high precision isotopic characterization of usgs reference materials by tims and mc icp ms the pacific centre for isotopic and geochemical research pcigr at the university of british columbia has undertaken a systematic analysis of the isotopic sr nd and pb compositions and concentrations of a broad compositional range of u s geological survey usgs reference materials including basalt bcr 1 2 bhvo 1 2 andesite agv 1 2 rhyolite rgm 1 2 syenite stm 1 2 granodiorite gsp 2 and granite g 2 3 usgs rock reference materials are geochemically well characterized but there is neither a systematic methodology nor a database for radiogenic isotopic compositions even for the widely used bcr 1 this investigation represents the first comprehensive systematic analysis of the isotopic composition and concentration of usgs reference materials and provides an important database for the isotopic community in addition the range of equipment at the pcigr including a nu instruments plasma mc icp ms a thermo finnigan triton tims and a thermo finnigan element2 hr icp ms permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the tims and mc icp ms methods e g nd isotopic compositions for each of the reference materials 5 to 10 complete replicate analyses provide coherent isotopic results all with external precision below 30 ppm 2 sd for sr and nd isotopic compositions 27 and 24 ppm for tims and mc icp ms respectively our results also show that the first and second generation usgs reference materials have homogeneous sr and nd isotopic compositions nd isotopic compositions by mc icp ms and tims agree to within 15 ppm for all reference materials interlaboratory mc icp ms comparisons show excellent agreement for pb isotopic compositions however the reproducibility is not as good as for sr and nd a careful sequential leaching experiment of three first and second generation reference materials bcr bhvo agv indicates that the heterogeneity in pb isotopic compositions and concentrations could be directly related to contamination by the steel mortar pestle used to process the materials contamination also accounts for the high concentrations of certain other trace elements e g li mo cd sn sb w in various usgs reference materials

tectonic evolution of the qinling orogenic belt central china new evidence from geochemical zircon u pb geochronology and hf isotopes abstract the qinling orogenic belt qob located between the north china craton ncc and the yangtze craton yzc is composed of the northern qinling belt nqb and the southern qinling belt sqb this study presents new geochemical data zircon u pb ages and hf isotopes from a suite of metamorphic rocks from the kuanping qinling danfeng douling and wuguan groups in the nqb and the sqb our results suggest that the qinling group in the nqb formed in an active continental margin related to the subduction of the songshugou ocean under the southern ncc during grenvillian period the kuanping group in the northern nqb was deposited in the within plate extension basin during late neoproterozoic to early paleozoic the detritus of sedimentary rocks of the kuanping group were mainly sourced from the nqb and subordinately from the basement rocks of the ncc the danfeng group in the southern nqb formed later than 827 ma with the sediments derived mainly from the qinling terrane the nqb witnessed multiphase tectono thermal events from mesoproterozoic to early paleozoic including several magmatic events and the early paleozoic metamorphic event the original douling group in the sqb represents the basement complex of the sqb which is composed of rocks with different formation ages the oldest rock in the complex is represented by 3 0 ga granitic gneiss which underwent at least two periods of metamorphism at 2 5 ga and 0 97 0 91 ga in this study the douling group is redefined as a suite of neoproterozoic 860 750 ma rocks formed in an extensional setting after the subduction of the songshugou ocean the wuguan group in the sqb formed in the middle late neoproterozoic later than 740 ma and was subjected to early paleozoic metamorphism our data indicate that the sqb experienced early neoproterozoic 970 865 ma and early paleozoic 444 ma metamorphism and strong middle neoproterozoic 870 730 ma magmatism the age spectra of zircons from the nqb trace major tectono thermal events at 1462 ma 927 ma and 412 ma which are different from those recorded in the southern ncc and northern yzc suggesting that the nqb had a distinct evolution during mesoproterozoic to early neoproterozoic grenvillian the hf isotopic compositions of zircons from the various rocks suggest that the nqb probably developed on the basement of the southern ncc the rocks in the sqb show zircon age spectra and hf isotope compositions similar to those in the northern yzc suggesting a close affinity we therefore interpret the sqb to have developed on the basement of the northern yzc integrating the new data in this study with those from previous works we propose a new tectonic model for the formation and evolution of the qob during late mesoproterozoic to early paleozoic involving the following major events 1 late mesoproterozoic to early neoproterozoic grenvillian northward subduction of the songshugou ocean 2 early middle neoproterozoic 870 800 ma bidirectional subduction and collision 3 middle neoproterozoic 800 710 ma post collision extension 4 middle late neoproterozoic 710 600 ma within plate extension 5 late neoproterozoic early paleozoic 600 520 ma opening of the shangdan ocean and 6 early paleozoic 520 420 ma subduction collision we thus trace at least two distinct wilson cycles in the qob

genetic relationship between 1780 ma dykes and coeval volcanics in the lvliang area north china abstract the 1780 ma dykes and coeval volcanics constitute a large igneous province in the north china craton however whether these dykes and volcanic rocks of varying compositions originated from one or multiple sources remains controversial the ca 1780 ma lvliang dykes are characterized by widespread e w oriented dykes and minor n w oriented diabase dykes the e w oriented dykes are bimodal and comprise two subgroups one is dominated by acidic high silica dykes sio 2 63 wt while the other is dominated by mafic to intermediate relatively low silica dykes sio 2 sims u pb dating on zircons from one high silica dyke and a rhyolite volcanic layer yields 207 pb 206 pb ages of 1783 7 ma and 1776 6 ma respectively and sims u pb dating on baddeleyites from a low silica dyke yields a 207 pb 206 pb age of 1789 5 ma they are all tholeiitic in composition mgo 0 3 6 1 wt sio 2 51 74 wt enriched in light rare earth elements la yb n 7 9 20 2 and show negative anomalies in nb ta sr and eu eu eu 0 3 0 9 they also have similar in situ hf isotopes of baddeleyite zircon ehf values of 14 5 to 1 8 and bulk rock end 6 7 to 3 0 isotopes furthermore immiscible textures are identified from the xiaoliangling group volcanics which are characterized by some silica rich melts globules in the fe rich magma these spatiotemporal affinities and geochemical similarities as well as the identified immiscible textures reveal that the low silicate dykes are conduits for the basalt andesite with significant fractionation of clinopyroxene and plagioclase while the high silica dykes are conduits for the rhyolite dacite with distinct immiscible segregation prior to eruption in addition there is a sharp change of ehf values at 1780 1730 ma and their hf t dm ages are 2750 1950 ma as these rocks originated from the subcontinental lithospheric mantle this may indicate that the subcontinental lithospheric mantle was metasomatized during this time period possibly by a paleo plume event

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

the lightning creek sill complex cloncurry district northwest queensland a source of fluids for fe oxide cu au mineralization and sodic calcic alteration the lightning creek cu au prospect is hosted by a cogenetic suite of plutonic i type granitoids the dominant rock type is a porphyritic quartz monzodiorite that is intruded by more fractionated rocks including monzogranite and alkali feldspar granite a series of flat lying sills are interpreted to be late stage differentiates based on their timing mineralogy and chemistry in parts of the prospect there is pervasive sodic calcic alteration pyroxene after amphibole albite after k feldspar and oligoclase of the plutonic rocks this alteration predates sill emplacement and is unrelated to veining or fracturing of any kind the presence of small amounts of carbonate in the altered rocks suggests that the fluids were co2 bearing quartz and feldspar separates from these altered rocks have oxygen isotope compositions similar to those from fresh quartz monzodiorite suggesting that the fluids were hot and of magmatic composition sodium and ca were added and k fe cl and cu were stripped during what is interpreted as an autometasomatic event the sills display considerable textural and mineralogical complexity and evolved from equigranular quartzofeldspathic rocks aplites with magmatic chemistry to unusual fe rich rocks albite magnetite quartz that exhibit a range of bizarre spherulitic textures some of the albite and magnetite in the sills is secondary albite forms pseudomorphs after k feldspar na fe ca alteration along sill margins and within sills at the contacts between different textural zones halos of disseminated magnetite clinopyroxene fe ca na alteration are developed adjacent to early magnetite veins fluid inclusion studies indicate that these rocks crystallized at temperatures in excess of 500 c and at pressures in excess of 1 5 kbar the range of spherulitic textures is taken to indicate crystallization under hydrous conditions with the episodic release of a fluid phase this magmatic fluid phase was dominated by h2o co2 and chlorine and underwent phase separation into a co2 rich vapor and a hypersaline brine 33 55 wt nacl equiv the hypersaline fluid was enriched in fe 10 wt and cu 1 wt pixe analysis in addition to na k and ca where this fluid was retained within fe rich portions of the sills it caused ca fe na alteration pyroxene albite magnetite growth at the expense of quartz where the fluid was expelled from the sills it produced quartz magnetite clinopyroxene albite veins broadly coeval with the early magnetite veins although rich in cu these granitoid derived magmatic fluids did not generate significant cu au mineralization perhaps because of the high temperatures involved and or a lack of reduced sulfur in the fluids or host rock however the amount of iron present is estimated from the aeromagnetic anomaly to be in excess of 2 000 million tonnes mt a later generation of calcite chlorite pyrite chalcopyrite veins contain traces of cu au mineralization fluid inclusion and stable isotope work indicate that these veins probably crystallized from cooler 200 c more dilute 15 28 wt nacl equiv fluids perhaps generated by the admixture of a meteoric component the conclusions reached in this study have implications for understanding the genesis of fe oxide cu au deposits and related sodic calcic alteration the study indicates the potential for co2 rich granitoid magmas to evolve hypersaline fe and cu rich fluids capable of causing intense magnetite veining and cu au mineralization autometasomatic sodic calcic alteration of the granitoids may be an important precursor to mineralization contributing fe k cu and cl to the magmatic fluids

timing of tibetan uplift constrained by analysis of volcanic rocks the tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1 2 and cenozoic global climate change3 the present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1 2 an age for the uplift would provide a valuable constraint on these models but because recently proposed indicators of uplift are all climate dependent they are equivocal possibly reflecting global cooling rather than regional uplift4 here we present new geochemical data on post mid miocene lavas from the plateau which show that the lavas were derived from the lithospheric mantle simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle thus volcanism is coincident with uplift providing a climate independent means of dating the onset of uplift dating by the laser 40ar 39ar technique places the beginning of this volcanism and therefore the time of uplift of the tibetan plateau at 13 myr ago

geochemistry and tectonics of the xionger group in the eastern qinling mountains of china a mid proterozoic volcanic arc related to plate subduction

tourmaline b isotopes fingerprint marine evaporites as the source of high salinity ore fluids in iron oxide copper gold deposits carajas mineral province brazil the carajas mineral province in northern brazil contains a variety of world class 100 mt ore iron oxide copper gold iocg deposits including the only archean examples of this deposit class e g the igarape bahia alemao and salobo deposits tourmaline of schorldravite composition a common gangue mineral in these deposits precipitated shortly prior to and after the ore assemblage a boron isotope study of texturally different tourmaline from three iocg deposits igarape bahia salobo and sossego using secondary ion mass spectrometry sims provides new evidence in the long standing debate of magmatic versus non magmatic sources for the high salinity up to 50 wt nacl equiv of ore fl uids in these deposits values of 11 b from 14 to 26 5 for the igarape bahia and salobo deposits confi rm marine evaporite derived brines in the ore fl uids whereas lower 11 b values for the igarape bahia deposit 5 8 to 8 8 suggest that these fl uids may have mixed with an isotopically different hydrothermal fl uid or one that had a mixed boron source more variable and isotopically lighter boron in tourmaline from the sossego deposit 8 to 11 is attributed to mixed sources including light boron leached from felsic intrusive and volcanic host rocks and heavy boron derived from marine evaporites the boron isotope data indicate that the characteristic high salinity of the ore fl uids in the carajas mineral province was acquired by the interaction of hydrothermal fl uids with marine evaporites for iocg deposits that contain tourmaline as a common gangue mineral boron isotopes offer a valuable tool to constrain the high salinity source problem which is a critical issue in metallogenesis of iocg deposits worldwide

la icp ms zircon u pb dating trace element and hf isotope geochemistry of the heyu granite batholith eastern qinling central china implications for mesozoic tectono magmatic evolution article i nfo mesozoic granitoids are widespread in the southern margin of the north china craton and of particular geo logical interests because of their indication for lithospheric evolution and close association with porphyry mo mineralization in this contribution in situ la icp ms u pb hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the heyu granitic bath olith which hosts the yuchiling porphyry mo system henan province china as inferred from field investiga tions the concentrically zoned heyu batholith mainly consists of four texturally distinguishable phases and displays a pattern of monotonically decreasing u pb age from 143 0 1 6 ma for phase 1 through 138 4 1 5 ma for phase 2 through to ca 135 ma for phase 3 and to 133 6 1 3 ma for the mo mineralized yuchiling granite porphyry phase 4 the ehf t values 27 7 to 3 4 and the two stage hf model ages 1403 to 2924 ma of zircon grains together with the ages of local strata suggest that the magmas forming the heyu batholith were dominantly sourced from the crust with input of a mantle component the higher ce ce ratios of the zircon crystals in the mineralized yuchiling porphyry compared to those in the mo barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for mo enrichment a regional synthesis suggests that intensive lithospheric thinning in the southern margin of the north china craton should not be earlier than 130 ma

the anatomy of shallow crustal transpressional structures insights from the archaean carajas fault zone amazon brazil abstract the carajas fault zone cfz is the most prominent structure in the e w trending carajas strike slip system casss an ancient upper crustal fault network of probable late archaean age that cuts across the precambrian amazonian craton in brazil the subvertical faults reactivated pre existing high grade basement shear zone fabrics itacaiunas shear zone and display a complex long lived history of movement 1 ga dominated by oblique and strike slip displacements a postulated early regional phase of dextral movement downfaulted units of low grade to unmetamorphosed basement rocks into dilational bends and offsets in the casss subsequent sinistral transpression ca 2 6 ga led to faulting and folding during partial inversion of the cover rocks in these dilational sites with much of the associated deformation focused in the immediate vicinity

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

tectono sedimentary evolution of the mesoproterozoic basins in the southern yan liao and mianchi queshan areas insights from stratigraphic pattern and detrital zircon geochronology the widespread mesoproterozoic successions around the world have recorded the breakup of the ancient supercontinent columbia in the north china craton ncc the mesoproterozoic basins in the yan liao and southern ncc are the important evidence to study the nature and evolution of the mesoproterozoic basins in this study we scrutinized the stratigraphic pattern and detrital zircon u pb geochronology in the southern yan liao and mianchi queshan areas in the southern ncc to investigate the evolutionary relationship between the mesoproterozoic basins in the north and south of ncc detrital zircons from the mesoproterozoic sequence in the southern yan liao areas showed monotonous source with age peak at ca 2500 ma corresponding well with the ages of the neoarchean complex in the central ncc however the mesoproterozoic sequence in the mianchi queshan areas which is represented by the ruyang group exhibited significantly different characteristics with influx of much younger zircons the southern yan liao and mianchi queshan areas showed distinct similarity in the stratigraphic pattern reflected by the mesoproterozoic successions in these two areas being both bracketed by two sequence boundaries and further divided into two sequences under a uniform sea level change the mesoproterozoic strata in these two areas probably possessed a correlative relationship in the stratigraphic patterns and basin evolutionary history

plate tectonics and island arcs the plate tectonic concepts that developed rapidly in the late l960s made possible the understanding of island arcs before that time mobilistic concepts evolved slowly hindered particularly in the united states by an obstructionist geoscience establishment the volcanic belts of island arcs form about 100 km above subducting plates convergent plate boundaries evolve complexly with time and at any one time vary greatly along their lengths seismicity defines positions but not trajectories of descending slabs which sink more steeply than they dip and are overridden by advancing upper plates subduction occurs beneath only one side at a time of an internally rigid plate and the common regime in an overriding plate behind a surficial accretionary wedge is extensional except where a collision is underway back arc basin lithosphere is built behind or by migrating island arcs which lengthen and increase their curvatures a collision can involve two active arcs in which case intervening lithosphere sinks beneath both of them or an active margin and a passive one either type of collision generally is followed by the breaking through of new subduction beneath the composite mass of light crust from a new trench on the outside of the aggregate conversely a new subduction system commonly is a by product of collision a strip of back arc basin crust is in many cases left attached to the aggregate in front of the new trench and becomes the basement for a fore arc basin the leading edge of which is raised as melange is stuffed under it sedimentation in trenches is predominantly longitudinal and can be from distant sources accretionary wedges are dynamic being thickened at both toes and bottoms by tectonic accretion and thinned by gravitational forward flow melange is largely a product of tectonic imbrication and flowage driven by these conflicting processes not of submarine sliding high pressure metamorphic rocks form beneath overriding plates not within wedges in front of them arc magmas incorporate much material from the lithosphere through which they rise and vary correspondingly with the evolving composition of that lithosphere arc crust is inflated into geanticlines by intrusive rocks and thermal expansion submarine island arc volcanic rocks are widely spilitized with na enrichment and ca depletion by hydrothermal reaction with sea water the lower crust of mature island arcs consists of granulite facies rocks of mafic intermediate and felsic intermediate compositions the mohorovicic discontinuity may be primarily a constructional boundary representing the shallow limit off crystallization of voluminous rocks of ultramafic composition or plagioclase free mineralogy

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

geochronology and petrogenesis of gray gneisses from the taihua complex at xiong er in the southern segment of the trans north china orogen implications for tectonic transformation in the early paleoproterozoic the taihua complex in the xiong er area along the southern segment of the trans north china orogen tnco consists of gray gneisses with minor amphibolites zircon u pb dating of the gray gneisses reveals at least two episodes of early paleoproterozoic magmatism 2 30 2 32 ga and 2 07 2 19 ga each with distinct geochemical features the tieluping ttg gneisses of the early suite have very low hree ybn 0 58 4 75 and y contents 2 05 13 2 ppm with moderate to high la yb n 14 3 192 6 and sr y ratios 38 5 220 1 pronounced negative ta nb and ti anomalies but positive sr and pb anomalies the protoliths of these gneisses were most likely derived from partial melting of thickened lower crust with residual garnet and amphibole and underwent garnet amphibole fractionation plagioclase accumulation and or fractionation the tieluping ttg gneisses have variable zircon hf model ages tdm hfc 2 48 3 06 ga and whole rock end t values 4 89 4 98 and the youngest whole rock depleted mantle nd model age tdm 2 32 ga is close to the crystallization age of the ttg 2318 8 ma the protolith of the gneisses formed from a combination of pre existing continental crust and juvenile materials implying an andean type continental margin arc environment it is suggested that crustal thickening was the result of accretionary orogenesis accompanied by basaltic underplating the ganshugou potassium rich gneisses of the later suite have low na2o and high k2o and show fractionated lree and nearly flat hree patterns with strong negative ta nb and ti anomalies they are characterized by negative end t values 5 01 to 2 33 and heterogeneous zircon ehf t values 10 65 2 10 with decoupling of zircon hf model ages tdm hfc 2 64 3 23 ga and whole rock nd model ages tdm 2 55 2 81 ga the protolith of the ganshugou gneisses was a potassium rich igneous rock which was likely the result of partial melting of pre existing crustal materials at shallow depth compatible with a post collisional setting there is therefore a tectonic transformation from an accretionary orogenesis to an extensional regime as a consequence of post collisional uplift in the southern segment of the tnco in the early paleoproterozoic

enriched archean lithospheric mantle beneath western churchill province tapped during paleoproterozoic orogenesis ultrapotassic rocks of the christopher island formation baker lake basin were emplaced across an enormous area 240 000 km 2 minimum of the western churchill province ca 1 83 ga these rocks extend across the snowbird zone a geophysical feature postulated by others to represent a paleoproterozoic suture that welded the rae and hearne domains minette dikes and flows of the rae and hearne domains display identical nd 1830 values and incompatible element patterns and thus appear to have originated from a common lithospheric mantle source christopher island nd model ages cluster at 2 8 ga and nd data from one archean lamprophyre and three 2 45 to ca 2 2 ga mafic suites suggest that enriched lithospheric mantle sources beneath both the rae and hearne domains existed well before ca 1 83 ga inconsistent with paleoproterozoic suturing along the snowbird zone in contrast to commonly invoked models that envisage melting of local enriched domains christopher island ultrapotassic rocks appear to have originated from an extensive reservoir we suggest that such a reservoir was created during an archean metasomatic event perhaps owing to flat subduction and that it remained in nearly complete isolation until tapped during paleoproterozoic extension related to squeezing of western churchill crust between flanking wopmay and trans hudson orogens

melting of enriched archean subcontinental lithospheric mantle evidence from the ca 1760ma volcanic rocks of the xiong er group southern margin of the north china craton abstract the xiong er group is an important geologic unit in the southern margin of the north china craton it is dominated by the volcanic rocks dated at 1763 15 ma that have sio2 contents ranging from 52 10 wt to 73 51 wt these volcanic rocks are sub alkaline and can be classified into three subgroups basaltic andesites andesites and rhyolites they unexceptionally show enrichment of light rare earth elements lree and share similar trace element patterns depletions in nb ta sr p and ti relative to the adjacent elements are evident for all the samples the volcanic rocks are evolved with low mgo contents 0 29 5 88 wt and accordingly low mg values of 11 53 the nd isotopes are enriched and show a weak variation with nd t 7 12 to 9 63 zircon hf isotopes are also enriched with hf t 12 02 0 45 the volcanic rocks of the xiong er group are interpreted to represent fractional crystallization of a common mantle source the volcanic rocks might have been generated by high degree partial melting of a lithospheric mantle that was originally modified by the oceanic subduction in the late archean this brings a correlation with the subduction modified lithospheric mantle in an extensional setting during breakup of the columbia supercontinent in the late paleoproterozoic rather than in an arc setting the elevated sio2 contents and evolved radiogenic isotope features indicate the possible incorporation into their source of lower crustal materials that have similar nd isotopic characteristics to the subcontinental lithospheric mantle the existence of extensive xiong er volcanic rocks 60 000 km2 indicates an early large scale subduction related metasomatism in the area and probably suggest a flat subduction model for the plate margin magmatism in the late archean

a long lived tectono metamorphic event in the late paleoproterozoic evidence from sims u th pb dating of monazite from metapelite in central south trans north china orogen abstract as a key accessory mineral in metapelite monazite forms in the metamorphic event and therefore places important direct constraint on the timing of the tectono metamorphic event in this study we investigate four representative metapelites from different metamorphic terranes in the central south trans north china orogen tnco applying secondary ion mass spectrometry sims u th pb dating on monazite the dating results reveal that monazite collected from the huashan luoning zanhuang and wutai metamorphic complexes record the metamorphic ages of 1 83 ga 1 95 ga 1 85 ga and 1 91 to 1 83 ga respectively combined with the literature data of metamorphic geochronology on the discrete terranes within the tnco it is suggested that the amalgamation between the western and eastern blocks of the north china craton along the nearly ns trending tnco stared as earlier as 1 97 ga and continued to as late as 1 80 ga which was in fact a long lived tectono metamorphic event

geochronology and origin of the qi189 porphyry gold deposit in qiyugou orefield qinling orogen china abstract the qi189 gold deposit is a recently discovered porphyry system in the qiyugou orefield located in the northeastern qinling orogen along the southern margin of north china craton the orebodies are hosted in the porphyritic granite emplaced in the taihua supergroup three molybdenite and five pyrite samples from the ores yield re os isochron ages of 129 5 2 8 ma and 127 5 8 2 ma respectively which are coincident with the zircon u pb age of the porphyritic granite within analytical error 128 6 0 8 ma zircon grains from the post ore quartz monzonite yield weighted mean 206pb 238u age of 124 7 0 6 ma n 31 1 mswd 0 23 these ages constrain that the qi189 gold system was formed in the period of 130 127 ma the porphyritic granite and quartz monzonite show high k calc alkaline affinity enrichment of lree and lile depletion of hree and hfse and negligible eu anomaly zircon grains show negative ehf t values of 20 7 to 14 9 with tdm2 hf ages of 2 49 2 13 ga this indicates that the qi189 porphyry system originated from a source mixed by the materials from the north qinling accretion belt and the basement of north china craton with minor contribution from the mantle and developed under a post collisional tectonic setting

meso neoproterozoic strata and target source rocks in the north china craton a review abstract along with the breakup of the supercontinent nuna and rodinia during the mesoproterozoic and neoproterozoic a series of sedimentary basins formed within or at the periphery of the ancient cratons under the regime of breakup of the supercontinent these basins underwent different evolutionary history hence formed different geological elements constituting the petroleum systems in this contribution the distribution and the stratigraphic successions of the meso neoproterozoic basins in the north china craton ncc were examined as well as the retrospective review for the mechanisms of the basin formation the synthesized geological and geochronological data support a long term extensional environment for the basins in the northern ncc the mesoproterozoic basins in the yanshan western liaoning yan liao and the zhaertai areas formed at the intracratonic position later than that in the bayan obo which possibly deposited in the continental margin the further efforts still need to be devoted to decipher the huge controversial around the tectonic nature of the basins in the southern ncc as well as their stratigraphic correlations with the basins in the north and central the distribution and organic geochemical characteristics of the mesoproterozoic source rock were also summarized three sets of source rock in the central ncc namely the chuanlinggou hongshuizhuang and xiamaling formations developed favorable geological and geochemical conditions for the generation of the hydrocarbon while in the south the cuizhuang formation was the only interval feasible for potential source rock the progress in seismic geophysics and borehole drilling suggested the existence of the mesoproterozoic beneath deep ordos basin this open a new window for the reconstruction of the mesoproterozoic paleogeography as well as the evaluation of the source potential of the mesoproterozoic basins in the north china craton

late mesozoic felsic magmatism and mo au pb zn mineralization in the southern margin of the north china craton a review abstract the widespread large scale mo au pb zn mineralization in the southern margin of the north china craton ncc is spatially and temporally associated with the voluminous late mesozoic granitic magmatism relationship between the granitic magmatism and ore mineralization has been extensively investigated in the last decade however controversy still exists regarding the magma source metallogeny and geodynamic settings this paper systematically reviews the major features of the mesozoic granitic magmatism and associated mo au pb zn mineralization in the southern margin of the north china craton including temporal and spatial variations of magmatic rocks composition of ore fluids sources of ore metals and metallogeny the granitic rocks were mainly formed in late mesozoic and emplaced in two stages the early stage 158 128 ma granites are of typical i type derived from remelting of ancient crust of the southern margin of the ncc with input of mantle material under lithospheric thinning tectonic regime the late stage 127 112 ma granites include a type and or highly fractionated i type granites which commonly contain more fractions of mantle materials as exhibited by more depleted isotopic signatures suggestive of an intracontinental extensional setting mo mineralization 155 130 ma related to the early stage granitic magmatism includes mainly of porphyry or porphyry skarn type with ore metals mainly derived from the mixed source of the mantle and crust whereas the late stage mo mineralization 127 116 ma is mainly of porphyry type with the ore metals from similar sources with more input of mantle materials pb zn deposits 144 130 ma associated with the early stage granitic magmatism are mainly of hydrothermal vein and skarn types whereas those 125 117 ma related to the late stage granites are of hydrothermal vein type the pb zn deposits are most likely distal products of the mo deposits together forming a metallogenic system au deposits are located in the xiaoqinling and xiong ershan areas and were formed during middle jurassic to early cretaceous 163 118 ma mostly from 132 to 120 ma the ores mainly occur in quartz veins and altered rocks and are hydrothermal magmatic in origin with au derived from a mixed source of crust and mantle

40 ar 39 ar dating of archean iron oxide cu au and paleoproterozoic granite related cu au deposits in the carajas mineral province brazil implications for genetic models 40ar 39ar dating of biotite from iocg and granite related cu au deposits in the carajas mineral province provides evidence for the timing of mineralization and constraints on genetic models of ore formation ages of biotite from greisen and quartz rich vein and breccia deposits alvo 118 1885 4 ma breves 1886 5 ma estrela 1896 7 ma and gameleira 1908 7 ma demonstrate the close temporal relationship between cu au mineralization and subjacent a type granites mineralization is hosted within granite cupolas breves or in vein breccia systems emanating from the cupolas estrela and gameleira consistent with a genetic relationship of mineralization to the b li f rich granites plateau and minimum ages of biotite from iocg deposits including igarape bahia cristalino corta goela and gt34 range from 2537 6 ma to 2193 4 ma the 40ar 39ar age of biotite from igarape bahia 2537 6 ma is similar to a previous shrimp 207pb 206pb age for monazite of 2575 12 ma when the uncertainties in the respective analyses and standards are taken into account the age spectrum for biotite from cristalino shows increasing ages for successive steps consistent with post crystallization ar loss and the age of 2388 5 ma for the last three steps is considered a minimum age for cu au mineralization the age of biotite from the gt34 prospect 2512 7 ma coincides with a previously identified period of basement reactivation and may indicate the formation of cu au mineralization at this time or resetting of biotite from an older mineralization event at this time at corta goela within the canaa shear zone the biotite age of 2193 4 ma lies between the ages of iocg 2 57 2 76 ga and granite related cu au 1 88 ga deposits elsewhere in the carajas district but is similar to previously reported 40ar 39ar ages for amphibole from sossego possibly indicating that mineralization at both sossego and corta goela was affected by a thermal event at this time the paleoproterozoic cu au deposits are commonly hosted within neoarchean iocg alteration systems and the common occurrence of potassic alteration especially biotite in both types of deposits means that special care is required in interpreting the paragenesis of alteration in both types of deposits the paleoproterozoic cu au deposits are reduced and sulfur and quartz rich deposits lacking in major amounts of iron oxides and are therefore unlike iocg deposits instead they share many characteristics in common with widespread paleoproterozoic sn w deposits in the amazon craton including close spatial and temporal relationships with reduced a type b li f granites and the occurrence of greisen and quartz rich vein breccia systems within and above granite cupolas the occurrence of sericitic alteration in the paleoproterozoic cu au deposits is not evidence for an upward transition to sericitic alteration in iocg deposits in the carajas mineral province

origin of fluids in iron oxide copper gold deposits constraints from δ 37 cl 87 sr 86 sr i and cl br the origin of the hypersaline fluids magmatic or basinal brine associated with iron oxide cu u au ree deposits is controversial we report the first chlorine and strontium isotope data combined with cl br ratios of fluid inclusions from selected iron oxide copper gold iocg deposits candelaria raul condestable sossego a deposit considered to represent a magmatic end member of the iocg class of deposit gameleira and a magnetite apatite deposit el romeral from south america our data indicate mixing of a high 37cl magmatic fluid with near 0 37cl basinal brines in the candelaria raul condestable and sossego iocg deposits and leaching of a few weight percent of evaporites by magmatic hydrothermal fluids at gameleira and el romeral the sr isotopic composition of the inclusion fluids of candelaria raul condestable and el romeral confirms the presence of a non magmatic fluid component in these deposits the heavy chlorine isotope signatures of fluids from the iocg deposits candelaria raul condestable sossego reflecting the magmatic hydrothermal component of these fluids contrast with the near 0 37cl values of porphyry copper fluids known from the literature the heavy chlorine isotope compositions of fluids of the investigated iocg deposits may indicate a prevailing mantle cl component in contrast to porphyry copper fluids an argument also supported by os isotopes or could result from differential cl isotope fractionation processes e g phase separation in fluids of iocg and porphyry cu deposits

early cretaceous subduction modified lithosphere beneath the eastern qinling orogen revealed from the daying volcanic sequence in central china abstract new geochronological geochemical and sr nd hf isotopic data for the early cretaceous daying volcanic sequence eastern qinling orogen provides a probe into the nature of and tectonic process operating in the underlying mesozoic mantle the volcanic rocks in the sequence are composed of basaltic trachyandesite pyroxene andesite trachyandesite and trachyte they yield zircon u pb and whole rock 40ar 39ar plateau ages of 134 124 ma roughly synchronous with the cretaceous igneous rocks throughout the eastern qinling and dabie orogens clinopyroxene and plagioclase phenocrysts of the volcanic rocks exhibit simple normal zonation with higher mg number and an content in the core relative to the rim the amphibole is characterized by tschermakite and tschermakitic hornblende with mg number of 50 67 the daying volcanic rocks have variable sio2 54 27 63 44 wt al2o3 15 39 20 34 wt feot 5 23 9 94 wt and mgo 1 05 4 03 wt contents with low mg number 26 49 they exhibit arc like ree and pm normalized patterns with significant negative nb ta anomalies and highly enriched sr nd isotopic composition with 87sr 86sr i ratios of 0 7066 0 7078 and end t values of 15 5 11 0 their zircons exhibit strongly negative ehf t values ranging from 27 3 to 17 2 and two staged model ages from 2 90 ga to 2 28 ga such geochemical signatures suggest that the daying volcanic rocks were derived from a hybridized source of the north china craton enriched mantle with the input of some yangtze crustal materials created by triassic deep subduction digestion they also share similar eruption time as well as elemental and sr nd hf isotopic compositions with those in the southern margin of the north china craton suggesting a northward subduction of the yangtze block it is proposed that the volcanic rocks are petrogenetically related to an early cretaceous extensional event along the qinling dabie orogenic belt in response to unrooting of the thickened lithosphere

u pb geochronology of archean magmatism and basement reactivation in the carajas area amazon shield brazil abstract the archean carajas subprovince is a metallogenic district bif bauxite cu ni mn au located in the easternmost amazonian craton in brazil the main conclusions from a u pb study of the itacaiunas supergroup and a locality in the xingu complex are the following the xingu basement complex the oldest unit underwent migmatization at 2859 2 ma and also grew new zircon at 2851 4 ma the luanga mafic intrusion is 2763 6 ma old and coeval with the 2759 2 ma felsic volcanics of the grao para group amphibolites from the salobo group contain 2851 ma zircons were metamorphosed 2761 3 ma and intruded by granitic veins ca 2758 ma at the time of grao para magmatism and also grew new zircon at 2732 2742 ma the data indicate that the salobo group is part of the xingu complex and not of the itacaiunas supergroup as heretofore believed the pojuca group possibly coeval with the salobo group was metamorphosed at 2732 3 ma a late archean reactivation event of regional extent is marked by titanite growth at 2581 5 ma in the mirim area intrusion of the old salobo granite at 2573 2 ma new zircon growth in salobo group amphibolites at 2555 4 3 ma and monazite growth in a metamorphosed iron formation at 2551 2 ma in addition k metasomatism associated with shear zones formed titanite in salobo group amphibolites at 2497 5 ma and new titanite at 2519 5 ma in the xingu complex events in the 2581 2497 ma interval are probably associated with the latest activity of a wnw ese sinistral shear system which could also be responsible for the establishment of a transtensional basin filled by the volcano sedimentary sequence of the grao para bahia and rio fresco groups finally undeformed proterozoic granitoid intrusions were dated at 1883 2 ma cigano 1883 5 2 ma musa 1880 2 ma carajas and 1874 2 ma pojuca

constraints on the early mesozoic denudation of the qinling orogen from upper triassic lower jurassic successions in the zigui basin central china abstract the qinling mountains are situated in central china and mark the collisional assembly between the north and south china blocks to understand the early mesozoic evolution of the qinling orogenic belt we present new paleocurrent data sandstone petrology and detrital zircon u pb ages for upper triassic lower jurassic sedimentary successions in the zigui basin in the northern margin of the south china block the deltaic sandstones in the upper triassic jiuligang formation have high concentrations of quartz grains and the basal alluvial conglomerates of the lower jurassic tongzhuyuan formation contain abundant chert gravels with sandy matrixs rich in quartz grains both the upper triassic sandstones and lower jurassic conglomerate have two major detrital zircon u pb age groups of 2100 1700 ma and 950 700 ma with very few phanerozoic ages the overlying fluvial sandstones of the tongzhuyuan formation display relative enrichment in volcanic and metamorphic rock fragments they are characterized by primary zircon u pb age groups of 250 200 ma and 950 700 ma consistent with the northwestward paleocurrents zircon grains of 2100 1700 ma and 900 700 ma were likely derived directly or recycled from the paleoproterozoic and neoproterozoic basement of the south china block with the latter also possibly sourced from the qinling orogen the 250 200 ma age group is understood to be associated with volcanic rock fragments and considering the southward paleocurrents indicates a volcanic source within the qinling orogen along with the increased low grade metamorphic rock fragments in sandstones this significant provenance change in the early jurassic indicates the initial massive erosion and rapid southward propagation of the south qinling orogen

geochemistry isotope systematics and petrogenesis of the volcanic rocks in the zhongtiao mountain an alternative interpretation for the evolution of the southern margin of the north china craton abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton which are composed primarily of basaltic andesites and andesites with minor dacites and dacitic rhyolites the basaltic andesites and andesites from the xiong er volcanic rocks in the zhongtiao mountain show consistent nd t la nb and th nb values irrespectively of sio 2 which preclude significant crustal contamination during ascent both of these volcanic rocks share similar incompatible ratios e g la sm zr nb la nb indicating that the basaltic andesites and andesites originated from the same source the basaltic andesites are characterized by high mg number 45 55 precluding the possibility of their derivation from the melting of the lower crust variable ti eu zr sm and nb la ratios for the basaltic andesites with higher partial melting degree suggest that amphiboles remained as residues in the magma source indicating that the xiong er volcanic rocks were derived from hydrous magma non radiogenic nd isotopes for the xiong er volcanic rocks are inherited from a mantle source which had been enriched by the subduction related crustal recycling during archean to paleoproterozoic time basaltic andesites show hfse enrichments especially nb 4 7 ppm and high fe ti contents comparable with nb enriched basalts suggesting that the xiong er volcanic rocks were derived from a metasomatized mantle source similar to that of nb enriched basalts therefore the mantle source of the xiong er volcanic rocks in the zhongtiao mountain has been enriched in fe ti oxides and hfse by equilibrium reactions with the slab melts during late archean and paleoproterozoic subduction processes as evidenced by nd isotopes in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative anomalies on the nb ta ti similar to arc related volcanic rocks produced by the hydrous melting of the metasomatized mantle wedge in the paleo mesoproterozoic the xiong er volcanic rocks in the zhongtiao mountain were produced by the slab dehydration induced melting of an existing metasomatized mantle source and the fluids from the slab dehydration introduced significant lile and lree to the source masking its inherent hfse enriched characteristics the arc related characteristics of the xiong er volcanic rocks in the zhongtiao mountain suggest the xiong er volcanic belt constructs a subduction zone along the southern margin of the north china craton in the paleo mesoproterozoic implying that the craton may have recorded the outbuilding history of the columbia supercontinent during paleo mesoproterozoic time

petrogenesis and tectonic setting of volcanic rocks in the xiaoshan and waifangshan areas along the southern margin of the north china craton constraints from bulk rock geochemistry and sr nd isotopic composition abstract as part of the xiong er volcanic belt along the southern margin of the north china craton volcanic rocks in the xiaoshan and waifangshan areas have a compositional range from the basaltic andesite andesite dacite to rhyolite which display consistent variation trends in terms of their major and trace elements and sr nd isotopic compositions the variable yb contents with nearly constant la yb and tb yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite through andesite and dacite to rhyolite the volcanic rocks in these two areas are characterized by the lile and lree enrichments and negative hfse anomalies implying hydrous melting of a mantle wedge in a subduction zone variable sr nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab non radiogenic nd isotopic compositions as well as high zr y and nb y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source on the other hand the volcanic rocks of the basaltic andesite and andesite possess markedly higher fe ti and hfse concentrations than those of typical intra oceanic arcs implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the archean to paleoproterozoic subduction collision in the trans north china orogen these data suggest that in the paleo mesoproterozoic the southern margin of the north china craton was most likely an andean type continental arc in which slab dehydration not only induced the melting of a pre existing metasomatised mantle source but also released lile enriched fluids into the mantle source masking the inherent hfse enriched characteristics of the volcanic rocks along the southern margin of the craton the results of this study indicate that the north china craton like many other continental components e g north america greenland baltica amazonia australia etc of the supercontinent columbia nuna also underwent a subduction related outgrowth along its southern margin during the paleo mesoproterozoic time

geochemical changes in baslts and andesites across the archean proterozoic boundary identification and significance abstract to identify accurately changes in rock composition across the archean proterozoic boundary it is necessary to compare rocks from similar lithologic associations to constrain the effect of tectonic setting most basalts and andesites from the greenstone association volcanic dominated submarine supracrustal rocks possess a geochemical subduction zone component similar to their counterparts from modern arc systems basalts with island arc geochemical affinities dominate in archean greenstones while those with calc alkaline affinities are most abundant in proterozoic greenstones basalts with morb or oceanic within plate geochemical characteristics are rare in precambrian greenstones of all ages preserved early archean greenstone basalts 3500 ma reflect mantle sources less depleted than late archean greenstone basalts 2500 3500 ma proterozoic greenstone basalts are derived from relatively enriched mantle sources compared to all archean sources a feature which may be due to recycling of continental sediments into the mantle following rapid late archean continental growth precambrian andesites are geochemically similar to andesites from modern arcs but archean andesites are unique in that they are depleted in heavy ree and y results are consistent with archean andesite production by partial melting of descending mafic crust with amphibole garnet remaining in the residue while proterozoic and younger andesites are produced by fractional crystallization of basalts

late triassic batang group arc volcanic rocks in the northeastern margin of qiangtang terrane northern tibet partial melting of juvenile crust and implications for paleo tethys ocean subduction the batang group btg volcanic rocks in the zhiduo area with nw trending outcrops along the northeastern margin of the qiangtang terrane northern tibet are mainly composed of volcaniclastic rocks dacite and rhyolite major and trace element sr and nd isotope zircon u pb and hf isotope data are presented for the btg dacites laser ablation inductively coupled plasma mass spectrometry zircon u pb dating constrains the timing of volcanic eruption as late triassic 221 1 ma major and trace element geochemistry shows that the btg volcanic rocks are classified as calc alkaline series all samples are enriched in large ion lithophile elements and light rare earth elements with negative slightly positive eu anomalies eu eu 0 47 1 15 and depleted in high field strength elements and heavy rare earth elements in addition these rocks possess less radiogenic sr 87sr 86sr i 0 7047 0 7078 much radiogenic nd end t 4 2 to 1 3 and hf ehf t 4 0 6 6 isotopes suggesting that they probably originated from partial melting of a crustal source containing a mantle derived juvenile component the inferred magma was assimilated by crustal materials during ascending and experienced significant fractional crystallization by combining previously published and the new data we propose that the btg volcanic rocks were genetically related to southwestward subduction of the ganzi litang ocean a branch of paleo tethys in the northeastern margin of the qiangtang terrane given the coeval arc affinity magmatic rocks in the region we envisage that the ganzi litang ocean may extend from the zhongdian arc through the yidun terrane to the zhiduo area probably even further northwest to the tuotuohe area

post orogenic extension in the eastern part of the jiangnan orogen evidence from ca 800 760ma volcanic rocks we present a systematic geochronological and geochemical study on ca 800 760 ma volcanic rocks in the eastern part of the jiangnan orogen the xucun composite dykes are dated at ca 805 ma the mafic components have oib like trace element patterns and positive anomalies in zr and hf the least contaminated sample has relatively depleted nd isotopic features suggesting the xucun mafic dykes may have been generated from the partial melting of oib like asthenosphere with later crustal contamination the xucun felsic dykes have decoupled nd hf isotopes and the hf isotope compositions of zircons indicate that the dykes may be derived from the partial melting of the early neoproterozoic juvenile crustal materials with minor incorporation of paleoproterozoic crustal components the ca 800 790 ma shangshu volcanics include two compositional series calc alkaline and tholeiitic the shangshu calc alkaline volcanics in the minjiawu area have low abundances of lile hfse and high na2o contents and sr y ratios similar to adakitic rocks the evident arc like geochemical features and radiogenic nd isotopes nd t values of 3 7 to 4 8 suggest that these rocks may have been generated from the partial melting of juvenile lithospheric mantle metasomatized by na rich melts released from the subducted slab the tholeiitic mafic rocks from the shangshu bimodal volcanics represent two different magma sources the partial melting of metasomatized lithospheric mantle led to the formation of arc like basalts with low tio2 contents negative anomalies in zr and hf and high values of mg and nd t 6 2 whereas the partial melting of asthenospheric mantle generated volcanic rocks with high tio2 contents and low positive nd t 1 4 to 2 7 without negative anomalies of nb ta zr and hf the shangshu felsic rocks were formed by the reworking of early neoproterozoic juvenile arc crustal materials the ca 760 ma mafic rocks from the puling bimodal volcanics generally have low tio2 contents 0 9 wt nearly flat ree distributions and arc like trace element patterns they may have been generated from the high degree partial melting of metasomatized lithospheric mantle one sample has a high tio2 content 2 41 wt and high nd t 6 2 with overall oib like trace element patterns implying the local partial melting of asthenospheric mantle the occurrence of significant volumes of bimodal volcanics in the eastern part of the jiangnan orogen suggests an extensional setting in the period ca 800 760 ma the evident partial melting of newly metasomatized lithospheric mantle and subordinate partial melting of asthenosphere suggest that post orogenic extension shortly after the neoproterozoic orogenesis may be a better explanation for the genesis of the mid neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen post orogenic extension may be diachronous along the whole orogenic belt and probably has no direct relationship with the rodinia rifting event a more detailed model is presented to illustrate the evolution of the eastern part of the jiangnan orogen

zircon u pb and k feldspar megacryst rb sr isotopic ages and sr hf isotopic composition of the mesozoic heyu pluton eastern qingling orogen china abstract mesozoic granitoids are ubiquitous in china and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material emplacement mechanisms and crustal architecture most of the plutons were created by multi stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history a multi isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings this study presents rb sr isotope data for k feldspar megacrysts and u pb ages and hf isotopic composition for zircons from the composite heyu pluton exposed in eastern qinling orogen central china zircon u pb concordia ages of 150 and 140 ma and single k feldspar rb sr isochron ages between 133 and 121 ma were obtained from early and late magmatic stages respectively consistent with slow cooling or isotopic re equilibration of the rb sr k feldspar system the distinct k feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth likely to be associated with a gravity driven sinking model corresponding zircon e hf t values are 21 8 to 18 0 and 17 2 to 10 3 for early and late intrusive phases respectively indicating different magma sources

the collision type porphyry mo deposits in dabie shan china abstract the dabie shan in central east china is a collisional orogenic belt suturing the north china and yangtze blocks it was formed by jurassic early cretaceous continental collision following the triassic closure of the northernmost paleo tethyan ocean in the area at least ten porphyry mo systems have been discovered including two giant ones with a total reserve of 3 mt mo metal the porphyry type mo mineralization mainly occurred during 156 110 ma in the post collisional extension setting the location of mo deposit is controlled by nw and nne trending faults mostly in the south of the gui mei fault suturing the north china and yangtze blocks mo mineralization is generally associated with the yanshanian high k calc alkaline metaluminous peraluminous granitic intrusions with orebodies being located in the intrusions and or host rocks the hydrothermal ore forming process generally includes four stages with the initial ore forming fluids being featured by high temperature high salinity and co 2 rich geochemical signatures indicate that the ore causative magmatism in the dabie shan mainly originated from either the northern or southern dabie complex but mixed with the precambrian rocks of the north china block except for the tianmugou porphyry system which shares more similar geological and geochemical characteristics with the porphyry mo deposits in eastern qinling orogen we also develop a scissor style intracontinental subduction model to interpret the differences in spatial distribution geneses and geochemical and geological characteristics between the mo deposits in dabie shan and qinling orogen in our model the basement of the north china block southwardly underthrusted beneath the dabie shan possibly along the gui mei fault whilst the basement of the yangtze block northwardly underthrusted beneath the qinling orogen and the inferred minggang xinyang fault zone served as a dextral strike slip fault zone in the north china block but acted as a sinistral transpressional fault zone within the orogenic area compared to the subduction or endako and rift or climax types of porphyry mo deposits the porphyry mo deposits in the dabie shan are unique because of their crustal source for the magma and ore forming materials and as such are assigned to the dabie or collision type hence we develop a new global tectonic model for porphyry mo deposits of three types showing their genetic tectonic settings

the early major warming in december 2001 exceptional the early major warming in december 2001 is described and compared to the two other december major warmings in 1998 and 1987 showing a strong tropospheric stratospheric coupling in all three cases we argue that the occurrence of free westward propagating rossby waves interacting with a forced quasi stationary wave number 1 led to these three early events the possible excitation of these waves is discussed with respect to the tropospheric circulation which showed strong blockings over the northern atlantic prior to the early major warmings

u pb geochronology and hf isotope geochemistry of detrital zircons from the zhongtiao complex constraints on the tectonic evolution of the trans north china orogen abstract the zhongtiao complex is located in the south segment of the trans north china orogen a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the north china craton the complex consists of the neoarchean to paleoproterozoic granitoid plutons and low grade supracrustal rocks of which the latter are subdivided into the songjiashan jiangxian lower zhongtiao upper zhongtiao and danshanshi groups the songjiashan jiangxian and lower zhongtiao groups are composed of metaclastic rocks carbonates and metavolcanic rocks interpreted as the products of a back arc basin whereas the upper zhongtiao and danshanshi groups consist of metaconglomerates and metasandstones interpreted as molasses type siliciclastic rocks deposited in a retro arc foreland basin the u pb ages of detrital zircons from the songjiashan lower zhongtiao upper zhongtiao and danshanshi groups form four populations of 3600 3100 ma 2850 2750 ma 2630 2200 ma and 2150 1850 ma of which the population of 2630 2200 ma is the most dominant and its major sources are considered to be derived from the 2560 to 2300 ma granitoids and metavolcanics in the zhongtiao complex the source rocks of the subordinate 3600 3100 ma detrital zircons were probably derived from the paleo mesoarchean crust of the eastern block since similar aged rocks have not been found in the western block and the trans north china orogen whereas the 2850 2750 ma detrital zircons are interpreted to be derived from the 2850 to 2752 ma ttg gneisses and amphibolites in the adjacent taihua complex the age population of 2150 1850 ma is coincident with the ages of paleoproterozoic granitoids in the trans north china orogen the youngest detrital zircons in the songjiashan and lower zhongtiao groups constrain their maximum depositional ages at 2253 ma and 2168 ma respectively whereas the maximum depositional age of the overlying upper zhongtiao and danshanshi groups is defined at 1848 ma the late paleoproterozoic shift from a back arc basin to a retro arc foreland basin is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga

zircon upb geochronology and isotopic geochemistry of the tangjiaping mo deposit dabie shan eastern china implications for ore genesis and tectonic setting abstract the tangjiaping mo deposit is located in the dabie shan in eastern china molybdenum mo mineralization mainly occurs as veinlets in the tangjiaping granite porphyry which is featured by the development of potassic silicic phyllic and propylitic alterations the mo mineralized granite porphyry yields a zircon u pb age of 118 1 0 8 ma mswd 1 6 2 n 24 and may have formed under post collision extensional tectonics after the yangtze north china collision the tangjiaping granite porphyry is characterized by the enrichments of liles and lrees depletions of ba nb ta sr p ti and hrees and negative eu anomaly zircons from the granite porphyry yield negative ehf t of 15 3 to 9 9 with tdm2 hf ages of 1 80 to 2 14 ga the 206pb 204pb 207pb 204pb and 208pb 204pb of the granite porphyry and its k feldspar are 16 842 17 342 15 388 15 439 and 37 706 38 260 respectively while those of the sulfides are 17 090 17 832 15 420 15 510 and 37 550 38 026 respectively the 34s of these sulfides exhibit a relatively narrow range of 3 2 4 9 with an average of 4 0 the hf pb s isotopic signatures indicate that the granite porphyry and the ore forming materials at tangjiaping were mainly derived from the partial melting of both the southern dabie complex and the precambrian basement of the north china craton

geochemical variations of the late mesozoic granitoids in the southern margin of north china craton a possible link to the tectonic transformation from compression to extension abstract the composition of the continental crust of the north china craton ncc is more felsic than that of the average bulk crust which is regarded to be the result of the delamination of the thickened lower crust during mesozoic however whether the thickened continental crust existed and when the delamination event happened along the southern margin of the ncc are still debated here we report geochronological geochemical and sr nd hf pb isotopic evidence that granitoids from the late jurassic wuzhangshan pluton and the early cretaceous huashani complex were derived by partial melting of the lower crust with different thickness our new data shows that the two lithofacies of the wuzhangshan pluton were mainly formed between ca 157 and 156 ma whereas the five lithofacies of the huashani complex were mainly emplaced between ca 132 and 125 ma the wuzhangshan pluton and the earlier four lithofacies granitoids of the huashani complex ca 160 125 ma both display adakitic geochemical features which are characterized by as high sio 2 63 26 72 71 wt al 2 o 3 13 97 16 89 wt and sr 413 1218 ppm contents and low y 6 30 14 98 ppm and yb n 1 55 4 43 and high sr y 33 112 and la yb n 11 53 29 72 ratios they also have high 87 sr 86 sr i 0 7066 0 7086 and low end t 9 9 to 18 8 and ehf t 11 to 26 values and two stage nd and hf model ages ranging from 2 4 to 1 7 ga and 2 7 to 1 7 ga respectively in contrast the late early cretaceous ca 125 110 ma granitoids have higher sio 2 71 30 76 78 wt and lower sr 64 333 ppm contents and lower sr y 17 29 and la yb n 13 25 18 36 ratios and similar end t 10 to 16 and relatively higher ehf t 10 to 14 values these geochemical variations suggest that the ca 160 125 ma granitoids were most probably produced by partial melting of thickened crust 45 km with eclogite garnet amphibolite or amphibolite residues whereas that the ca 125 110 ma granitoids were formed by partial melting of the thinner crust

petrogenesis of the early cretaceous intermediate and felsic intrusions at the southern margin of the north china craton implications for crust mantle interaction abstract new major and trace element whole rock sr and nd isotopes and zircon u pb ages and hf isotope data are presented for rocks from the early cretaceous tianqiaogou dioritic and taishanmiao granitic plutons at the southern margin of the north china craton ncc in order to investigate their petrogenesis and geological evolution la icp ms u pb analyses for zircons from these two plutons yield similar 206 pb 238 u ages of 122 ma and 115 125 ma respectively monzodiorites from the tianqiaogou pluton have whole rock e nd t values ranging from 6 2 to 1 3 and zircon e hf t values from 2 9 to 6 2 they are variably enriched in ra ba and sr and depleted in nb ta zr hf and ti indicating that they were derived from a depleted mantle and underwent subsequent magma differentiation and crustal contamination the taishanmiao pluton is composed of metaluminous to peraluminous highly fractionated i type granites that have high sio 2 na 2 o k 2 o rb th and u and low p ba sr ti and eu contents the granites have strong negative whole rock e nd t values 16 1 to 7 5 and zircon e hf t values 20 9 to 6 1 their nd t dm ages 1 19 to 2 01 ga and zircon hf t c dm ages 1565 to 2490 ma are much younger than the basement rocks beneath the southern margin of the ncc suggesting derivation from an ancient crustal source with minor involvement of mantle derived components therefore rocks from the tianqiaogou dioritic pluton were partial melts of the mantle source underplating of the mafic magmas initiated partial melting of the ancient continental crust resulting in the formation of the taishanmiao granitic pluton their complex petrogenesis reflects a strong crust mantle interaction process related to lithospheric thinning beneath the southern margin of the ncc in early cretaceous

the age origin and tectonics of the grao para group and associated rocks serra dos carajas brazil archean continental volcanism and rifting the grao para group which is host to the large serra dos carajas fe deposits is located in the eastern part of the central brazil shield ssw of belem brazil it is composed of a lower sequence of metavolcanic rocks a middle sequence of iron formation carajas formation and an upper sequence of mixed metavolcanic and metasedimentary rocks the grao para group is overlain by an unnamed sedimentary dominantly sandstone unit and unconformably overlies the older xingu complex the lower metavolcanic sequence of the grao para in the region of the serra norte fe deposits is bimodal with dominant metabasalts metabasaltic andesites and metatrachyandesites and subordinate 10 15 metarhyolitic tuffs and flows most of the metavolcanic rocks are at low to medium metamorphic grade with more intense metamorphism and deformation along the northern contact with the xingu complex the thickness of the metavolcanic section is not known but may be 4 6 km the mafic metavolcanic rocks are enriched in rb ba and k with respect to oceanic basalts and basalts of greenstone belts and are relatively depleted in th sr ta ti and p the mafic rocks also show an enrichment in lrees with flat hree patterns the hrees are correlated with mg number u pb zircon analyses of the metarhyolites from the grao para group yield an age of 2758 39 ma rb sr wholerock analyses of the mafic rocks yield an isochron with an age of 2687 54 ma with an initial ratio of 0 7057 0 0010 the results indicate a late archean age of volcanism in the grao para group much older than previously thought rb sr results from the metarhyolites have been partially reset yielding an age 2497 62 ma sm nd analyses from the grao para metavolcanic rocks were too scattered to yield an isochron but nd values relative to chur at 2758 ma indicate values similar to depleted mantle at this time although with some scatter the trace element data and the sr and nd isotopic results from the mafic rocks are consistent with contamination of mantle derived melts by significant but variable amounts of diverse older continental crust the stratigraphy geochemical and isotopic compositions show that the grao para group originated on extending older continental crust during the archean an age terrane boundary must exist between this archean continental terrane and the apparently ensimatic early proterozoic greenstone belts of the northern amazonian craton similarities to other sequences e g the fortescue group australia suggest that similar tectonic settings were widespread at this time many major iron formations were deposited within these environments indicating significant iron formation development on sialic crust in the late archean u ph zircon analyses from the serra dos carajas granite which intrudes the unnamed sedimentary unit overlying the grao para group yield an age of 1820 49 ma in agreement with previous age determinations this age is similar to the ages for the uatuma supergroup volcanic and shallow plutonic rocks which occur throughout the amazonian craton

late archean cu au mo mineralization at gameleira and serra verde carajas mineral province brazil constraints from re os molybdenite ages new re os molybdenite ages provide constraints on the timing of late archean cu au mo mineralization in the northern carajas mineral province molybdenite from the gameleira iron oxide cu au mo deposit yielded an age of 2 614 14 ma this age overlaps within its analytical error with re os ages of molybdenite from the serra verde cu au mo vein deposit 2 609 13 ma and from the nearby small garimpo fernando gold mining operation 2 592 13 and 2 602 13 ma which is probably related to the latter the geochronological data imply that the hydrothermal cu au mo mineralization in these three deposits was epigenetic and coincides with a regional tectonic regime changing from dextral transtension and clastic sedimentation at 2 7 2 6 ga to sinistral transpression and inversion at 2 6 ga previously reported stable isotope and microthermometric data are compatible with a magmatic affiliation of the cu au mo ores at gameleira and serra verde a genetic relationship of mineralization may therefore exist with 2 56 2 76 ga archean alkaline granitoids or with 2 6 2 7 calc alkaline to tholeiitic volcanic arc type magmatism

an f rich sn bearing volcanic intrusive complex in yanbei south china the igneous complex that hosts the yanbei porphyry tin deposit is situated along the eastern margin of the southeast china caledonian fold belt it intrudes a late jurassic granitic batholith and was unconformably covered by late cretaceous red beds the complex consists mainly of volcanic ignimbrites and minor rhyolitic lavas tuffs and subvolcanic rhyolite porphyry and intrusive rocks topaz bearing granite porphyry and granite these rocks are generally peraluminous with f and vi al rich biotite as the main mafic mineral and f rich and oh poor topaz as an accessory mineral in the granite porphyry and granite and as an essential mineral in the topazite topaz in the granites is usually interstitial and crystallized during the late magmatic stage the volcanic rocks and granites are rich in si k f sio 2 75 wt na 2 o k 2 o 0 03 0 72 f 0 06 6 48 wt and incompatible trace elements rb zr nb w sn and poor in mg ti ca p and compatible trace elements sr eu the chondrite normalized rare earth element ree patterns for the granites generally have a distinct v shape with strong eu depletion eu eu super whitesunwithrays 0 04 0 20 the main rocks of the complex have low epsilon nd t values 9 3 to 8 9 for volcanic rocks 4 0 to 4 8 for granites and high delta 18 o values of quartz from dacite 9 5ppm and granites 9 6 10 1ppm the difference in epsilon nd t between the volcanic rocks and granites indicates that they are not comagmatic the source of the volcanic rocks probably contains a greater metasedimentary component than that of the granites the yanbei porphyry tin deposit is located along the contact zone between topaz bearing granite porphyry and rhyolite porphyry and consists principally of one orebody which makes up 99 percent of the total reserves of the metallic minerals 5 by volume cassiterite pyrite and chalcopyrite are dominant sphalerite wolframite and galena are less important and siderite molybdenite and stannite are minor cassiterite accounts for 96 percent of the total sn reserves and stannite is the subordinate sn bearing mineral that occurs as rims around chalcopyrite cassiterite occurs mostly in disseminated form and as veinlets the wall rock alteration is intense and can be roughly grouped into three zones spatially arranged around the granite porphyry namely topaz quartz chloritic and sericitic zones most of the orebody occurs in the topaz quartz and chloritic zones hydrothermal alteration caused a decrease in k and na and an increase in al fe ca sn w and cu the delta 18 o values of quartz and cassiterite from the mineralized zones vary from 6 0 to 11 per mil and the calculated delta 18 o sub h 2 o values of the ore forming fluid range from 4 2 to 7 8 per mil the altered rocks have elevated delta 18 o sub h 2 o values 14 5 9 7ppm relative to fresh rocks the pyrite from the ore has a limited range of delta 34 s values 0 3 1 5ppm these data suggest a magmatic source for the ore forming hydrothermal fluid

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

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

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

metamorphism and geochronology of the luoning metamorphic terrane southern terminal of the palaeoproterozoic trans north china orogen north china craton abstract garnet bearing amphibolites and metapelites of the luoning metamorphic terrane taihua metamorphic complex southern terminal of the palaeoproterozoic trans north china orogen tnco preserve different metamorphic mineral assemblages formed at three metamorphic stages in the palaeoproterozoic the prograde mineral assemblages m1 comprise of hornblende plagioclase quartz biotite inclusions preserved in the garnet porphyroblasts in the amphibolites or quartz biotite plagioclase inclusions preserved in the garnet porphyroblasts in the metapelites the metamorphic peak mineral assemblages m2 are represented by the garnet porphyroblasts as well as the matrix minerals plagioclase hornblende biotite quartz in the amphibolites or quartz biotite plagioclase hornblende in the metapelites respectively the retrograde mineral assemblages m3 are the worm like fine grained white eye socket symplectitic assemblages formed between the relict garnet porphyroblasts and the matrix minerals consisting of plagioclase hornblende biotite intergrowths in the amphibolites or plagioclase biotite quartz intergrowths in the metapelites respectively geothermobarometric computation shows that the luoning terrane records clockwise p t trajectories including near isothermal decompression itd processes from 630 790 c 5 3 8 9 kbar through 720 820 c 8 9 10 7 kbar to 690 740 c 7 1 7 7 kbar sims u pb dating of zircons separated from the amphibolites and metapelites presents that the age of the protolith of the amphibolites is 2 32 ga and the metamorphism occurred during 1 97 1 94 ga suggesting that the subduction collision and the subsequent exhumation occurred in the late palaeoproterozoic combined with the literature data of the different discrete terranes within the trans north china orogen it is further deciphered that the tectono metamorphic event of the trans north china orogen started as early as 1 97 ga and lasted as late as 1 80 ga suggesting that the tectono metamorphic event of the orogen is a long and complex history

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

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

paleoproterozoic multistage evolution of the lower crust beneath the southern north china craton abstract it is generally recognized that the north china craton ncc resulted from the amalgamation of several micro blocks during the paleoproterozoic period however how the lower crust beneath the craton evolved during the amalgamation of these blocks is less well known four garnet bearing felsic granulite xenoliths entrained by the mesozoic xinyang volcanic rocks at the southwestern part of the eastern block of the craton were selected for analysis of whole rock major and trace elements and the u pb ages trace element patterns and lu hf isotopic composition of zircons these xenoliths are igneous in origin but with distinct sources the relict cores of magmatic zircon in the xenoliths give ages including ca 3 61 ga ca 2 22 ga and ca 2 05 ga and hadean neoarchean hf model ages tcrust 2 4 4 3 ga implying the existence of the hadean crustal components and a complex history in archean paleoproterozoic the metamorphic zircons from the xenoliths define three thermal episodes at ca 2 33 ga 1 86 1 91 ga and 1 72 1 77 ga and exhibit low but flat hree patterns and negative eu anomalies indicating that they formed in garnet bearing granulite facies rocks combined with the published data a vertical section of the lower crust can be built the upper part consists mainly of 3 4 3 6 ga garnet free felsic granulites and rare pyroxenites the middle part of 1 8 2 2 ga garnet bearing felsic granulites and meta gabbros and the lowermost part of 1 7 2 0 ga intermediate and mafic granulites and paleozoic eclogites these observations suggest that the lower crust beneath the area underwent multistage modification in the paleoproterozoic which was linked to the successive geological processes between the western and eastern blocks such as the subduction collision and rifting

genesis of the hengling magmatic belt in the north china craton implications for paleoproterozoic tectonics abstract the 2200 1880 ma igneous rocks in the central and eastern parts of the north china craton ncc constitute a new hengling magmatic belt hmb which includes the 2147 ma hengling mafic sill dyke swarm the 2060 ma yixingzhai mafic dyke swarm and the 1973 ma xiwangshan mafic dyke swarm the three swarms are contiguous and have experienced variable degrees of metamorphism from greenschist to low amphibolite facies hengling medium granulite facies yixingzhai and medium high pressure granulite facies xiwangshan they are all tholeiitic in composition typically with 47 52 wt sio 2 and 4 10 wt mgo and all show light rare earth element enrichments and nb and ta depletion their nd t dm ages are in the range of 2 5 3 0 ga specifically the hengling and yixingzhai dykes sills are depleted in th u zr hf and ti whereas the xiwangshan dykes are enriched in u and weakly depleted in other elements variable sr anomalies indicate significant feldspar accumulation positive anomalies or fractionation the end t values of the three swarms are 3 2 3 0 hengling 1 7 1 8 yixingzhai and 1 4 1 0 xiwangshan these mafic representatives of the hmb originated from the 2 5 ga sub continental lithospheric mantle of the ncc and with a type granites and other igneous associations in this belt they likely evolved in an intra continental rift the progressive changing compositions of the three swarms are interpreted in terms of their source regions at different depths i e shallower and shallower through time and the decrease in scale and size of the intrusions and their magma volumes indicate the progressive weakening of magmatism in this rift the rocks in this belt are different chronologically petrologically and chemically from those in the xuwujia magmatic belt xmb we propose that the two magmatic belts represent two different magmatic systems in different blocks of the ncc i e an eastern block with the hmb and a western block with the xmb terminal collision was possibly a result of ridge subduction between the two blocks which led to exhumation of the igneous rocks in the two belts from different crustal levels distinguishable by their different grades of metamorphism

magnetic fabric constraint on tectonic setting of paleoproterozoic dyke swarms in the north china craton china abstract locating the magma source for the mafic dyke swarms in the north china craton ncc is important for evaluating tectonic setting and emplacement mechanism here we have conducted systematic ams studies on paleoproterozoic dykes from the fengzhen fuping and lvliang areas of the ncc rock magnetic analyses indicate that psd magnetite is the predominant magnetic carrier although the lvliang dykes contain more sd magnetic grains than the fengzhen and fuping dykes the fengzhen and fuping dykes have mostly normal ams fabrics whilst the lvliang dykes exhibit a larger proportion of intermediate ams fabrics most of the fuping dykes are found to have intruded sub vertically upward although some fabrics indicate northward magma flow from imbrication and the distribution of k1 ams axes the lvliang dykes identify a southwestward magma flow from opposed imbrications and distributions of k1 ams axes the fuping area is thus interpreted to have been located near to the magma source which fed most dykes in the central ncc a variety of magma sources are suggested for dykes in other parts of the ncc dykes near the southern margin of the craton probably resulted from lateral migration of magma from the xiong er source and contrast with the dykes in the central ncc fed by the fuping magma source further paleoproterozoic magma sources likely remain to be identified

metallogeny of the large scale carboniferous karstic bauxite in the sanmenxia area southern part of the north china craton china abstract above two billion tons of bauxite were formed during the exposure of the north china craton ncc in 445 300 ma mineralogical geochemical and isotopic analyses of karstic bauxite deposits in the sanmenxia area situated within southern ncc were conducted to explore the genetic processes of carboniferous bauxite the bauxite contains three layers a lower fe bearing claystone layer a middle bauxite ore layer and an upper claystone layer fe bearing claystone is dominated by illite and hematite in the uplift and illite siderite and pyrite in the depression bauxite ore is composed of diaspore illite pyrite and anatase and the upper claystone consists of illite diaspore and anatase distinct pyrite 34s values 11 7 15 2 and 11 5 to 1 0 illite 87sr 86sr i 0 711917 0 713588 and 0 708000 0 711057 and end t 12 2 to 11 4 and 11 8 to 9 7 values and the immobile elemental ratios were obtained between the lower fe bearing claystone and upper bauxite ore and claystone together with chemistry of detrital rutile it is denoted the fe bearing claystone was formed from the underlying limestone whereas the bauxite ore and claystone were derived from both igneous rocks along craton margin and regional precambrian metamorphic rocks the visible microorganisms and wide development of framboidal pyrite with negative 34s within the bauxite ore provide evidences of microbial activity during bauxite formation bio leaching process after the deposition of allochthonous source materials caused the downward migration of ions al3 fe2 ti4 ree3 etc these ions encountered an alkaline and reducing condition in the karstic depression forming diaspore pyrite and anatase and ree enrichment at the bottom of bauxite ore this large input of raw materials warm and humid climate and microorganisms led to large scale bauxite formation in the ncc during late carboniferous

paleo position of the north china craton within the supercontinent columbia constraints from new paleomagnetic results abstract several new paleomagnetic and geological studies focused on the reconstruction of the north china craton ncc within the paleo mesoproterozoic columbia supercontinent in spite of these new data there are still widely divergent opinions regarding supercontinental reconstructions in addition to qualitative correlations of orogenic belts rift basin ages stratigraphy and distribution of igneous provinces paleomagnetic data can provide key constraints on the positioning of individual cratons on the globe in this paper we report a detailed paleomagnetic study on the coeval 1780 ma mafic dyke swarm and xiong er volcanic province which extended for more than one thousand kilometers in the central ncc rock magnetic studies including thermomagnetic curves hysteresis loops and the progressive acquisition of isothermal remanence conducted in selected samples indicate that the dominant magnetic carriers are psd magnetite stepwise thermal demagnetization isolated higher temperature components directed to nne ssw with shallow inclinations from 37 sampling sites 16 sites in yinshan area 13 sites in taihang area and 8 sites in xiaoshan area a baked contact test conducted on two yinshan dykes intruded by a younger dyke demonstrates the magnetization in the yinshan dykes pre dates 1320 ma the existence of dual polarity magnetizations in both taihang and xiong er areas support our contention that the chrm was acquired during the cooling of the magma the primary origin of the chrm is also supported by a positive fold test on the xiong er data and a coherent regional test between the results from the taihang and xiong er areas two different site mean directions were compiled from these new results along with previous publications the first direction from the taihang and xiong er areas yields declination d inclination i 12 4 3 7 20 5 95 4 3 n 57 sites the second from the yinshan area is at d 36 7 i 12 4 86 8 95 2 7 n 32 sites we argue that the difference is due to mesozoic and or cenozoic vertical axis rotation of the taihang and xiong er areas with respect to the fixed yinshan ordos basin the corresponding paleopoles for the yinshan dykes falls at 245 2 e 35 5 n a95 2 4 a comparison between the ncc laurentia siberia and baltica is consistent with possible links between these four blocks in a perhaps even larger continent the proximity of australia and india to the ncc is also evaluated

cenozoic volcanism in tibet evidence for a transition from oceanic to continental subduction geochronological k ar or ar ar major and trace element sr nd pb isotopic and mineral chemical data are presented for newly discovered cenozoic volcanic rocks in the western qiangtang and central lhasa terranes of tibet alkali basalts of 65 45ma occur in the western qiangtang terrane and represent primitive mantle melts as indicated by high mgnumbers 100 mg mg fe 54 65 cr 204 839 ppm and ni 94 218 ppm contents and relatively low ratios of sr sr 0 7046 0 7061 pb pb 18 21 18 89 pb pb 15 49 15 61 and pb pb 38 42 38 89 and high ratios of nd nd 0 5124 0 5127 in contrast younger volcanic rocks in the western qiangtang terrane 30ma and the central lhasa terrane 23 13 and 8ma are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source they are characterized by very high contents of incompatible trace elements negative ta nb and ti anomalies and radiogenic pb isotopic compositions pb pb 18 43 19 10 pb pb 15 64 15 83 pb pb 39 14 39 67 sr sr 0 7088 0 7092 and nd nd 0 5122 ratios of the western qiangtang terrane potassic lavas are similar to those of 45 29ma potassic volcanic rocks in the north central qiangtang terrane whereas sr sr 0 7167 0 7243 and nd nd 0 5119 ratios of central lhasa terrane lavas are similar to those of 25 16ma ultrapotassic volcanic rocks in the western lhasa terrane the 65 45ma alkali basalts in the western qiangtang terrane along with widespread calc alkaline volcanic rocks of this age in the lhasa terrane may be related to roll back of a previously shallow north dipping slab of tethyan oceanic lithosphere beneath tibet subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in tibet because of its occurrence in distinct east west trending belts 45 29ma in the qiangtang terrane 25 17ma in the northern lhasa terrane 16 8ma in the southern lhasa terrane and temporal and spatial relationships with major thrust systems

melting of a subduction modified continental lithospheric mantle evidence from late proterozoic mafic dike swarms in central australia geochemical and nd isotopic studies of two postorogenic late proterozoic 1083 23 ma high mg tholeiitec dike swarms in central australia indicate that the dike swarms were derived by partial melting of the continental lithospheric mantle which was modified by subduction processes during major crust formation events in the region both dike swarms stuart and kulgera which intrude the arunta and musgrave inliers respectively resemble island arc tholeiites in terms of geochemical features they yield whole rock sm nd ages of 1853 189 ma with nd 4 2 4 2 stuart and 1589 165 ma with nd 1 7 3 6 kulgera the two whole rock ages and initial nd values are remarkably similar to the oldest u pb zircon ages and initial nd values obtained from the corresponding basement blocks these isotopic data are interpreted as recording sm nd fractionation events in the continental lithospheric mantle associated with major episodes of crust formation in the early proterozoic

petrogenesis of the early cretaceous funiushan granites on the southern margin of the north china craton implications for the mesozoic geological evolution abstract late mesozoic granitoids are ubiquitous in the southern margin of the north china craton and are keys to the understanding of the mesozoic geological evolution the early cretaceous funiushan granitic pluton in the southern margin of the north china craton is composed of porphyritic biotite monzogranites rocks from the funiushan pluton have high sio2 64 45 73 98 wt na2o 3 19 4 67 wt and k2o 3 76 7 95 wt and low mgo 0 11 1 34 wt they are enriched in rb ba th u and lree la yb n 9 63 45 0 and depleted in nb ta ti and p and have negative eu anomalies eu eu 0 29 0 72 this geochemical feature is similar to those of typical i type granites zircons from the granites were dated using la icp ms and sims and yielded 206pb 238u ages of 115 131 ma they have ehf t values mainly vary from 17 7 to 0 9 and t dm c ages mainly from 2301 to 1118 ma whole rock end t values range from 20 3 to 9 6 and tdm ages from 1 49 to 2 29 ga indicating that the magma was produced by partial melting of the neoarchean to paleoproterozoic crustal rocks as represented by the taihua group basement rocks with minor involvement of mantle derived melts the funiushan pluton is considered to have been formed through a strong crust mantle interaction process under a low pressure condition in an extensional setting due to the lithospheric thinning caused by westward subduction of the paleo pacific oceanic crust

magnetic fabrics and rock magnetism of the xiong er volcanic rocks and their implications for tectonic correlation of the north china craton with other crustal blocks in the nuna columbia supercontinent abstract the tectonic background of the paleoproterozoic xiong er volcanic rocks xvr is important for understanding the tectonic evolution of the north china craton ncc as well as its paleogeographic position during the assembly of the nuna columbia supercontinent here we report the results of the first anisotropy of magnetic susceptibility ams study of the xvr and use the interpreted flow directions to constrain the emplacement mechanism and to assess its geological significance for the reconstruction of the nuna columbia supercontinent thirty lavas were sampled from three sections in western henan province detailed rock magnetic analyses including measurements of hysteresis loops magnetization versus temperature curves and first order reverse curves were performed to identify the main magnetic phases and grain sizes the inferred directions from the ams results reveal a radial flow pattern with an eruption center probably located near xiong er mountain our data suggest that the xvr may have been emplaced in a triple conjugated continental rift on the south margin of the ncc probably initiated from a paleoplume based on this interpretation a comparison of geological and paleomagnetic results among the proposed crustal blocks in the nuna columbia supercontinent suggests a close linkage of the ncc with sao francisco congo rio de la plate and siberia

late jurassic to early cretaceous magmatism in the xiong ershan gold district central china implications for gold mineralization and geodynamics the xiong ershan area is the third largest gold producing district in china the late jurassic to early cretaceous magmatism in the xiong ershan area can be divided into two episodes early 165 150 ma and late 138 113 ma laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating yields ages of 160 7 0 6 ma and 127 2 1 0 ma for the wuzhangshan and huashan monzogranites in the xiong ershan area respectively representing the two magmatic episodes the wuzhangshan monzogranites exhibit adakite like geochemical features e g high sr y ratios low yb and y contents their sr nd hf isotopic compositions are consistent with those of the amphibolites of the taihua group indicating that the wuzhangshan monzogranites were formed from partial melting of the taihua group metamorphic rocks compared to the wuzhangshan rocks the huashan monzogranites have higher mgo cr co and ni contents but lower sr y and fe 3 fe 2 all the samples from the huashan monzogranites plot in the area between the taihua group amphibolite rocks and the mantle rocks in the 87 sr 86 sr t vs e nd t and age vs e hf t diagrams suggesting that the huashan monzogranites were probably generated by mixing of mantle derived magmas and the taihua group metamorphic basement melts the gold mineralization 136 110 ma is coeval with the emplacement of the late episode magmas implying that crustal mantle mixed magma might be a better target for gold mineralization compared to the ancient metamorphic basement melt the data presented in this study further indicate that the transformation of the lithosphere from thickening to thinning in the xiong ershan area probably occurred between 160 ma and 127 ma and that the gold mineralization in this area was probably related to lithospheric thinning

the high k2o volcanism of northwestern tibet geochemistry and tectonic implications cenozoic volcanic rocks sampled during the 1989 sino french kunlun geotraverse have been analyzed to constrain the origin of widespread tertiary to neogene tibetan basic magmatism samples ranging from phonotephrites to trachyandesites are high k lavas k na always greater than 1 which exhibit typical calc alkaline characteristics although they are highly enriched in mobile trace elements and ree 600 times chondrites for la isotopic compositions exhibit radiogenic sr and pb 87sr 86sr 0 708 208pb 204pb 39 39 4 207pb 204pb 15 6 15 7 206pb 204pb 18 7 and unradiogenic nd 143nd 144nd 0 5123 0 5124 constancy of sr and nd isotopic values contrasts with variations in pb isotopes and highlights the problem of crustal contamination afc and simple mixing models are compatible with isotopic variations but were probably buffered by elemental concentration in sr and nd while pb isotopic values for the most primitive magmas are probably uncontaminated isotopic features are therefore proposed to be representative of a mantle source in which heterogeneity could be highlighted in the pb isotopic values such a source highly enriched in trace elements and radiogenic sr and pb is proposed to lay in the subcontinental mantle isolated from the overall convection movements the calc alkaline characteristics can date from the succession of enrichment phases linked to the numerous subduction events that have affected this part of asia while the isotopic characteristics are proposed to be the result of the aging of the concomitant lile enrichments the broad geographical geochemical and timing aspects of recent basic cenozoic magmatism are discussed in the light of our new data and we suggest that two mechanisms are acting together 1 a limited delamination of the base of the lithosphere or a thermal reequilibration of isotherms subsequent to thickening and 2 intracontinental subduction under the kunlun such mechanisms appear the most probable as they respect at the same time recent geophysical data and other geochemical studies

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

the qiyugou au orefield an intrusion related gold system in the eastern qinling ore belt china constraints from sims zircon u pb molybdenite re os sericite 40ar 39ar geochronology in situ s pb isotopes and mineralogy abstract the eastern qinling ore belt is the second largest au province in china and is estimated to contain more than 1300 metric tons of au most of the gold deposits in the belt are vein type fracture hosted au whether they are of metamorphic origin or magmatic hydrothermal origin is controversial the qiyugou au orefield developed granite hosted au breccia pipe hosted au and fracture hosted au and the present study investigates these three types of gold mineralization new zircon u pb and molybdenite re os ages along with previous published data are used to constrain the ages of the three types of au at about 131 ma corresponding to the emplacement age of hornblende monzogranite s pb isotope compositions telluride and bi sulfosalt minerals hematite alteration and metal zonation in the three types of au suggest a common oxidized magmatic hydrothermal origin these results suggest an intrusion related au system in the qiyugou au orefield this model confirms the magmatic hydrothermal origin for the fracture hosted au and provides important implications for further regional exploration

mo rich source and protracted crystallization of late mesozoic granites in the east qinling porphyry mo belt central china constraints from zircon u pb ages and hf o isotopes abstract in the east qinling orogenic belt central china there are numerous mo deposits with over 6 mt mo metal the giant nannihu shangfanggou and yuchiling porphyry mo deposits are hosted in porphyry stocks associated with the heyu batholith whereas the giant donggou porphyry mo deposit is hosted in a stock associated with the taishanmiao batholith zircon grains from the heyu batholith have concordant 238u 206pb ages scattered from 150 3 to 130 2 ma with an age interval of nearly 20 m y whereas ore hosting granitic porphyry stocks from the nannihu shangfanggou and yuchiling deposits have 206pb 238u ages ranging from 151 1 to 135 1 ma 143 1 to 132 1 ma and 143 5 to 131 5 ma respectively it is likely that the heyu batholith has a prolonged history of incremental assembly and the ore bearing granitic porphyry stocks may have originated from the same magma reservoir and emplaced in different stages likewise zircon grains from the taishanmiao batholith have concordant 238u 206pb ages spanning in a period from 130 2 to 111 3 ma whereas those from the donggou granitic porphyry stock have 238u 206pb ages ranging from 125 2 to 110 3 ma nearly coeval with the taishanmiao batholith the molybdenite re os model ages for each deposit are coincident with relatively young zircon 238u 206pb ages of the host stock indicating that mo mineralization is likely related to late stage magmatism zircon grains from the batholiths and granitic porphyry stocks have ehf t ranging from 10 to 30 tdm2 ages from 1 6 to 2 5 ga and 18o from 5 0 to 8 7 which are taken to suggest the involvement of the subducted continental crust of the yangtze block in the source we thus propose that the extensive mo mineralization in the east qinling porphyry mo belt is genetically related to the prolonged granitic magmatism in the late mesozoic and a mo rich source that was related to the subducted continental crust of the yangtze block stagnating beneath the southern margin of the north china craton

hydrothermal alteration fluid inclusions and stable isotope systematics of the alvo 118 iron oxide copper gold deposit carajas mineral province brazil implications for ore genesis the alvo 118 iron oxide copper gold iocg deposit 170 mt at 1 0 wt cu 0 3 g t au lies in the southern sector of the itacaunas shear belt carajas mineral province along a wnw ese striking 60 km long shear zone close to the contact of the 2 76 ga metavolcano sedimentary itacaiunas supergroup and the basement 3 0 ga xingu complex the alvo 118 deposit is hosted by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following hydrothermal alteration sequence towards the ore zones 1 poorly developed sodic alteration albite and scapolite 2 potassic alteration biotite or k feldspar accompanied by magnetite formation and silicification 3 widespread pervasive chlorite alteration spatially associated with quartz carbonate sulphide infill ore breccia and vein stockworks and 4 local post ore quartz sericite alteration the ore assemblage is dominated by chalcopyrite 60 bornite 10 hematite 20 magnetite 10 and subordinate chalcocite native gold au ag tellurides galena cassiterite f rich apatite xenotime monazite britholite y and a gadolinite group mineral fluid inclusion studies in quartz point to a fluid regime composed of two distinct fluid types that may have probably coexisted within the timeframe of the cu au mineralizing episode a hot 200 c saline 32 8 to 40 6 wt nacl eq solution represented by salt bearing aqueous inclusions and a lower temperature 200 c low to intermediate salinity 15 wt nacl eq aqueous fluid defined by two phase lh2o vh2o fluid inclusions this trend is very similar to those defined for other iocg systems of the carajas mineral province 18oh2o values in equilibrium with calcite 1 0 to 7 5 at 277 c to 344 c overlap the lower range for primary magmatic waters but the more 18o depleted values also point to the involvement of externally derived fluids possibly of meteoric origin furthermore sulphide 34s values 5 1 to 6 3 together with available boron isotope and cl br na cl data provide evidence for a significant component of residual evaporative fluids e g bittern fluids generated by seawater evaporation in this scenario that together with magma derived brines would be the main sources of the highly saline fluids involved in the formation alvo 118 iocg deposit the restricted high temperature sodic alteration the pervasive overprinting of the potassic alteration minerals by chlorite proximal to the ore zones ore breccias with open space filling textures in brittle structures microthermometric and stable isotope data indicate collectively that the alvo 118 iocg system developed at structurally high levels and may be considered the shallower representative of the iocg systems of the cmp

re os and pb pb geochronology of the archean salobo iron oxide copper gold deposit carajas mineral province northern brazil rhenium osmium ages were determined for two molybdenite samples and a pb pb age was derived from bornite chalcopyrite magnetite at the salobo iron oxide copper gold deposit to determine the timing of mineralization and its relation to the nearby old salobo granite rhenium osmium dating of molybdenite spatially associated with copper sulfide minerals yields ages with weighted means of 2576 8 and 2562 8 ma removing the error multiplier introduced by the decay constant uncertainty appropriate for comparing ages from the same isotopic system these data convincingly argue for two temporally separated pulses of molybdenite deposition at 2576 1 1 4 ma n 2 and 2561 7 3 1 ma n 3 the 2576 8 ma age coincides with a previously published u pb age of 2573 2 ma for the old salobo granite suggesting that main stage ore formation may have been contemporaneous with granite magmatism the slightly younger 2562 ma age most likely represents new molybdenite precipitation associated with the development or reactivation of local shear zones lead lead stepwise leaching of copper sulfide minerals yields a less precise isochron age of 2579 71 ma and supports an archean age for the salobo ores this is the first documentation of an archean iron oxide copper gold deposit and the re os and pb pb geochronology herein support 2580 2550 ma estimates for basement reactivation and regional granite magmatism associated with the development of brittle ductile shear zones