diagnostic features and field criteria in recognition of tectonic sedimentary and diapiric melanges in orogenic belts and exhumed subduction accretion complexes abstract multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction accretion complexes cause obfuscation of primary block in matrix fabric of melanges and thereby making the recognition of their tectonic sedimentary or diapiric origin difficult here we present a comprehensive overview and synthesis of a diverse set of field based stratigraphic and structural criteria which are at the base of geological mapping rules to differentiate between various melange types developed by disparate geological processes and mechanisms we first define the current concepts of melange and melange nomenclature and describe the most diagnostic features of tectonic sedimentary and diapiric melanges at different scales we discuss some of the main issues complicating the application of these diagnostic criteria such as i similarities between the block in matrix fabric of different melange types formed in partially lithified sediments at shallow structural levels ii transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes iii significance of exotic versus native blocks in melange matrix and iv age relationships between blocks and matrix in a melange we introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic melanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events these new criteria are based on i the coherence between lithological compositions of melange components blocks and matrix and characteristics and tectonic evolution of the geodynamic setting of their formation tectonic environment criterion and ii specificity and kinematic coherence in the distribution of deformation between blocks and the matrix deformation criterion the discussed diagnostic criteria can be applied to all field based investigations of melanges and broken formations in orogenic belts and exhumed subduction accretion complexes around the world regardless of their location age and tectonic history

reconstruction of northeast asian deformation integrated with western pacific plate subduction since 200 ma abstract the configuration and kinematics of continental deformation and its marginal plate tectonics on the earth s surface are intrinsic manifestations of plate mantle coupling the complex interactions of plate boundary forces result in plate motions that are dominated by slab pull and ridge push forces and the effects of mantle drag these interactions also result in continental deformation with a complex basin mountain architecture and evolution the kinematics and evolution of the western pacific subduction and northeast asian continental margin deformation represent a first order tectonic process whose nature and chronology remains controversial this paper implements a deep time reconstruction of the western pacific subduction continental accretion or collision and basin mountain deformation in northeast asia since 200 ma based on a newly revised global plate model we use gplates software to examine strain recovery geological and seismic tomography constraints for the western pacific plate subduction and sequentially backward rotations of deforming features the results indicate a nw se oriented shortening from 200 to 137 ma a nww see oriented extension from 136 to 101 ma a nearly n s oriented extension and uplift with a short term nww see oriented compressional inversion in northeast china from 100 to 67 ma and a nw se and nearly n s oriented extension from 66 ma to the present day the western pacific oceanic plate subducted forward under east asia along mudanjiang honshu island during the jurassic and the trenches retreated to the sikhote alin north shimanto and south shimanto zones from ca 137 128 ma ca 130 90 ma and in ca 60 ma respectively our time dependent analysis of plate motion and continental deformation coupling suggests that the multi plate convergent motion and ocean continent convergent orogeny were induced by advance subduction during the jurassic and earliest cretaceous our analysis also indicates that intra continent rifting and back arc extension were triggered by trench retreat during the cretaceous and that the subduction of the oceanic ridge and arc were triggered by trench retreat during the cenozoic therefore reconstructing the history of plate motion and subduction and tracing the geological and deformation records in continents play a significant role in revealing the effects of complex plate motions and the interactions of plate boundary forces on plate mantle coupling and plate motion intracontinental deformation coupling

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

imaging p to s conversions with multichannel receiver functions we present a new methodology in the direct imaging of p to s converted phases recorded on broadband seismic arrays our approach is based on conventional three component array processing and receiver function techniques with the key addition of a weighted stack based on an aerial smoothing function this creates synthetic arrays with a specified aperture whose image points vary continuously across the array with this approach it is possible to interpolate data from an array of broadband stations onto an arbitrarily fine grid we have applied this technique to a single deep event recorded by the lodore broadband array located in northern colorado and southern wyoming the resulting images show distinct differences in crustal structure across the array and also image major upper mantle discontinuities

three dimensional prestack plane wave migration of teleseismic p to s converted phases 1 theory 1 we present the theoretical foundations for a prestack migration technique to image teleseismic p to s converted phases the method builds on teleseismic p wave deconvolution pseudostation stacking neal and pavlis 1999 and on the idea of using a plane wave decomposition for imaging as introduced by treitel et al 1982 deconvolution operators are constructed by pseudostation stacking of the array aligned to the incident p wave arrival times to produce a space variable deconvolution operator the resulting data are then muted to remove the deconvolved direct p wave pulse and pseudostation stacked over a grid of feasible slowness vectors the pseudostation stack interpolates the wave field onto a regular grid along earth s surface producing a series one per slowness vector of uniformly sampled three dimensional data cubes two space variables and time the plane wave components can be propagated downward using a form of approximate ray tracing with a three dimensional earth model this yields a series of distorted cubes topologically equivalent to the original uniformly sampled data cubes these data volumes are summed as a weighted stack with the weights derived from an integration formula for inverse scattering based on the generalized radon transform this allows an image of the subsurface to be constructed on an event by event basis beneath the array we apply this technique to data from the lodore array that was deployed in northwestern colorado the results suggest the presence of a major lithospheric scale discontinuity defined by a south dipping boundary

p and s receiver function analysis of seafloor borehole broadband seismic data 1 the crustal and lithospheric structure of the normal oceanic plates is investigated using converted wave techniques p and s receiver functions rfs and novel stacking analysis techniques without deconvolution applied to the data from two seafloor borehole broadband seismic stations located in the central philippine sea and in the northwest pacific ocean we observe sufficient energy from at least two discontinuities within the error bounds one from the crust mantle moho boundary and the other from the seismic lithosphere asthenosphere boundary lab synthetic seismograms for seafloor stations show that the water reverberations interfere with the vertical component of seismograms but to a lesser extent with the radial part of p receiver functions on the other hand s receiver functions are devoid of such effects since all the multiples and converted waves are separated in time by the primary s wave in time waveform modeling of rfs shows that the crustal thicknesses of the western philippine sea plate and northwest pacific plate are 7 8 km and that depths of lab are 76 1 8 km and 82 4 4 km respectively with an abrupt vs drop at lab of 7 8 as reported by kawakatsu et al 2009 the lab depth for the eastern philippine plate is found to be 55 km to confirm the robustness of this observation we further analyze vertical and radial components of the data without deconvolution for p wave backscattered reflection phases and p to s converted phases the result indicates that the reflected converted phases from moho and lab are observed at timings consistent with the receiver function results the effect of seismic anisotropy for observed rfs is also investigated

new shrimp u pb zircon ages from the heilongjiang high pressure belt constraints on the mesozoic evolution of ne china the heilongjiang complex is a high pressure accretionary belt composed mainly of serpentinite glaucophane bearing metabasalt epidote glaucophane albite schist greenschist marble two mica schist muscovite albite schist quartz schist and quartzite chert located along the suture zone separating the jiamusi and songliao blocks in ne china shrimp u pb zircon analyses of two samples of granitic gneiss from yilan that are interleaved with the heilongjiang complex record diverse protolith ages that are consistent with derivation from regional permian granitoids 263 7 ma and the adjacent mashan complex 492 6 ma indicating tectonic incorporation of older granitic components into the accretionary complex the age of the basaltic protolith of two samples of glaucophane albite schist from yilan is 245 ma and is slightly younger than the protolith age of two samples of amphibole schist from mudanjiang located about 200 km south of yilan that define weighted mean 206pb 238u ages of 257 4 and 257 5 ma all four samples contain a few older inherited zircon grains and also show the effects of an isotopic disturbance at 200 to 190 ma most likely related to the subsequent high pressure metamorphism the timing of which has been determined in previous studies the basaltic rocks record rifting and ocean development from 260 to 210 ma based on previous studies in which both e morb and oib protolith signatures were identified detrital zircons in two samples of mica schist from mudanjiang show distinct populations at 700 ma 500 to 450 ma 350 to 213 ma peak at 255 ma 290 to 200 ma and 200 ma all except the youngest ages can be matched with rocks from the older components of the jiamusi block and with other areas in the central asia orogenic belt caob supporting the view that the jiamusi block was most likely the eastern segment of the caob prior to rifting the youngest concordant magmatic detrital grain with an age of 207 3 ma defines the maximum age of sedimentation this also limits the timing of high pressure metamorphism in the heilongjiang complex to post late triassic consistent with argon data obtained in previous studies final closure between the jiamusi and songliao blocks took place in the latest triassic early jurassic with the two blocks accreted as a result of pacific ocean subduction this suggests that the heilongjiang complex records the time when north south closure of the caob in china gave way to westward movement related to the pacific ocean subduction which has dominated the tectonics of ne china and far east russia since that time

debris flow olistostromes and slumping on a distal passive continental margin the palombini limestone shale sequence of the northern apennines an olistostrome accumulation up to 530 m thick occurs in the casanova area of the northern apennines it lies within or above the calciturbiditic palombini limestone shale sequence and is part of the allochthonous vara complex sediments originally deposited on oceanic crust the olistostromes are poorly sorted monomict matrix supported submarine debris flow deposits with rigid plugs they have a compactional foliation and a compaction modified planar clast fabric created during flow although diachronous in the main part of the area the olistostromes have a vertical gradational contact with the overlying slumped palombini in which recumbent asymmetric fold hinges and trains and slump boudins are present many criteria indicate soft sediment deformation fold asymmetry indicates a uniformly sw dipping palaeoslope the textural gradation from slumps to olistostrome beds plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps in vertical sections variations in limestone petrography volume percentage and size of clasts confirm that the olistostromes were derived from the palombini as a series of bed by bed slumps keeping pace with sedimentation of the palombini from olistostrome clast sizes and bed thicknesses a depositional slope of 4 is estimated the olistostromes are not precursor sediments shed from advancing nappes as in the bracco ridge model of some authors rather they were formed at the foot of a distal block faulted passive continental margin long before nappe emplacement

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

mesozoic radiolarian biostratigraphy of japan and collage tectonics along the eastern continental margin of asia abstract jurassic accretionary complexes mainly composed of carboniferous to permian limestone associated with greenstone triassic bedded chert jurassic siliceous shale and clastic rocks form the basement rocks of japan the stratigraphy of these complexes has recently been analysed utilizing radiolarian fossils resulting in the discovery that japan comprises a collage of disrupted terranes international co operative works reveal that lithologically and biostratigraphically similar terranes are distributed in northeast china nadanhada terrane and sikhote alin ussr khabarovsk terrane paleomagnetic studies demonstrate that prior to opening of the sea of japan the japanese islands were located much closer to the eastern margin of the asian continent where the nadanhada and khaborovsk terranes are now exposed features of the mino terrane in central japan are characteristic of these terranes which originally formed along the continental margin of east asia seamounts covered by fossiliferous limestone formed during the carboniferous to permian at low latitudes the seamounts drifted towards a continental margin together with upper paleozoic sediments triassic bedded chert and lower jurassic siliceous shale which accumulated around them upper paleozoic triassic and lower jurassic formations were accreted to the eastern continental margin which was a large tectonic collage developed as the chinese mainland during the late triassic enormous amounts of clastic detritus were deposited in sedimentary basins where jumbling and telescoping of pelagic sediments took place in a complicated fashion producing a melange the provenance of clastic detritus within the mino terrane is interpreted as a platform on which permian and carboniferous calcareous sediments containing diagenetic lutecite and orthoquartzite formations were widespread these formations covered a precambrian metamorphic and granodioritic basement similar to that seen in the south china region accretion culminated in the earliest cretaceous and the large disrupted terrane which had developed was transpressed northwards along the eastern margin of the continent during this period of dispersal the original terrane was sheared fragmented and separated into many smaller terranes some of which were transported to the sikhote alin region by the late cretaceous the most recent dispersal occurred during the opening of the sea of japan which is closely related to the latest movement of the pacific plate studies of radiolarian micropaleontology and the significance of these fossils to the resolution of the biostratigraphy and the tectonic history of japan are reviewed the results of biostratigraphic analyses are discussed in relation to the mesozoic tectonics of east asia

allochthonous oceanic basalts within the mesozoic accretionary complex of alexander island antarctica remnants of proto pacific oceanic crust the mesozoic lemay group accretionary complex of alexander island antarctica contains thrust bound slices of accreted ocean floor ocean islands and seamounts they represent fragments of proto pacific oceanic crust of which only a tiny remnant the phoenix plate remains off northern antarctic peninsula they therefore provide an excellent opportunity to sample the ancient oceanic crust that formerly occupied the southern pacific ocean all the basalts experienced sea floor and subduction accretion metamorphism ranging from zeolite to transitional blueschist facies on the basis of rare arth and other immobile trace element characteristics the basalts are divided into depleted morb n morb e morb and tholeiitic and alkaline oib oceanic basalts occur within two rock associations on alexander island basalt volcaniclastite chert and basalt volcaniclastite tuff the basalt volcaniclastite chert rock association is dominated by pillow lavas which have light ree depleted n morb geochemical characteristics and is interpreted as representing ocean floor formed at spreading centres locally sills of tholeiitic oib intrude the sequence the basalt volcaniclastite tuff rock association exposed in the lully foothills was formed in shallow water during the early jurassic it is geochemically varied consisting of basalts with n morb e morb and tholeiitic oib characteristics the association is interpreted to have been formed on a large seamount or ocean island

geometry and topology of tectonolineaments in the gorce mts outer carpathians in poland abstract the present study was focused on analysis of the geometrical and topological features of the lineament network in the gorce mountains polish outer carpathians the source data was a 1m high resolution lidar digital elevation model dem network topology was analysed using the networkgt toolset for arcgis software the topological analysis represented the first attempt to apply research of this type in the polish carpathians five lithostratigraphic units occurring in the research area characteristic of the krynica zone of the magura nappe were selected for analysis topology was studied for each of the units separately as well as for the whole area it was found that the units were differentiated in terms of some topological parameters such as 2d intensity moreover latitudinal trends were observed due to the presence of wide fault zones the geometry of the network is consistent with the general carpathian overview sets of conjugate strike slip faults with splaying ends were identified in the southern part of the area the strike of the oldest faults was e w this shows that on the scale of the observation hundreds to thousands of metres the network was a product of general thrusting processes rather than derivative of a local structural plan the applicability of both topological analyses and high resolution dem as supplementary to classical methods in a study of the outer carpathians was confirmed with analysis conducted despite the identification of some limitations such as gis operator related bias the scale of the analyses is linked in a multi scale approach to structural network analyses

seismic imaging of melanges pieniny klippen belt case study the authors present results of the first high resolution deep seismic reflection survey in the pieniny klippen belt pkb in poland this survey sheds new light on the matter of olistostromes and the melange character of the pkb the sedimentary mass transport deposits represented by olistoliths and olistostromes manifest themselves by different petrophysical parameters of rocks velocity density and resistivity and seismic attributes seismic attributes are very effective in the interpretation of the geology of complex melanges the authors used selected attributes low pass filter energy energy gradient dip steered median filter prewitt filter laplacian edge enhancing filter and square root of the energy gradient these attributes emphasize changes of the seismic image inside melange zones the distinguished olistoliths are now inside imbricated thrust structures and they are tectonically rearranged polygenetic melanges in the pkb originated as a result of sedimentary and tectonic processes the pkb in the investigated area forms several north vergent thrust sheets belonging to the zlatne and hulina nappes both nappes contain large chaotic non reflective olistoliths as well as the smaller mainly high reflective olistoliths olistoliths are arranged parallel to the flysch layering and thrusts the results presented confirm the postulated two olistostrome belts within the pkb structure

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

the pieniny klippen belt in the western carpathians of northeastern slovakia structural evidence for transpression abstract the pieniny klippen belt represents a 600 km long but only a few kilometers wide suture zone in the carpathian orogenic belt based on a quantitative analysis along a part of its nw trending segment in northeastern slovakia we present structural data supporting transpression the continuous interaction of strike slip shearing horizontal shortening and vertical lengthening as a major deformation style in its polyphase deformation history dextral transpression is expressed in the map scale and outcrop fault pattern the oblique orientation of fold axes to the faults bounding the klippen belt and extension parallel to the fold axes the transpression related strain field is described and quantified by the analysis of 1 orientation of rotated fold axes displaying an acute angle to the margins of the klippen belt 2 orientation and geometry of paleostress derived from mesoscale fault striae analysis e trend of 3 trajectories and flattening geometry and 3 the deformation history indicated by extension veins non coaxial regime different techniques using fault striae data quantify paleostress and subdivide heterogeneous data sets mathematically into homogeneous subsets the observed deformation history is modelled as a homogeneous transpression deformation the best fitting model requires a nw trending present day orientation external contraction direction e g plate slip vector and predicts 16 fold axes parallel extension and 23 axial plane normal shortening

late cretaceous deformation of the pieniny klippen belt west carpathians abstract the late cretaceous position and dynamics of the pieniny klippen belt of the west carpathians which lies behind the palaeogene flysch accretionary prism are reconstructed as shown by the reconstruction based on structural sedimentological and palaeomagnetic data the pieniny klippen belt occupied a wnw ese to nw se trending zone during the late cretaceous which acted as an oblique convergent boundary between the ancestral west carpathians and the oceanic lithosphere attached to the north european platform sediments of the pieniny klippen belt were part of both the mountain belt and foredeep at that time known change from pelagic micritic limestone to a flysch sequence is progressively younger seawards in the thrust slice stack forming the pieniny klippen belt the syn sedimentary record includes flysch olistostrome and wildflysch sediments both the nw se thrusting along the ne sw striking faults and dextral strike slip faulting along the wnw ese to nw se striking faults were active in the late cretaceous in the area of the current pieniny klippen belt

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

early paleozoic metamorphic rocks of the erguna block in the great xing an range ne china evidence for the timing of magmatic and metamorphic events and their tectonic implications abstract the erguna block is a crustal unit located along the eastern margin of the central asian orogenic belt caob in the far north of china it contains a variety of khondalitic rocks that include sillimanite and garnet bearing gneiss biotite plagioclase gneiss and carbonate in association with hornblende plagioclase gneiss and a variety of granitic orthogneisses these rocks are collectively referred to as the mohe complex and make up the basement rocks in this poorly exposed terrane four samples were analyzed for this study including two samples of biotite plagioclase gneiss one sample of garnet sillimanite gneiss and a sample of hornblende plagioclase gneiss all samples provide evidence of metamorphism in the form of discrete zircon grains or metamorphic rims around detrital cores and they record remarkably consistent 206 pb 238 u ages between 495 2 ma and 497 6 ma detrital zircon cores with oscillatory zoning from the two biotite plagioclase gneiss samples yield magmatic ages that range from 608 8 ma to 1015 12 ma whereas those in the garnet sillimanite gneiss range from 678 8 to 1373 17 ma these results establish that a range of meso to neoproterozoic magmatic rocks were present in the source area and contributed to the sedimentary protoliths the youngest zircon core with an age of 608 8 ma limits the maximum possible age of deposition indicating that the rocks of the mohe complex cannot be late archean to early proterozoic as previously considered the 500 ma age for the granulite facies metamorphic event in the mohe complex is identical to that recorded in the mashan complex of the jiamusi block and the hutou complex of the khanka block 1000 km to the south southeast implying that an extensive early paleozoic khondalite belt extended across much of the eastern caob rocks of similar age and metamorphic grade have also been recorded from the sayang baikal orogen along the southern margin of the siberia craton 1000 km to the west it is unclear at present whether these two belts are directly related but whatever the relationship it is evident that extensive tracts of khondalitic rocks were present in the eastern caob they were subsequently affected by high grade metamorphism in the early paleozoic forming collisional accretionary terranes that were accreted during the late pan african global event

basis pursuit receiver function abstract receiver functions rfs are derived by deconvolution of the horizontal radial or transverse component of ground motion from the vertical component which segregates the ps phases many methods have been proposed to employ deconvolution in frequency as well as in time domain these methods vary in their approaches to impose regularization that addresses the stability problem here we present application of a new time domain deconvolution technique called basis pursuit deconvolution bpd that has recently been applied to seismic exploration data unlike conventional deconvolution methods the bpd uses an l1 norm constraint on model reflectivity to impose sparsity in addition it uses an overcomplete wedge dictionary based on a dipole reflectivity series to define model constraints which can achieve higher resolution than that obtained by the traditional methods we demonstrate successful application of bpd based rf estimation from synthetic data for a crustal model with a near surface thin layer of thickness 5 7 10 and 15 km the bpd can resolve these thin layers better with much improved signal to noise ratio than the conventional methods finally we demonstrate application of the bpd receiver function bprf method to a field dataset from kutch india where near surface sedimentary layers are known to be present the bprfs are able to resolve reflections from these layers very well

volumetric curvature attributes add value to 3d seismic data interpretation horizon based curvature attributes have been used in seismic data interpretation for predicting fractures since 1994 when lisle demonstrated the correlation of curvature values to fractures measured on an outcrop different measures of curvature such as gaussian strike and dip have been shown by different workers to be highly correlated with fractures and many more applications are also possible by definition all such applications need the interpretation of a seismic horizon which may be simple if data quality is good and the horizon of interest corresponds to a prominent impedance contrast

marginal accretion processes of jiamusi block in ne china evidences from detrital zircon u pb age and deformation of the wandashan terrane abstract the eastern segment of central asian orogenic belt underwent not only a long evolution history related to the paleo asian ocean during paleozoic but also the tectonic overprinting by the westward subduction of paleo pacific ocean crust during mesozoic when the subduction of paleo pacific ocean crust started has been long debated issue for understanding the tectonic evolution of the eastern asian continental margin the eastern margin of the jimusi block wandashan terrane preserved complete records for the accretionary process of the westward subduction of paleo pacific ocean crust comprising the yuejinshan complex and raohe accretionary complex rac the wandashan terrane is located in the eastern margin of jiamusi block ne china and is considered to be an accretionary wedge of the westward subducting oceanic crust to reconstruct the marginal accretion processes of the jiamusi block the structural deformation of the wandashan terrane was investigated in the field and the geochronology of the dalingqiao and yongfuqiao formations were studied which were formed syn and post rac accretion respectively the yuejinshan and raohe complexes were discontinuously accreted to the eastern margin of the jiamusi block contrary to the previous consideration of the late triassic to early jurassic this study suggests that the yuejianshan complex in southwest wandashan terrane probably accreted from late carboniferous to middle permian which was driven by unknown oceanic crust subduction existing to the east present position of the jiamusi block at that time the siltstones of the dalingqiao fm yield the youngest zircon u pb age of 142 2 ma indicating the emplacement of the rac not earlier than the late jurassic thus the rac might start to accrete from the jurassic and emplace during 142 131 ma resulted from the paleo pacific subduction which started from the late triassic to early jurassic

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

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

the mesozoic accretionary complex in northeast china evidence for the accretion history of paleo pacific subduction abstract the mesozoic accretionary complex in northeast china which mainly consists of the jilin heilongjiang high pressure hp metamorphic belt and the nadanhada accretionary complex are the key area to understand the paleo pacific subduction accretion the jilin heilongjiang hp belt is a hp metamorphic zone between the jiamusi and songliao blocks and consists of the heilongjiang blueschist belt and the zhangguangcai complex previously published and our new geochronological data indicate that the collision between the jiamusi and songliao blocks along the jilin heilongjiang hp belt occurred between 210 and 180 ma suggesting that the jilin heilongjiang hp belt is an important unit for characterizing the geodynamic switch from the north south closure of the central asian orogenic belt to the onset of westward accretion related to subduction of paleo pacific plate in the latest triassic to early jurassic early permian igneous rocks with arc affinity in the eastern margin of the jiamusi block are more likely related to the mongol okhotsk subduction rather than the paleo pacific subduction or the collision between the jiamusi and khanka blocks as previously considered the nadanhada accretionary complex lies to the east of the jiamusi block and is composed of the yuejinshan and raohe complexes compilation of published geochronological data indicate that the yuejinshan complex was probably formed between 210 ma and 180 ma similar to ages for the jilin heilongjiang hp belt along the western margin of the jiamusi khanka block the raohe complex was formed later in the late jurassic to early cretaceous 170 137 ma likely more related to the subduction accretion of paleo pacific plate the final accretion in the target area took place in the early cretaceous 137 130 ma

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

building and exhumation of the western carpathians new constraints from sequentially restored balanced cross sections integrated with low temperature thermochronometry western carpathian orogeny has been the subject of intense scientific debate due to the occurrence of enigmatic features leading several authors to provide contrasting geological models in this paper a new interpretation for the tectonic evolution of the western carpathians is provided based on i an analysis of the stratigraphy of the mesozoic tertiary successions across the thrust belt domains ii a reappraisal of the stratigraphy and sedimentology of the tectonic melange i e the so called pieniny klippen belt marking the suture between the inner and outer carpathians and iii the construction of a series of balanced and restored cross sections validated by 2d forward modeling our analysis provides a robust correlation of the stratigraphy from the outer to the inner carpathians independently of the occurrence of oceanic lithosphere in the area and allows for the reinterpretation of the tectonic relationships among the inner carpathians the outer carpathians and the pieniny klippen belt and the exhumation mechanisms affecting this orogenic belt in order to constrain the evolution during the last 20 ma our model also integrates previously published and new apatite fission track and apatite u th sm he data these latter indicate a middle late miocene exhumation of the pieniny klippen belt in this study the recent regional uplift of the pieniny klippen belt is described for the first time using a 2d kinematic model for the tectonic evolution of the western carpathians

lithospheric and upper mantle structure of the indian shield from teleseismic receiver functions receiver functions derived from teleseismic p waveforms of 297 earthquakes recorded at broadband station hyderabad hyb are analysed to investigate the lithospheric and upper mantle structure in the vicinity of the station located in the northeastern part of the archaean dharwar craton the internal structure of the 33 2 km thick crust is simple it can be approximated by a single layer with s velocity linearly increasing with depth from 3 4 to 4 0 km s the average being 3 7 0 2 km s the crustal poisson s ratio is 0 25 0 01 a seismic discontinuity at 90 km depth is inferred from a signal particularly prominent on the sh component and possibly indicative of a layer of depth localized anisotropy in the lithospheric mantle the two principal mantle discontinuities are at depths of 406 and 659 km which are close to the global averages

provenance of cretaceous trench slope sediments from the mesozoic wandashan orogen ne china implications for determining ancient drainage systems and tectonics of the paleo pacific the wandashan orogen of ne china is a typical accretionary orogen related to paleo pacific subduction the raohe complex as a major part of the orogen consists of mid triassic to mid jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial sourced clastic trench slope sediments sensitive high resolution ion microprobe u pb dating and la mc icpms hf isotopic analysis of detrital zircons from the terrestrial sourced yongfuqiao formation sandstone show that most zircons are phanerozoic 90 140 150 ma 10 180 220 ma 25 240 270 ma 15 300 360 ma 15 391 395 ma 3 and 450 540 ma 20 whereas 10 are precambrian in age about 90 of the zircons have ehf t values ranging from 11 1 to 12 8 this suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the central asian orogenic belt and the jiamusi block the age of the yongfuqiao formation is constrained to the earliest cretaceous which represents the accretion time of the mid triassic to mid jurassic oceanic complexes when compared with the mino complex in japan and the tananao complex in taiwan three different provenances are identified suggesting three ancient drainage systems which transported sediments from ne china north china and south china to the paleo pacific subduction accretion system

detrital zircons from phanerozoic rocks of the songliao block ne china evidence and tectonic implications abstract rocks that crop out in the northern part of the songliao block are mainly consist of high grade metamorphic gneiss paleozoic strata and mesozoic granites they are essentially similar to rocks reported from beneath the songliao basin that occupies the majority of the songliao block four samples of paleozoic metasedimentary rocks from tieli in the north eastern part of the songliao block yield detrital zircon u pb ages ranging from 2690 to 501 ma with four age populations at 2071 2690 ma with a peak at 2585 ma 1776 1997 ma with a peak at 1890 ma 719 991 ma with a peak at 800 ma and 501 592 ma with a peak at 518 ma these are similar to age populations in other parts of the central asian orogenic belt caob although sediments from the songliao block contain more abundant archean and proterozoic detrital zircons than the neighboring jiamusi khanka block to the east and xing an block to the west this may indicate that rocks of this age comprise a minor component of the songliao block the pan african zircon ages from the songliao block taken together with 500 ma magmatic and high grade metamorphic zircons obtained from the nearby erguna xing an and jiamusi khanka blocks indicate that pan african events affected all blocks of the caob in ne china this suggests that these blocks not only share a common basement but that they had a common history an extensive late pan african 500 ma orogenic terrane thus occupies much of the caob in ne china

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

discussion of olistostromes of the pieniny klippen belt northern carpathians j golonka m krobicki a wa kowska m cieszkowski a l czka reply we welcome the comments by our slovakian colleagues and their critique of our results particularly as we have discussed and published papers together several times about our ideas sometimes more or less disputable aubrecht et al 2003 2006 krobicki et al 2003 krobicki aubrecht golonka 2003 golonka et al 2006 pienkowski et al 2008 we are pleased to see such warm reaction to our work paper which is focused on one of the rudimentary questions in the pieniny klippen belt pkb area how many what kind of olistoliths olistostromes occur within the inner structure of the pkb and when and why did they originate mostly during the palaeogene part of the mesozoic cenozoic history of this region we expected this discussion earlier the content of our paper was presented at the 6 th meeting of the central european tectonic studies group ceteg in upohlav pieniny klippen belt slovakia cieszkowski et al 2008 and later at the xix congress of the carpathian balkan geological association in thessaloniki greece cieszkowski et al 2010 golonka et al 2010 some ideas were also briefly mentioned in the paper by cieszkowski et al 2009 in a journal issue edited by d plasienka we assume that the comments are based on recent investigation because the authors list the grants received to conduct the research therefore the submitted comments sometimes present a point of view different from that published previously by some of the authors of the comments ra jm see aubrecht et al 2003 krobicki aubrecht golonka 2003 wierzbowski et al 2006 pienkowski et al 2008 the statement certainly there are many still unresolved problems in the geology of the pkb and it ought to be said that the co authors of this discussion also do not fully agree with all interpretations formulated and illustrated by the first author perhaps explains this controversy of course we agree that there are many still unresolved problems in the geology of the pkb we also agree with the statement olistostromes and olistoliths are quite frequent but not omnipresent we depicted the distribution of the olistoliths and their relationship to the non olistolith tectonic units of the pkb in golonka et al 2015 figs 3 8

tracing tectonic deformation using the sedimentary record the study of sediments and sedimentary basins in terms of their tectonic environment requires a multidisciplinary approach and has increasingly drawn both techniques and objectives from fields outside sedimentology the application of different theoretical experimental and empirical resources provided by structural geology geochemistry geophysics scale modelling and field geology complement sedimentological methods with the combined aim of achieving a deeper understanding of the origins evolution and significance of sedimentary sequences in terms of their tectonic history studies presented in this volume range across a wide spectrum from the analysis of sedimentary sequence architecture at basin scale down to the chemical properties of individual grains and include studies from a range of tectonic settings the volume will be of interest to those involved with or contemplating studies involving the linkages between tectonics and sedimentation as well as a wider audience to whom the results of such studies may provide fresh insight

reply to the seismic imaging of melanges pieniny klippen belt case study discussion we welcome the discussion by jurewicz et al 2020 whose main criticism focused on the fact that the authors main conclusions contradict the results of previous studies however this statement refers perhaps to the geological setting since we are not aware of any previous studies providing seismic imaging of melanges in the pieniny klippen belt pkb we did not consider the critical remarks by plasienka et al 2017 because we believe that sufficient answers were provided by golonka et al 2017 we are grateful to jurewicz et al 2020 for pointing out the erroneous term tectonic olistolith that we will correct it in future work the discussion is based on two sets of problems regional geology and interpretations of seismic data

three dimensional prestack plane wave migration of teleseismic p to s converted phases 2 stacking multiple events 1 in part 1 we developed the theoretical foundations of a prestack migration procedure to image forward scattered p to s pds converted waves in the coda of teleseismic p waves this paper addresses the issue of how to optimally stack data from multiple events migrated by this procedure we apply matrix perturbation theory to develop an objective way to quantify noise in deconvolved pds data application of the theory demonstrates that an optimal stack requires weighting the migrated data from each event by a signal to noise ratio criterion we also find that the migrated pds images have to be binned by back azimuth and balanced prior to the final stack this is necessary to mitigate coherent noise that results from aliased microseism noise that is enhanced by our processing method we processed 23 events recorded by the lodore array in northwestern colorado with our procedure the results indicate the presence of a major lithospheric scale discontinuity defined by a south dipping boundary within the crust that we interpret as the subsurface expression of the cheyenne belt the suture is also marked by a transition in crustal thickness from 35 km on the archean side to over 40 km on the colorado plateau side we also observe a strong difference in the lithospheric mantle pds conversion signature on opposite sides of the suture that suggests delamination and northward convergence of the colorado lithosphere beneath the wyoming province

formation of hp lt rocks and their tectonic implications in the western tianshan orogen nw china geochemical and age constraints the western tianshan high pressure low temperature metamorphic belt in northwestern china formed within a paleozoic accretionary wedge on the south side of the yili central tianshan plate it comprises various lithologies including mafic metavolcanic rocks metavolcaniclastic rocks metagreywacke marble and serpentinite the metavolcanics comprise eclogite omphacitite epidosite and blueschist the trace and rare earth element characteristics of these rocks indicate morb to oib affinities suggesting a seamount like setting for the protoliths of these rocks the end value of the eclogite 8 9 indicates that the protolith was derived from a long term depleted mantle i e an n morb source supporting the trace and rare earth element characteristics of these samples sm nd isochron dating of 343 44 ma omp gln grt wr and an age of 346 3 ma grt gln were determined using an eclogite boudin within blueschist a well defined 40ar 39ar plateau age of 344 1 ma was obtained for crossite from an omphacite phengite bearing blueschist and is concordant with the sm nd isochron age for the eclogite suggesting that neither argon loss nor excess argon affected the crossite a well defined 40ar 39ar plateau age of 331 2 ma was determined for phengite from the same sample the high pressure metamorphic rocks were formed by the b type subduction of a paleozoic south tianshan ocean about 344 ma ago they were however exhumed to higher crustal levels during the collision of the tarim and yili central tianshan plates about 331 ma ago similar to an alpine type tectonic regime

polygenetic melanges a glimpse on tectonic sedimentary and diapiric recycling in convergent margins a significant part of melanges recognized in exhumed convergent margins around the world has been recently documented to have chiefly originated from masse transport and subsurface remobilization and disruption i e melanges from sedimentary and mud serpentinite diapiric processes and from in situ fluidification disruption tectonic and or sedimentary processes occurring during subsequent multiple deformational events of convergent margin evolution commonly overprint and significantly rework the primary sedimentary or diapiric melange fabric forming polygenetic melanges this ultimately complicates their distinction from true tectonic melanges masking part of the recorded tectono sedimentary evolution of the associated convergent margin the contributions gathered in this thematic collection explore with different approaches from field structural and stratigraphic observations to geophysical analyses different types of polygenetic melange at various scales around the world these studies conclude that the understanding of this type of melange may provide crucial insights for a more detailed interpretation of the evolution of ancient and modern convergent margins and of processes and mechanisms triggering potential natural hazards earthquakes and tsunamis case studies include the apennines in the central mediterranean region the carpathians in central europe and the nankai prism in japan thematic collection this article is part of the polygenetic melanges a glimpse on tectonic sedimentary and diapiric recycling in convergent margins collection available at https www lyellcollection org cc polygenetic melanges

pan african metamorphic and magmatic rocks of the khanka massif ne china further evidence regarding their affinity the khanka massif is a crustal block located along the eastern margin of the central asian orogenic belt caob and bordered to the east by late jurassic early cretaceous circum pacific accretionary complexes of the eastern asian continental margin it consists of graphite sillimanite and cordierite bearing gneisses carbonates and felsic paragneisses in association with various orthogneisses metamorphic zircons from a sillimanite gneiss from the hutou complex yield a weighted mean 206 pb 238 u age of 490 4 ma whereas detrital zircons from the same sample give ages from 934 610 ma magmatic zircon cores in two garnet bearing granite gneiss samples also collected from the hutou complex yield weighted mean 206 pb 238 u ages of 522 5 ma and 515 8 ma whereas their metamorphic rims record 206 pb 238 u ages of 510 500 ma these data indicate that the hutou complex in the khanka massif records early palaeozoic magmatic and metamorphic events identical in age to those in the mashan complex of the jiamusi massif to the west the older zircon populations in the sillimanite gneiss indicate derivation from neoproterozoic sources as do similar rocks in the jiamusi massif these data confirm that the khanka massif has a close affinity with other major components of the caob to the west of the dun mi fault based on these results and previously published data the khanka massif is therefore confirmed as having formed a single crustal entity with the jiamusi and possibly the bureya massif since neoproterozoic time

regional wavefield reconstruction for teleseismic p waves and surface waves 1 with the recent availability of dense seismological array data there is the opportunity to reconstruct 2d wavefields of propagating seismic energy such a reconstruction allows seismic data to be viewed as wavefields rather than as single station traces reconstruction of such wavefields within an array will improve our understanding of complex wave propagation effects and hence the underlying earth structure beneath the array we propose an algorithm applicable for teleseismic waves that is based on wavefield expansion by cubic b splines application to the high density array in southern california shows that we can identify basin resonances and wavefront shifts such wavefield shifts could be caused by local structure or travel path structure as waves pass through major structural contrasts

enhanced structural interpretation from 3d seismic data using hybrid attributes new insights into fault visualization and displacement in cretaceous formations of the scotian basin offshore nova scotia abstract meta or hybrid attributes extracted from seismic data through artificial neural networks enhance structural details in subsurface strata cretaceous units within the penobscot prospect are devoid of such interpretations although these units are plausible zones for hydrocarbon generation and accumulation the role of geologic structures responsible for such entrapment is poorly understood the present study enlightens these latter geological structures through a case study that uses 3d time migrated seismic data from the penobscot prospect in the scotian basin a modern data conditioning approach used together with multi attribute analyses and a supervised neural network have brought out the minute details of subsurface geologic structures through a hybrid attribute called the fault probability cube fpc the present fault displacement analysis reveals that the major fault of the prospect has evolved by the coalescence of different fault segments grown over space and time and has demonstrated a predominant nnw sse structural trend such a geometry has structurally modulated the cretaceous units the logan canyon the dawson canyon and the wyandot formations giving rise to different horst graben structures and fracture networks as shown by the fpc attribute this generates complicated structural deformation and accommodation space thereby enabling different trapping zones for hydrocarbon accumulation within these units such a detailed structural understanding will provide significant input to the future exploration and development programme in the penobscot prospect

mesozoic plate tectonic reconstruction of the carpathian region abstract palaeomagnetic palaeobiogeographic and structural comparisons of different parts of the alpine carpathian region suggest that four terranes comprise this area the alcapa tisza dacia and adria terranes these terranes are composed of different mesozoic continental and oceanic fragments that were each assembled during a complex late jurassic cretaceous palaeogene history palaeomagnetic and tectonic data suggest that the carpathians are built up by two major oroclinal bends the alcapa bend has the meliata oceanic unit correlated with the dinaric vardar ophiolite in its core it is composed of the western carpathians eastern alps and southern alcapa units transdanubian range bukk this terrane finds its continuation in the high karst margin of the dinarides further elements of the alcapa terrane are thought to be derived from collided microcontinents czorsztyn in the n and a carbonate unit tisza in the se the tisza dacia bend has the vardar oceanic unit in its core it is composed of the bihor and getic microcontinents this terrane finds its continuation in the serbo macedonian massif of the balkans the bihor getic microcontinent originally laid east of the western carpathians and filled the present carpathian embayment in the late palaeozoic early mesozoic the vardar ocean occupied an intermediate position between the western carpathian austroalpine transdanubian high karst margin and the bihor getic serbo macedonian microcontinent the vardar and pindos oceans were opened in the heart of the mediterranean adriatic microcontinent in the late permian middle triassic vardar subducted by the end of jurassic causing the bihor getic serbo macedonian microcontinent to collide with the internal dinaric western carpathian margin an external penninic vahic ocean tract began opening in the early jurassic separating the austroalpine western carpathian microcontinent and its fauna from the european shelf further east the severin ceahlau magura also began opening in the early jurassic but final separation of the bihor getic ribbon and its fauna from the european shelf did not take place until the late middle jurassic the alcapa and the tisza dacia were bending during the albian maastrichtian the two oroclinal bends were finally opposed and pushed into the gates of the carpathian embayment during the palaeogene and neogene at that time the main n s shortening in distant alpine and hellenic sectors was linked by a broader right lateral shear zone along the former vardar suture

zircon u pb ages and geochemistry of newly discovered neoproterozoic orthogneisses in the mishan region ne china constraints on the high grade metamorphism and tectonic affinity of the jiamusi khanka block abstract the jiamusi khanka block located in the easternmost segment of the central asian orogenic belt caob is one of the least understood blocks in northeastern china the age of its basement the timing of the high grade metamorphism and the tectonic affinity of this block have all been subjects of controversy here we describe newly discovered neoproterozoic orthogneisses from the mishan region in the central jiamusi khanka block sims and la icp ms u pb dating of the magmatic cores of zircons from three of these high grade orthogneisses yielded weighted mean ages that range from 898 4 to 891 13 ma indicating that early neoproterozoic magmatism did occur in the jiamusi khanka block twenty two analyses of metamorphic zircons rims as well as some grains gave two groups of concordant ages one at ca 563 ma interpreted as the timing of the high grade metamorphism and the other around 518 496 ma interpreted as representing a subsequent retrograde metamorphism the orthogneisses represent metamorphosed peraluminous syn collisional syenogranites with sio2 71 29 78 08 wt a cnk 1 06 1 99 and na2o k2o 0 03 1 49 and they belong chemically to the high potassium calc alkaline series they have low sr 32 134 ppm contents and sr y ratios 1 6 16 9 and display strongly fractionated to nearly flat ree patterns with negative eu anomalies eu 0 22 0 95 and depletions in nb ta these geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks perhaps in a subduction related setting that was undergoing transition from compression to extension in the context of the reconstruction of gondwana the ca 898 891 ma magmatic activity and the ca 563 ma high grade metamorphism in the mishan region provide constraints on the possible linkages between the jiamusi khanka block and east gondwana during the neoproterozoic to early paleozoic

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

paleo pacific subduction accretion evidence from geochemical and u pb zircon dating of the nadanhada accretionary complex ne china the nadanhada terrane located along the eastern margin of eurasia contains a typical accretionary complex related to paleo pacific plate subduction accretion the yuejinshan complex is the first stage accretion complex that consists of meta clastic rocks and metamafic ultramafic rocks whereas the raohe complex forms the main parts of the terrane and consists of limestone bedded chert and mafic ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta sedimentary rocks geochemical data indicate that the yuejinshan metabasalts have normal mid ocean ridge basalt n morb affinity whereas the raohe basaltic pillow lavas have an affinity to ocean island basalts oib sensitive high resolution ion microprobe shrimp u pb zircon analyses of gabbro in the raohe complex yield a weighted mean 206pb 238u zircon age of 216 5 ma whereas two samples of granite intruded into the complex yield weighted mean 206pb 238u zircon ages of 128 2 and 129 2 ma laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon analyses of basaltic pillow lava in the raohe complex define a weighted mean age of 167 1 ma two sandstone samples in the raohe complex record younger concordant zircon weighted mean ages of 167 17 and 137 3 ma these new data support the view that accretion of the raohe complex was between 170 and 137 ma and that final emplacement of the raohe complex took place at 137 130 ma the accretion of the yuejinshan complex probably occurred between the 210 and 180 ma suggesting that paleo pacific plate subduction was initiated in the late triassic to early jurassic

mesozoic terrane accretion in northeast china sikhote alin and japan regions abstract the nadanhada range in northeast china is composed of upper paleozoic limestone greenstone middle to late triassic bedded chert and middle jurassic siliceous shale these rocks are enclosed in post middle jurassic clastic rocks the lithologic association ages radiolarian assemblages and geologic structure of the nadanhada range are very similar to those of the tamba mino ashio terrane in southwest japan this indicates that the nadanhada range is the northern extension of the tamba mino ashio terrane mesozoic tectonostratigraphic terranes identified in northeast china sikhote alin and southwest japan are the khanka terrane a micro continent composed of precambrian metamorhic rocks and paleozoic to mesozoic sedimentary and volcanic covers the nadanhada western sikhote alin terrane a disrupted terrane composed of upper paleozoic to jurassic sedimentary rocks the eastern sikhote alin terrane a terrane composed mainly of early cretaceous clastics the tetyukhe terrane a disrupted terrane composed of upper paleozoic to early cretaceous sedimentary rocks the hida terrane a continent type stratigraphic terrane composed of precambrian and upper paleozoic basement covered with jurassic to cretaceous coarse clastics and the tamba mino ashio terrane a disrupted terrane composed of upper paleozoic to earliest cretaceous sedimentary rocks accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data

imaging the seismic lithosphere asthenosphere boundary of the oceanic plate 1 the seismic lithosphere asthenosphere boundary lab or g discontinuity a seismologically characterized abrupt drop in wave speed in the uppermost mantle is one of the key issues in current geodynamics although plate tectonics started as a theory for the ocean reports on lab for normal oceanic regions are scarce due to paucity of seismic data and whether or not the oceanic lab grows with age is the key issue to be resolved we conduct a systematic survey for the oceanic lab using s to p converted seismic waves along three margins of oceanic plates whose crustal age ranges from 10 myr to 130 myr and we observe laterally continuous oceanic lab images the thickness of the oceanic plate estimated from labs increases with the plate age though scattered suggesting that the evolution of oceanic lithosphere is predominantly governed by temperature and that the oceanic seismic lab represents a boundary that grows with age

zircon u pb and lu hf isotope study of the neoproterozoic haizhou group in the sulu orogen provenance and tectonic implications abstract the neoproterozoic haizhou group crops out sporadically in the sulu orogen in east central china it is divided into the jinping and yuntai formations and consists of quartzite quartz schist marble and graphite and apatite bearing sequences major and trace element data for quartz schist from the two formations indicate that these rocks have a greywacke protolith and have been deposited during strong tectonic activity la icpms u pb dating of detrital zircon yields ages of 635 to 1074 ma for three samples from the jinping formation and 611 to 943 ma for two samples from the yuntai formation more than 78 of the detrital zircons from the two formations have u pb ages grouped between 700 and 890 ma with two clusters peaking at 758 ma and 828 ma respectively this indicates that their provenance is magmatic rocks of neoproterozoic age that have a tectonic affinity to the south china block scb a few older zircon populations with peak u pb ages at 943 and 1074 ma are also present a younger population shows peaks at 661 and 611 ma this suggests that deposition of the haizhou group was later than 611 ma rather than during the mesoproterozoic as previously thought zircon lu hf isotope data collected from the same u pb sites show negative ehf t values of 22 8 to 7 4 and hf model ages of 2341 to 3100 ma this indicates that the neoproterozoic magmatic rocks were derived from reworking of ancient paleoproterozoic to archean crust the results support the contention that the haizhou group is similar to the wulian group at the northwestern edge of the sulu orogen both having a scb affinity but that the penglai group does not belong to the scb because of the absence of neoproterozoic ages this lends support to the conclusion that the triassic suture between the north china and south china blocks is located along the baichihe yantai fault which lies north of the wulian complex and south of the jiaobei terrane thus the wulian yantai fault is not the suture zone as is traditionally proposed

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

a tectonic transition from closure of the paleo asian οcean to subduction of the paleo pacific plate insights from early mesozoic igneous rocks in eastern jilin province ne china abstract the timing of tectonic transition from the paleo asian oceanic regime to the paleo pacific regime in the easternmost central asian orogenic belt remains controversial to constrain the event we present new zircon u pb ages hf isotopic compositions and whole rock major and trace element data for early mesozoic igneous rocks from eastern jilin province ne china these new ages together with existing age data indicate that early mesozoic magmatism in the kaiyuan yanji area can be subdivided into four stages early triassic ca 250 ma early middle triassic 249 235 ma late triassic 229 208 ma and latest triassic to early jurassic 207 175 ma the early triassic igneous rocks constitute a bimodal igneous rock association that formed in an extensional environment caused by break off of the subducting slab during final closure of the paleo asian ocean the early middle triassic magmatism is dominated by adakitic granitoids whose primary magmas were derived from partial melting of thickened mafic lower crust suggesting that the north china craton and songliao xilinhot block were still undergoing collisional orogenesis at 249 235 ma the late triassic igneous rocks comprise a typical bimodal association of rocks in an e w trending belt formed in a post orogenic extensional environment related to final closure of the paleo asian ocean the latest triassic to early jurassic igneous rocks have calc alkaline characteristics were emplaced as a ne sw trending belt parallel to the eastern margin of eurasia and formed in an active continental margin setting associated with initial subduction of the paleo pacific plate we conclude that the tectonic transition between the paleo asian and the paleo pacific regimes took place during the latest triassic

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

discussion of olistostromes of the pieniny klippen belt northern carpathians d plasienka j michalik j sotak r aubrecht comment in their recent paper golonka et al 2015 described the cretaceous and palaeogene olistostromes and other types of mass transport deposits occurring within the pieniny klippen belt pkb of the western carpathians after a short introduction into the olistostrome concept and an overall description of the pkb structure the authors presented their views on the composition and evolution of the pkb with olistostromes as the leading phenomenon although novel in some aspects the model they present is largely oversimplified and partly erroneous in our opinion in the following we shall comment on the several most disputable statements and interpretations offered in the discussed paper

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

geochemistry of 1 9 ga morb and oib like basalts from the amisk collage flin flon belt canada evidence for an intra oceanic origin subaqueously erupted basalts that occur in kilometre scale allochthons within the 1 9 ga flin flon belt canada appear to have been generated at oceanic ridges and possibly oceanic plateaus remote from archean cratons the ocean floor basalts fall into two categories 1 n type resembling n morbs and mariana type back arc basin basalts depleted to flat ree patterns high zrnb variable thnb and initial nd 3 3 to 5 4 2 e type resembling transitional and plume morbs slightly enriched ree patterns lower zrnb initial nd 3 1 to 4 5 in the largest and best studied allochthon the elbow athapapuskow assemblage mixing between depleted n morb and enriched oib sources or melts coupled with variable addition of a subduction lile component can explain the chemical variations in the basalts zircon u pb dates of 1904 ma for a syn volcanic diabase sill and 1901 6 5 ma for a gabbro peridotite cumulate complex demonstrate that crystallization of the ocean floor basalts overlapped with in part eruption of the tectonically juxtaposed 1 90 1 88 ga arc volcanic rocks the elbow athapapuskow allochthon is interpreted as back arc basin crust that developed simultaneously with flin flon arc magmatism subaerially erupted basalts that chemically resemble tholeiitic oibs 8 14 mgo relative hree depletion initial nd 2 2 to 3 4 occur in tectonic contact with the elbow athapapuskow assemblage the oibs may have been generated by deeper garnet residue melting of enriched mantle tapped during extension in the elbow athapapuskow back arc basin and were possibly erupted onto a remnant arc deeper mantle melting is also indicated by the presence of the lree enriched oceanic plateau like basalts of the sandy bay assemblage the back arc 01b and plateau volcanic assemblages were jux taposed against ca 1 9 ga arc assemblages in a philippines like intraoceanic accretionary complex by 1 87 ga

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

on the occurrence trace element geochemistry and crystallization history of zircon from in situ ocean lithosphere we characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite evolved gabbro and metamorphosed ultramafic host rocks collected along present day slow and ultraslow spreading mid ocean ridges mors the geochemistry of 267 zircon grains was measured by sensitive high resolution ion microprobe reverse geometry at the usgs stanford ion microprobe facility three types of zircon are recognized based on texture and geochemistry most ocean crustal zircons resemble young magmatic zircon from other crustal settings occurring as pristine colorless euhedral type 1 or subhedral to anhedral type 2 grains in these grains hf and most trace elements vary systematically with ti typically becoming enriched with falling ti in zircon temperature ti in zircon temperatures range from 1 040 to 660 c corrected for a tio2 0 7 a sio2 1 0 pressure 2 kbar intra sample variation is typically 60 150 c decreasing ti correlates with enrichment in hf to 2 wt while additional hf enrichment occurs at relatively constant temperature trends between ti and u y ree and eu eu exhibit a similar inflection which may denote the onset of eutectic crystallization the inflection is well defined by zircons from plagiogranite and implies solidus temperatures of 680 740 c a third type of zircon is defined as being porous and colored with chaotic cl zoning and occurs in 25 of rock samples studied these features along with high measured la cl s ca and fe and low sm la n ratios are suggestive of interaction with aqueous fluids non porous luminescent cl overgrowth rims on porous grains record uniform temperatures averaging 615 26 c 2sd n 7 implying zircon formation below the wet granite solidus and under water saturated conditions zircon geochemistry reflects in part source region elevated hree coupled with low u concentrations allow effective discrimination of 80 of zircon formed at modern mors from zircon in continental crust the geochemistry and textural observations reported here serve as an important database for comparison with detrital xenocrystic and metamorphosed mafic rock hosted zircon populations to evaluate provenance

detrital zircon geochronology of the northeastern tibetan plateau u pb geochronologic analyses have been conducted on 413 detrital zircon grains collected from 16 samples in the altun shan nan shan and qilian shan the samples come primarily from quartz arenites and metaturbidites of middle to late proterozoic age and from feldspathic and volcanic clast rich sandstones of early paleozoic age zircon grains in proterozoic strata resting on tarim basement yielded mainly 2 0 1 9 ga ages whereas proterozoic strata of the qaidam and qilian terranes yielded mainly ca 930 820 ma and ca 1 9 1 1 ga ages the younger grains were apparently shed from local igneous rocks whereas the grains older than 1 1 ga were shed from an undetermined continental source grains in the lower paleozoic strata are mainly ca 500 430 ma and were shed from nearby plutonic and possibly volcanic rocks that formed in a magmatic arc setting our detrital zircon ages are consistent with a model first proposed by e r sobel and n arnaud in which early paleozoic magmatism occurred within a single northeast facing magmatic arc that was constructed across an assemblage of middle to late proterozoic accretionary complexes remnants of magmatic arcs and shallow marine strata this arc system was accreted to the tarim and sino korean cratons during silurian devonian time the resulting suture has been reactivated as tertiary thrust faults that currently define the structural and topographic margin of the tibetan plateau our data also provide two new estimates for the offset along the eastern altyn tagh fault a belt of middle proterozoic shallow marine strata is offset by 400 km whereas a belt of 490 480 ma magmatic arc rocks is offset by 370 km these values are generally similar to the 350 400 km offset reported in most previous studies

new paleomagnetic results from the upper cretaceous red marls of the pieniny klippen belt western carpathians evidence for general ccw rotation and implications for the origin of the structural arc formation abstract the pieniny klippen belt pkb is a narrow arcuate structure separating the central and outer western carpathians formed during several cenozoic deformational stages the primary aim of this study was to obtain paleomagnetic constraints for the mechanism of formation of the arc we investigate albian santonian red pelagic marls from 14 localities distributed along a strike length of ca 400 km ams measurements reveal a pattern characteristic of weakly deformed sedimentary rocks and magnetic lineations do not correlate with the general strike of the pkb paleomagnetic analysis revealed well defined hematite based ancient magnetization components at 13 localities which are dated using fold and inclination tests a within locality fold test is negative for two localities exhibiting large ccw rotations of similar magnitude situated at the two ends of the pkb remanences of pre folding age were documented for 11 localities with an overall mean paleomagnetic direction of d 311 i 53 and 95 11 the indicated general ccw rotation most probably took place during the miocene together with western central and outer carpathians paleolatitudes for the pkb indicate a considerable separation from the southern margin of stable europe leaving space for coordinated rotation a paleomagnetic oroclinal test involving all localities with primary magnetizations was negative when localities with monoclinal steep dips are omitted due to possible declination bias the overall mean paleomagentic direction does not change significantly but correlation is observed between the general trend of the pkb and the paleomagnetic declinations thus we conclude that the present shape of the arc can be partly due to oroclinal bending this must have happened before oligocene since paleomagnetic declinations for neighboring paleogene basins in the central and outer western carpathians reveal a uniform ccw rotation of ca 50 magnitude irrespective of the position of the localities in relation to the carpathian arc

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

a 1300 km late pan african metamorphic belt in ne china new evidence from the xing an block and its tectonic implications abstract the xing an block is one of several fault bounded crustal units in northern china located along the southeastern margin of the central asian orogenic belt caob and includes the great xing an range the basement rocks constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and felsic paragneiss named the xinghuadukou complex la icp ms zircon u pb dating of a sillimanite gneiss from hanjiayuan indicates high grade metamorphism occurred at 496 3 ma with several older detrital zircon grains with ages extending from 678 8 to 1373 17 ma a sample of hornblende plagioclase gneiss from the northern part of the xinghuadukou complex yields a metamorphic age of 496 7 ma whereas igneous zircon core ages range from 601 15 to 1637 23 ma another sample of hornblende plagioclase gneiss from farther south in the xinghuadukou complex yields a metamorphic age of 495 5 ma and magmatic core ages of 546 4 ma these data indicate that high grade metamorphism occurred at 500 ma and that several earlier magmatic events are recorded in the area including some in the neoproterozoic these new age data together with other recent data obtained from the erguna songliao jiamusi and khanka blocks establish a 1300 km pan african khondalite belt along the southern margin of the caob

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

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

record of permian early triassic continental arc magmatism in the western margin of the jiamusi block ne china petrogenesis and implications for paleo pacific subduction in this paper we report zircon u pb ages hf isotopes and whole rock geochemical data for the permian to early triassic granitoids from the western margin of the jiamusi block wjb ne china the intermediate to felsic sio2 59 67 74 04 wt granitoids belong to calc alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative nb ta and ti anomalies revealing typical continental magmatic arc geochemical signatures the zircon u pb determinations on the granodiorite monzogranite syenogranite and quartz diorite samples yielded ages between ca 275 245 ma which together with the published coeval intrusive rocks indicates that permian to early triassic continental arc magmatism occurred extensively in the wjb the low and mainly negative zircon e hf t values between 7 6 and 1 6 and the zircon hf model ages of 1 2 1 8 ga which are significantly older than their crystallization ages suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components the geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting assimilation storage and homogenization i e a mashed zone at the base of paleo to mesoproterozoic continental crust where large portions of igneous rocks and minor clay poor sediments involved in the source region in combination with regional geological data we argue that the jiamusi block was unlikely the rifted segment of the songliao block and two possible geodynamical models were proposed to interpret the formation of the ca 275 245 ma granitoids in the wjb in the context of permian global plate reconstruction we suggest that paleo pacific plate subduction was initiated in the permian to early triassic beneath the jiamusi block and even whole eastern ne china