geochronology and geochemistry of late paleozoic volcanic rocks on the western margin of the songnen zhangguangcai range massif ne china implications for the amalgamation history of the xing an and songnen zhangguangcai range massifs abstract we here elucidate the tectonic evolution of the xing an and songnen zhangguangcai range massifs during the early carboniferous early permian based on zircon u pb dating and whole rock geochemical analyses of volcanic rocks of the songnen zhangguangcai range massif in the sunwu area heilongjiang province ne china euhedral subeuhedral zircons from three rhyolites and one dacite from the study area display fine scale oscillatory growth zoning indicating a magmatic origin zircon u pb dating by la icp ms indicates that these acidic volcanic rocks formed in the early carboniferous early permian i e early carboniferous 351 ma early late carboniferous 319 ma and early permian 295 293 ma the early carboniferous rhyolites exhibit chemical affinities to a type rhyolites implying an extensional environment their positive ehf t values 8 67 to 13 4 except for one spot of 1 63 and hf two stage model ages t dm2 562 988 ma indicate that the primary magma was possibly derived from partial melting of newly accreted continental crust the early late carboniferous rhyolites and dacites 319 ma exhibit calc alkaline peraluminous signature molar al 2 o 3 cao k 2 o na 2 o ratio or a cnk 1 04 1 22 the ehf t values and t dm2 ages of zircons from the 319 ma dacites are in the range of 5 33 to 9 32 and 907 1268 ma respectively suggesting that the primary magma was derived from partial melting of newly accreted crust the early permian rhyolites 295 293 ma show chemical affinities to a type rhyolites implying an extensional tectonic environment their positive ehf t values 8 82 to 13 8 and hf two stage model ages 484 743 ma indicate that the primary magma was derived from partial melting of newly accreted crust combined with the geochemical features of coeval igneous rocks from the eastern margin of the xing an massif these data reveal the late paleozoic tectonic history and relationships of the xing an and songnen zhangguangcai range massifs i e early carboniferous westward subduction of the paleo asian oceanic plate beneath the xing an massif followed by early late carboniferous collision and amalgamation of microcontinental blocks and early permian post collisional extension

deep crustal carbonate rocks exposed by meteor impact on mars mars may have once had a co2 rich atmosphere but carbonate rocks that could provide evidence for such conditions are sparse spectral analyses of rocks exposed from deep within an impact crater reveal that carbonate deposits may be extensive on mars but are buried under layers of younger volcanic rocks

petrogenesis and geodynamic implications of neoproterozoic gabbro diorites adakitic granites and a type granites in the southwestern margin of the yangtze block south china abstract the occurrence of a type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone this paper presents a comprehensive study of zircon u pb hf isotopes and whole rock geochemistry on the neoproterozoic gabbro diorites biotite granites and k feldspar granites in the southwestern margin of the yangtze block south china zircon u pb dating of three distinctive intrusions yield concordant ages of 810 4 2 0 ma for gabbro diorites 800 3 2 1 ma for biotite granites and 749 1 2 0 ma for k feldspar granites the gabbro diorites are sodic and calc alkaline rocks with low sio2 52 62 53 87 wt medium mgo 2 67 3 41 wt high fe2o3t 7 18 7 49 wt and cao 5 68 7 50 wt contents they display high th zr and rb y ratios but low nb zr and nb y ratios together with their positive whole rock end t 1 0 to 1 5 and zircon ehf t values 3 66 to 8 18 we suggest that these gabbro diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction related fluids the biotite granites display relatively high sr contents 335 395 ppm sr y ratios 38 9 54 3 low y 7 04 9 71 ppm and yb contents 0 78 1 08 ppm resembling the adakitic granites their low mg 36 41 values cr 2 94 3 59 ppm and ni 1 32 1 55 ppm contents as well as positive end t 0 5 to 0 6 and ehf t values 1 62 to 8 07 indicate that they were formed by partial melting of thickened juvenile mafic lower crust probably within the existence of garnet the k feldspar granites have high sio2 76 61 77 14 wt and alkalis na2o k2o 8 55 9 69 wt contents high 10 000 ga al 2 56 2 80 ratios and differentiation index 95 3 96 9 indicating the affinity to highly fractionated a type granites we suggest that these a type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant taking into account previous studies from the western yangtze block south china we propose that the gabbro diorites adakitic granites and a type granites in this study were formed in persistent subduction process during the neoproterozoic

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

u pb zircon dating of granulite metamorphism in the sludyanskiy complex eastern siberia abstract conventional multigrain and single grain zircon u pb ages were obtained for syn and post metamorphic granitoids from the sludyanskiy complex in the south western baikal region regarded as a classical precambrian terrain in the eastern siberia single grains of magmatic zircon from the syn metamorphic hypersthene bearing biotite trondhjemite and two pyroxene trondhjemite have yielded concordant u pb ages of 488 5 0 6 ma and 488 0 5 ma concordant u pb data for zircons of metamorphic origin in the syn metamorphic two pyroxene trondhjemite yield an age for the peak of the granulite facies metamorphism in the sludyanskiy complex as 477 6 2 ma the pattern of multigrain magmatic zircon samples from syn metamorphic granitoids reflects significant pb loss during the metamorphic episode this came to an end before 471 1 2 ma as demonstrated by concordant zircon data for the intrusion of post metamorphic amphibole two pyroxene quartz syenite our zircon data establish that the granulite facies reworking of the sludyanskiy complex took place during the palaeozoic and not during the paleoproterozoic as was previously suggested the age span between the intrusions of syn metamorphic and post metamorphic granitoids constrains the duration of the metamorphic episode to about 20 ma

permian bimodal volcanism in the zhangguangcai range of eastern heilongjiang province ne china zircon u pb hf isotopes and geochemical evidence abstract in this paper we report on zircon u pb dating hf isotopes major and trace elements and sr nd isotope data with the aim of constraining the petrogenesis and regional tectonic evolution of late paleozoic volcanic rocks in the zhangguangcai range of eastern heilongjiang province ne china located in the eastern segment of the central asian orogenic belt caob between the siberian and north china cratons the late paleozoic volcanic rocks in the zhangguangcai range are composed mainly of basalt basaltic andesite rhyolite and minor dacite the results of la icp ms zircon u pb dating for two basaltic rocks three rhyolites and one dacite indicate that they formed in the early permian ca 292 ma the mafic rocks have sio2 50 13 53 80 wt k2o 0 98 2 28 wt mg 0 51 0 71 cr 144 541 ppm ni 74 260 ppm 87sr 86sr i 0 7044 and end t 4 28 whereas the felsic rocks have sio2 69 12 77 98 wt k2o 3 09 5 33 wt mg 0 17 0 36 87sr 86sr i 0 7032 and end t 4 32 these data are typical of bimodal volcanism the mafic volcanic rocks are characterized by a strong enrichment in large ion lithophile elements liles such as rb ba sr and pb depletion in high field strength elements hfses such as nb ta and ti depletion in heavy rare earth elements hrees and weak negative eu anomalies eu eu 0 88 0 94 on the other hand the felsic rocks show a strong depletion in nb ta sr p and ti enrichment in th u and k and relatively large negative eu anomalies eu eu 0 28 0 95 taken together these data suggest that the mafic magma was derived from the partial melting of a depleted lithospheric mantle modified by subducted slab derived fluids and that the felsic magma originated by partial melting of newly accreted crust the early permian bimodal volcanic rocks together with the coeval a type granites indicate an extensional environment similar to a back arc basin such a setting was possibly related to subduction of the paleo asian oceanic plate beneath the jiamusi and songnen zhangguangcai range massifs

origin of distinct silicic magma types from the guachipelin caldera nw costa rica evidence for magma mixing and protracted subvolcanic residence abstract lower pleistocene pyroclastic deposits in nw costa rica represent sequential eruptions of distinct dacitic rhyolitic 69 79 sio2 magmas from the guachipelin caldera that were emplaced in a period of 0 75 myr this southern segment of the central american arc the chorotega block evolved on the modified caribbean large igneous province an overthickened oceanic plateau silicic magmatism is uncommon in settings such as this void of continental crust previously models have proposed the generation of silicic magmas in this type of setting by the partial melting or extreme crystal fractionation of intermediate source rocks e g tamura y tatsumi y 2002 remelting of an andesitic crust as a possible origin for rhyolite magma in oceanic arcs an example from the izu bonin arc journal of petrology 43 1029 1047 in fact recent melting experiments performed by sisson et al sisson t w ratajeski k hankins w b glazner a f 2005 voluminous granitic magmas from common basaltic sources contributions to mineralogy and petrology 148 5 542 565 suggest that melting of andesite or high k basalts common along the central american volcanic arc could produce silicic melts with the characteristic alkali content of these types of eruptives geochemical evaluation of the pumice clasts through the complete sequence of guachipelin eruptive products allows for subdivision into two major silica groups first the dacites are 66 72 wt sio2 pumice clast 75 2 76 5 wt sio2 glass orthopyroxene bearing with plagioclase an36 65 magnesiohornblende which are found intermittently from the base of the sequence through the uppermost ash flow deposit second the rhyolites are 72 79 wt sio2 pumice clast 74 5 78 6 wt sio2 glass biotite and quartz bearing with plagioclase an24 51 and magnesiohornblende chemical heterogeneities were discovered within each of these groups through evaluation of incompatible trace element ratios consequently seven units were defined using the nb ta ratio which has a significantly wide range from 3 8 to 29 4 and is interpreted to reflect contributions from more than one intermediate source most of these units also display extensive geochemical and petrological evidence of mixing oxygen isotopes phenocryst composition banded pumice clasts and different glass compositions in single pumice fragments the distinct geochemical characteristics of these deposits and the stratigraphic occurrence of each flow unit require both limited fractional crystallization within units coupled with melt extractions and extensive mixing hence individual melts would reside in relatively close proximity in subvolcanic zones for extended periods prior to the inception of a particular eruptive event considering the temporal

geochronology and geochemistry of the heilongjiang complex and the granitoids from the lesser xing an zhangguangcai range implications for the late paleozoic mesozoic tectonics of eastern ne china abstract an integrated study on two subduction related units the heilongjiang complex and magmatic rocks in the lesser xing an zhangguangcai range was carried out to explore the paleozoic to early mesozoic tectonic framework of the eastern northeast china with a focus on the jiamusi block the heilongjiang complex which is considered as the suture between the jiamusi and songliao blocks is composed of blueschist amphibolite and ultramafic rocks the blueschist from the yilan area shows geochemical features similar to oib and has a 206pb 238u age of 288 2 ma which is interpreted as the crystallization age of protolith formed in an ocean island setting in contrast amphibolite from the xiachengzi area shows geochemical features similar to n morb zircons in this amphibolite show magmatic character and yield a 206pb 238u age of 248 4 ma which is interpreted as the protolith age calcic amphiboles in the amphibolite give a 40ar 39ar plateau age of 195 3 ma which is interpreted as the metamorphic age of the heilongjiang complex magmatic rocks in the lesser xing an zhangguangcai range mostly belong to i type granites that were formed in an active continental margin setting zircon u pb ages of these granites range from 200 ma to 174 ma with a westward younging trend shown as two groups of emplacing ages of 200 ma in the east and 180 ma in the west our new data support an early occurrence likely since the early permian of a large ocean namely the mudanjiang ocean in the area whose subduction resulted in the metamorphic unit the heilongjiang complex and the magmatic unit the lesser xing an zhangguangcai range in the jurassic

identification of carbonate rich outcrops on mars by the spirit rover decades of speculation about a warmer wetter mars climate in the planet s first billion years postulate a denser co2 rich atmosphere than at present such an atmosphere should have led to the formation of outcrops rich in carbonate minerals for which evidence has been sparse using the mars exploration rover spirit we have now identified outcrops rich in magnesium iron carbonate 16 to 34 weight percent in the columbia hills of gusev crater its composition approximates the average composition of the carbonate globules in martian meteorite alh 84001 the gusev carbonate probably precipitated from carbonate bearing solutions under hydrothermal conditions at near neutral ph in association with volcanic activity during the noachian era

petrogenesis of early middle jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china implications for the extent of spatial temporal overprinting of the mongol okhotsk and paleo pacific tectonic regimes abstract the mesozoic tectonic evolution of ne china was controlled mainly by the mongol okhotsk and paleo pacific tectonic regimes however the extent of the spatial and temporal overprinting of these two regimes is poorly understood here we report new zircon la icp ms u pb dating and geochemical analyses of jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china to discuss their petrogenesis and outline the extent of spatial and temporal overprinting of these two tectonic regimes dating results indicate that jurassic magmatism occurred in two stages during the early ca 175 ma and middle jurassic 170 163 ma these rocks represent two stage typical bimodal igneous rock associations composed mainly of olivine gabbro gabbro and gneissic granitoids the early and middle jurassic gabbros have low rare earth element ree abundances positive eu anomalies depletion in high field strength elements hfses and positive ehf t values 4 0 to 10 3 except for one value of 17 8 suggesting that the primary magma was derived from partial melting of depleted lithospheric mantle metasomatized by subducted slab derived fluids the early jurassic monzogranite exhibit high ree abundances 195 201 ppm weak negative eu anomalies eu 0 63 0 64 and negative ehf t values 11 9 to 8 2 suggesting a primary magma that was derived from partial melting of lower continental crust of the ncc the middle jurassic granodiorites are enriched in light rees lrees and large ion lithophile elements liles and are depleted in heavy rees hrees and hfses as well as high sr y 29 132 and la yb n 15 44 ratios in addition the middle jurassic granitoids near or within the ncc exhibit negative ehf t values 18 9 to 0 2 whereas those within the xing an mongolia orogenic belt xmob have generally positive ehf t values 0 6 to 6 4 suggesting their origin from partial melting of thickened ancient ncc and newly accreted continental crust of the xmob respectively the above findings combined with regional geologic data suggest that the early jurassic bimodal igneous rocks formed in an extensional tectonic environment related to subduction of the paleo pacific plate beneath the eurasian continent the middle jurassic bimodal igneous rocks possibly formed in an extensional environment related to the collapse of a thickened region of the lower crust after closure of the mongol okhotsk ocean

triassic volcanism in eastern heilongjiang and jilin provinces ne china chronology geochemistry and tectonic implications abstract with the aim of constraining the early mesozoic tectonic evolution of the eastern section of the central asian orogenic belt caob we undertook zircon u pb dating and geochemical analyses major and trace elements sr nd isotopes of volcanic rocks of the luoquanzhan formation and daxinggou group in eastern heilongjiang and jilin provinces china the analyzed rocks consist mainly of dacite and rhyolite with sio2 contents of 68 52 76 65 wt three samples from the luoquanzhan formation and one from the daxinggou group were analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms u pb zircon techniques three zircons with well defined oscillatory zoning yielded weighted mean 206pb 238u ages of 217 1 214 2 and 208 1 ma and one zircon with oscillatory zoning yielded a weighted mean 206pb 238u age of 201 1 ma these ages are interpreted to represent the timing of eruption of the volcanic rocks the triassic volcanic rocks are characterized by high sio2 and low mgo concentrations enrichment in large ion lithophile elements liles and light rare earth elements lrees depletion in high field strength elements hfses and heavy rare earth elements hrees 87sr 86sr i 0 7040 0 7050 luoquanzhan formation and 0 7163 0 7381 daxinggou group and end t 1 89 3 94 luoquanzhan formation and 3 42 3 68 daxinggou group these geochemical features indicate an origin involving the partial melting of juvenile lower crust nd model ages tdm2 of 651 821 ma and that compositional variation among the volcanic rocks arose from mineral fractionation and minor assimilation these volcanic rocks formed within an extensional environment following collision of the ncc and jiamusi khanka massif during the late paleozoic early triassic

permian tectonic evolution of the mudanjiang ocean evidence from zircon u pb hf isotopes and geochemistry of a n s trending granitoid belt in the jiamusi massif ne china abstract a combined study of la icp ms zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions for five permian granitic plutons mingyi tuoyaozi mengjiagang hengtoushan and qingbei plutons from the jiamusi massif was carried out to determine their ages petrogenesis and tectonic evolution the studied granitic plutons are composed of syengranites monzogranites and granodiorites and they were emplaced in the early middle permian 278 263 ma these granitic plutons are mostly high k calc alkaline and weakly peraluminous and show consistent correlations of different oxides versus sio 2 they are all enriched in large ion lithophile elements e g rb th k and light rare earth elements and depleted in high field strength elements e g nb ta ti and heavy rare earth elements and they have relatively homogeneous hf isotopic compositions with ehf t values varying from 6 16 to 2 95 and two stage model ages ranging from 1681 to 1111 ma according to their emplacement ages geochemical characteristics and hf isotopic compositions we conclude that these granitoids might be originated from parental magmas with similar compositions but evolved different degrees of fractionation and their magmas were derived from the partial melting of amphibolite facies mafic lower crust these data combined with previous studies on contemporaneous magma tectonic activities in the jiamusi massif and songnen zhangguangcai range massif indicate that two paralleled n s trending permian magmatic belts are distributed in these two massifs the eastwards subduction of the mudanjiang oceanic plate beneath the jiamusi massif induced crustal melting to produce the studied permian n s trending granitoids in the jiamusi massif furthermore westwards subduction of the mudanjiang oceanic plate beneath the songnen zhangguangcai range massif gave rise to permian magmatism along eastern margin of the songnen zhangguangcai range massif taken together we suggest that the jiamusi massif and songnen zhangguangcai range massif were not collided before the permian and a double side subduction model is favored for the tectonic evolution of the mudanjiang ocean during the permian

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

early middle paleozoic subduction collision history of the south eastern central asian orogenic belt evidence from igneous and metasedimentary rocks of central jilin province ne china abstract to constrain the early middle paleozoic tectonic evolution of the south eastern segment of the central asian orogenic belt caob we undertook zircon u pb dating and analyzed major and trace elements and zircon hf isotope compositions of late cambrian to middle devonian igneous and metasedimentary rocks in central jilin province ne china la icp ms zircon u pb dating indicates that the early middle paleozoic magmatism in central jilin province can be divided into four episodes late cambrian ca 493 ma middle ordovician ca 467 ma late ordovician early silurian ca 443 ma and late silurian middle devonian 425 396 ma the progression from subduction initiation to maturity is recorded by late cambrian low k tholeiitic meta diabase middle ordovician medium k calc alkaline pyroxene andesite and late ordovician to early silurian low k tonalite which all have subduction related characteristics and formed in an evolving supra subduction zone setting late silurian to middle devonian calc alkaline igneous rocks with the lithological association of granodiorite monzogranite rhyolite dacite and trachydacite show progressively increasing k 2 o contents from medium k to shoshonite series furthermore the early middle devonian monzogranites are characterized by high k 2 o sr y and la yb n values indicating they were generated by the melting of thickened lower crust these results suggest a transition from subduction to post orogenic setting during the late silurian middle devonian our interpretation is supported by the maximum age of molasse deposition in the zhangjiatun member of the xibiehe formation overall we suggest that late cambrian tholeiitic meta diabase middle ordovician pyroxene andesite and late ordovician early silurian tonalite formed above the northward subducting and simultaneously seaward retreating of paleo asian ocean plate subsequently the northern arc collided with the north china craton and post orogenic extension occurred during the late silurian middle devonian

the direction correction tilt test an all purpose tilt fold test for paleomagnetic studies abstract the tilt or fold test in paleomagnetism is used to infer whether paleomagnetic remanence was acquired before or after tectonic tilting while several tilt test formulations have been proposed none fully satisfies the requirements of statistical validity applicability to all bedding geometries and ease of use this paper introduces the direction correction dc test which examines the relationship between the paleomagnetic site mean directions and their corresponding bedding tilt corrections the dc test is similar to mcfadden s correlation test because both test whether or not the site directions contain information about the bedding tilts however the dc test gives greater weight to sites with greater counter bedding the dc test is similar to watson s numerical tilt tests because they determine the degree of untilting which gives optimal concentration of site directions however the dc test uses analytical rather than numerical methods graphical output aids the researcher in recognizing problem sites using both real and simulated data the dc test is demonstrated to be more discriminating than other tilt test formulations for all bedding geometries the simulations show that the power of the tilt test is inversely proportional to the 95 confidence interval 95 of the overall mean as a rule of thumb paleomagnetists should attempt to sample sufficient sites to obtain an 95 less than 1 6 of the bedding attitude difference

provenance of cretaceous trench slope sediments from the mesozoic wandashan orogen ne china implications for determining ancient drainage systems and tectonics of the paleo pacific the wandashan orogen of ne china is a typical accretionary orogen related to paleo pacific subduction the raohe complex as a major part of the orogen consists of mid triassic to mid jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial sourced clastic trench slope sediments sensitive high resolution ion microprobe u pb dating and la mc icpms hf isotopic analysis of detrital zircons from the terrestrial sourced yongfuqiao formation sandstone show that most zircons are phanerozoic 90 140 150 ma 10 180 220 ma 25 240 270 ma 15 300 360 ma 15 391 395 ma 3 and 450 540 ma 20 whereas 10 are precambrian in age about 90 of the zircons have ehf t values ranging from 11 1 to 12 8 this suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the central asian orogenic belt and the jiamusi block the age of the yongfuqiao formation is constrained to the earliest cretaceous which represents the accretion time of the mid triassic to mid jurassic oceanic complexes when compared with the mino complex in japan and the tananao complex in taiwan three different provenances are identified suggesting three ancient drainage systems which transported sediments from ne china north china and south china to the paleo pacific subduction accretion system

accretion subduction erosion and tectonic extrusion during late paleozoic to mesozoic orogenesis in ne china abstract the high pressure heilongjiang complex records a long and complicated evolution from the late paleozoic to mesozoic in ne china which is still subject to controversy in this paper we present a new detailed study including structural geochemical and geochronological analyses ar ar dating on metamorphic minerals u pb sims dating on zircons two main periods of oceanward accretionary growth are identified between 305 ma and 195 ma and around 112 101 ma these periods of accretionary growth were associated with the emplacement of voluminous magmatism slab roll back with continental back arc extension and growth of a forearc accretionary prism between these periods of accretionary growth a major phase of regional subduction erosion took place between 195 ma and 142 ma at the eastern edge of the songliao block the main effects of this subduction erosion phase were that regional jurassic early cretaceous extrusion overlapped with mesozoic accretion and erosion in ne china which disturbed the initial orogenic architecture with a review of relevant zircon ages of this accretionary orogen we unravel the complicated geodynamic history of accretion subduction erosion and tectonic extrusion that shaped ne china from the late paleozoic to mesozoic

late permian tectonic evolution at the southeastern margin of the songnen zhangguangcai range massif ne china constraints from geochronology and geochemistry of granitoids abstract this paper reports the la icp ms u pb zircon dating and geochemical data for the huangqigou xiaobeihu and lalagou granitic plutons at the southeastern margin of the songnen zhangguangcai range massif which will not only place important constraints on the rock forming ages source characteristics and tectonic setting of these granitic plutons but will also provide insights into understanding the tectonic evolution of the eastern segment of the central asian orogenic belt zircons from three plutons have distinct oscillatory zoning structures in their cathodoluminescene cl images which combined with the th u ratios of 0 28 1 06 indicate their magmatic origins zircon u pb dating results for these granitic plutons indicate that the granitic magmatism occurred mainly in the late permian 256 252 ma the granites have sio2 of 58 0 74 3 na2o of 2 74 3 76 k2o of 2 75 3 95 na2o k2o of 0 77 1 13 mg 100 mg mg fe2 of 21 8 39 9 and a cnk of 0 88 1 08 with ree patterns characterized by lree hree 7 75 12 82 la yb n 7 88 14 9 and eu 0 56 0 87 the trace element spider diagrams indicate that these granites are enriched in large ion lithosphile elements rb ba th u etc and relatively depleted in high field strength elements ti nb ta with sr and pb ranging from 205 to 350 ppm and from 2 02 to 3 60 ppm respectively the in situ hf isotope analysis reveals that ehf t values range from 2 22 to 11 65 and the two stage hf model ages tdm2 range between 641 and 1274 ma these geochemical characteristics indicate that the late permian granitic plutons at the se margin of the songnen zhangguangcai range massif can be assigned to metaluminous and weakly peraluminous high potassium calc alkaline i type granites with low sr and high yb features and that the magmas to have formed these granites were originated from the partial melting of mafic igneous rocks in the lower crust the source rocks are composed mainly of the juvenile crust with small contributions of ancient continental crust considering the existence of coeval mafic intrusive rocks and sedimentary basins we propose that the late permian magmatism in the study area occurred in a post collisional extensional setting following the collision of the xingkai block and the united jiamusi and songnen zhangguangcai range massifs

low temperature specific heat capacity measurements and application to mars thermal modeling abstract data returned from martian missions have revealed a wide diversity of surface mineralogies including in geological structures interpreted to be sedimentary or altered by liquid water these terrains are of great interest because of their potential to document the environment at a time when life may have appeared intriguingly martian sedimentary rocks show distinctly low thermal inertia values i e 300 700 jm 2k 1s 1 2 indicative of a combination of low thermal conductivity specific heat capacity and density these low values are difficult to reconcile with their competent bedrock morphologies whereas hundreds of bedrock occurrences interpreted as volcanic in origin have been mapped globally and display thermal inertia values 1200 jm 2k 1s 1 2 bedrock thermal inertia values are generally assumed to be driven by their bulk thermal conductivity which in turn is controlled by their micro and macro physical properties i e degree and style of cementation in the case of detritic rocks horizontal fractures and layering etc and not by their density well known from terrestrial analog measurements and with modest variability or specific heat capacity generally uncharacterized for non basaltic materials below room temperature in this paper we demonstrate that specific heat capacity cannot be a potential cause for the differential thermophysical behavior between magmatic and sedimentary rocks through a series of experimental cp t measurements at 100 350 k using differential scanning calorimetry the results on 20 martian relevant minerals investigated in this work indicate that these materials exhibit very similar specific heats ranging from 0 3 0 7 jg 1k 1 at 100 k to 0 6 1 7 jg 1k 1 at 350 k when used in a martian thermal model this range of cp values translate to very small surface temperature differences indicating that uncertainty in composition and its effect on the specific heat is not a noticeable source of thermal inertia variability for indurated units on mars we therefore conclude that the low thermal inertia value of sedimentary rocks compared to magmatic volcanic rocks is likely due to their low apparent bulk conductivity which bears information on their internal physical structure future work combining the analysis of thermal observations acquired at various local times and seasons will help further characterize this heterogeneity

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

late jurassic to early early cretaceous tectonic nature on the ne asian continental margin constraints from mesozoic accretionary complexes abstract it is widely accepted that subduction of the paleo pacific plate beneath eurasia began in the early mesozoic however the tectonic nature and processes of the ne asian continental margin in the late jurassic to early early cretaceous remain unclear in this contribution lithological provenance and metamorphic deformation data are used to constrain the formation of mesozoic accretionary complexes ac along the ne asian continental margin and determine the tectonic relationship between the ne asian continental margin and the paleo pacific plate in the late jurassic to early early cretaceous the mesozoic ac formed during the late jurassic including the raohe ac in ne china the khabarovsk samarka and taukha acs in the russian far east and the mino tamba ac in japan and early cretaceous including the shimanto ac in japan and the kiselevka manoma ac in the russian far east the jurassic ac underwent a complex evolution including the formation of seamounts middle late jurassic terrigenous clastic sedimentation adjacent to the trench collision of seamounts with eurasia northward migration of the ac early early cretaceous terrigenous clastic sedimentation a second period of accretion and final emplacement the earliest mesozoic ac arrived at the trench at ca 195 ma combined with the occurrence of early mesozoic calc alkaline igneous rocks along the ne asian continental margin we suggest that subduction of the paleo pacific plate beneath eurasia began in the early jurassic jurassic ac in japan was affected by a regional high p t metamorphic event at 160 ma which might have been related to subduction collision of seamounts with eurasia at the trench ages and hf isotopic compositions of detrital zircon grains from the middle upper jurassic and cretaceous ac sandstones together with paleontological and paleomagnetic data indicate that jurassic clastic sediments were sourced mainly from the south china block scb whereas the lower cretaceous sandstones were sourced from the eastern central asian orogenic belt caob the inferred northward migration of jurassic ac in the late jurassic to early early cretaceous indicates that the boundary between the ne asian continental margin and the paleo pacific plate was characterized by strike slip tectonics at this time likely due to a small angle of obliquity in the subduction of the paleo pacific plate beneath eurasia in the late early cretaceous westward subduction of the paleo pacific plate beneath eurasia resulted in the emplacement of the raohe and khabarovsk acs at 137 130 ma and the formation of acs in the russian far east and japan

ore geology fluid inclusion and 40ar 39ar geochronology constraints on the genesis of the yingchengzi gold deposit southern heilongjiang province ne china abstract the yingchengzi gold deposit located at the eastern margin of the zhangguangcai range southern heilongjiang province ne china is the only high grade gold deposit in the region the deposit is hosted in mylonitized paleozoic granite and metavolcanic rocks and is structurally dominated by brittle ductile shear zones and faults the orebodies consist of gold bearing quartz veins and gold bearing altered mylonites the hydrothermal ore forming process can be divided into early middle and late stages characterized by quartz pyrite veins quartz gold polymetallic sulfide veins and quartz carbonate veins or veinlets respectively ore minerals and gold mainly occurred in the middle stage four types of fluid inclusions were identified in the vein minerals based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type pure co 2 pc type and less common calcite bearing s type inclusions the early stage minerals contain c type and rare pc type fluid inclusions which have homogenization temperatures of 262 400 c and low salinities of 2 20 8 51 wt nacl equiv only the middle stage minerals contain all four types of fluid inclusions with homogenization temperatures of 173 316 c and salinities of 2 20 12 42 wt nacl equiv the late stage quartz and calcite crystals contain only w type fluid inclusions which have homogenization temperatures of 104 207 c and salinities of 1 05 6 58 wt nacl equiv fluid boiling and the mixing caused the rapid precipitation of sulfides and gold these indicate that the ore forming fluid system evolved from co 2 rich metamorphogenic to co 2 poor due to the boiling and input of meteoric water the trapping pressures estimated from c type fluid inclusions are 98 245 mpa in the main ore forming stage giving a reasonable estimate that an alternating lithostatic hydrostatic fluid system controlled a fault valve activity at a depth of 9 10 km 40 ar 39 ar dating of hydrothermal sericite from gold bearing altered rock shows that gold mineralization occurred at 248 ma we assume that the yingchengzi gold deposit was formed in a late permian early triassic continental collision regime following closure of the paleo asian ocean the regional geology ore geology fluid inclusions mineralization age and tectonic setting infer that the yingchengzi gold deposit is a mesozonal orogenic gold system making it the first orogenic gold deposit discovered in the zhangguangcai range ne china

planetary science hidden martian carbonates evidence for the sedimentary carbonate rocks proposed to be prevalent on mars has generally been lacking carbonate bearing rocks found in the leighton crater may be associated with the formation of methane detected in the martian atmosphere

age of palaeozoic granites and metamorphism in the tuvino mongolian massif of the central asian mobile belt loss of a precambrian microcontinent abstract the tuvino mongolian massif tmm was previously interpreted as a precambrian block within the central asian mobile belt according to this idea it consists of tectonic slices composed of metamorphic rocks of pre mesoproterozoic basement that experienced two episodes of regional metamorphism and mesoproterozoic cover rocks that were reworked together with the basement during high grade metamorphism zircon u pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536 6 ma significantly later than the deposition of the cover rocks regional upper amphibolite facies metamorphism which affected all metasedimentary units of the tmm occurred in the short time interval of 497 4 to 489 3 ma we propose that there is no simple basement cover relationship in the tuvino mongolian massif instead the massif consists of tectonic domains composed of heterogeneous metasedimentary successions with distinct pre metamorphic and pre tectonic histories that were juxtaposed by thrusting prior to 497 ma and then metamorphosed under upper amphibolite facies conditions we suggest that this thrusting event was associated with early palaeozoic collisional processes related to amalgamation of the central asian mobile belt our new model for the evolution of the tmm implies derivation of neoproterozoic terrigeneous metasediments from 800 900 ma granitoids formed in an andean type active continental margin setting

geochronology and isotope geochemistry studies of an epithermal gold deposit in the northern lesser khingan range ne china the gaosongshan example abstract the gaosongshan epithermal gold au deposit is located in the northern margin of the lesser khingan range polymetallic ore belt northeast ne china and contains au resources of more than 23 tons at an average grade of 6 3 g t gold orebodies are mainly hosted in intensely altered volcanic rocks of the lower cretaceous banzifang formation and as exploration has continued gold has also been discovered in extensively altered porphyritic intrusions with the highest au grade of 70 g t however the ages of metallogenesis and related magmatism have not been well constrained yet which have hindered the summary of metallogenic regularities in this study laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating from the granite porphyry yields a weighted mean 206pb 238u age of 101 6 1 2 ma slightly older than the rb sr isotope age of 98 1 6 ma for the auriferous quartz samples indicating that the gaosongshan au mineralization is genetically related to the granite porphyry the fluid d and 18oh2o values vary from 136 to 111 and from 9 3 to 2 5 respectively and the 4he and 40ar isotope compositions range from 15 7 10 9 to 35 5 10 9 cm3 stp g and 13 4 10 7 cm3 to 34 1 10 7 cm3 stp g respectively the obtained isotopic data show that the ore forming fluids were mixtures of magmatic and meteoric water but were dominated by meteoric water the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of ores in the gaosongshan deposit are 17 752 18 856 15 514 15 674 and 38 005 39 921 respectively which are similar to those of the gaosongshan granite porphyry implying that pb and possibly au originated primarily from late early cretaceous magmatic intrusions combining these results with data from previous studies we propose that the gaosongshan au deposit formed in an extensional tectonic setting during the rollback of the paleo pacific oceanic plate in ne china

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

oxygen isotope geochemistry of oceanic arc lavas variations of oxygen isotope ratios in arc related lavas can constrain the contributions of subducted crustal igneous rocks sediments and fluids to the sub arc mantle we have measured oxygen isotope ratios in 72 arc and back arc lavas from five ocean ocean subduction zone systems using laser fluorination analyses of olivine and other phenocrysts and glass eighty percent of our samples have delta 18o values for any given phase olivine plagioclase glass or biotite within 0 2 per thousand of the average value for that phase in upper mantle peridotites and mid ocean ridge basalt morb the range for each phase is 1 0 per thousand this result contrasts with previous studies of whole rock samples which are significantly more variable even after exclusion of samples believed to be altered or fractionated by magmatic differentiation and demonstrates that most arc related lavas contain 1 2 of 18o enriched crustal oxygen from any source i e assimilation or subducted contributions elevations in delta 18o that do occur in these basic arc derived magmas relative to values most common for mantle derived lavas are associated both with enriched radiogenic isotope signatures and even more strongly with chemical indices consistent with high integrated extents of melting of their peridotite sources we interpret these relationships as evidence that melting in the sources of the high delta 18o lavas we have studied was fluxed by addition of high delta 18o aqueous fluid or perhaps a hydrous melt from the subducted slab such that sources that contain relatively large components of slab derived fluid or melt are both relatively 18o enriched and also experienced relatively large amounts of melting we have developed a quantitative model linking the amount of melting to the extents of 18o radiogenic isotope and trace element enrichment in a mantle source being fluxed by addition of aqueous fluid comparison of this model with observed variations in the geochemistry of lavas from the vanuatu fiji new caledonia region the suite of related samples showing the greatest range in delta 18o observed in this study constrains the amounts and chemical and isotopic compositions of slab derived phases in the sources of these arc related lavas assuming a delta 18o value of 20 per thousand for the slab derived fluid 0 5 1 0 wt is added to the sources of most mantle derived arc magmas the maximum amount of slab derived flux in the sources of arc magmas according to our results is 2 5 wt

timing of deformation and location of the eastern liaoyuan terrane ne china constraints on the final closure time of the paleo asian ocean abstract the liaoyuan terrane lt in ne china formed as a result of accretion during the final closure of the paleo asian ocean between the north china and siberian cratons however the timing of the deformation and the location of the eastern lt remain controversial here we present structural data zircon u pb age dating and hf isotopic data to constrain the kinematics and timing of deformation and the southern boundary of the eastern lt in relation to the ne sw striking yilan yitong fault yyf one of two branches of the continental scale tan lu fault zone in ne china pre jurassic rocks in the eastern lt were widely involved in ductile deformation within wnw ese striking thrust belts the microstructures in these shear zones indicate a top to the ssw sense of shear and deformation temperatures of 450 500 c the northern margin of the north china craton ncc was also affected by the nne ssw contraction as shown by similar ductile deformation in the archean gneisses and wnw ese trending folds in the mesoproterozoic sedimentary cover the ages of crystallization in deformed and undeformed igneous rocks in the lt constrain the deformation to an interval between 241 and 193 ma u pb dating of zircons in syn kinematic migmatitic rocks indicates an age of 234 229 ma for the deformation we consider this middle triassic age to represent the final closure time of the paleo asian ocean along the eastern lt and this timing is consistent with the eastwards scissor style closure model lithological variations zircon age spectra ehf t values and model ages confirm the eastward extension of the lt across the yyf the data constrain the boundary between the lt and ncc to be roughly along the liao river to the west of the yyf and along the northern edge of the exposed archean gneisses to the east the boundary follows the bayan obo chifeng kaiyuan fault which was active as a thrust thrusting of material to the ssw during the middle triassic orogeny the newly determined boundary location indicates a 35 km sinistral displacement along the yyf

the lu hf isotope geochemistry of chondrites and the evolution of the mantle crust system earth planet sci lett 148 1997 243 258 1

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

tectonic implications of new zircon u pb ages for the xinghuadukou complex erguna massif northern great xing an range ne china abstract the nature and the timing of formation of the xinghuadukou complex of ne china are important to further our understanding of the precambrian geological evolution of the erguna massif and the eastern segment of the central asian orogenic belt caob here we present the results of zircon u pb dating of a metavolcanic rock and 11 granitoid basement samples collected from the complex we use these data to determine the age and tectonic origin of the complex and to examine the linkages between this complex and the surrounding tectonic domains and older cratonic areas igneous zircons from the metavolcanic rock yield a magmatic age of 850 ma indicating that the supracrustal rocks that represent the original xinghuadukou group formed during the neoproterozoic petrological data and new zircon u pb ages for these samples enabled the identification of multiple stages of granitoid magmatism within different sections of the xinghuadukou group indicating that this group which was originally thought to have formed contemporaneously actually records the emplacement of granitoids at 957 786 479 418 265 and 209 192 ma this result indicates that the xinghuadukou complex records multiple stages of magmatism and contains various neoproterozoic supracrustal components combining the new age data with regional geological data we propose that the erguna massif should be considered part of the mongol domain as it has a close affinity to other blocks that formed part of this domain during the neoproterozoic these data suggest that all of the complexes and terranes within the mongol domain belong to the caob and were finally accreted to the southern margin of the siberian craton in the early paleozoic

a jurassic garnet bearing granitic pluton from ne china showing tetrad ree patterns abstract ne china is characterized by the massive distribution of phanerozoic granitoids most of them are of i and a type granites whereas s type granites are rarely documented the present work deals with the dongqing pluton a small granitic body emplaced in the southern zhangguangcai range the pluton comprises a two mica garnet granite and a garnet bearing muscovite granite the latter occurs as veins in the former the pluton shows a gradational contact with the surrounding host granites rb sr and sm nd isotope analyses on whole rocks and minerals reveal that the two types of granites were emplaced synchronously at about 160 ma the pluton was emplaced coeval with the surrounding i type granitic pluton and had a rapid cooling history it is characterized by an initial sr isotopic ratio of 0 706 slightly negative end t values 0 5 to 1 9 and young depleted mantle model ages 970 1090 ma this suggests that the parent magma originated from partial melting of relatively juvenile crust which is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt geochemically the granites of the dongqing pluton are peraluminous with a shand index molar ratio a cnk of 1 0 1 1 for the two mica granites and 1 2 1 3 for the garnet bearing granites all the garnet bearing granites and some of the two mica granites show tetrad ree patterns tetrad group whereas most two mica granites show normal granitic ree patterns normal group the normal group granites exhibit depletion in nb ta p and ti in spidergrams and generally weak positive eu anomalies in ree patterns by contrast the tetrad group granites manifest depletion in ba nb ta sr p and ti and significant negative eu anomalies the trace element data constrain the parental magmas to having undergone extensive magmatic differentiation during their late stage magmatic evolution intense interaction of residual melts with aqueous hydrothermal fluids resulted in the non charac charge and radius controlled trace element behavior and the tetrad effect in ree distribution patterns this in turn leads to the invalidation of the commonly used tectonic discrimination criteria derived from trace element abundances of normal granites in view of this and previous studies we conclude that there were probably no s type granites produced in ne china during the phanerozoic consequently weathered sedimentary material did not play an important role in the genesis of the strongly peraluminous granites in the zhangguangcai range

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

geochronology geochemistry and deformation history of late jurassic early cretaceous intrusive rocks in the erguna massif ne china constraints on the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt abstract this paper presents new zircon and sphene u pb ages biotite and hornblende 40 ar 39 ar ages hf isotopic data and geochemical data for five mesozoic plutons in the erguna massif of ne china these data are used to constrain the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt this new dating when combined with previously published ages indicates that the late jurassic early cretaceous j 3 k 1 intrusive rocks can be subdivided into three stages that represent periods of magmatism during the late jurassic 155 ma early early cretaceous 137 ma and late early cretaceous 123 ma in addition the rocks have undergone later deformation recorded by peak ages of 137 and 123 ma the late jurassic and early early cretaceous intrusive rocks in the study area are dominantly syenogranites and are either a type granites or are classified as alkaline series suggesting that they formed in an extensional environment the late early cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment along with coeval bimodal volcanics these data combined with the presence of regional unconformities in the northern part of hebei province and western part of liaoning province and the spatial distribution of coeval volcanic rocks in ne china suggest the late jurassic and early early cretaceous magmatisms and the early early cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the mongol okhotsk ocean in comparison the late early cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the mongol okhotsk tectonic regime or the subduction of the paleo pacific plate or the combined influence of these two tectonic regimes

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

zircon u pb geochronology and petrogenesis of the late paleozoic early mesozoic intrusive rocks in the eastern segment of the northern margin of the north china block abstract zircon u pb dating and whole rock geochemical analysis have been undertaken on late paleozoic early mesozoic intrusive rocks of central jilin province ne china with the aim of constraining the tectonic evolution of the eastern segment of the northern margin of the north china block ncb during the late paleozoic early mesozoic zircon u pb dating indicates that late paleozoic early mesozoic magmatic events can be subdivided into four stages middle permian 270 ma late permian 259 255 ma early triassic 249 ma and late triassic 222 ma the middle permian magmatic event formed peraluminous garnet bearing monzogranites indicative of formation under a compressional tectonic regime related to collision between the ncb and the songnen zhangguangcai range massif the late permian magmatic event formed gabbros and syenogranites a bimodal association that is typical of magmatism within post collisional extensional setting the early triassic magmatic event formed adakitic monzogranites suggesting that they formed from magmas derived from partial melting of a thickened mafic lower crust the late triassic magmatic event formed a series of mafic ultramafic intrusive rocks together with coeval granitoids in adjacent regions and make up a typical bimodal association suggesting that they formed under an extensional environment related to the final amalgamation of the ncb and the songnen zhangguangcai range massif taken together we conclude that the northern margin of the ncb underwent multiple orogenic events between the middle permian and the late triassic with final amalgamation of the ncb and the songnen zhangguangcai range massif occurring in the early triassic an event that led to the final suturing of the solonker xra moron changchun zone

stratigraphic analysis of the distributary fan in eberswalde crater using stereo imagery the eroded remains of a fluvial distributary network in eberswalde crater are uniquely well preserved among similar structures on mars a quantitative analysis of the exposed stratigraphy has been performed to investigate the internal structure of the deposit using topographic information derived from stereo pairs of high resolution mars orbiter camera images we have for the first time quantified the orientation of individual layers exposed along the distal end of the distributary network in combination with topographic data from the mars orbiter laser altimeter we have examined plausible scenarios for the formation of this structure we find that the evidence is inconsistent with formation both as an alluvial fan and as a progradational delta instead we find that an aggradational delta best fits the observed characteristics of the channel network and the eberswalde basin as a whole we conclude that the delta likely formed not in a stable long lived lake but over the course of a small number of shorter lacustrine episodes which were not sustained at equilibrium conditions

geodynamic setting of mesozoic magmatism in ne china and surrounding regions perspectives from spatio temporal distribution patterns of ore deposits abstract north eastern china and surrounding regions host some of the best examples of phanerozoic juvenile crust on the globe however the mesozoic tectonic setting and geodynamic processes in this region remain debated here we attempt a systematic analysis of the spatio temporal distribution patterns of ore deposits in ne china and surrounding regions to constrain the geodynamic milieu from an evaluation of the available geochronological data we identify five distinct stages of ore formation 240 205 ma 190 165 ma 155 145 ma 140 120 ma and 115 100 ma the triassic 240 205 ma magmatism and associated mineralisation occurred during in a post collisional tectonic setting involving the closure of the paleo asian ocean the early mid jurassic 190 165 ma events are related to the subduction of the paleo pacific ocean in the eastern asian continental margin whereas in the erguna block these are associated with the subduction of the mongol okhotsk ocean from 155 to 120 ma large scale continental extension occurred in ne china and surrounding regions however the late jurassic magmatism and mineralisation events in these areas evolved in a post orogenic extensional environment of the mongol okhotsk ocean subduction system the early stage of the early cretaceous events occurred under the combined effects of the closure of the mongol okhotsk ocean and the subduction of the paleo pacific ocean the widespread extension ceased during the late phase of early cretaceous 115 100 ma following the rapid tectonic changes resulting from the paleo pacific oceanic plate reconfiguration

the hulan group its role in the evolution of the central asian orogenic belt of ne china the hulan group of central jilin province northeastern ne china consists of felsic volcanic and sedimentary rocks that underwent sub greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the central asian orogenic belt young nd model ages of 1100 ma obtained in this study do not support earlier models that the hulan group was either rifted from the north china craton to the south or from the jiamusi block to the north since both these blocks have much older nd model ages detrital zircon u pb ages from a meta sedimentary rock of the hulan group define a maximum age of deposition of 287 6 ma not early palaeozoic as previously believed rb sr mineral isochron data indicate that metamorphism of the hulan group occurred at 250 ma this conclusion is further supported by an age of 248 4 ma for the dayushan granite which intruded the hulan group these new isotopic data together with evaluation of the regional geology indicate that final oceanic closure in the chinese segment of the central asian orogenic belt took place in the late permian the hulan area is located along the solonker xra moronchangchun suture that extends from inner mongolia across to central jilin province it is this zone that marks the final ocean closure resulting in the amalgamation of the north china and siberian cratons 2007 elsevier ltd all rights reserved