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

tectonic entities connection between west junggar nw china and east kazakhstan abstract west junggar nw china and east kazakhstan are situated in the southwest of the central asian orogenic belt caob tectonic entities in the two areas share the same tectonic evolution history and make up the famous horseshoe shaped orocline in central asia this paper presents a newly compiled cross border tectonic sketch map of west junggar and east kazakhstan and proposes the extension of the chingiz tarbagatai belt and the north balkhash west junggar belt the chingiz tarbagatai belt in east kazakhstan consists mainly of middle late ordovician differentiated volcanic rocks pyroclastic sediments and flysch while in the tarbagatai mountain in china tarbagatai kujibai ophiolite is newly found with zircon gabbro age of 478 3 ma and the ordovician flysch metamorphosed to a greenschist facies is distinguished from devonian carboniferous rock associations therefore the early paleozoic chingiz tarbagatai belt of east kazakhstan evidently extends to the northern part of west junggar along the tarbagatai orogenic belt the north balkhash west junggar belt lying south to the chingiz tarbagatai belt is separated by the ew trending baiyanghe heshituoluogai depression in west junggar early ordovician early silurian ophiolitic fragments and related pyroclastic sediments are widely exposed in tekturmas north balkhash and agadyr of east kazashtan similarly early paleozoic ophiolites have also been verified in tangbale mayile baerluke darbut and karamay of west junggar in recent years therefore nearly all ophiolites in west junggar and east kazakhstan are proved to have formed in early paleozoic which suggests that the evolution of the paleo ocean in the two areas reached its peak in the early paleozoic based on the ages of the tangbale karamay and hongguleleng ophiolites an early paleozoic continental accretionary belt extending from tangbale to hongguleleng is determined at the nw margin of the junggar basin for the first time according to spatiotemporal comparison ophiolites exposed in west junggar and east kazakhstan might originate from the same paleo ocean tectonic region and then the north balkhash in east kazakhstan and the west junggar were offset for a long distance with respect to each other by the major junggar dextral fault because of the large scale accretion of continental crust before silurian the late paleozoic ocean in west junggar and east kazakhstan became smaller with residual nature and extensive arc basin trench systems might be absent during the closure of this residual ocean

upwelling asthenosphere beneath western arabia and its regional implications two distinct phases of continental magmatism are evident in western arabia the first from about 30 to 20 ma produced tholeiitic to transitional lavas emplaced along nw trends the second from about 12 ma to recent produced transitional to strongly alkalic lavas emplaced along n s trends the older phase is attributed to passive mantle upwelling during extension of the red sea basin whereas the younger phase is attributed to active mantle upwelling but was facilitated by minor continental extension perpendicular to plate collision the younger magmatic phase is largely contemporaneous with a major period of crustal uplift to produce the west arabian swell after about 14 ma a variety of evidence suggests that the west arabian swell is thermally supported by hot upwelling asthenosphere in contrast to the distinct asymmetry of uplift and magmatism on opposing sides of the red sea basin these processes were symmetric across a n s line marking the central axis of the west arabian swell this axis coincides with two fundamental features the ha il rutbah arch in the north and the makkah madinah nafud mmn volcanic line in the south the symmetry of magmatism is demonstrated by petrochemical evidence that the mmn harrats were derived by greater degrees of partial melting at shallower depths than those harrats lying to the west and east of the mmn line the potential temperature of the asthenosphere is estimated to be about 1436 c beneath the mmn line and about 1354 c beneath the flanking more undersaturated harrats the source of upwelling is either a mantle plume centrally located beneath the west arabian swell or an elongated and extended lobe of hot asthenosphere emanating from the ethiopian mantle plume convective flow may have been channelled along a preexisting regional flexure in the continental lithosphere which concentrated hot asthenosphere beneath the central axis of the afroarabian dome this crest of mantle upwelling underlies the mmn line in the north and the danakil depression and ethiopian rift system in the south it also passes through the red sea basin at the midpoint of an unusual doubly propagating rift system where axial seafloor spreading began 4 5 m y ago the nw trend of the red sea basin was well established by crustal attenuation during the older magmatic phase the pliocene invasion of this basin by a n s zone of mantle upwelling has resulted in seafloor spreading parallel to the preexisting structure along a rift system that has continued to propagate away from its eccentric mantle source in two opposing directions

hydrogen index and carbon isotopes of lacustrine organic matter as lake level indicators abstract optical and geochemical techniques were applied to organic matter of late quaternary sediments from lakes victoria and rukwa east africa variations in total organic carbon toc and hydrogen content expressed as hydrogen index hi can be related to known changes in lake level and used to identify periods of very low water or subaerial exposure in basinal sequences toc and hi both decline as an exposure surface is approached mainly due to the selective removal of unstable components by bacterial respiration and inorganic oxidation inert organic material of very low hi is typically concentrated at the overlying transgression surface the carbon isotopic composition of the particulate organic matter tends to be less negative in sediments associated with exposure surfaces although weathering may be partially responsible isotopic variations are mainly due to changes in the relative importance of material from plants using c4 photosynthesis such as grasses and sedges growing around the shore and on the exposed lake muds and of material from planktonic algae and terrestrial c3 plants

linking the southern west junggar terrane to the yili block insights from the oldest accretionary complexes in west junggar nw china abstract west junggar is known to tectonically correlate with east kazakhstan however the tectonic link of the southern west junggar terrane to adjacent regions still remains uncertain here we examined the oldest accretionary complexes thus constraining its tectonic evolution and link during the early middle paleozoic they have contrasting lithologic geochemical and geochronological features and thus provenances and tectonic settings the laba unit was derived from the late ordovician early devonian continental arc system peaking at 450 420 ma with precambrian substrate which formed as early as the early devonian and metamorphosed during the permian however the kekeshayi unit was accumulated in an intra oceanic arc setting and includes the pre late silurian and late silurian subunits with or without precambrian sources integrated with the regional data the southern west junggar terrane revealed a tectonic link to the northern yili block during the late silurian to early devonian as suggested by the comparable precambrian zircon age spectra between the southern west junggar terrane and the micro continents in the southern kazakhstan orocline the proximal accumulation of the laba unit in the continental arc atop the yili block and the sudden appearance of precambrian zircons in the kekeshayi unit during the late silurian this link rejects the proposals of the southern west junggar terrane as an extension of the northern kazakhstan orocline and the middle paleozoic amalgamation of west junggar a new linking model is thus proposed in which the southern west junggar terrane first evolved individually and then collided with the yili block to constitute the kazakhstan continent during the late silurian the independent and contrasting intra oceanic and continental arcs also support the paleozoic archipelago type evolution of the central asian orogenic belt

the arabian continental alkali basalt province part i evolution of harrat rahat kingdom of saudi arabia the harrat rahat lava field forms a major component of an extensive but poorly known continental alkali basalt province extending from yemen in the south through saudi arabia and jordan to syria in the north the continental intraplate volcanism which produced the arabian lava fields harrats was contemporaneous with opening of the red sea collision of the arabian and eurasian plates and uplift of the afro arabian dome harrat rabat has evolved over the past 10 m y it contains two prominent lateritic disconformities which separate three stratigraphic units the shawahit 10 2 5 ma hammah 2 5 1 7 ma and madinah 1 7 recent basalts comprising 68 19 and 13 of the total harrat volume respectively the shawahit basalt is composed of coarse grained dictytaxitic olivine transitional basalt otb and minor 10 alkali olivine basalt aob which erupted through scoria cones and shield volcanoes in contrast the hammah basalt is dominated by equal volumes of fine grained intergranular to intersertal aob and hawaiite which erupted mainly through scoria cones and relatively few shield volcanoes sparse domes and flows of mugearite and benmoreite first appear in the hammah basalt the madinah basalt spans the full compositional range of harrat rahat 103 analyzed samples comprise otb 8 aob 47 hawaiite 32 mugearite 4 benmoreite 8 and trachyte 2 here scoria cones dominate whereas shield volcanoes are sparse and occur only in the lower madinah basalt domes and associated pyroclastic deposits are common the final events of harrat volcanism include 11 post neolithic eruptions 4 500 yr old and two historical eruptions in 641 and 1256 a d arabian harrat magmatism may have been initiated by partial melting of garnet perido tite in the asthenosphere at a depth 100 km accumulation of this partial melt at the crust mantle boundary 37 44 km may have resulted in miocene uplift of the afro arabian dome harrat rahat volcanism began shortly after significant initial uplift with the voluminous extrusion of shawahit otb lava chemical and petrographic data suggest that these otb magmas ascended rapidly with little crustal residence time the data support a model of open system fractionation for aob and hawaiite lavas of the younger hammah and madinah basalts in this model some of the potential shawahit otb was trapped in crustal chambers during magma ascent crystal fractionation in these chambers was accompanied by their periodic replenishment by rising otb magma this resulted in the mixing of magma types and the development of aob and hawaiite magmas which are anomalously enriched in highly incompatible elements the mugearite benmoreite and trachyte lavas are the products of advanced fractionation in these crustal chambers with little or no magma replenishment

seismic gravity and magnetic surveys in the central part of the red sea their interpretation and implications for the structure and evolution of the red sea abstract while there is unanimous agreement that the axial part of the red sea has witnessed seafloor spreading since the early pliocene opinions diverge considerably with regard to the situation in the main trough and shelves new high precision data comprising palaeomagnetic seismic gravity magnetic and bathymetric measurements from the central and northern parts of the red sea have been examined to discriminate between the earlier proposed hypotheses and to formulate an evolutionary model for the red sea the results show that oceanic crust extends for about 80 km at 19 n on each side of the spreading axis symmetrical seafloor spreading magnetic anomalies are recognized out to anomaly 3a 6 m y b p between 18 30 and 19 45 n anomaly 2a between 19 45 and 20 n and near 21 n anomaly 2 near 22 n and only anomaly 1 near 23 30 n although anomaly 3a is the oldest recognizable magnetic anomaly the extent and configuration of the oceanic basement as determined from seismic measurements indicate that spreading has started and continued without a hiatus since 10 12 m y b p prior to the initiation of oceanic accretion an extension of 40 55 km i e 50 70 has taken place in the proterozoic continental lithosphere whereas a separation of 70 160 km has occurred during the seafloor spreading phase several lines of evidence indicate that the shelves and the marginal parts of the main trough are of continental nature

paleomagnetism of mid paleozoic subduction related volcanics from the chingiz range in ne kazakhstan the evolving paleogeography of the amalgamating eurasian composite continent the tectonic and paleogeographic evolution of the ural mongol belt between the cratons of baltica siberia and tarim is key to the formation of the eurasian composite continent during paleozoic time but the views on this complicated process remain disparate and sometimes controversial a study of three volcanic formations of mid silurian lower to middle devonian and middle devonian age from the southwestern boundary of the chingiz range ne kazakhstan yields what are interpreted as primary paleomagnetic directions that help clarify the evolution of the belt a single polarity characteristic component in mid silurian andesites yields a positive intraformational conglomerate test whereas dual polarity prefolding components are isolated from the two devonian collections post folding reversed polarity overprint directions have also been isolated and are likely of permo triassic age these new data can be evaluated together with previously published paleomagnetic results from paleozoic rocks in the chingiz range and allow us to establish with confi dence the polarity of each result and hence to determine the hemisphere in which the area was located at a given time we conclude that ne kazakhstan was steadily moving northward albeit with variable velocity crossing the equator in silurian time these new paleomagnetic data from the chingiz range also agree with and reinforce the hypothesis that the strongly curved volcanic belts of kazakhstan underwent oroclinal bending between middle devonian and middle permian time a comparison of the chingiz paleolatitudes with those of siberia shows insofar as the sparse data allow similarities between the northward motion of the chingiz unit and that of siberia which imposes important constraints on the evolving paleogeography of the ural mongol belt

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

new k ar ages of basalts from the harrat ash shaam volcanic field in jordan implications for the span and duration of the upper mantle upwelling beneath the western arabian plate the volcanism in the western arabian plate extends from the red sea through the harrat ash shaam system to western syria as far north as the bitlis suture in the taurides the harrat ash shaam volcanic system in jordan consists of northwest trending dikes and a volcanic field that together encompass a width of 220 km in terms of width direction and age of the main volcanic phases the system is similar to the red sea dike belt about 130 new k ar age determinations show that the ages of the harrat ash shaam system dikes and flows range from oligocene to quaternary however there is a distinct gap in the ages between 22 and 13 ma this gap coincides with an apparent decrease in volcanism in the red sea region from around 20 to 12 ma we interpret this 9 m y gap as a quiescent period interrupting the volcanic activity in the region and suggest that from 22 to 13 ma tectonic activity in the arabian plate was mainly restricted to the red sea region a renewal of volcanism along the western margins of the arabian plate at 13 ma was very likely associated with the sinistral movement along the north trending dead sea transform this renewal of volcanism and tectonic activity may reflect the emergence of upper mantle upwelling beneath the western arabian plate at that time

paleozoic tectonic evolution of the northern xinjiang china geochemical and geochronological constraints from the ophiolites 1 the northern xinjiang of china is a composite orogenic belt in the south central part of the altaids formed by subduction accretion mainly during the paleozoic geochronologic and geochemical data from the paleozoic ophiolites and associated assemblages are reported here to place constrains on the tectonic evolution of this region and to reconstruct its history using a model of subduction accretion plus large scale map view strike slip faulting geologic and geochronologic review indicates that the paleozoic ophiolites and associated assemblages of the western and eastern junggar regions are tectonically related occurring as a pattern with the early paleozoic tangbale mayile hongguleleng aermantai complexes in the center the late paleozoic darbut karamaili and the northern tianshan complexes in the south and the late paleozoic kekesentao qiaoxiahala kuerti complexes in the north available geochemical data suggest that the paleozoic ophiolites of the northern xinjiang are mainly oceanic fragments of these three types mid ocean ridge basalt oceanic island basalts and island arc basalts the paleozoic subduction accretion complexes grew mainly along different segments of the kipchak arc and in associated with migration of magmatic arc the paleozoic ophiolite associated sedimentary sequences and subduction related volcanic rocks exhibit an evolution history from intraoceanic early paleozoic to marginal settings late paleozoic implying coeval strike slip stacking with subduction accretion processes and by which to transport the respective complexes together and further to amalgamate with neighboring units of the altaids subduction accretion processes terminated in the mid carboniferous in this region in the late permian early triassic a counterclockwise rotation of fault blocks in a giant sinistral strike slip and extension domain between altay and tianshan lastly generated present configuration of the paleozoic subduction accretion complexes in the northern xinjiang

new data on the late cenozoic basaltic volcanism in syria applied to its origin abstract new data on geology and 21 k ar dates of the late oligocene quaternary basalts in syria combined with analysis of the new and previous data are used to reconstruct the volcanic history and relations between it and tectonic events volcanism began at the end of oligocene 26 24 ma and was concentrated in the late oligocene early miocene along a n trending band which stretches from the jebel arab harrat ash shaam up to kurd dagh and southern turkey activity waned in the middle miocene 17 12 ma but was resumed in the same band in the tortonian and increased in the messinian and early pliocene 6 3 4 ma when volcanism spread to the shin plateau and its coastal extension after a brief hiatus 4 3 5 ma volcanism became still more intensive and spread from the n trending band to the east into the northern margin of the mesopotamian foredeep and to the west into the dead sea transform zone additional eruptions continued into the holocene volcanism lasted 25 million years in the jebel arab highland and 15 million years in the aleppo plateau the long duration of volcanism in the same parts of the moving arabian plate and absence of records of one way migration of the activity mean that the magmatic sources moved together with the plate i e they were situated within the lithosphere mantle coincidence of the tectonic and volcanic stages of the arabian plate development proves that volcanic activity depended on the geodynamic situation caused by the plate motion situated within the lithosphere magmatic sources within this transverse band were possibly caused by thermal and deforming influences of the asthenospheric lateral flow moved laterally from the ethiopia afar deep superplume

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

tectonic control on peritidal carbonate parasequence formation an investigation using forward tectono stratigraphic modelling studies of quaternary extensional faults indicate that they have instantaneous amounts of throw 0 4 to 4 m average slip rates 0 05 to 2 8 m kyr 1 and frequency of recurrence 40 000 years accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences pcps hangingwall sites and graben are characterized by fault down dropping together with regional subsidence and footwall sites and horsts by fault related uplift alternating with periods of regional subsidence the relative sea level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program sedtec2000 to simulate how fault related changes in accommodation space can account for high frequency pcp formation each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings high frequency cycles in hangingwall sites are either symmetric deepening then shallowing upward or asymmetric shallowing upward the major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space high frequency cycles in footwall sites and horsts comprise shallow subtidal facies with no distinctive bathymetric trends capped by erosional boundaries generated by footwall uplift the modelled cycles are of the same thickness with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea level changes or autocyclic processes these numerical experiments demonstrate that high frequency pcps can be generated by tectonic fault related processes a hypothesis that is frequently discounted

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

chromian spinels in highly altered ultramafic rocks from the sartohay ophiolitic melange xinjiang nw china abstract the sartohay ophiolitic melange is located in western junggar xinjiang province nw china which is a major component of the core part of the central asian orogenic belt caob chromian spinels in serpentinite talc schist carbonate talc schist and listwaenite in sartohay ophiolitic melange retain primary compositions with cr of 0 39 0 65 mg 0 48 0 67 and fe3

evidence for high frequency cyclic fault activity from high resolution seismic reflection survey rukwa rift tanzania a high resolution seismic survey of the rukwa rift has imaged the upper 300 m of the pliocene holocene section the sediments are characterized by aggradational deposition in shallow lacustrine conditions that episodically dried out overall the reflection package expands northeastwards towards the lupa fault half graben bounding fault isopach maps for nine intervals 6 m to 65 m thick show four periods of marked expansion of the section towards the lupa fault interpreted to represent times of fault activity or infilling of fault created topography during the early stage of fault quiescence there are three periods of little or much reduced expansion interpreted to represent infilling of the accommodation space between the lake floor and the lake surface during periods of fault inactivity cyclicity of such high frequency has not been widely reported for faults which penetrate the crust the periods of activity show remarkably similar displacement patterns with no lateral migration of the main depocentre implying that seismic and aseismic slip has persistently clustered in the same parts of the fault identification of high frequency fault cyclicity has implications for sequence stratigraphy in tectonically active areas since there is a tendency to assume faults do not have cyclic effects on the scale of tens of thousands of years

tectonic evolution of the paleozoic barluk continental arc west junggar nw china abstract the barluk arc situated in west junggar is an important component of the kazakhstan domain in the central asian orogenic belt caob however the nature of the barluk arc active continental margin or oceanic island arc is in debate the igneous rocks in the shiwu area barluk arc have diagnostic petrologic geochronologic and geochemical signatures that uncover the attributes of the barluk arc in this paper we report detailed petrology whole rock geochemistry and sr nd isotopic zircon u pb dating and hf isotopic data of igneous rocks in the shiwu area our results reveal that 1 except for 302 2 ma gabbro igneous rocks from barluk arc in the shiwu area are dioritic and granitic have ages ranging from 323 8 to 310 5 ma and they have geochemical signatures originated from typical continental arcs including calc alkaline series rocks enrichment of lile depletion of hfse and higher th yb and ta yb values 2 the granitic porphyry and rhyolite in barluk arc have old tdm2 hf ages up to 1091 ma suggesting the existence of precambrian crust or similar materials as their sources and 3 the 302 2 ma gabbro dike has high values of end t 7 54 and ehf t 12 8 to 15 5 and a young t2dm nd age 455 ma and therefore it was possibly related to upwelling of asthenosphere mantle in a post subduction extensional tectonic setting based on these parameters we suggest that the barluk arc is defined as a late paleozoic continental margin arc along the margin of the kazakhstan continent westward subduction of the junggar oceanic plate in the barluk area started in early devonian and continued to the late carboniferous 310 ma subsequent post collisional tectonic processes between the junggar oceanic plate and kazakhstan continent continued to the late carboniferous 302 ma

geochemical sr nd and zircon u pb hf isotopic studies of late carboniferous magmatism in the west junggar xinjiang implications for ridge subduction abstract voluminous granitic intrusions are distributed in the west junggar nw china and they can be classified as the dioritic rocks charnockite and alkali feldspar granite groups the dioritic rocks sio 2 50 4 63 8 wt are calc alkaline and mg enriched average mgo 4 54 wt mg 0 39 0 64 with high sr y ratios average 21 2 weak negative eu average eu eu 0 80 and pronounced negative nb ta anomalies their sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7035 0 7042 e nd t 4 5 7 9 e hf t 14 1 14 5 show a depleted mantle like signature these features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials the charnockites sio 2 60 0 65 3 wt show transitional geochemical characteristics from calc alkaline to alkaline with weak negative eu average eu eu 0 75 but pronounced negative nb ta anomalies sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7037 0 7039 e nd t 5 2 8 0 e hf t 13 9 14 7 also indicate a depleted source suggesting melts from a hot juvenile lower crust alkali feldspar granites sio 2 70 0 78 4 wt are alkali and fe enriched and have distinct negative eu and nb ta anomalies average eu eu 0 26 low sr y ratios average 2 11 and depleted sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7024 0 7045 e nd t 5 1 8 9 e hf t 13 7 14 2 these characteristics are also comparable with those of rocks derived from juvenile lower crust despite of the differences in petrology geochemistry and possibly different origins zircon ages indicate that these three groups of rocks were coevally emplaced at 305 ma a ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks as the slab window opened upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms partial melting of the subducting slab formed the dioritic rocks partial melting of the hot juvenile lower crust produced charnockite and alkali feldspar granite and partial melting in the mantle wedge generated mafic rocks in the region these results suggest that subduction was ongoing in the late carboniferous and thus support that the accretion and collision in the central asian orogenic belt took place in north xinjiang after 305 ma and possibly in the permian

ar ar dating of late cenozoic basaltic volcanism in northern syria implications for the history of incision by the river euphrates and uplift of the northern arabian platform 1 ar ar dating of basalt flows capping terrace deposits of the river euphrates in northern syria has provided a new quantitative chronology for the late cenozoic evolution of this important river system and for the associated history of surface uplift of the northern arabian platform through which it flows a region of relatively strong crust that has experienced only slow deformation notably fluvial deposits 65 m above the euphrates are overlain by basalt dated to 2717 20 ka those 45 m above the river are overlain by basalt dated to 2116 39 ka and those 8 9 m above the river are overlain by basalt dated to 402 11 ka these new dates require the previous dating scheme based on paleolithic archaeology to be revised the euphrates terrace deposits and the associated incised valley are much older than was previously thought rates of incision by the euphrates providing a proxy for regional surface uplift that is inferred to be the isostatic response to regional erosion have varied significantly over the past 3 ma with indications that between 1 2 and 0 9 ma there was regional subsidence which gave rise to fluvial aggradation this unusual pattern involving reversals in the sense of vertical crustal motions is interpreted to be a consequence of a relatively cold and thin mobile lower crustal layer no more than 5 km thick evidently due to the presence of a much thicker underlying layer of mafic underplating at the base of the crust this study thus indicates previously unsuspected complexity in the isostatic response to regional erosion in an area of high crustal stability

short term development of intracontinental rifts with reference to the late quaternary of the rukwa rift east african rift system abstract relatively low resolution seismic data and high contemporaneous rift topography normally limit quantitative analysis of normal faults in rifts the availability of a recently collected high resolution reflection seismic survey in the se part of the presently active rukwa rift east african rift system coupled with high sedimentation rates in the submerged part of the rift makes detailed quantitative analysis possible high resolution down to about 1 m seismic data penetrate ca 300 m representing about 150 000 years of the uppermost sediments and show fine details of normal faulting and related structures displacements on the faults which occur in the hanging wall of the major rift boundary fault range from a few metres up to 100 m they show increasing displacements with depth and characteristic rollover folding of the hanging walls fault propagation occurred upwards through the rapidly accumulating lake sediments and was preceded by flexuring and folding of the sediments the geometry of the seismic sequences with alternating wedge shaped and tabular units reflects pulsed activity on the faults fault displacement rates of up to 1 6 mm yr 1 have been estimated each extensional pulse has a duration of 1000s to 10 000s of years the quiescent stages have a similar duration up to 2 5 extension has occurred during the recent evolution

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

middle paleozoic initial amalgamation and crustal growth in the west junggar nw china constraints from geochronology geochemistry and sr nd hf os isotopes of calc alkaline and alkaline intrusions in the xiemisitai saier mountains abstract as one of the important parts of the central asian orogenic belt the early middle paleozoic subduction accretion history of the west junggar is still needed to be further constrained although major progress has been made in the past years in particular the geodynamic setting for late silurian early devonian a type granites and associated mafic to felsic magmatism in the northern west junggar is still controversial in this study we report new geochronological and geochemical results for middle paleozoic plutons in the xiemisitai saier mountains northern west junggar including undeformed peralkaline granite alkali feldspar granite monzogranite quartz syenite syenite monzodiorite diorite and hornblende gabbro these plutons crop out in the eastern segment of the early middle paleozoic boshchekul chingiz arc and invade into early middle paleozoic marine volcanic and pyroclastic sequences new and published zircon u pb ages indicate that these intrusions were emplaced during the late silurian middle devonian 424 392 ma late silurian hornblende gabbro diorite and monzodiorite commonly contain abundant hornblendes and exhibit mantle like nb ta ratios 15 9 18 7 negligible eu anomalies with primitive sr nd hf i sr 0 70370 0 70375 end t 5 1 to 6 0 and ehf t 14 3 to 16 2 and radiogenetic os i os 0 2099 0 8795 isotopic signatures they may be originated from a fluid metasomatized h 2 o rich and isotopically depleted mantle source and suffered some crustal contamination early middle devonian calc alkaline monzogranite and alkaline peralkaline granitoids may have distinct origins the monzogranite is i type granite with high la yb ratios depleted end t values 5 1 and crust like nb ta ratios 8 5 8 9 which is suggested to be partial melt of juvenile lower crust containing massive hornblende garnet the peralkaline alkaline granitoids include a type and highly fractionated i type granites which contain mafic intermediate enclaves and chemically exhibit variable element ratios analogical end t values 5 1 to 6 2 and significantly high i os value 2 1247 they are interpreted to be produced by fractional crystallization of the hybrid magma contributed from mantle and crustal sources based on our new data along with other geological evidence it is speculated that these a type granites and associated mafic to felsic intrusions may occur in a post collisional extension setting since the end silurian after the initial amalgamation of the west junggar terrane during the middle late silurian on going lithosphere extension during the early middle devonian would result in the rifting of newly amalgamated west junggar and thus induce asthenosphere upwelling which gave rise to the mantle derived magmatism in the northern and southern west junggar and juvenile oceanic crust in central west junggar it is suggested that the middle paleozoic is an important episode of crustal growth in the west junggar

evolution of the early paleozoic hongguleleng balkybey ocean evidence from the hebukesaier ophiolitic melange in the northern west junggar nw china abstract the hebukesaier ophiolitic melange is located in west junggar northwest china based on detailed field mapping we identified three rock assemblages in the melange ophiolite seamount and rhyolite porphyry the ophiolite comprises mainly metaperidotites pyroxenites gabbros dolerites diabase dike plagiogranites basalts and cherts two gabbro and one plagiogranite samples have ages of 512 9 ma 505 5 ma and 502 5 ma respectively which constrain the formation time of the oceanic crust the geochemical characteristics of the basaltic rocks gabbros and basalts suggest that the ophiolite formed by intrusion of mid ocean ridge melts the ocean island basalts occur as tectonic blocks within the melanges that coexist closely with marble siliceous mudstone and chert with formation characteristics of a seamount the early silurian rhyolite porphyry samples 435 2 ma are characterized by high al2o3 14 30 15 31 wt sr y 22 26 78 42 and la yb n 20 27 24 24 similar to those of late silurian early devonian adakitic rocks 420 411 ma from the xiemisitai mountains furthermore the rhyolite porphyry samples display high positive ehf t values and low mg values as well as low concentrations of compatible elements cr co and ni suggesting that the rhyolite porphyry originated from partial melting of lower juvenile crust the rhyolite porphyry displays spatio temporal characteristics similar to those of the post collision plutons 434 405 ma of the xiemisitai mountains the rhyolite porphyry intruded the ophiolite in the melange implying that the hongguleleng balkybey ocean closed prior to the early silurian our results combined with other geological evidence indicate that the northern west junggar underwent ocean basin spreading intra oceanic subduction arc arc collision the closure of the ocean and post collisional extension during the middle cambrian early devonian

implications of palaeozoic ophiolites from western junggar nw china for the tectonics of central asia western junggar nw china contains fragments of several palaeozoic island arcs accretionary prisms and ophiolites which were accreted to each other and possibly to the southern margin of eurasia by the end of the palaeozoic the ophiolites of western junggar are important in reconstructions of these events four ophiolite belts are recognized from south to north these are tangbale mayila dalabute and barleik honggulueleng hebukesair they record the production and destruction of oceanic tracts in this region from the cambrian to the carboniferous the following characteristics are representative of them all 1 the ophiolitic successions are strongly deformed 2 sheeted dyke swarms are not preserved 3 basic igneous rocks show a range of chemical characteristics from depleted island arc tholeiite to ocean island basalt altered n type mid ocean basalts may be represented 4 large scale thrusts typically directed towards the southeast lie at the base of many individual ophiolitic bodies 5 the ophiolites rarely mark the position of possible sutures between arcs they are normally highly deformed and imbricated with other lithologies accretion of palaeozoic arcs and obduction of ophiolites was complete by the end of the carboniferous but the timing and sequence of events remain obscure no continental collisions occurred during this period of assembly crustal growth occurred by the amalgamation of non continental blocks

platinum group minerals and fe ni minerals in the sartohay podiform chromitite west junggar china implications for t ph fo2 fs2 conditions during hydrothermal alteration abstract complex assemblages consisting of native iron pentlandite pentlandite heazlewoodite magnetite heazlewoodite magnetite platinum group minerals pgm and millerite heazlewoodite are associated with three types of altered chromites partly altered chromite double rimmed chromite and porous chromite discovered in the sartohay podiform chromitite hosted by the sartohay ophiolitic melange in west junggar of china we propose a two stage genetic model to explain the chromite alteration processes based on detailed petrographic observations and thermodynamic calculations reactions between primary chromite and olivine formed porous fe2 rich chromite and chlorite patches under low temperature reducing conditions afterwards oxidizing fe3 and co2 rich fluids derived from host serpentinite were incorporated into the fe2 rich chromite shifting its composition to heterogeneous fe3 rich chromite ferrian chromite thermodynamic calculations suggest that the co evolution of fo2 and fs2 played a crucial role in controlling the formation and or transformation of the fe ni minerals coevally with the sulfides antimonides and alloys of platinum group elements pge pd and pt precipitated as sulfides while ir precipitated as an alloy when log fs2 ranged from 16 0 to 14 2 within the heazlewoodite stability field compared with the host serpentinite the fo2 in the sb bearing fluid equilibrated with chromitite was low enough to decrease the pd solubility leading to co precipitation of sb and pd

age geochemistry and tectonic implications of a late paleozoic stitching pluton in the north tian shan suture zone western china the central asian orogenic belt is the largest tectonic assembly of continental and oceanic terranes on earth due to closure of the paleo asian ocean in the phanerozoic among major suture zones in the north xinjiang region of western china the north tian shan suture zone because of collision between the yili terrane in the south and the junggar terrane in the north contains the youngest ophiolitic rocks and may represent the terminal stage of development of the central asian orogenic belt in western china but the timing of the suture zone remains poorly constrained a sensitive high resolution ion microprobe shrimp zircon u pb age of 316 3 ma i e the beginning of the late carboniferous from the undeformed sikeshu pluton which crosscuts the suture zone places a crucial upperage bound for the time of collision between the yili and junggar terranes this event occurred later than or nearly concurrent with other accretion collision events in the north xinjiang region implying that fi nal terrane amalgamation was completed in the late carboniferous the sikeshu pluton shares geochemical characteristics of the widespread late carboniferous to permian postcollisional a type and i type granitoids with depleted mantle like sr nd isotopic signatures in the north xinjiang region they all occurred during a protracted ca 320 270 ma episode of postcollisional magmatism that may have been induced by basaltic under plating due to either slab breakoff or delamination of thickened mantle lithosphere beneath the central asian orogenic belt the same postcollisional magmatism also generated cu ni sulfi de bearing mafi c ultramafi c magmatic complexes adakites and porphyry type coppermolybdenum bearing magmatic rocks in the north xinjiang region

closure time of the junggar balkhash ocean constraints from late paleozoic volcano sedimentary sequences in the barleik mountains west junggar nw china the junggar balkhash ocean was a major branch of the southern paleo asian ocean the timing of its closure is important for understanding the history of the central asian orogenic belt new sedimentological and geochronological data from the late paleozoic volcano sedimentary sequences in the barleik mountains of west junggar nw china help to constrain the closure time of the junggar balkhash ocean tielieketi formation fm is dominated by littoral sediments but its upper glauconite bearing sandstone is interpreted to deposit rapidly in a shallow water shelf setting by contrast heishantou fm consists chiefly of volcanic rocks conformably overlying or in fault contact with tielieketi fm molaoba fm is composed of parallel stratified fine sandstone and sandy conglomerate with graded bedding typical of non marine fluvial deposition this formation unconformably overlies the tielieketi and heishantou formations and is conformably covered by kalagang fm characterized by a continental bimodal volcanic association the youngest u pb ages of detrital zircons from sandstones and zircon u pb ages from volcanic rocks suggest that the tielieketi heishantou molaoba and kalagang formations were deposited during the famennian tournaisian tournaisian early bashkirian gzhelian and asselian sakmarian respectively the absence of upper bashkirian to kasimovian was likely caused by tectonic uplifting of the west junggar terrane this is compatible with the occurrence of coeval stitching plutons in the west junggar and adjacent areas the junggar balkhash ocean should be finally closed before the gzhelian slightly later or concurrent with that of other ocean domains of the southern paleo asian ocean

late silurian early devonian adakitic granodiorite a type and i type granites in nw junggar nw china partial melting of mafic lower crust and implications for slab roll back abstract late silurian early devonian magmatism of the nw junggar region in the central asian orogenic belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes in this study we report results of zircon u pb ages and systematic geochemical data for late silurian early devonian largely granitic rocks in nw junggar aiming to constrain their emplacement ages origin and geodynamic significance the magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks e g adakitic granodiorite k feldspar granite syenitic granite gabbro and rhyrolite u pb zircon ages suggest that the granitoids and gabbros were emplaced in the late silurian early devonian 420 405 ma adakitic granodiorites are calc alkaline characterized by high sr 407 532 ppm low y 12 2 14 7 ppm yb 1 53 1 77 ppm cr mostly

geology and geophysics of the rukwa rift east africa exploration in the rukwa rift using gravity and seismic reflection surveys fieldwork and drilling has defined the structure and stratigraphy of the basin in greater detail than any other part of the western rift the stratigraphy comprises precambrian basement karroo sandstones shales and coals upper miocene red beds and miocene recent lacustrine and fluvial sediments during miocene recent rifting the greatest sediment input apparently came from axial fluvial systems flowing from the northwest and southeast the southwestern area experienced alternating shallow lacustrine and fluviodeltaic conditions during the miocene recent cenozoic age rift structures have a dominant nw se and a subordinate n s trend the nw se trend tends to follow a precambrian basement and later karroo structural trend ne sw seismic lines indicate up to 10 km extension of the tertiary section in a direction oblique to the probable e w regional extension direction in the southeastern portion of the basin both karroo and tertiary quaternary sediments expand into the lupa fault zone reaching thicknesses of up to 3 and 7 km respectively tertiary quaternary sediment thicknesses decrease northwestward accompanied by a decrease in the amount of extension and a broadening of the basin as extension is transferred to the lake tanganyika rift

paleostress analyses in nw syria constraints on the cenozoic evolution of the northwestern margin of the arabian plate abstract fault analysis between the dead sea transform and the euphrates region in northern syria shows two main directions of compression connected to the recent evolution of the northwestern wedge of the arabian plate e w open folds due to n s compression gently deform the cretaceous to tortonian successions of the aleppo plateau and the eastern termination of the palmyrides west of the euphrates conjugate sets of strike slip and normal faults pre as well as post dating folding occur in the plateau and are still consistent with the same stress field n s normal faults cross recent deposits and control quaternary volcanoes along the euphrates suggesting the persistence of this stress regime a nw se compression related to the syrian segment of the dead sea transform dst was detected in the western part of the study area the activation of large n s left lateral strike slip and wnw ese right lateral faults follows in time the growth of in line folds and thrusts permutation of the 1 and 2 stress axes is related to activation of nw se normal faults which generally accompany strike slip faults and post date e w folds within the plateau recent e w extension in the euphrates region is consistent with a horizontal n s maximum direction of compression and seems to be partially coeval with the stress regime induced by the dst this stress pattern can be explained by the superposition of the northward push of the arabian plate to the n s left lateral shearing along the dst

growth of syndepositional faults in carbonate strata upper permian capitan platform new mexico usa abstract the upper permian capitan platform new mexico is cut by syndepositional faults and fractures these are parallel to platform margin and cluster within strata that steepen and thicken abruptly into the basin faults are steep dip slip have measurable displacements of up to 24 m are typically associated with growth strata and mostly tip out blindly within the platform basinward throwing faults are typically reverse and are steeper than shelfward throwing faults which have normal geometry the sense of displacement across some initially basinward throwing faults changed as they developed these patterns indicate that faults were rotated as they grew synkinematic rotation of faults is interpreted to have occurred due to syndepositional compaction driven down to basin tilting of the capitan platform faults grew through interaction with inherited fractures and by segment linkage vertically separated fault segments had a tendency to grow downward to link with underlying segments thus promoting accumulation of displacement across faults without vertical propagation of fault tips four fault types are distinguished on the basis of structures associated with their upper terminations i faults breaking free surface ii faults tipping out within non folded growth strata iii faults tipping out below growth monoclines and iv buried faults with no expression on free surface fault tips evolved from one type into another in response to variations in the rates of fault growth and deposition fault tip structures also vary laterally over distance of 750 1400 m inferably as a result of variable distances from fault centres

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

recent volcanism tectonics and plate kinematics near the junction of the african arabian and anatolian plates in the eastern mediterranean abstract in the eastern mediterranean plate convergence occurs between africa arabia and anatolia the africa arabia motion is a strike slip displacement along the dead sea fault the africa anatolia motion is taken up by subduction south of cyprus the convergence between arabia and anatolia is taken up along the east anatolian fault the analysis of the regional fault surfaces reveals the presence of two major tectonic phases that affected southeastern turkey near the junction of these three plates the older deformations are related to a n s compression the more recent movements are directed mainly westward and associated with strike slip and extension tectonics near the triple junction since 2 ma a fissure volcanism produced tholeiite followed by alkali basalt along the amanos fault the northern end segment of the dead sea fault in addition reconstruction of rigid plate kinematics between arabia africa and anatolia using recent plate motion parameters and space geodesy data suggest for the east anatolian fault a slip rate of 7 8 9 mm year the maximum finite displacement recognised for this structure being around 15 km we have obtained 1 9 ma as the maximum age for the fault formation the volcanic tectonic and kinematic data converge to propose a ca 2 ma age for the change of local tectonic regime in the junction area the structural mapping the geometry of the fractures used by the magma to reach the surface and the presence of alkali basalt of mantle source suggest that the deformation along the northern end of the dead sea transform i e the amanos fault was modified by the formation of the east anatolian fault zone in this region apparition of the east anatolian fault accommodating westward motion of the anatolian plate resulted in oblique slip tension along the amanos segment of the dead sea transform giving rise to a fissure fed mantle derived alkaline volcanism at ca 2 ma which lasted until recent times 0 4 ma

kinematics and age constraints of deformation in a late carboniferous accretionary complex in western junggar nw china abstract the karamay area situated in the eastern part of western junggar southern altaids contains an ophiolitic melange with ultramafic rocks gabbro basalt chert and limestone which show typical block in matrix structures and coherent turbidites and tuffs these lithological associations are interpreted as incoherent and coherent series formed in an accretionary complex on the basis of detailed field mapping and analyses of the asymmetry of imbricate thrusts duplexes tilted structures shear band cleavages and the nw verging inclined to overturned folds we conclude that the overall movement in the accretionary complex was top to the nw the youngest tuff involved in the deformation contains detrital zircons that have a u pb age la mc icp ms of 308 7 ma 39ar 40ar resistance furnace step heating of amphibole separates from a diorite dike which cuts the folded and imbricated rocks in the accretionary prism yielded a plateau age of 307 2 ma consequently the age of the deformation in the prism is tightly constrained at 307 308 ma implying that the deformation occurred in an extremely short time span during se ward subduction combined contemporaneous occurrence of baogutu adakite high mg sr enriched and y poor dioritic dikes miaoergou charnockite and maliya mafic rocks we further suggest the accretionary complex was cut by near trench volcanic rocks and plutons possibly due to interaction with a spreading ridge

how was the carboniferous balkhash west junggar remnant ocean filled and closed insights from the well tacan 1 strata in the tacheng basin nw china abstract the balkhash west junggar remnant ocean is a conspicuous tectonic feature that had an important effect on the paleozoic tectonic evolution of the central asian orogenic belt how the carboniferous balkhash west junggar remnant ocean was filled and closed is poorly understood in this study we focus on the integrated tectonic sedimentary evolution of the tacheng basin which is located in the eastern part of the balkhash west junggar remnant ocean using high resolution seismic reflection well line geochronological and geochemical data to establish the filling of the basin by sediments and its evolution the carboniferous balkhash west junggar remnant ocean basin was filled with early carboniferous deep marine mudstone and interbedded sandstone with minor andesite basalt and tuff and late carboniferous basalt andesite breccia and tuff and shallow marine mudstone and sandstone the carboniferous igneous assemblage mainly consists of basalt with high nb content and nb la pm values and concomitant magnesian andesites with adakite geochemical characteristics of high sr and low y and yb suggesting a subduction related tectonic setting zircons in the tuff that underlies the basalts and magnesian andesites were dated to ca 315 ma by la icp ms u pb the identified unconformity between the carboniferous and lower permian from seismic reflection profile in well tacan 1 subdivided the carboniferous early permian strata into two tectonostratigraphic units the lower permian sequences overlap the carboniferous strata and the facies transition from the submarine carboniferous to the terrigenous lower permian indicates that the balkhash west junggar remnant ocean closed during the early permian these new data suggest that the sedimentary filling of the basin was in response to subduction and accretionary processes and that oceanic subduction was an important mechanism that led to the shrinking filling and closure of the balkhash west junggar remnant ocean because of compression therefore lateral crust growth through subduction accretionary processes still played an important role in the carboniferous construction of western junggar

ichnological constraints of palaeoenvironmental and palaeoclimatological features of the middle palaeozoic palaeo asian ocean evidence from the western junggar nw china abstract late devonian to early carboniferous deep sea deposits of the western junggar nw china contain 21 ichnotaxa arenituba verso chamberlain chondrites cf intricatus brongniart chondrites targionii brongniart chondrites isp gordia marina emmons halopoa imbricata torell helminthoidichnites isp helminthopsis cf hieroglyphica wetzel and bromley laevicyclus isp lophoctenium comosum richter multina isp nereites missouriensis weller phycodes cf bilix ksi zkiewicz phycosiphon incertum fischer ooster phycosiphon isp planolites isp cf taenidium thalassinoides isp zoophycos isp undetermined short ridges and undetermined tubular structures they form three typical ichnoassemblages i e the helminthopsis helminthoidichnites arenituba ichnoassemblage characteristic of upper bathyal probably hyperpycnal flow influenced deposits zoophycos nereites phycosiphon ichnoassemblage in typical slope deposits and the phycosiphon nereites ichnoassemblage featuring bottom current influenced lower slope or basin floor muddy deposits they can be ascribed to the cruziana zoophycos and the nereites ichnosubfacies respectively comparison with contemporaneous deep water facies foremost the kulm facies in western and central europe reveals significant loss in the western junggar of otherwise common element dictyodora liebeana geinitz combining the global palaeozoic tectonic evolution we propose that dictyodora was probably originated from peri gondwana terranes and the larvae juveniles of dictyodora producers hadn t migrated to the northern palaeolatitudes open ocean kazakhstan archipelago in the early carboniferous the relatively global distribution of the phycosiphon nereites association indicates efficient larval dispersal of their producers intensive bioturbation in deposits dominated by the phycosiphon nereites ichnoassemblage implies a high level of food supply at certain stratigraphic levels most likely related to surface blooms and enhanced plant detritus input the monsoonal palaeoclimatic model is integrated with the archipelagic palaeogeography to account for the deep sea ichnofauna in the western junggar during the late devonian to early carboniferous the most important factors include seasonal climatic perturbations such as monsoon derived upwelling events and enhanced primary production and efficient food nutrients transport in the dotted island scenario

tectonic evolution and continental crust growth of northern xinjiang in northwestern china remnant ocean model abstract the northern xinjiang region is located in the southwestern part of the central asian orogenic belt caob also known as the altaid tectonic collage despite extensive research aimed at understanding the crustal growth of the caob and the evolution of the paleo asian ocean the tectonic evolution mechanism of continental crust growth in northern xinjiang remains controversial the geology of northern xinjiang is characterized by widespread ophiolites granitoids intermediate basic dikes most of the ophiolites were generated in the early paleozoic the ophiolites are widely spread around the junggar basin but their distribution does not indicate a well defined band their outcrops are generally related to various faults the basic rocks widespread in northern xinjiang are grouped into two categories i gabbros diabases basalts of the ophiolites and ii basic dikes that intrude into the paleozoic strata granite plutons the basic rocks associated with the early paleozoic ophiolites were reworked by later geothermal events with a peak 40ar 39ar age of 310 290 ma the basic dikes intruded into paleozoic strata and granite plutons during the carboniferous jurassic displaying three peaks of emplacement at 260 250 ma 220 ma and 200 190 ma these two types of basic rocks and the documented variscan magmatic rocks were derived from the same source their isotope geochemical characteristics and widespread distribution suggest that since the paleozoic a large geochemical province has existed in northern xinjiang with an affinity to mid ocean ridge basalts morb and ocean island basalts oib which is related to a long lived remnant ocean and the underlying early paleozoic oceanic crust the existence of remnant oceanic crust in northern xinjiang was confirmed by seismic gravity and aeromagnetic data therefore we propose the following remnant ocean model for the paleozoic tectonic evolution of northern xinjiang it consists of three stages 1 oceanic crust formation and deposition of the overlying volcanic sedimentary rocks during the early paleozoic 2 retaining of the remnant ocean with marine sediments deposited during the early stage of the late paleozoic and 3 widespread and pervasive emplacement of variscan granites intermediate basic dikes and their volcanic equivalents during the late carboniferous and early permian and termination of marine sedimentation at the end of the early permian the tectonic evolution of northern xinjiang has been in a state of intracontinental deformation since the mesozoic the variscan granitoids and basic dikes of northern xinjiang originated from the partial melting of the remnant oceanic crust formed in the early paleozoic these variscan intrusive rocks represent the production of continental crust transferred from the basic crust the phanerozoic continental growth of northern xinjiang was completed by mass transfer from the early paleozoic remnant oceanic crust this approach may considerably change our views of continental growth

late paleozoic emplacement and meso cenozoic reactivation of the southern kazakhstan granitoid basement abstract the ili balkhash basin in southeastern kazakhstan is located at the junction of the actively deforming mountain ranges of western junggar and the tien shan and is therefore part of the southwestern central asian orogenic belt the basement of the ili balkhash area consists of an assemblage of mainly precambrian microcontinental fragments magmatic arcs and accretionary complexes eight magmatic basement samples granitoids and tuffs from the ili balkhash area were dated with zircon u pb la icp ms and yield carboniferous to late permian 350 260 ma crystallization ages these ages are interpreted as reflecting the transition from subduction to post collisional magmatism related to the closure of the junggar balkhash ocean during the carboniferous early permian and hence to the final late paleozoic accretion history of the ancestral central asian orogenic belt apatite fission track aft dating of 14 basement samples gneiss granitoids and volcanic tuffs mainly provides cretaceous cooling ages thermal history modeling based on the aft data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late mesozoic and cenozoic late mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the cimmerian collisions at the southern eurasian margin and possibly of the mongol okhotsk orogeny in se siberia during the jurassic cretaceous following tectonic stability during the paleogene inherited basement structures were reactivated during the neogene constrained by miocene aft ages of 17 10 ma this late cenozoic reactivation is interpreted as the far field response of the india eurasia collision and reflects the onset of modern mountain building and denudation in southeast kazakhstan which seems to be at least partially controlled by the inherited basement architecture

paleomagnetic study of late paleozoic rocks in the tacheng basin of west junggar nw china implications for the tectonic evolution of the western altaids abstract to better understand the tectonic evolution of west junggar in the western altaids we have conducted a combined paleomagnetic and geochronological study on late devonian d3 late carboniferous c2 and early permian p1 successions from the tacheng basin northwest of china both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of c2 and late permian p2 ages the c2 and p2 poles reveal a significant clockwise rotation of 35 6 10 4 which is comparable to the rotation deduced in the western part of the chingiz range during the time interval c2 to p2 similar rotation patterns for the two units suggest that the chingiz west junggar has remained as a quasi rigid block by the p2 time and constituted the northeast limb of the kazakhstan orocline the differential rotation of ca 25 to 30 deduced between the northeast and middle limbs of the kazakhstan orocline further suggests that at least a part of the curvature of the balkhash arc was acquired during the c2 to p2 interval and was a continuation of the middle paleozoic oroclinal bending moreover the c2 poles for west junggar and the junggar block are significantly different while the p2 ones almost overlap supporting the view that final closure of the balkhash junggar ocean occurred during the c2 to p2 interval on the other hand a large scale counterclockwise rotation of ca 80 to 90 is observed in west junggar and junggar relative to the western part of the chingiz range since the p2 time and this rotation probably represents an important intra continental deformation within the western part of the altaids a reconstruction of the paleo asian ocean has been proposed in which the kazakhstan orocline was emphasized by using the paleomagnetic results and geological evidence

normal faulting vs regional subsidence and sedimentation rate abstract normal faults occur in a variety of geodynamic environments both in areas of subsidence and uplift normal faults may have slip rates faster or slower than regional subsidence or uplift rates the total subsidence may be defined as the sum of the hangingwall subsidence generated by the normal fault and the regional subsidence or uplift rate positive total subsidence obviously increases the accommodation space e g passive margins and back arc basins in contrast with negative total subsidence e g orogens where the hangingwall subsidence rate is faster than the sedimentation rate in cases of both positive and negative total subsidence the facies and thickness of the syntectonic stratigraphic package may vary from the hangingwall to the footwall a hangingwall subsidence rate slower than sedimentation rate only results in a larger thickness of the strata growing in the hangingwall with no facies changes and no morphological step at the surface the isostatic footwall uplift is also proportional to the amount and density of the sediments filling the half graben and therefore it should be more significant when the hangingwall subsidence rate is higher than sedimentation rate

neotectonic deformation in the transition zone between the dead sea transform and the east anatolian fault zone southern turkey a palaeomagnetic study of the karasu rift volcanism in southern turkey ongoing differential impingement of arabia into the weak anatolian collisional collage resulting from subduction of the neotethyan ocean has produced one of the most complex crustal interactions along the alpine himalayan orogen several major transforms with disputed motions including the northward extension of the dead sea fault zone dsfz meet in this region to evaluate neotectonic motion on the amanos and east hatay fault zones considered to be northward extensions of the dsfz the palaeomagnetism of volcanic fields in the karasu rift between these faults has been studied remanence carriers are low ti magnetites and all except 5 of 51 basalt lavas have normal polarity morphological polarity and k ar evidence show that rift formation occurred largely during the brunhes chron with volcanism concentrated at 0 66 0 35 ma and a subsidiary episode at 0 25 0 05 forty four units of normal polarity yield a mean of d i 8 8 54 7 with inclination identical to the present day field and declination rotated clockwise by 8 8 4 0 within the 15 km wide hassa sector of the karasu rift the volcanic activity is concentrated between the amanos and east hatay faults both with left lateral motions which have rotated blocks bounded by nw se cross faults in a clockwise sense as the arabian block has moved northwestwards an average lava age of 0 5 ma yields a minimum cumulative slip rate on the system bounding faults of 0 46 cm year according with the rate deduced from the africa arabia euler vector and reduced rates of slip on the southern extension of the dsfz during plio quaternary times estimates deduced from offsets of dated lavas flows and morphological features on the amanos fault zone tectonophysics 344 2002 207 are lower 0 09 0 18 cm year probably because they are limited to surface fault breaks and do not embrace the seismogenic crust results of this study suggest that most strike slip on the dsfz is taken up by the amanos east hatay afrin fault array in southern turkey comparable estimates of quaternary slip rate are identified on other faults meeting at an unstable fff junction dsfz east anatolian fault zone karatas fault zone a deceleration in slip rate across the dsfz and its northward continuation during plio quaternary times correlates with reorganization of the tectonic regime during the last 1 3 ma including tectonic escape within anatolia establishment of the north and east anatolian fault zones bounding the anatolian collage in mid late pliocene times a contemporaneous transition from transpression to transtension and concentration of all basaltic magmatism in this region within the last 1 ma

an early cambrian plume induced subduction initiation event within the junggar ocean insights from ophiolitic melanges arc magmatism and metamorphic rocks abstract the central asian orogenic belt caob is one of the largest accretionary orogens in the world the mechanism of continental growth and tectonic evolution of the caob remain debated here we present an overview of early paleozoic ophiolitic melanges calc alkaline intrusions and metamorphic rocks in west junggar with an aim to provide constraints on the time and mechanism of subduction initiation in the junggar ocean a branch of the southern paleo asian ocean pao the early paleozoic ophiolitic melanges are composed of ultramafic mafic rocks cherts pelagic limestones basaltic breccias and tuffs the mafic rocks from these ophiolitic melanges are divided into morb like and oib like types the morb like rocks were formed in a fore arc setting but the oib like mafic rocks were formed by the intra plate magmatism related to mantle plume activities the early paleozoic intrusions are occurred as small stocks with a dominant composition of diorite trondhjemite and granodiorite these granitoids display high k calc alkaline affinities and have high and positive end t and ehf t values formed in an arc related setting the metamorphic complex is mainly composed of blueschist and amphibolite blocks with metamorphism ages ranging from 500 ma to 460 ma their protoliths are calc alkaline andesite and tholeiitic and alkaline basalts formed in an arc related and seamount setting respectively it is clearly show that the west junggar was under an intra oceanic subduction regime during the early paleozoic and the initial subduction of the southern pao might have occurred in the early cambrian based on our observations and in combination with previous work we propose the plume induced subduction initiation model for the early middle cambrian tectonic evolutionary of the junggar ocean our new model not only shed light on subduction initiation dynamics of the southern pao but also contribute to tectonic evolution of the caob

petrogenesis of the yangzhuang nb and ta rich a type granite porphyry in west junggar xinjiang china abstract west junggar is featured with a wide spread of late carboniferous early permian a type granites systematic comparison of the yangzhuang granite porphyry and the regional coeval a type granites rcag shows that 1 all the late carboniferous early permian a type granites are of the a 2 group except the yangzhuang granite porphyry 2 the nb and ta contents of the yangzhuang granite porphyry are nearly 10 times that of the rcag while ti content is more depleted 3 end t of the yangzhuang granite porphyry is slightly lower and the sr isotope has a wider range relative to the rcag previous research revealed that highly incompatible elements including nb and ta can be transferred into the mantle wedge by precipitation of amphibole from the ascending fluids generated by dehydration of subducted slab it is inferred that enhanced heat flux brought by the late carboniferous ridge subduction decomposed amphibole in the mantle wedge to generate nb and ta rich melt and finally produced the yangzhuang granite porphyry

structure and stratigraphy of the rukwa rift abstract combining recently acquired multifold seismic data with well and gravity information and field mapping a comprehensive picture of the structure and stratigraphy of the rukwa rift has emerged the rukwa rift lies between the tanganyika and nyasa malawi rifts in the western branch of the east african rift system in southwest tanzania the rukwa rift is a nw trending half graben basin that is 350 km long and 40 km wide unlike the neighboring tanganyika and nyasa rifts there is no evidence of half graben polarity reversals in the rukwa rift the nw trending boundary fault system lies on the northeastern side of the basin and comprises a series of listric faults most internal faults also show listric forms and trend n s oblique to the boundary fault the basal sedimentary section is the permo triassic karroo sequence this is overlain by the red bed sandstone sequence in which both mesozoic and tertiary fauna have been found the cenozoic lake bed sequence is the highest unit and covers nearly all of the present basin sediment thicknesses commonly reach 7 km and attain a maximum of 12 km at the southeastern end of the basin the lake bed sequence is the thickest unit in the main depocentre but the karroo sequence is often the thickest unit on the shoaling side of the half graben the rukwa rift is here interpreted to have evolved as a strike to oblique slip pull apart basin based on numerous indications of nw trending strike slip faulting

late paleozoic paleogeographic reconstruction of western central asia based upon paleomagnetic data and its geodynamic implications abstract carboniferous to permian volcanoclastic rocks have been collected from south junggar and west junggar primary magnetizations have been observed from the characteristic components of 10 sites of early permian p1 and late permian p2 red beds of south junggar area the 14 early carboniferous sites from west junggar mountains expose post folding secondary magnetizations and according to their spatial distribution 9 remagnetized sites are related to late carboniferous early permian granite emplacement whereas 5 sites are located at the vicinity of late permian mafic dykes two new paleomagnetic poles have been consequently calculated for the periods of p1 at 79 5 n 36 6 e and of p2 at 60 4 n 4 7 e with a95 of 6 8 and 5 4 respectively they yield two paleomagnetic poles at 65 3 n 329 7 e with a95 of 6 3 and 64 8 n 179 5 e with a95 of 6 9 respectively compilation of available data shows stationary and consistent poles for south junggar area during the carboniferous and permian whereas nw junggar underwent a significant anticlockwise rotation between the late carboniferous early permian and the late permian indicating that junggar was not a rigid block up to the end of the paleozoic west junggar and south junggar may have experienced contrasting tectonic evolutions comparisons of late paleozoic poles of central asia blocks show 1 counterclockwise rotation of west junggar with respect to siberia contrasting with the clockwise rotation of north kazakhstan with respect to siberia 2 no significant movements between west junggar north kazakhstan and siberia since late permian indicating that they were rigidly welded since that time and 3 anticlockwise rotations of tarim yili and south junggar with respect to the welded siberia kazakhstan west junggar block such rotations may have been accommodated by late permian to early triassic strike slip faults with an estimation of the displacements of 1570 280 km along the irtysh gornotsaev shear zone 410 380 km along the nikolaiev nalati tectonic line and 490 250 km along the chingiz alakol north tian shan fault since late permian time

as sb bi au mineralization in the baogutu gold deposit xinjiang nw china here we report the occurrence of some uncommon mineral assemblages including paakonenite aurostibite native arsenic native antimony and native bismuth found in the baogutu gold deposit in the western junggar xinjiang nw china the mineralization could be generally subdivided into two types the gold bearing quartz vein type mineralization and disseminated mineralization in the wall rocks the sulfide minerals in gold lodes commonly include pyrite arsenopyrite marcasite and stibnite however the l7 lode in no 4 orebody and the l1 lode in no 11 orebody of the baogutu gold deposit are quite different in terms of their mineral assemblages the l7 lode contains native arsenic quartz veins in shallow levels and stibnite quartz veins at depth gold bearing minerals electrum native gold and rarely aurostibite mainly coexist with paakonenite stibnite native arsenic and native antimony the crystallization of as and sb bearing minerals was likely to have consumed h2s from the hydrothermal fluid which probably triggered the precipitation of native gold the l1 lode consists of several discontinuous sulfide dominated lensoid orebodies the massive sulfide ores that produced most of the gold resource are characterized by an intimate association between native bismuth and native gold mineralization

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

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

cenozoic volcanism in the middle east petrogenesis of alkali basalts from northern lebanon large discontinuous exposures of basaltic lava flows ranging in age mostly from miocene to recent are present in several localities extending from sinai jordan palestine israel to lebanon and syria dubertret 1955 baldridge et al 1991 mouty et al 1992 heimann et al 1996 shaw et al 2003 these form the cenozoic volcanic province of the middle east occurring mostly along or near the transform faulted boundary the dead sea ghab transform fault system between the arabian and african plates and the levantine subplate fig 1 further to the south several other extensive cenozoic volcanic provinces occur in arabia and east africa mostly ethiopia figure 1 regional geological map showing the distribution of the various cenozoic volcanic provinces in east africa arabia and the middle east the cenozoic continental flood basalts in ethiopia yemen western arabia and jordan have been extensively studied camp roobol 1989 1992 altherr henjes kunst baumann 1990 stein hofmann 1992 baker thirlwall menzies 1996 baker et al 1997 shaw et al 2003 the cenozoic volcanic province of ethiopia is clearly related to the east african rift system barberi et al 1975 mohr 1983 the quaternary intraplate basaltic volcanic field in yemen appears to be the result of melting shallow mantle perhaps in response to small amounts of lithospheric extension that were metasomatized and hydrated by the afar plume during or shortly after oligocene flood volcanism baker et al 1997 the lavas of this basaltic field of western yemen were subjected to variable degrees of contamination 0 20 of an early proterozoic to late archaean silicic lower crustal component baker thirlwall menzies 1996 baker et al 1997 the cenozoic continental flood basalt provinces of

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

early paleozoic tectonic evolution of the northern west junggar nw china constraints from early cambrian middle silurian felsic plutons of the chagantaolegai ophiolitic melange abstract the early paleozoic tectonic evolution of the junggar ocean a major branch of the southern paleo asian ocean pao remains a topic of debate this study mapped the chagantaolegai ophiolitic melange com in the northern west junggar nwj on a large scale and identified several tectonically juxtaposed lithotectonic units including the ophiolite suite and felsic plutons the ophiolite suite mainly comprises serpentinized ultramafic rock pyroxenolite gabbro dolerite plagiogranite basalt volcanic rock and radiolarian chert zircon u pb ages for two plagiogranite samples yielded ages of 515 4 ma and 513 6 ma constraining the existence of the junggar ocean to the early cambrian at least the felsic plutons can be subdivided into two groups group i 503 481 ma which intruded into the com shows low k calc alkaline features with remarkable depletion of nb ta and ti resembling rocks formed in an intra oceanic arc group ii 435 428 ma was found on both sides of the com and displays high k calc alkaline series characteristics similar to the silurian to early devonian a type granites in the nwj implying a post collisional environment based on a combination of existing observations and our new observations and data with regional geological evidence our new data indicate that the nwj underwent a transition from the tectonic processes of seafloor spreading and subduction to arc arc collision and post collisional extension during the early cambrian early devonian

evolution of the oseberg fault block in context of the northern north sea structural framework abstract the central segment 60 20 61 n of the northern north sea 170 km in width demonstrates contrasting basin geometries related to permo triassic and jurassic rift episodes in the oseberg area representing a part of this segment major faults of two generations dip in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin ca 20 km in width is underlain by a wider ca 35 km w tilted permo triassic half graben the early jurassic thickness distribution was governed by a westerly palaeotilt mild extensional tectonics influenced early jurassic rhaetian aalenian deposition whereas the middle late jurassic main rift episode is expressed by an accelerated fault related subsidence from the late bajocian during the middle late jurassic the oseberg area evolved through a series of high frequency rift phases characterized by rotational tilt events separated by periods during which extension was less severe this allows the subdivision of the jurassic stretching episode into distinct rift phases 4 6 myrs which involved smaller scale units corresponding to rotational tilt events 1 2 myrs the large scale pattern of middle late jurassic syn rift infill is overall one of upwards fining reflecting a deepening trend as the rift evolved syn rotational sediment architecture related to a single rift phase shows systematic variations from a threefold shallow marine sandstone mudstone sandstone motif tarbert fm through a twofold shallow marine sandstone mudstone motif heather fm to a twofold deep marine conglomerate sandstone mudstone motif draupne fm the vertical stacking of these syn rotational packages reflects an inability of sediment supply to keep pace with the rift related subsidence and the temporal evolution from a sediment balanced through a sediment underfilled to a sediment starved rift basin