evidence of isotopic equilibration between microgranitoid enclaves and host granodiorite warburton granodiorite lachlan fold belt australia abstract microgranitoid enclaves in the s type warburton granodiorite lachlan fold belt australia display a range in mineralogical and isotopic compositions many show obvious similarities to the host granodiorite they contain biotite as the sole ferromagnesian phase and have isotopic signatures similar to the host other enclaves contain cummingtonite actinolite and rare orthopyroxene mainly in the core of the enclaves these enclaves typically have higher nd i and lower sol 87 sr 86 sr i than the host rocks reversely zoned plagioclase megacrysts in some enclaves contain anhedral cores which are similar in composition to an poor plagioclase crystals in the host rock an45 these megacrysts are jacketed by an rich plagioclase an70 an80 the enclaves are interpreted to be globules of a more mafic magma which mingled with the host while it was still partially liquid megacrysts within the enclaves are thought to have been derived from the granodioritic magma the mafic enclave magma is likely to have been derived from a mantle source but equilibration between enclaves and host rock has changed the mineralogy and isotope geochemistry of all enclaves the equilibration process was incomplete for some enclaves resulting in mineralogical zoning and distinctions in isotopic signature between these enclaves and the host rock this equilibration process is likely to have been arrested as a result of rapid cooling of the pluton due to its small size and shallow emplacement level it is uncertain whether the compositions of the least equilibrated enclaves are truly representative of the original mafic enclave magma or whether their trace element signature has been affected by diffusional processes within a stratified magma chamber

an isotopic mixing model for the origin of granitic rocks in southeastern australia a simple mixing process was a significant element in the genesis of many southeastern australian granitic rocks major and trace element abundances are near linearly correlated nd and sr initial isotopic compositions define a simple hyperbolic trend and many initial 87sr 86sr ratios are a regular function of rb sr ratios geological arguments and regression of geochemical variation diagrams place limits on the nature of the end members the high si end member is meta sedimentary derived magma comparable in composition to the cooma granodiorite the one pluton in the region surrounded by and clearly derived from regional metamorphic rocks the low si end member is basaltic material with similarities to rare gabbros also found in the area isotope dilution calculations based upon initial sr and nd isotopic compositions deduced for the end members yield realistic hypothetical sr and nd concentrations for the end members in a demonstration of the internal consistency of the model all of the granitic rocks from hornblende tonalites to cordierite granodiorites are a single broad family products of variable mixing between distinct batches of basaltic material and a uniform partial melt of the regional basement

petrology geochemistry and zircon u pb lu hf isotopes of paleoproterozoic granite gneiss from bomdila in the western arunachal himalaya ne india

three s type volcanic suites from the lachlan fold belt southeast australia the concept that granitoids of the lachlan fold belt in southeast australia are derived from either igneous or sedimentary source rocks i or s type can be extended to volcanic rocks of the same age three suites of late silurian s type volcanics are described two of which can be matched quite closely with plutonic equivalents a large part of the paleozoic continental margin volcanic activity in southeast australia consisted of the magmatic recycling of old metasedimentary crust probably of late proterozoic age the three volcanic suites are moderately to strongly peraluminous with the corresponding presence of al rich minerals variation within the volcanic suites is ascribed chiefly to progressive removal of restite or source material residual from partial melting the most mafic suite the hawkins suite contains plagioclase cordierite orthopyroxene biotite and quartz as restite components with less abundant almandine these rocks are chemically equivalent to mafic biotite rich and cordierite bearing granitoids from parts of the berridale and murrumbidgee batholiths garnet is absent from the goobarragandra suite volcanics which are a little more felsic and close in compositon to granitoids of the young and maragle batholiths the s type character of the laidlaw suite is less pronounced although a sedimentary source seems to be established such a source would be less mature than those for the other two volcanic suites the laidlaw suite resembles but cannot be closely identified with felsic s type granitoids of the murrumbidgee and berridale batholiths low grade regional metamorphism in most of the volcanic rocks has resulted in much mineralogical alteration and mobility of alkali and alkaline earth elements despite this alteration unaltered rocks are present in all three suites compositional data for the phenocryst phases within the unaltered rocks has allowed estimation of some intensive parameters hawkins suite volcanics were extruded directly from their source region and preserve phenocryst equilibria established at 5 6 kbar at 800 c the laidlaw and goobarragandra suites reequilibrated at lower pressures than their source before extrusion the laidlaw suite reequilibrated at estimated temperatures of 725 730 c o2 of 10 15 5 to 10 14 bars and h2o of 2 to 2 5 kbar differing mineral compositions in the three suites are related to differing source rock compositons and oxygen fugacities relative biotite and orthopyroxene mg is possibly pressure dependent

petrogenesis of permian triassic felsic igneous rocks along the truong son zone in northern laos and their paleotethyan assembly abstract felsic igneous rocks in northern laos are key elements of the truong son and song ma tectonic zones and are important for constraining the paleotethyan evolution in southeastern asia this paper presents new geochronological geochemical and sr nd hf o isotopic data from granitoids and rhyolites in northern laos geochronological data show that these samples have zircon u pb ages ranging from ca 281 ma to 221 ma these samples can be subdivided into four groups based on their lithology and geochemical composition group 1 samples are granodiorite and granite with i type geochemical characteristics they have lower 87sr 86sr i ratios 0 7036 0 7059 and higher end t values 0 7 0 8 than group 2 biotite granite samples 87sr 86sr i 0 7087 0 7129 and end t 5 3 to 9 2 and group 3 rhyolite samples 87sr 86sr i 0 7092 0 7103 and end t 5 9 to 8 9 zircon grains from group 1 samples yield positive ehf t values of 5 1 13 8 tdm ages of 0 37 0 71 ga and 18o values of 5 6 6 3 in contrast zircons from group 2 and group 3 samples have mainly negative ehf t values 9 6 to 1 6 and 4 7 to 14 7 older tdm ages 1 08 1 70 ga and 1 42 1 97 ga and higher 18o values 5 7 10 3 and 6 7 8 0 respectively our geochemical data suggest that the group 1 granite samples are the products of the partial melting of newly underplated mafic rocks whereas the group 2 and 3 samples originated from a mixed source of ancient metaigneous and metagreywacke components group 4 samples include late triassic i type granodiorite and granite and have end t 1 9 to 3 9 87sr 86sr i 0 7079 0 7084 zircon ehf t 0 0 7 5 and 18o 5 1 6 9 indicating a derivation from a metagreywacke source with a component of juvenile mafic crust our data suggest that the permian felsic igneous rocks in northern laos formed in an arc setting related to the song ma paleotethyan branch bab subduction whereas the late triassic i type granitoids formed in a post collisional setting in response to the gravitational collapse of thickened crust during the collision of the south china and indochina blocks the temporal spatial pattern of igneous rocks along the truong son zone is related to the paleotethyan evolution and resembles that along the ailaoshan song ma zone and its eastward extension in northern hainan

the identification and significance of pure sediment derived granites the characterization of the geochemical reservoirs of the earth s continental crust including the determination of representative upper and lower crustal compositions underpins our understanding of crustal evolution the classic i and s type granite classification has often been invoked to distinguish between melts derived from igneous protoliths and those derived from the melting of a sedimentary source recent geochemical studies suggest that most granites even those cited as typical examples of s type show evidence for a mixture of mantle and upper crustal sources thereby implying that granite formation is evidence for overall crustal growth we have examined the source of leucogranite bodies in one of the world s youngest collisional orogens using novel zircon techniques that can resolve the presence of even minor mantle contributions 232 zircons from 12 granites from the bhutan himalaya were analysed by in situ techniques for o hf and u pb isotopic signatures in combination with data from the granite host rocks our data show that the himalayan leucogranites were derived solely from metamorphosed crustal sediments and do not record any mantle contribution this finding is consistent with the time lag between crustal thickening and widespread crustal melting and the heat producing capacities of the pelitic source rocks we conclude that himalayan leucogranites provide a more suitable type locality for s type granites than the lachlan area in south east australia where the term was first defined the himalayan leucogranites therefore provide evidence that syn orogenic melting during collisional events does not necessarily result in crustal growth importantly crustal growth models should not always assume that crustal growth is achieved during collisional orogenesis

geodynamic significance of s type granites in circum pacific orogens in phanerozoic circum pacific orogenic belts most post collisional s type granites and associated high temperature low pressure metamorphic complexes formed during early arc extension the granites are part of a tripartite association consisting of 1 inboard s type granite 2 outboard oceanic arc and 3 intervening turbidite filled backarc basin s type granites herald the formation of new outboard oceanic arc and extensional backarc systems but thickening of a preexisting sediment dominated back arc basin is a prerequisite for their generation in these environments s type plutonism is triggered by renewal of arc magmatism following thickening when hot basaltic magmas are intruded into the thickened backarc crust once slab retreat is reestablished with ongoing extension during retreat the crust becomes progressively thinned the sedimentary contribution is diminished and the granites lose their s type character such tripartite associations involving s type granite are probably diagnostic of repeated slab retreat episodes and the jurassic u s cordillera might be an example

high temperature s type granitoids charnockites in the jining complex north china craton restite entrainment and hybridization with mafic magma abstract the liangcheng garnet granitoids are parautochthonous s type granites that occur within granulite facies metasediments in the ultrahigh temperature uht jining complex eastern part of the khondalite belt north china craton these garnet granitoids contain mafic microgranular enclaves and are intimately associated with numerous small intrusions of the xuwujia gabbronorites showing magma mingling and mixing textures typical mineralogy in the garnet granitoids is plagioclase k feldspar quartz garnet biotite orthopyroxene u pb ion microprobe dating of zircon suggests that garnet granitoids and associated gabbronorites were coeval with uht metamorphism at 1 93 1 92 ga and also recorded 1 92 ga metamorphism during slow cooling garnet granitoids are characterized by the presence of orthopyroxene high modal proportion of garnet up to 25 and strongly peraluminous asi 1 11 1 55 along with lower sio2 57 8 70 1 wt and higher feot mgo 5 6 14 4 wt contents than typical s type granites mineral chemistry high ti biotite and high al orthopyroxene high al in orthopyroxene temperature 910 989 c and zr saturation temperature 825 901 c and low whole rock al2o3 tio2 ratios 11 28 indicate that garnet granitoids were derived from biotite dehydration melting of metasedimentary rocks under uht granulite facies conditions textural and compositional evidence suggests that a significant proportion of garnets in the liangcheng garnet granitoids are potentially a peritectic phase entrained from the source garnet aggregates may also represent entrained garnet rich restites the large hree variations of garnet granitoids also support the entrainment of garnet rich restites garnet granitoids display nearly linear trends with the mafic enclaves and gabbronorite for most major elements that demonstrates the involvement of mafic magma in the granitoid petrogenesis the ehf t values 1 0 5 6 and 18o values 9 2 11 6 of zircons in garnet granitoids partly overlap with those in gabbronorites ehf t 2 9 3 5 18o 7 7 10 9 suggesting the strong interaction and mixing process between them major element modelling suggests that the addition of 20 40 restites garnetites and gabbronorites to the anatectic melts was responsible for the large chemical variations therefore the liangcheng garnet granitoids represent high temperature 900 c h2o undersaturated strongly peraluminous granitoids and are produced by large scale melting of metasedimentary rocks and subsequent mixing between restite rich anatectic melt and mafic magma the voluminous high temperature granitoids coupled with uht granulites in the jining complex manifest the thermal response of a granulitic lower crust to the mafic underplating

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

generation of peraluminous granitic magma in a post collisional setting a case study from the eastern qilian orogen ne tibetan plateau abstract early paleozoic peraluminous granites are abundant in the eastern part of the qilian orogen northeastern margin of the tibetan plateau a combined study involving geochronology whole rock geochemical and sr nd hf isotopic compositions for three early paleozoic peraluminous granitic plutons jishishan ledu and shichuan plutons from the eastern qilian orogen was carried out to evaluate the causes of chemical variations and generation mechanisms of peraluminous granitic magmas these granitic plutons have magma crystallization ages of 455 427 ma and are moderately to strongly peraluminous a cnk 1 03 1 18 geochemical and sr nd hf isotopic data indicate that they consist substantially of crust derived melts the jishishan and ledu peraluminous granites were dominantly produced by partial melting of precambrian orthogneisses the shichuan monzogranites with low hree contents e g yb 0 80 1 83 ppm and slightly negative end t 5 3 to 2 3 and positive ehf t 1 6 to 3 4 could be derived from immature crustal materials relatively high average zircon saturation temperatures 750 c for each pluton obvious negative eu anomalies eu eu 0 28 0 80 and low pb ba ratios 0 03 0 16 for the jishishan ledu and shichuan granites are consistent with crustal melting involving biotite breakdown under fluid absent conditions our results suggest that compositional variations of moderately to strongly peraluminous granitic magmas are mainly controlled by source compositions and melting conditions while the processes such as mixing with mantle derived magma fractional crystallization restite unmixing and peritectic assemblage entrainment were insignificant or only play secondary roles in their genesis late ordovician to middle silurian crustal anatexis in the eastern central qilian was probably linked with slab break off which may be an important mechanism in addition to lithospheric delamination for the generation of moderately to strongly peraluminous granites in a post collisional setting

geochronology geochemistry and petrogenesis of late permian to early triassic mafic rocks from darongshan south china implications for ultrahigh temperature metamorphism and s type granite generation abstract the role of the mantle in generating ultrahigh temperature metamorphism and peraluminous s type granites and the extent of crust mantle interaction are topics fundamental to our understanding of the earth s evolution in this study we present geochronological geochemical and sr nd hf isotopic data for dolerites and mafic volcanic rocks from the darongshan granite complex belt in western cathaysia south china la icp ms u pb zircon analyses yielded magma crystallization ages of ca 250 248 ma for the dolerites which are coeval with eruption of the mafic volcanic rocks ultrahigh temperature metamorphism and emplacement of s type granites in the darongshan granite complex belt the mafic volcanic rocks are high k calc alkaline or shoshonitic enriched in th u and light rare earth elements and depleted in nb ta and ti the dolerites are characterized by high fe2o3tot 11 61 20 39 wt and tio2 1 62 3 17 wt and low mgo 1 73 4 38 wt cr 2 8 10 8 ppm and ni 2 5 11 4 ppm isotopically the mafic volcanic rocks have negative whole rock end t values 6 7 to 9 0 and high isr values 0 71232 to 0 71767 which are slightly depleted compared with the dolerite samples end t 10 3 to 10 4 and isr 0 71796 to 0 71923 zircons in the dolerites have ehf t values of 7 6 to 10 9 the mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent whereas the dolerites formed by late stage crystallization of enriched lithospheric mantle derived magmas after fractionation of olivine and pyroxene the formation of these mantle derived mafic rocks may be attributed to transtension along a ne trending strike slip fault zone that was related to oblique subduction of the paleo pacific plate beneath south china such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh temperature metamorphism and s type granites and act as a mafic end member for s type granite genesis

southward extension of the bangonghu nujiang suture evidence from early cretaceous intermediate and felsic magmatism in the gaoligong orogen china abstract it remains debated as to whether the gaoligong orogen between the tengchong and baoshan blocks in yunnan china is the southward extension of the tibetan bangonghu nujiang suture bns here we present new geochronological and petrochemical data for early cretaceous magmatic rocks of the gaoligong orogen the la icp ms u pb dating of zircons from diorites granodiorites and granites yielded weighted mean 206pb 238u ages of 120 118 128 122 and 109 128 ma respectively for the diorites the ehf t values of zircons fall in a range of 1 2 to 5 4 with tdmc ages of 744 979 ma for the granodiorites they fall in a range of 9 8 to 2 9 with tdmc ages of 888 1564 ma and for the granites the range is 8 0 to 1 1 with tdmc ages of 1101 1488 ma they are magnsian calc alkaline enriched in liles and lrees and have strong negative nb ta p and ti anomalies and high values of mg all these features are indicative of continental arc affinities the data suggest that the dioritic and granitic magmas were produced by the mixing of variable proportions of mantle and crust derived magmas at an active continental margin the ages and tectonic settings of the diorites granodiorites and granites are similar to rocks found within the bns considering the ophiolitic melange belt the middle jurassic basaltic magmatism and the marine facies stratigraphic features of the gaoligong orogen are very similar to features in the bns we conclude that the gaoligong orogen represents the suture between the tengchong and baoshan blocks and is the southward extension of the bns

igneous and metamorphic enclaves in the s type deddick granodiorite lachlan fold belt se australia petrographic geochemical and nd sr isotopic evidence for crustal melting and magma mixing the deddick granodiorite a mafic s type pluton in the lachlan introduction fold belt contains abundant enclaves most are derived from enclaves in granites and volcanic rocks can provide high grade metasediments of pelitic psammitic composition and petrogenetic information not readily available from their migmatites are common among these discrete fragments of host rocks didier 1973 didier barbarin 1991 for melanosomes rich in cordierite and garnet are restites from partial example metasedimentary enclaves can place constraints melting however compositional and nd sr isotopic data indicate on the age composition and deformational history of they are not restite in equilibrium with the melt component of the magma source regions within continental crust fleming host magma but may have formed part of a spectrum of diverse 1991 steele et al 1991 enclaves formed by acmagma source lithologies alternatively they may be accidental cumulation of early phenocrysts autoliths document xenoliths regardless of their origin data for these enclaves suggest the early evolution of the host magma whereas others their precursors could represent deeply buried age equivalents of the may represent commingled magmas and illustrate the ubiquitous ordovician turbidites of the lachlan fold belt three possible role of hybridization didier 1987 types of microgranular enclaves with igneous textures are disenclave suites in the relatively mafic s type granitoids tinguished the most common type are small and rounded mafic of se australia are often diverse including abundant enclaves of tonalitic composition they carry xenocrysts derived from enclaves of metasedimentary origin and microgranular the host magma and some contain high mg pyroxene derived from enclaves phillips et al 1981 price 1983 chen et al a mafic magma isotopic data form an array with end from 6 to 1989 wyborn et al 1991 the metasedimentary en 12 and sr sr from 0 7130 to 0 7167 host rock 10 and claves are lithologically diverse including gneissic 0 715 respectively these enclaves formed as globules of hybrid migmatitic types and biotite rich surmicaceous types mafic magma commingled with and contaminated by the more apart from their potential as indicators of crustal structure felsic host magma other enclave types were derived from disrupted and composition they are of interest as possible fragments syn plutonic dykes having a distinct isotopic composition and from of source material and or refractory residue from which a cogenetic marginal facies of the host peraluminous melts were generated and extracted by

petrogenesis of the early paleozoic strongly peraluminous granites in the western south china block and its tectonic implications abstract strongly peraluminous sp granites have a cnk molecular al 2 o 3 cao na 2 o k 2 o ratios 1 1 indicating a predominant origin from the partial melting of metasedimentary rocks however an increasing number of studies have documented that mantle derived magmas can also be involved in the petrogenesis of some sp granites this is the case in the dulong batholith in the southeastern yunnan province southwestern south china block which is typically composed of sp granitic rocks with high a cnk values 1 1 zircon u pb dating of four samples from this batholith yielded consistent crystallization ages of ca 430 ma synchronous with the widespread late orogenic magmatism including s and i type granites and mafic igneous rocks in the wuyi yunkai orogen south china block scb all the granites have fractionated ree patterns la yb n 1 28 12 3 and conspicuous negative eu anomalies eu eu 0 07 0 43 with a similar depletion in hfse nb zr hf p ba and sr suggesting that these granitic magmas had a dominantly crustal source likely the neoproterozoic metasedimentary rocks i e the danzhou or banxi groups that are dominated by pelitic rocks with minor interlayered siltstones in the western yangtze block however their zircon hf isotopic results also reveal an important input of the mantle derived melts into their parental magma taken together their geochemical and isotopic compositions reflect a derivation by magma mixing between the crust and mantle derived 10 in volume magmas their chemical variations resulted from the fractionation process during the emplacement from the magma chamber after magmatic mixing in conjunction with regional data within the scb it is most likely that the magmatism younger than 435 ma was generated in a post collisional extensional regime related to the partial delamination of an overthickened lithospheric mantle root without lower crust

s type granite from the gongpoquan arc in the beishan orogenic collage southern altaids implications for the tectonic transition abstract voluminous paleozoic intrusions occur in the beishan orogenic collage boc and their genesis and tectonic background are important to reconstruct the accretion collision processes in the southernmost altaids paleozoic is an important period for arc development in the boc where the gongpoquan and huaniushan arcs are located there are two pulses of magmatism in the huaniushan and gongpoquan arcs i e the ca 470 423 ma i type and ca 424 395 ma s and a type granitoids in this study we focus on two peraluminous granitic plutons in the gongpoquan arc i e the baitoushan muscovite granite and haergen two mica granite aiming at unraveling their petrogenesis and tectonic background zircon la icp ms u pb dating yields emplacement ages of ca 409 395 ma and ca 409 ma for the baitoushan and haergen plutons respectively both the granitic plutons are strongly peraluminous with a cnk ratios of 1 10 1 20 indicative of s type affinities the rocks are characterized by high sio 2 and k 2 o contents with high cao na 2 o ratios moreover the rocks possess low mgo contents rb sr and rb ba ratios together with their relatively high initial 87 sr 86 sr ratios 0 7139 0 7152 and less radiogenic end t values 3 15 to 5 17 implying a clay poor and plagioclase rich crustal source compared with earlier pulse of arc related magmatism ca 470 423 ma the latter pulse of magmatism ca 424 395 ma consists mainly of normal granite characterized by higher sio 2 66 and k 2 o contents weaker fractionated ree patterns and lower eu values and gabbroic to dioritic intrusions are only sporadic moreover the granitoids of the latter pulse show variable but more crust like sr nd isotopic compositions 87 sr 86 sr 0 0 7038 0 7327 end t 6 70 to 0 33 than the earlier ones 87 sr 86 sr 0 0 7024 0 7080 end t 2 56 to 8 86 indicating that the early devonian ca 424 395 ma experienced extensive crustal melting with minor involvement of mantle materials considering early devonian geological evidence the transition from i to s and a type magmatism probably reflects the early devonian amalgamation between the gongpoquan and huaniushan arcs which caused not only regional unconformity and strong deformation metamorphism but also extensive melting of the accreted crustal materials in the boc

petrogenesis of middle ordovician peraluminous granites in the baoshan block implications for the early paleozoic tectonic evolution along east gondwana abstract peraluminous granitic magmatism in the baoshan block is long lasting roughly from 500 ma to 450 ma the petrogenesis and geodynamics for this long lived magmatism remain controversial to address this controversy this study reports the zircon u pb age and hf isotope and bulk rock major and trace element data of the granites from the shuangmaidi and mengmao areas in the baoshan block la icpms zircon u pb dating reveals that the granitic rocks from the two areas were emplaced between 470 and 459 ma these rocks are high silicic and strongly peraluminous with sio 2 73 6 77 6 wt a cnk ratios of 1 0 1 6 and cipw normative corundum contents of 0 7 5 3 wt they are enriched in lrees liles e g rb th u and k and pb and depleted in hfses e g nb ta p zr and ti eu sr and ba the e hf t values for co magmatic zircons of the shuangmaidi coarse and fine grained porphyritic granites show wide ranges from 11 6 to 5 2 and from 8 1 to 7 0 concentrating in 7 1 to 0 5 and 8 1 to 0 7 respectively and those of the mengmao granites concentrate between 4 6 and 0 5 the primary magmas of these granites can be mainly attributed to the partial melting of ancient metasedimentary rocks while small amounts of mantle derived components were introduced into the magma sources for the shuangmaidi granites the primary magma of the shuangmaidi granites experienced biotite dominant mineral fractionation and that of the mengmao granite mainly fractionated k feldspar and plagioclase combining our data with the regional sedimentary unconformity multi type magmatism and high pressure metamorphism in the baoshan and its periphery blocks we propose that these ca 470 460 ma peraluminous granites were formed in the tectonic setting of the thickened lithospheric delamination following the final amalgamation of outboard asian microcontinents onto the east gondwana margin at ca 490 475 ma our study favors that the long lasted ca 500 450 ma peraluminous granitic rocks in the baoshan block constitute of the early paleozoic magmatic belt along the east gondwana marginal blocks like himalaya lhasa and qiangtang this magmatism was produced in successive stages including proto tethyan slab rollback period to ca 500 ma slab break off at ca 500 490 ma lithospheric thickening at ca 490 475 ma and lithospheric delamination at ca 475 460 ma and then it vanished at ca 450 ma signifying the end of proto tethyan accretionary orogenesis

a hybrid origin for lachlan s type granites the murrumbidgee batholith example the murrumbidgee batholith is typical of other composite s type granite batholiths in the lachlan fold belt lfb of southeastern australia consisting of discrete peraluminous cogenetic granite suites however it contains a unique suite murrumbucka at its southern extremity that has chemical and petrological features transitional with metaluminous i type granites previous detailed structural and metamorphic studies have shown that the batholith is tilted northward exposing subvolcanic plutons in the north and root zones in the south originally located at depths of not vert similar10 km a transition from mafic foliated sheet like granites in the south to felsic generally less foliated homogeneous granites in the north is consistent with magma ascent via subvertical structurally controlled sheets to emplacement in an overlying magma chamber in the inferred root zones the murrumbucka suite hosts migmatitic metasedimentary and gabbroic rocks both of which have transitional contacts and show evidence for mafic felsic interaction with the murrumbucka suite the migmatites extend southward to become part of the high t low p cooma metamorphic complex which contains a core of heterogeneous remobilised diatexitic granite cooma suite lenses of which also occur throughout the southern deeper parts of the murrumbidgee batholith the composition of the most mafic rocks from the batholith lies on a chemical tie line between cooma suite granites and the gabbros for almost all elements this chemical coincidence is interpreted to reflect derivation of parental murrumbidgee s type granite magmas by bulk mixing between a felsic crustal and mafic mantle derived component consistent with sr and nd isotopic results and field observations based on the tie lines and simple numerical modelling the murrumbucka suite is estimated to be a 50 50 mix of mantle and crustal derived magmas whereas the more peraluminous and widespread clear range suite which is very typical of lachlan s type granites is modelled as a 40 60 mix chemical variation trends diverge from the mixing lines and suggest that much of the fractionation process operated after mixing mixing occurred within sheets during the ascent of the magmas whereas fractionation was the dominant process generating chemical diversity during emplacement in the magma chamber generation of the s type granites probably occurred in an extensional tectonic environment

slab pull mantle convection and pangaean assembly and dispersal two global scale mantle convection cells presently exist on earth centred on upwelling zones in the south pacific ocean and northeast africa one cell panthalassan contains only oceanic plates the other pangaean contains all the continental plates they have remained fixed relative to one another for 400 ma a transverse rheic tethyian subduction system splits the pangaean cell poloidal plate motion in the oceanic cell reflects circumferential pull of panthalassan slabs but toroidal flow in the pangaean cell reflected by vortex type motion of continents toward the altaids of central east asia throughout the phanerozoic has resulted from the competing slab pull forces of both cells the combined slab pull effects from both cells also controlled pangaean assembly and dispersal assembly occurred during palaeozoic clockwise toroidal motion in the pangaean cell when gondwana was pulled into pangaea by the ne trending rheic subduction zone forming the appalachian variscide altaid chain pangaean dispersal occurred when the rheic trench re aligned in the jurassic to form the nw trending tethyside subduction system which pulled east gondwanan fragments in the opposite direction to form the cimmerian himalayan alpine chain this re alignment also generated a new set of indian mid ocean ridge systems which dissected east gondwana and facilitated breakup 100 200 myr long phanerozoic wilson cycles reflect rifting and northerly migration of gondwanan fragments across the pangaean cell into the rheic tethyian trench pangaean dispersal was amplified by retreat of the panthalassan slab away from europe and africa which generated mantle counterflow currents capable of pulling the americas westward to create the atlantic ocean thermal blanketing beneath pangaea and related hotspot activity were part of a complex feedback mechanism that established the breakup pattern but slab retreat is considered to have been the main driving force the size and longevity of the two cells organised and maintained by long lived slab pull forces favours deep mantle convection as the dominant circulation process during the phanerozoic

sedimentary fractionations between al ti and zr and the genesis of strongly peraluminous granites sedimentary sorting produces alternating shales and sandstones with complementary chemistries the preferential partitioning of quartz and zircon in the coarse grained fraction of the sediments results in a strong fractionation between sio 2 zr and other components al 2 o 3 tio 2 as a consequence shales may be defined chemically as having higher al 2 o 3 sio 2 and tio 2 zr ratios than their source rocks sandstones have the opposite characteristics and vary in composition according to the maturity of their source and the intensity of sorting processes most sedimentary suites display a good correlation between al 2 o 3 sio 2 and tio 2 zr this result is used to evaluate an average bulk composition for recent clastic materials and to model their composition on a ternary al ti zr diagram because the al 2 o 3 tio 2 ratio of igneous rocks is highly sensitive to magmatic differentiation igneous and sedimentary trends crosscut in the al ti zr di

hybridization of a shallow i type granitoid pluton and its host migmatite by magma chamber wall collapse the tokuwa pluton central japan the miocene tokuwa pluton of i type granitoid affinity was emplaced discordantly into a cretaceous to paleogene accretionary complex and induced a contact aureole in which various thermally metamorphosed rocks were developed including hornfels metatexite diatexite and cordierite bearing tonalite crd tonalite of s type granite affinity the thermally metamorphosed rocks show low pressure reaction textures culminating in partial melting peak p t conditions of 3 kbar at 7808c are estimated on the basis of the twq thermobarometer for the garnet bearing rocks the rocks in the contact aureole exhibit a gradual transition from hornfels through metatexite and diatexite to crd tonalite the sr isotopic composition at the time of tokuwa pluton emplacement at 12 ma decreases systematically from metatexite 0 7100 0 7112 through diatexite 0 7078 0 7094 to crd tonalite 0 7067 0 7068 this trend is interpreted in terms of mixing between the tokuwa magma and the aureole migmatites the field relationships geochemical data and isotopic data collectively suggest that the emplacement of the tokuwa pluton triggered partial melting of the surrounding metasedimentary rocks subsequent hybridization of the tokuwa magma with the metatexite in variable proportions produced the crd tonalite and diatexite the hybridization was caused by invasion of the tokuwa magma into the migmatite zone accompanied by gravitational collapse of the previously crystallized wall of the magma chamber the data presented demonstrate that even a relatively low temperature shallow i type granitoid pluton can induce contact anatexis and hybrid s type granitoid formation at the intrusive contact

data for the role and significance of juvenile sediments in the formation of a type granites west junggar oceanic arc nw china zircon hf o isotopic perspectives

the occurrence and timing of high pressure metamorphism on margarita island venezuela a constraint on caribbean south america interaction the metamorphic rock sequences exposed on the island of margarita venezuela located in the southeastern corner of the caribbean plate margin are composed of a high pressure lowtemperature hp lt nucleus subducted to at least 50 km depth now structurally overlain by lower grade greenschist facies units lacking any sign of high pressure subduction zone metamorphism the hp lt nucleus involves protoliths of both oceanic metabasalts and intimately associated carbonaceous schists of the la rinconada unit peridotite massifs and continental affinity metapelites marbles and gneisses of the juan griego unit all hp lt units were joined together prior to the peak of high pressure metamorphism as shown by their matching metamorphic pressure temperature evolution the metamorphic grade attained produced barroisite as the regional amphibole glaucophane is not known from margarita contrary to a widely propagated assumption there are no major nappe structures post dating

stepping stones and pitfalls in the determination of an anticlockwise p t t deformation path the low p high t cooma complex australia low pressure high temperature low p high t metamorphic rocks of the cooma complex southeastern australia show evidence of an anticlockwise pressure temperature time deformation p t t d path similar to those of some other low p high t metamorphic areas of australia prograde paths are reasonably well constrained in cordierite andalusite schists cordierite k feldspar gneisses and andalusite k feldspar gneisses these paths are inferred to be convex to the temperature axis involving increase in pressure with increase in temperature evidence of the retrograde path is inconclusive but is consistent with approximately isobaric cooling as are available isotopic data on the cooma granodiorite which indicate initially rapid cooling following attainment of peak temperatures the retrograde path is inconsistent with either a clockwise p t t d path involving rapid or even moderate decompression immediately post dating the peak of metamorphism or a path in which the retrograde component simply reverses the prograde component because both these paths should cross reactions forming cordierite from aluminosilicate for which no evidence has been observed determination of the deformational metamorphic history of the complex is not straightfoward and depends on careful examination of critical samples evidence necessary for successful elucidation of the prograde and part of the retrograde deformational metamorphic history in the cooma complex includes 1 sequentially grown porphyroblasts that can be timed relative to surrounding foliations 2 partial replacement microstructures providing relative timing of metamorphic reactions that cannot be timed relative to foliation development 3 a tectonic marker foliation s4 at cooma that allows correlation of foliations from one location to another and 4 single samples containing all of the foliations and all generations of porphyroblast growth within a single metamorphic zone the latest two or three foliations involve low strain accumulation allowing relative timing relationships between foliations and porphyroblasts to be more clearly determined sequential porphyroblast growth and foliation development in the cordierite andalusite schists is examined for situations involving rotation and non rotation of porphyroblasts relative to geographically fixed coordinates although the number of foliations developed varies in the rotational situation depending on the deformation history proposed the sequential order of porphyroblast growths does not differ from the non rotational situation thus whether or not porphyroblasts rotated in the cooma rocks the sequence of reactions and therefore p t t paths inferred from the relative timing of porphyroblast growths remain the same for the deformational histories evaluated

wrenching in the external zone of the betic cordilleras southern spain abstract regional structural trends in the caravaca huescar area forming the central part of the external zone in the betic cordilleras indicate that deformation of the area results from right lateral wrenching subparallel to the paleogeographic zonation the structural trends do not fit the nappe interpretation generally used elsewhere in the external zone arguments for wrenching in the area are the structural inverse symmetry with respect to a central transcurrent fault zone the crevillente fault zone the distributional pattern of stratigraphic anomalies and types of deformation and the outcrop pattern of the paleogeographic zones it is argued that certain tectonic units in the area formerly interpreted as klippes in a nappe configuration form centers of flower structures and are vertically squeezed out blocks a theoretical model is sketched illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics many of the features of the caravaca huescar area are also present elsewhere in the external zone and support the idea that wrenching was a major deformational mechanism it is therefore suggested that the external zone should in general not be described in terms of a nappe structure as has been done so far but in terms of a strike slip orogen or a wrenched continental margin

petrogenesis of late paleoproterozoic liangcheng charnockites and s type granites in the central northern margin of the north china craton implications for ridge subduction abstract the 1930 1890 ma garnet bearing peraluminous liangcheng granitoids are mainly distributed in the fengzhen belt in the north china craton ncc they consist of early porphyritic coarse grained charnockites magmatic orthopyroxene granitic rocks and late medium to coarse grained s type crustal melt granites the charnockites are distinguished from the s type granites by their higher tio 2 al 2 o 3 feo t mgo cao and trace element contents especially the heavy rare earth elements ree the charnockites show varied light ree enrichments la yb n 1 92 18 0 negative eu anomalies eu eu 0 2 0 9 and negative anomalies in high field strength elements hfses e g nb ta ti and in sr compared with the neighbouring elements in spidergrams their 87 sr 86 sr t t 1900 ma ratios vary from 0 704 to 0 707 with one at 0 74 and nd t t 1900 ma values range from 4 to 1 in contrast the liangcheng s type granites show strong light ree enrichments la yb n 13 3 230 positive eu anomalies eu eu 1 1 3 6 negative anomalies in hfses e g nb ta ti and negative or positive anomalies in sr compared with neighbouring elements in spidergrams their 87 sr 86 sr t t 1900 ma ratios vary from 0 703 to 0 712 and nd t t 1900 ma values range from 3 to 1 both the charnockites and s type granites originated by melting of in situ meta sediments with significant charnockites or little s type granites amounts of additional melts from the parental magma of the adjacent xuwujia gabbronorites high mg 19 23 wt samples of the xuwujia gabbronorites have whole rock re contents of 0 16 1 93 ppb os contents of 1 6 9 8 ppb 187 re 188 os ratios of 0 08 1 76 and 187 os 188 os ratios of 0 1168 0 1186 with one exception at 0 1845 these values are comparable with those of typical komatiites and agree with a depleted source for these rocks the charnockites have received 10 30 wt or even larger amounts of melt contribution from the xuwujia gabbronorites whereas the s type granites received only few melts from the gabbronorites and they possibly had lower melting temperature than the charnockites we consider that the charnockites and s type granites had surface counterparts represented by two types of rhyolitic to dacitic volcanics in the halaqin succession which also contains basalts to basaltic andesites that are geochemically comparable to the xuwujia gabbronorites or the charnockites some andesites from their field relations and geochemical and thermal characteristics we propose that the peraluminous charnockites and s type granites were most likely generated by ridge subduction at 1930 ma prior to the final cratonization of the ncc at 1850 ma and that this ridge subduction was also responsible for the regional 1950 1880 ma gabbronorites charnockites s type granites volcanics as well as the 1930 ma ultrahigh temperature metamorphism in the ncc

geology geochemistry and emplacement conditions of the vega intrusive complex an example of large scale crustal anatexis in north central norway

geochronological elemental and sr nd hf o isotopic constraints on the petrogenesis of the triassic post collisional granitic rocks in nw thailand and its paleotethyan implications abstract new u pb geochronological petrologic elemental and sr nd hf o isotopic data for the granites from the inthanon and sukhothai zones in nw thailand in conjunction with correlations with sw china are presented to constrain the age and position of the paleotethys ocean in this region and the associated assembly of southeast asia the geochronological data show that the granitic rocks in the inthanon and sukhothai zones herein named group 1 and group 2 granites respectively yield similar crystallization ages of 230 200 ma group 1 samples are characterized by monzogranite and granite with i and s type geochemical affinity and group 2 samples by i type monzogranite and granodiorite they have generally similar chondrite normalized ree and pm normalized multi element patterns but distinct sr nd hf o isotopic compositions group 1 samples have slightly higher initial 87sr 86sr ratios 0 7111 0 7293 but lower end t values 11 1 to 14 1 than those of group 2 samples 87sr 86sr i 0 7073 0 7278 and end t 8 3 to 11 0 group 1 samples show the lower ehf t values 5 4 to 18 2 older tdm 1 62 2 40 ga and higher 18o values 7 95 to 9 94 than those of group 2 samples ehf t of 11 1 to 4 80 tdm of 0 96 1 95 ga and 18o of 4 95 to 7 98 for the triassic crystallization zircons these geochemical signatures are similar to the kwangsian and indosinian granites in the south china and indochina blocks but distinct from those of the gangdese i type granite and sibumasu paleozoic granite our data suggest that group 1 samples mainly originated from the early paleozoic supracrustal rocks containing metapelite and metavolcanic components which had previously experienced the surface weathering group 2 samples were derived from a hybridized source of an old metamorphic and a newly underplated mafic component synthesis of our data with available regional observations indicates that the inthanon zone represents the main suture zone of the eastern paleotethyan ocean in nw thailand and links with the changning menglian suture zone in sw yunnan sw china in nw thailand a switch from the eastward subduction of the paleotethyan oceanic plate to the collision of the sibumasu with indochina blocks occurred at 237 ma and syn and post collisional time being at 237 230 ma and 200 230 ma respectively the late triassic granites in the inthanon and sukhothai zones are representative of the post collisional magmatic products

f rich strongly peraluminous a type magmatism in the pre andean foreland sierras pampeanas argentina geochemical geochronological isotopic constraints and petrogenesis abstract the petrogenetic nature of a type granites is a controversial problem the vinquis batholith in the sierras pampeanas of argentina contains unusual f rich and strongly peraluminous a type monzogranites a new la mc icp ms u pb zircon crystallization age of 355 7 ma indicates emplacement in latest devonian or earliest carboniferous time overlapping with extensive metaluminous a type magmatism in the area the monzogranites have a restricted range of sio 2 content 71 5 74 8 they are poor in ca 0 54 1 4 cao and rich in feo t with relatively high feo t feo t mgo values ranging from 0 77 to 0 86 average 0 80 both feo t feo t mgo vs sio 2 and na 2 o k 2 o cao vs sio 2 plots indicate ferroan and alkali calcic signatures typical of a type granitoids the samples have mgo tio 2 1 2 and are moderately enriched in total alkalis average 8 18 with high k 2 o na 2 o values of 1 40 2 24 the granites are strongly peraluminous with asi molar al 2 o 3 cao na 2 o k 2 o values of 1 2 to 1 3 the high p 2 o 5 content 0 23 0 37 is distinctive and close to values reported for other paleozoic f rich peraluminous a type granites in the sierras pampeanas they have moderate contents of high field strength elements e g zr nb th y etc and moderately fractionated to flat ree patterns la yb n in the range 4 8 19 6 showing significant negative eu anomalies eu eu 0 41 biotite has a distinctive composition with relatively high fe 2 fe 2 mg ratios 0 61 0 74 and high f 0 55 1 42 wt content together with the whole rock chemistry this may be useful in identifying strongly peraluminous a type granites in addition the rb sr vs th zr ce diagram may be an appropriate discriminant between metaluminous and peralkaline a type granites strongly peraluminous a type granites and strongly peraluminous orogenic granites the geochemical evidence indicates that differentiation of the granitic rocks occurred by mineral fractionation from a f rich peraluminous parental magma dominant of plagioclase k feldspar biotite and accessory minerals such as zircon monazite xenotime and oxides the peraluminous composition and isotope data e hf 355 and e nd 355 ranging from 9 5 to 1 5 and 6 1 to 7 8 respectively together with abundant inherited ordovician and cambrian zircon strongly suggest a dominantly metasedimentary source the whole rock and biotite compositions indicate that the vinquis batholith crystallized under mainly oxidizing conditions whereas early carboniferous metaluminous to weakly peraluminous a type granites of the sierras pampeanas crystallized under dominantly reduced conditions

continental crust formation seen through the sr and nd isotope systematics of s type granites in the hercynian belt of western france the isotopic compositions of sr nd and pb in leucogranites which are intercorrelated bernard griffiths et al 1985 1 may be explained by the mixing of ancient basement 1800 ma with juvenile crust late precambrian or early palaeozoic this hypothesis does not involve the existence of mid proterozoic crust as apparently indicated by thetdm model ages of the leucogranites ranging between 1600 and 1100 ma the nd isotopes reveal the crustal reworking while sr isotopes mainly record juvenile crust formation this paradox is explained by the geochemical heterogeneity of the sources involved

was late triassic tanggula granitoid central tibet western china a product of melting of underthrust songpan ganzi flysch sediments geochronological laser ablation inductively coupled plasma mass spectrometry la icp ms mineral chemistry major and trace element and sr nd hf isotopic data are presented for the tanggula granitoid the largest granitic pluton in the northern tibetan plateau the tanggula pluton yields a late triassic emplacement age 228 223 ma and is magnesian mg 29 10 49 81 high k calc alkaline k2o na2o 0 76 3 51 mostly 1 and strongly peraluminous molar al2o3 cao na2o k2o a cnk 1 06 1 42 mostly 1 1 high initial 87sr 86sr ratios 0 716849 to 0 730577 and low nd t 10 95 to 9 60 and hf t values 16 to 5 1 along with an abundance of aluminosilicate minerals e g biotite enrichments in light rare earth and large ion lithophile elements negative eu anomalies and depletion in high field strength elements suggest that the tanggula granitoid is an s type granite derived mainly from the anatexis of metasedimentary source rocks geochemical fingerprinting using sr nd hf isotopes and detrital zircon u pb age spectra shows that triassic flysch sediments from the songpan ganzi paleo tethyan ocean to the north of the pluton are the most likely source of the tanggula granitic magmas the tanggula granitoid could thus have been formed by the partial melting of the flysch sediments from the songpan ganzi complex as they were underthrust beneath the qiangtang terrane along the jinsha subduction zone during the late triassic

early neoproterozoic granitic gneisses in the chinese eastern tianshan petrogenesis and tectonic implications abstract early neoproterozoic granitic gneisses are known from several locations such as the xingxingxia alatage and baluntai areas in the central tianshan arc terrane of the chinese eastern tianshan which is one of several precambrian microcontinents within the southern central asian orogenic belt caob the petrogenesis and the tectonic significance of the early neoproterozoic granitic gneisses have not been well constrained yet resulting in an ambiguous understanding of the early tectonothermal evolution of the chinese eastern tianshan geochronological results suggest that the protoliths of these granitic gneisses formed during a relatively short time period between ca 970 and 915 ma mainly clustering at ca 940 ma these peraluminous to strongly peraluminous granitic rocks show a common geochemical s type granite affinity involving low cao na 2 o th and y contents zircon saturation thermometry and ti in zircon thermometry yielded a relatively low crystallization temperature of approximately 750 800 c for the magmatic protolith of the granitic gneisses zircon hf isotopic compositions of the xingxingxia and alatage granitic gneisses show e hf t values of 5 4 to 4 2 with t dm2 model ages of 1 53 2 14 ga indicating that their protoliths were derived by the recycling of older continental crust we suggest that the early neoproterozoic granitic rocks in the chinese eastern tianshan were formed along an active continental margin furthermore we propose that the central tianshan arc terrane was located at the periphery of rodinia and separated from the tarim craton terrane in the early neoproterozoic

fingerprinting feldspar phenocrysts using crystal isotopic composition stratigraphy implications for crystal transfer and magma mingling in s type granites microsampling of cm scale feldspar crystals within an s type granite from the lachlan fold belt of southeastern australia has revealed complex internal sr and nd isotopic variations the observed isotopic zonations are in part interpreted as recording feldspar crystallisation in a dynamically mixing magma system the isotopic composition of which was varying in response to the influx of more mafic and isotopically more mantle like magmas the latter stages of which are now represented in modified form by microgranular enclaves similar core to rim isotopic variations in feldspar megacrysts from a microgranular enclave and the adjacent host granite strongly suggest megacrysts in the enclave were transferred from the granitic magma during crystallisation feldspar rims have higher 87sr 86sri and lower nd i than adjacent whole rock analyses but match those of mineral separates from the surrounding enclave matrix this suggests that the final stages of megacryst growth occurred in the presence of a component that had previously interacted with a high 87sr 86sr low nd i component such as metasedimentary wall rocks isotopic heterogeneities are also presererved within different mineral phases in the enclave matrix suggesting that differing phases grew at differing stages of equilibration between the enclave magma and its host granitic magma our results reveal major isotopic heterogeneities on a single crystal and also inter mineral scale in a pluton which shows well constrained evidence for magma mingling these results indicate the suitability of feldspars as recorders of isotopic change in magmatic systems even those which have cooled slowly in the plutonic environment and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

geochronology petrogenesis and tectonic significance of peraluminous granites from the chinese altai nw china abstract the paleozoic granites in the chinese altai are important for the study of tectonic evolution and crustal growth in the central asian orogenic belt caob four representative peraluminous granitic intrusions were selected for systematic studies of zircon u pb and hf isotopic compositions and whole rock geochemical and nd sr isotopic analyses these rocks have high asi alumina saturation index al 2 o 3 cao na 2 o k 2 o 1 01 1 46 molecular ratios with 0 6 5 6 wt of normative corundum and are characterized by moderately negative eu anomalies eu eu 0 38 0 98 and strong depletion in ba nb and sr elements our data suggest that these intrusions were emplaced from 419 to 393 ma consistent with a period of intensive magmatic activities and high temperature metamorphism in the chinese altai while in situ zircon hf isotopic analyses for these granites give predominantly positive e hf t values 0 8 to 12 8 a few inherited zircons yield negative e hf t values from 12 5 to 1 53 the u pb age and hf isotopic data of these inherited zircons are similar to that of the widespread metasediments in addition the peraluminous granitic rocks have near zero or negative e nd t values 3 3 to 0 5 and relatively high initial 87 sr 86 sr ratios 0 7079 0 7266 distinct from those of the i type granites in the study region but similar to the early paleozoic habahe sediments these isotopic compositions suggest that the newly accreted metasediments of habahe group may be the major source rock of the peraluminous granites the geochemical compositions indicate that their precursor magmas were derived from a relatively shallow crustal level p 5 kbar and zircon saturation temperatures suggest that these granitic intrusions were emplaced at 672 861 c the peraluminous granitic magmas were generated by dehydration melting of newly accreted materials which were possibly brought to at least middle crustal depth by subduction related processes in an active margin and were subsequently molten by strikingly high ambient temperature probably caused by upwelling of the hot asthenosphere associated with ridge subduction in the paleozoic

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

geochronology and petrogenesis of middle permian s type granitoid in southeastern guangxi province south china implications for closure of the eastern paleo tethys abstract the bangxi chenxing suture zone is an important region to address the history of closure of the eastern paleo tethys ocean among the widespread s type granite batholiths in the se guangxi province adjacent to this suture is the nali granodiorite here we report zircon u pb ages major and trace element geochemistry and sr nd hf isotope geochemistry of a newly found middle permian s type granite in this region la icp ms zircon u pb geochronology yields emplacement ages of 265 2 to 262 2 ma for the nali granodiorite both the inner and outer phases are characterized by variable sio 2 66 91 71 39 wt high al 2 o 3 12 99 14 04 wt k 2 o na 2 o 4 78 5 98 wt and a cnk values 1 11 1 50 resembling those of typical s type granites the rocks are enriched in rb th u and light rare earth elements with weak negative eu anomalies and show depletion in nb ta ti with typical arc like affinity they have relatively high 87 sr 86 sr i ratios of 0 7228 to 0 7331 low e nd t values of 13 6 to 11 9 and low zircon e hf t values 21 9 to 8 8 high whole rock nd isotopic model ages 2 00 2 02 ga and zircon hf isotopic model ages 1 59 2 20 ga indicate that they might have been generated by partial melting of ancient lower crust with minor contribution from mantle sources the granodiorite shows continental arc affinity and likely formed within a subduction setting by combining previously extant data for permo triassic arc collision related magmatism in the jinshajiang ailaoshan song ma and bangxi chenxing suture zones we propose that the subduction of the eastern paleo tethys might have started during middle permian triggered by the northward subduction of the indochina block icb beneath the south china block scb and closure during middle triassic

geochemical investigations of microgranitoid enclaves in the s type cowra granodiorite lachlan fold belt se australia the cowra granodiorite is a relatively mafic enclave rich s type pluton in the lachlan fold belt which has been cited as a type example of a restitic origin for all varieties of enclaves in lachlan fold belt s type granites microgranitoid enclaves from the pluton are subordinate to metasedimentary varieties and can be subdivided into two groups according to their mafic mineral assemblage pyroxene microtonalites and biotite microgranites no geochemical or isotopic distinction can be made between the two varieties petrographic evidence acicular apatites xenocrysts from the host granite suggests an origin as mingled more mafic magmas which have been variably contaminated by the more felsic host magma this is supported by the fact that the microgranitoid enclaves have isotopic compositions 87sr 86sr i 0 7095 to 0 7144 end i 9 2 to 6 9 that are generally more primitive than or similar to those of the host granite 87sr 86sr i 0 7142 end i 8 8 the spread in isotopic compositions like their trace element compositions is considered to be the consequence of variable degrees of diffusive exchange between the felsic and more mafic magmas during slow cooling several studied metasedimentary enclaves are not in isotopic equilibrium with their host granite and therefore cannot represent pristine samples of the bulk source region of the granite instead they represent portions of a lithologically and compositionally diverse source terrane or accidental xenoliths entrapped during emplacement

nd o hf isotopic decoupling in s type granites implications for ridge subduction abstract the generation of s type granites in the continental crust generally requires partial melting of metasedimentary rocks at relatively high temperatures and is typically associated with syn or post collisional tectonics these melts are generally expected to inherit the geochemical characteristics of their metasedimentary protoliths and their nd hf and o isotopic compositions have been widely used to trace the origin of the magmas here we show that these isotopic systems are decoupled in s type granites from the chinese altai displaying a wide range of zircon hf t values 0 7 to 6 2 and a limited range of whole rock nd t values 6 1 to 2 2 and zircon 18o values 8 49 to 12 91 zircon xenocrysts are common in these plutons and show markedly negative hf t values from 30 7 to 18 and highly positive 18o values from 9 61 to 13 03 in addition these granites exhibit high lu hf 0 15 to 1 38 ratios and substantial depletions in zr and hf we develop a new model to explain the observed relationship between residual zircon content and nd hf o isotope decoupling we propose that these s type granites formed from partial melting of metasedimentary crustal rocks associated with a ridge subduction related heat source limited crustal heating due to mantle upwelling through the slab window on a small scale may have resulted in significant disequilibrium melting of the metasedimentary crust our findings provide new insights into melting processes in the deep continental crust

late cretaceous granites from the giant dulong sn polymetallic ore district in yunnan province south china geochronology geochemistry mineral chemistry and nd hf isotopic compositions abstract as a world class tin tungsten province south china is well known for its extensive mesozoic granitic magmatism the dulong district located in the western cathaysia block of the south china tin tungsten province is characterized by widespread mesozoic granitoids and accompanying sn polymetallic ore deposit 30 mt of sn it is one of the most important polymetallic tin ore districts in china in this study three mineralization related granite types were identified in the dulong district including the dulong coarse grained granite dcg the dulong fine grained granite dfg and the dulong porphyritic granite dpg detailed studies are presented on zircon u pb ages major and trace elements mineral chemical and nd hf isotopic compositions of the tin bearing granites from the dulong district la icp ms u pb dating of zircon grains from these three granite bodies yields ages of 90 1 0 7 ma 89 7 0 8 ma and 86 0 0 5 ma respectively geochemically the granites are strongly peraluminous with high contents of alkalis enrichment in p li rb cs ta sn w and u depletion in ti mg co ni sr ba zr hf th and rare earth elements fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations whereas rare earth elements were fractionated by accessory minerals such as apatite and monazite the geochemical data suggest that the rocks are highly fractionated s type granites the granites show bulk rock e nd t values in the range of 12 2 to 10 8 and zircon e hf t values from 15 5 to 2 5 with meso paleoproterozoic t dm c ages for both nd and hf isotopes geochemical and isotopic data suggest that these highly fractionated s type granites dcg dfg and dpg were originated from the same episode of partial melting of the protolith which have analogous components of metamorphosed pelitic rocks from the meso paleoproterozoic continental crust extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma and the reduced magmas fo 2 below nno would efficiently remove sn into a hydrothermal fluid and lead to deposition of sn rich mineral phases the association of dulong and gejiu magmatism in the western cathaysia block may be likely to mark the onset of back arc extension or intra arc rift in the region during late cretaceous the upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the s type granitic magmas

late triassic post collisional granites related to paleotethyan evolution in northwestern lao pdr geochronological and geochemical evidence abstract the late paleozoic to early mesozoic granites exposed in northwestern lao pdr provide important constraints on the tectonic evolution of the eastern paleotethyan ocean and regional correlation with the giant granitic belt in southeast asia new geochronological data show that the granites have late triassic zircon u pb ages of 231 220 ma they are dominated by monzogranite and biotite granite with an i type geochemical affinity these granites are enriched in lrees and liles and depleted in hfses the geochemical variations for these granites indicate the fractional crystallization of plagioclase k feldspar biotite apatite and fe ti oxides their initial 87sr 86sr ratios range from 0 7021 to 0 7105 and end t values from 1 6 to 7 3 zircon in situ ehf t values are in range of 6 0 5 3 peaks at 2 8 and 2 5 respectively hf model ages of 0 67 1 64 ga peaks at 0 83 ga and 1 45 ga respectively and 18o values of 6 6 8 0 similar to the late triassic granitoids from the eastern province in southeast asia these granites originated from a mixed source of ancient metamorphic rocks with juvenile mafic crust the late triassic granites in northwestern lao pdr formed in a post collisional setting in response to the thickened crustal collapse during the assembly of the sibumasu with indochina blocks these granites can southerly link with the eastern granite province of the eastern paleotethyan domain in southeast asia

closure of the east paleotethyan ocean and amalgamation of the eastern cimmerian and southeast asia continental fragments abstract the phanerozoic record of southeast asia preserves the history of opening and subsequent consumption of the paleotethyan ocean and the assembly of continental fragments into asia as part of the broader scale reconstruction of pangea however uncertainty remains as to which of the many suture zones in southeast asia represents the relict of the main ocean when final ocean closure occurred and the assembly history of the eastern cimmerian and southeast asia continental fragments our overview of the geological features of the suture zones the bounding continental fragments and their magmatic metamorphic and sedimentary records resolves many of these key issues the sedimentary biogeographical structural lithological geochemical and geochronological data from the changning menglian inthanon and bentong raub suture zones argue for their linkage with the longmu co shuanghu suture zone in central tibet and together constitute the main east paleotethyan ocean relict the eastward subduction of the ocean resulted in the development of a series of magmatic arc back arc basin and continental fragments in southeast asia including from west to east the lincang sukhothai east malaya arc the jinghong nan sa kaeo back arc basin the simao west indochina fragment the luang prabang loei back arc basin the south indochina fragment the wusu and truong son back arc basins the north indochina fragment the jinshajiang ailaoshan song ma branch back arc basin and the south china block assembly of these fragments resulted in indosinian high temperature and high pressure metamorphism and related tectonothermal event available data indicate a switch from subduction of the main east paleotethyan ocean to the collision of the sibumasu with simao indochina blocks at 237 ma with subsequent syn and post collisional events at 237 230 ma and 230 200 ma respectively along the changning menglian inthanon and bentong raub suture zones the timing of initial syn and post collision events along the jinshajiang ailaoshan song ma suture zone with its record of back arc basin closure is at 247 ma 247 237 ma and 237 200 ma generally 10 ma older than that along the changning menglian inthanon and bentong raub suture zones our synthesis of all available data enables establishment of a comprehensive geodynamic model for the east paleotethyan evolution this model links the spatial temporal pattern across southeast asia into a series of tectonic events including ocean back arc basin opening subduction closure subsequent assemblage and orogenic collapse along with associated igneous metamorphic and sedimentary activities

glass rich cordierite biotite rhyodacite valle ninahuisa puno se peru petrological evidence for hybridization of lachlan s type and potassic mafic magmas

chemistry of the ordovician and silurian greywackes of the snowy mountains southeastern australia an example of chemical evolution of sediments with time abstract the ordovician quartz rich greywackes of the snowy mountains region are essentially mixtures of two components these are quartz and clay minerals the chemistry of any rock is largely determined by its proportions of clay minerals so that there is a strong negative correlation between si and those elements other than si contained in clay minerals elements that occur only in feldspar but not in clay minerals that is ca na sr and pb have a low and variable concentration these four elements have even lower abundances in the silurian greywackes deposited in basins on a basement of the ordovician rocks this is interpreted to have resulted from a further cycle of chemical weathering that acted on ordovician source rocks to produce the silurian detritus in a similar fashion the ordovician rocks are thought to have formed by weathering of more feldspar rich sedimentary rocks at the margins of the lachlan fold belt two episodes of chemical weathering are therefore recognised the first produced the feldspar poor ordovician rocks the second acted on part of these to form the almost feldspar free silurian strata in both cases ca na sr and pb were lost as feldspars were converted to clay minerals

the tectonic significance of ordovician magmatism in the eastern lachlan fold belt abstract the shoshonitic rock series is a suite of igneous rocks derived from the mantle and containing high potassium plus low abundances of high field strength elements it is commonly associated with calcalkaline igneous rocks but in most modern examples a contemporary active subduction zone is not present mantle derived shoshonitic magmatism in the lachlan fold belt commenced in the early ordovician and terminated at the end of the ordovician when it was replaced by tholeiitic magmatism and the onset of wholesale melting of the lower to middle crust associated calcalkaline igneous rocks are insignificant the shoshonites are widely distributed across the eastern part of the fold belt in a series of discontinuous belts and volcanic centres the largest of which is the orange wellington belt extending from east of cowra to dubbo the broad geographical distribution is not typical of the curvilinear belts of volcanics associated with subduction zones and would be even greater if the intervening basins or troughs were unfolded all rocks analyzed to date are either clearly shoshonitic or show chemical features that indicate shoshonitic affinities prior to alteration and metamorphism in some areas lavas rich in olivine and clinopyroxene potassic trachybasalts dominate in others the more evolved plagioclase rich shoshonites are most abundant it is suggested that the ordovician magmatism was not accompanied by coeval subduction as has been generally assumed more likely the lithospheric mantle beneath the lachlan fold belt was modified during an earlier subduction event associated with the assembling of the basement blocks recognized from granite studies the cause of melting in the ordovician may be related to lithospheric heating or overturning prior to the upwelling of unmodified asthenosphere the hot 1200 c asthenosphere was the source for the silurian tholeiites and provided conductive heat for the melting of the lower to middle crust

application of the restite model to the deddick granodiorite and its enclaves a reinterpretation of the observations and data of maas et al 1997 mafic s type granites of the lachlan fold belt always contain a introduction distinctive suite of enclaves dominated by schists and gneisses of high maas et al 1997 have proposed complex models of metamorphic grade generally with lesser numbers of microgranular crustal melting and magma mixing to account for the enclaves maas et al 1997 journal of petrology 38 chemical and isotopic features of several kinds of enclaves 815 841 recently described enclaves from the s type deddick in the s type deddick granodiorite of the lachlan fold granodiorite they concluded that the metasedimentary enclaves belt lfb exposed at mckillops bridge that grancould be either source lithologies or accidental xenoliths and that odiorite is a member of the bullenbalong suite area the most common microgranular enclaves formed as globules of 3100 km white chappell 1988 itself part of the hybrid magma that mingled with the host magma all features of very extensive and slightly more diverse bullenbalong the metasedimentary enclaves are consistent with an origin as lithic supersuite total area 8750 km plus 4000 km of restite fragments from the source and their ubiquity in the mafic svolcanic rocks it occurs near the southern extremity of type granites and their rarity in both felsic varieties and in i type those granites these are the rocks that have been used granites conform with such an origin the argument that these as primary examples of restite and of the restite model enclaves are not in chemical equilibrium with the host granite in s type granites hine et al 1976 white chappell because they do not complement its composition is not valid as they 1977 chappell et al 1987 chappell 1996b and the represent less fertile parts of the source that did not melt to the point enclosed enclaves have been regarded by us as lithic of disaggregation unaltered cores of microgranular enclaves in the restite white chappell 1988 chen et al 1989 s type granites have compositions that do not match those of any chappell white 1991 white et al 1991 wyborn known igneous rock and an origin by metamorphism of a calcareous et al 1991 sediment is probable partial melting during that metamorphism maas et al 1997 mostly reject the presence of restite accounts for the pseudo igneous textures seen in these enclaves enclaves in the deddick granodiorite however the

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

the cooma metamorphic complex a low p high t lpht regional aureole beneath the murrumbidgee batholith the cooma complex of the lachlan fold belt south eastern australia is characterised by a large c 10 km wide low p high t metamorphic aureole surrounding a small 3 6 km granite pluton the aureole extends northward to envelop the eastern lobe of the murrumbidgee batholith and progressively narrows to a kilometre wide hornfelsic aureole some 50 km north of cooma at its northern extremity the batholith has intruded its own volcanic cover these regional relations suggest that the murrumbidgee batholith is gently tilted to the north with the cooma complex representing the aureole beneath the batholith two main deformation events d3 and d5 affected the aureole the inner high grade migmatitic domain contains upright f5 folds defined by a composite transposed s3 s0 fabric and s3 s0 concordant leucosomes the folded stromatic migmatites define the western limb of a f5 synform with its axis located in the batholith lenses and sheets of the murrumbidgee batholith intruded along s3 but also preserve s3 as a strong solid state foliation s3 and the granite sheets but are also folded by f5 outlining a fanning positive flower structure these relations indicate that most of the batholith was emplaced before and during d3 but intrusion persisted until early syn d5 formation of the cooma granodiorite occurred post d3 to early syn d5 after formation of the wide metamorphic aureole during early syn d3 to early syn d5 the murrumbidgee batholith was emplaced between pre d3 to early syn d5 synchronous with the formation of the cooma complex the structural and metamorphic relations indicate that the murrumbidgee batholith was the ultimate heat source responsible for the cooma metamorphic complex d3 structures and metamorphic isograds are subparallel to the batholith margin for over 50 km this concordance probably extends vertically suggesting that the isograds also fan outward from the batholith margin this implies an inverted metamorphic sequence focused on the murrumbidgee batholith although the base has been almost completely removed by erosion in the cooma complex the field evidence at cooma combined with previous thermal modelling results suggest that extensive lpht metamorphic terranes may represent regional metamorphic aureoles developed beneath high level granitic batholiths

zircon u pb dating and in situ hf isotopic analysis of permian peraluminous granite in the lhasa terrane southern tibet implications for permian collisional orogeny and paleogeography article i nfo the lhasa terrane has long been interpreted as a simple tectonic block rifted from gondwana during the late paleozoic and then drifted northward before finally amalgamating with the qiangtang terrane during the early cretaceous in this paper we document permian peraluminous granites near pikang in the southern margin of the central lhasa terrane close to the recently documented songdo eclogite of permian age zircon shrimp and la icpms u pb dating for a pikang granite sample gives an identical crystallization age of about 263 ma and a wide age range of inherited zircons 283 2141 ma in situ hf isotopic analyses for 20 zircons of 263 ma yielded ehf t values of 4 5 to 1 9 the pikang granites have high a cnk values 1 08 and high normative corundum 1 3 2 0 indicative of peraluminous s type granite they are characterized by moderately negative eu anomalies eu eu 0 48 0 61 and strongly negative ba nb sr p and ti anomalies the granites have high end t values 6 4 to 6 0 and low initial 87 sr 86 sr ratios 0 7082 0 7096 relative to melts derived from mature continental crust these rocks are interpreted to have been generated by mixing between mantle melts and their induced melting of mature crustal materials we interpret the pikang peraluminous granite magmatism the regional angular unconformity between the middle and the upper permian and the eclogite of the same metamorphic age 262 ma from the same geotectonic location to represent different products of a common event in time and space we tentatively term this common event as syncollisional orogeny i e the permian gangdese orogeny we further hypothesize that the orogeny may be genetically associated with the collision between the lhasa terrane and the northern margin of australia following the closure of the paleo tethyan ocean south of the lhasa terrane

the mongol okhotsk ocean subduction related permian peraluminous granites in northeastern mongolia constraints from zircon u pb ages whole rock elemental and sr nd hf isotopic compositions abstract northeastern mongolia represents a unique area that experienced evolution of both the mongol okhotsk ocean moo and the central asian orogenic belt caob in order to better understand the evolution of moo and its effect on the caob we performed zircon u pb dating and hf isotope and whole rock elemental and sr nd isotopic analyses on three permian peraluminous granitic plutons in northeastern mongolia zircon dating result revealed that granitoids of east monhhaan south monhhaan and tuvshinshiree plutons were emplaced at 254 3 265 5 and 273 3 ma respectively the result provides permian ages for the permian triassic volcanic plutonic belt in northeastern mongolia geochemical analysis suggests that all the granitoids are of peraluminous s type granites elemental and sr nd hf isotopic data indicate that these s type granites were generated from mainly clay poor greywacke with some contribution of juvenile mantle component the permian s type granites emplaced likely in an active margin related to the subduction of the mongol okhotsk ocean the protracted intermittent extension during the long lived compression was considered as a likely geodynamic mechanism for the upwelling of mantle derived basaltic magma and melting of crustal materials

petrology geochemistry and geochronology of trondhjemites from the qori complex neyriz iran metamorphism magmatism and thrusting were the result of subduction of neotethys beneath the continental margin arc of the sanandaj sirjan shear zone sssz during the mesozoic the qori metamorphic complex is a part of the southern sssz leuco granitic trondhjemitic rocks crop out in the qori metamorphic complex and are rare rock types in the sssz these rocks have intruded into the marbles and garnet amphibolites the highest grade metamorphic rocks of the qori metamorphic complex and in some outcrops a transitional boundary between the amphibolites and the granitoids can be distinguished the granitoids are granular in texture and consist of plagioclase albite oligoclase quartz k feldspar muscovite and subordinate garnet spinel rutile and apatite which primarily occur as inclusions in the main phases the peraluminous trondhjemitic rocks are enriched in na2o and sio2 and depleted in feo mgo and cao similarities with some trondhjemitic liquids produced through partial melting of amphibolites or hydrous basalts i e low al2o3 content less than 15 wt low ba sr tio2 and eu content all with negative anomalies moderately enriched lrees and y and flat hree patterns suggest that the evolution of the parental magma was controlled by residual plagioclases during partial melting of a garnet amphibolite source concentrations of ferromagnesian elements mg fe and mn are low suggesting that the granitic rocks were not produced by high degrees of partial melting furthermore they display low amounts of ferromagnesian components from the protolith garnet amphibolite this is supported by consideration of compatible elements especially cr ni and ti and the less robust hree which respectively show very high and high bulk partition coefficients for relatively small degrees 20 of partial melting of the source the partial melting of the garnet amphibolites occurred at pressures and temperatures between 7 5 and 9 5 kbar at a depth of 25 to 32 km and 680 and 720 degrees c respectively based on the grt hbl and hbl pl thermometers and a grt hbl pl qtz barometer precise u th zircon shrimp ages of the trondhjemite show magmatic ages of 147 4 0 76 ma volgian late jurassic and suggest that neotethys began to subduct beneath the continental margin arc of the sssz as a result of this process an arc related metamorphism occurred leading to the development of the garnet amphibolites in the qori metamorphic complex c 2009 elsevier b v all rights reserved

petrogenesis of ore forming granites with implications for w mineralization in the super large shimensi tungsten dominated polymetallic deposit in northern jiangxi province south china abstract the shimensi deposit is a newly discovered super large tungsten w polymetallic deposit in northwestern jiangxi province south china in this paper we reported new zircon u pb ages for the ore bearing porphyritic biotite granite 151 3 2 8 ma and fine grained granite 150 1 1 2 ma and 150 7 2 4 ma which represent the oldest mesozoic granitic magmatism reported at shimensi our ore bearing granite porphyry ages 142 7 2 3 ma and 143 3 1 5 ma have better constrained the timing of the jurassic early cretaceous ore forming magmatism geochemically the shimensi granitoids are strongly peraluminous with high contents of sio2 70 7 78 7 wt and k2o 4 0 wt p2o5 rb ta and u and low contents of ti sr ba and hrees the rocks also show positive p2o5 vs sio2 correlation suggesting a highly fractionated s type affinity different from most w bearing granites in the jiangxi region the calculated zircon ehf t 10 0 to 2 4 two stage model ages 1350 1824 ma and 18ozircon values 6 40 to 8 87 of the shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks probably with combined contributions from the neoproterozoic shuangqiaoshan group metamorphic rocks and jiuling granodiorite the calculated zircon eu eu 0 05 0 58 mean 0 20 and ce4 ce3 3 83 96 49 mean 20 99 ratios of the granites indicate very low oxygen fugacity fo2 for the ore forming magmas a highly favorable factor for w mineralization potentially w and cu rich source rocks and highly fractionated and reducing granitic magmas were important factors that triggered super large w mineralization at shimensi

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

origin of cordierite bearing monzogranites from the southern central iberian zone inferences from the zoned sierra bermeja pluton extremadura spain abstract voluminous peraluminous biotite biotite cordierite and cordierite muscovite bearing granitic plutons were emplaced in the southern part of the central iberian zone iberian massif during the waning stages of the variscan orogeny the role of the mantle and the nature of the crustal sources involved in the generation of these remarkable granites are still a matter of discussion to address these issues a detailed study of the sierra bermeja pluton a 60 km2 cordierite bearing monzogranite intrusion representative of the regional nisa alburquerque los pedroches magmatic alignment has been carried out this pluton was formed by an inward sequence of three distinct but near contemporaneous magma pulses outer unit ou middle unit mu and inner unit iu the nested pluton is cut by a number of syn plutonic vaugneritic dykes while lamprophyres were distinctly later the age of the pluton has been established at ca 306 ma 309 3 to 304 3 ma by la icp ms u pb dating of zircon and monazite the peraluminosity a cnk 1 01 1 33 and p2o5 contents 0 19 0 35 wt of the monzogranitic units increase inwards ou mu iu this is accompanied by an overall decrease in tio2 mgo cao and feot and most trace elements including ree the three units display similarly low 87sr 86sr306ma ratios 0 7033 0 7046 but decreasing end306ma ou 2 7 mu 3 8 iu 7 5 to 4 7 vaugneritic rocks have homogeneous composition with similar 87sr 86sr306ma ratios 0 7043 to those of the monzogranites but higher end306ma 1 1 values whole rock geochemical data imply a partial melting of mainly cambro ordovician felsic metaigneous rocks ou with increasing proportion of neoproterozoic lower cambrian metasediments of the schist greywacke complex mu that formed almost exclusively the source of the iu thermobarometric data suggest that melting processes progressed upward through the geological record and magma emplacement took place at bt ap mnz xtm the present results could be extensible to other cordierite bearing granites of the southern central iberian zone although forthcoming experimental work and detailed comparisons are required to confirm such extrapolation

field evidence for successive mixing and mingling between the piolard diorite and the saint julien la vetre monzogranite nord forez massif central france recent mapping of the nord forez region massif central france reveals a variety of complex field relationships along contacts between a large enclave of diorite and its enclosing monzogranite field relations hybrid rocks and a wide variety of mafic magmatic enclaves can be explained by a succession of processes between coexisting mafic and felsic magmas that either prevent or promote exchanges the large volume of mafic magma and consequently the large amount of heat it brought with it favored exchange processes because the distribution of heat varied with both time and place the nature and intensity of the compositional exchange processes also varied most of the features attributed to exchange are related to processes that occurred at the level of emplacement and after the beginning of crystallization of the two magmas these processes affected both the granitic and dioritic magmas already thoroughly hybridized by nearly similar processes that took place earlier at depth

aluminum in zircon as evidence for peraluminous and metaluminous melts from the hadean to present zircon structurally accommodates a range of trace impurities into its lattice a feature which is used extensively to investigate the evolution of silicate magmas one key compositional boundary of magmas is defined by whether the molar ratio of al2o3 cao na2o k2o is larger or smaller than unity here we report 800 al in zircon concentrations from 19 different rocks from the lachlan fold belt southeastern australia new england usa and arunachal leucogranites eastern himalaya with al2o3 cao na2o k2o whole rock values that range from 0 88 to 1 6 zircons from peraluminous rocks yield an average al concentration of 10 ppm which distinguishes them from crystals found in metaluminous rocks 1 3 ppm this difference is related to the materials involved in the melting assimilation and or magma differentiation processes for example magmas that assimilate al rich material such as metapelites are expected to produce melts with elevated alumina activities and thus zircons with high al concentrations these observations are applied to the archean and hadean jack hills detrital zircon record detrital archean zircons with ages from about 3 30 to 3 75 ga yield al in zircon concentrations consistent with origins in peraluminous rocks in 8 of the cases n 236 a single zircon from the pre 3 9 ga age group n 39 contains elevated al contents which suggests that metaluminous crustal rocks were more common than peraluminous rocks in the hadean weathered material assimilated into these hadean source melts was not dominated by al rich source material

petrogenesis of granitoids from the lachlan fold belt southeastern australia the role of disequilibrium melting abstract s and i type granites from the lachlan fold belt southeastern australia have been investigated to assess the role of disequilibrium melting in their petrogenesis differences between the median initial ehf compositions of magmatic zircon populations and the host bulk rock ehfblk zrc range from 0 6 to 2 5 e units providing evidence for intra sample and hence inter phase hf isotopic heterogeneity linear variations on harker diagrams and o and hf isotope compositions of magmatic zircon preserved in many i and s type granites are inconsistent with assimilation or simple mixing hypotheses in contrast isotopic disequilibrium between the melt and a restite assemblage can explain the bulk rock versus zircon differences observed in these samples assuming that magmatic zircon records the melt composition differences between the bulk rock ehf and ehf of magmatic zircon ehfblk zrc values measured for i type granites 0 4 2 5 can largely be explained by disequilibrium amphibole dehydration melting of meta igneous protoliths that were either isotopically heterogenous at the time they were formed or perfectly homogeneous before being aged in the crust for 0 4 1 0 billion years prior to partial melting the currowong suite exhibits petrographic features and preserves geochemical and isotopic compositions that do not lend themselves to simple restite model or magma mixing explanations however these observations could be explained by the restite unmixing of magma batches generated from a single source rock if as modelling has suggested separate batches contain different melt compositions by investigating the application of disequilibrium melting to granite genesis this study demonstrates that isotopic heterogeneity at various sampling scales should actually be expected for the production of granites from a single source rather than necessitating the involvement of multiple sources and mixing processes as a result great care should be taken in the interpretation of isotope data from granitic bulk rocks or their zircons

weathering rates and carbon storage along a climosequence of soils developed from contrasting granites in northeast brazil abstract i and s type granites comprise large areas and play a key role in global soil weathering patterns i type granites are originated from melting of igneous source rocks whereas s type granites result from melting of sedimentary sources this gives rise to differences in mineralogical and geochemical characteristics of the rocks the objective of this study was to address the effect of petrology and mineralogy of i and s type granites on weathering pedogenesis and total organic carbon stocks across a climosequence significant differences in morphological physical and chemical properties of soils derived from i and s type granites were observed and directly linked to petrological mineralogical and geochemical signatures of the underlying granites e g presence of more mafic minerals in the i type granite and therefore a higher clay and iron content in their derived soils in addition this higher iron content favored the hematite pathway and thus the red soil development despite the influence of the climate on weathering patterns i e higher soil development in humid areas parent material seems to play a decisive role in determining soils characteristics in the studied area the type of parent material also governed the rates of carbon accumulation in soils i type granites originated soils with higher toc stocks than soil profiles developed from s type granites this carbon accumulation is mainly due to soil chemical and physical characteristics driven by the type of granite notably soil fertility and clay content

late triassic post collisional granites related to paleotethyan evolution in se thailand geochronological and geochemical constraints abstract a set of new u pb geochronological elemental and sr nd hf isotopic data is presented to constrain the formation age and petrogenesis of granites in se thailand which are significant for understanding eastern paleotethyan tectonic evolution and regional correlation in se asia six granite samples from the chonburi rayong bang lamung and chanthaburi plutons yielded similar crystallization ages of 222 218 ma these granites can be geochemically classified into s type group 1 and i type group 2 granites both groups have similar chondrite normalized ree and primitive mantle normalized multi element patterns but distinctly different sr nd hf isotopic compositions group 1 is characterized by more enriched initial 87sr 86sr i ratios 0 7101 0 7272 and lower end t values 12 0 to 13 2 compared with those of group 2 with 87sr 86sr i of 0 7027 0 7053 and end t of 0 6 to 1 2 consistently zircons from group 1 yield negative ehf t values of 7 3 to 27 4 and mesoproterozoic or older hf model ages tdm 1 53 2 63 ga distinct from those of group 2 with positive ehf t values 5 0 11 3 and younger tdm 0 42 0 67 ga group 1 granites mainly originated from ancient greywackes but group 2 from juvenile mafic crust with the input of meta sedimentary component these data along with available observations synthetically indicate that these granites formed in the post collisional gravitational collapse setting of the thickened crust in response to the assemblage of the indochina with sibumasu blocks they linked northerly and easterly to the late triassic granitoids in nw thailand and east malay peninsula related to the paleotethyan tectonic regime respectively

geochronological and geochemical constraints on the petrogenesis of middle paleozoic kwangsian massive granites in the eastern south china block abstract to achieve a better understanding of the kwangsian orogenic event of the eastern south china block this paper documents a set of new zircon u pb geochronological and hf isotopic data and whole rock elemental and sr nd isotopic analytical results for the representative massive granite intrusions across the jiangshan shaoxing fault the studied samples are classified into two groups representing the rocks from the cathaysia block to the east of the jiangshan shaoxing fault group 1 and those from the eastern yangtze block between the anhua luocheng and jiangshan shaoxing faults group 2 the group 1 samples gave the zircon u pb ages of 405 454 ma and e hf t values of 3 6 to 15 2 with hf model ages of 1 6 2 4 ga group 2 yielded the zircon u pb ages of 400 432 ma and e hf t values of 0 2 to 12 7 with hf model ages of 1 3 2 2 ga geochemically the group 1 samples a cnk 1 02 1 43 have relatively lower al 2 o 3 mgo cao p 2 o 5 and e nd t but higher k 2 o na 2 o than those of group 2 a cnk 0 93 1 44 both groups show similar chondrite normalized patterns of rare earth elements with eu eu values of 0 15 0 92 and strongly negative ba sr nb p and ti anomalies in primitive mantle normalized spider diagrams their e nd t values range from 11 1 to 8 0 for group 1 and 8 9 to 5 0 for group 2 generally similar to those of precambrian paragneiss and contemporaneous gneissoid granites in the eastern south china block our geochronological results indicate that the kwangsian massive granites in the eastern south china block were crystallized between 400 ma and 454 ma synchronous to the kwangsian gneissoid granites along the wugong and wuyi baiyun yunkai domains in the eastern south china block the synthesis of these whole rock geochemical and in situ zircon hf isotopic data suggests that both the group 1 and 2 granites across the jiangshan shaoxing fault were predominantly derived from a crustal source with some proportional metapelitic and metaigneous components from the precambrian basement the input of juvenile mantle derived magma is insignificant taking into account other available evidences it is proposed that the jiangshan shaoxing fault might be a pre existing boundary between the yangtze and cathaysia blocks which was reactivated during the middle paleozoic kwangsian orogenic event the massive granitic magmatism was probably resulted from the doubly crustal thickening and subsequent isostatic readjustment in an intracontinental tectonic regime

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation