unexposed archean components and complex post archean accretion reworking processes beneath the southern yangtze block revealed by zircon xenocrysts from the paleozoic lamproites south china abstract integrated u pb dating and hf isotope analysis of zircon xenocrysts from the baifen lamproites of the zhenyuan area in the southeastern guizhou province offer a unique glimpse into the evolution of the deep continental crust beneath the southern part of the yangtze block south china a total of 148 zircons with 90 110 concordance yield u pb ages varying from 3458 9 ma to 252 2 ma they generally have high th u ratios 0 3 indicating a magmatic origin the two youngest magmatic zircons give a weighted mean 206pb 238u age of 253 0 2 8 ma which is interpreted as the emplacement age of the host baifen lamproites most zircons with pre eruption ages are xenocrysts derived from the deeper crust of the southern yangtze block they define two major paleoproterozoic age populations at 2 17 ga and 1 8 ga with similar hf model ages tcrust of 2 4 2 8 ga peak at 2 64 ga the oldest zircon has a 207pb 206pb age of 3458 9 ma with ehf t 1 47 and tcrust 3 7 ga this demonstrates the presence of archean crustal components or remnants as old as 3 7 ga beneath the southern yangtze block magmatic events involving significant addition of juvenile mantle derived materials mainly occurred at 2 2 2 1 ga and 2 0 1 8 ga but the latter event also involved reworking of the neoarchean crust and might represent the cratonization of the yangtze continent during the middle paleoproterozoic which could be correlated to the assembly of the columbia supercontinent this segment of the yangtze block became tectonically quiescent until 1 2 ga implying that the crustal stabilization lasted for ca 600 million years a few late mesoproterozoic zircon xenocrysts within the age range 1 3 1 0 ga suggest the occurrence of grenville aged events these neoproterozoic zircon xenocrysts 992 547 ma have a wide range of ehf t values 8 47 to 22 07 consistent with the zircon hf isotopic compositions of widespread coeval igneous rocks in the yangtze block the data show that the yangtze block has undergone important crustal growth and reworking during the neoproterozoic in response to the breakup of the rodinia supercontinent the early middle paleozoic zircon xenocrysts 513 357 ma have negative ehf t values 2 97 to 12 69 and tcrust hf model ages of 1 59 2 27 ga indicating reworking of the precambrian crustal basement without juvenile contributions during the caledonian orogeny the positive ehf t values 13 79 to 0 22 of twelve late paleozoic zircons 284 264 ma with a major age peak at ca 275 ma suggest that the precambrian basement beneath the southern yangtze block experienced an episode of strong rejuvenation during the permian we propose a possible linkage between the baifen lamproite magmatism 284 252 ma and the emeishan flood basalt volcanism

geochemistry and geochronology of mylonitic metasedimentary rocks associated with the proterozoic miaowan ophiolite complex yangtze craton china implications for geodynamic events an early neoproterozoic collisional event 935 942 ma is reported in the yangtze craton siliceous and carbonaceous mylonitic rocks were deposited in a fore arc setting mylonitic metasandstone formed in the foredeep detrital zircons show positive ehf t values consistent with ophiolitic rocks

paleo to mesoproterozoic magmatic and tectonic evolution of the southwestern yangtze block south china new constraints from ca 1 7 1 5 ga mafic rocks in the huili dongchuan area abstract paleo to early mesoproterozoic rocks in the yangtze block are extremely sparse and are predominately exposed along the southwestern margin their petrogenesis and tectonic significance remain unclear resulting in a limited understanding of the tectonic evolution of the southwestern yangtze block during this period therefore we report here detailed geochronological and geochemical analyses of newly discovered paleo to early mesoproterozoic mafic intrusive rocks in the huili dongchuan area southwestern yangtze block and interpret their petrogenesis and tectonic significance secondary ion mass spectroscopy sims zircon and baddeleyite u pb dating yielded crystallization ages of ca 1716 1714 ma for gabbros and diabases referred to as the 1 72 1 71 ga group ca 1705 1700 ma for gabbros and a diabase porphyrite the 1 70 ga group and ca 1519 1504 ma for a gabbro and a diabase the 1 52 1 50 ga group which effectively constrain the minimum depositional age of the tong an and dongchuan groups that they intrude to 1 72 ga the three groups or episodes of intrusive rocks differ from each other in their chemical compositions and isotopic characteristics most likely because of varying degrees of melting in a convective upper mantle probably the asthenosphere which had been metasomatized by melts with enriched components input by a plume from the lower mantle modeling calculations suggest that fractional crystallization fc and assimilation and fractional crystallization afc were the most important processes involved in modifying the chemical compositions of these rocks these magmatic activities are interpreted to have been related to mantle plumes and continental rifting that occurred in the huili dongchuan area near the southwestern margin of the yangtze block

zircon lu hf isotopic constraints on neoproterozoic subduction related crustal growth along the western margin of the yangtze block south china abstract voluminous neoproterozoic igneous rocks along the western margin of the yangtze block south china provide an ideal opportunity for examining the nature of the mantle source petrogenesis of the felsic plutons and processes and timing of crustal growth the dadukou tongde gaojiacun and shaba mafic plutons and datian and dajianshan adakitic plutons were selected for zircon lu hf isotope analysis zircons from the mafic plutons have hf t values ranging from 1 86 to 11 63 with average hf t values of the different samples ranging from 4 78 0 42 to 7 60 1 1 their single stage model ages range from 0 86 to 1 28 ga the two adakitic plutons have hf t values ranging from 2 26 to 11 68 and single stage model ages from 0 86 to 1 24 ga our data further confirm that the mafic plutons were extracted from depleted mantle sources whereas the datian and dajianshan adakitic plutons were products of melting of a subducted oceanic slab the arc geochemical affinity relatively high 143 nd 144 nd ratios and high zircon hf t values as well as the relatively young hf single stage model ages of these neoproterozoic plutons suggest that the continental crustal growth in the region was related to oceanic subduction rather than upwelling of a mantle plume in a rifting setting the neoproterozoic magmatism along the western margin of the yangtze block lasted more than 200 my not show episodic emplacement and contrasting zircon hf isotopes suggesting that continental crustal growth in south china was continuously resulted from subduction

fe cu deposits in the kangdian region sw china a proterozoic iocg iron oxide copper gold metallogenic province numerous fe cu deposits are hosted in the late paleoproterozoic dongchuan and dahongshan groups in the kangdian region sw china the dongchuan group is composed of siltstone slate and dolostone with minor volcanic rocks whereas the dahongshan group has undergone lower amphibolite facies metamorphism and consists of quartz mica schist albitite quartzite marble and amphibolite with local migmatite deposits in the dongchuan group are commonly localized in the cores of anticlines in fault bends and intersections and at lithological contacts orebodies are closely associated with breccias which are locally derived from the host rocks fe oxides magnetite and or hematite and cu sulfides chalcopyrite bornite form disseminated vein like and massive ores and typically fill open spaces in the host rocks the deposits have extensive albite alteration and local k feldspar alteration overprinted by quartz carbonate sericite and chlorite deposits in the dahongshan group have orebodies sub parellel to stratification and show crude stratal partitioning of metals fe oxide ores occur as massive and or banded replacements within the breccia pipes whereas cu sulfide ores occur predominantly as disseminations and veinlets within mica schists and massive magnetite ores ore textures suggest that cu sulfides formed somewhat later than fe oxides but are possibly within the same mineralization event both ore minerals predated regional neoproterozoic metamorphism both orebodies and host rocks have undergone extensive alteration of albite scapolite amphibole biotite sericite and chlorite silica and carbonate alterations are also widespread ore hosting strata have a la icp ms zircon u pb age of 1681 13 ma and a dolerite dyke cutting the fe oxide orebodies has an age of 1659 16 ma thus the mineralization age of the dahongshan deposit is constrained at between the two all ores from the two groups have high fe and low ti with variable cu contents locally they are rich in mo co v and ree but all are poor in pb and zn sulfides from the fe cu deposits have 34s values mostly in the range of 2 to 6 per mil suggesting a mix of several sources due to large scale leaching of the strata with the involvement of evaporites isotopic dating and field relationships suggest that these deposits formed in the late paleoproterozoic ore textures mineralogy and alteration characteristics are typical of iocg type deposits and thus define a major iocg metallogenic province with significant implications for future exploration

ages and compositions of primary and secondary allanite from the lala fe cu deposit sw china implications for multiple episodes of hydrothermal events numerous fe cu deposits in southwestern china form the kangdian iron oxide copper gold iocg metallogenic province these deposits have a close association of fe oxides and cu sulfides formed at different stages which are possibly related to multiple hydrothermal events in this paper u pb dating and chemical analyses on allanite from different stages of the lala deposit were used to constrain timing and origin of such events allanite occurs as disseminated grains or patches in fe cu ores and is closely associated with chalcopyrite molybdenite calcite and minor titanite postdating magnetite and apatite high resolution backscattered electronic bse imaging electron microprobe compositions and x ray scanning profiles demonstrate that ree rich primary allanite was replaced by later relatively porous and ree poor secondary allanite such a replacement was promoted by interaction between primary allanite and fluid fluxes infiltrating the minerals following an exchange scheme of ree3 fe2 ca2 al3 the secondary allanite has higher fe3 fe3 fe2 ratios and u contents indicating involvement of relatively oxidized fluids during alteration the alteration has also produced unidentified secondary ree minerals in fractures indicating re deposition of some of the removed rees the primary and secondary allanites are dated by in situ la icp ms technique and have u pb ages of 1 067 41 ma and 880 850 ma respectively the 1 07 ga primary allanite was contemporaneous with the main mo cu lree mineralization with a molybdenite re os age of 1 08 ga the 880 850 ma secondary allanite is comparable with the ar ar ages 890 830 ma of biotite from hosting schists and undeformed sulfide veins occurring throughout the kangdian province suggesting that such an event was possibly syn deformational and represents a younger hydrothermal event occurrences of both primary and secondary allanites suggest that the mineralization may have involved multiple tectonothermal events including the 1 05 1 1 ga intra plate and subsequent 960 740 ma arc magmatism in the kangdian region

crustal evolution in the georgetown inlier north queensland australia a detrital zircon grain study abstract the use of in situ hf isotope analysis of zircon allows a more detailed evaluation of magma generation processes than the analysis of whole rock isotopic systems and is a powerful tool for studying crustal evolution detrital zircon grains have been analysed by in situ lam icpms and lam mc icpms for u pb ages trace element patterns and hf isotope composition to evaluate patterns of magma genesis and crustal evolution in the central part of the precambrian georgetown inlier north queensland australia archean zircons and low hf in proterozoic and phanerozoic magmatic zircons provide direct evidence for the existence of archean crustal components in the georgetown inlier although the surface geology is dominated by mesoproterozoic basement rocks and palaeozoic granitoids crustal evolution in the georgetown inlier has involved at least three stages of heating and granitoid magmatism possibly associated with basaltic magma underplating and or overplating 1545 1585 ma 420 ma and 340 ma in general granitoids with high hf are typical of the percyvale area closest to the phanerozoic tasman fold belt and may reflect thinner and younger crust granitoids with less radiogenic hf isotope compositions are typical of the einasleigh and mount surprise areas in the central part of the inlier and may reflect the presence of older and thicker crust the most significant juvenile additions to the crust after archean time occurred in the einasleigh and mount surprise areas during mesoproterozoic time and in the percyvale area during carboniferous time in the mount surprise area resorbed zircon cores of mesoproterozoic age are overgrown by magmatic rims of siluro devonian age similarities in the hf isotope composition of core rim pairs suggest that the large range in hf observed in zircons from siluro devonian granitoids reflects remelting of a heterogeneous 1545 1585 ma old crust rather than mixing between juvenile and crustal sources crustal remelting has been the main process responsible for the production of granitoid magmas in the georgetown inlier however minor addition of mantle derived material may have occurred during both mesoproterozoic and carboniferous time similarities and differences in the crustal evolution of the mt isa broken hill and georgetown blocks suggest that the proterozoic history of the australian continental margin involved the accretion and subsequent dispersal of individual originally archean microcontinents

late paleoproterozoic sedimentary and mafic rocks in the hekou area sw china implication for the reconstruction of the yangtze block in columbia abstract the paleoproterozoic hekou group in the western yangtze block is a volcano sedimentary succession that is intruded by gabbroic plutons sedimentary rocks in the group include slates marble and meta siltstones interlayered with felsic metavolcanic rocks metabasalts and metatuffs both the volcanic rocks of the hekou group and gabbros have undergone upper greenschist to lower amphibolite facies metamorphism metatuff samples from different layers have average zircon u pb ages of 1697 ma slightly older than the intruding gabbroic plutons with zircon u pb ages of 1684 ma both metabasalts and metagabbros have similar elemental and isotopic compositions indicative of a co magmatic origin they are rich in tio2 mostly 2 5 wt zr 94 5 347 ppm ta 0 48 3 00 ppm and th 1 05 7 61 ppm with high nb y ratios mostly 0 6 and lree enriched chondrite normalized ree patterns resembling within plate mafic rocks their positive whole rock nd t 0 2 to 3 4 and zircon hf t values 3 3 to 8 4 suggest contributions from a depleted mantle source the large range of nd t and hf t values and variable degrees of nb ta anomalies ta lapn 0 17 1 75 are indicative of crust contamination during magma ascending both the metabasalts and metagabbros are considered to have formed in a continental rift setting detrital zircon grains from meta siltstones in the hekou group have u pb age populations mainly at 2070 1880 ma 2330 2250 ma and 2900 2700 ma these age populations are comparable to those of the north australian and north china cratons in the columbia supercontinent however in terms of geochemical features the 1 7 ga within plate mafic rocks at hekou are similar to those from the 1 7 ga leichhardt and calvert superbasins of the north australian craton but different from those from the 1 7 1 2 ga zhaertai bayan obo rift zone of the north china craton it is thus suggested that the yangtze block was more likely linked with the north australian craton in columbia during the late paleoproterozoic these rifting basins and mafic rocks may record the initial break up of the columbia supercontinent

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

geochemical sm nd isotopic characteristics and petrogenesis of paleoproterozoic mafic rocks from the georgetown inlier north queensland implications for relationship with the broken hill and mount isa eastern succession fe rich tholeiites intruded the lower etheridge group of the georgetown inlier north queensland during the late paleoproterozoic ca 1685 1640 ma emplacement of the tholeiites occurred during a prolonged period of rift related sedimentation associated with extension the tholeiites comprise two lithologically distinct units the extrusive dead horse metabasalt dhm a conformable 1000 m thick series of fine to coarse grained basalts and pillow lavas and the intrusive cobbold metadolerite cmd a multitude of sills and lesser dykes that range up to 500 m thick the dhm and cmd are comagmatic and have compositions typical of relatively evolved low k fe rich continental rift tholeiites immobile major and trace element patterns suggest that the tholeiites were derived from a depleted upper mantle source initial nd values range between 2 6 and 5 3 the parental melts evolved along a trend of increasing fe enrichment fe2o3 6 81 21 11 wt via closed system fractionation with little or no replenishment several samples show distinct ree patterns consistent with limited crustal contamination trace element and isotopic data show that the crustal contaminants were derived from the host metasediments of the lower etheridge group the age and geochemical characteristics of the etheridge group fe rich tholeiites show striking similarities to similar mafic sills in the southeastern curnamona province around broken hill in western new south wales and to basaltic lavas and dolerites of the soldiers gap group in the eastern edge of the mt isa block some 400 km west of the georgetown inlier suggesting a spatial link between these terranes during the paleoproterozoic they may have formed along a more than 2000 km segment of a ca 1685 1640 ma volcanic passive margin tectonically and magmatically akin to the modern east greenland margin

geochemistry of magnetite from the giant paleoproterozoic dahongshan fe cu deposit sw china constraints on nature of ore forming fluids and depositional setting abstract the dahongshan fe cu ore deposit hosted in the paleoproterozoic meta volcanic and meta sedimentary sequences is a giant deposit in the fe cu metallogenic province of southwestern china two ore types have been identified 1 massive and disseminated fe ores hosted dominantly in meta volcanic rocks and 2 disseminated and banded fe cu ores in meta sedimentary rocks magnetite presents in all orebodies and is dominant in the fe ores chemistry of magnetite suggest that the fluids for iron mineralization in the fe and fe cu orebodies are likely chemically similar and cogenetic minor sulfides e g molybdenite occur at the end of iron mineralization stage indicating the gradually decrease in oxygen fugacity for the mineralizing fluids with magnetite precipitation along with evolution mineralizing fluids generate magnetite with depletions in cr ni ga and v but enrichments in mn sn and co which are primarily reflective of the temperature decrease of fluids we have discovered some magnetite grains that are extremely rich in v 10000 ppm but low in ti and cr geochemical patterns suggest that they were formed by fluids similar to those of ordinary ores available knowledge about the unique high v magnetite indicates highly reduced marine environments for its generation ore bulk ree patterns showing remarkable positive eu anomalies and absence of obvious ce anomalies suggest a bif like marine environment consistent with the morphology of both fe and fe cu orebodies our results provide independent evidence for submarine environment in the formation of the giant precambrian stratiform fe cu ore deposit

geologic history of natural coal bed fires powder river basin usa abstract coal bed fires ignited by natural processes have baked and fused overlying sediments to form clinker a hard red or varicolored rock through much of the northern great plains of the united states usa the gently dipping coal beds in the region burn when regional downwasting brings them above the local water table the resulting clinker forms a rim along the exposed edge of the coal bed in an ongoing process through geologic time the resistant clinker is left capping buttes and ridges after the softer unbaked strata erode away clinker outcrops cover more than 4100 km2 in the powder river basin prb which lies in wyoming wy and montana mt the clinker in place records tens of billions of tons of coal that have burned releasing gases into the atmosphere the amount of clinker that has eroded away was at least an order of magnitude greater than the clinker that remains in place fission track and uranium thorium helium ages of detrital zircon crystals in clinker and paleomagnetic ages of clinker show that coal beds have burned naturally during at least the past 4 million years ma the oldest in place clinker that has been dated collected from a high isolated clinker capped ridge has a fission track age of 2 8 0 6 ma evidence of erosion and downcutting is also preserved by clinker clasts in gravel terraces one clinker boulder in a terrace 360 m above the yellowstone river has a fission track age of 4 0 0 7 ma coal bed fires are caused by lightning wildfires spontaneous combustion or human activity on coal outcrops and in mines miners government agencies and ranchers have extinguished thousands of coal bed fires but natural ignition continues where fresh coal has access to air at any given time hundreds of fires mostly small are burning in the powder river basin the total amount of coal burned by natural fires in the last 2 ma is one to two orders of magnitude greater than the total amount of coal removed by mining in the past century however current annual rates of coal mining are three to four orders of magnitude greater than estimated prehistoric annual rates of coal consumption by natural fires

multiple episodes of mineralization revealed by re os molybdenite geochronology in the lala fe cu deposit sw china the lala fe cu deposit is one of the largest iron oxide copper gold iocg deposits in the kangdian copper belt southwest china the paragenetic sequence of the lala deposit includes six hydrothermal stages pre ore pervasive na alteration i magnetite stage with k feldspar and apatite ii polymetallic disseminated massive magnetite sulfide stage iii banded magnetite sulfide stage iv sulfide vein stage v and late quartz carbonate vein stage vi fifteen molybdenite separates from stages iii to vi were analyzed for re os dating our new re os data together with previous studies identify four distinct hydrothermal events at the lala deposit molybdenite from the stage iii disseminated to massive chalcopyrite magnetite ores yielded a weighted average re os age of 1306 8 ma mswd 1 1 n 6 which represents the timing of main ore formation molybdenite from the stage iv banded magnetite chalcopyrite ores yielded a weighted average re os age of 1086 8 ma mswd 2 2 n 7 i e a second ore forming event molybdenite from the stage v sulfide veins yielded a weighted average re os age of 988 8 ma mswd 1 3 n 7 which represents the timing of a third hydrothermal event molybdenite from the quartz carbonate veins stage vi yielded a weighted average re os age at 835 4 ma mswd 0 66 n 10 and documented the timing of a late hydrothermal event our results indicate that the lala deposit formed during multiple protracted mineralization events over several hundred million years the first three mesoproterozoic mineralization events are coeval with intra continental rifting breakup of the supercontinent nuna and share a temporal link to other iocg style deposits within the kangdian copper belt and the last neoproterozoic hydrothermal event is coeval with the sibao orogeny which culminated with the amalgamation of the yangtze block with the cathaysia block at 860 815 ma

is the precambrian basement of the tarim craton in nw china composed of discrete terranes abstract the precambrian evolution of the tarim craton in ne china in particular during the early precambrian stage remains enigmatic in this contribution we report field observation petrology geochemistry zircon lu hf isotopes and u pb ages of the major rock formations of the aketage area in the southeastern section of the tarim craton the milan group in aketage is dominantly composed of 2 7 2 5 ga gneissic amphibolite ttg complex with minor paragneiss both the mafic and silicic rocks exhibit geochemical features consistent with an arc affinity the arc signature of the 2 01 2 03 ga gneissic granites and gabbros which intrude the archean basement as well as the major 2 0 ga metamorphic event revealed by zircon u pb dating suggest an important subduction collision event possibly related to the assembly of the paleoproterozoic columbia supercontinent the ca 1848 1856 ma massive potassic granites 1867 ma mafic dyke swarm and 1844 ma massive leucogranite dykes reveal magmatism in a post collisional extensional setting a comprehensive synthesis of the major orogenic events and continental crust growth process from the different precambrian terranes in tarim craton show significant discrepancy in time related to the late neoarchean crust formation ages and the paleoproterozoic orogenic events for example the major orogenic event took place at 1 85 ga in quruqtagh dunhuang terrane at 1 90 ga in the southwest tarim craton and at 2 0 ga in the aketage qaidam terrane these different terranes exhibit distinct periods of continental crust growth in the early precambrian continental growth in the aketage area took place during 2 7 4 3 ga the 3 6 ga xenocrystic zircons as well as the peak of 4 2 ga zircon hf model ages indicate the possible existence of paleoarchean and even hadean crust in the aketage area in the quruqtagh dunhuang terrane the growth of early precambrian continental crust took place at 2 6 3 3 ga with peaks at ca 2 6 2 7 ga and 3 0 ga the diachronous late paleoproterozoic orogenic events and the significant difference in continental growth process suggest that the precambrian basement of the tarim craton is composed by independent continental terranes possibly detached from the cores of discrete ancient cratonic nuclei which were not unified until the early neoproterozoic during assembly of the rodinia supercontinent

early paleoproterozoic magmatism in the yangtze block evidence from zircon u pb ages sr nd hf isotopes and geochemistry of ca 2 3 ga and 2 1 ga granitic rocks in the phan si pan complex north vietnam abstract our understanding of the early evolution of the yangtze block is limited by the sparsely dispersed nature of pre neoproterozoic exposures new integrated petrographic zircon u pb age and hf nd isotope analyses and whole rock geochemical data for early paleoproterozoic granites in the phan si pan complex provides new insights into the evolution of the yangtze block as well as its role in the pre nuna supercontinent la icp ms zircon u pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207pb 206pb ages of 2306 12 ma and 2096 15 ma respectively zircons from the quartz monzonite have ehf t values ranging from 4 1 to 2 1 corresponding to tdm2 model ages of 3002 2890 ma whereas zircons in the gneissic granite have ehf t values between 0 95 and 1 72 and corresponding tdm2 model ages of 2660 2516 ma which are consistent with their whole rock nd isotope values geochemically the quartz monzonites are i type granites combined with their relatively high sr y ratios and low y concentrations as well as fractionated ree patterns with relatively high lree but low hree concentrations they were probably generated by partial melting of the thickened middle lower crust under elevated temperature geochemical and isotopic signatures suggest that the ca 2 1 ga gneissic granites are high k calc alkaline ferroan a type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material the phan si pan complex has a distinct early paleoproterozoic crustal evolution history compared with the other crustal provinces of the yangtze block suggesting independent histories that were not unified until the late paleoproterozoic during the assembly of nuna moreover the magmatism and tectonic evolution of the north vietnam region is broadly similar to that of the arrowsmith orogen of the rae craton in laurentia suggesting a potential spatial linkage the geologic record of the yangtze block does not support an early paleoproterozoic shutdown of plate tectonics

in situ sr isotope analysis of apatite by la mc icpms constraints on the evolution of ore fluids of the yinachang fe cu ree deposit southwest china apatite is a ubiquitous accessory mineral in a variety of rocks and hydrothermal ores strontium isotopes of apatite are well known to retain petrogenetic information and have been widely used to investigate the origin of igneous rocks but such attempts have rarely been made to constrain ore forming processes of hydrothermal systems we here report in situ la mc icpms sr isotope data of apatite from the 1660 ma yinachang fe cu ree deposit southwest china the formation of this deposit was coeval to the emplacement of regionally distributed doleritic intrusions within a continental rift setting the deposit has a paragenetic sequence consisting of sodic alteration stage i magnetite mineralization stage ii cu sulfide and ree mineralization stage iii and final barren calcite veining stage iv the stage ii and iii assemblages contain abundant apatite allowing to investigate the temporal evolution of the sr isotopic composition of the ore fluids apatite of stage ii apt ii is associated with fluorite magnetite and siderite whereas apatite from stage iii apt iii occurs intimately intergrown with ankerite and cu sulfides apt ii has 87sr 86sr ratios varying from 0 70377 to 0 71074 broadly compatible with the coeval doleritic intrusions 0 70592 to 0 70692 indicating that ore forming fluids responsible for stage ii magnetite mineralization were largely equilibrated with mantle derived mafic rocks in contrast apt iii has distinctly higher 87sr 86sr ratios from 0 71021 to 0 72114 which are interpreted to reflect external radiogenic sr likely derived from the paleoproterozoic strata some apt iii crystals have undergone extensive metasomatism indicated by abundant monazite inclusions the metasomatized apatite has much higher 87sr 86sr ratios up to 0 73721 which is consistent with bulk rock rb sr isotope analyses of cu ores with 87sr 86sri from 0 71906 to 0 74632 the elevated 87sr 86sr values of metasomatized apatite and bulk cu ores indicate that later fluids were dominated by highly radiogenic sr equilibrated with the paleoproterozoic country rocks results of this study highlight the utilization of in situ sr isotope analysis of apatite in unraveling the evolution of hydrothermal systems

the oldest known rocks in south western china shrimp u pb magmatic crystallisation age and detrital provenance analysis of the paleoproterozoic dahongshan group abstract the paleoproterozoic dahongshan group outcrops along the present day southwest margin of the yangtze craton it is the oldest rock found in the region and forms the basement for the late mesoproterozoic sedimentary successions the dahongshan group is a sequence of volcanic and sedimentary rocks which have undergone structural deformation and metamorphism to upper greenschist lower amphibolite facies some of the original sedimentary features such as unimodal cross bedding in quartzite and rounded conglomerate clasts are still preserved suggesting deposition in a fluvial environment abundant carbonate rocks also found within the sedimentary sequence indicate periods of shallow marine or lagoonal conditions a weighted mean shrimp 206pb 207pb age of 1675 8 ma for a tuffaceous schist unit confirms the paleoproterozoic formation age of the group shrimp and lam icp ms u pb analysis of detrital zircon grains from metasedimentary units indicate a late archean to paleoproterozoic ca 2780 1860 ma source region the age spectrum of the detrital zircons is similar to that of the late archean and early paleoproterozoic basement rocks previously identified in the yangtze craton but includes a population of paleoproterozoic grains ca 2400 2100 ma which have no known source region in the exposed yangtze craton

constraints of sr isotopic compositions of apatite and carbonates on the origin of fe and cu mineralizing fluids in the lala fe cu mo lree deposit sw china abstract numerous fe cu deposits with mineralization styles similar to iron oxide copper gold iocg deposits form the kangdian fe cu metallogenic province southwestern sw china as one of the largest deposits in the region the 1 0 ga lala fe cu deposit is hosted in a paleoproterozoic volcanic sedimentary succession named the hekou group which is alternately intruded by 1 0 ga doleritic plutons this deposit has a paragenetic sequence evolving from stage i of na alteration to stage ii of fe mineralization and finally to stage iii of cu mo ree mineralization coeval with mafic felsic intra plate magmatism in the region this study conducted in situ sr isotopic analyses on apatite and carbonate aiming to resolve the long controversial issue regarding the origin of the fe and cu mineralizing fluids in the deposit apatite of stage ii has 87sr 86sr ratios varying from 0 71380 to 0 72733 much higher than those of synchronous igneous rocks in the region 0 7074 to 0 7091 but similar to the paleoproterozoic host rocks 0 71368 to 0 71837 at 1 0 ga this similarity indicates that radiogenic sr of the fe mineralizing fluid was dominantly sourced from the host rocks apatite and calcites of stage iii have 87sr 86sr ratios 0 75758 0 79293 much higher than apatite of stage ii and the host rocks but similar to the archean basement rocks as high as 0 80 at 1 0 ga beneath the cover of the yangtze block suggesting that the highly radiogenic sr isotopic composition of the cu mineralizing fluid was mainly inherited from the old basement rocks in combination with previous c o s isotopic data indicating a magma hydrothermal origin it was suggested that the fe mineralizing fluid was exsolved from a mafic magma that generated the 1 0 ga doleritic plutons and inherited radiogenic sr from the host rocks during fluid rock interaction by contrast the cu mineralizing fluid might have been sourced from another pulse of magmatic cu mo ree and co2 rich fluid which have once interacted with archean basement rocks prior to mineralization the source of such a cu mo ree rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma we propose that intrusions of the bimodal magmas in kangdian are responsible for regional hydrothermal circulation which led to fe cu mo ree mineralization in the kangdian province

combining nd isotopes in monazite and hf isotopes in zircon to understand complex open system processes in granitic magmas mapping the age and trace element and sm nd isotope compositions of monazite grains from a peraluminous cretaceous granite using laser ablation split stream analysis reveals a wide range in nd isotope and rare earth element ree compositions within and between single grains these data corroborate isotopic variability indicated by hf isotope analysis of zircon in the same granite sample the ree variations indicate that monazite grew during fractional crystallization hf and nd isotopes indicate that the granitic magma was generated from at least two distinct proterozoic sources of approximately the same age one component that had highly radiogenic initial 176hf 177hf and 143nd 144nd and a second component that was notably less radiogenic this study highlights the utility of in situ ree and sm nd isotope data in monazite in magmatic systems further it refines the zircon based constraints on magmatic processes because of sensitivity of light rees to fractional crystallization lower probability of complications owing to inheritance and smaller analytical volumes required

early crustal evolution in the western yangtze block evidence from u pb and lu hf isotopes on detrital zircons from sedimentary rocks abstract in situ u pb and lu hf data on detrital zircons from paleo to neoproterozoic sediments have been used to gain a clearer picture of the regional tectonic background and crustal evolution in the western part of the yangtze block the youngest concordant zircon ages for sedimentary units suggest maximum depositional ages of 1014 ma for the kunyang group 750 649 ma for the sinian sequences and 525 ma for the cambrian sediments the yinmin formation previously assigned to the middle part of the kunyang group was actually deposited after 1667 ma and contains zircons whose ages are dominantly from late archean to paleoproterozoic 2 8 2 7 ga 2 5 2 3 ga and 1 85 ga the heishantou formation in the lower part of the kunyang group has two major age populations of 1 0 ga and 1 8 1 6 ga the sinian and cambrian sedimentary rocks are dominated by neoproterozoic zircons with age peaks at 760 ma and 825 ma consistent with the ages of widespread igneous rocks around the yangtze block the lu hf isotope data suggest that a significant juvenile input took place during archean and neoproterozoic times respectively while crustal reworking was dominant during the paleoproterozoic time the archean paleoproterozoic detritus is isotopically distinct from the archean paleoproterozoic basement exposed in the northern part of the yangtze block suggesting that a subarea of old crust lies beneath the young sediments covering the craton the presence of abundant 1 85 ga zircons suggests that the yangtze block was probably part of the columbia supercontinent during paleoproterozoic time comparisons to the other parts of columbia suggest that the yangtze block could have been adjacent to the north china craton and or australia

detrital zircon u pb geochronological and lu hf isotopic constraints on the precambrian magmatic and crustal evolution of the western yangtze block sw china abstract in situ u pb geochronological and lu hf isotopic studies of detrital zircon from a variety of precambrian strata along the western margin of the yangtze block of south china show that the rocks have maximum depositional ages of ca 1000 740 ma all of the strata probably formed in a subduction related tectonic setting the kunyang group heishantou formation and huili group tongan formation have maximum depositional ages of 960 1000 ma and contain zircons whose ages are dominantly paleoproterozoic 2500 2300 1900 1700 and 1650 1500 ma the yanbian group has a zircon population ranging mainly from 860 to 1000 ma different from that of the bikou group with ages from 745 to 890 ma ages of zircons from the lieguliu and guanyinya formations range from 740 to 900 ma the paleoproterozoic detrital zircons commonly have negative or slightly positive hf values from 8 0 to 2 3 whereas most of the 1000 740 ma zircons have moderately to significantly high positive hf values from 0 3 to 13 0 the new detrital zircon u pb and lu hf isotopic dataset suggests four major episodes of magmatism in the region 2500 2300 1900 1700 1650 1500 and 1000 740 ma and the presence of widespread archean basement of the western yangtze block the data also suggest an important period of juvenile magmatism at 1000 740 ma our results favor a model in which continuous subduction 1000 740 ma along the western margin of the yangtze block lasted for 260 million years

growth and evolution of precambrian continental crust in the southwestern tarim terrane new evidence from the ca 1 4 ga a type granites and paleoproterozoic intrusive complex abstract the precambrian tectonic evolution and growth of continental crust in the southwestern tarim craton in nw china remain enigmatic in this contribution we report petrography zircon u pb ages geochemistry and nd hf o isotope data on the ca 1 4 ga granitic pluton in southwestern tarim terrane we also present zircon u pb ages and hf isotope data on the paleoproterozoic intrusive complex from this area and use the combined data to evaluate precambrian tectonic evolution of the region in relation to the columbia supercontinent the ca 1 4 ga azibailedi pluton is mainly composed of biotite monzogranite with contents sio2 72 8 75 1 wt the major element chemistry of the pluton reveals alkali calcic and ferroan affinities and metaluminous to peraluminous feature with a cnk ranging from 0 86 to 1 15 the granite shows high total ree contents with variable enrichment in lree la yb n 8 5 12 2 both ree and other incompatible elements features define a type affinities the initial epsilon nd values vary from 3 5 to 2 2 and zircon hf t and 18o values range from 4 1 to 6 1 and 7 1 to 8 6 integrating geological geochemical and nd hf o isotope data we suggest that the azibailedi a type granites were derived from pre existing early paleoproterozoic mafic lower crust with involvement of variable amount of paleoproterozoic juvenile crust possibly trigged by basaltic magma upwelling during the breakup of the columbia supercontinent u pb geochronology and hf isotopic analyses of zircons from the paleoproterozoic heluositan intrusive complex show crustal growth episodes during 2 2 4 2 ga with peaks at 2 3 2 5 ga 3 3 ga and 3 6 3 8 ga distinct from the other precambrian terranes of the tarim craton a comprehensive synthesis of the records of assembly and breakup of columbia supercontinent from different precambrian terranes in the tarim craton show significant differences the temporal distinction in tectonothermal events and the marked difference in the continental crust growth processes suggest that the early precambrian basement of the tarim craton was possibly composed of discrete terranes which were fragmented from different ancient cratonic nuclei

uranium enrichment in the lala cu fe deposit kangdian region china a new case of uranium mineralization associated with an iocg system abstract elevated uranium concentrations have been reported in many iocg deposits but detailed information about the occurrences of uranium minerals and their relationships with other minerals remains scarce which hinders understanding of the mineralization mechanisms and the nature of the association of these metals this paper reports a new case of uranium enrichment in an iocg system the lala cu fe deposit in the kangdian region sw china whole rock analyses of ores and barren rocks yielded highly variable u concentrations ranging from 0 76 to 266 ppm uranium shows a strong positive correlation with mo broadly positive correlations with cu and ree and a vague negative correlation with th four uranium minerals uraninite uo2 uranothorite th u sio4 polycrase y ca ce u th ti nb ta 2o6 and coffinite u sio4 1 x oh 4x were identified the uraninite is divided into two phases phase 1 ur1 characterized by corroded or irregular crystal shapes and phase 2 ur2 showing well developed subhedral to euhedral crystal shapes ur1 is interpreted to be formed in the primary cu fe mo ree u mineralization together with the bulk of cu and other metal sulfides as well as other u and ree minerals including uranothorite polycrase bastnasite and xenotime and accompanied by k alteration k feldspar and biotite ur2 is interpreted to be formed in a secondary hydrothermal event characterized by introduction of fluorite and carbonates in which u and mo and to lesser extent cu and ree were remobilized while th remained relatively stable the primary mineralization is inferred to have taken place in a period from ca 1086 to 1053 ma based on previous re os geochronology and the secondary mineralization remobilization likely took place from ca 888 to 828 ma as suggested by uraninite chemical ages obtained in this study and other published geochronological data these ages correspond to tectonomagmatic events taking place in generally extensional environments in the western margin of the yangtze block during the meso to neoproterozoic time the lala cu fe deposit represents a new case of iocg deposits with u and ree enrichment the economic potential of which warrants further examination

mineralogical and geochemical constraints on mobilization and mineralization of rare earth elements in the lala fe cu mo ree deposit sw china the lala fe cu mo ree deposit in the northern kangdian iocg metallogenic province sw china has a paragenetic sequence that includes pre ore na alteration stage i fe p mineralization stage ii and sulfide mineralization stage iii rare earth element ree minerals which are chiefly monazite parasite and bastnasite with minor xenotime are associated with sulfide mineralization these ree minerals together with biotite muscovite and calcite are accompanied with k ca carbonate alteration of stage iii where magnetite and apatite of stage ii are overprinted by minerals of stage iii the apatite grains are commonly embayed or eroded and contain abundant rounded to subrounded and needle like inclusions of monazite and minor bastnasite calcite and sulfide minerals these monazite bearing apatite grains are texturally similar to metasomatized apatite in the laboratory and can be attributed to the formation from stage ii apatite via a dissolution precipitation process during fluid infiltration the monazite bearing apatite has ree contents and la sm ratios much lower than the original stage ii apatite suggesting that rees were leached and mobilized from this stage ii apatite and that these processes were responsible for the formation of monazite inclusions within the apatite hosts the monazite inclusions have compositions similar to those of stage iii monazite suggesting that rees in stage ii apatite were mobilized by stage iii fluids consistent with occurrences of sulfide and calcite inclusions within the apatite mass balance analysis using bulk compositional data for host rocks that underwent k ca carbonate alteration indicates that rees of the hosting rocks were also mobilized and that up to 70 percent of the light rees were leached out during alteration therefore ree mobilization recorded in apatite grains and country rocks support a model in which the country rocks were important sources for rees in the lala deposit compositions of amphibole and biotite together with previously acquired fluid inclusion data demonstrate that stage iii fluids are dominated by na and cl but had higher k co2 or hco3 and co32 and hf hcl fugacity and lower salinity nacl than stage ii fluids elevated k and co2 in stage iii fluids or associated k carbonate alteration is proposed to be important for extensive ree mobilization on country rocks the rees leached from country rocks are inferred to have been transported as chloride complexes prior to being deposited as ree minerals deposition of ree minerals from stage iii fluids was likely triggered by mixing with external relatively low temperature f rich and high ph fluids and or by local interaction with carbonate host rocks we suggest that the common association of rees with cu ores in many iocg deposits is related to the unique nature of the cu mineralizing fluids

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

paleoproterozoic porphyries and coarse grained granites manifesting a vertical hierarchical structure of archean continental crust beneath the yangtze craton abstract granites generated by anatexis are ideal crustal probes to decipher the differentiation processes within deep continental crust in this study the successive emplacement of granites including the porphyries and the coarse grained granites was found in the nucleus the kongling complex of the yangtze craton the porphyries intruding at 1840 17 ma shrimp ages occur as veins and contain phenocrysts of k feldspar 15 quartz 5 plagioclase 4 and garnet 1 setting in a fine grained groundmass 75 of k feldspar plagioclase quartz and biotite the coarse grained granites emplacing at 1821 8 ma shrimp ages are outcropped as pluton and comprise k feldspar 60 quartz 30 biotite 5 plagioclase 5 they are similar to a type granites with relatively high sio2 69 2 71 5 wt 72 6 74 5 wt high fe2o3t mgo 21 5 27 7 5 9 19 5 104 ga al ratios 3 6 4 3 2 7 3 5 respectively and enriched hfses th u pb ga the porphyries contain higher total trace element contents and zirconium saturation temperature mean 892 c than those of the coarse grained granites mean 803 c magmatic zircons from the porphyries and coarse grained granites have ehf t values of 17 6 to 11 7 and 21 0 to 14 8 which yield two stage hf model ages of 3 6 3 3 ga and 3 8 3 4 ga respectively both falling into the evolutionary trend of the 2 9 2 8 ga kongling ttgs it implies both granites are anatectic crustal reworking derivatives from partial melting of the archean ttgs under sustaining extension in paleoproterozoic applying trace element modelling we further identify a unique tonalitic source for both granites which is analogous to the exposed natural kongling tonalite and find the porphyries slightly affected by the juvenile crust based on the intrusion of porphyry veins into granitic gneisses we envisage the crustal structure beneath the craton is layered from older 2 94 ga tonalites upward to younger 2 87 ga granitic gneisses such hierarchical structure could shed new light on the imperceptible vertical differentiation process as cratonization

u pb zircon and sm nd isotopic study of the huangtuling granulite dabie sulu belt china implication for the paleoproterozoic tectonic history of the yangtze craton sims data demonstrate archean 2 9 to 2 7 ga and paleoproterozoic 1991 43 ma ages for rounded detrital zircon cores and unzoned rims respectively in a graulite sample collected from huangtuling dabie sulu orogenic belt china the granulite rocks in this locality have pelitic compositions and represent an exposure of the northern margin of the yangtze craton the rounded zircon cores show oscillatory zoning and have th u ratios 0 17 0 78 systematically higher than those of the unzoned luminescent rims 0 005 0 03 the age of the detrital zircon cores and whole rock nd isotope model age suggest that the huangtuling granulite was possibly derived from a provenance dominated by archean rocks similar to the kongling complex exposed 200 km in the southwest multiple phases of metamorphism have been identified for the granulites with the dominant granulite facies mineral assemblage defining an early clock wise metamorphic p t path orthopyroxene plagioclase and whole rock material define a linear trend in a 147sm 144nd 143nd 144nd diagram corresponding to an age of 1926 146 ma this result and the u pb data for the zircon rims suggest that a collisional event may have occurred along the northern margin of the yangtze craton at 2 0 ga inviting further study on whether the yangtze craton was involved in the assembly of the recently proposed paleo mesoproterozoic supercontinent columbia

hydrothermal alteration of magmatic zircon related to nacl rich brines diffusion reaction and dissolution reprecipitation processes magmatic zircon from altered gabbros adjacent to the 1 07 ga lala fe cu deposit sw china was modified by nacl rich brines related to the fe cu mineralization the modified zircon grains are composed mostly of both inclusion free and porous domains and some grains also have overgrowth rims the inclusion free domains commonly overgrown by the porous domains are roughly homogeneous under bse imaging but display oscillatory or sector zoning under cl imaging in contrast the porous domains are distinctly mosaic like under cl imaging and contain abundant pores and mineral inclusions such as thorite xenotime ree rich phases actinolite albite biotite and calcite the inclusion free domains have concentrations of non formula elements for example al ca and fe much higher than the magmatic zircon and are thus interpreted to be products of interaction between magmatic zircon possibly metamictized and the fluids via a diffusion reaction process however these resultant domains have retained the th and u contents ree patterns u pb ages and hf isotopes of the precursor magmatic zircon on the other hand the porous domains have stoichiometric end member compositions that is lowered th u ree y and p and given that they are porous and inclusion rich we proposed that they have formed from the precursor element rich inclusion free domains or magmatic zircon via a fluid induced dissolution reprecipitation process it is notable that the porous domains retained the 177hf 176hf ratios of the precursors but possess modified and meaningless u pb ages instead a meaningful u pb age 1006 62 ma similar to the timing of the lala deposit is well recorded by the overgrowth rims with distinctly high lrees la 50 700 ppm and elevated hf isotopic ratios our new results reveal that in the presence of the nacl rich brines the nature of the precursor magmatic zircon that is high element budgets and or metamictization plays a key role on hydrothermal alteration of zircon

early neoproterozoic assembly of the yangtze block decoded from metasedimentary rocks of the miaowan complex abstract the present yangtze block was proposed to be formed as a unified block in the mesoproterozoic neoproterozoic transition but the detailed timing and process are poorly constrained here we report integrated in situ u pb and hf o isotopic analyses of detrital zircons from the xiaoxikou metamorphosed sedimentary rocks of the miaowan complex in the yangtze block as well as u th pb and nd o isotopic analyses of magmatic monazites from an undeformed and unmetamorphosed leucocratic vein intruding these metasedimentary rocks u pb dating results for detrital zircons from the metasedimentary rocks display two main age peaks at ca 970 and 900 ma the 970 ma zircons are dominantly characterized by mantle like 18ozir values 4 5 5 8 and highly depleted ehf t values 5 to 14 the 900 ma zircons mostly have o and hf isotopic features similar to the 970 ma zircons except relative small proportion of grains with high 18o values 6 0 9 2 and variable ehf t values 33 to 7 monazites from the vein are dated at ca 850 ma and have uniform 18o values 5 4 6 6 but significantly enriched end t values 14 5 to 12 6 based on the new isotopic results and immature lithology the xiaoxikou metasedimentary rocks are interpreted to be deposited between 900 ma and 850 ma in a fore arc basin and clastic materials derived from 970 900 ma arc rocks were related to the northward subduction present day coordinates of the miaowan oceanic plate the 850 ma leucocratic vein shows geological and isotopic characteristics consistent with local 860 840 ma post tectonic granitic plutons and may represent a fractionated product of local coeval granitic magmas we propose that the closure of the miaowan oceanic basin and formation of the current unified yangtze block occurred between 900 ma and 860 ma i e later than the deposition of the fore arc metasedimentary rocks while earlier than the emplacement of the post tectonic plutons

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

petrogenesis of archean ttgs and potassic granites in the southern yangtze block constraints on the early formation of the yangtze block abstract the southern yangtze is underlain by mesoarchean igneous rocks that were emplaced in two pulses including trondhjemites at ca 3092 3071 ma followed by potassic granites at 2920 ma these represent the oldest ttg suites identified in the southern yangtze and the oldest potassic granites in the entire yangtze block hf isotopic analysis reveals ehf t values of 2 49 7 49 and hf crustal model ages tdmc of 3601 3000 ma for zircons from the trondhjemites whereas those from the potassic granites show ehf t values of 1 79 4 18 and tdmc ages of 3453 3043 ma the trondhjemites have high sio2 mg and low al2o3 and k2o na2o and are highly evolved with low ni cr and co the trondhjemites are characterized by low sr y eu gd and la yb n and high y and hree typical of high hree and low pressure ttgs their geochemical and isotopic compositions indicate that they are derived from melting of juvenile mafic crust with little contribution from older crustal materials consistent with a plagioclase bearing basaltic source the multielement patterns of potassic granites are similar to that of the trondhjemites albeit with lower hree and y contents their high k2o values strongly fractionated ree patterns and low y contents indicate the presence of garnet and or amphibole as residual phases in the source region which indicates they formed at higher pressure than the trondhjemites the isotopic and geochemical data imply that the formation of the potassic granites could be related to reworking of older ttgs the increasing k2o na2o of the 3092 3071 ma trondhjemites to potassic 2920 ma granites corresponds with stabilization maturation and thickening of the archean continental crust in the southern yangtze the geochemical data of the ttgs in the kunming region show important differences from that of contemporaneous ttgs from the kongling complex suggesting that southern yangtze is composed by an independent old nucleus which is exotic to the northern yangtze a synthesis of petrogenesis geochronology geochemistry and isotope data of archean granites of the yangtze block provides important insights into the architecture of its archean crust we propose that the yangtze block can be subdivided into discrete northwestern northeastern and southern domains but which are all affected by late paleoproterozoic tectonothermal events suggesting that they had been assembled together by then to form the united yangtze block

geochemistry of magnetite from proterozoic fe cu deposits in the kangdian metallogenic province sw china fe cu deposits in the kangdian fe cu metallogenic province sw china are hosted in paleoproterozoic meta volcanic sedimentary sequences and are spatially associated with coeval mafic intrusions several well known examples are the giant lala dahongshan and yinachang deposits they have a common paragenetic sequence of an early fe oxide stage associated with sodic alteration and a late cu sulfide stage associated with potassic carbonate alteration magnetite dominates the fe oxide stage of these deposits but is also present in the cu sulfide stage of the lala deposit this study uses trace element compositions of magnetite to examine the nature and origin of the ore forming fluids the magnetite has variable concentrations of ti al mg mn si v cr ca co ni sc zn cu mo sn and ga which are thought to have been controlled mainly by fluid compositions and or intensive parameters e g temperature and oxygen fugacity fo2 fluid rock interaction and coprecipitating mineral phases appear to be less important in controlling the magnetite compositions magnetite grains in the fe oxide stage of the lala and dahongshan deposits have comparable trace element compositions and were likely precipitated from chemically similar fluids high ni contents of magnetite in both deposits coupled with previous isotopic data and the fact that the two deposits are spatially associated with coeval mafic intrusions strongly suggest that the ore forming fluids were genetically related to the mafic magmas that formed the intrusions magnetite grains in the fe oxide stage of the yinachang deposit have much lower v and ni but higher sn and mo contents than those of the lala and dahongshan deposits and are thus thought to have precipitated from more oxidized and mo sn rich fluids that may have evolved from relatively felsic magmas magnetite grains from the cu sulfide and fe oxide stages of the lala deposit are broadly similar in composition but those in the cu sulfide stage have slightly higher cu zn and mn and are thought to have crystallized from relatively low temperature and cu zn mn rich fluids evolved from the fluids of the early fe oxide stage our results show that magnetite from the fe cu deposits in the kangdian province banded iron formation fe skarn deposits diabase hosted hydrothermal fe deposits and magmatic deposits has significantly different compositions we propose that covariations of co ni zn sn and co ni mn can be used to effectively discriminate different deposit types

neoproterozoic adakitic plutons and arc magmatism along the western margin of the yangtze block south china abstract neoproterozoic adakitic plutons that crop out along the western margin of the yangtze block south china from kangding on the north to panxi on the south provide constraints on the origin of the giant jinningian magmatic event of south china representative plutons include the xuelongbao 750 ma datian 760 ma and dajianshan intrusions the latter two bodies consist mainly of granodiorite with relatively high sio2 51 0 73 4 wt and mg s 0 36 0 55 they have fractionated rare earth element patterns with la yb n ratios ranging from 2 6 to 101 8 and are characterized by high sr 344 1018 ppm and low y 4 3 17 9 ppm yielding sr y ratios ranging from 27 to 111 on primitive mantle normalized trace element diagrams these rocks show enrichment of large ion lithophile elements and depletion of high field strength elements nb ta with positive zr hf and negative ti anomalies consistent with an arc related setting they have relatively constant initial whole rock 87sr 86sr ratios 0 70

geology mineralization styles and age of ore hosting rocks of the proterozoic longbohe sin quyen fe cu belt implications for regional metallogeny abstract a number of proterozoic fe cu deposits or prospects are distributed along the ailao shan red river shear zone asrr in south yunnan china and northern vietnam defining the potentially important longbohe sin quyen fe cu belt this belt was tentatively considered to be initially part of the proterozoic kangdian fe cu province in southwestern yangtze block sw china before being southeastward displaced into the cenozoic asrr however such a model is still not confirmed convincingly due to poor understanding of ore genesis of the belt and lack of comprehensive comparisons in this paper we described the geology and mineralization styles of typical deposits the longbohe and sin quyen deposits in the longbohe sin quyen fe cu belt and obtained new zircon u pb ages of ore hosting rocks and intruding granites to evaluate if this belt is comparable with the kangdian fe cu province both the longbohe and sin quyen deposits which are located in northwestern south yunnan china and southeastern northern vietnam sections of the belt respectively are hosted in volcanic sedimentary rocks that were traditionally named as the longbohe and sin quyen groups respectively both the ores and hosting rocks in the two deposits are variably metamorphosed or deformed but our results reveal that both deposits have similar paragenetic sequences including pre ore na alteration and early fe ree mineralization magnetite and allanite followed by cu mineralization chalcopyrite such mineralization styles are broadly comparable to those of the fe cu deposits in the kangdian province our new zircon u pb dating on meta volcanic and sedimentary rocks of the ore hosting longbohe group and intruding granites indicate that this group consists of at least two parts forming at 1000 750 and 1700 ma and thus is termed as the upper and lower longbohe groups in this study on the other hand the new zircon ages of the ore hosting sin quyen group and intruding granites tightly constrain the depositional age of this group as 870 830 ma broadly synchronous with the upper longbohe group sedimentary rocks of the upper longbohe group contain detrital zircon with ages dominantly clustering at 2 9 2 7 2 3 2 2 1 9 1 7 1 5 1 3 and 1 2 1 05 ga broadly similar to those of the sin quyen group even though the latter also contains an additional spectrum of 1 0 0 87 ga in total these ages of detrital zircon are comparable with those of the synchronous strata in the kangdian fe cu province such as the kunyang huili and yanbian groups it is also important to note that our newly identified 1700 ma lower longbohe group is comparable to synchronous strata in the kangdian fe cu province such as the 1700 ma hekou and dahongshan groups such similarities of ore hosting rocks in both regions provide robust evidence to support that the longbohe sin quyen fe cu belt is initially part of the kangdian fe cu metallogenic province before being displaced into the cenozoic asrr shear zone this new recognition has important implications for regional fe cu exploration particularly in the asrr shear zone

zircon ages and nd hf isotopic composition of the zhaertai group inner mongolia evidence for early proterozoic evolution of the northern north china craton the mesoproterozoic rifting and accompanying magmatism and sedimentation in the north china craton are interpreted to be related to the breakup of the paleoproterozoic supercontinent columbia this study presents zircon ages and nd hf isotopic data of the low grade mesoproterozoic zhaertai group exposed along the northern margin of the north china craton sandstones of the zhaertai group contain detrital zircon populations of about 2500 ma which originated from the late archean basement rocks underlying this group a close match between the u pb ages and the tdm hf ages with high initial ehf values at 2500 ma for the detrital zircon grains imply a juvenile origin for protoliths of the basement rocks sedimentation of the zhaertai group likely began around 1750 ma tentatively constrained by the formation time of an intercalated volcanic layer the volcanic rocks have low initial end values of 8 0 to 8 5 at 1750 ma similar to those of contemporaneous mafic dyke swarms within the north china craton which have been interpreted to be related either to the breakup of the supercontinent columbia or to the post collisional collapse of the trans north china orogen a progressive increase of end values of whole rock samples upwards in the stratigraphic sequence likely indicates an increase of juvenile material with time probably related to the contribution of mesoproterozoic mantle derived rocks 2007 elsevier ltd all rights reserved

petrogenesis of the huashanguan a type granite complex and its implications for the early evolution of the yangtze block abstract an integrated study of petrography zircon u pb ages hf o isotope compositions as well as whole rock geochemistry was carried out for a paleoproterozoic granite complex in the northern yangtze block to investigate its petrogenesis and geological significances petrographically the huashanguan complex is a granite complex comprised of monzogranite in the marginal facies and k feldspar granite in the central facies u pb dating of magmatic zircons from the monzogranite and k feldspar granite yielded ages of 1816 50 ma and 1843 9 ma respectively the more precise age of 1843 9 ma is suggested to represent the formation age of the huashanguan complex the granites have uniform negative zircon e hf t values of 20 2 to 15 8 with corresponding t dm2 ages of ca 3 6 3 5 ga the 18 o values average at 6 80 0 09 these indicate that the granites were generated by partly melting of archean rocks implying the widespread of archean basement in the yangtze block the monzogranites display low feo t and mgo contents and evolved trace element features suggesting their formation by more fractional crystallization from similar parent magma of the k feldspar granites the occurrence of the huashanguan granite complex indicates that the yangtze block has experienced a tectonic transition from tectonic convergence to extension at ca 1 85 ga possibly due to the collapse of the ca 2 0 ga orogeny

paragenesis stable isotopes and molybdenite re os isotope age of the lala iron copper deposit southwest china the lala fe cu deposit in the kangdian iron oxide copper gold iocg metallogenic province sw china is hosted in the paleoproterozoic hekou group this volcanic sedimentary sequence has undergone upper greenschist lower amphibolite facies metamorphism at 850 ma the deposit contains more than 200 million metric tons mt of fe cu ores with an average grade of 13 wt fe and 0 92 wt cu orebodies are roughly strata bound but occur along foliation lithologic contacts and shear zones the paragenetic sequence of the lala deposit includes metamorphosed i ii and iii and unmetamorphosed iv and v stages stage i is characterized by extensively pervasive na alteration forming abundant albite but minor scapolite stage ii occurs as massive and banded replacements consists of ti v poor magnetite and apatite with minor disseminated sulfide minerals and was associated with pervasive k fe alterations forming k feldspar chlorite and actinolite stage iii occurs predominantly as bands and disseminations confined along foliations with minor veinlets cross cutting hosting rocks this stage is characterized by abundant fe cu mo sulfides intergrown with angular magnetite and minor titanite and allanite and is associated with alteration of carbonate quartz fluorite and mica stage iv has an assemblage dominated by chalcopyrite with variable pyrite and bornite occurring as veins of sulfides quartz calcite biotite muscovite fluorite stage v occurs chiefly as veins of hematite calcite quartz and also results in extensive hematization stages ii and iii have fluids with high 18 o 7 2 11 7 and 34 s values 0 4 indicative of a magmatic hydrothermal origin however the stage iii fluids have 34 c values 0 5 close to the least altered marble 0 2 of the hosting rocks indicating a possible contribution of strata sourced carbon the stage iv fluids have 34 c values similar to and 18 o 4 1 6 7 lower than the stage iii fluids and a wider range of 34 s values 9 0 to 10 5 consistent with significant contributions of strata sourced sulfur fluids of the late barren vein stage v have relatively low 34 c 4 0 to 2 4 and 18 o values 2 9 to 0 6 indicative of significant contributions of meteoric and oxidized fluids molybdenite from stage iii has an re os isotope age of 1086 8 ma providing tight constraints on the timing of the main stage of mineralization this age indicates that the lala deposit is coeval with the 1100 ma intraplate magmatism in the western yangtze block we propose that the majority of the fe cu deposits in the kangdian iocg metallogenic province may have formed in an intraplate extensional setting although it is possible that some of the deposits may have involved in multiple events including modification by the neoproterozoic metamorphism forming the mineral assemblages of stage iv

new insights into the genesis of iocg deposits from a case study of the yinachang deposit in sw china abstract the yinachang fe cu au u ree deposit is hosted by the lower part of the paleoproterozoic kunyang group in the central yunnan province of sw china in an area known to contain iron oxide cu au mineralisation the deposit includes i the sulphide assemblage chalcopyrite pyrite magnetite cobaltite molybdenite cassiterite ii rare earth element assemblage bastnaesite parasite fergusonite xenotime monazite iii the uranyl hydroxide mineral vandendriesscheite iv gold commonly hosted by ankerite and v the gangue mineral assemblage apatite biotite fluorspar quartz calcite the ore is commonly massive disseminated banded or in calcite veins the banded mineralisation contains high concentration of au co mo u fe cu and ree and the vein type mineralisation has abundant ree minerals of bastnaesite parisite fergusonite and xenotime monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite and the uranium is associated with chalcopyrite the mineralising process can be divided into an initial na alteration followed by the ore forming assemblages of fe ree and cu au u ree mineralisation the average 18oh2o values in the quartz and calcite change are between 3 5 and 10 7 with dv smow values ranging between 98 2 and 47 7 the calcite siderite and ankerite have 13c isotope composition ranges from 14 to 1 and 18o compositions of 6 9 to 22 the h o c isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources whereas the carbon is sourced from marine carbonate and the low temperature alternation of polyphase mantle material in situ 34s sulphide value ranges between 1 1 and 11 9 and the bulk 34s value ranges between 4 7 and 10 5 in situ pb isotopes of sulphide samples have 206pb 204pb values of 18 58 18 76 207pb 204pb values of 15 51 15 66 and 208pb 204pb values of 37 47 38 06 these values plot in the upper crust pb evolution curve indicative of a complex source of pb in the deposit the pb is interpreted to have a deep seated magmatic source with a contribution from the crust it is also proposed that the ree mineralised fluids are derived from a late stage of alkaline magma differentiation the 40ar 39ar biotite date indicates that the precambrian rocks in the kangdian region were regionally metamorphosed at ca 900 ma the yinachang fe cu au u ree deposit is interpreted as an iocg deposit based on geological and isotopic studies the banded ore and vein type ore are the main exploration targets for uranium gold and ree this study helps us better understand iocg deposits in china

zircon u pb age and trace element evidence for paleoproterozoic granulite facies metamorphism and archean crustal rocks in the dabie orogen abstract zircon u pb ages and trace elements were determined for granulites and gneiss at huangtuling which are hosted by ultrahigh pressure metamorphic rocks in the dabie orogen east central china cl images reveal core rim structure for most zircons in the granulites the cores show oscillatory zoning relatively high th u ratios and hree enriched patterns consistent with a magmatic origin they gave a weighted mean 207pb 206pb age of 2766 9 ma interpreted as dating magma emplacement of the protolith the rims are characterized by sector or planar zoning low th u ratios negative eu anomalies and flat hree patterns consistent with their formation under granulite facies metamorphic conditions zircon u pb dating yields a weighted mean 207pb 206pb age of 2029 13 ma which is interpreted to record a metamorphic event possibly during assembly of the supercontinent columbia the gneiss has a protolith age of 1982 14 ma which is younger than the zircon age of the granulite facies metamorphism suggesting a generally delay between ht metamorphism and the intrusion of post collisional granites a few inherited cores with igneous characteristics have 207pb 206pb ages of 2 90 3 28 and 3 53 ga suggesting the presence of mesoarchean to paleoarchean crustal remnants in the yangtze craton a few cretaceous metamorphic ages were also obtained suggesting the influence of post collisional collapse in response to cretaceous extension of the dabie orogen it is inferred that the recently discovered archean basement of the yangtze craton occurs as far north as the dabie orogen

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen