies normalization to chondrite low y and yb contents and no clear negative eu sr or ti anomalies similar to adakites the andesite dacite series likely formed by partial melting of foundering juvenile mafic lower crust with residual garnet followed by the interaction of this melt with peridotite the rhyolite series was emplaced at c 81 ma and has positive zircon ehf t values 1 0 3 5 the rhyolites are characterized by non adakitic signatures and have high k calc alkaline to shoshonite compositions with low mgo contents mg 21 34 and sr y and la yb n ratios coupled with flat hree patterns and marked negative eu sr and ti anomalies geochemical data indicate that these rhyolites were generated by partial melting of a much shallower crustal root with a plagioclase rich residue zircon u pb ages and different compositional trends for the two series indicate that the lithospheric mantle keel was partially removed by small scale mantle convection that triggered the late cretaceous high mg adakitic magmatism in the lhasa qiangtang collisional orogen partial lithospheric delamination increased heat flow at the base of the crust and caused the thinned crust to melt producing the low mg non adakitic rocks

petrological and organic geochemical properties of lignite from the kolubara and kostolac basins serbia implication on grindability index abstract the influence of different coal lithotypes on grindability has been investigated using lignite from two of the most important upper miocene lignite basins in serbia kolubara and kostolac yellow xylite rich types demonstrated the most negative impact on hardgrove grindability index hgi all different types of xylite rich coal as well as total xylite rich coal from the kolubara basin have a negative influence on the grindability properties while only the yellow type of xylite rich coal from the kostolac showed a negative impact on hgi matrix coal does not show a clear effect on hgi a negative correlation between textinite content and hgi is observed in both basins whereas contents of other macerals do not show influence on grindability properties content of total organic carbon demonstrated the negative impact on hgi correlation analysis indicates that the negative impact of the yellow type of xylite rich coal and the sum of total xylite rich coal on the grindability properties partly can be related to content of total organic carbon and high amount of soluble organic matter matrix lithotype does not show any significant correlation with bulk geochemical parameters in both basins the peat forming vegetation of all samples from both basins were dominated by decay resistant gymnosperm coniferous plants belonging to one or several of the families taxodiaceae podocarpaceae cupressaceae araucariaceae phyllocladaceae and pinaceae lignite from the kolubara basin is characterized by a higher contribution of angiosperm vegetation than coal from the kostolac basin peatification of the kolubara coal occurred under more oxic conditions than the kostolac one analysis of biomarkers indicated that the negative impact of all types of xylite rich coal from the kolubara on hgi can be related to the higher proportion of angiosperms abundance of mid chain n alkanes and sesquiterpenoids aromatization of non hopanoid triterpenoids and hopanoids and intense degradation of wood tissues in a more oxic environment the positive impact of matrix coal on hgi in the kolubara samples can be attributed to elevated content of non aromatic hopanoids and low amounts of aromatic non hopanoid triterpenoids and sesquiterpenoids which seems to hinder the grindability properties

assessment of organic richness and hydrocarbon generation potential of raniganj basin shales west bengal india abstract high energy prices and severe energy shortage has led shale gas to become the focus of study and exploration in many countries india like many other countries around the world with shale gas potential recognizes the strategic importance of developing its shale gas resources for the purpose of shale gas assessment the authors have selected sixty six borehole shale samples of different formations from different parts of raniganj basin west bengal india rock eval pyrolysis and total organic carbon toc analysis and petrographic characterization of the shales were carried out shales from barakar lower permian barren measures upper permian and raniganj formation upper permian are marked by good to excellent toc content input of type iii organic matter and are capable of generating oil and thermogenic gas upon thermal cracking igneous intrusives dykes and sills in the formations occurring in and around the areas of sitarampur si and kulti ku in western part of the basin might have resulted in cooking of the shales increasing their maturities estimated vitrinite reflectance vro as indicated by the barren measures shales of shallow depths from the above mentioned areas majority of the samples are marked by low oxygen index oi values

genesis of alkaline and peralkaline syenite granite series the kharitonovo pluton transbaikalia russia the kharitonovo pluton is located in the central part of the large mongolian transbaikalian province of late paleozoic alkaline syenites and granites the province stretches for a distance of almost 2000 km and contains over 350 plutons the kharitonovo pluton occupies an area of 230 km 2 it is made up of a type granitoids forming two successive alkaline and peralkaline syenite granite series syenites largely predominate over granites rocks of both series are characterized by abundant mesoperthitic feldspar about 90 vol in syenites more than 60 in granites while plagioclase is almost absent in the peralkaline series mafic minerals are riebeckite arfvedsonite kataphorite and aegirine with secondary annitic biotite in the alkaline series edenite and iron rich biotite are the major mafic minerals in the alkaline series coeval mafic rocks commonly occur in the form of synplutonic composite dikes they indicate at least two stages of mafic magma injection into the silicic magma chamber major

early cretaceous low mg adakitic granites from the dabie orogen eastern china petrogenesis and implications for destruction of the over thickened lower continental crust it is generally accepted that the low mg adakitic rocks were derived from the partial melting of metabasalts eclogites in this study we demonstrate that the early cretaceous low mg adakitic granites in the north dabie complex ndc were generated by the partial melting of the ndc orthogneisses here we present in situ u pb and lu hf isotopes in zircon with whole rock geochemical and sr nd isotopic compositions were carried out for the tiantangzhai porphyritic monzogranites from the dabie orogen eastern china the monzogranites are characterized by high sr 576 988 ppm low y 7 3 19 0 ppm and depletion in hree yb 0 50 1 78 ppm thus resulting in high sr y 34 3 135 2 and la yb n 17 0 105 2 ratios without a negative eu anomaly they also exhibit high sio2 66 5 73 5 wt and k2o 2 7 4 7 wt and low mgo 0 4 1 6 wt or mg 28 2 45 3 mostly 40 values whole rock geochemical compositions suggest that the monzogranites represent low mg adakitic rock with high si and rich k features equilibrated with residues rich in garnet sr nd isotopic compositions end t 16 2 to 20 3 87sr 86sr i 0 707798 0 708804 tdm2 nd 2 3 2 6 ga of the monzogranites are distinct from that of the eclogites and amphibolites in the dabie orogen but similar to that of the neoproterozoic 700 800 ma gneisses in the ndc u pb dating of zircons gives a consistent age of 130 0 3 4 ma with discordia upper intercept age of 716 34 ma for inherited cores identified by cl imaging correspondingly in situ lu hf analyses of early cretaceous young age spots from zircons yield initial 176hf 177hf ratios from 0 281898 to 0 282361 ehf t values from 28 1 to 17 6 and two stage crust hf model ages tdm2 from 2293 89 to 2949 108 ma which are generally in agreement with values of 0 281891 to 0 282218 28 2 to 11 7 and 1927 87 to 2963 92 ma for the pre mesozoic inherited cores respectively as for individual core rim pairs in zircon th u ratios increase from the inherited cores to the young growth rims possibly due to variable degrees of partial melting whereas 176lu 177hf ratios greatly decrease because of the garnet effect in residues thus we suggest that the early cretaceous low mg adakitic granites were derived from the partial melting of the ndc neoproterozoic 700 800 ma gneisses and the foundering of the garnet bearing residues could have caused the destruction of the over thickened lower continental crust

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

petrogenesis and geodynamics of late archean magmatism in eastern hebei eastern north china craton geochronological geochemical and nd hf isotopic evidence abstract the eastern part of the north china craton contains large volumes of late archean hornblenditic tonalitic dioritic granodioritic and granitic rocks la icpms zircon u pb dating of three plutons from eastern hebei eastern north china craton record emplacement ages of 2526 2515 ma and metamorphic ages of 2500 2490 ma for the diorite granodiorite and monzogranite and 2440 ma for the k feldspar granite hornblendites have high mgo 8 6 10 6 wt cr 674 1126 ppm ni 125 159 ppm and v 224 315 ppm at low basic silica contents sio2 45 7 49 0 wt they are enriched in light rare earth elements lrees and large ion lithophile elements liles and depleted in high field strength elements hfses with positive nd t values 1 2 to 2 0 indicating they were derived from an enriched mantle source the monzogranites have high sr and ba contents and sr y and la yb ratios low y and hrees abundances and positive nd t and zircon hf t values with nd and hf model ages less than 3 0 ga reflecting that they were derived from partial melting of a juvenile lower crust at high pressure however the k feldspar granites with low sr and ba concentrations and high hree and y contents are considered to have originated from partial melting of juvenile crustal materials at shallow crustal levels the diorites and granodiorites have variable major and trace element concentrations magmatic zircons from these rocks have heterogeneous hf t values but record uniform homogeneous u pb ages indicating they resulted from mixing of mafic and felsic magmas coupled with fractional crystallization because of the widespread distribution of late archean magmatism and evidence for magma mixing possibly related to mafic magma underplating it appears likely that this event in the eastern north china craton may relfect mantle plume activity that resulted in significant growth of continental crust during the late archean

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

geochemistry of miocene trachytes in bugasi lhasa block tibetan plateau mixing products between mantle and crust derived melts abstract it is generally believed that cenozoic potassic and ultrapotassic volcanic rocks of the tibetan plateau were generated by partial melting of an enriched mantle region or lower crustal materials the miocene bugasi volcanic rocks bvr in the western part of the lhasa block are composed mainly of trachyandesites and trachytes both of which belong to the shoshonite series the trachytes show somewhat transitional compositions between the mantle derived trachyandesites of the bvr and the crust derived potassic rocks of konglongxiang most evident in their sr ba and ni concentrations nb ta rb sr th nb zr nb and ba rb trace element ratios and sr and nd isotopic compositions these features coupled with the relatively high cr and ni concentrations and mg suggest that the trachytes are the product of mixing between mantle derived and lower crust derived melts

multiple sources for archean granitoids in the yalgoo area yilgarn craton western australia geochemical and isotopic evidence abstract in the yalgoo area of the north central yilgarn craton three small granitoid bodies named the lady lydia llg yalgoo east yeg and yalgoo north granitoids yng intruded 2 8 ga mafic supracrustal rocks they form two suites i granodiorites from both the llg and yeg with strongly fractionated ree patterns high lree contents low hree contents weakly positive eu anomalies and of archean ttg affinity and ii biotite monzogranites from the yng with very high lree contents and prominent negative eu anomalies all the granitoids are calc alkaline with the granodiorites recording ages of 2763 2752 ma and the biotite monzogranites recording ages of 2636 2634 ma the ree and hfse characteristics of the granodiorites favor an archean subduction environment abundant xenocrystic zircons 3 00 2 94 ga in the granodiorites and their lu hf isotopic characteristics imply a long history of crustal recycling in the north central yilgarn the lu hf isotopes indicate that the 2 76 ga granodiorites and xenocrysts were formed from a composite source ranging in age from 3 5 to 3 0 ga increased crustal thickening due to convergence after cessation of subduction caused melting in the upper mid crustal levels with generation of parental melt at 2 64 ga to source the biotite monzogranites the latter are characterized by strongly ve ehf t 10 to 12 and largely eoarchean tdm2 hf model ages 3 85 3 6 ga significantly they provide evidence of eoarchean crustal material in this part of the yilgarn craton

a synoptic view of the distribution and connectivity of the mid crustal low velocity zone beneath tibet 1 based on 1 2 years of continuous observations of seismic ambient noise data obtained at more than 600 stations in and around tibet rayleigh wave phase velocity maps are constructed from 10 s to 60 s period a 3 d vsv model of the crust and uppermost mantle is derived from these maps the 3 d model exhibits significant apparently inter connected low shear velocity features across most of the tibetan middle crust at depths between 20 and 40 km these low velocity zones lvzs do not conform to surface faults and significantly are most prominent near the periphery of tibet the observations support the internal deformation model in which strain is dispersed in the deeper crust into broad ductile shear zones rather than being localized horizontally near the edges of rigid blocks the prominent lvzs are coincident with strong mid crustal radial anisotropy in western and central tibet and probably result at least partially from anisotropic minerals aligned by deformation which mitigates the need to invoke partial melt to explain the observations irrespective of their cause in partial melt or mineral alignment mid crustal lvzs reflect deformation and their amplification near the periphery of tibet provides new information about the mode of deformation across tibet