minor and trace element partitioning between pyroxene and melt in rapidly cooled chondrules we present minor and trace element ree sr y and zr data for pyroxenes and mesostases in four porphyritic chondrules from the semarkona ordinary chondrite apparent partition coefficients for clinoenstatite orthoenstatite pigeonite and augite are compared with experimental and petrologic data from the literature and the effects on apparent partition coefficients of the rapid cooling rates at which chondrules crystallized are evaluated for most elements the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition however for lree apparent partition coefficients are significantly higher than comparable equilibrium data and the ratio of hree lree partition coefficients is lower particularly for ca poor pyroxene we attribute this flattening of ree patterns to the effect of rapid cooling apparent partition coefficients of all ree and y in augite are higher than equilibrium data particularly in one chondrule with a high al 2o3 content we suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge balanced substitutions with al 31 cations

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

the role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at arenal volcano costa rica evidence from clinopyroxene and spinel the bulk composition of magma erupted from volcan arenal has remained nearly constant sio2 53 6 54 9 wt mgo 5 0 4 5 wt during almost 30 years of continuous activity 1969 1996 none the less clinopyroxene cpx phenocrysts and their spinel inclusions record a much more complex open system evolution in which steady state production of the erupted basaltic andesitic magma is linked to episodic injections of basalt into arenal s magma conduit reservoir system high resolution major element zoning profiles electron microprobe on a large number of phenocrysts 14 000 analyses tied to back scattered electron bse images have been used to assess the compositional characteristics of the magmatic end members as well as the timing and dynamics of magma replenishment events no two cpx phenocrysts have exactly the same zoning profile the vast majority of our analyses record the crystallization of cpx cr2o3 0 12 wt mg 65 79 al ti 2 7 from a liquid comparable to or more evolved than erupted magma compositions however half of all cpx grains are cored by high cr cpx cr2o3 0 2 0 72 wt or contain similar basaltic compositions as abrupt growth bands in phenocrysts with and without high cr cores phenocrysts with high cr cpx occur throughout the ongoing activity in a few cases high cr cpx occurs very near the outer margin of the grain without an apparent growth hiatus particularly in 1968 69 and 1992 93 the main conclusions are 1 all basaltic andesitic lavas erupted at arenal during the ongoing activity that began in july 1968 are the products of magma mixing 2 clinopyroxenes record multiple replenishment events of basaltic magma in contrast to the near constancy of erupted bulk compositions 3 some phenocrysts preserve records of multiple interactions with basaltic magmas requiring magmatic processes to operate on timescales shorter than residence times of some phenocrysts 4 multiple occurrences of clinopyroxene with high cr rims suggest that basalt replenishment events have occurred with sub decadal frequency and may predate eruption by months or less from this we infer that arenal volcano is underlain by a continuously active small volume magmatic reservoir maintained in quasi steady state by basalt recharge over several decades the monotony of erupting arenal magmas implies that fractionation recharge ascent and eruption are well balanced in order for magmas to be essentially uniform while containing phenocrysts with vastly different growth histories at the time of eruption

petrogenesis of angrites abstract the recent discovery of two new angrites sahara 99555 and d orbigny has revived interest in this small group of achondrites we measured trace element abundances in the individual minerals of these two angrites and compared them with the three antarctic angrites lew 86010 lew 87051 and asuka 881371 trace element variations in four of these meteorites lew 87051 asuka 881371 sahara 99555 and d orbigny indicate rapid crystallization under near closed system conditions consistent with their mineralogical and textural features all four appear to be closely related and crystallized from very similar magmas discrepancies between their bulk ree compositions and melts calculated to be in equilibrium with the major phases may be due in part to kinetic effects of rapid crystallization prior crystallization of olivine and or plagioclase may also account for the elevated parent melt composition of clinopyroxene in some of the angrites such as asuka 881371 lew 86010 also crystallized from a melt and represents a liquid composition but trace element trends in clinopyroxene and olivine differ from those of the other angrites this meteorite seems to have crystallized from a different source magma

compositional data analysis in the geosciences from theory to practice since karl pearson wrote his paper on spurious correlation in 1897 a lot has been said about the statistical analysis of compositional data mainly by geologists such as felix chayes the solution appeared in the 1980s when john aitchison proposed to use iogratios since then the approach has seen a great expansion mainly building on the idea of the natural geometry of the sample space statistics is expected to give sense to our perception of the natural scale of the data and this is made possible for compositional data using iogratios this publication will be a milestone in this process this book will be of interest to geologists using statistical methods it includes the intuitive justification of the methodology convincing through case studies and presenting user friendly software which includes a section for those who need to see the proof of the mathematical consistency of the methods used

compositional trends in arc related deep marine sand and sandstone a reassessment of magmatic arc provenance detrital modes for 524 deep marine sand and sandstone samples recovered on circum pacific caribbean and mediterranean legs of the deep sea drilling project and the ocean drilling program form the basis for an actualistic model for arc related provenance this model refines the dickinson and suczek 1979 and dickinson and others 1983 models and can be used to interpret the provenance tectonic history of ancient arc related sedimentary sequences four provenance groups are defined using qfl qmkp lmlvls and lvflvmilvl ternary plots of site means 1 intraoceanic arc and remnant arc 2 continental arc 3 triple junction and 4 strike slip continental arc intraoceanic and remnant arc sands are poor in quartz mean qfl q 75 they are predominantly composed of plagioclase feldspar and volcanic lithic fragments continental arc sand can be more quartzofeldspathic than the intraoceanic and remnant arc sand mean qfl q values as much as 10 mean qfl f values as much as 65 and mean qmkp qm as much as 20 and has more variable lithic populations with minor metamorphic and sedimentary components the triple junction and strike slip continental groups compositionally overlap both are more quartzofeldspathic than the other groups and show highly variable lithic proportions but the strike slip continental group is more quartzose modal compositions of the triple junction group roughly correlate with the qfl transitional arc field of dickinson and others 1983 whereas the strike slip continental group approximately correlates with their dissected arc field

building the hindu kush monazite records of terrane accretion plutonism and the evolution of the himalaya karakoram tibet orogen in situ u th pb la icp ms monazite ages from the hindu kush of nw pakistan provide new petrochronologic constraints on the tectonic evolution of the himalaya karakoram tibet orogen monazites from two adjacent garnet staurolite schist specimens yield multiple age populations that record the major mesozoic and cenozoic deformational magmatic and metamorphic events along the southern margin of eurasia these include the accretion of the hindu kush sw pamir to eurasia during the late triassic followed by the accretion of the karakoram terrane in the early jurassic younger jurassic and cretaceous ages record the development of an andean style volcanic arc along the southern eurasian margin which ended with the docking of the kohistan island arc and the emplacement of the kohistan ladakh batholith during the late cretaceous the initial eocene collision of india with eurasia was followed by widespread high temperature metamorphism and anatexis associated with crustal thickening within the himalaya system in the late oligocene and early miocene

the low temperature thermo tectonic evolution of the western tian shan uzbekistan abstract the kyzylkum nurata region represents a key area in understanding the tectonic evolution of the western tian shan in this study we present new thermochronological data apatite fission track and apatite u th sm he and associated thermal history models for 45 igneous samples from the kyzylkum nurata segment of south tian shan on the territory of uzbekistan and tajikistan our data show that the kyzylkum nurata segment experienced a multi phase mesozoic thermal history that differs from previously studied segments of the tian shan a triassic 220 200 ma cooling signal is widespread throughout the tian shan and is interpreted as being associated with exhumation following the closure of the palaeo asian ocean following this period of fast cooling the kyzylkum nurata segment experienced a period of slow cooling and erosion in the early jurassic 190 160 ma however in contrast to other parts of the tian shan our study area preserves evidence for rapid cooling during the late jurassic early cretaceous 160 120 given that this rapid cooling signal was only recorded for samples in association with major structures e g relic suture shear zones we interpret this event as a period of fault reactivation related with tectonic processes at the eurasian margin of the tethys ocean subsequently the late cretaceous early palaeogene 100 50 ma is characterised by slow cooling and erosion since the late palaeogene the basement of the tian shan experienced cooling related to the india eurasia collision the thermal signal of this collision has been extensively recorded in the high altitude kyrgyz tian shan within the low relief kyzylkum nurata segment this cenozoic overprint is not recorded allowing for a detailed assessment of the mesozoic thermal and landscape evolution of the western tian shan our study demonstrates that the cretaceous uzbek tian shan was characterised by a series of parallel linear mountain belts that formed along suture zones during fault reactivation

reconnaissance geology in upper chitral baroghil and karambar districts northern karakorum pakistan during the summer of 1992 a geological expedition crossed the northern karakorum range in northern pakistan from the chitral to karambar valleys from the villages of mastuj to imit some of the areas visited were geologically unknown a number of structural units were crossed belonging to the karakorum block or to other crustal blocks north of it they are a the axial batholith in which three plutonic bodies have been identified and b the northern sedimentary belt nsb in which three major tectonostratigraphic units form thrust stacks dipping to the north their internal stratigraphy and structural style are partly different the most complete contains a crystalline basement transgressed by a marine succession during the early ordovician the youngest strata are represented by the reshun conglomerate of inferred cretaceous age the northernmost unit of the nsb is tightly folded whereas the central one forms a monocline vertical faults mainly strike slip dissect the thrusted slabs metamorphic deformation is absent or reaches only the anchizone in the studied sector of the karakorum nsb to the north of the karakorum proper there are several other tectonic units separated by vertical faults they are from south to north a the tas kupruk zone with metavolcanics of basaltic to latibasaltic composition b the atark unit mostly consisting of massive carbonate rocks of mesozoic age and c the wakhan slates which consist of a thick widespread succession of dark slates metasiltites and sandstones the fine grained elastic rocks are supposed to be palaeozoic to early triassic in age the wakhan slates are intruded by plutons belonging to the east hindu kush batholith from which a single k ar age on muscovite gave a jurassic age

the eo cimmerian late triassic orogeny in north iran the eo cimmerian orogen results from the late triassic collision of iran a microplate of gondwanan affinity with the southern margin of eurasia the orogen is discontinuously exposed along the northern side of the alborz mountains of north iran below the siliciclastic deposits of the shemshak group late triassic jurassic a preserved section of the external part of the belt crops out in the neka valley eastern alborz south of gorgan here the mesozoic successions shemshak group upper cretaceous limestones overlay a pre jurassic eo cimmerian thrust stack with a sharp unconformity the stack includes the gorgan schists an upper ordovician lower silurian low grade metamorphic complex overthrusted southward above a strongly deformed late palaeozoic middle triassic succession belonging to north iran in the talesh mountains western alborz the shanderman complex previously interpreted as an ophiolitic remnant isolated along the eo cimmerian suture is considered an allochthonous nappe of deeply subducted continental crust the new evidence for this is the occurrence of previously unknown eclogites dating to the carboniferous and probably related to the variscan history of transcaucasia south of the shanderman complex upper palaeozoic slates and carbonates occurring below the lower jurassic shemshak group also record the occurrence of an eo cimmerian metamorphic event based on our new data the eo cimmerian structures exposed in the alborz appear to be remnants of a collisional orogen consisting mainly of deformed continental crust where no ophiolites are preserved

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

guadalupian middle permian paleobiogeography of the neotethys ocean abstract a matrix of presence absence data of guadalupian middle permian brachiopod genera from sicily tunisia oman turkey north iran central afghanistan karakoram salt range and south thailand has been analyzed by multivariate methods cluster analysis principal coordinate analysis minimum spanning trees and parsimony analysis of endemicity the application of these different and independent paleobiogeographical methods has led to the individuation of three bioprovinces the cathaysian sicily and tunisia cimmerian oman turkey north iran salt range south thailand and transhimalayan karakoram and central afghanistan provinces these provinces have been placed on a paleogeographical reconstruction based on paleomagnetic data which we used to decipher the principal factors that governed brachiopod distribution in the neotethys ocean during the guadalupian as a conclusion the pattern of biotic provinces at this time resulted from the complex interplay between latitudinal thermal gradient oceanic paleocurrents and the continental drift of the cimmerian terranes across zonal climate belts

tethyan oceanic currents and climate gradients 300 m y ago we reconstruct the oceanic circulation pattern of the tethys ocean 300 m y ago by placing late carboniferous early permian climate sensitive biotic associations from gondwana and laurasia on a pangea paleogeography constrained by selected paleomagnetic data warm climate fossils and facies from iran located at that time along the gondwanan margin of arabia are compatible with the existence in the tethys ocean of a warm subtropical surface current gyre whereas cold surface currents swept the glaciated gondwanan margin at higher southern latitudes redistributing cold biota toward the tropics this tethyan surface current system and the associated narrow zonal barrier show similarities to recent glacial climate patterns when placed on a large scale paleogeographic reconstruction of pangea of the b type it neatly explains the otherwise problematic observation that the carboniferous permian biota of iran and northern arabia is dominated by warm euramerican and or russian taxa that are strikingly different from typical cold gondwanan associations

arcuate pamir in the paleogene insights from a review of stratigraphy and sedimentology of the basin fills in the foreland of ne chinese pamir western tarim basin abstract the tectonic evolution of the pamir bears essential information for understanding intracontinental tectonic processes within the context of india asia convergence however it is unclear whether the arcuate shape of the pamir is entirely the result of the india asia collision or may have been in part an inherited pre cenozoic feature in this study we address the evolution of the ne chinese pamir during the paleogene by reviewing the stratigraphy of twelve sections in the western tarim basin and the establishment of sedimentary facies the results indicate three episodes of deposition of alluvial coarse sediments in the foreland regions of ne chinese pamir during the 1 early paleocene 2 late paleocene to early eocene and 3 middle eocene to oligocene respectively these are correspondingly attributed to 1 retroarc deformation in an andean type margin of the southern asia during subduction of the neo tethys ocean 2 the immediate response in the pamir to the india asia collision and 3 continued india asia convergence the alluvial conglomerates with grain size up to 5 10 cm imply a transport distance

permian oolitic carbonates from the baoshan block in western yunnan china and their paleoclimatic and paleogeographic significance marine carbonate ooids are environment sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions this paper describes permian ooids from the baoshan block in western yunnan china in order to offer a new means to refine the uncertain paleogeographic details of this gondwana derived block four major types of ooids micritic ooids compound ooids leached ooids and half moon ooids are documented from the hewanjie formation in the northern and the shazipo formation in the southern baoshan block these ooids are dated via biostratigraphic analysis to be wordian early wuchiapingian and signify an ameliorated shallow marine temperature for the guadalupian strata of the baoshan block results of this study coupled with literature data reveal diachronous debut of permian ooids among the gondwana derived blocks mostly sakmarian in central taurides of turkey central iran central pamir and karakorum block versus wordian capitanian in baoshan block peninsular thailand and south qiangtang in contrast asselian sakmarian strata of baoshan block as well as peninsular thailand and south qiangtang are characterized by glaciomarine diamictites these observations suggest that the baoshan block was probably situated at a considerably higher paleolatitude under distinct influence of gondwana glaciation during the asselian sakmarian than those blocks yielding sakmarian ooids moreover marine ooids are virtually absent nearby the equator within the permian tethys similar to the modern situation the baoshan block is accordingly interpreted to drift to warm water southern mid latitudes during the wordian capitanian and remain to the south of central iran karakorum block and south china which were equatorially located in the capitanian

old origin for an active mountain range geology and geochronology of the eastern hindu kush pakistan prior to accretion of the kohistan island arc during the late cretaceous and final suturing of india with asia at ca 50 ma the hindu kush mountains along the border of afghanistan and northwest pakistan were situated on the active southern margin of asia geology and geochronology of the eastern hindu kush range in pakistan demonstrate that localized crustal melting and leucogranite intrusion took place in the gharam chasma area at ca 24 ma more regionally developed and widespread deformation metamorphism and magmatism took place before collision between both india and the kohistan island arc with asia ca 195 ma u pb monazite ages on a deformed leucogranite dike from the upper lutkho valley indicate an early jurassic phase of crustal melting u pb monazite ages of 135 126 ma on a staurolite schist from near gharam chasma are interpreted as a minimum age for staurolite grade metamorphism within the tirich mir fault zone pegmatite dikes crosscut the staurolite schists u pb dating of uraninites from one of these pegmatite dikes reveals an age of 114 2 ma monazites from the same rock give ages of 125 121 ma possibly due to inheritance of older cores these jurassic early cretaceous constraints on metamorphism and magmatism relate to subduction and accretion processes perhaps including the suturing of the karakoram and hindu kush terranes along the tirich mir fault in general high temperature low pressure metamorphism and subduction related granitoid magmatism in the eastern hindu kush suggest a high thermal gradient in an active margin setting from early jurassic to cretaceous time

petrology of feo poor porphyritic pyroxene chondrules in the semarkona chondrite abstract the mineralogy and petrology of feo poor porphyritic pyroxene and olivine rich chondrules in the semarkona ll3 0 chondrite are described in detail in an extension of the textural classification scheme these chondrules are designated types iab and ib in type iab chondrules the proportion of olivine phenocrysts is between 20 80 and in type ib chondrules olivine constitutes

trace element variations in olivine from the eastern deeps intrusion at voisey s bay labrador as a monitor of assimilation and sulfide saturation processes ni cu co sulfide mineralization in the mesoproterozoic voisey s bay intrusion is spatially and genetically associated with magmatic breccia zones within an extensive dike system and in particular with the entry point of this system into a larger intrusion eastern deeps intrusion the massive sulfide and breccia bearing inner basal margin of this upper intrusion is enveloped by weakly mineralized variable textured troctolite that progressively decreases in sulfide content contains fewer paragneiss fragments and eventually grades into a largely sulfide barren homogeneous plagioclase and olivine meso cumulate termed normal troctolite toward the top of the intrusion olivine from the troctolite lithologies the mineralized basal breccia sequence and the uppermost olivine gabbro in the eastern deeps intrusion was analyzed with secondary ion mass spectrometry sims we present multitrace element data including petrogenetically important elements v cr mn co ni zn sr and y which indicate that four petrological processes important to ore formation are recorded by the compositional diversity of olivine the heterogeneous ni co fo contents of olivine in the eastern deeps intrusion co ni ratios in olivine gabbro 0 18 1 1 normal troctolite 0 07 0 26 variable textured troctolite 0 11 0 29 basal breccia sequence 0 20 0 34 are due to variable modification of original compositions by reequilibration with trapped silicate and sulfide liquids the abrupt changes of fe fo79 fo66 and ni 2 500 to 80 ppm contents and some trace elements up to 1 5x more sr up to 3x more y than average normal troctolite olivine in olivine from intervals in the barren upper normal troctolite indicate that olivine crystallized from separate pulses of magma with variable degrees of differentiation the severe ni depletion of one troctolite melt batch 10 ppm ni vs 290 ppm ni for average normal troctolite magma is likely a result of sulfide saturation and segregation either in a deeper staging chamber or in the conduit prior or contemporary to olivine precipitation and emplacement the gradational increase of fe from fo80 to fo62 mn from 4 000 to 10 000 ppm and zn from 400 to 620 ppm in olivine from the weakly mineralized and contaminated lower part of the variable textured troctolite downward into the massive sulfide bearing and strongly contaminated basal breccia sequence is consistent with olivine fractionation from an increasingly country rock contaminated sulfide saturated silicate magma olivine here crystallized prior to or contemporaneously with the segregation of an immiscible sulfide liquid olivine grains that are enclosed by sulfide display homogeneous forsterite contents fo62 with pronounced intragrain trace element zonation mn ni co zn diffusion profiles mn ni indicate a relatively short immersion time 1 000 years of these olivine grains in sulfide liquid which likely resulted in the partial retention of ni in the olivine olivine in the vicinity of massive sulfides in the eastern deeps intrusion from variable textured troctolite to basal breccia sequence has a distinct minor and trace element signature v cr mn co ni zn compared to olivine from the barren troctolite and olivine gabbro a multiple regression analysis using these data yields an index that describes the relative vertical proximity of olivine to massive sulfides in conjunction with the stratigraphic context of the host lithology this information could potentially be used as a vector toward massive sulfide mineralization in the eastern deeps intrusion and also support ni exploration in other olivine bearing mafic intrusions with similar style of sulfide mineralization

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

space weathering by simulated micrometeorite bombardment on natural olivine and pyroxene a coordinated ir and tem study abstract we studied space weathering effects caused by micrometeorite bombardment simulated by pulsed intense infrared laser generating 15 mj per pulse in high vacuum for our investigation we selected a natural olivine san carlos olivine fo91 and a natural pyroxene bamble orthopyroxene en87 as important rock forming minerals of the earth upper mantle as well as key planetary minerals irradiated areas of powdered pressed samples were examined by optical reflection spectroscopy in a broad optical and infrared wavelength range visible near and mid infrared and transmission electron microscopy to identify changes due to micrometeorite impacts the present study aims to investigate especially the effects of micrometeorite bombardment on reflectance spectra in the mid ir in preparation for future space missions as well as for the mertis experiment onboard the bepicolombo mission for both irradiated samples we found a reduction in albedo and in the reflectance of characteristic reststrahlen bands and an increase of the transparency feature vis and nir spectra of both minerals show the typical darkening and reddening as described for other space weathered samples tem studies revealed that space weathered layers in olivine and pyroxene differ in their respective thickness 450 nm in olivine 100 250 nm in pyroxene as well as in developed nanostratigraphy of laser ablated material like nanophase iron npfe in conclusion our spectral and structural findings were compared to samples in which space weathering was caused by different processes a comparison with these data demonstrates that there is no difference in optical reflectance spectroscopy but a significant difference in the microstructure of minerals due to the weathering source in space as there are solar wind and solar flares cause other structural and chemical changes as the bombardment with micrometeorites

tectonic evolution of the early mesozoic blueschist bearing qiangtang metamorphic belt central tibet this is the published version copyright 2003 american geophysical union all rights reserved

differentiation and evolution of the iva meteorite parent body clues from pyroxene geochemistry in the steinbach stony iron meteorite we analyzed the steinbach iva stony iron meteorite using scanning electron microscopy sem electron microprobe analysis empa laser ablation inductively coupled plasma mass spectroscopy la icp ms and modeling techniques different and sometimes adjacent low ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions subsequently type 2 pyroxene crystallized over an extensive fractionation interval steinbach probably formed as a cumulate produced by extensive crystal fractionation 6070 fractional crystallization from a high temperature 1450 1490 c silicate metallic magma the inferred composition of the precursor magma is best modeled as having formed by 30 50 silicate partial melting of a chondritic protolith if this protolith was similar to an ll chondrite as implied by o isotopic data then olivine must have separated from the partial melt and a substantial amount 53 56 of feo must have been reduced in the silicate magma a model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for steinbach and other iva meteorites impact disruption occurred while the parent body was substantially molten causing liquids to separate from solids and oxygen bearing gas to vent to space leading to a molten metal rich body that was smaller than the original parent body and that solidified from the outside in this model can simultaneously explain the characteristics of both stony iron and iron iva meteorites including the apparent correlation between metal composition and metallographic cooling rate observed for metal

thermochronological insights into the structural contact between the tian shan and pamirs tajikistan gilby jepson stijn glorie dmitry konopelko jack gillespie martin danisik noreen j evans yunus mamadjanov alan s collins

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

petrology of silicate inclusions in the sombrerete ungrouped iron meteorite implications for the origins of iie type silicate bearing irons the petrography and mineral and bulk chemistries of silicate inclusions in sombrerete an ungrouped iron that is one of the most phosphate rich meteorites known was studied using optical scanning electron microscopy sem electron microprobe analysis empa and secondary ion mass spectrometry sims techniques inclusions contain variable proportions of alkalic siliceous glass 69 vol of inclusions on average aluminous orthopyroxene 9 wo1 4fs2535 up to 3 wt al plagioclase 8 mainly an7092 cl apatite 7 chromite 4 yagiite 1 phosphaterich segregations 1 ilmenite and merrillite ytterbium and sm anomalies are sometimes present in various phases positive anomalies for phosphates negative for glass and orthopyroxene which possibly reflect phosphate melt gas partitioning under transient reducing conditions at high temperatures phosphate rich segregations and different alkalic glasses k rich and na rich formed by two types of liquid immiscibility yagiite a k mg silicate previously found in the colomera iie iron appears to have formed as a late stage crystallization product possibly aided by na k liquid unmixing trace element phase compositions reflect fractional crystallization of a single liquid composition that originated by low degree 48 equilibrium partial melting of a chondritic precursor compositional differences between inclusions appear to have originated as a result of a filter press differentiation process in which liquidus crystals of cl apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions this process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host yielding a dacite composition for some inclusions solidification was relatively rapid but not so fast as to prevent flow and immiscibility phenomena sombrerete originated near a cooling surface in the parent body during rapid probably impact induced mixing of metallic and silicate liquids we suggest that sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted possibly in a breakup and reassembly event simultaneous endogenic heating and impact processes may have widely affected silicate bearing irons and other solar system matter

trace element distributions within ordinary chondrite chondrules implications for chondrule formation conditions and precursors the concentrations of thirty six lithophile elements in the major silicate phases of chondrules have been determined by ion microprobe two types of porphyritic chondrule olivines normal and incompatible rich have been identified the incompatible rich olivines which have forsterite contents that are greater than fo98 appear to have formed under highly reducing conditions the olivine and low ca pyroxene grains in porphyritic chondrules have relatively unfractionated l chondrite normalized ree abundances compared to expectations from equilibrium distribution coefficients this is consistent with porphyritic chondrules having formed at cooling rates of the order of 1000 c h or faster the alkali metal na k rb and cs to al ratios in chondrule glasses vary by two orders of magnitude the lower values possibly being the result of volatile loss from chondrules no correlation was found between alkali metal depletions in chondrule glasses and enrichments in the surrounding rims but any such correlation may have been destroyed by the diffusive redistribution of these elements in rims that is likely to occur even under mild metamorphic conditions the refractory lithophiles with the exception of mg are all highly incompatible in silicate melts and are as a result concentrated in the chondrule glasses the refractory lithophiles in the glass are in most cases unfractionated from one another suggesting that neither vapor phase nor crystal liquid fractionation played a major role in the formation of chondrules or their precursors based largely on the observation that the refractory lithophiles are concentrated in the chondrule glasses it is suggested that previously reported correlations between these elements in bulk chondrule analyses are due to chondrules themselves as opposed to refractory condensates having been their own immediate precursors a simple monte carlo simulation using the compositions of the major chondrule silicate phases reported here supports this hypothesis it is argued that the upper limit of about one observed in the atomic na al ratios of chondule glasses is not due to an albitic precursor but simply reflects that for na to be incorporated into the structure of the melt it must take part in the coupled substitution naalo2 sio2

itqiy a metal rich enstatite meteorite with achondritic texture itqiy is a unique coarse grained metal rich enstatite meteorite that was found in the western sahara and consists of two rocks together weighing 4 72 kg which are both completely coated with fusion crust we report results from our electron microprobe and instrumental neutron activation analysis techniques itqiy consists of subhedral equigranular millimeter sized enstatite 25 vol of millimeter sized kamacite and a few tiny intergrowths of sulfides and kamacite relic chondrules are absent pyroxene fs0 2 is chemically similar to enstatite in el chondrites but the metal is closer in composition to that in eh chondrites sulfides resemble those in e chondrites but their compositions are distinct from those in both el and eh chondrites itqiy clearly formed under very reducing conditions but it does not appear to have formed from eh or el chondrites two thermal events can be distinguished silicate compositions including rare earth element abundances indicate loss of partial melt and slow cooling heterogeneous sulfides indicate a subsequent reheating and quenching event which may have been due to shock as many enstatite grains show shock stage s3 features

the cimmerian geopuzzle new data from south pamir based on its permian triassic stratigraphic and biotic evolution we correlate the se pamir to the karakoram terrane and we consider them equivalent along with the central pamir to the qiantang terrane of tibet all of palaeozoic gondwanan ancestry we prove the occurrence of a marked cimmerian unconformity documented by lowermost jurassic deposits suturing intensively faulted and folded permian and triassic units which suggests that the south pamir collided around the t j boundary with the central pamir along the rushan pshart suture collision of the karakoram to the south pamir happened slightly later along the wakhan tirich boundary zone progressive time shifting of deformation can be related to the complex setting of the cimmerian belt which was subdivided into minor blocks by incipient oceanic basins providing strong crustal mobility terra nova 25 352 360 2013

experimentally determined mineral melt partition coefficients for sc y and ree for olivine orthopyroxene pigeonite magnetite and ilmenite our current lack of understanding of the partitioning behavior of sc y and the ree rare earth elements can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set to address this problem we conducted a series of experiments using several different natural composition lavas doped with the elements of interest as starting compositions microprobe analyses of orthopyroxene pigeonite olivine magnetite ilmenite and co existing glasses in the experimental charges were used to calculate expressions that describe ree partitioning as a function of a variety of system parameters using expressions that represent mineral melt reactions versus element ratio distribution coefficients it is possible to calculate terms that express low ca pyroxene melt partitioning behavior and are independent of both pyroxene and melt composition compositional variations suggest that sc substitution in olivine involves either a paired substitution with al or more commonly with vacancies the partitioning of sc is dependent both on melt composition and temperature our experimentally determined olivine melt ree ds partition coefficients are similar to but slightly higher than those reported by mckay 1986 and support their conclusions that olivines are strongly lree depleted y and ree mineral melt partition coefficients for magnetite range from 0 003 for la to 0 02 for lu ilmenite partition coefficients range from 0 007 for la to 0 029 for lu these experimental values are two orders of magnitude lower than many of the published values determined by phenocryst matrix separation techniques

trace element geochemistry of ordinary chondrite chondrules the type i type ii chondrule dichotomy we report trace element concentrations of silicate phases in chondrules from ll3 ordinary chondrites bishunpur and semarkona results are similar to previously reported data for carbonaceous chondrites with rare earth element ree concentrations increasing in the sequence olivine 10 k h than type i chondrules appreciable na concentrations 3 221 ppm are measured in olivine from both chondrule types type ii chondrules seem to have behaved as closed systems which may require chondrule formation in the vicinity of protoplanets or planetesimals at any rate higher solid concentrations in type ii chondrule forming regions may explain the higher oxygen fugacities they record compared to type i chondrules type i and type ii chondrules formed in different environments and the correlation between high solid concentrations and or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for

directions of lithosphere interactions in the pamir hindu kush junction inferred from anisotropic tomography the pamir and hindu kush are examples of a puzzling collision system where a complex junction of colliding lithospheric plates coexists with intermediate depth seismicity at 300 km in this study

jurassic tectonostratigraphic evolution of the junggar basin nw china a record of mesozoic intraplate deformation in central asia mesozoic basins in northwest china provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study using well seismic outcrop and thermochronology data in the junggar basin and neighboring areas describes the main features of jurassic strata in the basin analyzes the jurassic evolution of the basin and neighboring mountain belts and discusses possible mechanisms of jurassic intraplate deformation in central asia during the early middle jurassic episodic uplift of surrounding mountain belts kept the junggar basin a contractional closed basin and alluvial fan fluvial delta and lacustrine depositional environments successively developed from surrounding ranges to the central basin during the late jurassic the western and central parts of the basin were folded and uplifted and deposition migrated mainly to the eastern basin during the latest jurassic earliest cretaceous pre cretaceous strata in the eastern and northeastern junggar basin were folded and uplifted and coarse grained sediments were transported from surrounding uplifts to the central basin we suggest that jurassic episodic deformation events in the junggar basin and other areas of central asia are related to the qiangtang collision during the late triassic early jurassic the closure of the western mongol okhotsk ocean at the early middle jurassic boundary a collision of a microcontinent in the pamir with the southern asian margin during the late middle jurassic early late jurassic the collision of the kolyma omolon block with siberia at the end of the jurassic and the subsequent closure of the eastern mongol okhotsk ocean during the latest jurassic earliest cretaceous

multi element variations in olivine as geochemical signatures of ni cu sulfide mineralization in mafic magma systems examples from voisey s bay and pants lake intrusions labrador canada olivine from the olivine gabbro to troctolite intrusions at voisey s bay and at pants lake labrador was analyzed for multiple elements ca sc mg si ti v cr mn fe co ni cu zn sr y and zr with secondary ion mass spectrometry sims both intrusions have similar lithologies and petrographic characteristics and are approximately coeval 1 34 and 1 32 ga respectively members of the mesoproterozoic nain plutonic suite the voisey s bay intrusion hosts a producing economic ni cu sulfide deposit whereas the pants lake intrusion displays evidence of ni cu sulfide mineralization but to date a viable ore deposit has not been discovered olivine from both barren and mineralized lithologies was analyzed to assess the potential of the olivine composition for providing a record of silicate melt evolution and sulfide saturation related to formation of a massive sulfide deposit two detailed transects were sampled using five diamond drill holes that laterally approach the basal massive sulfide in the eastern deeps portion of the voisey s bay intrusion from the barren central part olivine displays distinct trace element distributions that vary coherently with host lithology and proximity to sulfide mineralization in particular olivine shows an increase in fe fo80 to fo60 mn 2500 to 5000 ppm and zn 280 to 700 ppm generally coupled with a decrease in ni 1600 to 900 ppm co 270 to 190 ppm and cr 110 to 45 ppm from barren troctolite normal troctolite nt and weakly mineralized troctolite variable textured troctolite vtt towards the heavily mineralized brecciated basal succession basal breccia sequence bbs the enrichment in fe mn zn is most pronounced in samples that laterally approach but do not directly intersect the massive sulfide deposit at the base of the intrusion particularly in samples from the lower variable textured troctolite and the basal breccia olivine from gabbro lithologies within the basal gabbro bg and upper gabbro ug of the pants lake intrusion is fairly homogeneous fo60 4300 ppm mn 460 ppm zn 340 ppm ni 50 ppm cr with a more evolved composition 2100 ppm ca 20 ppm sc 300 ppm ti 4 ppm y than the average olivine of the voisey s bay intrusion 570 ppm ca 6 ppm sc 65 ppm ti 0 3 ppm y pants lake olivine also commonly lacks the mutually mn zn rich signature of olivine from the basal breccia at voisey s bay that is characteristic of contamination of the parent magma by country rock gneiss and there reflects a close proximity to massive sulfides in conjunction with petrographic observation and the stratigraphic context a multiple element v cr mn fe co ni zn regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the eastern deeps part of the voisey s bay intrusion over a distance exceeding 150 m the compositional variations in olivine from the economic voisey s bay intrusion bimodal and primitive and the mainly barren pants lake intrusion homogeneous and evolved provide potential as a regional scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

queen alexandra range 93148 a new type of pyroxene pallasite trace elements including the rare earth elements were measured in olivine and orthopyroxene from queen alexandra range que 93148 and in olivine from two main group pallasites springwater and mount vernon although que 93148 was originally classified as a lodranite a variety of data including oxygen isotopic compositions goodrich and righter 2000 preclude a genetic relationship with the acapulcoites lodranites incompatible trace element e g ti zr distributions in orthopyroxene do indicate large amounts of melting and are consistent with the ultramafic assemblage observed in this meteorite trace element abundances in olivine are consistent with suggestions that que 93148 may be related to the main group pallasites goodrich and righter 2000 although there are some inconsistencies its trace element distributions are most like those of the pyroxene pallasites suggesting that it may have formed in a similar manner que 93148 may represent a new type of pyroxene pallasite with links to the main group pallasites

new embolomerous tetrapod material and a faunal overview of the mississippian aged point edward locality nova scotia canada embolomerous tetrapods moderately sized to large aquatic predators form a major faunal constituent of permo carboniferous tetrapod communities embolomeres are recognized by their distinct circul

eurydesma lyonia fauna early permian from the itarare group parana basin brazil a paleobiogeographic w e trans gondwanan marine connection abstract here the biocorrelation of the marine invertebrate assemblages of the post glacial succession in the uppermost portion of the late paleozoic itarare group parana basin brazil is for the first time firmly constrained with other well dated gondwanan faunas the correlation and ages of these marine assemblages are among the main controversial issues related to brazilian gondwana geology in total 118 brachiopod specimens were analyzed and at least seven species were identified lyonia rochacamposi sp nov langella imbituvensis oliveira streptorhynchus sp cyrtella sp tomiopsis sp cf t harringtoni archbold and thomas quinquenella rionegrensis oliveira and biconvexiella roxoi oliveira the presence of tomiopsis sp cf t harringtoni and the bivalve atomodesma aphanaia orbirugata harrington in the teixeira soares beds plus myonia argentinensis harrington and heteropecten paranaensis neves et al both of which recorded in deposits in the teixeira soares and mafra beds butia suggests a biocorrelation with the eurydesma fauna from the bonete formation sauce grande colorado basin argentina furthermore the presence of lyonia archbold and praeundulomya cf subelongata dickins in the taciba formation indicates affinities with deposits in the lyons group carnarvon basin and the fossil cliff member perth basin western australia suggesting a late asselian early sakmarian age even more importantly the collected data suggest the existence of an w e trans gondwanan marine seaway between the parana brazil sauce grande colorado argentina huab hardap shale of the dwyka group aranos area namibia southwest africa the carnavon western australia basins and beyond eastward to the cimmerian region a v proto rift system through two major axes of extensional basin development facilitated the w e marine connection main axes formed by a north northwesterly trending axis paralleling the future south atlantic and a broadly north northeasterly trending line of separation related to the future indian ocean this proto rift system coupled with a sea level rise of at least 100 m favored the establishment of a long narrow shallow seaway allowing the exchange of eurydesma fauna between eastern and western gondwana

structural and thermal evolution of the karakoram crust prior to the eocene c 50 ma collision of the indian and asian plates the southern margin of asia along the karakoram plate was an andean type margin dominated by tonalitic granodioritic magmatism of jurassic lower cretaceous age hushe gneiss muztagh tower gneiss and k2 ortho gneiss and associated low pressure andalusite staurolite and garnet grade metamorphism m1 following india asia collision crustal shortening thickening and regional barrovian metamorphism m2 occurred between 50 37 ma thermobarometry of kyanite grade metapelites indicate burial to depths of around 30 35 km simultaneous solution of the garnet biotite geothermometer with the garnet muscovite biotite plagioclase and garnet ai 2 sio 5 quartz plagioclase geobarometers indicates peak m2 p t conditions of 696 20 c at 8 6 0 7kbar 860 mpa temperatures may have exceeded 700 c in sillimanite grade metapelites to produce in situ partial melting and leucogranitic melt pods peak m2 metamorphism occurred prior to 37 0 8 ma the crystallization age of the mango gusar two mica granite pluton which cross cuts syn metamorphic deformation fabrics post m2 thermal relaxation followed from 37 25 ma after which localized high heat concentrations at the base of the thickened crust caused widespread crustal melting and intrusion of the baltoro granite batholith at 25 21 ma a high temperature low pressure thermal aureole m3 along the northern contact is synchronous with the 21 0 5 ma zircon age of the baltoro granite andalusite hornfels along the northern contact of the batholith mitre thermal aureole indicates maximum pressures of 3 75 kbar 375 mpa a 75 c increase of temperature in kyanite sillimanite grade gneisses approaching the southern granite contact of the baltoro granite is interpreted as the thermal upwarping of pre 37 ma barrovian metamorphic m2 isograds around the 21 ma contact aureole m3 isotherms

early cretaceous granitoids in the southern pamir implications for the meso tethys evolution of the pamir plateau abstract although it is generally accepted that the pamir was formed by long term terrane drifting and accretion to the south margin of the asia the tectonic evolution during the mesozoic remains unclear the voluminous cretaceous intrusions in the southern pamir karakorum provide key information for understanding the mesozoic evolution in this region in this contribution we report detailed petrography ages mineral geochemistry whole rock elemental and sr nd geochemistry and in situ zircon lu hf isotopic compositions of the early cretaceous granitoids from the chinese wakhan corridor southern pamir these granitoids are composed primarily of granodiorite and minor monzogranite and host dioritic enclaves the granitoids were emplaced at 107 102 ma based on their zircon u pb ages they have 63 73 wt sio2 mg between 39 and 53 and acnk mostly lower than 1 1 and are i type granites the granitoids display arc like geochemical signatures characterized by lree enriched patterns variable negative eu anomalies lan ybn 11 38 23 27 eu eu 0 36 0 74 and a significant nb ta trough nb la 0 24 0 41 isotopically the granitoids have negative whole rock end t 8 73 7 35 and zircon ehf t 17 7 5 3 values the coeval dioritic enclaves ca 104 ma contain 57 63 wt sio2 and have high mg 46 57 low cr 6 86 79 50 ppm and ni 2 88 10 00 ppm these enclaves exhibit arc like trace element patterns nb la 0 34 0 43 with variable negative eu anomaly eu eu 0 52 0 87 uniform whole rock end t 4 74 4 73 and a large range of zircon ehf t values 13 3 3 7 in line with their rock association and geochemistry we suggest that the dioritic enclaves were derived from melting of a phlogopite bearing mantle source modified by subduction related process followed by fractional crystallization and later assimilation by granitic hosts these early cretaceous granitoids were most likely generated by partial melting of the precambrian lower crust with variable involvement of mafic magma parental to the dioritic enclaves our new data combined with the previous studies reveal that the widespread early cretaceous magmatism in the southern pamir karakorum were most likely generated by flat slab subduction of the meso tethys ocean during the cretaceous

clinopyroxene ree distribution coefficients for shergottites the ree content of the shergotty melt abstract ree distribution coefficients were measured between synthetic pyroxenes and melts similar in composition to the inferred shergotty intercumulus liquid by in situ analysis with the electron microprobe using samples doped to per cent concentration levels these coefficients exhibit a strong positive correlation with pyroxene wollastonite content recommended values for augites similar in composition to the shergotty cumulus augite cores wo32en48 are d la 0 023 d ce 0 039 d nd 0 10 d sm 0 17 d eu 0 16 d gd 0 20 d yb 0 29 and d lu 0 30 recommended values for pigeonites similar in composition to the shergotty cumulus pigeonite cores wo12en58 are d la 0 002 d ce 0 004 d nd 0 019 d sm 0 031 d yb 0 13 and d lu 0 13 these values resemble distribution coefficients measured for terrestrial basalts of higher mg fe than the shergotty melt rather than those of more evolved siliceous rocks of similar mg fe to the shergotty melt thus it appears that mg fe is considerably less important than other factors in determining distribution coefficient values for pyroxenes ree abundances were computed for the shergotty intercumulus melt using distribution coefficients measured for the natural phase compositions these computed abundances display lree depletion such lree depleted abundance patterns cannot be generated by simple partial melting of a mafic mineral assemblage having the lree enriched patterns required for a two stage sm nd evolution history this result implies that either 1 the melting process was complex e g continuous melting 2 the source region had a more complex history than that of the simple 2 stage model or 3 shergotty does not satisfy the closed system assumption of the calculation and has suffered post magmatic lree enrichment

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

chondrule thermal history from unequilibrated h chondrites a transmission and analytical electron microscopy study sixteen texturally different porphyritic barred radial cryptocrystalline feo rich chondrules from the unequilibrated ordinary chondrites brownfield frontier mountain fro 90003 and fro 90032 were characterized by optical and scanning electron microscopy and then thoroughly studied by transmission and analytical electron microscopy nanotextural and nanochemical data indicate similar thermal evolution for chondrules of the same textural groups minor yet meaningful differences occur among the different groups olivine is the earliest phase formed and crystallizes between 1500 and 1400 c protoenstatite crystallizes at temperatures higher than 1350 1200 c it later inverts to clinoenstatite in the 1250 1200 c range enstatite is surrounded by pigeonitic or less frequently augitic rims the minimal crystallization temperature for the rims is 1000 c high pigeonite later inverts to low pigeonite between 935 and 845 c the outer pigeonitic or augitic rims are constantly exsolved producing sigmoidal augite or enstatite precipitates sigmoidal precipitates record exsolution temperatures between 1000 and 640 c cooling rate determined using the speedometer based upon ortho clinoenstatite intergrowth was in the order of 50 3000 c h at the clinoenstatite orthoenstatite transition temperature close to 1250 1200 c but decreased to 5 10 c h or slower at the exsolution temperature between 1000 and 650 c thus revealing nonlinear cooling paths nanoscale observations indicate that the individual chondrules formed and cooled separately from 1500 down to at least 650 c accretion into chondritic parent body occurred at temperatures lower than 650 c

early permian pangea b to late permian pangea a the pre drift wegenerian model of pangea is almost universally accepted but debate exists on its pre jurassic configuration since tedirving introd ucedpangea b by placing gond wana farther to the east by v3000 km with respect to laurasia on the basis of paleomagnetic data new paleomagnetic data from radiometrically dated early permian volcanic rocks from parts of adria that are tectonically coherent with africa gondwana integrated with published coeval data from gondwana and laurasia again only from igneous rocks fully support a pangea b configuration in the early permian the use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for pangea b the ultimate option to reject pangea b is to abandon the geocentric axial dipole hypothesis by introducing a significant non dipole zonal octupole component in the late paleozoic time averaged geomagnetic field we demonstrate however by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from gondwana as well as laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for pangea b in the early permian we therefore regard the paleomagnetic evidence for an early permian pangea b as robust the transformation from pangea b to pangea a took place during the permian because late permian paleomagnetic data allow a pangea a configuration we therefore review geological evidence from the literature in support of an intra pangea dextral megashear system the transformation occurred after the cooling of the variscan mega suture andlasted v20 myr in this interval the neotethys ocean opened between india arabia and the cimmerian microcontinents in the east while widespread lithospheric wrenching and magmatism took place in the west around the adriatic promontory the general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right lateral shear couple between gondwana and laurasia during the permian transcurrent plate boundaries associated with the pangea transformation reactivated variscan shear zones andwere subsequently exploitedby the opening of western neotethyan seaways in the jurassic