facies and architectural element analysis of a meandering fluvial succession the permian warchha sandstone salt range pakistan abstract the 30 to 155 m thick early permian artinskian warchha sandstone of the salt range pakistan is a conglomerate sandstone and claystone succession within which seven lithofacies types gt st sp sr sh fl and fm occur in a predictable order as repeated fining upward cycles common sedimentary structures in the conglomerates and sandstones include planar and trough cross bedding planar lamination soft sediment deformed bedding compound cosets of strata with low angle inclined bounding surfaces and lags of imbricated pebbles structures in the finer grained facies include desiccation cracks raindrop imprints caliche nodules and bioturbation groups of associated facies are arranged into nine distinct architectural elements channels gravel bars sandy bedforms downstream and laterally accreting barforms sand sheets crevasse splays levees floodplain units and shallow lakes which is consistent with a fluvial origin for the succession the types of architectural elements present and their relationship to each other demonstrate that the warchha sandstone preserves a record of a meandering river system that drained the northern margin of gondwanaland the dominance of fine grained floodplain facies over gravel grade channel base facies and the widespread occurrence of large scale lateral accretion elements supports the interpretation of a high sinuosity meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant although the regional and temporal distribution of these deposits is complex in broad terms the lower part is dominated by stacked multistorey channel bodies whereas single storey channel elements isolated in abundant fine grained floodplain deposits dominate the middle and upper parts of the formation

early jurassic carbon isotope excursion in the qiangtang basin tibet the eastern tethys implications for the toarcian oceanic anoxic event abstract the early jurassic was characterized by a global disturbance of the carbon cycle known as the toarcian oceanic anoxic event t oae this event is recorded by a large negative carbon isotope excursion cie in marine carbonates and marine organic matter as well as fossil wood here we present new high resolution carbonate 13 c carb and organic 13 c org carbon isotope records and total organic content from the bilong co section in the qiangtang basin the eastern tethys this section is high in organic carbon and black shale facies are also identified the bilong co section shows heavy 13 c org values compared to other reported marine organic carbon isotope values for the t oae this is explained by variable mixing of terrestrial and marine organic matter compared to european sections the magnitude of the negative cie in the bilong co section is slightly different which could be explained by different local paleoenvironmental conditions and strata missing although these the carbon isotope profile from the bilong co area displays a similar trend to those in contemporaneous strata in the western tethyan and boreal realms of nw europe which is characterized by a distinct negative excursion in the early toarcian our new data from the bilong co section in n tibet provide the first high resolution record of the early toarcian oceanic anoxic event in the eastern tethys

late triassic paleolatitude of the qiangtang block implications for the closure of the paleo tethys ocean abstract to better constrain the late triassic paleolatitude of the qiangtang block and the closure of the paleo tethys ocean a combined paleomagnetic and zircon u pb geochronological study has been conducted on the upper triassic jiapila formation volcanic rocks on the northern edge of the qiangtang block of central tibet 34 1 n 92 4 e these rocks are dated to 204 213 ma progressive thermal or alternating field demagnetization successfully isolated stable characteristic remanent magnetizations chrm that pass both the fold and reversal tests consistent with a primary magnetization these are the first volcanic based paleomagnetic results from pre cretaceous rocks of the qiangtang block that appear to average secular variation well enough to yield a reliable paleolatitude estimate based on our new paleomagnetic data from upper triassic lavas we conclude that the late triassic pole of the qiangtang block was located at 64 0 n 174 7 e with a 95 6 6 n 29 we compile published paleomagnetic data from the qiangtang block to calculate a late triassic latitude for the qiangtang block at 31 7 3 0 n the central paleo tethys ocean basin was located between the north china ncb and tarim blocks to the north and the qiangtang block to the south during late paleozoic early mesozoic a comparison of published early triassic paleopole from the qiangtang block with the coeval paleopoles from the ncb and tarim indicates that the paleo tethys ocean could not have closed during the early triassic and that its width was approximately 32 38 latitude 3500 4200 km however the comparison of our new combined late triassic paleomagnetic result with the late triassic poles of the ncb and tarim as well as numerous geological observations indicates that the closure of the paleo tethys ocean at the longitude of the qiangtang block most likely occurred during the late triassic

correction for the static shift in magnetotellurics using transient electromagnetic soundings shallow inhomogeneities can lead to severe problems in the interpretation of magnetotelluric mt data by shifting the mt apparent resistivity sounding curve by a scale factor which is independent of frequency on the standard log apparent resistivity versus log frequency display the amount of parallel shift commonly referred to as the mt static shift can not be determined directly from conventionally recorded mt data at a single site one method for measuring the static shift is a controlled source measurement of the magnetic field unlike the electric field the magnetic field is relatively unaffected by surface inhomogeneities the controlled source sounding which may be a relatively shallow sounding made with lightweight equipment can be combined with a deep mt sounding to obtain a complete undistorted model of the earth inversions of the static shift corrected mt data provide a much closer match to well log resistivities than do inversions of the uncorrected data the particular controlled source magnetic field sounding which we used was a central induction transient electromagnetic tem sounding correction for the static shift in the mt data was made by jointly inverting the mt data and the tem data a parameter which allowed vertical shifts in the mt apparent resistivity curves was included in the computer inversion to account for static shifts a simple graphical comparison between the mt apparent resistivities and the tem apparent resistivities produced essentially the same estimate of the static shift within 0 1 decade as the joint computer inversion central induction tem measurements were made adjacent to over 100 mt sites in central oregon the complete data base of over 100 sites showed an average static shift between 0 and 0 2 decade however in the rougher topography and more complex structure of the cascade mountain range the majority of the sites had static shifts of the order of 0 3 to 0 4 decade the static shifts in this area are probably due to a combination of topography and surficial inhomogeneities the tem apparent resistivity which is used to estimate the unshifted mt apparent resistivity does not necessarily agree with either the transverse electric te or the transverse magnetic tm mt polarization tem apparent resistivity may occur between the two or may agree with one of the two polarizations or may lie outside the mt polarizations

geochronological and geochemical constraints on mesozoic suturing in east central tibet 1 this paper reports isotopic major and minor element geochemistry of igneous and metamorphic rocks from the kokoxili and yushu regions of central and eastern tibet the first region lies along the kunlun suture which separates the bayan har songpan ganze songpan terrane from the tarim and qaidam blocks two kokoxili granitoids yield u pb zircon dates of 217 10 and 207 3 ma late triassic which represent the time of emplacement and rb sr isochron dates of 195 3 and 190 3 ma early jurassic which are interpreted as cooling ages the geochemical signatures of these granitoids suggest that they are related to subduction continuing into the late triassic in the yushu area three samples help constrain the age of the jinsha suture which separates the songpan terranes from the qiangtang blocks a leucocratic granite and an orthogneiss in the suture zone yield u pb zircon dates of 206 7 and 204 1 ma respectively and a paragneiss south of it a u pb monazite date of 244 4 ma the existence of coeval magmatism in both the jinsha and kunlun sutures suggests that the two subduction zones were simultaneously active combining isotopic dating with structural evidence on subduction polarity and paleomagnetic reconstructions we propose that the kunlun and qinling block boundaries which were distinct in the permian subsequently formed a continuous late triassic northward subducting plate margin our data suggest that the jinsha suture correlates with the benzilan and nan uttaradit sutures which together belong to a major late triassic subduction zone

paleoclimate and extensional tectonics of short lived lacustrine environments lower cretaceous of the panormide southern tethyan carbonate platform nw sicily abstract subaerial erosion and continental sedimentation interbedded with shallow water carbonates are unequivocal stratigraphic records to evaluate paleoenvironmental and paleoclimate evolution of emerged landmass stratigraphic analysis of the cretaceous monte gallo section of the mesozoic panormide carbonate platform in the northern side of the palermo mountains nw sicily records a peculiar continental derived clays that interrupted the shallow water carbonate sedimentation these clays rest with lenticular geometries above the tectonically enhanced subaerial erosional unconformity of the barremian lower aptian requienid limestones and are covered by the upper cretaceous rudistid limestone sedimentological investigation combined with mineralogical and petrographic results reveal the occurrence of alkaline to saline lake clays deposition in pond filling depositional environment recording stressed conditions evaporation especially in its final living phase they were formed when a half graben tilted block tectonics produced footwall uplift of the gallo faulted blocks carbonate platform paleoclimate evaluations of the continental derived clays highlighted that a period of warm humid conditions which favoured their formation interrupted the uniform warm climate conditions highlighting a greenhouse climate phase

the permian triassic transition in ocean island setting environmental disturbances and new high resolution carbon isotope record from the qiangtang basin nw china abstract the permian triassic boundary ptb events such as carbon isotope excursion volcanism and environmental disturbances are not well understood in an ocean island setting here we develop a new case study for the permian triassic transition in the qiangtang basin tibet by combining existing biostratigraphy new carbon isotope data sedimentological data u pb zircon age mineralogical and geochemical data these new data defined the permian triassic transition age as about 252 3 0 9 ma corresponding to the lowermost sea level a long term negative carbonate carbon isotope trend is present at the same stratigraphic level in different depositional environments strongly suggesting its global nature however our new ocean island setting is characterized by an abrupt shift in carbon isotope values across the level which is different from many chemostrtigraphic studies that show a gradual shift in carbon isotope values across the event horizon the most likely explanation for the abrupt shift in 13c values is a sedimentary hiatus at this level in the study section three stage climatic models through the ptb in the ocean island setting are identified stage 1 is characterized by a warm and humid climate with moderate chemical weathering while a hot and humid climate with intense chemical weathering dominates stage 2 the climate in stage 3 is a relatively hot and arid climatic condition with weak chemical weathering

integrating facies and structural analyses with subsidence history in a jurassic cretaceous intraplatform basin outcome for paleogeography of the panormide southern tethyan margin nw sicily italy abstract we illustrate the tectono sedimentary evolution of a jurassic cretaceous intraplatform basin in a fold and thrust belt present setting cala rossa basin detailed stratigraphy and facies analysis of upper triassic eocene successions outcropping in the palermo mts nw sicily integrated with structural analysis restoration and basin analysis led to recognize and describe into the intraplatform basin the proximal and distal depositional areas respect to the bordered carbonate platform sectors carbonate platform was characterized by a rimmed reef growing with progradational trends towards the basin as suggested by the several reworked shallow water materials interlayered into the deep water succession more the occurrence of thick resedimented breccia levels into the deep water succession suggests the time and the characters of synsedimentary tectonics occurred during the late jurassic the study sections involved in the building processes of the sicilian fold and thrust belt were restored in order to obtain the original width of the cala rossa basin useful to reconstruct the original geometries and opening mechanisms of the basin basin analysis allowed reconstructing the subsidence history of three sectors with different paleobathymetry evidencing the role exerted by tectonics in the evolution of the narrow cala rossa basin in our interpretation a transtensional dextral lower jurassic fault system wnw ese present day oriented has activated a wedge shaped pull apart basin in the frame of the geodynamic evolution of the southern tethyan rifted continental margin the cala rossa basin could have been affected by jurassic transtensional faults related to the lateral westward motion of africa relative to europe

eustatic and tectonic control on the evolution of the jurassic north qiangtang basin northern tibet china impact on the petroleum system abstract the qiangtang basin is the largest mesozoic marine hydrocarbon bearing basin in china investigating its tectonic and sedimentary evolution is therefore relevant for hydrocarbon exploration here we present a detailed stratigraphic and sedimentological analysis of five jurassic stratigraphic sections in the north qiangtang basin nineteen facies associations were identified and allowed us to reconstruct changes of water depth the north qiangtang basin experienced two transgressive regressive cycles during the jurassic the first cycle started in the mid jurassic bajocian bathonian with braided river and floodplain sediments passing up section to tidal flat and eventually inner to mid ramp deposits tidal flat deposition resumed during the callovian the second cycle began in the late jurassic oxfordian with transgressive inner to mid ramp sediments followed by a shallowing upward trend during the late oxfordian leading again to tidal flat sedimentation in the kimmeridgian tithonian petrographic analysis and detrital zircon geochronology indicate provenance constantly from the hoh xil songpan ganzi terrane kunlun arc and central qiangtang because jurassic magmatic activity and active syn depositional faults have not been reported and steady detrital supply indicates a stable tectonic environment eustatic change is inferred to represent the principal control on sedimentary evolution in the north qiangtang basin during the jurassic a comparison with the amu darya basin in central asia characterized by similar sedimentological conditions and distribution of reservoir and source rocks emphasizes the importance of eustatic control for the development of the source reservoir seal system of the north qiangtang basin

diachronous evolution of late jurassic cretaceous continental rifting in the northeast atlantic west iberian margin 1 regional 2 d seismic reflection profiles outcrop and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest iberia alentejo basin the interpreted data indicate the bulk of late jurassic earliest cretaceous subsidence occurred in the present day continental slope area as shown by 1 significant thickening of synrift strata basinward from a slope bounding fault system sfs west of which the total thickness of sediment can reach more than 9 0 km and 2 relatively thin mesozoic strata east of the sfs where thickening of synrift units against principal faults is limited five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins which were located on the rift shoulder to subsiding tilt blocks west of the sfs these regressive events are correlated with major rift related events occurring on the deeper margin direct comparisons with the peniche basin of northwest iberia reveal that significant portions of the iberian lower plate margin were uplifted and eroded during the last stages of continental rifting this process was repeated at different times and in different areas as the locus of rifting and continental breakup migrated northward as a result two distinct rift axes are recognized in west iberia a first axis extending from the porto basin to the alentejo basin and a second axis located on the outer proximal margin north of 38 30n in addition the sfs delimited 1 prograding deposits of cretaceous paleogene age and 2 late cenozoic deposits draping the modern continental slope these latter facts demonstrate that on lower plate passive margins the relative position of the continental slope is established during the final rifting episode s preceding continental breakup

form and extent of the dufek intrusion antarctica from newly compiled aeromagnetic data the dufek intrusion in the northern part of the pensacola mountains antarctica is part of an extensive middle jurassic igneous province that was related to and emplaced just prior to gondwana break up it has been described as one of the largest layered gabbro intrusions in the world and is exposed as two non overlapping gabbro sequences in the dufek massif and the forrestal range a new compilation of aeromagnetic data over the dufek intrusion and surrounding region is based on mapping at two scales a 2 km grid spacing over the dufek intrusion and a 6 km grid spacing over the surrounding region advanced processing of the data is used to produce an analytical signal and a terrace map as a basis for a new interpretation modelling and interpretation of the data show that the dufek intrusion is not as extensive as was thought and that it is more similar in size to the stillwater intrusion in north america than to the bushveld complex in south africa to which it has previously been compared the reduced size of the dufek intrusion is due to reinterpretation of an anomaly over berkner island to the north of the pensacola mountains as that of an uplifted basement block rather than a continuation of the dufek intrusion the dufek intrusion is modelled as two separate intrusive phases of a composite intrusion the main part is a dipping intrusive sheet displaced by a normal fault which accounts for two parallel magnetic anomalies over the forrestal range the minor part forms the dufek massif itself which the magnetic data show was emplaced on a separate trend and is of a shallower origin than the forrestal phase magnetic lineaments on the compilation map are used to establish a possible chronology of events we suggest that the emplacement of both phases of the dufek intrusion was preceded by a period of extensional block faulting which uplifted the berkner island basement block and was succeeded by a further period of extensional faulting involving a component of strike slip deformation during the initial stages of gondwana break up

the subduction accretion history of the bangong nujiang ocean constraints from provenance and geochronology of the mesozoic strata near gaize central tibet abstract the mesozoic strata within the bangong nujiang suture zone in central tibet recorded critical information about the subduction accretion processes of the bangong nujiang ocean prior to the lhasa qiangtang collision this paper reports detailed field observations petrographic descriptions sandstone detrital zircon u pb ages and hf isotopic analyses from an accretionary complex preserved as mugagangri group and the unconformably overlying shamuluo formation near gaize the youngest detrital zircon ages together with other age constraints from literature suggest that the mugagangri group was deposited during late triassic early jurassic while the shamuluo formation was deposited during late jurassic early cretaceous based on the differences in lithology age and provenance the mugagangri group is subdivided into the upper middle and lower subunits these units are younging structurally downward southward consistent with models of progressive off scrapping and accretion in a southward facing subduction complex the upper subunit comprising mainly quartz sandstone and siliceous mud shale was deposited in abyssal plain environment close to the qiangtang passive margin during late triassic with sediments derived from the southern qiangtang block the middle and lower subunits comprise mainly lithic quartz sandstone and mud shale containing abundant ultramafic ophiolitic fragments the middle subunit of late triassic early jurassic age records a transition in tectono depositional setting from abyssal plain to trench wedge basin with sudden influx of sediments sourced from the central qiangtang metamorphic belt and northern qiangtang magmatic belt the appearance of ultramafic ophiolitic fragments in the middle subunit reflects the subduction initiation the lower subunit was deposited in a trench wedge basin during early jurassic with influx of jurassic aged zircons originating from the newly active southern qiangtang magmatic arc the lower subunit records the onset of arc magmatism related to the northward subduction of the bangong nujiang ocean the shamuluo formation comprising mainly lithic feldspar sandstone with limestone interlayers was deposited in a post collisional residual sea or pre collisional trench slope basin with sediments derived entirely from the qiangtang block

palaeoclimatic evolution during eocene and its influence on oil shale mineralisation fushun basin china the fushun basin is a small explored coal and oil shale bearing cenozoic fault basin in the liaoning province northeast china the basin mainly consists of eocene swamp to lacustrine deposits of the guchengzi to xilutian formation and contains the biggest opencast oil shale mine in asia this mine has provided an ideal opportunity to undertake palaeoclimate reconstruction in this basin based on a single geological profile and the analyses of 93 samples using various approaches namely field geological observation clay mineralogical and geochemical sr ba sr cu stable c and o isotope analyses all of which were compared with palaeobotanical data the eocene climate of fushun basin evolved from warm temperate to north subtropical and generally changed from warm humid to subhumid semiarid paleoclimatic and geochemical parameters shows that the very warm and humid climate during jijuntun formation increased the initial productivity of lake water and caused a steady stratification of the lake water then caused oxygen lack in the bottom of water productivity of the lake provides the mean origin of organic matters for oil shale formation and steady anoxic environment is beneficial for the conservation of organic matters

triassic subduction of the paleo tethys in northern tibet china evidence from the geochemical and isotopic characteristics of eclogites and blueschists of the qiangtang block abstract a 500 km long high pressure metamorphic belt occurs in the qiangtang block of northern tibet the occurrence of high pressure metamorphic rocks eclogite and blueschist has a significant bearing on the paleo tethys subduction and plate suturing processes a few studies have been conducted on petrology mineralogy and geochronology of high pressure rocks in this paper we present the results of a geochemical and isotopic investigation on eclogite and blueschist from this belt and discuss the probable geodynamic implications geochemical analyses show that the two rock types eclogite and blueschist have grossly similar bulk compositions but they can be subdivided into two groups based on their tio 2 contents the low tio 2 2 2 75 wt rocks are more akin to ocean island basalts oib the positive e nd t values ranging from 0 4 to 6 3 for all samples suggest that the basaltic protoliths of the eclogites and blueschists were derived from a long term depleted mantle source however their geochemical characteristics require that the source be metasomatized and enriched in large ion lithophile and light rare earth elements shortly before the formation of these basaltic protoliths like for most oib and e morb of the world the recognition of oceanic basalts suggests that a paleozoic ocean should be present in the central qiangtang block this ocean was hypothesized to be the western extension of the changning menglian paleo tethys ocean in the eastern margin of the tibetan plateau the eclogite and blueschist were formed by northward subduction of this paleozoic ocean in the triassic

remnants of a late triassic ocean island in the gufeng area northern tibet implications for the opening and early evolution of the bangong nujiang tethyan ocean abstract in this paper we present new major and trace element compositions of basaltic rocks in the gufeng ocean island gfoi area in the western segment of the bangong nujiang suture zone northern tibet our aim was to assess the genesis of these rocks and discuss the implications of this new dataset for the evolution of the bangong nujiang tethyan ocean an ocean island type double layer structure comprising a basaltic basement and an oceanic sedimentary cover sequence found within the gfoi provides direct evidence for the interpretation that the assemblage is a typical ocean island the basalts in the gfoi can be divided into three types named g1 g2 and g3 basalts and these basalts range in composition from morb to oib types which is typical of ocean islands the g1 basalts have morb type affinities possibly indicating the existence of morb oceanic crust under the gfoi the g2 basalts represent the early stage of formation of the gfoi and are produced by the interaction of rising oib type basaltic magma and the existing morb oceanic crust the g3 basalts are typical oib basalts and they are the products of the direct eruption of oib type basaltic magmas the g3 basalts have high la yb n 12 3 14 4 ce yb n 10 8 11 8 la sm n 2 39 2 76 and sm yb n 4 89 5 23 ratios indicating the presence of oceanic lithosphere below the gfoi with a thickness of 50 60 km geochemical analyses of the gfoi cherts show that they contain terrigenous material indicating the gfoi formed close to a continental margin norian conodont fossils within the gfoi limestones indicate the gfoi formed during the late triassic these data combined with geological evidence and a half space model of lithosphere cooling where the thickness of the oceanic lithosphere is determined from the age of the lithosphere indicate that the western segment of the bangong nujiang tethyan ocean opened initially in the late permian expanded rapidly during the early middle triassic and was a mature ocean during the late triassic

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

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

provenance of mesozoic clastic rocks within the bangong nujiang suture zone central tibet implications for the age of the initial lhasa qiangtang collision abstract the bangong nujiang suture zone separating the lhasa and qiangtang blocks of the tibetan plateau is marked by remnants of the bangong nujiang oceanic basin in the gaize area of central tibet mesozoic sedimentary strata recording the evolution of the basin and subsequent collision between these two blocks include the upper triassic lower jurassic turbidites of the mugagangri group the upper jurassic lower cretaceous sandstone dominated wuga and shamuluo formations and the upper cretaceous molasse deposits of the jingzhushan formation the shamuluo and jingzhushan formations rest unconformably on the underlying mugagangri group and wuga formation respectively in this contribution we analyze petrographic components of sandstones and u pb hf isotopic compositions of detrital zircons from the wuga and jingzhushan formations for the first time based on the youngest detrital zircon ages the maximum depositional ages of the wuga and jingzhushan formations are suggested to be 147 150 ma and 79 91 ma respectively petrographic and isotopic results indicate that sediments in the wuga formation were mainly sourced from the accretionary complex preserved as the mugagangri group in the north while sediments in the jingzhushan formation have mixed sources from the lhasa block the qiangtang block and the intervening suture zone provenance analysis together with regional data suggests that the upper jurassic lower cretaceous wuga and shamuluo formations were deposited in a peripheral foreland basin and a residual sea basin respectively in response to the lhasa qiangtang collision whereas the upper cretaceous jingzhushan formation reflects continental molasse deposition during the post collisional stage the development of the peripheral foreland basin evidenced by deposition of the wuga formation reveals that the age of the initial lhasa qiangtang collision might be the latest jurassic 150 ma

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

provenance analysis of the mesozoic hoh xil songpan ganzi turbidites in northern tibet implications for the tectonic evolution of the eastern paleo tethys ocean 1 mesozoic strata of the hoh xil songpan ganzi complex in northern tibet are exposed in a vast 370 000 km2 triangle shaped orogenic belt bound by the longmen shan thrust belt in the east the kunlun terrane and north china block in the north and the qiangtang terrane and yidun arc in the south these strata consist of middle upper triassic submarine fan and deep marine facies rocks that were deposited in the paleo tethys ocean late triassic early jurassic contractional deformation in the eastern hoh xil songpan ganzi complex marks the demise of the paleo tethys ocean basin and the accretion of the gondwana derived qiangtang terrane to eurasia we conducted geological mapping regional stratigraphic analyses and u pb geochronology of detrital zircons n 4128 on the mesozoic sequences exposed in the hoh xil songpan ganzi complex kunlun terrane and qiangtang terrane we identify for the first time marine silciclastic sandstone and shale of jurassic age in the northwestern hoh xil songpan ganzi complex that unconformably overlie upper triassic turbidites zircon age data indicate that the middle upper triassic marine gravity flow deposits of the hoh xil songpan ganzi complex were shed from the north and south china blocks and middle late triassic ultrahigh pressure qinling dabie orogenic belt as well as the kunlun and qiangtang terranes in addition the detrital zircon results suggest vast sediment source to sink distances 1500 km for the middle upper triassic hoh xil songpan ganzi strata which is consistent with tectonic models for the paleo tethys ocean basin that incorporate significant components of horizontal tectonic transport like opening of large back arc basins in response to oceanic slab rollback

the late triassic rift related volcanic rocks from eastern qiangtang northern tibet china age and tectonic implications abstract the late triassic nadi kangri volcanic rocks with nearly ew trending outcrops within the qiangtang basin northern xizang tibet china are composed mainly of acid tuff dacite rhyolite and minor basic volcanic rocks there exists a significant depositional hiatus between the nadi kangri volcanic rocks and underlying strata therefore the nadi kangri volcanic rocks represent a new evolution history of the mesozoic qiangtang basin the magma emplacement age of the nadi kangri volcanic rocks in the geladaindong area is 220 4 2 3 ma representing the onset of the mesozoic qiangtang basin the nadi kangri basalts have high nb zr 0 049 0 058 ta hf 0 12 0 15 and zr y 4 95 6 01 ratios in the tectonic discrimination diagrams such as zr vs zr y and th hf vs ta hf the nadi kangri basaltic rocks mostly plot in the within plate setting field the geological background and the geochemical characteristics suggest that the nadi kangri volcanic rocks were formed in a continental rift setting

carbon isotope record and paleoceanographic changes prior to the oae 1a in the eastern tethys implication for the accumulation of organic rich sediments abstract the barremian and aptian correspond to periods of marked changes in the atmosphere ocean system and offer valuable information about global tectonic events here we present integrated high resolution carbonate carbon isotope 13ccarb and geochemical data that precede the early aptian oceanic anoxic event oae 1 a in the qiangtang basin eastern tethys we identified a characteristic and well correlatable barremian lower aptian carbon isotope pattern that can be categorized into 10 segments the most notable features of the 13ccarb record are multiple negative carbon isotope excursions in the barremian aptian and each is possibly linked to environmental changes two carbon isotopic plateaus are observed in the upper barremian which are generally related to increased primary productivity and to the concomitant development of dys to anaerobic conditions our data indicate the development of anoxic conditions during shale deposition which occurred under the conditions of a semi enclosed lagoon environment such conditions were likely localized and not the primary mechanism responsible for the deposition of organic rich sediments within the shenglihe succession the deposition of organic rich shales was very likely due to global regional warming rising temperatures and hydrological cycle strengthening during shale deposition are believed to have increased primary productivity and thus resulted in the expansion of the local oxygen minimum zone within the water column

basin analysis in the southern tethyan margin facies sequences stratal pattern and subsidence history highlight extension to inversion processes in the cretaceous panormide carbonate platform nw sicily abstract in the mediterranean the south tethys paleomargin experienced polyphased tectonic episodes and paleoenvironmental perturbations during mesozoic time the cretaceous shallow water carbonate successions of the panormide platform outcropping in the northern edge of the palermo mountains nw sicily were studied by integrating facies and stratal pattern with backstripping analysis to recognize the tectonics vs carbonate sedimentation interaction the features of the requienid limestone including geometric configuration facies sequence lithological changes and significance of the top unconformity highlight that at the end of the lower cretaceous the carbonate platform was tectonically dismembered in various rotating fault blocks the variable trends of the subsidence curves testify to different responses both uplift and downthrow of various platform blocks impacted by extensional tectonics physical stratigraphic and facies analysis of the rudistid limestone highlight that during the upper cretaceous the previously carbonate platform faulted blocks were subjected to vertical movements in the direction opposite to the displacement produced by the extensional tectonics indicating a positive tectonic inversion comparisons with other sectors of the southern tethyan and adria paleomargins indicate that during the cretaceous these areas underwent the same extensional and compressional stages occurring in the panormide carbonate platform suggesting a regional scale significance in time and kinematics for these tectonic events

the early triassic andean type halagatu granitoids pluton in the east kunlun orogen northern tibet plateau response to the northward subduction of the paleo tethys ocean abstract voluminous granitoids located in the east kunlun orogen eko play an important role in characterizing the crustal growth and northward subduction of the paleo tethys oceanic lithosphere this paper presents new petrological whole rock geochemical zircon u pb isotope geochronological and sr nd hf isotopic data for the halagatu granitoids hg pluton the hg pluton comprises several different textural and compositional types i e medium to fine grained granodiorites mg porphyritic monzogranites pmg coarse grained monzogranites cmg and dark mafic microgranular enclaves me u pb dating of zircons from the hg pluton yielded a weighted mean 206pb 238u age of 248 244 ma which represents the crystallization age of the hg pluton the whole rock geochemical data indicate that the pmg cmg and mg have similar geochemical features for example they are classified as high k calc alkaline metaluminous to wildly peraluminous i type granitoids with negative nb ta and ti anomalies low mg and al2o3 feot mgo tio2 values and high th y ratios these characteristics suggest the parent magmas were crustally derived in contrast the me are characterized by medium k calc alkaline and metaluminous compositions low th y ratios and relatively high mg cr and ni values likely suggesting these magmas were derived from a mantle source furthermore the host granodiorites and microgranular enclaves have consistent sr nd hf isotopic features with end t values of 6 10 to 4 30 and zircon ehf t values of 7 8 to 0 4 indicating an enriched subcontinental lithospheric mantle sclm on the basis of these values and the whole rock geochemistry the hg pluton magmas were the result of mixing between lithospheric mantle derived and crust derived magmas and that fractional crystallization fc played an important role in the formation of the hg pluton the combination of these new data with previously published data reveals that the hg pluton was emplaced in a continental magmatic arc setting by the northward subduction of a branch of the paleo tethys ocean buqingshan ocean beneath the east kunlun qaidam terrane ekt and that the buqingshan ocean began to subduct strongly northward in the late permian ca 260 ma with subduction terminating during the late middle triassic ca 240 ma

new insights about petroleum geology and exploration of qiangtang basin northern tibet china a model for low degree exploration abstract the qiangtang basin is the biggest petroleum bearing basin in the qinghai tibet plateau this basin experienced a foreland basin evolution during the early middle triassic and a rift basin evolution during the late triassic early cretaceous triassic and jurassic hydrocarbon source rocks were widely distributed throughout the basin the triassic tumen gela formation coal bearing mudstones represent the best source rocks because of high total organic carbon toc content 1 25 3 45 and hi values 2 8 123 mg g toc and the xiali formation mudstones are moderately good source rocks with an average toc content ranging from 0 55 to 7 30 and hi values ranging from 7 0 to 165 mg g toc the jurassic buqu formation and suowa formation carbonates however exhibit poor to fair quality as hydrocarbon source rocks excellent dolomite and paleokarst reservoirs and mudstones and bearing evaporite marl cap rocks together with well developed structural traps are recognized in the basin additionally a large paleo oil reservoir zone has also been discovered based on an integrated petroleum systems analysis nine favorable hydrocarbon exploration areas are proposed of which the tuonamu area and badaohu area are selected as the potential targets for the exploration for oil and gas resources in the basin good reservoir quality dolomites in the buqu formation are considered to have a significant exploration potential

the jinshajiang ailaoshan suture zone china tectonostratigraphy age and evolution abstract the jinshajiang suture zone is important for enhancing our understanding of the evolution of the paleo tethys and its age tectonic setting and relationship to the ailaoshan suture zone have long been controversial based on integrated tectonic biostratigraphic chemostratigraphic and isotope geochronological studies four tectono stratigraphic units can be recognized in the jinshajiang suture zone the eaqing complex the jinshajiang ophiolitic melange the gajinxueshan group and the zhongxinrong group isotope geochronology indicates that the redefined eaqing complex composed of high grade metamorphic rocks might represent the metamorphic basement of the jinshajiang area or a remnant micro continental fragment eaqing complex protolith rocks are pre devonian and probably of early middle proterozoic age and are correlated with those of the ailaoshan complex two zircon u pb ages of 340 3 and 294 3 ma separately dated from the shusong and xuitui plagiogranites within the ophiolitic assemblage indicate that the jinshajiang oceanic lithosphere formed in latest devonian to earliest carboniferous times the oceanic lithosphere was formed in association with the opening and spreading of the jinshajiang oceanic basin and was contiguous and equivalent to the ailaoshan oceanic lithosphere preserved in the shuanggou ophiolitic melange in the ailaoshan suture zone the latter yielded a u pb age of 362 41 ma from plagiogranite the re defined gajinxueshan and zhongxinrong groups are dated as carboniferous to permian and latest permian to middle triassic respectively on the basis of fossils and u pb dating of basic volcanic interbeds the gajinxueshan group formed in bathyal slope to neritic shelf environments and the zhongxinrong group as bathyal to abyssal turbidites in the jinshajiang ailaoshan back arc basin latest permian earliest middle triassic synorogenic granitoids with ages of 238 18 and 227 5 255 8 ma respectively and an upper triassic overlap molasse sequence indicate a middle triassic age for the jinshajiang ailaoshan suture formed by collision of the changdu simao block with south china

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

petrogenesis and tectonic significance of the late permian middle triassic calc alkaline granites in the balong region eastern kunlun orogen china numerous calc alkaline granitoid intrusions in the eastern kunlun orogen provide a valuable opportunity to constrain the evolution of the orogen the age and genesis of these intrusions however remain poorly understood the granitoid intrusions near the balong region eastern kunlun orogen consist of granodiorite diorite and syenogranite the granodiorite contains crystallized segregations abundant mafic microgranular enclaves mmes and small quartz diorite stocks in situ zircon u pb dating reveals that the granodiorites and quartz diorites were emplaced between 263 and 241 ma whereas the syenogranite was produced at c 231 ma the granodiorite and quartz diorite have a calc alkaline affinity and are metaluminous and na rich with slightly enriched sr nd isotope compositions the granodiorite is characterized by fractionated ree patterns whereas the quartz diorite displays a relatively flat ree pattern the mmes are consistent with the granodiorite in terms of incompatible elements and sr nd isotope composition compared to the granodiorite and diorite the syenogranite has higher sio 2 k rb th and sr contents and a lower rb sr ratio the results presented here when combined with regional geological data indicate that the granodiorite and quartz diorite were derived from dehydration melting of mafic lower crustal rocks during the n directed subduction of the anyemaqen ocean lithosphere in late permian middle triassic times whereas the syenogranite was produced at a higher crustal level in a syn collisional setting compared to the granodiorite

paleomagnetic data bearing on the mesozoic deformation of the qiangtang block implications for the evolution of the paleo and meso tethys paleomagnetism has played an important role in quantifying the mesozoic evolution of proto tibet in this paper we present new paleomagnetic data from five middle upper jurassic sedimentary sequences quemo co buqu xiali suowa and xueshan fms of the eastern north qiangtang terrane qt at yanshiping 33 6 degrees n 92 1 degrees e the new paleomagnetic results form a large dataset 99 sites 1702 samples and reveal a paleopole at 79 1 degrees n 306 9 degrees e dp 3 9 degrees dm 6 3 degrees for the quemo co fm at 68 9 degrees n 313 8 degrees e dp 2 1 degrees dm 3 7 degrees for the buqu fm at 66 1 degrees n 332 1 degrees e dp 2 7 degrees dm 4 6 degrees for the xiali fm at 72 4 degrees n 318 6 degrees e dp 3 9 degrees dm 6 7 degrees for the suowa fm and at 76 9 degrees n 301 1 degrees e dp 7 9 degrees dm 13 2 degrees for the xueshan fm these results indicate clockwise cw rotations of similar to 19 8 9 4 degrees between similar to 171 2 and 161 7 ma and counterclockwise ccw rotations of similar to 15 4 13 4 degrees between similar to 161 7 and 157 2 ma for yanshiping we attribute the change in rotation sense at approximately similar to 161 7 ma to the initial collision of the lhasa and qiangtang terranes using this and other paleomagnetic data from the lhasa qiangtang and tarim terranes as well as other geological evidence e g tectonism related sedimentary sequences volcanism and hp metamorphism we propose a new conceptual evolution model for the mesozoic qt and tethyan oceans the longmo co shuanghu oceanic slab was subducted before 248 ma followed by continental collision of the north south qiangtang subterranes between similar to 245 and 237 ma the qiangtang terrane experienced post collisional exhumation between similar to 237 and 230 ma during subduction of the jinsha oceanic slab the collision of the qiangtang and songpan ganzi terranes occurred between similar to 230 and 225 ma the qt experienced post collisional relaxation from similar to 225 to similar to 200 ma followed by subsidence and extension related exhumation between similar to 200 and 162 ma in association with subduction of the bangong nujiang oceanic slab finally these events were followed by the scissor like diachronous collisions of the lhasa and qiangtang terranes between similar to 162 ma and the mid cretaceous c 2016 international association for gondwana research published by elsevier b v all rights reserved

late triassic granitic magmatism in the eastern qiangtang eastern tibetan plateau geochronology petrogenesis and implications for the tectonic evolution of the paleo tethys abstract triassic granites are widely exposed in the central qiangtang northern tibetan plateau they therefore made an important contribution to the growth of the tibetan plateau in this paper we present zircon u pb dating and hf isotopic results and whole rock elemental and sr nd isotopic analyses of the dongdashan dds batholith in the central qiangtang in order to understand their petrogenesis and tectonic setting la mc icp ms zircon u pb results show that the dds batholith was emplaced at 220 3 0 7 ma all the granites in the dds possess high a cnk values 1 0 and display peraluminous characteristics similar to s type granite their strongly fractionated ree patterns la yb n 6 98 13 9 with conspicuous negative eu anomalies eu eu 0 51 0 67 together with negative e nd t and e nd t values and depleted nd and hf model ages suggest that the dds granitic magma had a dominantly crustal source likely the paleoproterozoic basement i e the ningduo and caoqu group metasediments in the area in combination with regional studies our new geochemical data and geochronological results demonstrate that the late triassic magmatism was generated in a post collisional tectonic setting the spatial distribution pattern of the mesozoic igneous rocks coupled with the exhumation of high pressure metamorphic rocks in the central qiangtang favors a slab breakoff model which resulted in post collisional extension and asthenospheric upwelling that induced large scale partial melting of the middle lower crust to produce voluminous amounts of felsic magma therefore the occurrence of the late triassic post collisional magmatism and particularly the exhumation of high pressure eclogites and blueschists as well as their presence in the lowermost portion of the late triassic volcanoclastics in the qiangtang basin clearly indicate that the final closure of the of paleo tethys ocean and associated continent continent collision between the gondwana derived western qiangtang and eastern qiangtang terranes had not been completed until the early mid triassic

sedimentary successions and onset of the mesozoic qiangtang rift basin northern tibet southwest china insights on the paleo and meso tethys evolution abstract the mesozoic qiangtang basin is investigated to reconstruct the tectonic evolution of the paleo and meso tethys oceans we present a detailed sedimentary facies analysis of the nadi kangri and quemoco formations and the systematic zircon u pb ages of the volcanoclastic rocks in the nadi kangri formation to understand the onset and nature of the mesozoic qiangtang basin the nadi kangri formation consisting of volcanic volcanoclastic facies associated with alluvial diluvial facies association which represents continental volcanic succession the quemoco formation consisting of braided fluvial restricted platform and tidal flat facies associations represents continental siliciclastic and marine carbonate successions the deepening upward transgressive sequences reconstructed from the two formations are indicative of a rift basin zircon u pb ages of the volcanoclastic rocks in the bottom middle and upper sections of the nadi kangri formation in the fanghu area are 221 7 1 3 ma 217 0 1 5 ma and 207 1 1 3 ma respectively combined with the previous zircon ages of the nadi kangri formation we interpreted that 221 7 220 4 ma is the initial age for the onset of the mesozoic rift basin an evolution pattern for the tethys ocean and mesozoic qiangtang basin has been proposed based on the magmatism metamorphism sedimentary sequence and deformation data obtained from the kunlun klt hoh xil bayan har hbt north qiangtang nqs central uplift belt cub south qiangtang sqs and north lhasa subterranes terranes nls during the early triassic middle jurassic based on the new data we interpret a double sided subduction and subsequently a collision of the paleo tethys ocean beneath the klt to north and nqs to south probably occurring at ca 252 237 ma and 237 227 ma respectively this interpretation is consistent with the late triassic residual sea ocean model that attributed to the origin of the hoh xil bayan har basin the qt and nls experienced a strong extension between ca 225 and 201 ma owing to the rapid expansion of the bangong lake nujiang ocean meso tethys ocean which is consistent with the massive volcanic eruption and deposition of volcanic sediments in the qt and nls in addition the qt and nls experienced a stabilized subsidence during 201 166 ma due to the existence of the mature bangong lake nujiang ocean

middle triassic volcanic rocks in the northern qiangtang central tibet geochronology petrogenesis and tectonic implications abstract although voluminous magmatism occurred during the triassic in the qiangtang terrane the petrogenesis of the volcanic rocks and the associated tectonic scenarios remain mysterious this study focuses on new identified primitive volcanic rocks from the yanshiping area northern qiangtang subterrane the whole rock major trace elemental sr nd isotopic data and zircon u pb age of volcanic rocks are reported in this paper in order to understand their petrogenesis and tectonic setting the studied volcanic rocks can be grouped into two types i e nb enriched basalts and basaltic andesites nebs in the low sequence and arc basalts in the upper sequence zircon u pb dating using la icp ms techniques yields the concordant age with a weighted mean 206 pb 238 u age of ca 242 241 ma for the nebs and ca 240 ma for the arc basalts the distinct geochemical and isotopic characteristics of whole rock and varying th u ree components of zircon grains from the volcanic rocks suggest that the nebs were derived from partial melting of relatively enriched mantle wedge that have been metasomatised by slab related melts and that the arc basalts originated from partial melting of mixing of mantle wedge and depleted asthenospheric mantle in response to the slab breakoff our new geochemical and geochronological results in combination with regional studies imply that the middle triassic magmatism was generated in the tectonic setting of northward subduction of the paleo tethys or bangong nujiang ocean subduction related processes that include melting of the slab and the slab breakoff during the permian middle triassic made an important contribution to crustal growth in the qiangtang terrane whereas vertical crustal growth associated with collision related setting during the late triassic is nonsignificant

petrogenesis and tectonic setting of triassic granitoids in the qiangtang terrane central tibet evidence from u pb ages petrochemistry and sr nd hf isotopes abstract triassic granitoids including the 220 ma shuanghu and 210 ma rongma granitoids studied here are widely distributed around the longmu shuanghu suture and in the qiangtang terrane central tibet the majority of these granitoids can be classified as high k calc alkaline in nature and yield negative ba and sr anomalies on primitive mantle normalized diagrams in addition they are enriched in light rare earth elements lree la yb n 1 61 21 79 strongly enriched in large ion lithophile elements lile e g cs rb and k and depleted in high field strength elements hfse e g nb and ti magma mixing played a role in the genesis of the shuanghu granodiorites as indicated by the occurrence of dioritic enclaves and the wide range in zircon hf compositions ehf t 15 0 to 2 5 the i type shuanghu granodiorites and s type shuanghu and rongma granites might have been derived from melting of southern qiangtang crust given the high initial sr 0 7131 0 7272 low end t 8 9 to 11 1 and zircon ehf t values 15 to 7 2 the granitoids may have formed during melting of southern qiangtang crust heated by upwelling asthenosphere mantle a result of break off and delamination of the paleo tethys slab in a collisional setting

three dimensional inversion of magnetotelluric mt resistivity data from reykjanes high temperature field in sw iceland abstract the resistivity structure of reykjanes is presented derived from a three dimensional 3d model developed in 2016 the model is the final results of a 3d inversion of mt data corrected for static shift by joint inversion with tem soundings at the same location as the mt soundings in the model presented here reysand a total of 136 sounding pairs are used for the inversion the model covers reykjanes area and sandvik potential geothermal area the resistivity structure of a high enthalpy system reflects the thermal alteration of the rock the reykjanes models reveal a conventional resistivity structure for a high enthalpy geothermal system i e a low resistivity cap underlain by a high resistivity core the low resistivity cap reaches surface in the hot spring area gunnuhver and dips down in all directions forming an elongated area of 2 5 km 3 km in strike direction down to 1 km depth bounded by the low resistivity the resistivity of the low resistivity cap is less 3 m and is underlain by a high resistivity core with resistivity of 10 30 m down to 3 km depth at greater depth high resistivity anomalies are prominent with a zone of lower resistivity in strike direction under the main field this zone coincides with an aseismic zone at depth and may indicate a fracture zone with higher temperature and or permeability within the geothermal system comparison to data from the iddp 2 drilling as well as seismic monitoring confirms that suggestion

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems