an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

integrated 3d density modelling and segmentation of the dead sea transform a 3d interpretation of the newly compiled bouguer anomaly in the area of the dead sea rift is presented a high resolution 3d model constrained with the seismic results reveals the crustal thickness and density distribution beneath the arava araba valley av the region between the dead sea and the gulf of aqaba elat the bouguer anomalies along the axial portion of the av as deduced from the modelling results are mainly caused by deep seated sedimentary basins d 10 km an inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the av the intrusion is displaced at different sectors along the nnw sse direction the zone of maximum crustal thinning depth 30 km is attained in the western sector at the mediterranean the southeastern plateau on the other hand shows by far the largest crustal thickness of the region 38 42 km linked to the left lateral movement of approx 105 km at the boundary between the african and arabian plate and constrained with recent seismic data a small asymmetric topography of the moho beneath the dead sea transform dst was modelled the thickness and density of the crust suggest that the av is underlain by continental crust the deep basins the relatively large intrusion and the asymmetric topography of the moho lead to the conclusion that a small scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the dead sea basin during the left lateral movement a clear segmentation along the strike of the dst was obtained by curvature analysis the northern part in the neighbourhood of the dead sea is characterised by high curvature of the residual gravity field flexural rigidity calculations result in very low values of effective elastic lithospheric thickness te 5 km this points to decoupling of crust in the dead sea area in the central av the curvature is less pronounced and te increases to approximately 10 km curvature is high again in the southernmost part near the aqaba region solutions of euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures

petrogenesis and tectonic implications of early paleozoic granitic magmatism in the jiamusi massif ne china geochronological geochemical and hf isotopic evidence abstract this paper reports geochronological whole rock geochemical and zircon hf isotopic data for the early paleozoic granitic rocks in the jiamusi massif in the eastern segment of the central asian orogenic belt caob in order to investigate their precise geochronological framework petrogenesis sources and tectonic setting la icp ms zircon u pb age data indicate that the syenogranite monzogranite and granodiorite were emplaced during the period of 530 484 ma geochemically these granitoids have high sio2 64 66 79 17 and k2o 3 08 7 33 low mgo 0 14 2 63 and cao 0 37 3 87 with a cnk and eu values of 0 89 1 10 and 0 16 1 77 respectively these rocks are characterized by enrichment in rb and nd and depletion in nb ta p and ti in addition in situ hf isotopic analyses of zircons from the granitic rocks reveal that they have ehf t 5 8 to 2 3 with two stage hf model ages tdm2 varying from 1 3 ga to 2 4 ga indicating that they probably originated from the partial melting of a dominantly old paleo mesoproterozoic crustal source additionally these granites have variable major and trace element concentrations magmatic zircons from these rocks record consistent homogeneous u pb ages but have heterogeneous ehf t values reflecting that they resulted from fractional crystallization and crustal assimilation based on these geochemical data combined with regional geological investigations we propose that the early paleozoic granitic magmatism in the study area occurred in a post collisional extensional setting which was probably related to the collapse of a thickened crust

high pressure methane and carbon dioxide sorption on coal and shale samples from the parana basin brazil abstract an experimental study has been conducted to assess the potential for coalbed methane production and carbon dioxide storage in coals carbonaceous shales and source rocks in the parana basin in brazil high pressure sorption tests with methane and carbon dioxide were performed on coal and carbonaceous shales from the santa terezinha coalfield and samples from two principal petroleum source rocks measured excess sorption capacities ranged from 0 03 to 0 47 mmol g for methane and 0 14 to 0 81 mmol g for carbon dioxide showing a decrease with decreasing organic matter content linear regression lines for methane sorption capacity vs toc extrapolated to approximately zero whereas for carbon dioxide the intercept of the regression line indicated a residual sorption capacity of 0 2 mmol g on the mineral matter present day gas contents of coals collected from the first cbm well in the santa terezinha coalfield correspond to 13 38 of the measured maximum sorption capacities carbon dioxide sorption capacities exceed methane sorption capacities by a factor of 1 9 to 6 9 for these coals free sorption capacities of the under saturated coals in combination with preferential sorption of carbon dioxide could favour co 2 enhanced methane recovery and co 2 storage in coals and shales of the study area based upon the calculated coal reserves gas contents and measured sorption capacities a total storage potential of 15 4 gt co 2 was estimated for an area of 20 40 km 2 in the santa terezinha coal field assuming a combined co 2 enhanced coalbed methane ecbm production and co 2 storage operation to fully evaluate the potential for carbon dioxide storage and coalbed methane production further studies are required to assess producibility of methane and efficiency of long term co 2 storage in the study area

production of gas from coal seams in the upper silesian coal basin in poland in the post injection period of an ecbm pilot site a pilot site for co2 storage in coal seams was set up in the upper silesian coal basin in poland in the scope of the recopol project funded by the european commission about 760 tons co2 were injected into the reservoir from august 2004 to june 2005 breakthrough of the injected co2 was established which resulted in the production of about 10 of the injected co2 in this period this paper reports on activities performed under the european commission project movecbm that aimed at the assessment of the storage performance of the reservoir in the follow up period i e whether the injected co2 was adsorbed onto the coal or whether it was still present as free gas in the pore space the injection well was used for this purpose as the production well had to be abandoned for permitting reasons several operational periods can be defined between the last injection in june 2005 and the abandonment of the well in october 2007 in the first period the well was shut in to observe the pressure fall off from about 15 0 mpa at the wellhead after the last injection until about 4 5 mpa at the end of 2005 this pressure fall off curve showed that the reservoir permeability was very low this seemed to confirm the observed swelling of the coal during the injection period in the first months of 2006 the pressure at the wellhead was decreased by releasing gas in a controlled way the amount and composition of the gas were measured as a result of the pressure reduction the well flooded with water a production pump was placed on the former injection well enabling active production from the coal from march to september 2007 results of these operations showed that whereas the gas production rates were as expected based on the experience with the production well the water production was remarkably low this could be related to permeability issues or alternatively indicate a drying effect of the co2 in the reservoir further the gas composition showed a predominance of co2 over ch4 during the gas release that changed gradually into a predominance of ch4 over co2 during the production phase although stabilization was not reached within the given production period the composition approached a 60 methane 40 co2 ratio this indicates that the exchange of these gases is more complex than often envisaged after removal of the pump the well was filled with water which ceased the gas release this indicates that the pressure in the reservoir was back to its original hydrostatic state as the total volume of co2 produced was only a fraction of the amount that was injected it can be concluded that the co2 was taken up by the coal and is currently adsorbed this gives confidence in the long term stability of the injected co2 2008 elsevier b v all rights reserved

a reconnaissance ion probe study of hafnium isotopes in zircons a sims technique for the isotopic analysis of hafnium in zircons using the shrimp ion microprobe has been developed and a precision of typically 0 5 2 achieved in the mean reduced 176hf177hf ratio measured at several spots on a single grain unfractionated chondritic initial hf isotopic compositions have been measured on a number of archaean zircon populations these include the oldest known terrestrial minerals the 4 2 ga old mount narryer detrital zircons thereby confirming their antiquity in contrast positive initial hf relative to the chondritic model composition has been found in several post archaean zircon populations reflecting the increasing involvement of isotopically evolved depleted mantle sources in the formation of younger crust the 570 ma old sri lankan zircon standard sl7 yielded an exceptionally low initial hfof 23 implying a metamorphic origin as a reworked product of ancient crust shrimp u pb analyses of zircons from archaean tonalitic gneiss at watersmeet michigan yield a precise crystallization age of 3636 6 ma 2 and show that a previously reported correlation between 176hf177hf and u pb isotopic discordance in bulk zircon samples patchett 1983 was caused by the addition of radiogenic hf in discrete overgrowths of new zircon ca 2 7 ga ago the original 3 64 ga grains show no evidence of disturbance to their original chondritic hf isotopic composition there is presently no evidence for significant isotopic exchange of hf between zircon and other minerals in crustal rocks

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

u pb and hf isotope analysis of zircons in mafic xenoliths from fuxian kimberlites evolution of the lower crust beneath the north china craton mafic xenoliths from the paleozoic fuxian kimberlites in the north china craton include garnet granulite and minor pyroxene amphibolite metagabbro anorthosite and pyroxenite the formation conditions of the amphibolites are estimated at 745 820 c and 7 6 8 8 kb 25 30 km the granulites probably are derived from greater depths in the lower crust lam icpms u pb dating of zircons from four granulites reveals multiple age populations recording episodes of magmatic intrusion and metamorphic recrystallisation concordant ages and upper intercept ages interpreted as minimum estimates for the time of magmatic crystallisation range from 2 620 to 2 430 ma in three granulites two amphibolites and two metagabbros lower intercept ages represented by near concordant zircons are interpreted as reflecting metamorphic recrystallisation and range from 1 927 to 1 852 ma one granulite contains two metamorphic zircon populations dated at 1 927 55 ma and 600 700 ma separated minerals from one granulite and one amphibolite yield sm nd isochron ages of 1 619 48 ma 143nd 144nd i 0 51078 and 1 716 120 ma 143nd 144nd i 0 51006 respectively these ages are interpreted as recording cooling following metamorphic resetting model ages for both samples are in the range 2 40 2 66 ga lam mc icpms analyses of zircon show a range in 176hf 177hf from 0 28116 to 0 28214 corresponding to a range of ehf from 34 to 12 the relationships between 207pb 206pb age and ehf show that 1 the granulites amphibolites and metagabbro were derived from a depleted mantle source at 2 6 2 75 ga 2 zircons in most samples underwent recrystallisation and pb loss for 100 200 ma after magmatic crystallisation consistent with a residence in the lower crust 3 metamorphic zircons in several samples represent new zircon growth incorporating hf liberated from breakdown of silicates with high lu hf 4 in other samples metamorphic and magmatic zircons have identical 176hf 177hf and the younger ages reflect complete resetting of u pb systems in older zircons the fuxian mafic xenoliths are interpreted as the products of basaltic underplating derived from a depleted mantle source in neoarchean time an important period of continental growth in the north china craton paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1 8 1 9 ga corresponding to the timing of collision between the eastern and western blocks that led to the final assembly of the north china craton the growth of metamorphic zircon at 600 700 ma may record an asthenospheric upwelling in neoproterozoic time related to uplift and a regional disconformity in the north china craton

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

structure of the crust and uppermost mantle of the yanshan belt and adjacent regions at the northeastern boundary of the north china craton from rayleigh wave dispersion analysis abstract we have used rayleigh wave dispersion analysis and inversion to produce a high resolution s wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the north china craton ncc using waveform data from 45 broadband ncisp stations rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the s wave velocity structure from 15 km down to 120 km depth the inverted lower crust and uppermost mantle velocities about 3 75 km s and 4 3 km s on average are low compared with the global average the moho was constrained in the depth range of 30 40 km indicating a typical crustal thickness along the profile however a thin lithosphere of no more than 100 km was imaged under a large part of the profile decreasing to only 60 km under the inner mongolian axis ima where an abnormally slow anomaly was observed below 60 km depth the overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern ncc during mesozoic cenozoic time distinctly high velocities up to 4 6 km s were found immediately to the south of the ima beneath the northern yanshan belt ysb extending down to 100 km depth the anomalous velocities are interpreted as the cratonic lithospheric lid of the region which may have not been affected by the mesozoic cenozoic deformation process as strongly as other regions in the eastern ncc based on our s wave velocity structural image and other geophysical observations we propose a possible lithosphere asthenosphere interaction scenario at the northeastern boundary of the ncc we speculate that significant undulations of the base of the lithosphere which might have resulted from the uneven mesozoic cenozoic lithospheric thinning may induce mantle flows concentrating beneath the weak ima zone the relatively thick lithospheric lid in the northern ysb may serve as a tectonic barrier separating the on craton and off craton regions into different upper mantle convection systems at the present time

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

crustal structure across the yanshan belt at the northern margin of the north china craton abstract we applied an integrated receiver function imaging technique to the teleseismic data from 54 ncisp iii broadband seismic stations to study the fine scale crustal structure beneath the eastern yanshan belt ysb and adjacent areas at the northern margin of the north china craton ncc the robustness and reliability of the resultant crustal image were noticeably improved by achieving imaging consistency between common conversion point stacking and waveform inversion of the receiver functions our imaging result revealed substantial lateral heterogeneities in the crust of the study region as displayed by the undulating intra crustal interfaces highly varying upper middle and lower crust thicknesses and interlayers of low and high velocities the crustal structure of the ysb is characterized by significant structural variations together with a sharp moho a thin to normal crust and a lower crust with lower velocity and normal thickness it differs markedly from the bohai bay basin and the taihang mountains within the interior of the ncc the distinct features and structural complexity of the ysb might be attributed to the complex tectonic history of the region especially the multiple phases of contraction and possible occurrence of crustal delamination which is in large contrast to other subregions of the ncc where tectonic extension likely dominated the crustal deformation since the late mesozoic

permeability evolution during progressive deformation of intact coal and implications for instability in underground coal seams abstract we report measurements of deformation strength and permeability evolution during triaxial compression of initially intact coals permeability is continuously measured by the constant pressure differential method together with axial and volumetric strains for both water h2o and strongly adsorbing carbon dioxide co2 gas strength and young s modulus increase with increasing confining stress and permeability is hysteretic in the initial reversible deformation regime as deviatoric stress and strain increase permeability first decreases as pre existing cleats close and then increases as new vertical dilatant microcracks are generated post peak strength the permeability suddenly increases by 3 4 orders of magnitude during loading the inflection point where permeability begins to increase occurs earlier than the turning point of volumetric strain which may be explained by the competing processes of axial crack opening and closure of oblique and transverse cracks the generation of these vertical microcracks does not enhance gas migration in the horizontal direction but will accelerate the rate of gas desorption and weaken the coal based on this mechanistic observation we propose a process based model for bursting in underground coal seams horizontal and vertical stresses redistribute ahead of the mining face immediately after the excavation and influence pore pressure permeability and desorption rate due to this redistribution the zone closest to the mining face may experience tensile failure interior to this zone a region may develop with gas overpressures induced by desorption and this may contribute to the occurrence of coal and gas outbursts beyond this an overstressed zone may initiate shear failure driven by gas pressures if the desorption rate outstrips the rate of drainage we discuss the implications of this on the instability of coal seams to co2 injection and the potential for induced fault slip

nd hf o isotopic evidence for subduction induced crustal replacement in ne china abstract convergent plate margins represent an ideal setting to understand the formation and evolution of the earth s crust nevertheless the geodynamic processes involved in crustal evolution remains highly debatable based on a large geochemical dataset of permian cretaceous granitic rocks from the yanbian area in ne china we propose a new geodynamic model involving crustal replacement to decipher crustal evolution during a superimposed multi stage subduction system these phanerozoic granitic rocks from two adjacent zones show contrasting hf nd isotopic variation trends with decreasing age of magmatism whole rock end t and zircon ehf t decrease gradually in the north granite zone ngz but show the opposite trends in the south granite zone sgz zircon 18o shows a slight rise in the ngz but it initially increases from permian to jurassic and then decreases to cretaceous in the sgz the nd hf o isotopic compositions of the cretaceous granitic rocks in both zones converge four crustal components are identified in the source of granites across the yanbian area including 1 juvenile crust 2 subduction accretionary complex 3 new arc crust and 4 precambrian crust the contributions made to the bulk crustal melting source of granites by the juvenile crust component in the ngz and by the precambrian crust in the sgz were both gradually decreased whereas the proportion of the new arc crust increased in both zones pre existing crustal components were extensively eroded destructed diluted and replaced by the new arc crust formed during paleo pacific slab subduction considering the prevalence of these two nd hf o isotopic variation trends in many orogenic belts subduction induced crustal replacement represents an important mechanism for crustal evolution in convergent plate margins

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

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

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

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

on the use of seismic reflection surveys from oil exploration in deep crustal studies abstract a very large number of seismic reflection surveys is carried out by the oil industry throughout the world some of these surveys are designed to study deep oil traps and may use field parameters which for the most part are not significantly different from those used in deep crustal reflection studies the one parameter which always varies is the record length listening time in the case of a vibratory source the record length can be increased at the processing stage by the equivalent reduction of vibration time through partial correlation we have used an oil exploration survey from a deep sedimentary basin in the coastal plain of israel and extended its record length using this technique we show that if a survey with appropriated field parameters i e a survey for a deep target is chosen deep crustal reflectors can be traced since a cocorp type deep crustal reflection study was also carried out in the same region we can compare the two sets of results we note that in this case the extended oil exploration record is at least equivalent to and probably of better quality than the cocorp type survey this result is due mostly to a better s n ratio in the oil exploration survey where input power was significantly larger than in special purpose study this result indicates the as yet untapped potential of oil exploration data in deep continental crustal studies

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

emplacement ages geochemical and sr nd hf isotopic characterization of mesozoic to early cenozoic granitoids of the sikhote alin orogenic belt russian far east crustal growth and regional tectonic evolution abstract the sikhote alin range of the russian far east is an important accretionary orogen of the western pacific orogenic belt in order to study the formation and tectonic evolution of the orogen we performed zircon u pb dating as well as geochemical and sr nd hf isotopic analyses on 24 granitoid samples from various massifs in the primorye and khabarovsk regions the zircon dating revealed that the granitoids were emplaced from 131 to 56 ma cretaceous to paleogene in the primorye region granitoids in the coastal sikhote alin intruded the cretaceous taukha accretionary terrane from ca 90 to 56 ma whereas those along the central sikhote alin fault zone intruded the jurassic samarka accretionary terrane during ca 110 75 ma the oldest monzogranite 131 ma was emplaced in the lermontovka area of the nw primorye region granitoid massifs along the central sikhote alin fault zone in the khabarovsk region formed from 109 to 58 ma thus the most important tectonothermal events in the sikhote alin orogen took place in the cretaceous geochemical analysis indicates that most samples are i type granitoids they have initial 87sr 86sr ratios ranging from 0 7040 to 0 7083 and initial nd isotopic ratios expressed as end t values from 3 0 to 5 0 mostly 0 to 5 the data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies including the subducted accretionary complex hidden paleozoic proterozoic basement rocks based on whole rock nd isotopic data we estimated variable proportions 36 77 of juvenile component mantle derived basaltic rocks in the generation of the granitic magmas furthermore zircon hf isotopic data ehf t 0 to 15 indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation the quasi continuous magmatism in the sikhote alin orogen suggests that the paleo pacific plate subduction was very active in the late cretaceous the apparently regular progression of granitic intrusion ages from 80 to 56 ma in the taukha terrane may reflect oblique underflow of the paleo pacific plate beneath the eurasian continental margin subduction was not only manifested by granitic intrusion but also by abundant silicic volcanism the late cretaceous paleo pacific plate motion probably changed from parallel or sub parallel to oblique relative to the continental margin of the sikhote alin leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks late cretaceous rapid sea floor spreading at ca 100 ma induced highly active subduction and led to voluminous magmatism in the entire circum pacific realm finally the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between sikhote alin and sw japan

petrogenesis of the linxi granitoids northern inner mongolia of china constraints on basaltic underplating five representative granitoid plutons in the linxi area northern inner mongolia of china divided into two suites are mainly granodiorite and syenogranite and correspond to i and a type granites respectively zircon u pb dating yields an age of 230 ma but most ages range from 149 ma to 111 ma for intrusion of the five plutons suite 1 granitoids show lower sio2 66 1 72 51 and k2o higher al2o3 cao mgo feo and tio2 higher sr ba and eu and lower sm gd nb y and yb than suite 2 granitoids 71 73 78 14 sio2 modeling of major and trace elements shows that fractional crystallization of hornblende and lesser amounts of feldspars for suite 1 and plagioclase and alkali feldspar for suite 2 with overprint of magmatic hydrothermal fluids can explain the geochemical variations the linxi granitoids have initial end t values varying between 5 60 and 2 89 and initial 87 sr 86 sr t ratios ranging from 0 701764 to 0 707654 geochronology of inherited zircons coupled with the nd sr isotopic comparison between granitoids late jurassic basalts and proterozoic gneisses indicates that the linxi granitoids derive from a mixed source of dominantly underplated material or mafic magma with various amounts of the proterozoic gneiss basaltic underplating provides both material and heat to produce the late jurassic to early cretaceous granitoids variation of end t and 87 sr 86 sr t with age suggests involvement in the melting of increasingly greater amounts of the old lower crustal rock our refined equation yields less scattered nd isotope depleted mantle model ages the least fractionated granitoids from each suite have low ca sr rb sr rb ba and k ba ratios and hence represent parental magmas suite 1 parent magma is produced by dehydration melting or derives principally from the fluid metasomatized mantle melting of the underplated tholeiites and their differentiated products generates suite 2 parent magma d 2005 elsevier b v all rights reserved

deep seismic reflection studies in israel an update summary the results of three deep crustal reflection lines are presently available from israel a 90 km line from near the dead sea rift to the mediterranean coast was carried out for deep study two other lines in the mediterranean coastal area were derived by recorrelation of oil exploration lines the data shows a division between continental inner israel and the coastal plain in the first area a reflective lower crust is apparent with transparent upper crust and almost transparent upper mantle near the coast in an area which was previously suggested as underlain by an ancient fossil oceanic crust strong reflections characterize the uppermost mantle comparison between the reflection pattern and previous deep refraction and mt data indicates some agreement away from the coast and lack of correlation in the area of possible fossil oceanic crust near the coast

petrogenesis of the majiari ophiolite western tibet china implications for intra oceanic subduction in the bangong nujiang tethys abstract the majiari ophiolite lies in the western bangong nujiang suture zone which separates the qiangtang and lhasa blocks in central tibet the ophiolite consists of peridotite gabbro diabase and basalt zircon u pb dating yielded an age of 170 5 1 7 ma for the gabbro whereas 40 ar 39 ar dating of plagioclase from the same gabbro yielded ages of 108 4 2 6 ma plateau age and 112 2 ma isochron age indicating that the ophiolite was formed during the middle jurassic and was probably emplaced during the early cretaceous zircons from the gabbro have e hf t values ranging from 6 9 to 10 6 and f lu hf values ranging from 0 92 to 0 98 mafic lavas plot in the tholeiitic basalt field but are depleted in nb ta and ti and enriched in rb ba and th in the n morb normalized trace element spider diagram these lavas have whole rock e nd t values of 5 9 to 6 6 suggesting that they were derived from a depleted mantle source which was probably modified by subducted materials the majiari ophiolite probably formed in a typical back arc basin above a supra subduction zone ssz mantle wedge intra oceanic subduction occurred during the middle jurassic and collision of the lhasa and south qiangtang terranes likely occurred in the early cretaceous thus closure of the bangong nujiang tethys ocean likely occurred before the early cretaceous

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

a dual poroelastic model for co2 enhanced coalbed methane recovery although co2 enhanced coalbed methane ecbm recovery has been comprehensively investigated the impact of coal matrix fracture interactions on the evolution of coal permeability under in situ conditions is still unclear in prior studies on this issue the influences of coal matrix fracture interactions have not rigorously coupled with the binary gas transport system in this work general porosity and permeability models are developed to explicitly quantify the interactions between binary mixtures co2 and ch4 and dual solid media coal matrix and fracture under the full spectrum of mechanical conditions spanning prescribed in situ stresses through constrained displacement these models are implemented into a fully coupled finite element fe model of coal deformation binary gas flow and transport in the matrix system and binary gas flow and transport in the fracture system the fe model represents important non linear responses due to the effective stress effects that cannot be recovered where mechanical influences are not rigorously coupled with the binary gas transport system the fe model is applied to simulate the results of a single well injection micro pilot test performed in the anthracitic coals of the south qinshui basin shanxi province china the modeled ch4 production rates are in good agreement with the observed production history in addition to this agreement model results also demonstrate 1 co2 injection increases the total pressure gradients 2 as the co2 injection progresses the partial co2 pressure increases while the partial ch4 pressure decreases 3 without co2 injection the ch4 content at a specific point decreases almost linearly while with the co2 injection the ch4 content at a specific point decreases exponentially 4 without co2 injection the ch4 production rate decreases linearly while with co2 injection the ch4 production rate increases dramatically 5 without co2 injection coal permeability increases almost linearly while with co2 injection coal permeability decreases near exponentially 6 co2 injection enhances cumulative ch4 production and the enhancement is proportional to the injection pressure and 7 cumulative co2 injection volume is also proportional to the injection pressure

pan african metamorphic and magmatic rocks of the khanka massif ne china further evidence regarding their affinity the khanka massif is a crustal block located along the eastern margin of the central asian orogenic belt caob and bordered to the east by late jurassic early cretaceous circum pacific accretionary complexes of the eastern asian continental margin it consists of graphite sillimanite and cordierite bearing gneisses carbonates and felsic paragneisses in association with various orthogneisses metamorphic zircons from a sillimanite gneiss from the hutou complex yield a weighted mean 206 pb 238 u age of 490 4 ma whereas detrital zircons from the same sample give ages from 934 610 ma magmatic zircon cores in two garnet bearing granite gneiss samples also collected from the hutou complex yield weighted mean 206 pb 238 u ages of 522 5 ma and 515 8 ma whereas their metamorphic rims record 206 pb 238 u ages of 510 500 ma these data indicate that the hutou complex in the khanka massif records early palaeozoic magmatic and metamorphic events identical in age to those in the mashan complex of the jiamusi massif to the west the older zircon populations in the sillimanite gneiss indicate derivation from neoproterozoic sources as do similar rocks in the jiamusi massif these data confirm that the khanka massif has a close affinity with other major components of the caob to the west of the dun mi fault based on these results and previously published data the khanka massif is therefore confirmed as having formed a single crustal entity with the jiamusi and possibly the bureya massif since neoproterozoic time

multi chronometric ages and origin of archaean tonalitic gneisses in finnish lapland a case for long crustal residence time the tojottamanselka gneisses of the koitelainen region northern finland have been dated by the sm nd and the common pb methods the sm nd data of seven samples from a small area 100 m 100 m define an isochron oft 3 06 0 12 2 ga with correspondingind 0 50848 9 2 orend t 3 7 1 8 this age is in good agreement with the zircon u pb discordia age 3 1 ga reported by kroner et al 1981 and is interpreted as the time of magmatic emplacement the distinctly negativeend t value is found for the first time for archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long 200 500 ma crustal residence time a few samples on the other hand possessend t values close to zero hence they are thought to be derived by partial melting of basaltic sources with nearchondritic ree distribution patterns

geochronology and geochemistry of early paleozoic intrusive rocks from the khanka massif in the russian far east petrogenesis and tectonic implications abstract this paper presents new geochronological and geochemical data for early paleozoic intrusive rocks from the khanka massif in the russian far east with the aim of elucidating the paleozoic evolution and tectonic attributes of the khanka massif new u pb zircon data indicate that early paleozoic magmatism within the khanka massif can be subdivided into at least four stages 502 492 462 445 and 430 ma the 502 ma pyroxene diorites contain 58 28 59 64 wt sio2 2 84 3 69 wt mgo and relatively high cr and ni contents negative ehf t values 1 8 to 0 4 along with other geochemical data indicate that the primary magma was derived from partial melting of mafic lower crust with the addition of mantle material the 492 ma syenogranites have high sio2 and k2o contents and show positive eu anomalies indicating the primary magma was generated by partial melting of lower crust at relatively low pressure the 445 ma na rich trondhjemites display high sr y ratios and positive ehf t values 1 8 to 3 9 indicating the primary magma was generated by partial melting of thickened hydrous mafic crust the 430 ma granitoids have high sio2 and k2o contents zircon ehf t values of 5 4 to 5 8 and two stage model ages of 1757 1045 ma suggesting the primary magma was produced by partial melting of heterogeneous proterozoic lower crustal material the geochemistry of these early paleozoic intrusive assemblages indicates their formation in an active continental margin setting associated with the subduction of a paleo oceanic plate beneath the khanka massif the ehf t values show an increasingly negative trend with increasing latitude revealing a lateral heterogeneity of the lower crust beneath the khanka massif regional comparisons of the magmatic events indicate that the khanka massif in the russian far east has a tectonic affinity to the songnen zhangguangcai range massif rather than the adjacent jiamusi massif

improvements of precision and accuracy in in situ hf isotope microanalysis of zircon using the laser ablation mc icpms technique abstract we have developed a new analytical technique for precise and accurate in situ hf isotope ratio measurements for zircons by means of laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icpms newly designed sample cell and n 2 mixing technique provided higher elemental sensitivity with smoother signal intensity profiles in order to improve the accuracy of the hf isotope ratio analysis previously reported correction methods for isobaric interferences on 176 hf by 176 yb and 176 lu were rigorously evaluated and we found that the use of independent mass bias factors for hf and yb in the isobaric interference correction resulted in more reliable hf isotopic data in order to test the reliability of the hf isotopic data from 35 m diameter ablation pits that are smaller than the typical size of most zircon grains lu hf isotopes for three zircons harvard 91500 antarctic zircon pma7 and acasta zircon ay199 were measured the present 176 hf 177 hf isotope ratio of 0 282321 46 2 s d and initial 176 hf 177 hf isotope ratio of 0 282315 47 2 s d were obtained for zircon standard 91500 the resulting present 176 hf 177 hf isotope ratio shows an excellent agreement with the previously reported data our in situ isotopic data revealed that the lu hf ratio varied significantly within the 91500 grain 176 lu 177 hf 0 000130 0 000345 suggesting the existence of slight isotopic heterogeneity in present 176 hf 177 hf approximately 15 ppm for antarctic zircon pma7 despite the smaller size of the single grain 50 100 m wide 80 300 m long and the presence of various mineral inclusions resulting analytical precision for the initial 176 hf 177 hf ratio was 128 ppm 0 281208 36 2 s d for acasta zircon ay199 despite the high yb hf 0 05 and lu hf 0 01 isotope ratios with the early archean crystallization age 3 74 ga resulting analytical precision for the initial 176 hf 177 hf ratio was 187 ppm 0 280160 52 2 s d these results demonstrate clearly that in situ hf isotope ratio microanalysis developed here has the potential to become a significant tool for zircon lu hf isotopic study

himalayan architecture constrained by isotopic tracers from clastic sediments we report the first geochemical traverse to integrate u pb ages and hf data on single detrital zircons with bulk rock sm nd rb sr isotopic measurements across the breadth of the himalayan orogen in northwest india our dataset from key tectonostratigraphic units in the sutlej valley provides detailed insights into both the provenance of the sedimentary formations and their tectonic history whole rock nd data provide information on the mean age of source areas contributing detritus to the sedimentary units in the mountain belt regardless of their current metamorphic grade u pb ages of detrital zircons from the same units identify the age of melt formation in the source rocks while lu hf isotope data from zircons resolve discrete crust formation ages in the multiple eroding terrains complex whole rock sr systematics hint at the extent of pre himalayan thermal events our data confirm the geochemical distinction between the older lesser himalayan formations and those of the depositionally younger units including the high himalayan crystalline series that has been recorded along the strike of the himalaya from the western syntaxis to nepal palaeoproterozoic metasediments of the jutogh group and rampur formation yield end 500 values below 17 whereas neoproterozoic and younger metasediments yield end 500 above 13 the latter group encompasses the vaikrita group gneisses of the high himalayan crystallines and the overlying haimanta group but also includes a number of units in thrust sheets north of the main boundary thrust in the lesser himalayan zone designated the douter lesser himalayat to distinguish them from the palaeoproterozoic dinner lesser himalayat zircon populations from the inner lesser himalaya are characterised by palaeoproterozoic late archaean ages 2 6 1 8 ga whereas the depositionally younger units contain populations both of this age and a younger period meso to neo proterozoic 1 1 0 8 ga detrital zircon ages are younger than their respective hf isotope derived crustal formation ages by 0 7 2 1 ga indicating that the source regions of the detrital zircons consisted of older terranes with considerable amounts of reworking and renewed magmatism the

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

1700 ma shachang complex northeast china proterozoic rapakivi granite not associated with paleoproterozoic orogenic crust proterozoic rapakivi granites are found on all continents and are characteristically associated with paleoproterozoic crustal domains that predate the granites by

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

geochronological and geochemical constraints on the genesis of the huanren skarn cu zn deposit northeast china abstract the huanren skarn cu zn deposit is located in southeastern liaoning on the eastern edge of the north china craton ncc in this paper we present a study on the geochronologic geochemical and sr nd hf and s isotopic data for the magmatic rocks and sulfide minerals exposed in the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircon grains from two mining pits in the monzodiorite yields ages of 128 2 1 1 ma and 128 6 1 5 ma these results indicate that the magmatism in the huanren cu zn deposit might have occurred in the early cretaceous geochemically the huanren monzodiorite belongs to the high k calc alkaline and shoshonitic series is enriched in rb ba and k and is depleted in nb ta and ti the rocks also have relatively high 87sr 86sr i 0 7091 0 7099 and low end t 13 2 to 10 3 and ehf t values 14 3 to 7 8 the sr nd hf isotopic data for the monzodiorite indicate that the magma may be derived from mixed sources of the crust and mantle the 34s values of chalcopyrite galena and pyrite range from 4 4 to 5 8 with an average of 5 1 indicating that the sulfur in the deposit was mainly derived from a magmatic source the huanren cu zn deposit resulted from the magmatism and mineralization induced by the rollback of the paleo pacific plate

zircon shrimp u pb and in situ lu hf isotope analyses of a tuff from western beijing evidence for missing late paleozoic arc volcano eruptions at the northern margin of the north china block abstract zircon shrimp u pb and in situ lu hf isotopic analyses via laser ablation microprobe inductively coupled plasma mass spectrometer lam icpms of a tuff within the upper paleozoic from western beijing were carried out to give new constraints on volcano eruption ages and source area of the tuffs within the north china block ncb shrimp u pb zircon dating of the tuff yielded a 206 pb 238 u weighted mean age of 296 4 ma 95 confidence mswd 3 3 which is very similar to the emplacement age of the newly discovered carboniferous calc alkaline i type continental arc granitoid plutons in the inner mongolia paleo uplift impu on the northern margin of the ncb in situ lu hf analysis results of most zircons from the tuff yielded initial 176 hf 177 hf ratios from 0 282142 to 0 282284 and e hf t values from 15 9 to 10 7 these lu hf isotopic compositions are very similar to those of the late carboniferous granitoids in the impu but are very different to those of the central asian orogenic belt caob together with the sedimentary and tectonic analyses results we inferred that the source area of the tuffs within the ncb is the impu instead of the caob therefore some arc volcanoes once existed in the impu on northern margin of the ncb during the late carboniferous but they were entirely eroded due to strong exhumation and erosion of the impu during the late carboniferous to early jurassic

the evolution of the vindhyan basin vis a vis the narmada son lineament central india from deep seismic soundings abstract the evolution of the vindhyan basin has been studied from deep seismic soundings block tectonics appear to be active throughout the geological history in this region the crust is divided into four major blocks by deep faults at narsinghgarh katangi and jabalpur the crustal block between narsinghgarh and katangi forms a graben in the crystalline basement giving rise to the great vindhyan basin in which precambrian vindhyan sediments of about 5 5 km thickness are deposited the crustal block between katangi and jabalpur is a horst block which represents the narmada son lineament a crustal depth section obtained from wide angle reflections shows a large number of reflector segments up to the mono boundary indicating crustal heterogeneity the boundary faults at the northern and the southern ends of the vindhyan basin extend up to the moho the crustal thickness varies from 39 5 to 45 km

crustal structure of northern israel abstract in the course of a seismic refraction wide angle reflection experiment in the eastern mediterranean an east west reversed refraction profile was recorded onshore northern israel the purpose of the line was to obtain reliable velocity and structural information about the crust in this area in addition a multi coverage reflection profile was shot over part of the refraction profile the results indicate that the crust in northern israel is a high velocity continental crust considerably thinner than the crust to the south the reflection profile indicates an unusually reflective upper crust and a transparent lower crust similar to those recorded at a number of compressional belts the overall results confirm the presence of a crust which is markedly different from that encountered to the south the provenance of which is probably very different

geophysical investigation of crystalline basement between dead sea rift and mediterranean sea long seismic refraction lines across central and northern israel combined with magnetic and gravity investigations help to define the total thickness of sedimentary rocks and crystalline basement structure significant lateral variations in thickness of the infra upper jurassic sediments seem to be related to tectonic movement and may influence possible deposition of early mesozoic and paleozoic reservoir rocks

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

collision belt between the khanka block and the north china block in the yanbian region northeast china the pre jurassic geotectonics in northeast china and its adjacent regions are characterized by collision of microcontinental blocks the yanbian region lies between the north china block ncb and the khanka block kb along the dashanzui antu kaishantun collision belt the yanbian pre jurassic fold belt can be divided into two parts one part represents the western margin of the kb which consists of late proterozoic metamorphic basement and a permian active continental margin the other one is located at the eastern margin of the ncb and is composed of proterozoic passive margin deposits where the seluohe and qinglongcun groups are developed and rocks of the permian passive margin collision of these two parts took place along the dashanzui antu kaishantun collision zone during the late permian to early triassic as evidenced by the emplacement of syncollision granites and a type granites in northeast china and adjacent regions a series of microcontinental blocks collided with one other from the end of early paleozoic to the early triassic the collision event that took place in the yanbian region may represent the latest collision event in the paleo asian oceanic domain c 2003 elsevier ltd all rights reserved

sr nd isotopic and geochemical constraints on provenance of late paleozoic to early cretaceous sedimentary rocks in the western hills of beijing north china implications for the uplift of the northern north china craton late paleozoic to mesozoic strata which were deposited in the western hills of beijing north china recorded the contemporary tectonic evolution of the northern part of the north china craton ncc fine grained sandstones and siltstones of these strata were analyzed for their major and trace element concentrations and sr nd isotope compositions their la sc th sc la co th co and cr th ratios are similar to those of sediments derived from felsic source rocks indicating that the original source materials were mostly intermediate to acidic rocks their end 0 values show dramatic shifts implying changes in provenances from the late paleozoic to the early cretaceous the end 0 values of the late paleozoic and the late jurassic to early cretaceous formations are very low whereas the end 0 values of the xingshikou and the xiaoyaopo formations are much higher indicating that a juvenile component has been added into their sources based on the sr nd isotope compositions the late paleozoic and the late jurassic to early cretaceous samples fall in the paleozoic to mesozoic magmatic rocks distributed in the northern part of the ncc however the sr nd isotope compositions of the xingshikou and the xiayaopo formations vary between the xing meng orogenic belt xmob and the north part of the ncc components these changes can be interpreted by the complex uplift and exhumation history of the northern ncc from the late paleozoic to the early cretaceous during the late carboniferous the uplift of the inner mongolia paleo uplift impu which probably commenced at the late carboniferous might supply detrital materials to the late paleozoic strata in the late triassic the uplift of the xmob and impu was responsible for the mixing source of the xingshikou formation after that the northern xmob became the main source of the xiayaopo formation resulting from the uplift of the xmob due to the collision of siberia and north china mongolia plates during the middle to late jurassic finally the uplift of the yftb which occurred from the late jurassic to early cretaceous provided the source materials and blocked the input of the xmob components

the formation of the suyunhe large porphyry mo deposit in the west junggar terrain nw china zircon u pb age geochemistry and sr nd hf isotopic results abstract newly discovered suyunhe mo deposit 0 57 mt mo metal located in the barluk mountains of the west junggar terrain xinjiang nw china is the largest porphyry mo deposit discovered in xinjiang so far the suyunhe mo deposit is associated with the suyunhe intrusive complex which was emplaced into the volcano sedimentary sequences of the middle devonian barluk group the suyunhe complex consists of the deep granite intrusion and the shallow granite porphyry granodiorite porphyry monzonitic granite porphyry and tonalite porphyry stocks which are cut by the felsic dikes dominant mo mineralization is hosted in the barluk group volcano sedimentary rocks but is minor in the granite granite porphyry granodiorite porphyry and monzonitic granite porphyry of the suyunhe complex we report in situ zircon u pb ages whole rock geochemistry sr nd isotopic and zircon lu hf isotopic data for the ore bearing intrusive rocks from the suyunhe deposit secondary ion mass spectrometry sims zircon u pb dating indicates that the deep granite emplaced at 298 4 1 9 ma 295 3 3 ma and the shallow granodiorite porphyry intruded during 294 7 2 1 ma 293 7 2 3 ma the suyunhe granite intrusion including fine and medium grained granite belongs to the high k calc alkaline series most of them have low zr nb y ce 2 7 values showing a geochemical affinity to i type granite these granites are enriched in light rare earth elements lree and depleted in heavy rare earth elements hree and eu ba sr nb p and ti indicating that they have experienced advanced fractional crystallization they have low initial 87sr 86sr ratios 0 70318 0 70380 high whole rock end t values 4 4 to 6 0 high zircon ehf t values 10 8 to 14 6 and young whole rock nd and zircon hf model ages they also show low mg 0 35 these features demonstrate that the ore bearing granite formed by partial melting of the juvenile lower crust and experienced advanced fractional crystallization the suyunhe granite porphyry and monzonitic granite porphyry are compositionally similar to the granite indicating that they share a common magma source and process with the granite the suyunhe granodiorite porphyries belong to slightly high k calc alkaline series and have lree enrichment and hree nb and ti depletion they have low 87sr 86sr i ratios 0 70421 0 70444 high end t values 4 9 to 6 2 high zircon ehf t values 9 6 to 15 2 and young whole rock nd and zircon hf model ages they also show low mg

core flooding experiments of co2 enhanced coalbed methane recovery abstract this paper presents the results of co 2 enhanced coal bed methane ecbm core floods on intact coal core from the bowen basin and the hunter valley australia at pore pressures of 4 mpa and 10 mpa the core floods involved flooding with co 2 to displace methane from the core and then reversing the flood by injecting methane to displace the co 2 from the previous flood an important parameter for ecbm is the displacement or sweep efficiency which was estimated directly from the mass balance over the core flood displacement efficiencies obtained through co 2 injection were excellent with more than 99 of the ch 4 recovered during the core floods the reverse experiments in which ch 4 was injected to displace co 2 were notably less effective with an average of 95 displacement obtained for the bowen basin core sample and only 71 displacement obtained for the hunter valley core sample by the end of the experiment history matching was performed with the reservoir simulator simed ii which used a hydrostatic permeability model the extended langmuir model and a bi disperse diffusion model in general good history matches were obtained between simulated and observed flow rates mass balances and breakthrough times demonstrating that the model could accurately represent the ecbm process it was found that the triple porosity gas diffusion model provided an improved agreement to observations over the unipore model connell lu pan s hydrostatic permeability model was used in the history matching which differentiates between bulk and pore sorption strain during the co 2 flooding experiments a change in permeability was observed as co 2 displaced ch 4 in the core as the stress conditions were constant this was the result of the sorption strain impacting on the porosity and thus permeability however for the reverse core flood in which ch 4 was injected to displace co 2 no permeability changes were observed implying that pore and bulk strain were the same and thus cancelled out

geochronology and geochemistry of late pan african intrusive rocks in the jiamusi khanka block ne china petrogenesis and geodynamic implications abstract to constrain the early paleozoic tectonic evolution of the jiamusi khanka block and its relationship to the late pan african event in gondwana we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic intrusive rocks in the jiamusi khanka block ne china la icp ms zircon u pb age data demonstrate that these intrusive rocks were emplaced at three stages during the late pan african event represented by 540 ma syenogranite 515 ma quartz syenite and 500 ma monzogranite and gabbro geochemically the 500 ma gabbros in the jiamusi khanka block have low sio 2 50 26 51 21 wt relatively high mgo 4 08 5 67 wt ni 13 1 14 1 ppm and cr 28 4 56 0 ppm and are slightly enriched in liles e g ba k and lrees and depleted in zr hf nb ta and p the e hf t values of zircons in the gabbro range from 2 6 to 6 4 all these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab in contrast the ca 540 500 ma granites and quartz syenites contain high sio 2 64 49 72 20 wt and low mgo 0 40 0 75 wt cr 1 69 6 88 ppm and ni 1 26 3 26 ppm they have relatively low 176 hf 177 hf ratios of 0 282247 0 282599 with hf two stage model ages of 1173 2280 ma and most of the magmatic zircons have positive e hf t values varying from 0 2 4 8 indicating that these granites and quartz syenites were probably derived from a dominantly paleo mesoproterozoic old crustal source with possible different degrees of addition of juvenile materials according to the geochemical data and global geological investigations we propose that the 541 498 ma intrusive rocks in the jiamusi khanka block formed in a post collisional or post orogenic extensional setting linked to the collapse of a late pan african orogen associated within the gondwana

late paleozoic final closure of the paleo asian ocean in the eastern part of the xing meng orogenic belt constrains from carboniferous permian meta sedimentary strata and meta igneous rocks abstract zircon u pb dating and whole rock geochemical data for carboniferous permian meta sedimentary sequences igneous rocks and precambrian amphibolite in the eastern xing meng orogenic belt xmob were used to constrain the final stage evolution and the position of closure of the paleo asian ocean pao detrital zircons from late paleozoic strata range in age from archean to late paleozoic with major age groups at 1 0 0 7 ga and 0 5 0 25 ga in the northern part and at 2 7 2 5 ga 2 1 1 8 ga and 0 5 0 25 ga in the southern part of the xmob striking changes in zircon age distribution patterns indicate inputs to these strata were separated by the paleo asian ocean pao in the late paleozoic the pao closed along the solonker linxi suture the late paleozoic formation ages 346 ma 303 ma and 269 ma of the igneous rocks with arc like geochemical features south to the pao together with previously published data on the regional igneous rocks and ophiolites indicate double side subduction of the pao in the late paleozoic

zircon u pb and molybdenite re os dating and geological implications of the shimadong porphyry molybdenum deposit in eastern yanbian northeastern china the shimadong porphyry mo deposit is located in eastern yanbian in the eastern part of the north margin of the north china craton northeastern china here we present the whole rock major and tra

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 hf isotopes bulk rock geochemistry and petrogenesis of middle to late triassic i type granitoids in the xing an block northeast china implications for early mesozoic tectonic evolution of the central great xing an range abstract we report zircon u pb age data hf isotopes and bulk rock geochemical data for the middle to late triassic granitoids in the taerqi chabaqi kutihe region within the xing an block of the central great xing an range northeast china euhedral to subhedral zircon grains were extracted from the nine representative granitoids these zircons exhibit oscillatory zoning typical of a magmatic origin the zircon u pb determinations on the monzogranite syenogranite and quartz diorite samples yielded ages between 244 ma and 206 ma which essentially suggests that the magmatism in the xing an block occurred during the middle to late triassic period geochemically these granitoids have sio2 62 97 76 31 wt a cnk 1 03 1 51 and k2o na2o 0 40 2 39 we infer that they belong to high k calc alkaline series and are peraluminous i type granites in nature the major and trace element systematics indicate that these granitoids have different origins among them the 244 ma syenogranite of taerqi and the 230 206 ma monzogranite and syenogranite of kutihe were probably generated from partial melting of pre existing juvenile arc type rocks in a relatively shallow crustal level the 210 ma quartz diorite of chabaqi likely originated from the hybridization between a depleted mantle component and the juvenile subducted oceanic crustal materials that were buried to depths of the middle to lower continental crust the 212 ma monzogranite and syenogranite of kutihe were probably generated from the partial melting of miscellaneous lower crustal materials at high pressure conditions by combining these new data with regional geological data we conclude that the early mesozoic evolution of the central great xing an range was governed by two superimposed tectonic regimes i e 1 post orogenic extension due to slab break off after the closure of the paleo asian oceanic basin along the hegenshan heihe suture belt and 2 back arc extension associated with the southward subduction of mongol okhotsk oceanic plate

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

detrital zircon u pb ages of middle late permian sedimentary rocks from the southwestern margin of the north china craton implications for provenance and tectonic evolution abstract the southwestern margin of the north china craton ncc is located between the alxa terrane to the northwest the north qilian orogen to the west and the north qinling orogen to the south however the paleogeographic and tectonic evolution for the southwestern part of the ncc in the late paleozoic is still poorly constrained in order to constrain the late paleozoic tectonic evolution of the southwestern ncc we carried out detailed field work and detrital zircon u pb geochronological research on middle late permian sedimentary rocks at the southwestern margin of the ncc the u pb age spectra of detrital zircons from six samples are similar showing four populations of 2 6 2 4 ga 2 0 1 7 ga 500 360 ma and 350 250 ma moreover on the basis of the weighted mean age of the youngest detrital zircons 257 4 ma combined with the published results and volcanic interlayers we propose that the shangshihezi formation formed during the middle late permian our results and published data indicate that the detrital zircons with age groups of 2 6 2 4 ga and 2 0 1 7 ga were likely derived from the khondalite belt and yinshan block in the northwestern ncc the junction part between the north qinling and north qilian orogen may provide the 500 360 ma detrital zircons for the study area the 350 250 ma detrital zircons were probably derived from the northwestern part of the ncc the majority of materials from shangshihezi formation within the study area were derived from the northwestern part of the ncc indicating that the northwestern part of the ncc was strongly uplifted possibly resulting from the progressive subduction and closure of the paleo asian ocean a small amount of materials were sourced from southwestern part of the ncc indicating that the north qinling orogen experienced a minor uplift resulting from the northward subduction of the south qinling terrane

lower cretaceous alkali feldspar granites in the central part of the great xing an range northeastern china chronology geochemistry and tectonic implications the mingshui jilasitai suolun area located in the central part of the great xing an range is characterized by large volumes of alkali feldspar granites however the formation time and tectonic setting of these rocks remains controversial owing to a lack of precise geochronological and detailed geochemical data in this paper we report new sims u pb zircon ages and mineralogical petrographical and geochemical data for lower cretaceous alkali feldspar granites from the mingshui jilasitai suolun area the sims zircon dating results indicate that these granites formed at 133 6 135 9 ma the mineralogical petrographical and geochemical data show that these granitic rocks belong to highly fractionated i type granites combined with the regional geology data we propose that the formation of the lower cretaceous alkali feldspar granitic rocks was related to an extension induced by delamination of the lithosphere that arose from subduction of the palaeo pacific plate

geochronology and geochemistry of late cretaceous paleocene granitoids in the sikhote alin orogenic belt petrogenesis and implications for the oblique subduction of the paleo pacific plate we present zircon u pb ages major and trace element analyses and zircon hf isotope data on the late cretaceous paleocene granitoids at the southern end of the sikhote alin orogenic belt of the russian far east these data are used to discuss the petrogenesis of the granitoids in the context of the paleo pacific subduction beneath the eastern eurasia zircons from four granitoid samples give emplacement ages of 56 83 91 and 92 ma these granitoids with high sio2 73 43 76 76 wt are metaluminous to weakly peraluminous a cnk 0 97 1 03 and belong to the high k calc alkaline series k2o 3 75 4 95 wt they are all enriched in light rare earth elements lrees and large ion lithophile elements liles and relatively depleted in high field strength elements hfses with striking depletion also in ba sr p and eu they are petrographically and geochemically consistent with being of i type granitoids the zircons have ehf t values 0 8 to 7 6 higher than whole rock ehf t values predicted from whole rock end t 4 1 to 0 5 in the literature all these observations suggest that primary magmas parental to these granitoids were likely to have derived from partial melting of a juvenile lower crust accompanied by assimilation with ancient mature crust during magma ascent and evolution a recent study illustrates that the collision of an exotic terrane carried by the paleo pacific plate with the continental china at 100 ma accreted the basement of the chinese continental shelf beneath east and south china seas and resulted in a new plate boundary of transform nature between the nnw moving paleo pacific plate and the eastern margin of the shelf our new data and analysis of existing data support this hypothesis but we hypothesize that this transform becomes transpressional in its northern segment with oblique subduction of the paleo pacific plate beneath northeastern asia as manifested by the late cretaceous paleocene granitoids in the russian far east ne china 97 56 ma and south korea sw japan 96 71 ma these tectonic and magmatic events took place prior to the opening of the huanghai bohai and japan seas which are of rift origin from continental china much later our study emphasizes the necessity and significance of plate tectonics reconstruction in the greater northwestern pacific region since the cretaceous