ultrahigh temperature metamorphism and decompression history of sapphirine granulites from rajapalaiyam southern india implications for the formation of hot orogens during gondwana assembly sapphirine bearing mg al granulites from rajapalaiyam in the southern part of the madurai block provide critical evidence for late neoproterozoic cambrian ultrahigh temperature uht metamorphism in southern india poikiloblastic garnet in quartzo feldspathic and pelitic granulites contain inclusions of fine grained subidioblastic to xenoblastic sapphirine associated with quartz suggesting that the rocks underwent t 1000 c peak metamorphism quartz inclusions in spinel within garnet are also regarded as clear evidence for a uht condition inclusions of orthopyroxene within porphyroblastic garnet in the sapphirine bearing rocks show the highest al 2 o 3 content of up to 10 3 wt suggesting t 1050 1070 c and p 8 5 9 5 kbar temperatures estimated from ternary feldspar and other geothermometers t 950 1000 c further support extreme thermal metamorphism in this region xenoblastic spinel inclusions in sapphirine coexisting with quartz suggest that the spinel quartz assemblage pre dates the sapphirine quartz assemblage probably implying a cooling from t 1050 c or an anticlockwise p t path the fmas reaction sapphirine quartz garnet orthopyroxene sillimanite indicates a cooling from the sapphirine quartz stability field after the peak metamorphism corona textures of orthopyroxene cordierite sapphirine orthopyroxene sapphirine cordierite and cordierite spinel around garnet suggest subsequent near isothermal decompression followed by decompressional cooling toward t 650 750 c and p 4 5 5 5 kbar the sapphirine quartz association and related textures described in this study have an important bearing on the uht metamorphism and exhumation history of the madurai block as well as on the tectonic evolution of the continental deep crust in southern india our study provides a typical example for extreme metamorphism associated with collisional tectonics during the late neoproterozoic cambrian assembly of the gondwana supercontinent

ultrahigh temperature metamorphism under isobaric heating new evidence from the north china craton abstract the khondalite belt within inner mongolia suture zone imsz in the north china craton ncc preserves evidence for extreme crustal metamorphism under ultra high temperature uht conditions at ca 1 92 ga associated with the subduction collision tectonics between the yinshan and ordos blocks here we report a new locality in hongsigou where cordierite and spinel bearing granulites record uht metamorphism the prograde peak and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as bt1 grt1 sil1 kfs1 pl1 ilm qtz1 grt1 sil2 kfs2 pl2 spl ilm qtz2 liq and crd grt2 sil3 kfs2 pl2 ilm qtz2 respectively the peak metamorphic conditions of the pelitic granulite were estimated as 930 1050 c and 6 5 7 5 kbar based on pseudosection analysis in the system nckfmashto suggesting extreme thermal metamorphism we report la icpms zircon u pb data from the granulite which show weighted mean 207pb 206pb age of 1881 6 6 ma marking the timing of uht metamorphism lu hf analyses of the zircons show ehf t values within a restricted range of 4 2 to 0 3 and together with hf model ages a paleoproterozoic arc magmatic source is inferred for the detrital zircons the estimated p t path for the uht granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory different from the anti clockwise p t paths defined in earlier studies for the 1 92 ga uht rocks from the imsz the younger age and the isobaric heating trajectory suggest that the hongsigou uht rocks are related to heat input from underplated mafic magmas following continental collision

multiple mafic magmatic and high grade metamorphic events revealed by zircons from meta mafic rocks in the daqingshan wulashan complex of the khondalite belt north china craton abstract meta mafic rocks in the daqingshan wulashan complex in the central segment of the paleoproterozoic khondalite belt of the north china craton are composed predominantly of garnet bearing mafic granulites mafic granulites and amphibolites they occur mainly as irregular lenses and as a set of deformed dyke sill swarms within dioritic granitic orthogneisses and al rich paragneisses an integrated study involving laser raman and scanning electron microscope analyses of mineral inclusions from zircons cathodoluminescence imaging and la icp ms u pb dating of zircons shows that magmatic zircons in these meta mafic rocks record four age groups of 2500 2450 2300 2100 1970 1930 and ca 1850 ma indicating multiple mafic magmatic events occurred within the daqingshan wulashan complex in addition four groups of metamorphic zircons with ages of ca 2450 ca 1950 ca 1900 and ca 1850 ma are present within these meta mafic rocks zircons of the first oldest group contain medium to low pressure mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz and yield ages of ca 2450 ma representing the timing of the early mlp granulite facies metamorphic event within the daqingshan wulashan reworked basement complex in contrast zircons of the second group are free of mineral inclusions and yield ages of ca 1950 ma which is considered to be the timing of the regional high grade metamorphic and structural event probably caused by the collision of the yinshan and ordos blocks zircons of the third group contain mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz similar to the zircons of the first group but yield younger ages of ca 1900 ma interpreted as the timing of the regional mlp granulite facies metamorphism that most likely occurred during the early stage of post orogenic exhumation of the daqingshan wulashan complex zircons of the fourth group contain mlp amphibolite facies mineral inclusions of clinopyoxene amphibole plagioclase quartz and yield the youngest ages of ca 1850 ma which probably represent the timing of the regional amphibolite facies metamorphism during the late stage of post orogenic exhumation of the daqingshan wulashan complex combined with previous geological data of the khondalite belt it is speculated that the multiple mafic magmatism and contemporaneous high grade metamorphism of the daqingshan wulashan complex from the khondalite belt were most likely generated by an orogenic process involving early subduction collision and late exhumation in an active continental margin arc

evolution of the archean and paleoproterozoic lower crust beneath the trans north china orogen and the western block of the north china craton abstract we report u pb ages and hf isotopes of zircons in granulites from two continental suture zones in the north china craton ncc from granulite xenoliths entrained in the cenozoic hannuoba basalts within the trans north china orogen tnco that amalgamates the western and eastern blocks and from a mafic granulite associated with ultrahigh temperature uht granulites within the inner mongolia suture zone imsz that welds the yinshan and ordos blocks the zircons in these rocks together with the inherited zircons from mesozoic subalkalic intrusives of these regions show several distinct u pb age populations and provide constraints on the evolution of the lower crust beneath the ncc parts of the older zircons from the tnco yield discordant data that project to ages of about 2 5 to 2 7 ga these old zircons show hf tdm model ages of 2 6 2 9 ga suggesting the existence of archean lower crust beneath the tnco which is coupled with the neoarchean metamorphic basement and greenstone belt a major zircon population grew at 1 75 2 0 ga consistent with the timing of the paleoproterozoic collision between the various crustal blocks within the ncc suggesting that this event had a significant effect on the archean lower crust the older inherited zircons from the western block also yield discordant data that project to younger ages of about 1 8 to 1 9 ga this age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the uht rocks in the khondalite belt within the imsz these older zircons yield hf tdm model ages of 2 0 2 5 ga suggesting that the lower crust beneath the western block in the ncc to be dominantly paleoproterozoic and decoupled with the archean metamorphic basement of the region yet another population of zircons from the hannuoba banded granulite xenoliths garnet bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of phanerozoic concordant ages ranging from 470 ma to 40 ma with peaks at 315 ma 220 230 ma 120 ma and 46 ma the late paleozoic zircons predominantly occur in the garnet bearing pyroxenite xenoliths and yield variable ehf t values of 24 to 18 triassic cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable ehf t values ranging from 48 to 16 the tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted ehf t with a dominant range from 0 to 18 these data suggest episodic magmatic underplating in the ancient lower crust of the ncc lasting continuously throughout phanerozoic producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust our data clearly demonstrate the important events of phanerozoic magmatic underplating beneath the neoarchean paleoproterozoic crust of the ncc

dehydration and incipient charnockite formation a phase equilibria and fluid inclusion study from south india a 3 m traverse across a charnockite lens in a biotite garnet graphite gneiss quarry from southern india has provided mineral equilibria that indicate charnockite formation occurred under fluid conditions of x h 2 o 0 2 to 0 3 at p 5 5 pm 1 9 kb and t 700 to 750 c dehydration of biotite loss of garnet and growth of orthopyroxene are related to a decrease in x h 2 o in the fluid phase within the charnockite lens isotopic analysis of the fluid entrapped in quartz from the charnockite indicates delta 13 c 8 2 0 3 0 heavier than delta 13 c values from smaller volumes of co 2 entrapped in quartz from the gneiss although the increase in fluid inclusion abundance in the charnockite can be related to oxidation of graphite without influx of co 2 an external source of co 2 is required in order to account for the shift to heavier carbon isotope values observed in both graphite and entrapped co 2 within the charnockite carbon isotope data across the gne

origin of paired high pressure ultrahigh temperature orogens a ridge subduction and slab window model introductionmetamorphism at elevated pressure temperature conditions and distinct uid regimes generates ultrahigh pres sure uhp high pressure hp andultrahigh temperature uht rocks harley 2004 brown 2006 2007 2009 kelsey 2008 santosh andomori 2008a b santos et al 2009 santosh et al 2009a zhang et al 2009 although previous studies havecorrelated these di erent orogens todistinct tectonic settings recent inves tigations record high pressure anduht conditions from the same tec tonic environment within the sameorogenic belt and in some cases evenwithin the same samples mostoftheseexamples come from major collisionalzones along which continental blocksweresuturedatdi erenttimesinearthhistory including from the neoarch ean hp uht rocks of the limpopobeltinsouthafrica tsunogaeandvanreenen 2006 the palaeoproterozoichp guo et al 2004 obrien et al 2005 and uht santosh et al 2007a b 2008 2009b belts in thenorth china craton and the hp uht belts in the neoproterozoiceastern ghats belt as well as thecambrian gondwana suture in south ern india shimpo et al 2006 tsuno gaeet al 2008a santoshet al 2009c notably the thermal regimes for thesepaired hp and uht rocks are similar 1000 c and they also share acommon uid history characterizedby co

extremely high density pure co2 fluid inclusions in a garnet granulite from southern india abstract a late archean 2 4 2 7 ga garnet granulite from the southern margin of the south indian craton preserves fluid inclusions with the highest density co2 yet reported from lower crustal rocks the rock comprises garnet clinopyroxene salite plagioclase amphibole pargasite orthopyroxene hypersthene biotite scapolite and quartz with accessory k feldspar ilmenite apatite and ankerite pressure temperature estimates of 9 11 kbar and 740 800 c are computed from electron microprobe data on equilibrium assemblages we report here detailed inclusion petrography and microthermometric data on fluids trapped in garnet feldspar and quartz from the granulite the dominant category in all these minerals are composed of monophase carbonic inclusions with melting temperatures close to 56 6 c indicating a co2 rich composition for the fluid laser raman microscopic studies confirm that the fluid is pure co2 with no traces of impurities such as n2 and or ch4 the inclusions homogenize into the l

elasticity of plagioclase feldspars elastic properties are reported for eight plagioclase feldspars that span compositions from albite nasi3alo8 to anorthite casi2al2o8 surface acoustic wave velocities measured using impulsive stimulated light scattering and compliance sums from high pressure x ray compression studies accurately determine all 21 components of the elasticity tensor for these triclinic minerals the overall pattern of elasticity and the changes in individual elastic components with composition can be rationalized on the basis of the evolution of crystal structures and chemistry across this solid solution join all plagioclase feldspars have high elastic anisotropy a the direction perpendicular to the b and c axes is the softest direction by a factor of 3 in albite from albite to anorthite the stiffness of this direction undergoes the greatest change increasing twofold small discontinuities in the elastic components inferred to occur between the three plagioclase phases with distinct symmetry c1 i1 and p1 appear consistent with the nature of the underlying conformation of the framework linked tetrahedra and the associated structural changes measured body wave velocities of plagioclase rich rocks reported over the last five decades are consistent with calculated hill averaged velocities using the current moduli this confirms long standing speculation that previously reported elastic moduli for plagioclase feldspars are systematically in error the current results provide greater assurance that the seismic structure of the middle and lower crusts can be accurately estimated on the basis of specified mineral modes chemistry and fabric

composite nature of the north china granulite facies belt tectonothermal and geochronological constraints granulite facies rocks are intermittently exposed in a roughly e w trending belt that extends for approximately 2000 km across the north china craton from the helanshan qianlishan wulashan daqingshan guyang and jining complexes in the western block through the huai an hengshan xuanhua and chengde complexes in the trans north china orogen to the jianping western liaoning eastern hebei northern liaoning and southern jilin complexes in the eastern block the belt is generally referred to as the north china granulite facies belt previously interpreted as the lowest part of an obliquely exposed crust of the north china craton recent data indicate that the north china granulite facies belt is not a single terrane instead it represents components of three separate terranes the eastern and western blocks and trans north china orogen each of these units records different metamorphic histories and reflect the complex tectonic evolution of the ncc during the late archean and paleoproterozoic mafic granulites in the eastern block and the yinshan terrane western block underwent medium pressure granulite facies metamorphism at about 2 5 ga with anticlockwise p t paths involving near isobaric cooling following peak metamorphism reflecting an origin related to intrusion and underplating of mantle derived magmas pelitic granulites in the khondalite belt western block underwent medium pressure granulite facies metamorphism at about 2 0 1 9 ga with clockwise p t paths which record the paleoproterozoic amalgamation of the yinshan and ordos terranes to form the western block mafic and pelitic granulites in the trans north china orogen experienced high to medium pressure granulite facies metamorphism at 1 85 ga with clockwise p t paths involving nearly isothermal decompression following peak metamorphism which are in accord with the final collision between the eastern and western blocks to form the north china craton at 1 8 ga the ncgb cannot therefore represent a separate unique terrane instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times d 2005 international association for gondwana research published by elsevier b v all rights reserved

fluids in coesite bearing rocks of the tso morari complex nw himalaya evidence for entrapment during peak metamorphism and subsequent uplift fluid inclusions trapped in coesite bearing rocks provide important information on the fluid phases present during ultrahigh pressure metamorphism the subduction related coesite bearing eclogites of the tso morari complex himalaya contain five major types of fluids identified by microthermometry and raman spectroscopy these are 1 high salinity brine 2 n 2 3 ch 4 4 co 2 and 5 low salinity aqueous fluids these fluids were trapped during both deep subduction and exhumation processes the coesite bearing rocks are inferred to have been buried to a depth of 120 km where they experienced ultrahigh pressure metamorphism the fluid rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica carbonate assemblages in eclogite high salinity brine n 2 and ch 4 inclusions are remnants of prograde and peak metamorphic fluids whereas co 2 and low salinity aqueous fluids appear to have been trapped late during uplift the high salinity brine was possibly derived from subducted ancient metasedimentary rocks whereas the n 2 and ch 4 fluids were likely generated through chemical breakdown of nh 3 bearing k minerals and graphite alternatively ch 4 might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks high density co 2 is associated with matrix minerals formed during granulite facies overprinting of the ultrahigh pressure eclogite during retrogression to amphibolite facies conditions low salinity fluids were introduced from external sources probably the enclosing gneisses this source enhances salinity differences as compared to primary saline inclusions the subducting indian lithosphere produced brines prior to achieving maximal depths of 120 km where fluids were instead dominated by gaseous phases subsequently the indian lithosphere released co 2 rich fluids during fast exhumation and was then infiltrated by the low salinity aqueous fluids near the surface through external sources elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions

carbonic fluids in ultrahigh temperature metamorphism evidence from raman spectroscopic study of fluid inclusions in granulites from the napier complex east antarctica

fluids in high to ultrahigh temperature metamorphism along collisional sutures record from fluid inclusions abstract petrographic studies and microthermometric investigations on fluid inclusions associated with high to ultrahigh temperature metamorphic rocks in three major precambrian suture zones on the globe demonstrate the dominant occurrence of co 2 rich fluids these rocks form part of hot orogens developed along collisional plate boundaries the sapphirine quartz bearing mg al rich rock from the palghat cauvery suture zone a trace of the cambrian gondwana suture zone in southern india preserves evidence for a prograde high pressure event and subsequent peak ultrahigh temperature metamorphism along a clockwise path and contains abundant co 2 rich inclusions in corundum garnet and sapphirine most of the fluid inclusions are either primary or secondary and preserve low density co 2 rich fluids 0 569 0 807 g cm 3 similar low density co 2 rich fluid inclusions 0 853 0 953 g cm 3 are also present in pelitic granulites from the limpopo complex of southern africa a neoarchean granulite facies orogen formed by continent continent collision in contrast the garnet orthopyroxene granulite from tonagh island in the neoarchean napier complex in east antarctica contains very high density primary 1 095 1 129 g cm 3 and secondary 0 960 1 179 g cm 3 carbonic inclusions in garnet and quartz the calculated isochores for the fluid inclusions from the palghat cauvery suture zone and the limpopo complex yield significantly lower pressure estimates than those predicted from peak metamorphic conditions we interpret this as a result of significant density decrease due to rapid decompression along a clockwise p t trajectory in contrast the estimated isochores for primary inclusions in garnet orthopyroxene granulites from the napier complex are consistent with the peak p t conditions estimated from mineral phase equilibria for the tonagh island rocks suggesting that most of the fluid inclusions in these rocks did not undergo any marked effect of volume change and density decrease the contrasting fluid densities among the localities investigated in this study are probably related to the nature of the p t trajectory the tonagh island rocks had a near isochoric exhumation history whereas the metamorphic orogens in the other two sutures witnessed rapid decompression our results suggest that whereas the composition of the syn metamorphic fluids are preserved in all cases density reversal occurs within inclusions as a function of the tectonic history and exhumation style

fluid inclusions of the high pressure granulites from the namche barwa complex of the eastern himalayan syntaxis tibet fluid composition and evolution in the continental subduction zone abstract the namche barwa complex in the eastern himalayan syntaxis has experienced high medium pressure granulite facies and amphibolite facies metamorphism the high pressure granulites contain complex fluid inclusion assemblages including h 2 o co 2 ch 4 carbonic co 2 ch 4 n 2 co 2 solid brine medium to low salinity aqueous inclusions and low density gaseous inclusions textural evidence suggests that the isolated h 2 o co 2 ch 4 inclusions occurring in quartz blebs enclosed in garnet porphyroblasts were trapped in the peak metamorphic stage whereas isolated and trail bound co 2 inclusions along intragranular fractures in quartz plagioclase and garnet were mainly trapped during the early decompression stage of the high pressure granulites although some co 2 rich inclusions have formed by selective leakage of h 2 o out of h 2 o co 2 inclusions this together with wide variations in homogenization temperatures indicates modifications and density resetting of the fluid inclusions during exhumation in contrast to the common presence of high density co 2 fluid inclusions in granulite terrains worldwide the high pressure granulites in the namche barwa complex contain dominantly medium to low density h 2 o co 2 ch 4 and co 2 inclusions this may be explained as that the high pressure granulites occur in the continental subduction zone tectonic setting

northern iberian abrupt climate change dynamics during the last glacial cycle a view from lacustrine sediments abstract we present a palaeoclimatic reconstruction of the last glacial cycle in iberia ca 120 000 11 600 cal yrs bp based on multi proxy reconstructions from lake sediments with robust chronologies and with a particular focus on abrupt climate changes the selected lake sequences provide an integrated approach from northern iberia exploring temperature conditions humidity variations and land sea comparisons during the most relevant climate transitions of the last glacial period thus we present evidence that demonstrates i cold but relatively humid conditions during the transition from mis 5 to mis 4 which prevailed until ca 60 000 cal yrs bp in northern iberia ii a general tendency towards greater aridity during mis 4 and mis 3 ca 60 000 to 23 500 cal yrs bp punctuated by abrupt climate changes related to heinrich events he iii a complex highly variable climate during mis 2 23 500 to 14 600 cal yrs bp with the mystery interval mi 18 500 to 14 600 cal yrs bp and not the global last glacial maximum lgm 23 000 to 19 000 cal yrs bp as the coldest and most arid period the last glacial transition starts in synchrony with greenland ice records at 14 600 cal yrs bp but the temperature increase was not so abrupt in the iberian records and the highest humidity was attained during the allerod gi 1a to gi 1c and not during the bolling gi 1e period the younger dryas event gs 1 is discernible in northern iberian lake records as a cold and dry interval although iberian vegetation records present a geographically variable signal for this interval perhaps related to vegetation resilience

uht metamorphism peaking above 1100 c with slow cooling insights from pelitic granulites in the jining complex north china craton

extreme thermal metamorphism associated with gondwana assembly evidence from sapphirine bearing granulites of rajapalayam southern india

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

fluid inclusions in granulites granulitized eclogites and garnet clinopyroxenites from the dabie sulu terranes eastern china minor granulites believed to be pre triassic surrounded by abundant amphibolite facies orthogneiss occur in the same region as the well documented triassic high and ultrahigh pressure hp and uhp eclogites in the dabie sulu terranes eastern china moreover some eclogites and garnet clinopyroxenites have been metamorphosed at granulite to amphibolite facies conditions during exhumation granulitized hp eclogites garnet clinopyroxenites at huangweihe and baizhangyan record estimated eclogite facies metamorphic conditions of 775 805 c and 15 kbar followed by granulite to amphibolite facies overprint of ca 750 800 c and 6 11 kbar the presence of na ca ba sr feldspars in garnet and omphacite corresponds to amphibolite facies conditions metamorphic mineral assemblages and p t estimates for felsic granulite at huangtuling and mafic granulite at huilanshan indicate peak conditions of 850 c and 12 kbar for the granulite facies metamorphism and 700 c and 6 kbar for amphibolite facies retrograde metamorphism cordierite orthopyroxene and ferropargasite plagioclase coronas and symplectites around garnet record a strong rapid decompression possibly contemporaneous with the uplift of neighbouring hp uhp eclogites carbonic fluid co2 rich inclusions are predominant in both hp granulites and granulitized hp uhp eclogites garnet clinopyroxenites they have low densities having been reset during decompression minor amounts of ch4 and or n2 as well as carbonate are present in the granulitized hp uhp eclogites garnet clinopyroxenites early fluids are high salinity brines with minor n2 whereas low salinity fluids formed during retrogression syn granulite facies carbonic fluid inclusions occur either in quartz rods in clinopyroxene granulitized hp garnet clinopyxeronite or in quartz blebs in garnet and quartz matrices uhp eclogite for hp granulites a limited number of primary co2 and mixed h2o co2 liquid inclusions have also been observed in undeformed quartz inclusions within garnet orthopyroxene and plagioclase which contain abundant low density co2 carbonate inclusions it is suggested that the primary fluid in the hp granulites was high density co2 mixed with a significant quantity of water the water was consumed by retrograde metamorphic mineral reactions and may also have been responsible for metasomatic reactions giant myrmekites occurring at quartz feldspar boundaries compared with the uhp eclogites in this region the granulites were exhumed in the presence of massive externally derived carbonic fluids and subsequently limited low salinity aqueous fluids probably derived from the surrounding gneisses

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

zircon u pb and trace element data from rocks of the huai an complex new insights into the late paleoproterozoic collision between the eastern and western blocks of the north china craton abstract the trans north china orogen tnco is interpreted as a continent continent collisional belt along which the discrete archean eastern and western blocks amalgamated to form the basement of the north china craton the timing of its formation has not been precisely constrained yet six samples including five high grade metamorphic rocks and a pegmatite dike from the huai an complex in the northern segment of the tnco were selected for zircon u pb dating and trace element analysis a tonalite trondhjemite granodiorite ttg gneiss sample and a high pressure hp mafic granulite sample contain magmatic zircon cores yielding protolith formation ages of 2503 17 and 1964 38 ma respectively detrital zircons of magmatic origin in two metasedimentary rocks show concordant or moderately discordant u pb ages of 2683 22 to 1964 13 ma indicating that they were mainly derived from the tnco with some possibly derived from the archean continental rocks of the north china craton metamorphic zircons in the ttg gneiss and two metasedimentary rocks exhibit low hree contents flat hree patterns and negative eu anomalies implying their formation coeval with garnet and feldspar under grannulite facies conditions metamorphic zircons in an hp mafic granulite and a sample of leucosome from a ttg gneiss also have depleted hree contents flat hree patterns but only weak negative eu anomalies which may also indicate formation under granulite facies conditions whereas the weak eu anomalies may be due to the whole rock composition all these metamorphic zircons have formation temperatures of 702 749 c approaching the peak metamorphic temperatures of hp granulite rocks in this area they have identical ages of ca 1845 ma within analytical errors which is the best estimate age for hp granulite facies metamorphism of the huai an complex these results confirm previous models proposing late paleoproterozoic collision between the eastern and western blocks of the north china craton along the tnco on the other hand some metamorphic zircons in the leucosome sample show planar or polygonal zoning high th u contents and high th u ratios high ree contents and steep hree patterns indicating that they crystallized during partial melting with abundant garnet decomposition they yielded a weighted mean age of 1819 13 ma which we interpret to register the time of retrograde metamorphism combined with previously published data there are three age peaks at 1876 6 1849 2 and 1814 4 ma for metamorphic zircons from high grade metamorphic rocks in the tnco these may indicate either a protracted event or at least three peaks of metamorphism a pegmatite dike cutting the foliation of a mafic granulite boudin was dated at 1806 15 ma which signifies termination of collision between the eastern and western blocks in the huai an area

co2 rich fluid inclusions in staurolite and associated minerals in a high pressure ultrahigh temperature granulite from the gondwana suture in southern india abstract we report the first detailed fluid inclusion study on mg al rocks from the gondwana suture zone along the palghat cauvery shear zone system in southern india these rocks underwent high pressure p 12 kbar and ultrahigh temperature t 990 c metamorphism during the late neoproterozoic associated with the collisional assembly of the gondwana supercontinent fluid inclusions of texturally primary and pseudosecondary categories occur in plagioclase staurolite and kyanite in these rocks inclusions of secondary nature are found in garnet and apatite all the trapped fluids show melting temperatures in the range of 58 6 to 56 6 c suggesting a dominantly pure co 2 composition the secondary inclusions show high homogenization temperatures t h of 12 9 to 30 0 c indicating low density of 0 59 0 83 g cm 3 although most of the primary and pseudosecondary inclusions also contain moderate to low density fluids 0 67 0 95 g cm 3 t h 3 5 to 27 4 c rare high density inclusions 1 00 1 06 g cm 3 t h 26 1 to 14 1 c were discovered in matrix plagioclase and porphyroblastic staurolite the estimated co 2 isochores for the high density primary and pseudosecondary inclusions intersect the clockwise p t trajectory of the rocks at around 8 3 9 0 kbar at 1000 c which broadly coincide with the peak metamorphic conditions of the area since these fluid inclusions show textural evidence for entrapment during the growth of the host high grade minerals we interpret the high density co 2 fluids to be traces of a co 2 rich synmetamorphic fluid that was present during the peak ultrahigh temperature metamorphism despite the preservation of high density co 2 inclusions in staurolite and plagioclase the primary and pseudosecondary inclusions in most of the other minerals show wide density variation which suggests the fluids in these inclusions underwent significant density reversal density decrease during decompression of the rocks from high pressure through the peak ultrahigh temperature stage along a clockwise p t trajectory the finding of pure co 2 inclusions in these mg al granulites conforms with similar observations from many other granulite facies terrains with the carbonic fluids probably derived from mantle reservoirs and transferred through deep seated shear zones that characterize this gondwana suture

la icp ms u pb zircon ages of the qianlishan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the qianlishan complex is located in the westernmost part of the khondalite belt a continent continent collisional belt along which the yinshan block in the north and the ordos block in the south amalgamated to form the western block which then collided with the eastern block along the trans north china orogen to form the north china craton the complex is dominated by high grade supracrustal rocks and minor s type granites of which the supracrustals consist of graphite bearing sillimanite garnet gneiss garnet quartzite felsic paragneiss calc silicate rock and marble cl images reveal the existence of detrital and metamorphic zircons in major rocks of the qianlishan complex in most cases detrital zircons occur as either single grains with oscillatory zoning or oscillatory zoning cores typical of igneous origin which are surrounded by metamorphic overgrowth rims that are structureless high bright and low in th u ratio detrital zircons from the qianlishan complex yield nearly concordant 207 pb 206 pb ages ranging from 2 3 to 2 0 ga suggesting that the protoliths of the high grade supracrustal rocks in the qianlishan complex were deposited at some time after 2 0 ga metamorphic zircons yield two age populations with one at 1 95 ga and another at 1 92 ga of which the former is interpreted as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the later is considered to be the age of subsequent post orogenic extensional event minor s type granites were emplaced at 1 88 ga as a result of partial melting of supracrustals at the stage of the exhumation of the qianlishan complex these new zircon ages combined with structural and metamorphic considerations enable resolution of the tectonothermal events involving the collision between the yinshan and ordos blocks to form the western block followed by the post collisional extension and subsequent exhumation of the khondalite belt

mesozoic crust mantle interaction beneath the north china craton a consequence of the dispersal of gondwanaland and accretion of asia we present evidence from zircons entrained within lower crustal xenoliths in the cenozoic hannuoba basalt of multiple melting events beneath the north china craton in the late mesozoic peak activity was between 180 and 80 ma the upper crustal signature of which was the generation of voluminous granitoids and related volcanic rocks emplacement of dioritic and lamprophyric dikes and widespread gold mineralization the process involved partial loss of mantle lithosphere accompanied by wholesale rising of asthenospheric mantle beneath eastern china we correlate these events with lithospheric thinning resulting from the breakup and dispersal of gondwanaland accompanied by a major mantle overturn fueled by the destruction of oceanic lithosphere and triggered by its sinking into the lower mantle during the subsequent accretion of asia

destruction of the eastern north china craton in a backarc setting evidence from crustal deformation kinematics abstract the eastern north china craton ncc west of the pacific ocean has a long history of rifting from early cretaceous to the end of paleogene when the craton experienced destruction and significant thinning of the lithosphere the cause and geotectonic environment for this destruction remain controversial we use a set of field observation including basin patterns fault geometry and kinematics fault plane slip data dike distribution and fabric data from metamorphic core complexes to determine the kinematic evolution of the deformation in the eastern ncc during this period we show that the principal extension direction in the eastern ncc evolved from wnw ese in the earliest middle early cretaceous via nw se in the latest early cretaceous to nearly n s in the late cretaceous paleogene the movement history from late mesozoic to early cenozoic of the oceanic plates in the pacific ocean with respect to the eastern ncc is available from previous studies the izanagi plate first subducted nearly orthogonally wnw wards during earliest middle early cretaceous time and then moved obliquely nnw wards in the latest early cretaceous while the relaying pacific plate moved generally northwards from the late cretaceous to paleogene both the movement direction of oceanic plates and the principal extension direction of the continental deformation rotated clockwise we suggest that such a correlation can be explained by the eastern ncc being in a backarc setting in the cretaceous paleogene period the results support the backarc extensional model for the destruction and significant lithospheric thinning of the eastern ncc

fluid inclusion studies on the koraput alkaline complex eastern ghats province india implications for mid neoproterozoic granulite facies metamorphism and exhumation abstract following ultrahigh temperature granulite metamorphism at 1 ga the eastern ghats province of india was intruded by the koraput alkaline complex and was subsequently re metamorphosed in the granulite facies in the mid neoproterozoic time fluid inclusion studies were conducted on silica undersaturated alkali gabbro and syenites in the complex and a pre metamorphic pegmatitic granite dyke that intrudes it high density 1 02 1 05 g cc pseudo secondary pure co2 inclusions are restricted to metamorphic garnets within the gabbro and quartz within the granite whereas moderate 0 92 0 95 g cc and low density 0 75 g cc secondary inclusions occur in garnet magmatic clinopyroxene plagioclase hornblende and quartz the isochores calculated for high density pseudo secondary inclusions pass very close to the peak metamorphic window 8 kbar 750 c and are interpreted to represent the fluid present during peak metamorphism that was entrapped by the growing garnet microscopic round inclusions of undigested relict calcite in garnet suggest that the co2 present during metamorphism of the complex was internally derived through carbonate breakdown pure to low salinity 0 00 10 1 wt nacl equivalent aqueous intra intergranular inclusions showing unimodal normal distribution of final ice melting temperature tm and temperature of homogenization th are present only in quartz within the granite these represent re equilibrated inclusions within the quartz host that were entrapped at the metamorphic peak rare chemically precipitated graphite along the walls of carbonic inclusions is interpreted as a post entrapment reaction product formed during decompression the fluid inclusion evidence is consistent with rapid exhumation of a thickened lower crust following the mid neoproterozoic granulite facies metamorphic event the study suggests that mantle co2 transported by alkaline magma into the crust was locked up within carbonates and released during granulite metamorphism

carbonic fluid inclusions in granulites from tanzania a comparison of geobarometric methods based on fluid density and mineral chemistry abstract high density carbonic fluid inclusions with well developed negative crystal shape occur in host quartz plagioclase and garnet in intermediate to high pressure granulites from the furua granulite complex southern tanzania they are most abundant in intercalated metapelitic units detailed microthermometric data on inclusions in combination with electron microprobe analyses of associated solid phases are presented for a kyanite bearing garnet granulite and a garnet two pyroxene granulite both selected from the same locality the inclusions contain virtually pure co2 and are believed to be of primary syngenetic origin this is indicated by their distribution in the host minerals and by the homogenization temperatures which give well defined single maxima between 30 and 50 c the corresponding fluid pressures are only 1 3 kbar lower than the pressure range of 10 13 kbar that is inferred from the solid phase geobarometers based on element partitioning in garnet kyanite plagioclase and orthopyroxene clinopyroxene garnet plagioclase assemblages associated temperature estimates of 770 870 c are based on the compositions of garnet biotite garnet clinopyroxene and orthopyroxene clinopyroxene pairs although the co2 density data fit within the regional pressure regime of 7 12 kbar for the metamorphism in the furua area the detailed comparison with solid phase geobarometers at the scale of a single outcrop reveals a small underestimate of pressure which may be explained by minor adjustment of the inclusions after peak metamorphism or by partial h2o pressures in the order of 0 1ptot to 0 2ptot

high density early co2 fluids in the ultrahigh temperature granulites of ihouhaouene in ouzzal algeria abstract fluid inclusion studies in rocks from the lower proterozoic granulites from western hoggar algeria provide new evidence for the hypothesis that a co 2 rich h 2 o poor fluid was present during the high grade metamorphism co 2 inclusions represent the main fluid trapped in the ihouhaouene ultrahigh temperature over 1000 c and high pressure 10 to 14 kbar granulites the microthermometric and raman microspectrometric measurements indicate that the carbonic fluid is mainly composed of co 2 with minor amounts of ch 4 and n 2 detected in some inclusions 4 carbonic fluid densities range from 1 18 to 0 57 g cm 3 the highest densities are recorded in superdense carbonic inclusions presenting evidence of the earliest trapping and they correspond to the fluid densities expected for the p t conditions of the peak of metamorphism in the area previously determined from mineral geothermobarometers lower densities of carbonic fluids mainly result from the reequilibration of earlier trapped fluid inclusions during retrograde metamorphism and final uplift of the metamorphic terrane but a new influx of carbonic fluids during the retrograde event remains possible carbonic fluids can be produced in situ from decarbonation reactions in interlayered impure marbles during the prograde event or derived from co 2 flushing from underlying basic intrusions the aqueous fluids present large variations of composition 0 5 to 30 wt nacl equivalent and densities 1 16 to 0 57 g cm 3 they clearly correspond to post metamorphic fluids because they mainly occur along microfractures they do not show any evidence of immiscibility with the carbonic fluids and mixed aquo carbonic inclusions have not been observed the percolation of aqueous fluids is related to the pan african tectonometamorphic event

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

petrography and zircon u pb isotopic study of the bayanwulashan complex constrains on the paleoproterozoic evolution of the alxa block westernmost north china craton abstract the bayanwulashan metamorphic complex bmc exposes along the eastern margin of the alxa block the westernmost part of the north china craton ncc bmc is principally composed of metamorphic rocks with amphibole plagiogneiss biotite plagioclase gneiss and granitic gneiss our research has been focused on the petrography and zircon u pb geochronology of the bmc to better understand the evolution of the alxa block and its relationship with the ncc evidences from field geology petrography and mineral chemistry indicate that two distinct metamorphic assemblages the amphibolite and greenschist facies had overprinted the preexisting granitic gneiss and suggest that the bmc experienced retrograde metamorphic episodes the la icp ms zircon u pb ages reveal that the primary magmatic activities of bmc were at ca 2 30 2 24 ga and the two metamorphic events were at ca 1 95 1 91 ga and ca 1 88 1 85 ga respectively these ages indicate that bmc initially intruded during paleoproterozoic not as previously suggested at archean period the early paleoproterozoic metamorphic records and the magmatic thermochronological data in bmc exhibit different evolution paths between the alxa block and the ncc the alxa block was most likely an independent early paleoproterozoic terrain following different amalgamation processes the alxa block combined with western block at ca 1 95 ga and then united with ncc at ca 1 85 ga

carbonic metamorphism of charnockites in the southwestern indian shield a fluid inclusion study abstract forming the southwestern segment of the precambrian granulite facies terrain of the indian shield the kerala region largely comprises charnockites khondalites and migmatitic gneisses fluid inclusions in quartz from the charnockites show distinct distribution patterns consistent with three generations of inclusions the early monophase type records entrapment of high density co2 rich fluid 0 95 1 0 g cm 3 a subsequent monophase type with lower density co2 rich fluid 0 65 0 75 g cm 3 coexists with co2 h2o inclusions having an average degree of filling of 0 2 h2o 20 co2 80 late aqueous biphase inclusions show coexistence with a second category of co2 h2o inclusions showing a degree of filling of 0 6 h2o 60 co2 40 the co2 isochores for early carbonic inclusions yield a pressure range of 4 6 6 1 kbar at granulite facies temperatures of 650 800 c depicting the entrapment of fluids present during or close to the peak metamorphic stage a definite sequence of fluid evolution is traceable for the subsequent stages thus the coexisting co2 and co2 h2o inclusions were entrapped at 510 c and 2 2 kbar marking the waning of carbonic regime and the beginning of aqueous regime at 330 c and 0 4 kbar fluid unmixing occurred leading to the simultaneous entrapment of mixed co2 h2o and h2o inclusions along rehealed microfractures the data presented indicate that the metamorphic fluids evolved from early high density carbonic through mixed carbonic aqueous to late aqueous types the dry granulite mineral assemblage of charnockites is a result of metamorphic equilibration under water deficient and high pco2 conditions

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

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

ree geochemistry of carbonates from the guanmenshan formation liaohe group ne sino korean craton implications for seawater compositional change during the great oxidation event abstract the worldwide 2 33 2 06 ga positive 13 c carb excursion has been correlated with the great oxidation event goe and termed as the lomagundi event the 2 3 1 85 ga guanmenshan formation in the liaohe group of the northeastern sino korean craton is characterized by positive 13 c carb excursion and is a potential candidate to evaluate the lomagundi event using rey rare earth element and yttrium ree y chemical fingerprints here we present major and trace element analysis of 42 samples from the guanmenshan formation which are pure marine chemical sediments and use the data to trace the seawater composition during 2 3 1 85 ga 15 least altered dolomicrite samples 600 m strata have ree values of 0 739 4 175 ppm 2 414 1 184 ppm and the y ho ratios of 34 5 56 6 44 1 5 7 they show uniform positive la sn la sn 1 04 0 27 and gd sn gd sn 1 64 0 40 anomalies and notable lree depletions indicated by nd sn yb sn values of 0 24 0 92 average 0 56 0 19 these features are consistent with the geochemistry of well oxygenated shallow ambient seawater and suggest that these samples provide a robust record of the primary rey signature of seawater during the lomagundi event the rey patterns of 15 silicified dolomites marbles locally with veinlets from the pb zn mining camps in the region with average eu cn eu cn 1 56 0 95 are identical to those of high temperature hydrothermal fluids 250 c characterized by a flat pattern and marked positive eu anomalies indicating that these rocks were subjected to metasomatism by hydrothermal fluids the guanmenshan formation shows average ce sn ce sn of 0 93 0 09 and sm cn yb cn of 1 which are higher than those of the archean 2 33 ga chemical sediments generally f o 2 and p co 2 the rey in the dolomicrite were mainly sourced from fluxes of solutes from terrestrial weathering and also from seafloor hydrothermal processes on a subordinate scale the guanmenshan dolomicrites have eu sn eu sn values of 1 34 2 55 i e around 1 53 indicating that they were deposited during 2 33 2 06 ga as the eu sn eu sn 1 53 can be used as a proxy for the 2 33 2 06 ga marine chemical sediments our study shows that the guanmenshan formation was formed at a critical turning point in earth history when the global atmosphere hydrosphere system witnessed a dramatic change from reducing to oxidizing conditions

possible southwestward extrusion of the ordos block in the late paleoproterozoic constraints from kinematic and geochronologic analysis of peripheral ductile shear zones abstract the paleoproterozoic is a pivotal period of the tectonic evolution of the north china craton ncc various models have been postulated by previous researchers through the study of petrology and metamorphism but the lack of structural analyses has hampered further understanding of the tectonic evolution of the ncc a series of well exposed ductile shear zones developed on the northern northwestern and eastern edges of the ordos block in the western part of the ncc we carried out detailed field studies along with isotopic dating focused on the kinematics and geochronology of the ductile shear zones on the north margin of the ordos block the wulashan daqingshan ductile shear zone is characterized by an e w trending shearing foliation that steeply dips 75 80 to the north or south with subhorizontal stretching lineation plunging 10 15 toward the east or west and dextral strike slip shearing kinematics on the west margin of the ordos block is the zongbieli ductile shear zone with top to the nw thrusting kinematics on the east margin of the ordos block is the xueling ductile shear zone with top to the se thrusting accompanied by sinistral strike slip shearing kinematics the 40ar 39ar ages of deformed minerals from mylonitic high grade metamorphic rocks and la icp ms u pb dating results of zircons from syn tectonic anatectic granites reflect that the ductile shear zones surrounding the ordos block deformed between 1 85 and 1 81 ga the similar deformation ages indicate that the ductile shear zones might be genetically correlated the geometry kinematics and geochronology characteristics of the wulashan daqingshan ductile shear zone on the north margin the zongbieli ductile shear zone on the west margin and the xueling ductile shear zone combined with the zhujiafang sinistral ductile shear zone on the east margin defined the possible southwestward extrusion of the ordos block in the late paleoproterozoic which might have resulted from the westward subduction collision of the eastern block under the western block at approximately 1 85 ga and which is correlated with the amalgamation of the columbia supercontinent

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

multiphase inclusions in peritectic garnet from granulites of the athabasca granulite terrane canada evidence of carbon recycling during neoarchean crustal melting abstract in the last decade the study of fluid and melt inclusions in partially melted rocks has become a key tool to acquire unprecedented information about crustal anatectic processes in this study we report the results of the microstructural and microchemical investigation on multiphase inclusions trapped within peritectic garnet of a neoarchean felsic granulite from the upper deck domain of the athabasca granulite terrane canada inclusions have been studied by sem eds fib sem serial sectioning and raman microspectroscopy and classified in terms of size and hosted phases type i multiphase inclusions are small 15 m primary in origin and do not show evidence of decrepitation their multiphase assemblage is made of ferroan magnesite quartz and graphite in association with minor amounts of corundum pyrophyllite and zn spinel calcite dolomite and zinc bearing sulphide may also be present the coexistence of quartz and corundum in these inclusions is interpreted as the product of metastable growth within pores of extremely small size the fluid phase of type i inclusions always present in amounts 40 vol is co2 rich 96 5 mol with traces of n2 3 3 mol and ch4 0 2 mol these carbon rich type i inclusions coexist in the same cluster with primary melt inclusions nanogranitoids type ii these are large up to 50 m and composed of k feldspar quartz and plagioclase with minor amounts of graphite biotite and aluminosilicate because nanogranitoids are droplets of anatectic silicate melt formed and trapped during incongruent melting of crustal rocks the coexistence of type i multiphase inclusions proves the presence of a carbon rich fluid during the neoarchean anatexis 800 950 c 0 6 1 4 gpa of this portion of continental crust in a likely situation of melt fluid immiscibility according to phase equilibria modelling the uncommon multiphase assemblage within type i inclusions is here interpreted as the result of a post entrapment carbonation reaction between an original co2 bearing fluid and the garnet host during rock cooling from uht conditions

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

fluid characteristics of high to ultrahigh temperature metamorphism in southern india a quantitative raman spectroscopic study abstract we report the first quantitative compositional data on fluid inclusions in late neoproterozoic to cambrian ultrahigh temperature uht granulites from major crustal blocks and shear zones in southern india fluid inclusions in various high grade minerals such as garnet orthopyroxene plagioclase cordierite and quartz from these rocks were studied in terms of petrography microthermometry and laser raman spectroscopy measured melting temperatures of the inclusions indicate that the trapped fluid phase is dominantly carbonic raman analyses confirmed a co2 rich composition with only minor dilutants such as n2 5 0 mol h2o 0 50 mol and ch4 0 47 mol the range of most co2 isochores computed from density measurements in fluid inclusions from the uht granulites pass below the peak pressure temperature conditions of metamorphism indicating considerable resetting of fluid densities during decompression in contrast garnetiferous granulites from the salem area along the palghat cauvery shear zone system which underwent high pressure prograde metamorphism contain very high density syn metamorphic pure co2 inclusions such dense carbonic fluid inclusions in garnet and plagioclase coexist with carbonate minerals calcite or dolomite indicating probable derivation from deep seated primary magmatic sources although models on the origin of co2 are debatable the ubiquitous association of carbonic fluids in the uht mineral assemblages is in favour of large scale infiltration of co2 rich fluids during extreme crustal metamorphism associated with collisional orogeny and subsequent extensional collapse at the final stage of amalgamation of the gondwana supercontinent

paleoproterozoic granulites from the xinghe graphite mine north china craton geology zircon u pb geochronology and implications for the timing of deformation mineralization and metamorphism abstract the xinghe graphite deposit is located in the north central part of the north china craton ncc where archean gray gneiss metasedimentary rocks khondalites and mafic high pressure granulites constitute the dominant rock types in this study we report results of detailed geological and structural mapping around the xinghe graphite mine we identify three stages of deformation d 1 d 3 and the graphite mineralization is correlated with d 1 or between d 1 and d 2 the first stage of deformation represented by rootless intrafolial folds whose axial surface cuts across the regional penetrative gneissosity s 2 of d 2 was constrained at ca 1 95 1 90 ga by u pb age of zircon grains from a mafic high pressure granulite the second stage of deformation is represented by tight folds with formation of regional penetrative foliation and strong ductile shearing when garnet broke down to plagioclase pyroxene this stage is dated as ca 1 85 ga from u pb analysis of zircons in leucosome from a migmatitic gneiss the third stage of deformation is represented by large scale folding which probably formed between 1 85 and 1 80 ga as constrained from the ca 1 80 ga emplacement age of an undeformed pegmatite that cuts across the host metasediments prior to the high pressure granulite metamorphism voluminous ca 2 15 2 0 ga granites were emplaced within the khondalites the graphitization postdates the emplacement of these granites as deduced from the presence of flaky graphites in the metagranites the protolith of the mafic high pressure granulite dike that intruded the khondalite at ca 2 0 ga was also metamorphosed at 1 95 1 90 ga and is part of the exploited graphite ore body we therefore constrain the timing of graphite mineralization to be between ca 1 95 and 1 85 ga our geological and geochronological data indicate that all the rock units in the xinghe graphite mine were subjected to high pressure granulite facies metamorphism at ca 1 95 1 90 ga

he ar s pb and o isotope geochemistry of the dabaiyang gold deposit implications for the relationship between gold metallogeny and destruction of the north china craton abstract the dabaiyang gold deposit is located within the zhang xuan gold mineralized zone along the northern margin of the north china craton ncc the ore mineralization is hosted within precambrian metamorphic rocks and is a typical quartz vein type gold deposit with minor sulfide mineralization here we report he ar s pb and o isotopes from this deposit with a view to trace the source of the ore forming fluids and metals and to evaluate the relationship among ore formation magmatism and craton destruction in the ncc the ratios of 3he 4he and 40ar 36ar of the fluid inclusions in the pyrite of the dabaiyang ores show a range of 1 4ra 1 8ra and 4974 4 15669 5 respectively with the concentrations of 4he and 40ar varying from 0 8 to 6 6 10 7 cm3 stp g and 4 3 to 218 1 10 7 cm3 stp g respectively our data suggest that mixed mantle and crust derived fluids were involved in the dabaiyang gold mineralization with ca 17 1 27 6 mantle derived helium as computed from crust mantle mixing model the 34s values in the pyrite range from 10 40 to 11 90 with an average of 10 96 suggesting that the sulfur in the ore forming fluids was derived from a mixed source of the precambrian metamorphic basement and mantle the pb isotopic ratios in the pyrite from the ores show 206pb 204pb 207pb 204pb and 208pb 204pb in the range of 16 82 to 17 16 15 33 to 15 43 and 36 77 to 37 22 respectively indicating that the ore forming fluids and by inference the ore metals were mainly derived from lower continental crust with minor contribution of mantle the 18oh2o values of the fluid inclusions in the gold bearing quartz veins range from 1 04 to 4 36 suggesting the dominant role of magmatic water with minor contribution of meteoric water in the ore precipitation based on the analytical results of the isotopic compositions obtained in this study combined with the previously published geochronological and he ar s pb o isotopic data we suggest that the ore fluids and metals were derived from a mixed source involving contributions from mantle crust and atmospheric water and that the ore formation was associated with destruction of the north china craton

asynchroneity of maximum glacier advances in the central spanish pyrenees the deglaciation history of the escarra and lana mayor glaciers upper gallego valley central spanish pyrenees had been reconstructed on the basis of detailed geomorphological studies of glacier deposits sedimentological and palynological analyses of glacial lake sediments and an accelerator mass spectrometry ams 14c chronology based on minimum ages from glacial lake deposits the maximum extent of the pyrenean glaciers during the last glaciation was before 30 000 yr bp and pre dated the maximum advances of the scandinavian ice sheet and some alpine glaciers a later advance occurred during the coldest period around 20 000 yr bp synchronous with the maximum global ice extent but in the pyrenees it was less extensive than the previous one later there were minor advances followed by a stage of debris covered glaciers and a phase of moraine formation near cirque backwalls the deglaciation chronology of the upper gallego valley provides more examples of the general asynchroneity between mountain and continental glaciers the asynchroneity of maximum advances may be explained by different regional responses to climatic forcing and by the southern latitude of the pyrenees copyright 2002 john wiley sons ltd

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

fossil oceanic subduction zone beneath the western margin of the trans north china orogen magnetotelluric evidence from the luliang complex abstract the trans north china orogen tnco is a major collisional belt along which the western and eastern blocks of the north china craton were amalgamated through subduction accretion collision tectonics during paleoproterozoic the luliang complex along the western margin of the tnco is thought to be the trace of an ancient suture zone here we employ magnetotelluric array to build a lithosphere scale high resolution 3 d resistivity model for this region between 36 n and 38 n e w trending slices of the resistivity model show relatively high conductivity 10 100 m lithospheric mantle of the western block that extends eastward beneath the relatively high resistivity lithosphere of the tnco at depths from 80 to 180 km we interpret this east dipping upper mantle conductivity contrast as the lithosphere scale suture between the western block and tnco that formed through eastward subduction the enhanced conductivity of the fossil oceanic subduction zone might be a reflection of the reduction in grain size of olivine grains in mantle peridotite by the localized shearing stress associated with the subduction combined with the interconnecting high conductivity minerals along grain boundaries formed through metasomatism by slab derived fluids similar subduction related boundaries are absent in the resistivity models beneath the northern luliang complex near 39 n where prominent high conductivity anomalies indicating asthenosphere upwelling and lower crustal underplating are seen such mantle architecture could result from the subduction of an oceanic ridge or slab window as also proposed for the origin of the subduction related luyashan charnockite suite in this region our data also suggest that the phanerozoic tectonic and magmatic events in this region only locally modified the precambrian lithospheric tectonic framework without total destruction we propose a 3 d model to illustrate the contrasting paleoproterozoic tectonic evolution between the northern and southern domains of the luliang complex and the tnco during the transition stage between the termination of oceanic subduction and the subsequent continental collision

precambrian geology of china preface abstract the north china south china and tarim cratons compose the tectonic framework of china in the last decade extensive structural metamorphic geochemical geochronological and geophysical investigations have been carried out on these cratonic blocks producing an abundant amount of new data and competing interpretations which have resulted in refinement of and in some cases significant reinterpretations of the precambrian crustal formation and evolution of china this forms a justification for organizing this special issue in which we invited representative experts working in the north china south china and tarim cratons to present overviews or detailed studies on the formation and tectonic evolution of major precambrian blocks in china twenty four contributions collected in this special issue provide current knowledge of the components and tectonic evolution of major precambrian blocks in china and discuss some key issues based on new data and interpretations which will provide important insights into understanding the precambrian geology of china

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

the paleoproterozoic north hebei orogen north china craton s collisional suture with the columbia supercontinent abstract understanding the geologic history and position of the north china craton in the paleoproterozoic columbia supercontinent has proven elusive paleoproterozoic orogenic episodes 2 00 1 85 ga are temporally associated with ultimate stabilization of the north china craton ncc followed by the development of extensive craton wide rift systems at 1 85 1 80 ga the age difference between the sedimentary cover and the metamorphic basement is up to 500 700 ma suggesting that uplift and doming of cratonic basement occurred in the latest paleoproterozoic mafic dike swarms 1 80 1 77 ga and anorogenic magmatism 1 80 1 70 ga record the extensional breakup and dispersal of the north china craton during this stage the late paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the ncc within the late paleoproterozoic supercontinent of columbia an east west striking thousand kilometer long belt of khondalites granulite facies metapelites stretches along the northern margin of the north china craton on the cratonward side of the northern hebei orogenic belt this granulite belt includes mg al sapphirine bearing granulites that reached ultrahigh temperature peak metamorphic conditions of 1000 c at 10 kbars at 1927 11 ma following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and these trajectories are interpreted to be part of an overall anti clockwise p t evolution indicating that the northern margin of the craton experienced continental collision at 1 93 1 92 ga the position of the khondalite belt south of the northern hebei orogenic belt makes it analogous to tibet a continental collision related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth we suggest that the tectonic evolution of the ncc during this period was closely related to the assembly and break up of the columbia supercontinent and that the ncc was adjacent to the baltic and amazonian cratons in the period 2 00 1 70 ga craton wide extension occurred within 100 150 ma of collision along the northern margin of the craton at 1 93 1 92 ga it is concluded that mantle upwellings are chiefly responsible for the breakup of the ncc from the paleoproterozoic supercontinent

arrested charnockite formation in southern india and sri lanka arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high grade terrains of southern india and sri lanka two major kinds of orthopyroxene producing reactions are recognized breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic granitic gray gneiss produced the regional orthopyroxene isograd manifest in charnockitic mottling and veining of mixed facies exposures as at kabbal karnataka and in the kurunegala district of the sri lanka central highlands chemical and modal analyses of carefully chosen immediately adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of cao mgo and feo and gains of sio2 and na2o rb and y are depleted in the charnockite another kind of charnockitization is found in paragneisses throughout the southern high grade area and involves the reaction of biotite and quartz garnet to produce orthopyroxene and k feldspar although charnockite formation along shears and other deformation zones at such localities as ponmudi kerala is highly reminiscent of kabbal close pair analyses are not as suggestive of open system behavior this type of charnockite formation is found in granulite facies areas where no prograde amphibole bearing gneisses exist and connotes a higher grade reaction than that of the orthopyroxene isograd metamorphic conditions of both kabbaltype and ponmudi type localities were 700 800 c and 5 6 kbar lower p h2o in the ponmudi type metamorphism was probably the definitive factor

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

high density carbonic fluids in a slab window evidence from the gangdese charnockite lhasa terrane southern tibet abstract charnockites occurring in the well studied gangdese batholith in the southern lhasa terrane eastern himalayan orogen consist of orthopyroxene clinopyroxene plagioclase and minor quartz and k feldspar and show adakitic affinity here we present a systematic study on the fluid inclusions in gangdese charnockites which reveals that the primary fluid inclusions occur isolated or randomly distributed and as trails along intragranular fractures in quartz and that the secondary ones occur along healed mircofractures and coexist commonly with mineral inclusions of calcite magnetite and hematite within the host plagioclase and quartz the fluid inclusions contain dominantly near pure co 2 with traces of n 2 most of the primary fluid inclusions have low co 2 homogenization temperatures and with densities of 1 138 1 013 g cm 3 suggesting trapping pressures of 0 7 1 0 gpa at temperatures of 850 950 c we propose a model in which the southward subduction of neo tethyan mid oceanic ridge beneath the lhasa terrane resulted in the release of heat and co 2 from the upwelling asthenosphere through a slab window providing high temperatures ht and dry co 2 rich fluids for the formation and stabilization of the adakitic charnockite as well as the associated ht granulite facies metamorphic rocks in the late cretaceous prior to the final collision of the indian plate with the asian continent our study provides new insights into the geodynamics of andean type orogeny in the southern tibetan plateau during the late mesozoic

metamorphic fluids in the deep crust most of the inferences about fluid action in the deep crust are drawn from field petrographic and geochemical studies in the granulite facies terrains deductions on the nature of fluids are made from major and minor element distributions and isotopic patterns in metamorphic rocks calculations of fluid mineral equilibria based on observed assemblages fluid inclusions and field evidence of fluid pathways discussion of these features has focused attention on several major problems concerning the timing flow mechanisms and origin of the fluids a key issue concerns episodicity versus secular activity of fluids there are strong arguments that most fluid action in the deep crust is linked to thermal deformational events including magmatism and regional meta morphism discrete radiometric ages of high grade terrains often define relatively short periods of crystallization or recrystallization the late archean granulite facies metamorphism of southern india is an example where u pb systems of zircons buhl et al 1983 whole rock u pb data peucat et al 1 987 and sm nd systems of whole rocks and minerals bernard griffiths et al 1 987 all show a major high temperature recrys tallization event inferred by several workers to have involved pervasive fluid action centered closely around 2 5 ga another geochemical indi cation of episodic fluids comes from stable isotope studies of progressive metamorphic sequences as in the damara orogen namibia where whole rock b 180 increases slightly at isograds representing arrested dehydration events but is monotonous between isograds hoernes hoffer 1 985

geothermobarometry and fluid inclusions of dioritic rocks in bangladesh implications for emplacement depth and exhumation rate abstract application of hornblende thermobarometry and fluid inclusion studies to the palaeoproterozoic 1 7 ga basement rocks from maddhapara nw bangladesh provide information on the pressure and temperature p t conditions of crystallization the emplacement depth and composition of magmatic fluid the basement rocks are predominantly diorite or quartz diorite with a mineral assemblage of plagioclase hornblende biotite quartz k feldspar titanite and secondary epidote and chlorite the calculated p t conditions of the dioritic rocks are 680 725 c and 4 9 6 4 kbar which probably correspond to crystallization conditions fluid inclusion studies suggest that low to medium salinity 0 6 4 wt nacl eq h 2 o rich fluids are trapped during the crystallization of quartz and plagioclase the isochore range calculated for primary aqueous inclusions is consistent with the p t condition obtained by geothermobarometry the basement rocks likely crystallized at a depth of 17 22 km with a minimum average exhumation rate of 12 15 m ma during palaeoproterozoic to lopingian time such slow exhumation indicates low relief continental shield surface during this period

can we extract ultrahigh temperature conditions from fe rich metapelites an example from the khondalite belt north china craton abstract in this study garnet sillimanite gneisses at hongshaba in the eastern segment of the khondalite belt north china craton ncc are interpreted to have experienced ultrahigh temperature uht metamorphism 980 1040 c followed by post tmax cooling at pressures of 8 9 kbar to the solidus 810 830 c consistent with rare sapphirine bearing assemblages in surrounding regions this interpretation is mainly based on the combination of p t fields and garnet xgr ca ca mg fe2 isopleths on the pseudosection of three garnet sillimanite gneiss samples spinel tends to be enclosed in the outer margins of garnet commonly closely associated with quartz we interpret this to reflect the partial break down of garnet along the prograde path during heating with decompression followed by new garnet growth during cooling along an overall clockwise p t evolution although fe rich uht metapelites tend to contain neither diagnostic mineral assemblages nor orthopyroxene from which to extract t via al in orthopyroxene thermometry isopleths of ca in garnet may aid in retrieving uht conditions from these compositions this is attributed to ca diffusion in garnet being much slower than fe and mg diffusion leading to little change in ca contents during post tmax cooling la icp ms u pb dating of metamorphic zircon in one garnet sillimanite gneiss sample yields a mean 207pb 206pb age of ca 1 91 ga which is interpreted to record the timing of cooling of the uht rocks to the solidus this uht metamorphism is interpreted to have been generated by mantle derived magma during a tectonic extension from ca 1 95 to 1 92 ga within a post orogenic setting

on the formation of granulites the tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure temperature time p t time paths and constrained by petrological and geophysical considerations p t conditions deduced for regional granulites require transient average geothermal gradients of greater than 35 c km 1 implying minimum heat flow in excess of 100 mwm 2 such high heat flow is probably caused by magmatic heating tectonic settings wherein such conditions are found include convergent plate margins continental rifts hot spots and at the margins of large deep seated batholiths however particular p t time paths do not allow specific tectonic settings to be distinguished at this time under different conditions both clockwise cw pmax attained before tmax and anticlockwise acw pmax attained slightly after tmax paths are possible in the same tectonic setting both cw and acw end member paths can yield nearly isobaric cooling ibc paths such cooling paths are clearly not an artefact of thermobarometry but can be constrained by solid solid and devolatilization equilibria and geophysical modelling in terms of understanding the evolution of the deep crust a potentially significant group of regional granulite terranes are those that show evidence for acw ibc paths such paths are the likely result of i episodic igneous activity resulting in intrusions within all levels of the crust ii thickening of the crust by magmatic underplating iii slow uplift as a result of the formation of a deep garnet rich crustal root and iv excavation resulting from a later tectonic event unrelated to that resulting in the formation of the granulites the later event might be triggered by the delamination of the garnet rich lowermost crust

very high density co2 associated with ultrahigh temperature metamorphism in the eastern ghats granulite belt india spinel bearing high mg al granulites of the vizianagram area in the eastern ghats granulite belt show textural features clearly establishing that the association spinel ss quartz fe ti oxide solid solution sillimanite porphyroblastic orthopyroxene was stable during peak metamorphic conditions pressure temperature p t conditions estimated from both mineralogical thermobarometry and phase equilibrium limitations indicate that the peak metamorphism occurred under ultrahigh t conditions 1000 c at 8 9 kbar pressure retrograde p t conditions of 750 800 c 6 7 kbar are deduced from the compositions of coronal garnet and orthopyroxene which have rims of spinel against quartz indicating significant cooling with slight lowering of pressure quartz associated with the ultrahigh t assemblage at vizianagram contains ubiquitous single phase carbonic inclusions as isolated clusters that belong to two categories group i shows extremely high density homogenization temperature 51 1 8 c density 1 15 g cm 3 and group ii trapped relatively lower density fluids homogenization temperature 18 4 2 4 c density 1 05 g cm 3 the iso chores for group i inclusions pass through the peak metamorphic p t conditions whereas those for group ii coincide with the p t conditions of the formation of coronal garnet and orthopyroxene our study is the first report of very high density co 2 associated with the eastern ghats granulite belt rocks and provides a strong case for the presence of co 2 rich fluids during ultrahigh t metamorphism at lower crustal levels

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

a petrologic and fluid inclusion study of charnockites from the lutzow holm bay region east antarctica evidence for fluid rich metamorphism in the lower crust abstract the proterozoic terrain of lutzow holm bay in east antarctica comprises an amphibolite to granulite facies progression from north to south exposing an oblique section of the lower crust the granulite terrain is represented dominantly by orthopyroxene bearing anhydrous granulites charnockites garnet and biotite bearing gneisses leptynites and garnet sillimanite and graphite bearing aluminous metapelites khondalites thus it is petrographically identical with its gondwanian counterparts in sri lanka and southern india charnockite formation is characterized by the consumption of garnet biotite and quartz to produce orthopyroxene alkali feldspar and plagioclase under isothermal conditions and at reduced water activities a number of mineral reaction textures including orthopyroxene plagioclase symplectites around clinopyroxene relics in intermediate charnockites and spinel rims between adjacent garnet and sillimanite in khondalites suggest near isothermal conditions of equilibration mineral phase equilibria barometry traverse across the granulite terrain indicates an increase in pressure from c 5 kbar in the north to c 8 9 kbar in the south the temperature gradient of c 100 c is less pronounced fluid inclusion studies indicate abundant co 2 trapped within the charnockite minerals the systematic variation in fluid densities with a garnet feldspar quartz succession within individual samples argues against post metamorphic fluid infiltration and fits a scenario of mineral equilibration during near isothermal uplift following a clockwise pressure temperature time path along the pressure gradient the fluid densities show an increase from c 0 98 to c 1 10 g cm 3 this strengthens other evidence of a synmetamorphic entrapment of co 2 preliminary carbon isotope measurements of co 2 extracted from inclusions yield 13 c values of c 5 to 6 suggesting a sub continental mantle source the gondwanan lutzow holm bay terrain had undergone substantial extension during the late proterozoic with displacement along megafaults and emplacement of several alkaline subalkaline granite and syenite plutons and also k basalts it is therefore envisaged that the abundant co 2 in the charnockites could have been derived from an attenuated continental lithosphere and transferred through magmatic conduits

fluids in granulites since the discovery of co2 fluid inclusions in granulites the role of fluids in the formation of these rocks has been widely studied owing to the complexity of the tectono metamorphic history of granulite terrains fluid inclusion data alone are not sufficient they need to be integrated with geochemical and mineralogical studies done on the same rock samples a clear understanding of the tectono metamorphic history of granulite terranes is also indispensable the widespread occurrence of co2 and the later discovered high salinity aqueous fluid inclusions support the idea that the lower crust underwent fluid flow and that both carbonic and brine fluids played a role in its formation both low h2o activity fluids play a similar role in destabilizing hydrous mineral phases furthermore experimental studies have shown that brine fluids have a much larger geochemical effect on granulites than initially expected these fluids are far more mobile in the lower crust compared with co2 and also have the capability for dissolving numerous minerals as in the example of the limpopo complex fluid inclusions and many metasomatic features observed in granulite terranes can thus be explained only by large scale movement of high salinity aqueous fluids and to a lesser extent co2 implying that lower crustal granulites are not as dry as previously assumed similar brines and co2 rich fluids are also found in mantle material most likely derived from deeply subducted supracrustal protoliths

metamorphism of reduced granulites in low co 2 vapour free environment pervasive flooding of co2 has been proposed as the cause of granulite facies metamorphism that is capable of producing many distinctive characteristics of the deep continental crust reduced water activity orthopyroxene bearing assemblages depletion of large ion lithophile lil elements and dehydration1 6 the calculations presented here of c o h fluid composition for conditions of granulite facies metamorphism show that oxygen fugacity f o2 estimates from many terranes are sufficiently low that the addition of co2 rich fluid causes graphite to precipitate for values of pressure p and temperature t common to granulites and with f o2 slightly below the quartz fayalite magnetite buffer qfm the addition of co2 sufficient to grow 10 vol orthopyroxene requires the precipitation of 1 5 vol graphite as 0 1 vol graphite is readily recognizable but is not reported in most low f o2 granulites these rocks have not been flooded by co2 and low f h2o is probably due to extraction of a magma or recrystallization of an already dry rock7 8 granulite terranes may thus result from a combination of these three processes and the dominance of any one cannot now be demonstrated on a regional basis

deformation history of the qianlishan complex khondalite belt north china structures ages and tectonic implications abstract the qianlishan complex is a multiply deformed granulite terrane of the khondalite belt that represents a paleoproterozoic continent continent collisional orogen in the western block of the north china craton two major stages of deformation d1 and d2 were identified in the qianlishan complex d1 mainly produced nww trending overturned to recumbent intrafolial isoclinal folds f1 sub horizontal penetrative foliations s1 nne ssw mineral lineations l1 associated with top to the ssw thrust shear reflecting crustal thickening due to the nne ssw compression d1 was developed with the prograde m1 and peak m2 granulite facies metamorphism d2 successively superposed the d1 structures and was characterized by nww see trending doubly plunging open to tight upright folds f2 and minor sub vertical axial planar foliations cleavages s2 d2 was accompanied by post peak near isothermal decompression m3 probably related to exhumation following the crustal thickening sims u pb zircon ages of deformation related leucocratic dykes demonstrate that d1 broadly occurred at 1976 1936 ma and d2 subsequently happened at 1936 1854 ma these results indicate that the khondalite belt underwent long term 100 myr polyphase deformation and high grade metamorphism associated with magmatism timing constraints and kinematic compatibility suggest that the deformation sequence resulted from the nne ssw collision between the yinshan and ordos blocks to form the western block at 1 95 ga

carbonic metamorphism at ultrahigh temperatures evidence from north china craton abstract the north china craton ncc constitutes one of the fundamental precambrian nuclei of asia the paleoproterozoic khondalite belt along the northern margin of the ncc shows evidence for extreme crustal metamorphism at temperatures exceeding 1000 c and pressures of 10 12 kbar with the formation of diagnostic ultrahigh temperature uht mineral assemblages including sapphirine quartz high alumina orthopyroxene sillimanite and high temperature mesoperthites here we record for the first time the common occurrence of co2 rich fluid inclusions in peak uht minerals in the mg al granulites of ncc and trace the fluid evolution history from microthermometric and laser raman spectroscopic studies we show that the syn metamorphic fluid in the uht rocks was pure co2 while very high density carbonic fluids are preserved in some cases corresponding to entrapment at peak conditions many of the inclusions underwent density modification during the rapid and near isothermal exhumation of the rocks following peak uht metamorphism and initial cooling at depth the present study area within the northern margin of the ncc defines a collisional orogenic belt where continental collision and deep subduction were possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusions of paleoproterozoic age that are seen emplaced within the granulite facies supracrustals the thermal anomaly displayed by the uht granulites may thus correlate with asthenospheric upwelling and emplacement of mafic magmas possibly associated with plume activity which provided the heat and co2 input to achieve extreme crustal metamorphism and generation of dry granulite facies assemblages our study is the first report of syn metamorphic co2 rich fluids in uht granulites from a paleoproterozoic ca 1 92 ga terrane and provide evidence for carbonic metamorphism at ultrahigh temperatures as north china craton joined the columbia supercontinent amalgam

primary co2 bearing fluid inclusions in granulitic garnet usually do not survive abstract co2 bearing fluid inclusions fi from granulites have been the main advocate for an active role of fluids during high temperature metamorphism yet the fluid regime of the deep crust and the role of fluids remain largely debated topics in this dispute one of the most controversial issues is the timing of fi entrapment relative to peak metamorphic conditions here we investigate three world renowned high to ultra high temperature metamorphic terranes to evaluate the fate of primary co2 and coh fluid inclusions certainly trapped during the prograde path fluid inclusions coexist along with nanogranitoids in peritectic garnet combination of cutting edge techniques indicates that the fi are composed of fluid and aggregates of solid phases the latter usually comprises siderite ferroan magnesite pyrophyllite calcite corundum quartz and in some cases kaolinite dolomite biotite and muscovite in the fluid phase low density co2 is the most common component and no free h2o has been detected methane and n2 may be also present the high proportion of solids in the fi with carbonates and oh bearing phases cannot have precipitated as daughter phases directly from a simple coh fluid as daughter phases these minerals require additional cations e g fe mg ca al si which may be dissolved in very small amounts in crustal fluids and yet are very abundant in the host the solids therefore imply that the initial composition of high density carbonic inclusions must have been changed by the interaction with the host garnet during cooling thermodynamic modelling of such fluid garnet interaction demonstrates that the assemblages found in fi are metastable and that whatever retrograde path is followed by the host rock primary c bearing fi must change their nature to a multiphase assemblage of stepdaughter minerals as a natural consequence of cooling it follows that supposed primary unmodified fi in garnet previously reported in the literature are in most cases secondary retrograde features whose low temperature of entrapment inhibited fluid host interaction our finding undermines the main pillar of the theory of carbonic fluid assisted metamorphism the presence of superdense co2 inclusions in granulites but at the same time it offers a novel perspective to identify prograde coh fluids in the deep hot crust

petrology geochemistry and zircon u pb and lu hf isotopes of the cretaceous dykes in the central north china craton implications for magma genesis and gold metallogeny abstract the trans north china orogen tnco a paleoproterozoic suture that amalgamates the western and eastern blocks of the north china craton ncc witnessed extensive magmatism and metallogeny during mesozoic associated with intraplate tectonics and differential destruction of the cratonic lithosphere here we investigate a suite of porphyry dykes surrounding the mapeng batholith in the fuping complex within the tnco in relation to the mesozoic gold and molybdenum mineralization the major element chemistry of these dykes show a range of sio 2 57 92 to 69 47 wt na 2 o 3 20 to 4 77 wt k 2 o 3 12 to 4 60 wt and mgo 0 51 to 3 67 wt together with high concentration of lree and lile and relatively low contents of hree and hfse the rocks display la yb n 13 53 48 11 negative nb ta th u and zr anomalies and distinctly positive ba k and sm anomalies the mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high k calc alkaline and i type with adakitic features similar to those of the adjacent mapeng batholith the source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials the zircon u pb data from these rocks show ages in the range of 124 to 129 ma broadly coinciding with the emplacement age of the mapeng intrusion the inherited zircons of ca 2 5 2 0 and 1 8 ga in the dykes represent capture from the basement rocks during melting the zircon lu hf isotopic compositions show negative e hf t values varying from 27 8 to 11 3 with hf depleted model ages t dm ranging from 1228 ma to 1918 ma and hf crustal model ages t dm c of 1905 ma to 2938 ma suggesting that the mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the ncc we present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization we envisage that these dykes probably acted as stoppers impermeable barriers that prevented the leakage and run off of the ore bearing fluids and played a key role in concentrating the gold and molybdenum mineralization

archean to paleoproterozoic continental crust growth in the western block of north china constraints from zircon hf isotopic and whole rock nd isotopic data abstract this study presents new zircon hf isotopic data which combined with previous zircon u pb geochronological in situ hf and whole rock nd isotopic data from the western block of the north china craton ncc provide a new insight into global scale continental crustal growth and evolution of early earth in particular igneous zircons and detrital zircons from the yinshan block yield 207 pb 206 pb ages of 2446 2733 ma with an age peak at 2524 ma of those 86 have positive e hf t values and archean hf model ages t dm c 2 6 2 9 ga peaking at 2840 ma this indicates that those basement rocks of the western block are most likely derived from a depleted mantle source implying a crust mantle differentiation event at 2 8 2 7 ga followed by extensive reworking at 2 5 ga more than 95 detrital zircons from the khondalite belt have ages converging on 2 2 2 0 ga and their e hf t values vary from 5 43 to 9 54 of which 80 are positive and yield hf model ages t dm c peaking at 2250 ma these characteristics of e hf t values in the khondalite belt are also documented in the basement rocks of the ordos block under same age frame of 2 2 2 0 ga this suggests that the ordos block may be a juvenile crust with addition of older materials the initiation of subduction under the southern margin of the ordos block leads to the formation of a 2 2 2 0 ga magmatic arc which is likely related to the assembly of the supercontinent columbia

paleoproterozoic ultrahigh temperature granulites in the north china craton implications for tectonic models on extreme crustal metamorphism abstract ultrahigh temperature uht metamorphic rocks associated with the khondalite belt within the inner mongolia suture zone imsz provide robust evidence for extreme thermal metamorphism in the north china craton ncc the imsz marks the collisional suture between the yinshan block to the north and the ordos block to the south as the ncc was incorporated within the columbia supercontinent amalgam during paleoproterozoic here we present a synthesis of the salient features of the uht rocks from the ncc including petrologic indicators fluid characteristics and monazite and zircon chronometry on the extreme crustal metamorphism the granulites carry diagnostic uht mineral assemblages including sapphirine quartz low zn fe3 spinel quartz high alumina orthopyroxene sillimanite quartz and high temperature mesoperthite the stability fields of the typical mineral assemblages conventional geothermobarometry and phase equilibria modeling using pseudosections as reported in a number of recent studies converge to indicate that these uht rocks experienced metamorphic temperatures up to or in excess of 1000 c at ca 10 kbar followed by an isobaric cooling segment the rocks were exhumed along a near isothermal decompression path microstructures mineral reactions and phase equilibria modeling suggest an anti clockwise p t path similar to those displayed by metamorphic orogens developed in subduction collision settings the dominant category of fossil fluids preserved within the major uht minerals is co2 consistent with the stability of the broadly anhydrous mineral assemblage in these rocks both chemical and radiogenic isotopic ages from monazite and zircon chronometry suggest the timing of the uht event as around 1 92 ga the paleoproterozoic high grade metamorphism younging from 1 95 ga in the western domain to 1 92 ga in the eastern domain of the khondalite belt might suggest a scissor like closure of oblique collision between the yinshan and the ordos blocks the salient features of the uht metamorphism in the ncc include 1 extreme metamorphic temperatures at moderate pressures 2 dominantly anhydrous nature of the mineral assemblages typically the stability of orthopyroxene 3 common presence of co2 rich fluid inclusions as the trace of the ambient fluid 4 regional extent of the uht granulites and 5 the association of the uht orogen with an accretionary belt in a continental collisional suture we evaluate the diverse models on the generation of uht orogens including their formation in thickened and inverted back arcs orogen self heating through heat producing elements heat and co2 input by plume impingement below a carbonated tectosphere and asthenospheric upwelling through ridge subduction and slab window process or during post collisional slab break off the ultra hot and dry uht rocks in the ncc provide one of the well preserved examples from the paleoproterozoic globe for investigating extreme metamorphism and related tectonic processes within the plate tectonic paradigm

textural evolution of synthetic fluid inclusions in quartz during reequilibration with applications to tectonic reconstruction experimental reequilibration of synthetic 10 wt nacl h2o inclusions in natural quartz reveals that reequilibration textures show distinct differences depending upon the p t path followed by the inclusion after formation these differences combined with other geological information may be used to determine whether the sample rock followed a dominantly isothermal or isobaricp t path following entrapment the intensity and style of inclusion reequilibration features is related to the direction and magnitude of the departure of thep t path from the original isochore for the inclusion thus fluid inclusion reequilibration textures not only permit inclusionists to determine whether the rocks followed an isothermal or isobaric retrogradep t path but also the magnitude of departure of this path from one that is isochoric

u pb and hf isotopic study of detrital zircons from the yejishan group of the luliang complex constraints on the timing of collision between the eastern and western blocks north china craton abstract the trans north china orogen is a recently recognized continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the coherent basement of the north china craton however there is a hot debate on the timing of the collision between the two blocks with one school of thought arguing the collision occurred at 2 5 ga whereas others believe it took place at 1 85 ga u pb ages and hf isotopic data of detrital zircons from foreland basins in the trans north china orogen can provide rigorous constraints on this controversial issue one of such foreland basins is represented by the yejishan group in the luliang complex in the middle sector of the western margin of the trans north china orogen the group consists of conglomerates quartz wackes sandstones and minor limestones most of which contain large amounts of detrital zircons cl images reveal that nearly all detrital zircons from the yejishan group possess oscillatory zoning with th u ratios of 0 2 2 34 typical of an igneous origin the 207 pb 206 pb ages of detrital zircons range between 3 24 and 1 81 ga with most having paleoproterozoic ages of which the youngest group ages are around 1 87 1 81 ga this indicates that the foreland basin in which the yejishan group was deposited must have formed not earlier than 1 87 1 81 ga thus supporting the collision between the eastern and western blocks at 1 85 ga not at 2 5 ga

carbonic fluid inclusions in south indian granulites evidence for entrapment during charnockite formation field evidence and fluid inclusion studies on south indian incipient charnockites suggest that charnockite formation occurred during a decompressional brittle regime following the peak of metamorphism and regional deformation the most abundant type of inclusions in quartz and garnet grains in these charnockites contain high density carbonic fluids although lower density fluids occur in younger arrays of inclusions discrete fluid inclusion generations optically are observed to decrepitate over well defined temperature intervals and quantitative measurements of co2 abundance released from these inclusions by stepped thermal decrepitation show up to a four fold increase by volume in the incipient charnockites relative to the adjacent gneisses from which they are derived studies based on optical thermometry visual decrepitation and stepped heating inclusion release together indicate that entrapment of carbonic fluids coincided with charnockite formation we confirm that an influx of carbon dioxide rich fluids is associated with the amphibolite granulite transition as recorded by the incipient charnockites the remnants of which are commonly preserved as the earliest generation of high density fluid inclusions

application of zr in rutile thermometry a case study from ultrahigh temperature granulites of the khondalite belt north china craton zr in rutile thermometry was applied to ultrahigh temperature uht granulites from three localities dongpo tuguishan and dajing tuguiwula of the khondalite belt north china craton zr concentrations of analyzed rutiles were detected by la icp ms and emp which display a mutative composition zoning a large inter grain variation a bimodal distribution at around 1 500 and 6 000 ppm and no relationship with the textural setting matrix vs inclusion these characteristics were likely caused by post peak diffusional resetting associated with slow cooling rates and the presence of a co2 rich fluid the grains with lower zr concentrations 500 to 3 000 ppm and temperature estimates 650 to 850 c occur close to or in contact with zircon which was easily affected by post peak processes for example diffusion dissolution reprecipitation the lowest temperatures 650 to 700 c we obtained represent the closure temperature of zr in rutile rutiles with higher zr concentrations 3 000 to 8 000 ppm and calculated temperatures 850 to 1 000 c were least affected by late resetting giving near peak metamorphic temperatures these temperature results higher than 900 c even in excess of 1 000 c from the three localities reconfirm the presence of uht metamorphism our results also suggest that zr in rutile thermometry is valid for ultrahigh temperature estimates in addition there are positive correlations between concentrations of zr and hf nb and ta of the investigated rutiles but the correlations weaken as the concentrations increase especially for nb and ta implying fractionation of nb and ta