formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

late ordovician to early devonian adakites and nb enriched basalts in the liuyuan area beishan nw china implications for early paleozoic slab melting and crustal growth in the southern altaids abstract we report newly defined nb enriched basalts adakites and dacites from the beishan nw china of the southern altaids based on field geochemical isotopic and geochronology studies two phases of adakites adakite i and adakite ii have been defined which are calc alkaline and characterized by high na 2 o k 2 o ratios 1 49 1 71 and 2 32 3 64 and sr contents 494 1213 ppm and 325 494 ppm negligible to positive eu anomalies strong depletion of hree e g yb 0 48 0 93 ppm and 0 50 0 99 ppm and y 6 87 9 80 ppm and 6 02 10 30 ppm and enriched in rb sr ba k and depleted nb and ti they are characterized by relatively low e nd t values 0 8 to 0 9 and 0 6 to 3 8 and relatively constant high 87 sr 86 sr i ratios 0 70635 0 70636 and 0 70583 0 70651 the zircons of adakite i have relatively low e hf t 0 8 to 2 7 the nb enriched basalts are sodium rich n 2 o k 2 o 1 31 4 44 with higher tio 2 p 2 o 5 zr and nb contents and nb th pm nb la pm and nb u ratios than typical arc basalts they are relatively enriched in rb ba u pb and k depleted in nb and minor negative to positive ba zr sr and ti they have low positive e nd t 0 9 to 2 3 and relatively high 87 sr 86 sr i 0 70556 0 70691 ratios the dacites are typical arc magmas with moderately enriched lile distinctly negative eu nb sr and ti anomalies they have positive e nd t 2 2 and relatively high 87 sr 86 sr i 0 70786 we argue that the liuyuan adakites were most probably related to the melting of young hot subducted crust of the paleo asian ocean which included tectonically subducted radiogenic crustal material and or inheritance from highly radiogenic oceanic crust e g oib the nb enriched basalts likely resulted from mantle wedge peridotites metasomatized by adakites and or further changed by components other than adakites e g minor slab derived fluids based on own zircon sims u pb dating of these key rock types we further propose that from the late ordovician to early devonian large volumes of magma consisting of late ordovician nb enriched basalts 451 ma and dacites 442 ma late silurian adakite i 424 ma early devonian adakite ii 374 ma and i s a type granites 436 ma 380 ma developed in the southern altaids together with other geochronological data from the literature we conclude that subducted oceanic slab melting was frequent from 470 ma to 370 ma our results suggest that frequent hot and or young oceanic crustal subduction and slab melting were important mechanisms in the accretionary growth of the southern altaids

a synthesis of zircon u pb ages and hf isotopic compositions of granitoids from southwest mongolia implications for crustal nature and tectonic evolution of the altai superterrane abstract granitoid magmatism is extensively developed in the altai superterrane but the timing of magmatic events is not so well determined in this study twelve granitoid intrusions from southwest mongolia were dated by the zircon u pb method and analyzed for zircon hf isotopic compositions the new age data indicated three phases of magmatic emplacement middle paleozoic 398 350 ma late paleozoic 317 289 ma and triassic ca 244 211 ma the first phase magmatism is mainly composed of hornblende bearing i type granitoids formed during a long lasting subduction process in the early to middle paleozoic the second phase magmatism was manifested by a few small intrusions primarily distributed along the erqis fault zone and probably formed in a transitional tectonic regime from subduction to post tectonic setting in the late paleozoic the third phase magmatism was represented by post tectonic granitoids emplaced in an intraplate extensional setting model ages that were calculated using the composition of new continental crust are predominantly neoproterozoic to early paleozoic indicating that the protoliths of granitoids were likely dominated by paleozoic juvenile crust with minor neoproterozoic materials the altai superterrane was a huge paleozoic tectonic collage produced by amalgamation of subduction accretion complexes in the margin of the siberian continent and the tuva mongol microcontinent

palaeomagnetic study of vendian and early cambrian rocks of south siberia and central mongolia was the siberian platform assembled at this time abstract a palaeomagnetic study of vendian and early cambrian sediments from the angara block of the siberian platform shaman 52 08 n 108 83 e and minya 58 0 n 110 0 e formations and the tuva mongolian block tsagan olom and bayan gol formations 46 76 n 96 37 e isolated three different components of magnetization through thermal demagnetization the stable high temperature characteristic remanence directions show both normal and reverse polarities the mean palaeopoles computed after these high temperature components are 32 0 s 71 1 e dp dm 6 9 13 8 for the vendian shaman formation 10 sites 80 samples 33 7 s 37 2 e dp dm 8 6 14 7 for the vendian minya formation 12 samples 22 8 s 28 4 e dp dm 10 8 21 6 for the vendian tsagan olom formation 4 sites 25 samples and 21 4 s 167 1 e dp dm 9 6 19 1 for the early cambrian bayan gol formation 6 sites 49 samples from a compilation of vendian and early cambrian palaeopoles from the anabar angara and aldan blocks of the siberian platform and tuva mongolia block we propose a model where these blocks were situated in an equatorial to low south palaeolatitude position with their present day southern boundaries facing the north pole from the analysis of the scatter of these poles we conclude that the siberian platform might not have fully amalgamated by this time and that significant rotations occurred after the early cambrian our new palaeopoles for the tuva mongolia block together with previously published ones show that this block was already adjacent to siberia by the vendian and early cambrian we propose that the large counterclockwise rotation of the tuva mongolia block with respect to angara block could mark the end of the closure of the part of the palaeo asian ocean separating these two blocks and could account for the occurrence of vendian early cambrian ophiolites in the region

present day deformation of the qaidam basin with implications for intra continental tectonics abstract the qaidam basin is a plateau of low relief about 3 km in elevation and covering a large area of 1 2 105 km2 physiographically the basin marks a transitional region between the northeastern tibetan plateau 5 0 5 km in elevation and the surrounding low lying areas the northeastern and southwestern edges of the basin are bounded by the qilian shan nan shan and qimantag eastern kunlun shan mountain belts respectively at present the entire region is under northeast southwest compression based on a synthesis of recent geological and geophysical results we propose that each flanking mountain belt consists of a sequence of crustal nappes originating from ramp thrusts at mid crustal levels 15 km deep over a distance range of 700 km these two broad fold and thrust belts operating in tandem and with some uniform shortening in the intervening qaidam basin successively raised the surface elevation from below 2 km to 5 km at depth the crust is correspondingly thickened from 40 km beneath the foreland of the qilian shan to approximately 55 km under the interior of the qaidam basin and then to nearly 70 km beneath tibet in contrast to the himalayan front where earthquake faulting occurs down to a depth of 50 km in the foreland but the zone of active thrust faulting is less than 200 km in width plateau building in the qaidam region illustrates how a wide orogen is developing along northeastern tibet in the interior of eurasia

geochemistry of the loessic sediments on delhi ridge eastern thar desert rajasthan implications for exogenic processes abstract quartzite ridges in the delhi region include in their local depressions thick piles of unconsolidated unstratified yellowish brown homogenous loamy sediments these delhi ridge sediments drs have textural mineralogical and geochemical characteristics similar to those of loess sediments geochemically drs just as other loess sediments are similar to average exposed upper continental crust of taylor and mclennan taylor s r mclennan s m 1985 the continental crust its composition and evolution blackwell london 311 pp the calculated chemical index of alteration nesbitt h w young g m 1984 prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations geochim cosmochim acta 54 1523 1534 nesbitt h w young g m 1989 formation and diagenesis of weathering profiles j geol 97 129 147 and other chemical parameters suggest a provenance of chemically less weathered rocks during the process of wind transport and deposition not only the dilution effect of silica on the ree abundance was counterbalanced but also the ree pattern was kept similar to the ucc and paas by the appropriate concentration and mixing of the ree bearing phases the immediate source to these sediments is likely to be mechanically ground sediments of glacial origin the last phase of the upliftment of the himalayas accompanied by pleistocene glaciation could have provided a vast glacio fluvial outwash plain the aeolian processes associated with prevailing w to sw winds in the hot arid condition seem to have been selectively transporting fertile silt materials leaving behind infertile desert sands

tectonic framework of the northern junggar basin part i the eastern luliang uplift and its link with the east junggar terrane abstract the luliang uplift preserves relatively complete carboniferous strata and is an important region to study the spatio temporal framework and tectonic evolution of the junggar basin here we report new shrimp sims u pb ages whole rock sr nd data and in situ zircon hf isotopic compositions for carboniferous strata samples in the eastern luliang uplift the gravity and magnetic data suggest that the carboniferous volcanics are distributed as nw trending bands and also bring out n s oriented parallel amalgamation the sedimentary units and structural deformation of the eastern luliang uplift suggest that the basin evolution involved late carboniferous extensional graben stage and latest carboniferous early permian compressional stage the carboniferous batamayineishan formation is divided into the lower volcanic unit followed up sedimentary unit and an upper volcanic unit as inferred from the lithology and unconformities the lower volcanic unit from the drill cores mainly consists of andesite dacite rhyolite and tuff intercalated with minor basalt the middle sedimentary unit is made up of sandstone and mudstone with tuff and tuffaceous sandstone and the upper volcanic unit is composed of basalt rhyolite tuff and breccia with minor clastic sedimentary rocks zircon shrimp u pb age 337 2 ma for the tuff and sims u pb age 308 6 ma for basalt suggest that the lower and upper volcanic units belong to lower carboniferous and upper carboniferous respectively the basalts from upper volcanic unit in the eastern luliang uplift show typical calc alkaline affinity with low nb y ratios 0 17 0 28 and sio2 contents 47 54 and moderate th abundances 0 45 3 74 ppm enrichment in lree and liles and depletion in nb ta and ti they have low initial 87sr 86sr ratios 0 703571 0 705122 and positive end t values 5 5 8 6 and constant sm yb ratios 1 56 2 03 and variable trace element ratios e g ba th ba la and ba nb suggesting that the parental magmas were mainly derived from 2 to 8 partial melting of a spinel iherzolite mantle source metasomatized by hydrous fluids and melts of subducted sediments furthermore relatively high tio2 1 52 3 76 and zr contents 172 414 ppm indicate that they were formed in an extensional setting taking into account the occurrence of coeval island arc related volcanics we propose an intra arc rift basin model for the eastern luliang uplift the eastern luliang uplift and east junggar terrane display different tectonic features during the closure of the junggar ocean during the late carboniferous continued northward subduction prevailed and generated a fault controlled intra arc basin in the eastern luliang uplift intra arc basin contraction in permian is probably indicative of the closure of junggar ocean in the northern junggar basin our study confirms the important role of subduction accretion process associated with the carboniferous crustal growth in the junggar terrane

late paleozoic retrograded eclogites from within the northern margin of the north china craton evidence for subduction of the paleo asian ocean abstract retrograded eclogites from the central part of the northern margin of the north china craton hebei province china occur as separate tectonic lenses or boundins within garnet biotite plagioclase gneisses of the paleoproterozoic hongqiyingzi complex characterized by amphibolite facies paragneisses the petrographic features and mineralogical compositions represent three main metamorphic stages 1 the peak eclogite facies stage p 1 40 1 50 gpa t 680 730 c 2 the granulite facies stage and 3 the amphibolite facies stage p 0 67 0 81 gpa t 530 610 c formed during decompression the major and trace element and sm nd isotopic data suggest that most of the retrograded eclogite samples had protoliths of tholeiitic oceanic crust with geochemical characteristics of mid ocean ridge basalt morb or island arc tholeiite iat environment and were contaminated by crustal components during subsequent subduction zircon shrimp isotopic dating of two different textural varieties of retrograded eclogite defines a weighted mean age of 325 ma which is interpreted as the peak metamorphic age of the eclogites and reflects the occurrence of eclogite facies metamorphism related to subduction of paleo asian oceanic crust beneath the north china craton during the late paleozoic finally we show that the retrograded eclogite from hebei province is not related to the baimashi retrograded eclogite at the northern foot of the heng mountains approximately 300 km to the southwest

variscan accretionary complex of northwest iberia terrane correlation and succession of tectonothermal events the allochthonous terranes of northwest iberia can be correlated with specific paleogeographic realms of the continental masses and intervening oceans involved in the variscan collision assuming that the existing ophiolites represent the suture formed by the closure of the rheic ocean the units in the footwall to the suture correspond to the outer edge of the gondwana continental margin and the units in the hanging wall are interpreted as fragments of the conjugate margin represented by the meguma terrane this correlation establishes a precise link between circum atlantic terranes and makes it possible to draw a relatively simple scenario of the successive tectonothermal events recorded following the amalgamation of avalon to laurentia the remaining outboard terranes underwent a progressive accretion to this continent that ended with the collision between laurentia and gondwana

crustal structures revealed from a deep seismic reflection profile across the solonker suture zone of the central asian orogenic belt northern china an integrated interpretation abstract the solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the central asian orogenic belt caob an 630 km long reflection seismic profile across this suture was recently completed by the chinese sinoprobe project the processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models the moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of 40 45 km 14 5 s two way travel time which is in agreement with the refraction data recorded along the same profile in a broad view the profile images an orogen that appears bivergent with and approximately centered on the solonker suture zone the southern portion of this profile is dominated by a crustal scale cratonward propagating fold and thrust system that formed during the late permian and triassic through collision and subsequent convergence in a post collisional stage the major thrust faults are truncated by mesozoic granitoid plutons in the upper crust and by the moho at the base of the crust this geometry suggests that the moho was formed after the thrusting event the northern portion of the profile although partially obliterated by post collisional magmatic bodies shows major south dipping folding and thrusting bands of layered reflectors immediately overlying the moho are interpreted as basaltic sills derived from the mantle episodic mafic underplating may have occurred in this region giving rise to post collisional magmatic events and renewal of the moho a few mantle reflectors are also visible the overall geometry of these mantle reflectors supports the tectonic models that the southern orogen manchurides experienced south directed subduction and the northern orogen altaids underwent north directed subduction prior to collision along the solonker suture zone

zircon ages and geochemical compositions of the manlay ophiolite and coeval island arc implications for the tectonic evolution of south mongolia abstract numerous small dismembered ophiolite fragments occur in south mongolia but they are very poorly studied the lack of age data and geochemical analysis hampers our understanding of the paleozoic tectonic evolution of the region we conducted detailed studies on the manlay ophiolitic complex and huree volcanic rocks south of the main mongolian lineament mml to provide some constraints on these rocks the manlay ophiolite consists of dunite harzburgite pyroxenite gabbro plagiogranite basalt and chert locally with chromite mineralization in dunite the gabbro and plagiogranite yielded shrimp zircon weighted mean 206 pb 238 u ages of 509 5 ma and 482 4 ma respectively the basalt and dolerite samples of this complex show enrichment in lree and lile and negative nb ta and ti anomalies and the chrome spinel from the chromitite lens in the dunite is characterized by high cr and low tio 2 contents these features suggest a supra subduction zone ssz origin for the ophiolitic complex the huree volcanic rocks ranging from basalt to dacite display enrichment in lree and lile weak eu anomalies and distinctly negative nb ta and ti anomalies consistent with those of typical magmas in a subduction environment an andesite sample from this arc yielded a shrimp 206 pb 238 u zircon age of 487 5 ma which is the oldest reliable age for an island arc in south mongolia recognition of an early paleozoic ophiolitic complex and a coeval island arc indicates that south mongolia underwent a period of active volcanism during late cambrian to ordovician additionally the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have shrimp zircon u pb ages of 391 5 ma and 304 4 ma respectively combining the available data we propose that the early paleozoic subduction accretionary complexes likely constitute the basement of the late paleozoic arc formations and correlate with the lake zone in western mongolia

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

tertiary strike slip faulting in southeastern mongolia and implications for asian tectonics abstract geologic maps have long portrayed the late cretaceous recent geologic history of southeastern mongolia as tectonically quiescent we present new data based on outcrop observations that indicate the northeast trending east gobi fault zone egfz was reactivated in the cenozoic as a sinistral strike slip fault system inversions of cenozoic fault slip data imply that faulting was associated with north northwest subhorizontal shortening and east northeast subhorizontal extension we propose that faulting is tertiary in age based on published interpretations of seismic reflection data which reveal that the mid cretaceous 100 95 ma unconformity is deformed by strike slip faults and based on field observation of strike slip faults and fracture sets that cut upper cretaceous and cenozoic strata but lack evidence for neotectonic activity published seismicity maps also appear to argue against significant quaternary faulting within the egfz these new data may lend credence to published models proposing a middle miocene or older kinematic linkage between the egfz and the altyn tagh fault in china the recognition that the egfz has a history of left lateral displacement in both the early mesozoic and cenozoic means that currently available estimates of offset based on displaced paleozoic rocks constrain total offset only this reactivation history supports the notion that inherited lithospheric structures are important in controlling the location and thus modes of intracontinental deformation in asia as a function of collisional far field effects and evolving boundary conditions of the pacific margin

petrogenesis and implications for tectonic setting of cambrian suprasubduction zone ophiolitic rocks in the central beishan orogenic collage northwest china abstract the hongliuhe ophiolite is a fragment of the early paleozoic oceanic crust situated in a suture zone central to the beishan orogenic collage which is a subset to the central asian orogenic belt in northwest china it has lithologic geochemical and chronological similarities to the yueyashan xichangjing ophiolite 400 km east along strike allowing for correlative interpretations of marginal seafloor spreading processes the hongliuhe ophiolite is explored in this study with complete petrologic geochemical and structural descriptions the ultramafic body comprises cumulate layered lherzolite and gabbro plutonic lithologies tectonized with syn magmatic extension a u pb age of 520 3 5 8 ma was obtained by shrimp analysis of zircons from a pegmatitic gabbro the ultramafic rocks are variably depleted and some show refertilization of lile s consistent with slab dehydration in a supra subduction mantle wedge mineral chemistry shows high cr 36 82 populations of spinel and wide ranging lower mg 8 50 consistent with known forearc peridotite chemistry partially re equilibrated by tectonism or through staged magmatism olivine and pyroxene chemistries are consistent with this interpretation a thin volcanic cover is interlayered with red cherts and has a bimodal set of geochemical signatures both island arc tholeiite and calc alkaline they bear distinct nb ta anomalies consistent with slab derived fluid initiated melting in a supra subduction environment coarse volcaniclastic turbidites infilled paleo topography along the ophiolite and they are interbedded with quartzofeldspathic sandstones indicating an initial proximity to an arc the sandstones contain detrital spinel with analyses showing relation to both the ophiolite and possibly a secondary alkalic volcanic source the supracrustal sequence continues with a thick contiguous covering of margin related rocks including interlayered limestone pyroclastic and siliciclastic rocks and basalts as a constraint on emplacement we provide an u pb zircon shrimp date 413 6 3 5 ma from an undeformed granitoid body intruded within the overlying stratigraphy the entire analysis paints a picture of subduction rollback related extension affecting the margin of an emerging or mature arc just prior to a known magmatic cycle that ended with a collision in the devonian at the latest this suture is one of many in the beishan and our interpretation provides evidence in a long running debate supporting accretionary orogenesis in an island arc archipelago as the main system for growing sialic crust in the paleozoic central asia

controls on the locus of intraplate deformation in central australia abstract the locus of intraplate deformation in central australia changed from the presently preserved southern margin of the amadeus basin during the late neoproterozoic to early phanerozoic petermann orogeny to the northern margin in the late phanerozoic alice springs orogeny immediately prior to each event the thickness of the amadeus basin sediments varied from as little as 1 5 km in the central parts of the basin to as much as 7 km in the vicinity of the presently preserved margins of the basin with the locus of deformation mimicking the locus of maximum sedimentary thicknesses at the onset of each orogenic event as such these orogenies represent extreme examples of basin inversion a process observed in many intracratonic basins worldwide we show that differential burial of the central australian proterozoic basement complexes beneath the amadeus basin is capable of producing variations in moho temperature of up to 30 c prior to the petermann orogeny and up to 110 c prior to the alice springs orogeny for a brace goetze model of lithospheric rheology the variations in moho temperature equate to variations in effective lithospheric strain rate of 1 4 orders of magnitude implying that variations in thickness of the sedimentary blanket may have played a primary role in localising phanerozoic intraplate deformation in central australia an appealing aspect of this model lies in its corollary that the removal of the sedimentary blanket during denudation of the orogen will be accompanied by dramatic cooling and strengthening of the lithosphere this may provide a plausible explanation for the long term persistence of the extraordinary gravity anomalies 150 mgal developed during these central australian intraplate orogenies

paleozoic multiple accretionary and collisional processes of the beishan orogenic collage in the paper by xiao and others american journal of science v 310 p 1553 1594 1 please substitute figure 16 reproduced here for figure 16 that appears between pages 1573 and 1574 the original figure 16 2 was printed at an improper size figure 3 1 lookup volpage 310

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

late paleozoic to early triassic multiple roll back and oroclinal bending of the mongolia collage in central asia abstract the architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined because of unavailable data the central asian orogenic belt caob provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage in this paper we review several lines of available evidence which enable us to propose a new tectonic model of huge roll back in the formation of the accretionary tectonics of the mongolian collage in central asia in the early paleozoic the mongolia collage comprised the southern siberian and the tuva mongol oroclines the siberia craton and the mongolia collage jointly formed a giant tadpole shape within the paleo asian and panthanlassic oceans its head siberia was to the south and the tail tuva mongol to the northwest the structures and tectonic zonation of the mongolia collage are characteristic of multiple arcs which have been separately described in detail in different segments southwards from the southern siberia east sayan west sayan gorny altai chara via the lake zone junggar tianshan gobi altai beishan alxa to the manlay hegenshan baolidao solonker segments almost all segments underwent early paleozoic to permian or even triassic frontal subduction and accretion while rifting in the late carboniferous to permian or triassic occurred in the outward oceanward westward advancing mongolian collage therefore we suggest that a huge complex roll back active from the carboniferous to permian or even to late triassic facilitated the formation of the mongolian collage the outward multiple roll back process was compatible and almost coeval with the start of the tuva mongol orocline and rotation of the siberian craton as confirmed by paleomagnetic and structural data during the roll back processes an archipelago paleogeography was formed behind the frontal subduction and accretion in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times the roll back process was affected by the collision of the kazakhstan collage along the chara and karamay zones in the early permian the collision of the tarim craton along the south tianshan zone in the early permian the collision of the dunhuang block along the liuyuan zone in the early permian triassic the collision of the alxa block along the qugan qulu zone in the permian and the collision of the north china craton along the solonker zone in the middle late triassic the tectonic styles and architecture of accretionary orogenic belts like the caob are characterized both by the amalgamation of multiple terranes and by oroclinal bending the systematic anatomy of the multiple roll back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens

major and trace elements of stream sediments from the lowermost amazon river geochemical results from river bottom sediments taken from the lowermost amazon river are presented bedload sediments were analyzed for 10 major and 38 minor elements mud bulk sediments exhibit a tendency to a slight enrichment in cr mn rb sr zr cs ba and hf pointing to the importance of these elements in the silt fraction generally cu zn rb cs ba and sn are clearly associated with clay minerals while y zr hf th and u are associated with heavy minerals the location of this area in an intensive chemical weathering environment results in the strong modification of sediment composition chemical weathering processes strongly modify original sediment composition and can be recognized apart from provenance processes on the basis of their geochemical signature discriminant analysis makes the detection of less marked differences in sediment characteristics possible thus improving the accuracy of distinctions between groups the amazon mouth and xingu mouth xm are discriminated principally by the textural maturity of their sediments the jari mouth jm shows highest co and fe2o3 contents despite similarities between the amazon north branch anb and amazon south branch asb the anb can be differentiated on the basis of its higher sr p2o5 and na2o contents the asb on the basis of its higher zn mno and cao contents and the estreitos de breves est based on its higher abundance of ni and cu higher contents in p2o5 fe and mn are related to laterite covers

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

the zhaheba ophiolite complex in eastern junggar nw china long lived supra subduction zone ocean crust formation and its implications for the tectonic evolution in southern altaids abstract the composite zhaheba ophiolite complex exposed in eastern junggar in the southern altaids records an unusually long record of oceanic crust and magmatic arc evolution the zhaheba ophiolite complex consists of ultramafic rocks gabbro diorite basalt and chert intruded by diabase dikes and diorite porphyry these rocks are overlain by a several km thick section of tuffaceous rocks volcaniclastic sedimentary rocks and intermediate volcanic rocks the igneous rocks of the ophiolite complex show negative nb and ta anomalies and lree enrichment relative to hree suggesting the influence of fluids derived from a subducting oceanic slab the la icpms u pb age of zircons from gabbro is 495 1 3 5 ma zircon ages from diorite and basalt are 458 3 7 2 ma and 446 6 6 0 ma respectively the basalt is locally overlain by bedded chert diabase dikes and diorite porphyry yield the u pb ages of 421 5 4 1 ma and 423 7 6 5 ma respectively the age of stratigraphically lower part of the overlying volcanic volcaniclastic section is constrained to be about 410 ma the maximum depositional age of the tuffaceous sandstone from u pb detrital zircon ages late rhyolite at the top of the stratigraphic section yielded a u pb zircon age of 280 3 3 7 ma the age and stratigraphic relationships for the zhaheba ophiolite complex and related rocks suggest that the period of 70 ma of initial supra subduction magmatism was followed by construction of a mature island arc that spanned an additional 140 ma many other ophiolites in the southern altaids appear to record similar relationships and are represented as substrates of oceanic island arcs covered by island arc volcanism in supra subduction zone the occurrence of the zhaheba ophiolite complex with tuffaceous and intermediate to felsic volcanic rocks is different from the rock association of classic tethyan ssz ophiolites but similar to some ophiolites in north america although the zhaheba ophiolite belt is flanked by the dulate arc in the north and yemaquan arc in the south it cannot stand a suture between two arcs it is suggested that devonian carboniferous dulate arc was built on the late cambrian middle ordovician zhaheba supra subduction oceanic crust the late carboniferous rocks and early permian rocks in dulate arc are interpreted to form in the extensional process within zhaheba dulate arc composite system

climate vs parent material which is the key of stagnosol diversity in croatia abstract stagnosols are the most widespread soils in the pannonian region of croatia in croatia they are referred to as pseudogleys and considered to form primarily by normal top down pedogenesis however the formation of their non calcareous loess parent materials probably involved different sources transports and depositional environments we aimed to determine the courses of soil formation and the characteristics of three stagnosol profiles studied along the mean annual precipitation map gradient 700 1100 mm in the pannonian region of croatia we found that soil redoximorphic features formed in situ by ongoing pseudogleization vertical trends for the clay silt and coarse fine silt ratios pointed to top down pedogenesis however high organic c content at the bottom of one soil profile is the result of erosion sedimentation processes whereas high clay content in the subsoil of another profile was largely the result of sedimentation in a shallow paleo lake therefore some croatian stagnosols should be considered polygenetic each soil profile was classified using the wrb system and the new wrb 2014 version proved more suitable than the previous one wrb 2006 however suggestions for improvements are given in line with the map gradient were several morphological and only two chemical ph and base saturation soil characteristics organic c content did not correspond to map due to variability of forest topsoils clay content and cec did not agree with map due to variability of loess parent materials across the pannonian region of croatia the existence of more than one source of loess material confirmed by the modal analysis and the differences in depositional paleo environments resulted in slightly different mechanical compositions of the investigated parent materials we concluded that both climate and parent material must be regarded as key factors for the formation and characteristics of stagnosols in the pannonian region of croatia and the wider southwestern pannonian basin

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

geochemical and geochronological study of early carboniferous volcanic rocks from the west junggar petrogenesis and tectonic implications abstract a series of early carboniferous volcanic rocks i e basalt andesite and dacite occur in the west junggar zircon u pb isotopic data indicate that these rocks coevally erupted at 331 344 ma these volcanic rocks have comparable trace element patterns characterized by the enrichment of large ion lithophile elements lile and the depletion of high field strength elements hfse isotopically they display consistently depleted sr nd isotopic compositions initial 87sr 86sr ratios 0 7034 0 7054 end t 4 2 7 7 these rocks are interpreted to be derived from a slightly metasomatized depleted mantle in a normal subduction environment in the context of a previously proposed ridge subduction model this study constrains that ridge subduction if it indeed occurred commenced between 331 and 310 ma in the central west junggar

age and evolution of late mesozoic metamorphic core complexes in southern siberia and northern mongolia numerous cretaceous metamorphic core complexes mccs extend from transbaikalia in russia to northern mongolia within the central asian orogenic belt we investigated the buteel and zagan mccs in detail shear sense indicators in mylonitized rocks show footwall to the nw tectonic transport single zircon dating of footwall rocks in the buteel mcc establishes the emplacement of granitoid orthogneiss precursors at 240 211 ma a felsic metavolcanic rock at 265 0 1 2 ma a syenite at 265 5 1 2 ma and a metarhyolite of the pre granitoid basement at 553 6 2 9 ma a peralkaline granite intruding orthogneisses of the zagan mcc has a new u pb zircon age of 151 6 0 7 ma 40 ar 39 ar ages of 133 5 1 8 ma of hornblende from amphibolite and 122 6 1 8 ma of biotite from mylonitized gabbro dolerite of the buteel mcc are interpreted as cooling ages representing the time of deformation in the footwall geological data suggest that the mccs in transbaikalia and northern mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc alkaline magmatism in an andean type setting on the border of the closing mongol okhotsk ocean by widespread collisional to post collisional thrusting and by extensive alkaline peralkaline magmatism

geometry and timing of mesozoic deformation in the western part of the xuefeng tectonic belt south china implications for intra continental deformation abstract the xuefeng tectonic belt is an important intraplate structural system in the south china block its west margin is up to 1300 km away the present day continental margin and the mesozoic structural trends in this belt are perpendicular to and have no correlation with the triassic qinling dabie orogenic belt this belt provides important clues for understanding the mechanism of intraplate deformation and the tectonic history of south china we identified two generations of folding with different strike directions in the xuefeng tectonic belt based on the youngest folding involved strata and their overprinting relationship the early one is ne striking overprinted by the n s striking folds both during late jurassic and late cretaceous thrust faults in the xuefeng tectonic belt mainly show top to west thrust movement which is approximately coeval with the n s striking folding the thrust fault system can be divided into three zones the root zone with steep thrusts the middle zone characterized by imbricate thrusts and the frontal zone with a few shallow thrusts in addition two generations of strike slip faults with different structural trends have been identified e w striking strike slip faults showing dextral transpression and ne striking strike slip faults with sinistral offset and controlling the upper cretaceous basins according to regional geological relationship and structural overprinting we interpret that the e w trending strike slip faults formed in the first stage whereas the ne striking strike slip faults formed later during an e w oriented compressional event therefore the principal stress direction varies from nw se to e w

the contorted new england orogen eastern australia new evidence from u pb geochronology of early permian granitoids 1 a series of sharp bends oroclines are recognized in the paleozoic to early mesozoic new england orogen of eastern australia the exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated here we present zircon u pb ages that confirm the lateral continuation of early permian 296 288 ma granitoids and shed new light on the oroclinal structure orogenic curvature is defined by the alignment of early permian granitoids parallel to the structural grain of the orogen as well as the curved geometry of sub vertical deformation fabrics forearc basin terranes and serpentinite outcrops alternative geometrical interpretations may involve two bends texas and coffs harbour oroclines three bends manning orocline or even four bends nambucca orocline we argue that the model involving four bends is most consistent with available data although further kinematic constraints are required to confirm the existence of the manning and nambucca oroclines a subsequent phase of younger magmatism 260 ma cuts across the curved structural grain providing a minimum age constraint for orocline development assuming a structure of four oroclines we suggest a tentative tectonic model that involves an early stage of subduction curvature during slab rollback at 300 285 ma followed by bending associated with dextral transpression a final tightening of the curved structures was possibly obtained by e w shortening during the late permian to triassic 265 230 ma hunter bowen orogeny

eolian contribution to geochemical and mineralogical characteristics of some soil types in medvednica mountain croatia abstract six pedological profiles were analyzed above five typical lithological units in medvednica mountain to determine the effect of eolian additions to the soil composition as well as the possible influence of relief vegetation cover and anthropogenic input on the dynamics of pedogenesis bedrock composition was defined using petrographic thin sections and chemical analyses major and trace element contents whereas pedological sedimentological and geochemical characteristics of six cross sections were determined by chemical major and trace element contents mineralogical modal analysis and grain size analysis soils developed on sedimentary bedrock mollic rendzic leptosols calcaric and albic luvisol sceletic mostly originate from weathering of siliciclastic detritus that was exposed to oxidization before diagenesis furthermore soils on metasiltstone marble and lithothamnium limestone exhibit similar modal and geochemical composition and element distribution across the soil profile in contrast soils developed on igneous bedrock originate mostly from weathering of minerals of the first weathering cycle and thus abound with chemically less resistant minerals and less mobile elements however all profiles contain higher concentrations of lead with respect to bedrock indicating airborne contamination

a pedostratigraphic marker in the geomorphological evolution of the campanian apennines southern italy the paleosol of eboli abstract the paleosol of eboli is interbedded within an early pleistocene coarse alluvial succession the eboli conglomerates located in the campanian apennines southern italy infilling the morphostructural depression of the sele river plain quaternary climatic changes and related morphodynamic response were investigated using a multidisciplinary geomorphological sedimentological and pedological approach the alluvial sequence of the eboli conglomerates shows remarkable vertical changes marked by clear erosional discontinuities that identify four stacked formations called from the bottom fontana del fico colle mancuso castelluccia and s anna formations the clastic facies of these formations are mainly indicative of an alluvial fan environment with most sediments emplaced by flooding of distributary streams the paleosol of eboli is formed at the top of the castelluccia formation we investigated its morphological physical chemical micromorphological and mineralogical properties many discontinuities appear in the field due to various erosional events that are related to hillslope dynamics each of these events was followed by the emplacement of new and different colluvial deposits that were derived from upslope and were subsequently affected by pedogenesis all the horizons of the paleosol of eboli have reddish and brown matrix colours secondary carbonate angular blocky structure and clayey texture on the basis of the field data and chemical and physical analysis three different pedogenetic cycles can be distinguished in the paleosol of eboli these cycles depict differing degrees of pedogenic expression depending on water regime and duration of pedogenesis the micromorphology showed the presence of eluvial tongues fe dynamics coatings segregations vertic features optically anisotropic lines in the soil matrix and pedorelicts kaolinite is the most abundant clay mineral but vermiculite and illite are also present the fe minerals especially the hematite goethite ratio have provided a new approach to understand the main paleoclimatic changes through the studied sequence the overall pedogenetic scenario depicts a highly weathered environment disordered kaolinite fe oxides low feo fed ratio depletion zones characterized by marked climatic seasonality witnessed by vertic properties and abundant rainfall depletion zones the general scenario is coherent with a highly weathered subtropical environment that probably occurred during mis 25 based on age control the widespread outcrop pattern consistent stratigraphic position thickness ranging from 1 to 5 m and the uniformity of pedological features of the paleosol of eboli make it clearly recognizable in the field and allow us to consider the paleosol of eboli a reliable pedostratigraphic marker

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

provenance and tectonic setting of the carboniferous sedimentary rocks of the east junggar basin china evidence from geochemistry and u pb zircon geochronology abstract the modern junggar basin was located in the central asian orogenic belt caob during the devonian and carboniferous few data concerning the weathering provenance and tectonic setting of the carboniferous sedimentary rocks in the junggar basin have been published the recent discovery of an oil gas field in the east junggar basin provides the impetus for this study twenty eight sediment samples were recovered from eight boreholes and all were analysed for major and trace element geochemistry two samples of sedimentary rocks were selected for zircon u pb dating low chemical index of alteration cia values 44 71 and relatively high index of compositional variability icv values 0 72 1 83 suggested weak chemical weathering and an immature source for these samples the relatively low th u 2 16 10 55 and rb sr 0 03 5 44 ratios of the drill core samples reflect a simple recycling history two samples indicated upper carboniferous ages 314 6 ma and a lower middle devonian age 397 9 ma geochemistry and detrital zircon geochronology from the east junggar basin reveal a distinct difference in the composition and source rock ages of clastic rocks from the lower and the upper carboniferous major and trace element compositions of the lower carboniferous sedimentary rocks lcrs were derived from typical mafic rocks and an intermediate ocean island arc of early to middle devonian age whereas the upper carboniferous sedimentary rocks ucrs were derived from a continental island arc or active continental margin setting with a dominantly felsic to intermediate late carboniferous age the current data provide little support for tectonic models that show a passive continental margin of a precambrian crystalline basement our study suggests that a volcanic arc accretion or archipelago early carboniferous to early middle devonian model for the east junggar basin is more viable

characterizing potential offshore seismic sources using high resolution geophysical and seafloor sampling programs an example from cape egmont fault zone taranaki shelf new zealand standard marine geological techniques high resolution seismic reflection methods piston cores are used to investigate the neotectonics and paleoseismology of an active part of an offshore fault system the cape egmont fault zone taranaki continental shelf new zealand the main active structure within the zone the cape egmont fault is a reactivated pliocene to recent normal to oblique slip fault that is associated with shallow crustal seismicity and exhibits a 53 km long 1 to 5 m high low angle drape fold or scarp at the seafloor four possibly five fault segments varying in length from 7 51 km are delineated using geometric structural and stratigraphic information empirical estimates of maximum credible earthquake magnitudes based upon seismic moment calculations surface rupture lengths and vertical surface offsets suggest that the prehistoric earthquake s that formed the present seafloor surface trace probably had a magnitude of at least mw 6 4 mw moment magnitude and could have been as large as ms 7 3 7 4 ms surface wave magnitude tentative maximum recurrence intervals for such events inferred for each segment range from 8000 13 000 years with lower magnitude events having correspondingly shorter recurrence intervals of 500 900 years without careful study of offshore late quaternary faults and fault zones particularly where they are contiguous with areas of active onshore deformation existing regional seismic hazard predictions may be inaccurate

subduction dynamics and the origin of andean orogeny and the bolivian orocline the building of the andes results from the subduction of the oceanic nazca plate underneath the south american continent however how and why the andes and their curvature the bolivian orocline formed in the cenozoic era 65 5 million years myr ago to present despite subduction continuing since the mesozoic era 251 0 65 5 myr ago is still unknown three dimensional numerical subduction models demonstrate that variations in slab thickness arising from the nazca plate s age at the trench produce a cordilleran morphology consistent with that observed the age dependent sinking of the slab in the mantle drives traction towards the trench at the base of the upper plate causing it to thicken thus subducting older nazca plate below the central andes can explain the locally thickened crust and higher elevations here we demonstrate that resultant thickening of the south american plate modifies both shear force gradients and migration rates along the trench to produce a concave margin that matches the bolivian orocline additionally the varying forcing along the margin allows stress belts to form in the upper plate interior explaining the widening of the central andes and the different tectonic styles found on their margins the eastern and western cordilleras the rise of the central andes and orocline formation are directly related to the local increase of nazca plate age and an age distribution along the margin similar to that found today the onset of these conditions only occurred in the eocene epoch this may explain the enigmatic delay of the andean orogeny that is the formation of the modern andes

unraveling the early middle paleozoic paleogeography of kazakhstan on the basis of ordovician and devonian paleomagnetic results abstract it is a common concept that different tectonic units in the western part of the central asian orogenic belt were united into the landmass of the kazakhstania continent in the paleozoic but many important details of its history remain enigmatic and controversial recently published paleomagnetic data from this region demonstrate that the 2000 km long horseshoe shaped devonian volcanic belt was created by oroclinal bending of an originally rectilinear active margin of kazakhstania still the silurian and devonian paleomagnetic results which this interpretation is based upon are limited and unevenly spread along the belt and additional middle paleozoic data are highly desirable accordingly we studied three mid paleozoic objects from different segments of this volcanic belt two of the three new objects yielded paleomagnetic directions that fit perfectly into the oroclinal scenario whereas the third one provided no interpretable data the earlier history of kazakhstania however remains misty we obtained three new ordovician results in north central kazakhstan and found similar inclinations but widely dissimilar declinations previously published data show a large scatter of ordovician declinations in south kazakhstan and kyrgyzstan as well we analyzed all seven middle late ordovician paleolatitudes and came to the conclusion that a nearly e w trending active margin of the kazakhstania landmass had existed at low 10 s latitudes at that time we hypothesize that this margin of the kazakhstania landmass collided with another island arc called baydaulet akbastau and with the aktau junggar microcontinent by the ordovician silurian boundary as a result of this collision subduction ceased and regional deformation magmatism and rotations of crustal fragments took place in most of kazakhstania in silurian time kazakhstania moved northward crossing the equator and rotating clockwise by 45 this changed the orientation of the kazakhstania to nw se and thereby established the rectilinear predecessor of the modern curved devonian volcanic belt

progressive accretionary tectonics of the beishan orogenic collage southern altaids insights from zircon u pb and hf isotopic data of high grade complexes abstract high grade gneissic rocks of the southern altaids in central asia bear one of the key elements needed to solve a basic architectural controversy in accretionary orogenesis high grade gneissic rocks widely crop out across the beishan orogenic collage southern altaids mapped as the beishan complex or dunhuang group which was previously regarded as neoarchean to paleoproterozoic crystalline basement but without systematic field geochronological and geochemical data this study provides field geochemical and zircon u pb and hf isotopic data for gneissic rocks from the beishan complex geochemical data show that the gneissic rocks were probably formed in a subduction environment most zircons from the beishan complex are magmatic origins because their th u ratios are mostly in the range of 1 0 0 1 they show age peaks at 494 ma 464 ma and 375 ma with a few precambrian ages zircon hf isotopic compositions indicate that both old and juvenile materials were involved in the formation of the beishan complex which is different from the basement rocks of the tarim craton both in radiometric age and hf isotopic composition all these data thus do not support a uniform precambrian basement in the beishan area as previously proposed but instead the beishan complex probably formed in a subduction accretion environment combined with regional geology and geochemical data we conclude that the beishan orogenic collage was characterized by progressive long lived accretionary tectonics during late precambrian to paleozoic time therefore shedding light on the controversy regarding the architecture of accretionary orogens

mineralogical and geochemical characteristics of quaternary sediments from the island of susak northern adriatic croatia middle and upper pleistocene loess palaeosol sequences up to 90 m thick are exposed on the island of susak located in the northern adriatic sea in croatia during glacial times the sea level was up to about 120 m lower and a significant part of the adriatic became land the source area of the primary aeolian sediments was in the vicinity of the island and is related to the southward extended river po plain the loess has a mainly clayey to sandy silt or sand grain size and is intercalated by at least three tephras numerous palaeosols and calcareous segregations the heavy mineral association points to metamorphic and igneous rocks from alpine regions as source material of the loess geochemical and mineralogical properties of loess and palaeosols differentiate one from another and reflect the intensity of weathering and pedogenesis the oldest tephra contains vitroclasts and serrated clinopyroxene while the middle and the youngest tephra along with vitroclasts contain idiomorphic augite as diagnostic volcanic features based on bulk rock and vitroclast chemistry morphology of pyroxenes and the age of the loess sandwiching the tephra the potential source of this volcanic material could very likely be the campanian or aeolian volcanic province in southern italy infrared stimulated luminescence dating results show that the major part of the aeolian deposits including the tephra layers correlates to mis 3 mis 5

overview of ophiolites and related units in the late palaeozoic early cenozoic magmatic and tectonic development of tethys in the northern part of the balkan region abstract the northern balkan peninsula including serbia montenegro bosnia croatia and the former yugoslavian republic of macedonia represents an excellent region for the study of tectonic processes related to mesozoic tethyan ophiolite genesis and emplacement we first summarise the main tectonic units of the northern balkan peninsula and then use this information to discuss tectonic processes including rifting sea floor spreading ophiolite genesis and emplacement melange accretion ocean basin closure and collision we then discuss alternative models of ophiolite genesis and emplacement for the region and suggest that multi ocean basin interpretations fit the data better than single ocean basin interpretations rifting of adria gondwana during the triassic created a rift in the south budva zone and opened a triassic oceanic basin further north dinaride ocean occurrences of inferred sub continental mantle lithosphere in the dinaride ophiolite belt e g zlatibor may record extensional exhumation within an ocean continent transition zone bordering the adria dinaride continent this was followed by emplacement together with ophiolites and melange during upper jurassic early cretaceous time upper triassic radiolarites and mid ocean ridge type basalts formed at a spreading ridge after continental break up the oceanic lithosphere of the dinaride ophiolite belt was partly generated above a subduction zone the metamorphic soles of the dinaride ophiolites formed during mid late jurassic mainly based on k ar dating widespread melange that is associated with the ophiolites represents a subduction complex controlled by tectonic accretion and sedimentary reworking in trench and fore arc basin settings a possible cause of jurassic dinaride ophiolite emplacement was collision of a subduction trench with a continental margin further north mesozoic oceanic lithosphere subducted northeastwards present coordinates opening a late jurassic marginal basin in the main vardar zone the dinaride ocean in the south closed during late jurassic early cretaceous time tithonian berriasian deformed oceanic crust melange and magmatic arc rocks further north main vardar zone were transgressed by mainly clastic sediments during the early cretaceous however part of the vardar ocean vardar zone western belt or sava zone remained partially open until latest cretaceous time generally northward subduction within this remnant ocean triggered further supra subduction zone ophiolite genesis during the late cretaceous the ocean closed by the maastrichtian followed by early cenozoic regional scale southward thrusting that locally intercalated older and younger mesozoic ophiolites and melanges future progress particularly depends on determining the crystallisation ages of the ophiolites obtaining better structural data on the direction of initial ophiolite emplacement and unravelling the palaeozoic tectonic development of the eurasian continental margin

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

the hongliuhe fold and thrust belt evidence of terminal collision and suture reactivation after the early permian in the beishan orogenic collage northwest china abstract the early permian strata of the hongliuhe formation are located in the beishan orogenic collage a tectonically significant region between the tianshan orogen and the southern mongolian accretionary system of the central asian orogenic belt also called the altaids stratigraphic reconstruction of the formation shows a general fining upwards sequence of rhythmically interbedded sandstones and siltstones with thick basal successions of conglomerates all unconformably overlying an earlier mid paleozoic volcanic assemblage the clast lithotypes of conglomerates successively change from being polymictic metamorphic tectonites at the base to a nearly monomictic granitoids mid section illustrating the unroofing sequence of an arc related provenance the intra oceanic gongpoquan composite arc that comprises most of the central beishan fits the clast lithotype profile of the conglomerates and is the most probable provenance the hongliuhe formation stratigraphy experienced a thin skinned fold and thrust belt style of deformation that has a consistent southward vergence deformation in the lower stratigraphic levels created thrust imbrication of formation scale blocks each separated by steep north over south brittle ductile shear zones the blocks are internally deformed with large scale folding with one significant block containing a sheath fold 15 km in breadth the upper stratigraphic levels accommodated strain through low angle thrust ramping shear folding imbricate fanning and duplexing this indicates that the hongliuhe formation was syn orogenically deposited in a progressively deepening terrestrial to nearshore environment within the gongpoquan composite arc our observations and data indicate that the basin overlies an earlier paleozoic suture zone this implies that the northern half of the gongpoquan composite arc overrode the southern half in a fault system reactivation centered about this zone of weakness and created a stratigraphic and structural response consistent with a subduction or collision driven fold and thrust belt its southward structural vergence is supporting evidence of a north dipping subduction related fault system under the northern gongpoquan the timing of both the genesis of the hongliuhe formation and this deformation event coincides with the subduction of the liuyuan ocean or docking of the dunhuang block further south at the southern margin of the gongpoquan composite arc

zircon ages of metamorphic and magmatic rocks within peridotite bearing melanges crucial time constraints on early carboniferous extensional tectonics in the chinese tianshan abstract we dated and geochemically characterized peridotite bearing melanges in the chinese south tianshan and within the main tianshan shear zone the yushugou tonghuashan melange in the chinese south tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite predominantly lherzolite massif with a high grade metamorphic terrane ca 10 km long protolith age ca 445 466 ma metamorphic zircons of a mafic granulite end t 5 0 yielded a weighted mean 206pb 238u age of 341 8 ma that we interpret as the time of granulite facies metamorphism the youngest zircon rims of an intermediate granulite end t 4 3 have a mean age of 332 13 ma that records a retrogressive metamorphic event these ages determine the timing ca 341 332 ma of mantle diapirism through continental crust a dolerite dike end t 2 3 emplaced into metaperidote has a crystallization age of 335 5 ma that on the basis of geochemistry we interpret as representing e morb oib magmatism that accompanied mantle diapirism an undeformed pink granite end t 3 6 intrudes the melange matrix and has an emplacement age of 324 5 ma thus providing an upper time limit for a tectonic movement that led to melange formation the older time limit of deformation ca 362 352 ma is constrained by the youngest ages of thermo tectonically modified zircons in a mylonitized metagabbro and a foliated meta andesite magmatic zircons in the meta andesite end t 3 3 and a dacite end t 5 6 have eruption ages of 433 4 ma and 435 3 ma that date formation of the melange matrix a microgabbro dike end t 10 0 cutting metasediments i e melange matrix has an emplacement age of 279 3 ma and contains abundant zircon xenocrysts ranging in age from archean to late paleozoic similarly a dolerite dike a meta andesite an intermediate granulite and a metagabbro all contain inherited precambrian to paleozoic zircons we accordingly conclude that the melange was formed by mantle diapirism in the early carboniferous and was subsequently affected by an early permian volumetrically minor mafic episode two foliated garnet granites end t 7 0 and 6 9 in direct contact with metaperidotite within the main tianshan shear zone have emplacement ages of 341 2 ma and 329 4 ma that reflect an early carboniferous episode of crustal anatexis they also contain neoproterozoic zircon xenocrysts also within the main tianshan shear zone a gabbro end t 8 7 has an emplacement age of 297 3 ma and contains abundant neoproterozoic to late paleozoic zircon xenocrysts based on the regional geological relationships we associate early carboniferous mantle diapirism and crustal anatexis with lower crustal delamination induced asthenospheric upwelling the numerous precambrian zircon xenocrysts support a chinese tianshan tarim connection the early permian mafic episode coincided in time with the development of an early permian unconformity in the chinese north tianshan

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

palaeoenvironmental reconstruction of the milna valley on the island of vis central adriatic during the late holocene abstract this study provides a reconstruction of the 1 5 ka palaeoenvironmental evolution of the small and presently dry milna valley on the island of vis sediments from the valley were studied using multi proxy approach applying sedimentological mineralogical petrological anthracological malacological 14c and land cover analyses in regard to climatic vegetation and hydrological changes the mineral composition of the siliciclastic detritus from the milna valley points to the dinaride ophiolite zone in bosnia as its dominant source of origin eroded by the neretva river and deposited in the form of alluvial sediments in the central adriatic area however cetina and drin rivers may have also contributed some of the sediments regional aeolian resedimentation of the material occurred during pleistocene which later accumulated and became preserved in the milna valley beside the dinaride ophiolite zone part of the mineral composition is influenced by minerals from the alpine region and by neutral to basic volcanism probably of italian origin during the dark age cold period dacp the milna valley was covered by forests of the pinus sylvestris group within which cold resistant and closed forest habitat preferring species molluscs lived this forested environment probably lasted until the little ice age lia period when fires occurred in the 15th and 16th centuries the opening of the landscape corresponded to the resettling of the population from the interior to the coast and to the expansion of vineyards on the island the deforestation enabled the formation of torrential flows and deposition of unsorted sediments most of the pebbles are rounded clasts of the middle cretaceous cenomanian dolomite in which the valley is formed however pebbles which are not present in outcrops of the milna valley have also been identified after the lia the valley became dry again and has been continuously under anthropogenic impact ever since different cartographic sources enable the further tracing of land cover changes from the beginning of the 19th century to present day the analysis revealed that the highest anthropogenic impact on the landscape occurred in the second part of the 19th century after which afforestation started moreover the major issue today relates to changes influenced by the current relative sea level rise this study adds to the knowledge on coastal fluviokarst valley evolution in typical mediterranean conditions relating our understanding of holocene deposition human activity and land cover changes on the island of vis

recognizing oib and morb in accretionary complexes a new approach based on ocean plate stratigraphy petrology and geochemistry abstract we present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy ops and on the petrology and geochemistry of basalts from mid oceanic ridges morb and oceanic islands oib using examples from four accretionary complexes ac in sw japan akiyoshi mino tamba chichibu and shimanto the key to the problem is the model of ops which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid oceanic ridge to a subduction zone we propose the reconstruction of the tectonic settings of basalts according to their relationships with associated ops sediments their petrogenesis and their geochemical features five types of ops are recognized in the accretionary complexes of sw japan 1 sandstone shale 2 sandstone shale and chert 3 sandstone shale chert and morb 4 sandstone shale chert morb and gabbro peridotite 5 seamount ops including oib cap carbonates slope clastics and basal shale chert the alkaline tholeiitic or calc alkaline composition of basaltic melts which are typical of oceanic islands mid oceanic ridges and island arcs respectively can be identified by the sequence in crystallization of their major phenocrysts i e olivine ol clinopyroxene cpx and plagioclase pl and by their compositions alkaline and calc alkaline mafic lavas are characterized by an ol cpx pl succession whereas tholeiitic melts by their ol pl cpx succession titanium rich minerals e g ti augite kaersutite ti biotite are typical of alkaline lavas the application of geochemistry based tectonic discrimination diagrams is also a powerful tool if not supported by geological and petrological data may result in confusion due to magma contamination post magmatic alteration and secular change of mantle thermal conditions we propose that a direct comparison of normalized multi element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination our ops petrology geochemistry method allows us to confirm the above conclusions that the lavas of the akiyoshi mino tamba and southern chichibu ac formed in oceanic islands because they are associated with seamount ops sediments crystallized from ol to cpx and pl contain ti augite and kaersutite and are enriched in tio2 lree and nb in this paper we present geochemical data from the inuyama basalts of the mino tamba ac and from the toba complex in the huge mikabu greenstone belt of the chichibu ac the inuyama basalts are in contact with jurassic pelagic cherts but their geochemical features are confusing they contain phenocrysts of ol ti augite and kaersutite and therefore probably formed in seamounts the toba volcanic rocks are a part of the huge ophiolite belt they have flat to slightly lree enriched ree patterns are characterized by an ol cpx succession of phenocrysts and they plot in the oib field in binary plots suggesting they formed in an oceanic plateau

caribbean island arc rifting and back arc basin development in the late cretaceous geochemical isotopic and geochronological evidence from central hispaniola this work froms part of the mcyt projects bte 2002 00326 and cgl2005 02162 bte and also received aid from the cartographic project of the dominican republic funded by the sysmin program of the european union careful reviews from j geldmacher a c kerr and an anonymous reviewer are much appreciated

sea level change during mis 5a based on submerged speleothems from the eastern adriatic sea croatia abstract two stalagmites were collected from below sea level in u vode pit on the krk island eastern adriatic sea at elevations of 14 5 and 18 8 m they exhibit a growth history indicating a double high sea level stand during marine isotope stage mis 5a 87 77 ka thin layers of halite and gypsum were found to be associated with hiatuses in speleothem growth probably caused by seawater inundation during sea level highstands these mineral deposits are likely to have been precipitated during marine regression phases under evaporitic conditions we constrain the age of the speleothem growth below and above growth hiatuses and hence timing of possible marine incursions using multi collector inductively coupled plasma mass spectrometry mc icpms u th techniques age estimates indicate that during mis 5a relative sea level elevations were greater than 14 5 m from 87 to 82 ka and 18 8 m from 77 to 64 ka and constrained to be lower than 18 8 m from 93 to 90 ka 82 to 77 ka and 64 to 54 ka assuming no tectonic adjustment however present speleothem depths could indicate long term regional tectonics

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

transition from frontal accretion to underplating in a part of the nankai trough accretionary complex off shikoku sw japan and extensional features on the lower trench slope abstract migrated multichannel seismic reflection profiles and bathymetry from a 200 120 km area of the nankai trough inner slope reveal three physiographic tectonic domains on the lowermost slope linear ridges demarking laterally continuous hangingwall anticlines above ramps in a relatively simple imbricate stack of trench turbidites characterize the western domain an imbricate fan underlies a relatively flat structural terrace in the east between these two domains lies a compound knoll minami muroto knoll some 40 km long opposite which the thrust front pushes some 10 km further seaward than is the case in the domains to east and west in the western linear ridge domain previous dsdp drilling penetrated turbiditic trench fill uplifted in the lowermost thrust fold terrace above a decollement within the underthrusting shikoku basin oceanic plate sequence the shikoku basin sequence in the western domain is divided into an upper poorly reflective hemipelagic claystone unit and a lower strongly reflective unit comprising pliocene turbidites the lower unit is traceable intact up to c 20 km landward below the lower trench slope and in the better resolved profiles the decollement lies along the base of the claystone unit a similar decollement within the shikoku basin sequence in the eastern domain is traceable up to c 22 km landward a critical seismic record crossing the western part of minami muroto knoll shows that the decollement is traceable only 8 km landward to a point under the steep slope at the front of the knoll landward of which the subducting shikoku basin sequence is apparently thickened by as much as twice this thickening occuring as it does immediately along strike from a simple imbricate fan to the east of the knoll and a relatively simple imbricate stack to the west both evidently involving no strata from the lower shikoku basin unit we ascribe to underplating by formation of duplexes of shikoku basin strata strike parallel extension akin to that postulated for high structural levels in certain thrust belts is caused by uplift of the knoll as a result either of the underplating or segmentation of the subducting oceanic crust or both a normal fault throws to the west off the west flank of the knoll it bounds a transverse trough like slope basin with at least 900 m of fill upslope from the knoll broadly slope parallel normal faults cut and pond recent slope sediments the most impressive is a listric growth fault which dips trenchward alternative explanations for these involve extensional collapse of this part of the prism resulting from the subduction of a topographic high or a zone of selective underplating below the trenchward portion of minami murato knoll

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

influence of sediment provenance on background values of potentially toxic metals from near surface sediments of po coastal plain italy systematic variability in metal concentrations is recorded in near surface 1 m deep late quaternary sediments of po coastal plain across the boundary between alluvial deposits of apenninic provenance and a formerly active now abandoned delta lobe of the po river in the latter area high cr and ni concentrations exceeding the national standard limits are attributed to sediment provenance from ultramafic source rocks of po catchment basin and not to anthropogenic impact spatial distribution of carbonate related elements such as ca and sr displays consistent differences between the two areas confirming a primary control of provenance domains on sediment composition accurate facies characterization of near surface sediments coupled with detailed information on sediment dispersal patterns enable a reliable interpretation of the spatial variability of major elements and trace metals in the study area particularly detailed reconstructions of source area composition and changes in flow directions through historical times allow precise correlation of apparently anomalous geochemical patterns with distinctive depositional events such as shifts in channel course crevasse splay formation and beach ridge evolution the findings of unusually high natural provenance controlled heavy metal concentrations in pre industrial near surface levels highlight the contribution of a sedimentological approach to a reliable interpretation of geochemical data this should be taken into account when determining background values versus anthropogenic impact

the characteristics of cultivated soils developed from coastal paleosand korcula island croatia the problem of maintaining soil quality and fertility of soil developed from pleistocene eolian sand deposits arises from improper management and conservation of the highly fragile sandy soil environment the research was undertaken to determine howvarious aspects of cultivated soil fertility can be related to specific pedological and geological factors and which one of these relationships plays an essential role in lumbarda polje korcula island croatia soil survey was done by examining and sampling one hundred locations to the depth of 100 cm within 40 ha of the winegrowing site geostatistical analysis was applied to characterize the spatial variability and produce the soil map of the area soil profiles were sampled for laboratory analysis including physicochemical characteristics and mineralogy modal analysis and petrographic microscopy of soil concretions were conducted as well two soil units su were identified both containing more than 80 sand su1 hypoluvic arenosols and su2 haplic arenosols fao 2006 in su1 reddish brown color originated from fe oxide coatings on sand grains whereas su2 is characterized by the rise of ph with depth and the presence of calcite as a cementing material cation exchange capacity was significantly higher in su2 the documented variability of element content and distribution in the soil profiles indicates differentweathering stages of the sandy layers diagrams of cr v and co v ratios indicate different origin of sand deposits light mineral fraction is dominant in both su most of the sand grains are intensively weathered and well rounded indicating long transportation from the source area the results of mineralogical and geochemical characterization of lumbarda polje grapevine growing site are applicable and useful to future studies that involve fingerprinting regional wines

pleistocene calcareous aeolian alluvial deposition in a steep relief karstic coastal belt island of hvar eastern adriatic croatia abstract pleistocene aeolian and alluvial deposits occur on the island of hvar belonging to the eastern adriatic karstic coastal belt along the north eastern mediterranean margin the depositional mechanism of the aeolian alluvial and talus sediments are interpreted based on facies analysis and mineralogical composition aeolian deposits are represented by cross bedded cross laminated and sub horizontally laminated fine to medium grained calcareous sands the cross bedded units form tabular sets stacked into cosets sets and cosets are separated by distinct low angle bounding surfaces which mostly dip towards the east interpreted as the upwind direction cross laminated units form isolated sets within the cross bedded and sub horizontally laminated units cross bedded and cross laminated units represent dunes dominated by grain fall and wind ripple deposition respectively dunes produced by sand flow also occur but are less common the cross bedding is truncated by reactivation surfaces transverse dunes and some small dome shaped dunes were also present sub horizontally laminated sandy units represent aeolian sand sheets developed by wind ripple migration in the interdune area a few wind rippled dune apron deposits also occur trace fossils are locally very abundant within the aeolian deposits mostly produced by plants soft sediment deformation such as contorted cross bedding and pocket structures occur scattered and rare reddish horizons show pedogenesis unlikely most quaternary coastal aeolian sands these sands do not include marine bioclasts in composition the sands are composed of extraclasts dominated by limestone with subordinate chert quartz sericite schist quartzite and quartz amphiboles pyroxene and epidote are the most abundant translucent heavy minerals the mineralogical composition and palaeoflow directions indicate that the dinarides were the main provenance of the sand transported by primary easterly and northerly continental winds causing migration of dunes towards the palaeo adriatic sea alluvial deposits are intercalated with the aeolian sands they are composed of breccia derived from a nearby steep hill ridge and by resedimented aeolian sand deposited by traction currents during flash floods talus fragments reached the aeolian sands only sporadically climate strongly affected aeolian alluvial and talus depositions during arid conditions dunes migrated forming a dune field whilst more humid climate triggered heavy rains and generated erosion of aeolian deposits alluvial sedimentation colonisation of plants and pedogenesis deposition was in a topographic basin and was controlled by capacity of source area and wind however local orography characterised by developed and steep karstic relief strongly affected wind directions and in that way had specific controls on the dune field evolution dominating winds caused seaward dune migration differing from most mediterranean quaternary coastal aeolian dune localities characterised by landward migration