permian paleomagnetism of the tien shan fold belt central asia post collisional rotations and deformation permian volcanic and sedimentary rocks were sampled from eight localities in the western and central parts of the tien shan fold belt high temperature sometimes intermediate temperature components isolated from these rocks at seven localities after stepwise thermal demagnetization are shown either to predate folding or be acquired during deformation the conglomerate test at some localities is positive the observed inclinations fit rather well with the eurasian reference data whereas the declinations are strongly deflected westward westerly declinations have already been observed from the other parts of the tien shan from the turan plate in the west to the northern rim of tarim and the urumque area in the east our analysis shows that a considerable counterclockwise rotation of the tien shan fold belt as a rigid body is geologically improbable we hypothesize that a sinistral shear zone existed over the fold belt thus accounting for systematically westerly declinations this zone is about 300 km wide and is traced along the tien shan fold belt for 2500 km a large area of permian alkali magmatism in the west and central tien shan is interpreted as an extensional domain conjugated with the shear zone this shear zone can be accounted for by translation of the kara kum and tarim blocks along the eurasian boundary after their oblique collision in the late carboniferous two phases of rotation are recognized in the tien shan the earlier rotation took place under shear strain during the d3 stage of deformation in the artinskian ufimian the later rotation is connected with transpression d4 stage of deformation and could occur from the late permian to early jurassic 1999 elsevier science b v all rights reserved

sims zircon u pb geochronology and sr nd isotopes of ni cu bearing mafic ultramafic intrusions in eastern tianshan and beishan in correlation with flood basalts in tarim basin nw china constraints on a ca 280 ma mantle plume zircon sims u pb dating of the poshi hongshishan bijiashan and huangshan ni cu bearing and xiangshan ni cu ti fe bearing mafic ultramafic intrusions in the eastern tianshan and beishan rift yields a relatively restricted range of 278 6 ma to 284 0 ma the histogram of compiled age data of basalts in the tarim basin and mafic ultramafic intrusions in the eastern tianshan and beishan rift has a peak of 280 ma which probably represents the time of mantle plume activity the basalts have lower end t values in the range of 9 2 1 7 and mg of 2 wt indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting the mafic ultramafic intrusions have higher end t of 1 3 11 2 and mg of 33 90 and lower tio2

postcollisional magmatism in the south tien shan variscan orogenic belt kyrgyzstan evidence for high temperature and high pressure collision abstract the south tien shan collisional belt consists of two segments divided by the largest in the central asia talas fergan diagonal dextral strike slip fault the narrow eastern kokshal segment where the late carboniferous collision was followed by continental subduction of the precambrian tarim platform beneath the caledonian kazakh continent is characterized by overthickened 60 65 km crust and ultrahigh pressure coesite eclogite regional metamorphism the permian postcollisional magmatism is represented there by a small volume of relatively cool two mica peraluminous leucogranites moderate volumes of k rich calk alkaline transitional from i to s type granites and several large plutons of a type rapakivi granites the latest could have formed by a two step process involving 1 syncollisional submersion of the tarim platform granulitic basement into the mantle accompanied by considerable heating of the source rocks 2 rapid postcollisional exhumation accompanied by decompression and extensive high degree of melting in the western alay segment which is much wider the collision was not followed by continental subduction the thickness of crust decreases westward dramatically from 60 to 45 km the alay segment is characterized by the high temperature low pressure regional metamorphism and significant volume of permian shoshonitic ultrapotassic magmatism connected with postcollisional strike slip tectonics the shoshonitic magmatism is indicative of lithosphere delamination and input of mantle derived melts and heat into the crust in contrast to the kokshal segment the postcollisional granitic magmatism in the alay segment is represented by relatively hot cordierite and sillimanite bearing strongly peraluminous s type granites locally rooted in the high temperature low pressure metamorphic rocks and large volume of calc alkaline i type granitoides of mixed crust mantle origin

possible source dichotomy of contemporaneous post collisional barren i type versus tin bearing a type granites lying on opposite sides of the south tien shan suture abstract two granitoid complexes in the eastern kyrgyz tien shan situated north and south of the southern tien shan suture were studied the suture formed as a result of the closure of the turkestan ocean and collision of the tarim microcontinent in the south with the middle tien shan in the north the timing of collision is still disputed the deformed calc alkaline terektinsky complex situated immediately north of the suture represents one of the largest shear zone related intrusions in the tien shan 130 5 15 km in size small stocks of evolved a type granites of the inylchek complex hosting economic tin mineralization were emplaced immediately south of the suture opposite the terektinsky complex two samples from the terektinsky complex and 3 samples from three a type stocks were collected for u pb zircon shrimp ii geochronology the ages at 2 level obtained for the terektinsky complex north of the suture 294 5 ma and 291 5 ma and ages of the small granite bodies south of the suture 299 4 ma 295 4 ma 289 6 ma tashkoro inylchek and maida adir intrusions respectively are nearly identical within error limits they show that the southern tien shan suture in the eastern kyrgyz tien shan had already formed by 295 ma and had evolved into a transcrustal mega shear zone controlling emplacement of granitoids geochemical distinction between the two magmatic systems is based on 10 original bulk and trace analyses of rocks from this study and on a large dataset extracted from previously published research and unpublished reports geochemically the rocks of the terektinsky complex comprise calc alkaline high potassium i type series while the granites of the inylchek complex are typical a type granites with an elevated alumina saturation index and higher boron contents compared to a standard a type rapakivi granite contrasting metallogenic features of the two granitoid complexes south and north of the southern tien shan suture are defined by their sources a fertile fore arc complex and or passive margin sediments of tarim to the south and barren metamorphic precambrian basement of the middle tien shan to the north

ongonite and topazite dikes in the flying w ranch area tonto basin arizona the petrogenesis of the topaz rich ongonite and topazite dikes in the flying w ranch area tonto basin arizona was investigated and the possible origin of the topaz in the flying w rhyolite is discussed the field textural geochemical and mineralogical characteristics of the topaz bearing dikes in the flying w ranch area all were found to support the genesis of the topaz bearing bodies from a magma the evidence obtained contradicts an origin for these rock types by greisenization or veining

the structural geometry and evolution of foreland thrust systems northern virginia seismic reflection data reveal that the structural geometry of the central appalachians of northern virginia consists of three distinct thrust systems each thrust system is characterized by a unique internal geometry the blue ridge thrust sheet is a composite thrust sheet composed primarily of imbricated precambrian crystalline rocks it over rode cambrian ordovician carbonates and formed a sheared basement cored fault bend fold thrusts within the sheet may be taconic and earliest alleghanian whereas final thrusting and emplacement of the sheet were probably slightly younger but still early alleghanian the north mountain thrust sheet is characterized by imbricated cambrian ordovician carbonates that are deformed into large amplitude mode ii fault bend folds and fault propagation folds rocks of this sheet were transported more than 60 km across a similar section of carbonates the leading edge of the north mountain thrust sheet was deformed into a fold with a mode ii fault bend fold geometry and was juxtaposed against middle paleozoic rocks the middle paleozoic rocks occur in a ramp across which displacement along the north mountain thrust was transferred to a higher detachment more than 60 km of cover rocks displaced during the emplacement of the north mountain thrust sheet either were transported across this ramp and thrust over a similar section in the western valley and ridge province or were backthrust above the sheet the timing for imbrication and emplacement of the north mountain thrust sheet is probably main phase alleghanian the lower carbonate duplex extends from beneath the blue ridge and north mountain thrust sheets westward across the western valley and ridge province the lower carbonate duplex is characterized by imbricated cambrian ordovician carbonates that form low amplitude fault bend folds this thrust system also probably formed during main phase alleghanian deformation

late precambrian crustal extension preserved in fries fault zone mylonites southern appalachians mesoscopic and microscopic kinematic indicators throughout ca 690 ma peralkaline plutonic rocks in the footwall of the fries fault zone blue ridge province southwest virginia record dip slip normal southeast down movement under greenschist facies deformation conditions mylonites cataclasites and associated precursor mineralized fractures and dikes are consistent in geometry and movement history with extensional faulting although over 50 km of northwest directed thrust movement was proposed by earlier workers for parts of the 300 km long rockfish valley fries fault system along major sections of the fries fault the only concrete evidence for thrusting is in the form of late stage shear bands that crosscut the earlier extension related mylonitic fabric we suggest that the entire rockfish valley fries fault zone formed during the late precambrian extension of the now eastern margin of the north american craton to create the iapetus ocean and was locally reactivated as a thrust zone during paleozoic time

genesis of the maikhura tungsten tin skarn deposit tajik tien shan insights from petrology mineralogy and fluid inclusion study abstract the maikhura w sn skarn deposit is situated in the gissar segment of the southern tien shan it associates with a late carboniferous early permian composite granitoid pluton which includes earlier ilmenite series transitional metaluminous to peraluminous i type granodiorite and later magnetite series biotite to biotite tourmaline granite leucogranite the oxidized granitic intrusions exhibit a type granite affinity and define a geochemically and genetically distinct group of w sn deposits the deposit incorporates both pyroxene and garnet dominant prograde and retrograde skarns with scheelite and locally magnetite overprinted by highly reduced pyrrhotite stable post skarn mineral assemblages of hydrosilicate and phyllic alteration stages containing scheelite cassiterite and sulfides the fluid inclusions data indicate the involvement of carbonic free aqueous moderately saline 9 9 16 wt nacl eq high pressure 2 1 0 5 kbar hot fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid evolved into a sodic chloride slightly less saline 8 6 11 wt nacl eq lower pressure 1 7 0 5 kbar cooler fluids toward the retrograde skarn stage this stage was characterized by deposition of scheelite in association with magnetite the hydrosilicate propylitic alteration was formed from a low salinity ca enriched homogenous aqueous carbonic methane rich fluid at lower temperatures 350 400 c with precipitation of scheelite and cassiterite particularly in phlogopite chlorite oligoclase quartz assemblage corresponding ph decrease explains the trend toward overlapping fields of insoluble cassiterite and scheelite the phyllic alteration assemblages were formed from a boiling aqueous carbonic co2 dominated low salinity fluid at temperatures of 310 250 c and pressure of 1 85 0 1 kbar the alteration evolving from chlorite through muscovite to albite dominant paragenesis indicates a trend toward higher ph less acidic conditions and was accompanied by precipitation of scheelite and cassiterite with further deposition of sulfides a homogeneity of 34s values suggests sulfur isotope homogenization in a magmatic chamber whereas their proximity to the meteorite standard supports a magmatic source of sulfur the depletion in heavy sulfur isotope of sulfides from hydrosilicate propylitic alteration 34s 1 8 to 0 7 to sulfides from phyllic alteration 34s 0 1 to 0 8 is consistent with the evolution from ilmenite series to magnetite series magmatic source

structural evolution of the pulaski thrust system southwestern virginia the pulaski fault system is a complex series of alleghanian thrusts which has juxtaposed rocks of the pulaski thrust sheet over rocks as young as early to middle mississippian maccrady formation of the saltville thrust sheet the salem branch a later major branch of the pulaski fault system within the pulaski thrust sheet displaced the complexly deformed plate containing a broken formation a lithotectonic assemblage of complexly folded and faulted elbrook and rome carbonates and shales with associated breccias over rocks as young as early mississippian lower price formation of the salem synclinorium the classic ubiquitous max meadows breccias generally are confined to the broken formation which forms the basal part of the complexly deformed plate and which is interpreted as an exhumed lower level decollement zone formed during an earlier alleghanian stage and transported during a later alleghanian stage of deformation to a much higher structural level minimum displacement of the complexly deformed plate is on the order of 100 110 km on the basis of a new palinspastic reconstruction of the pulaski thrust sheet on the basis of this reconstruction and of two balanced and restored cross sections for the western portion of the valley and ridge minimum shortening for the pulaski thrust sheet is 80 whereas that for the western part of the valley and ridge province is only 10 20 the pulaski fault system is interpreted to have originated below the appalachian wide basal decollement zone near the contact between the cambrian rome and elbrook formations

geology mineralization and fluid inclusion characteristics of the koitash redox intermediate w mo skarn and w au stockwork deposit western uzbekistan tien shan the koitash w mo skarn deposit in the tien shan gold belt contained resources of 60 kt wo3 in altered skarn averaging 0 56 wo3 and 0 029 mo and an additional 42 kt wo3 in separate zones of phyllic alteration averaging 0 30 wo3 0 97 g t au 0 67 cu and 0 02 bi it is related to an early permian multiphase granodiorite granite leucogranite pluton that is composed of medium to high k transitional metaluminous to peraluminous weakly oxidized weakly reduced ilmenite titanite series granitoids the pluton was emplaced in a tectonic domain with inferred ancient continental crust the latter coupled with possible ascent of hot asthenospheric material has likely defined a distinct w mo au metallogenic assemblage forming in a post collisional environment the deposit includes redox intermediate prograde and retrograde pyroxene garnet skarns partially overprinted by propylitic and phyllic alteration assemblages comprising scheelite molybdenite cu bi ag te sulfides and sulfosalts as well as native bi and au compositional similarities between w mo deposits containing au w cu bi mineralization in late alteration assemblages and coeval intrusion related au dominant with minor w bi etc deposits in the region support their possible genetic links fluid inclusion data indicate the involvement of carbonic free moderately saline 10 5 15 0 to 8 0 11 7 wt nacl eq high pressure 2000 to 1500 bars hot 550 600 c aqueous fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid was followed by moderately saline ca rich 14 16 wt nacl 19 21 wt cacl2 lower pressure 800 bars fluids toward the retrograde skarn stage with the deposition of scheelite in association with pyrrhotite and molybdenite locally with minor fluorite propylitic quartz amphibole chlorite oligoclase calcite with scheelite pyrrhotite locally molybdenite assemblages formed from boiling high methane aqueous carbonic fluids at temperatures of 370 400 c and pressures of 950 1000 bars phyllic quartz sericite fe carbonate locally with albite fluorite chlorite scheelite molybdenite and other sulfides also bi and au minerals alteration assemblages initially formed from homogeneous and then from boiling aqueous carbonic low salinity fluids at temperatures of 365 370 to 300 315 c and pressures of 2000 bars 34s increases from retrograde skarn 34s 2 0 to 2 3 through propylitic 34s 3 0 to 3 4 to phyllic alteration 34s 4 2 to 4 7 stages

comparison of proterozoic and phanerozoic rift related basaltic granitic magmatism abstract this paper compares the 1 67 1 47 ga rapakivi granites of finland and vicinity to the 1 70 1 68 ga rapakivi granites of the beijing area in china the anorogenic 130 ma granites of western namibia and the 20 15 ma granites of the colorado river extensional corridor in the basin and range province of southern nevada in finland and china the tectonic setting was incipient aborted rifting of paleoproterozoic or archean continental crust in namibia it was continental rifting and mantle plume activity that led to the opening of southern atlantic at 130 ma the 20 15 ma granites of southern nevada were related to rifting that followed the triassic paleogene subduction of the farallon plate beneath the southwestern united states in all cases extension related magmatism was bimodal and accompanied by swarms of diabase and rhyolite quartz latite dikes rapakivi texture with plagioclase mantled alkali feldspar megacrysts occurs in varying amounts in the granites and the latest intrusive phases are commonly topaz bearing granites or rhyolites that may host tin tungsten and beryllium mineralization the granites are typically ferroan alkali calcic metaluminous to slightly peraluminous rocks with a type and within plate geochemical and mineralogical characteristics isotope studies nd sr suggest dominant crustal sources for the granites the preferred genetic model is magmatic underplating involving dehydration melting of intermediate felsic deep crust juvenile mafic magma was incorporated either via magma mingling and mixing or by remelting of newly hybridized lower crust in namibia partial melting of subcontinental lithospheric mantle was caused by the tristan mantle plume in the other cases the origin of the mantle magmatism is controversial for the fennoscandian suites extensive long time mantle upwelling associated with periodic migrating melting of the subcontinental lithospheric mantle governed by heat flow and deep crustal structures is suggested

displacement and strain patterns from naturally occurring shear zone terminations abstract strain distribution patterns are described from several naturally occurring ductile shear zone terminations and a two fold classification is suggested type i termination patterns show a symmetrical decrease in strain area and intensity and are associated with very low shear strain values in the main shear zone the more common type ii termination patterns show a symmetrical increase in strain area with decrease in strain intensity some brittle ductile examples of type ii terminations contain secondary shears that resemble splay faults all the available evidence suggests that the deformation near the terminations of these shear zones is not plane strain nor do the observed strain patterns readily fit the existing theoretical models

changes in dip of subducted slabs at depth petrological and geochronological evidence from hp uhp rocks tianshan nw china article high resolution seismic imaging has previously revealed sudden changes in the dip of subducted oceanic plates this kinking feature is crucial because in many subduction zones it is thought to coincide with the disappearance of the low velocity layers associated with subducted oceanic crust in this study we present petrological evidence for this phenomenon derived from oceanic blueschist and eclogite facies rocks from the chinese tianshan the investigated samples span a large range of peak metamorphic conditions with temperatures between 330 and 580 c at 1 5 to 2 3 gpa such variable peak metamorphic conditions together with the intimate interlayering of high and ultrahigh pressure rocks have also been reported from other tianshan localities these observations suggest that the rocks were derived from varying depths within the subduction zone and then juxtaposed during exhumation in the subduction channel multi point lu hf isochrons from four high pressure rocks yield consistent garnet growth ages of 313 12 315 8 2 9 313 9 4 8 and 315 2 1 6 ma these inconjunctionwiththe 311 maclusterof published 40

postcollisional granites in the south tien shan variscan collisional belt kyrgyzstan abstract two major types of the potassium rich postcollisional granites of permian age were studied in the south tien shan variscan collisional belt the first type metaluminous granites of the jangart complex are located along the southeastern boundary of this belt with the precambrian tarim block the plagioclase rims on k feldspar megacrysts rapakivi texture extremely high feot feot mgo ratio indications of the low h2o and o2 fugacities high concentrations of the incompatible elements especially light rare earth elements lree ba nb along with heightened contents of the compatible elements especially ni cr and moderately initial 87sr 86sr ratio sr0 0 7075 make those granites similar to other rapakivi granites the second type peraluminous granites of the inylchek complex is located along the northwestern boundary of the belt with the caledonian kazakh microcontinent those granites are rich in f b li rb cs sn ta and heavy rare earth elements hree but are poor in ba sr ni and cr and are characterized by the relatively high initial 87sr 86sr ratio sr0 0 7098 li mica granites are distributed widely among them the granites of a transitional type uchkoshkon complex occupy an intermediate geographic position between major granite types the initial sr isotopic composition of the transitional granites varies widely sr0 from 0 7080 to 0 7256 the variation in chemical composition of the coeval postcollisional granites across the collisional belt together with the variability of initial sr isotopic ratios of the transitional granites are thought to indicate basement heterogeneity this heterogeneity in turn is probably related to thrusting of the tarim block under south tien shan during the collision

geology mineralization and fluid inclusion characteristics of the chorukh dairon w mo cu skarn deposit in the middle tien shan northern tajikistan abstract the chorukh dairon deposit is part of the metallogenic belt of w mo cu mo au w and au deposits along the late paleozoic active continental margin of the tien shan it is related to the late carboniferous multiphase pluton with successive intrusive phases of early monzogabbro through monzonite quartz monzonite to monzogranite and leucogranite and the latest lamprophyre dikes the deposit is an example of complex w mo cu magmatic hydrothermal system related to magnetite series shoshonitic igneous suite it contains zones of w cu mo oxidized prograde and retrograde skarns with abundant scapolite plagioclase k feldspar andradite garnet magnetite as well as molybdoscheelite and minor chalcopyrite and molybdenite skarns are overprinted by hydrosilicate alteration assemblages with amphibole chlorite epidote quartz calcite scapolite albite scheelite and chalcopyrite and are cut by quartz carbonate barite fluorite sulfide veins the fluid evolution included a release of high temperature 400 500 c high pressure 900 1100 to 700 800 bars high salinity magmatic hydrothermal aqueous chloride fluid with its direct separation from crystallizing magma and formation of prograde and retrograde skarns fluid enrichment in ca up to 15 22 wt cacl 2 at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid in contrast hydrosilicate alteration assemblages were formed at lower temperatures 350 400 c initially from a homogenous and then from a boiling ca rich 20 22 wt cacl 2 magmatic hydrothermal fluid with the latter contributing to the most intense scheelite deposition the stable isotope data 13 c co 2 3 0 0 5 and 18 h 2 o 6 5 0 5 34 s 7 5 to 7 7 obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate possibly evaporites although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber some light sulfur isotope enrichment of sulfides from the quartz carbonate barite fluorite sulfide veins 34 s 6 0 to 6 1 may be linked to the evolution of the magmatic source toward more mantle related sulfur species as these veins were formed after emplacement of the late mafic lamprophyre dikes

chemical changes associated with deformation of granites under greenschist facies conditions the example of the zawidow granodiorite se lusatian granodiorite complex poland abstract small scale subvertical retrograde shear zones are developed in the zawidow granodiorite located in the eastern part of the lusatian massif southwest poland heterogeneous deformation under conditions of greenschist facies metamorphism has produced mylonite zones that show a broad range of microstructural development three fabric types in the granodiorite deformation have been distinguished a weakly deformed protolith b moderately deformed in lens shaped domains c strongly foliated in fabric types b and c whole rock analyses show a decrease in cao mno cr sr pb whereas na2o and sio2 increase slightly overall al2o3 tio2 and zr remain essentially constant this pattern of element variation is consistent with the observed feldspar breakdown and increase of sericite and also with the transformation of biotite into chlorite mass balance calculations based on major and trace element geochemistry indicate constant volume or less than 10 volume loss from this study it is apparent that a low grade metamorphic deformation event does not have to have a profound influence on whole rock geochemical composition

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

hercynian post collisional magmatism in the context of paleozoic magmatic evolution of the tien shan orogenic belt abstract the hercynian tien shan tianshan orogen formed during late palaeozoic collision between the karakum tarim and the kazakhstan paleo continents in order to constrain timing of hercynian post collisional magmatism 27 intrusions were sampled for u pb zircon dating along a ca 2000 km long profile in uzbekistan and kyrgyzstan the samples were dated utilizing sensitive high resolution ion microprobe shrimp ii the obtained ages together with previously published age data allowed the timing of hercynian post collisional magmatism to be constrained and interpreted in the context of the paleozoic magmatic evolution of the region apart from hercynian post collisional magmatism two older magmatic episodes have been recognized and the following sequence of events has been established 1 approximately 10 ma after cessation of continuous caledonian magmatism a number of late silurian early devonian intrusions were emplaced in the middle and northern tien shan terranes between 420 and 390 ma the intrusions probably formed in an extensional back arc setting during coeval subduction under the margins of caledonian paleo kazakhstan continent 2 the next relatively short late carboniferous episode of subduction under paleo kazakhstan was registered in the kurama range of the middle tien shan calc alkaline volcanics and granitoids with ages 315 300 ma have distinct metallogenic affinities typical for subduction related rocks and are not found anywhere outside the middle tien shan terrane west of the talas farghona fault 3 the early permian hercynian post collisional magmatism culminated after the closure of the paleo turkestan ocean and affected the whole region across terrane boundaries the post collisional intrusions formed within a relatively short time span between 295 and 280 ma the model for hercynian post collisional evolution suggests that after collision the tien shan was affected by trans crustal strike slip motions which provided suitable conduits for ascending asthenospheric material and heat influx in the crust this produced both granitoid magmas and hydrothermal fluid flow as a result post collisional intrusions and orogenic au deposits known in the region formed coevally and were tectonically controlled 4 between 240 and 220 ma a triassic thermal event affected the region resulting in resetting and growth of new zircon grains which is detected on a regional scale probably the influx of heat into the crust during the triassic was tectonically focused and varied significantly in different terranes in the region under investigation the triassic thermal event was not accompanied by any significant magmatic activity thus after cessation of hercynian post collisional magmatism ca 280 ma ago there was a long magmatically quiet period in the tien shan

microstructural evolution and rheology of quartz in a mid crustal shear zone abstract we present microstructural and crystallographic preferred orientation cpo data on quartz deformed in the middle crust to explore the interaction and feedback between dynamic recrystallization deformation processes and cpo evolution the sample investigated here is a moderately deformed quartz rich mylonite from the blue ridge in virginia we have created high resolution crystallographic orientation maps using electron backscatter diffraction ebsd of 51 isolated quartz porphyroclasts with recrystallized grain fractions ranging from 10 to 100 recrystallized grains are internally undeformed and display crystallographic orientations dispersed around the orientation of the associated parent porphyroclast we document a systematic decrease in fabric intensity with recrystallization suggesting that progressive deformation of the recrystallized domains involves processes that can weaken a pre existing cpo relationships between recrystallization fraction and shear strain suggest that complete microstructural re equilibration requires strains in excess of 5 variation in the degree of recrystallization implies that strain was accumulated heterogeneously and that a steady state microstructure and rheology were not achieved

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

late palaeozoic and meso cenozoic tectonic evolution of the southern kyrgyz tien shan constraints from multi method thermochronology in the trans alai turkestan alai segment and the southeastern ferghana basin abstract in this paper we present new geochronological and thermochronological data from the turkestan alai segment of the southern kyrgyz tien shan the ferghana basin transition and the trans alai pamir foreland in the southern and central parts of the alai range towards the alai valley mainly post collisional granitoids were targeted for zircon u pb dating by laser ablation inductively coupled plasma mass spectrometry la icp ms apatite fission track aft and apatite u th sm he ahe thermochronology these granitoids and their thermally metamorphosed contact aureole yielded middle permian zircon crystallization ages of 284 4 to 264 5 ma aft ages both using the traditional external detector approach as well as using la icp ms for these samples are constrained to the miocene and range between 22 3 1 1 and 8 4 0 3 ma while the ahe ages are somewhat younger between 12 5 0 8 and 5 0 0 3 ma this low temperature thermochronological data suggests an early miocene onset of denudation in this area in the tien shan orogen continuing through the miocene and pliocene this denudation is interpreted as a response to reactivation of the mountain belt in the framework of india eurasia convergence and specific to this region of the pamir tien shan interaction on the northern slopes of the alai range at the edge of the ferghana basin a late palaeozoic conglomerate yielded a reset early cretaceous aft age of 118 7 ma pointing to an older denudation event with respect to those identified in the southern and central parts of the alai range a mesozoic sediment sample from the same region only contains a late triassic age component of 223 ma mesozoic and cenozoic age components on the other hand are all detected in the cenozoic sediments of the trans alai range at the transition between the southern alai valley and the pamirs revealing several meso cenozoic denudation events in the adjoining basement source rocks the age components in these detrital apatites are 207 ma 75 ma 18 ma and 3 ma

geology mineralization and fluid inclusion study of the kuru tegerek au cu mo skarn deposit in the middle tien shan kyrgyzstan the kuru tegerek cu au mo deposit is situated in a system of late carboniferous subduction related magmatic arcs of the middle tien shan which together constitute a metallogenic belt of cu au mo w porphyry with local skarns deposits the deposit is related to magnetite series gabbro diorite to tonalite intrusion it contains prograde magnesian and calcic skarns with abundant magnetite associated with gabbro diorite and retrograde skarn with cu mineralization formed after intrusion of tonalite subsequent propylitic alteration introduced abundant chalcopyrite and pyrrhotite and native au culminating in zones overprinting magnetite and garnet skarn later quartz muscovite carbonate veins formed after intrusion of late mafic quartz monzogabbro dikes contain chalcopyrite pyrite arsenopyrite and other sulfides and sulfosalts tellurides and native au the earliest retrograde skarn garnet contains gaseous low salinity 1 7 3 4 wt nacl eq fluid inclusions homogenizing at 460 500 c into vapor indicating that the early fluid released from crystallizing magma was a low density vapor it was followed by more saline 4 0 5 0 wt nacl eq high temperature 400 440 c aqueous fluid as fluid release from the magma progressed boiling of this fluid at temperatures of 420 to 370 c and a pressure of 350 300 bar produced a low salinity 0 6 1 2 wt nacl eq essentially gaseous and high salinity from 39 to 31 wt nacl eq brine with possible metal including cu partitioning into both gaseous and aqueous saline phases boiling was coeval with sulfide deposition in the retrograde skarn the latest episode of the retrograde skarn stage included direct separation of saline 40 42 wt nacl eq fluid from crystallizing magma the separation of saline 40 to 14 wt nacl eq fluids from a crystallizing magmatic melt continued during the propylitic stage when fluid cooling from 370 to 320 c together with decreasing fo2 caused cu and especially au precipitation a new influx of possibly magma derived low salinity 4 5 6 7 wt nacl eq aqueous and then nacl co2 h2o fluids corresponds to the phyllic quartz muscovite carbonate sulfide stage these fluids may have a deeper source associated with the late mafic quartz monzogabbro dikes fluid cooling from 340 to 255 c and boiling of the nacl co2 h2o fluid together with increased fs2 increased the au endowment

state of strain in mylonites from the western blue ridge province southern appalachians the role of volume loss abstract this study examines the state of finite strain in quartzo feldspathic mylonites from two localities in the western blue ridge province of the southern appalachians mineral shape fabric and whole rock chemical and modal data suggest that the mylonites deformed by inhomogeneous shortening normal to the foliation and progressive shear parallel to the foliation the deformation involved substantial bulk rock volume loss strain was partitioned between solution transfer processes in feldspar and dislocation creep processes in quartz and micas at temperatures of between 300 and 450 c initially feldspars underwent grain size reduction by cataclasis but at advanced stages of mylonitization alkali feldspar grains display subrounded oblate shapes 0 k k values 0 2 k 60 bulk volume loss density changes were minor on the basis of feldspar grain shapes and modal and whole rock chemical data volume loss was largely accommodated by fluid infiltration and incongruent dissolution of alkali feldspar producing muscovite and involved the loss of alkalis and silica to the fluid phase the mylonites may have nucleated as solution zones which subsequently underwent strain softening and displacement parallel to the zone boundaries

extensional and contractional deformation in the blue ridge province virginia basement rocks of the blue ridge anticlinorium in central and northern virginia were involved in two temporally distinct deformation episodes the older event is characterized by a locally pervasive low strain fabric and high strain shear zones a preferred grain shape orientation in recovered quartz feldspar and biotite combined with a poorly developed symmetric quartz c axis pattern defines the low strain fabric kinematic indicators are typically symmetric but where asymmetric they consistently indicate top down to the southeast extensional motion discrete shear zones are within and close to late proterozoic plutons kinematic evidence fron these zones records large noncoaxial strains also with a down to the southeast extensional shear sense feldspar microstructures range from cataclastic fractures to complete recovery suggesting that deformation occurred at greenschist to amphibolite grade both low strain foliations and high strain shear zones are cut by paleozoic thrust related tectonites on the basis of kinematic evidence and spatial association with late proterozoic plutons cross cutting relations with thrust related structures and regional geologic relations we suggest that extensional deformation is related to late proterozoic rifting of the laurentian margin the kinematic histories of the rockfish valley fault zone and related shear zones appear to be relatively simple and consistent with paleozoic west to northwest directed thrusting the rockfish valley fault zone does not separate distinctly different basement terranes and thus its displacement is thought to be small mylonitic rocks from this fault zone display crystal plastic deformation in quartz and cataclastic deformation in feldspars under lower to middle greenschist facies conditions solution transfer processes were an important deformation mechanism in these tectonites thrust related mylonitic rocks are overprinted by related cataclasite and semibrittle shear bands suggestive of a transition toward more brittle deformation as the thrust system cut higher in the crust the rockfish valley fault zone appears to predate the formation of the south mountain cleavage in the valley and ridge province but it may be part of a lengthy progressive thrust related deformation

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

solution mass transfer deformation adjacent to the glarus thrust with implications for the tectonic evolution of the alpine wedge in eastern switzerland abstract we have studied aspects of absolute finite strain of sandstones and the deformation history above and below the glarus thrust in eastern switzerland the dominant deformation mechanism is solution mass transfer smt which resulted in the formation of a semi penetrative cleavage our analysis indicates that the verrucano and melser sandstones which lie above the thrust were deformed coaxially with pronounced contraction in a subvertical z direction and minor extension in a subhorizontal x direction trending at 200 most of the contraction in z was balanced by mass loss volume strains averaging 36 below the glarus thrust sandstones of the north helvetic flysch have smaller principal strains but similar volume strains deformation there was also approximately coaxial the x direction is horizontal and trends 160 which is different by 40 from the x direction in the hanging wall the hanging wall of the glarus thrust verrucano and melser sandstones was deformed first after it was accreted deep beneath the alpine wedge continued northward advance of the wedge accomplished in part by motion on the glarus thrust allowed the wedge to override and accrete the north helvetic flysch which then started to form an smt cleavage the difference in x directions may reflect a change in transport direction but this conclusion is difficult to accept since extension was minor and was accommodated by coaxial flattening and not simple shear our work indicates that mass loss volume strains were important in sandstones of the helvetic nappes the missing mass cannot be accounted for at the local scale and appears to have been transported beyond the helvetic zone

volume loss and tectonic flattening strain in granitic mylonites from the blue ridge province central appalachians abstract granitic mylonites from the blue ridge province in the central appalachians demonstrate the contribution of various deformation mechanisms to the strain geometry that developed during greenschist facies deformation in thrust related shear zones strain accumulated through cataclasis in feldspar crystal plastic processes in quartz and a significant contribution of pressure solution in both feldspar and quartz strain analysis was performed using r f f techniques on quartz grain shapes and by measuring stretched and boudinaged feldspars petrographic and geochemical evidence indicates that deformation ranged from isovolumetric to upwards of 60 bulk rock volume loss quartz and feldspar strain values plot within the field of apparent flattening feldspars in both xz and yz sections are boudinaged and separated by transverse veins and record a true tectonic flattening strain strain data indicate that the bulk deformation path in shear zones throughout the blue ridge province significantly deviated from plane strain

geology mineralization and fluid inclusion characteristics of the kensu w mo skarn and mo w cu au alkalic porphyry deposit tien shan kyrgyzstan the kensu deposit is located within a large metallogenic belt of w mo cu mo w au au and pb zn deposits along the late paleozoic active continental margin of tien shan the deposit is related to a small late carboniferous to early permian multiphase gabbro monzonite syenite granite pluton representing an alkaline potassic shoshonitic suite the igneous rocks are related to a deep rooted magmatic source but the pluton emplacement corresponds to shallow porphyry levels the deposit represents an example of a complex w rich alkalic magmatic hydrothermal system that complements the typical mineral deposits related to shoshonitic igneous suites it contains large bodies of w mo skarn of the oxidized type with abundant andradite garnet scapolite k na feldspars and fe oxides magnetite hematite the skarns are overprinted and surrounded by extensive halos of stockwork disseminated porphyry style mo w mo w cu pb zn and au w mineralization with propylitic chlorite amphibole epidote dominated and phyllic quartz sericite carbonate sulfide alteration assemblages consistent with the oxidized nature of the major mineral assemblages the deposit may represent the oxidized lithophile w mo cu au metallogenic type the hydrothermal stages alternate with magmatic phases and fluid inclusion data show the predominance of high temperature 550 450 c high pressure 1 200 700 bars and high salinity 60 45 wt nacl equiv magmatic hydrothermal fluid at prograde and early retrograde skarn stages with its possible direct exsolution from crystallizing magma the general trend of cooling and dilution was complicated by the influx of higher temperature and higher salinity fluid that correlates to the intrusion of quartz monzonite and the initial stages of its degassing and cooling this more advanced phase of magmatic differentiation likely corresponded to the enrichment of residual melt and related magmatic fluids in w and mo intense fluid boiling and phase separation triggered the deposition of molybdoscheelite in skarns that formed at t 625 500 c and p 510 300 bars and continued to a nonboiling fluid at t 420 370 c and p 1 150 750 bars mineralization in propylitic alteration zones was formed by highly to moderately saline nonboiling fluids late quartz sericite carbonate sulfide stage involved both high to low salinity aqueous fluids and co2 rich fluids under decreasing temperature from 400 c to 200 300 c and varying pressure from 1 200 bars to 750 600 bars

rapakivi granites within phanerozoic collisional orogens as a possible consequence of continental subduction and following exhumation of the precambrian crust evidences from the permian jangart rapakivi in south tien shan collisional belt eastern kyrgyzstan abstract all worldwide known rare occurrences of phanerozoic a type granites with typical rapakivi texture do not usually have any significant volume of contemporaneous basic rocks in magmatic association and occur only in those collisional orogens which border ancient cratons and contain hp uhp metamorphic terranes suggesting connection of their petrogenesis with a deep continental subduction and subsequent exhumation of the ancient crust early permian jangart rapakivis and genetically related leucogranites and li mica granites widely spread within the saryjaz syntaxis which is distinguished by the shortest distance between the tarim craton and caledonian kazakh continent collided in the late carboniferous with the possibly deepest continental subduction of the tarim under the south tien shan collisional belt rapakivi plutons occur within the remarkable huge 20 120 km mega melange mega breccia terrane of diapiric not tectonic origin which was identified by the latest geological data and deciphering of satellite imagery according to geophysical data the most of subducted tarim continental crust was trapped within lithospheric mantle and never exhumed but in the saryjaz syntaxis where the collisional suture has been subjected to flecsure like oroclinal bending due to sinistral strike slip tectonics during oblique collision between the tarim and kazakh plates the subduction channel was weakened and exhumation occurred the suggested p t t path of exhumed slices of the subducted tarim continental crust presumes a relatively long around 20 ma residence time on a mantle depth as well as additional internal radiogenic heating and rapid around 2 ma isothermal exhumation which were favorable for extensive melting and subsequent rapakivi formation phanerozoic rapakivis originated from the same ancient lower crust granulite source rocks as their abundant proterozoic counterparts but mechanism of heating and melting of those source rocks was radically different

metallogeny of the saryjaz ore district eastern kyrgyz tien shan abstract the saryjaz ore district relates to the tien shan metallogenic belt in the eastern part of the kokshal segment of the tien shan collisional belt the regional structure is known as the saryjaz syntaxis also partially capturing the middle and south tien shan the ore district was formed during multiple changes of tectonic regimes in relation to subduction of the turkestan ocean in the silurian to the carboniferous to the collision of the kazakh and tarim continents in the late carboniferous to the early permian and to postcollisional permian geological events a distinctive feature of the tectonic evolution of the region is the transition from the subduction of the oceanic crust to the continental subduction of the tarim continent under the kazakh continent followed by the impact of the tarim mantle plume after the collision sinistral strike slip tectonics caused by oblique collision between the tarim and kazakh continents led to formation of postcollisional transcrustal fault zones of great importance as the main magma and ore controlling conduits these fault zones penetrated into the mantle and controlled the distribution of heat and fluid flows as well as localization of granite plutons and mineralization in the consolidated crust the metallogenic zoning of the ore district reflects its geological and structural heterogeneity relationship features of mineralization and magmatism and the varying depth of formation of mineral deposits within the south tien shan portion of the district mineralization is associated with late postcollisional permian a type granites related to a one petrogenetic series namely granite rapakivi biotite leucogranite li mica leucogranite rapakivi granites of the jangart suite were formed in the course of exhumation and melting of overheated continental slabs of the tarim craton previously subducted into the mantle leucogranite uchkoshkon complex and leucogranite li mica granite inylchek complex were formed during complex interaction of the rapakivi magma fractionation with further melting of the continental crust under the influence of the tarim mantle plume at the bottom of the collisional edifice the megamelange terrain includes togolok gold deposit and several rare tin occurrences associated with rapakivi granites of the jangart complex within the lower and middle thrust sheets the leucogranite plutons of the uchkoshkon complex control a large uchkoshkon tin deposit and a medium sized sarybulak tin polymetallic deposit within the upper thrust sheet the leucogranite li mica granite plutons of the inylchek complex control a large trudovoe tungsten tin deposit and a small atjailau tin deposit within the middle tien shan portion of the district neoproterozoic carbonaceous shales intensively deformed in a thick thrust zone accommodated a giant kumtor orogenic gold deposit it has no proven links with granites it is structurally controlled by a system of postcollisional transcrustal fault zones the spatial proximity and synchronism of permian magmatic activity in tarim 300 272 ma and a types granites in the saryjaz ore district 299 269 ma as well as the age of kumtor gold deposit 288 284 ma support a hypothesis about the influence of the tarim mantle plume upon the formation of the ore district

the role of solution in the formation of boudinage and transverse veins in carbonate rocks at rheems pennsylvania the interaction of pressure solution with extensional strain is the most important factor influencing boudinage and vein structures in a mesoscopically folded sequence of subgreenschist grade carbonate rocks from the overturned limb of the lebanon valley fold nappe at rheems pennsylvania the formation of stylolites and slickolites in association with boudins and veins indicates that extreme bed normal contraction is intimately connected with bed parallel extension a variety of boudin shapes in dolomitic beds from rectilinear to pinch and swell and fish mouth structures are formed by a combination of cataclastic flow and heterogeneous pressure solution many veins record catastrophic failure and collapse of wallrock prior to or during crystallization of the vein fill at the earliest stage of boudinage veins in boudin necks are straight and perpendicular to bedding with continued extension they adopt a bow tie form in cross section as a result of inward flow of the surrounding matrix and pressure solution of the fragment corners and vein margins with continued stylolitization and separation of boudins bow tie veins are converted into transverse veins of extraordinary dimension failure to recognize the role of pressure solution in the formation of boudinage structure may result in inaccurate estimates of extension erroneous assumptions regarding volume change and incorrect interpretations of the changes in stress regime with time

perovskite and baddeleyite from kimberlitic intrusions in the tarim large igneous province signal the onset of an end carboniferous mantle plume several tens of kimberlitic pipes and dykes are exposed in the wajilitag area in the western tarim large igneous province here we report for the first time secondary ion mass spectrometric u pb age data on perovskite and baddeleyite grains in a kimberlitic pipe and a kimberlitic dyke from the tarim craton the perovskite yielded a well defined intercept age of 299 87 4 3 ma which is consistent with its corresponding concordia and 206 pb 238 u ages corrected for the common pb contribution of about 300 ma the baddeleyite separated from two kimberlitic samples from a dyke display identical concordia u pb ages of 300 87 4 7 ma and 300 57 4 4 ma our age data show that the kimberlitic intrusions were emplaced at ca 300 ma rather than in the late permian as previously regarded these new ages are slightly older than the eruption ages of tarim flood basalts 291 273 ma offering a critical regional time marker for the onset of permo carboniferous magmatism in the tarim craton detailed petrographic observations did not reveal any ultrahigh pressure mineral assemblage in the wajilitag kimberlitic intrusions phlogopites from these intrusions show end t values of 3 7 to 4 2 the baddeleyites which are texturally primary and therefore inferred to have crystallized directly from the kimberlitic magma yield a range of ehf t from 4 8 to 8 7 these results combined with previously reported geochemical data suggest that the wajilitag kimberlitic intrusions were most likely derived from a moderately refractory and depleted subcontinental lithosphere mantle metasomatized by subduction components associated with an early middle paleozoic convergent regime the kimberlitic magma was generated by small degree partial melting of the lithospheric mantle in response to the impingement of the tarim mantle plume thus our new geochronological data suggest the arrival of the mantle plume beneath the tarim lithosphere at least 10 million years before the onset of tarim flood basalt volcanism the end carboniferous wajilitag kimberlitic intrusions the oldest known phase associated with carboniferous magmatism in the tarim craton signals the initial magmatic pulse triggered by mantle plume impingement

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

a strain reversal method for estimating extension from fragmented rigid inclusions abstract in the standard method of strain analysis using fragmented rigid inclusions such as stretched belemnites extension is estimated by comparing the initial length of the inclusion with its final stretched length this approach fails to recognise that not all of the total extension is recorded by separation of the fragments even when cross fractures are present at the onset of deformation this paper presents an alternative approach in which the extensional strain is reversed the inter fragment gaps being incrementally closed until the inclusion is restored to its original state this allows an estimate of the unrecorded extension accommodated by inhomogeneous matrix flow near the inclusion as well as that recorded by fragment separation model experiments in which the fragmented inclusion is represented by wooden blocks set in a ductile matrix allow the strain reversal method to be compared with the standard method the mean percentage relative error is much smaller in the former 10 2 than in the latter 37 2 the main disadvantage of the strain reversal method is that it requires the collection of more data fragment lengths and gap lengths in correct sequence which must be processed by computer a short basic program is provided although there is no one to one correspondence between strain estimates derived from the two methods an approximate numerical transformation from one to the other may be possible one such transformation based on a study of natural boudinage has been applied to the experimental data and reduces the mean percentage relative error in the standard method estimates to 11 5

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

temporal evolution of the permian large igneous province in tarim basin in northwestern china abstract the temporal relations of different types of rocks in the tarim large igneous province tlip are studied using stratigraphic correlation lithologically spatial distribution and isotopic ages the tlip covers an area 250 000 km2 in the western and central part of the tarim basin the lithological units of the tlip include basalt diabase layered intrusive rock breccia pipe mica olivine pyroxenite olivine pyroxenite gabbro ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke this is the first report for the spatial distribution of the tlip from the spatial section lines which shows the stratigraphic correlation among basaltic lava tuff interlayered mudstone siltstone and sandstone and the thicknesses of the basaltic lavas from different field sections and drill holes and the basalts from the kupukuziman and kaipaizileike formations were subdivided in the drill hole sections this indicates that the basaltic lavas were widely distributed in the tarim basin combined with previous study of geochemical and sr nd pb isotopic characterization from the basalts and their genetic link with mantle plume activity and large diabase swarms developments the permian igneous units constitute a tarim large igneous province zircon shrimp u pb dating firstly yields 284 3 2 8 ma for the quartz syenite porphyry recent shrimp and la icp ms zircon u pb and 40ar 39ar ages are used to discuss temporal relations of different rock units in the tlip formed between 290 and 274 ma and these data are more reliable than the k ar ages of 220 310 ma reported previously the sequence of magmatism of the tlip in the central and western parts of the tarim basin are basaltic lava in the kupukuziman and kaipaizileike formations 285 290 ma layered mafic ultramafic rock mica olivine pyroxenite breccia pipe diabase and ultramafic dyke quartz syenite quartz syenite porphyry and bimodal dyke 274 284 ma

geology and mineralization of the uchkoshkon tin deposit associated with a breccia pipe eastern kyrgyzstan abstract the uchkoshkon tin deposit is one of the largest deposits in the sn w saryjaz ore district of eastern kyrgyzstan the district coincides spatially with the saryjaz syntaxis which is the narrowest portion of the south tien shan collisional belt the syntaxis is distinguished by collisional thrust tectonics and postcollisional a type granite magmatism of permian age the uchkoshkon deposit is in the exocontact zone of a 260 km 2 273 279 ma ilmenite series high heat production biotite granite pluton a satellite granite stock 400 250 m and an explosive breccia pipe 450 150 m crosscutting the stock are the central structural features of the deposit area the main stock accompanied by li f felsite dykes controlled early stage mo w and sn w greisen stockwork mineralization that surrounds the apical portion of the stock the breccia pipe postdates the emplacement of the li f felsite dykes and greisen stockwork mineralization the pipe is rooted in main pluton and has been traced by a borehole to a depth of 800 m the breccia was injected by a swarm of tree like branching dykes with diffuse contours consisting of k and b rich rhyolite porphyry cementing the breccia fragments the main breccia body has been intruded by a much smaller 150 100 m hydrothermal breccia pipe with quartz tourmaline matrix which immediately preceded main stage lode mineralization the majority of the lodes occur outside the breccia pipe within a zone of pervasive scapolitization that surrounds the main pluton the main stage lodes are represented by quartz tourmaline cassiterite veins with minor sulfides which occupy a series of steeply dipping near parallel north northeast trending shear fractures that are related to postcollisional strike slip tectonics where quartz tourmaline cassiterite veins crosscut moderately dipping skarn deposits the latter are commercially mineralized with cassiterite nordenskioldine and borosilicate minerals the formation of both explosive breccia and main stage lode mineralization was related to the evolution of b and h 2 o rich residual magma deep within the main pluton the suggested formation model of the uchkoshkon tin deposit is generally applicable to other major sn and sn w deposits in the saryjaz ore district

origin and significance of compositional layering in late precambrian sediments blue ridge province north carolina u s a abstract basal arkosic sandstones of the late precambrian grandfather mountain formation contain smallscale deformation zones usually 1 mm thick and spaced 5 to 10 mm apart the deformation zones are composed of green phengitic muscovite which concentrated in the deformation zones during pressure solution removal of quartz assuming plane strain the deformation zones have lost 34 of their area due to solution of quartz and axial ratios of strain ellipses are on the order of 16 1 in the principal plane the deformation zones and associated tight to isoclinal folds in the basal arkoses form a structural style which is transitional between ductile deformation zones in the crystalline basement and kink style folding in the interbedded siltstones and arkoses of the upper grandfather mountain formation since deformation zones may be more common in sedimentary rocks and low grade metasediments than previously realized one should exercise caution when using penetrative fabrics to unravel the structural history of multiply deformed rocks small scale deformation zones can be misinterpreted as a crenulation cleavage cutting an earlier penetrative fabric

crustal scale structure of south tien shan implications for subduction polarity and cenozoic reactivation based on new structural and petrological investigations we present two crustal scale cross sections of the kyrgyz south tien shan and correlations of main faults and units between kyrgyzstan and china the overall structure corresponds to a doubly vergent mountain belt the kyrgyz and chinese areas exhibit identical structural and metamorphic histories to the west the atbashi range comprises high pressure oceanic and continental units stacked by north verging thrusts above a low metamorphic accretionary prism high pressure hp gneisses are bound to their south by a south dipping detachment exhibiting mantle relicts the high pressure oceanic and continental units underwent similar pressure temperature p t paths with peak conditions of around 500 c 20 kbar followed by rapid exhumation the overall south dipping structure and kinematics indicate a south dipping subduction of the central tien shan ocean at 320 310 ma ending with the docking of the tarim block to the kazakh continent to the east the pobeda massif shows a narrow push up structure a major north vergent thrust exhumes deep crustal level granulites constituting the highest summits which were thrust towards the north onto low grade devonian carboniferous schists the southern part of south tien shan is made up of a south verging thrust stack that formed later during ongoing convergence reactivated throughout post 30 ma phases

pressure solution structures in a granite abstract syntectonic two mica granites in northwest spain have suffered regional late variscan shear deformation the deformed corcoesto granite shows a marked planar and linear fabric resulting from ductile behaviour and contains quartz veins at about 60 to the foliation offsets of these quartz veins along shear planes are commonly contrary to the general sense of shear and thus provide evidence for pressure solution processes

continental vertical growth in the transitional zone between south tianshan and tarim western xinjiang nw china insight from the permian halajun a1 type granitic magmatism article i nfo the south tianshan collisional belt stcb and northern margin of the tarim block ntb are key areas for understanding the prolonged tectonic evolution of the central asian orogenic belt caob the halajun region in xinjiang province nw china is located within the tectonic transition zone between stcb and tarim blocks several granitic intrusions and one mafic ultramafic complex piqiang complex are exposed in this region zircon u pb dating whole rock major oxide trace element and nd isotopic data are presented for the huoshibulake tamu kezi ertuo and halajun ii granitic intrusions in this area new la icp ms u pb age for kezi ertuo intrusion coupled with previously published shirmp u pb ages for huoshibulake and halajun ii intrusions and piqiang complex reveals that all the igneous rocks in the halajun region are coeval 275 ma geochemically the four granitic intrusions show high contents of sio2 k 2o and total alkalis and possess trace element patterns characterized by rb nb ta zr and hf enrichment and significantly negative ba sr p eu and ti anomalies these features strongly favor an a1 type affinity for the halajun granitic intru sions among the four intrusions the kezi ertuo tamu and halajun ii intrusions possess positive to slightly negative end t values ranging from 0 9 to 0 6 whereas the huoshibulake intrusion displays less deplet ed end t values of 2 6 to 2 9 our new elemental and isotopic data suggest that the four granitic intru sions were generated by the partial melting of a common neoproterozoic gabbroic source probably as a result of the 275 ma underplating of the asthenosphere mantle derived magmas the variable involvement of the mantle components accounts for the range of end t values after the generation of the parental magma alkali feldspar arfvedsonite biotite fe ti oxides and zircon seem to have fractionated prior to the final emplacement of the granitic magmas in combination with the regional geological history we propose that the 275 ma a1 type granitic magmatism in the halajun region and other areas of the ntb provides a good proxy record for the vertical continental crustal growth in the southern margin of the caob during the permian our study in combination with other geological evidence indicates that these a1 type felsic and oib like mafic ultramafic rocks with ages from 282 ma to 275 ma in the southern margin of the caob are parts of the permian tarim large igneous province and could be genetically related to the tarim mantle plume