mesozoic structural evolution of the hangjinqi area in the northern ordos basin north china abstract this study analyzes the structural evolution of the hangjinqi area in the northern ordos basin based on seismic sections and exploration well data this area shows excellent examples of the relationship between tectonics and sedimentation three tectonic sequences separated by four erosional surfaces have been recognized overlying a paleoslope surface t9 in this area 1 the late carboniferous permian and triassic tectonic sequence ts 1 sedimentation of the lowest part of this succession is strongly controlled by the hangjinqi fault zone hfz whereas the rest of the sequence indicates much less fault control 2 the middle jurassic tectonic sequence ts 2 3 the late early cretaceous tectonic sequence ts 3 and the ts 2 and ts 3 sequences are more extensive than the ts 1 sequence throughout the hangjinqi area the structural framework displayed by the ts 2 sequence is very different from that displayed by the ts 3 sequence more specifically the general structure beneath the unconformity t3 between the late jurassic strata and the early cretaceous strata consists of an e w trending transtensional fault system this resulted from a multi stage dextral phase which was caused by oblique subduction of the paleo pacific plate under the eurasian plate and dextral movement of the hfz and a subsequent inversion event which caused significant reverse movement along previous transtensional structures the study area which underlies the unconformity t2 between the late jurassic strata and the early cretaceous strata has been deformed since the late cretaceous when tectonic inversion occurred possibly due to changes in the strike slip motion from dextral to sinistral of the hfz late cretaceous erosion was responsible for an important and unequal denudation the timing of the transition from extension to uplift cannot be determined due to continuous erosion but this uplift finally marked the end of the structural evolution of the hanjinqi area and even the ordos basin

post rift tectonic history of the songliao basin ne china cooling events and post rift unconformities driven by orogenic pulses from plate boundaries

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

motion of the pacific plate relative to eurasia and its potential relation to cenozoic extension along the eastern margin of eurasia extension along the eastern margin of eurasia has been regarded commonly as a far field effect of the india eurasia collision however some aspects of the timing and location of this extension make a link between the collision and extension difficult we suggest that some extensional features commonly interpreted as effects of the collision may be related more simply to changes in plate convergence rates along the eastern plate boundary of eurasia an analysis of the motion of the pacific plate relative to eurasia suggests that the rate of pacific eurasia convergence varied significantly during the tertiary period from a late cretaceous convergence rate of 120 140 mm yr the rate declined substantially during early tertiary time and reached a minimum in eocene time of 30 40 mm yr in oligocene to earliest miocene time the average convergence rate increased moderately to 70 95 mm yr then decreased again to 65 70 mm yr during early to middle miocene time from late miocene to the present the rate of convergence increased to an average of 100 110 mm yr the paleocene through middle miocene episode of relatively slow convergence correlates with a period of widespread extension along the eastern margin of eurasia decreased convergence may have been related to a net reduction in horizontal compressional stress transmitted between the pacific and eurasian plates which resulted in widespread extension adjacent to the margin of eurasia

late cretaceous cenozoic exhumation of the helanshan mt range western ordos fold thrust belt china insights from structural and apatite fission track analyses abstract the western ordos fold thrust belt is an intracontinental chain predominately formed in the jurassic and subsequently reworked in the late cretaceous and cenozoic the structural deformation of the western ordos fold thrust belt was driven by the force transmitted from the plate boundary of asian collage this study presents new structural analysis apatite fission track and thermal modeling data in the helanshan mt range of the western ordos fold thrust belt the apatite fission track analysis and thermal modeling suggest that the helanshan mt range underwent two stages of cooling and exhumation since the late cretaceous the first fast cooling stage in the late cretaceous 90 70 ma led to ca 1 1 2 km exhumation and the second fast cooling was after ca 30 ma with an exhumation of ca 1 8 2 2 km structural studies indicate that the late cretaceous exhumation was related to nw se compression and the exhumation of after ca 30 ma was associated with wnw ese transtension the wnw ese transtension produced high angle normal faults by reworking the mesozoic pre existing factures comprehensive analyses of the synchronous structures around the boundaries of the asian collage suggest that the late cretaceous exhumation of the helanshan mt range might be the far field results of the convergence between the pacific and eurasian plates the varying rates of the pacific plate subduction may transmit nw sw horizontal stress across the north china plate in contrast the post oligocene

chronology and tectonic significance of cenozoic faults in the liupanshan arcuate tectonic belt at the northeastern margin of the qinghai tibet plateau abstract the liupanshan arcuate tectonic belt latb is located at the northeastern margin of the qinghai tibet plateau major strike slip and thrust faults in the liupanshan area are prominent cenozoic structures which are critical in understanding and reconstructing the tectonic deformation history this paper not only provides detailed investigations on geometric and kinematic characteristics of these faults in the latb but also dates the faults movements by electron spin resonance esr the latb underwent a succession of compression extension and again compression tectonic deformation processes since the cenozoic the liupanshan curved faults first experienced sinistral strike slip shear during 57 61 ma the liupanshan curved faults responded to the deformation caused by the eastward escape of the qinghai tibet plateau and acted as the northeastern boundary of the deformation timing for the formation of the liupanshan curved faults shows that the collision of the indian and eurasian plates must have occurred earlier than these faults activity because the latter is reflected the far field effect of the collision

post rift anomalous thermal flux in the songliao basin ne china as revealed from fission track thermochronology and tectonic analysis abstract the songliao basin in northeastern china contains a nearly complete cretaceous sedimentary record it offers an unparalleled opportunity for studying the thermal behavior of a rifting basin adjacent to a subduction zone during various stages of its evolution the post rift thermal history of the songliao basin is here documented by systematic apatite and zircon fission track analyses on newly exhumed sandstone samples from the upper cretaceous quantou and qingshankou formations the combination of thermochronology results and stratigraphic records indicates that there was an unambiguous post rift thermal overprinting event in the songliao basin during the deposition of the nenjiang formation at 85 80 ma this fossil thermal anomaly has not been previously recognized from organic maturity indicators and or subsidence modeling the zircon fission track results indicate an estimated maximum paleo temperature as high as 170 220 c near the daqing placanticline fission track analyses of sampled apatites further define a restricted thermal anomaly in the central part of the basin based on the context of local lithospheric structure and adjacent plate tectonic history we conclude that the late cretaceous westward subduction of the paleo pacific plate not only produced vertical motions and directly controlled the topography of the songliao lake but also dominated the mantle heat flow beneath east asia this finding has significant implications for the evolution of thermal flux in the basin

plastic deformation of metamorphic pyrite new evidence from electron backscatter diffraction and forescatter orientation contrast imaging application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods specifically use of forescatter solid state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images which map the distribution of deformation domains within grains use of electron backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images combination of these techniques shows that the pyrite studied deforms by slip on 100 and more rarely 110 systems slip is often associated with distributed rotation of up to 20 about and more rarely axes pyrites may have simple histories involving rotation about a single axis or more complex histories involving rotation about different axes and more rarely in different domains of the same pyrite grain or sequential rotations about quite different systems typically distributed rotation about followed by discrete rotation about a non crystallographic axis

crustal structure beneath aso caldera southwest japan as derived from receiver function analysis abstract aso volcano experienced a huge pyroclastic eruption 90 thousand years ago and formed a large caldera 18 km 25 km in order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically we investigated seismic velocity discontinuities and velocity structure beneath aso caldera using receiver functions and a genetic algorithm inversion we confirm the existence of the moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath aso caldera from imaging of receiver functions observed only at stations outside the caldera as a result of a more detailed examination with ga inversion a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera s wave velocity of the layer is estimated to be 2 0 2 4 km s we estimate that the low velocity layer contains at most 15 melt or 30 aqueous fluid the layer exists near the conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle eastern part of the caldera fluid contained in the layer might be related with huge pyroclastic eruptions of aso volcano

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

inferences for the socorro magma body from teleseismic receiver functions receiver functions constructed from teleseisms arriving from the northwest and recorded at station wtx in socorro nm show strong p to s conversions we interpret as coming from a mid crustal sill like magma body analysis of these conversions suggest that both the upper and lower surfaces of the magma body are distinct and provide sharp velocity contrasts with the surrounding host rock models that provide acceptable fits to these conversions all have magma body thicknesses less than 200 m the absence of similar phases in data from the south and southeast suggests that the magma body is discontinuous near its edges

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

thrusting and exhumation of the southern mongolian plateau joint thermochronological constraints from the langshan mountains western inner mongolia china abstract the mongolian plateau has undergone multi stage denudation since the late triassic and the ne trending langshan mountains in the southern margin of the mongolian plateau is crucial to unraveling the meso cenozoic cooling and exhumation history of the mongolian plateau the langshan mountains are dominated by precambrian gneiss and permian middle triassic granitic plutons crosscut by a set of ne striking thrust faults a joint thermochronological study was conducted on 31 granitic and gneissic samples along the hq and cu transects across the langshan mountains and other two samples from the bq in the north of the langshan mountains four biotite muscovite and three k feldspar 40ar 39ar plateau ages range from 205 1 to 161 1 and 167 1 to 131 1 ma respectively thirty three apatite fission track aft ages are between 184 11 and 79 4 ma with mean track lengths from 11 1 1 8 to 13 1 1 4 m of mostly unimodal distributions thirty one single grain raw ahe ages are in a range of 134 8 to 21 1 ma the aft ages decrease monotonously from nw to se until thrust faults along the two transects with an age jump across thrust f35 joint thermal history modelling shows a three stage cooling history as a result of denudation especially with spatial differentiation in the first stage relative slow cooling at c 0 6 1 0 c ma occurred in the bq and the northern part of the hq transect during 220 100 ma and the northern part of the cu transect during 160 100 ma respectively with an amount of c 2 3 km denudation between 160 and 100 ma implying little movement along the thrusts f13 and f33 in the middle and southern parts of the hq transect and the southern part of the cu transect rapid cooling at c 4 0 7 0 c ma with c 6 9 km denudation during 170 130 or 160 100 ma respectively is probably influenced by thrusting of f35 f38 and f42 and the resultant tilting a combination of thrusting tilting and denudation led to the youngering trends towards thrusts in different parts however there was no significant denudation across the langshan mountains in the second stage from c 100 or 80 ma until the last stage of rapid denudation c 2 km since 20 10 ma which is simultaneous with the rapid uplift of the northern part of the tibetan plateau at c 15 ma a youngering trend of aft ages from the inner to the peripherals of the mongolian plateau implies the outward propagation of the mongolian plateau since the mesozoic

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

miocene cooling in the northern qilian shan northeastern margin of the tibetan plateau revealed by apatite fission track and vitrinite reflectance analysis apatite fission track and vitrinite reflectance data from phanerozoic rocks of the northern qilian shan and jiuxi basin at the northeastern margin of the tibetan plateau show a complex thermal history with multiple paleothermal events peak paleotemperatures reached in the middle cretaceous suggest that hydrocarbon generation occurred in the basin at that time paleozoic mesozoic samples show evidence of a middle tertiary cooling episode between 20 and 10 ma this thermal fingerprint is significant because stratigraphic evidence for miocene exhumation is overwhelmed by spectacular pliocene pleistocene deformation and erosion we interpret the miocene cooling as recording initial exhumation of the northern qilian shan earlier than other models have proposed i e after 6 5 ma miocene cooling is broadly coincident with cenozoic uplift and exhumation recorded elsewhere in the tibetan tarim region

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

late triassic tuff intervals in the ordos basin central china their depositional petrographic geochemical characteristics and regional implications abstract tuff intervals of upper triassic yanchang formation are laterally widespread in the ordos basin central china this paper focuses on magmatic origins and potential source regions of these tuff intervals through detail depositional petrographic and geochemical analyses most of the tuff intervals are well documented at the bottom of the chang7 oil reservoir unit and can be correlated laterally and certain tuff beds are reworked by turbidity current or seismic activity petrographic studies of the chang7 tuffs indicate that they are composed of crystal shards lithic shards and altered glass shards and the crystal shards include plagioclase quartz and biotite alteration of the chang7 tuffs is ubiquitous thus most of these tuffs transformed into illite smectite i s mixed layers which are identified by scanning electron microscopy sem and x ray diffraction xrd less common minerals are also detected in the chang7 tuffs such as zircon hematite siderite anatase major elements are determined by the x ray fluorescence xrf analysis the results indicate that the chang7 tuffs are enriched in k2o average 4 21 the ratio of sio2 al2o3 ranges from 1 73 to 2 85 average 2 17 and the ratio of tio2 al2o3 varies between 0 006 and 0 032 average 0 017 which imply that the chang7 tuffs originated from a felsic parental magma trace elements are determined by inductively coupled plasma mass spectrometry icp ms indicating the total rare earth element ree concentrations are variable and range from 117 46 to 466 83 ppm average 251 88 ppm ree distribution pattern of the chang7 tuffs presents a lree rightward incline with flat hree curve the value of eu ranges from 0 151 to 0 837 average 0 492 suggesting a strong to weak negative eu anomaly the chang7 tuffs show positive anomalies in rb th and u and negative anomalies in nb sr and eu on a primitive mantle normalized spidergram a preliminary analysis of the geochemical composition of the chang7 tuffs suggests a parental magma origin of rhyodacite dacite which came from volcanic arc related setting along an active continental margin combined with the chronology and geochemical studies of the synchronous tianshui rhyolite in the west qinling mountains we propose that the west qinling mountains is one of the potential source regions of these tuffs and the middle late triassic terminal closure of eastern tethys provided the arc related magma

thermochronological evidence for mesozoic tertiary tectonic evolution in the eastern sardinia apatite fission track analyses on samples from eastern sardinia document a complex tectonic history whose reconstruction is problematic because of the reactivation of faults and structures at different times from jurassic to miocene the oldest ages 150 154 ma have been detected on the southern margin of the gulf of orosei and are related to the extensional tectonics that characterize the european passive margin during early and middle jurassic times thermal modelling of these data allows reconstruction of the burial history of the mesozoic basin and estimation of a sedimentary thickness of 2000 m part of these sediments was eroded during the following uplift documented by mid cretaceous fission track ages a further exhumation episode of eocene age has been revealed by fission track data on granite samples and has been inferred to be related to the alpine orogenic phase this tectonic episode caused the exhumation of crustal blocks bound by faults that were finally reactivated during the late oligocene early miocene

ocean basin evolution and global scale plate reorganization events since pangea breakup we present a revised global plate motion model with continuously closing plate boundaries ranging from the triassic at 230 ma to the present day assess differences among alternative absolute plate motion models and review global tectonic events relatively high mean absolute plate motion rates of approximately 9 10 cm yr 1 between 140 and 120 ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time an event at 100 ma is most clearly expressed in the indian ocean and may reflect the initiation of andean style subduction along southern continental eurasia whereas an acceleration at 80 ma of mean rates from 6 to 8 cm yr 1 reflects the initial northward acceleration of india and simultaneous speedups of plates in the pacific an event at 50 ma expressed in relative and some absolute plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4 5 cm yr 1 indicates that an increase in collisional forces such as the india eurasia collision and ridge subduction events in the pacific such as the izanagi pacific ridge play a significant role in modulating plate velocities

mineralogy of the sulphide deposits at sulitjelma northern norway abstract the pyritic vms deposits at sulitjelma northern norway have been regionally metamorphosed at amphibolite facies during the caledonide orogen the deposits contain a wide diversity of sulphide sulphosalt and related minerals which are systematically discussed with reference to their occurrence paragenesis and mineral chemistry most of these minerals are however rare to absent within the massive deposits which are dominantly composed of pyrite with subordinate chalcopyrite sphalerite and pyrrhotite galena arsenopyrite cubanite molybdenite stannite and tetrahedrite occur in minor amounts syn metamorphic mobilisation has however resulted in the redistribution of a range of elements including cu pb sb as ni and au these elements have been reconcentrated into mobilised segregations where they have crystallised under retrograde conditions into a range of discrete phases ore mobilisation which took place along tectonically controlled pathways is however of a highly localised nature with a considerable range in mineral textures and parageneses observed in different samples typical associations within these mobilisates include a range of cu pb sb and cu pb as sulphosalts including bournonite meneghinite seligmannite and jordanite breithauptite nisbite costibite arsenopyrite and gudmundite co existing galena is characterised by elevated concentrations of ag bi and se argentian tetrahedrite 9 17 wt ag the chief ag carrier in the deposits as well as other ag bearing phases including pyrargyrite hessite and empressite are strongly enriched in the mobilisates gold as electrum 50 75 wt au and more rarely as aurostibite is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits a further range of minerals including native antimony native arsenic allargentum dyscrasite argentite mckinstryite jalpaite and native silver occur as low temperature breakdown products of earlier formed minerals preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution

apatite fission track thermochronological constraints on the pattern of late mesozoic cenozoic uplift and exhumation of the qinling orogen central china abstract the qinling orogen of central china was formed by intracontinental collision between the north and south china blocks the orogen comprises several micro blocks bounded by sutures and faults and has undergone long term intracontinental deformation since the late triassic the micro blocks include the southern margin of the north china block s ncb the northern qinling belt nqb the southern qinling belt sqb and the northern margin of the south china block n scb under a uniform tectonic setting in late mesozoic cenozoic these micro blocks have been subjected to a range of deformation styles as demonstrated by their structural deformation history of magmatism and the development of sedimentary basins to investigate the differences among the micro blocks and to quantify their uplift and exhumation we obtained 45 rock samples from eight mesozoic granites in these micro blocks and conducted apatite fission track aft thermochronological modeling the results reveal that the qinling orogen underwent four distinct stages of rapid cooling histories during the late mesozoic cenozoic and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south the n scb and propagated to the north s ncb in the first stage during the late jurassic early cretaceous ca 160 120 ma rock cooling occurred mainly in the n scb attributed to the clockwise rotation and northward subduction of the south china block beneath the qinling orogen in the second stage compression and extension related uplift was initiated during the late early cretaceous early late cretaceous ca 120 90 ma in the sqb consistent with the southward subduction of the north china block and broadly extensional deformation in the eastern china continent in the third stage a gentle regional scale cooling event that occurred during the latest cretaceous paleocene ca 90 50 ma started in the nqb and became widespread in the qinling orogen this regional scale uplift and exhumation event was probably a response to the opposite polarity subduction beneath the qinling orogen combined with the effects of subduction of the pacific plate from the southeast the fourth stage eocene oligocene ca 50 20 ma was marked by another phase of rapid cooling in the s ncb the nqb and the nw sqb and is interpreted as being cause by the eastward tectonic escape of tibetan plateau related to india asia collision furthermore the record of variable timings and rates of cooling of these micro blocks together with regional structural analysis indicates that the late mesozoic cenozoic intracontinental deformation in the qinling orogen was characterized by a spatiotemporally variable and propagating style uplift and exhumation of the micro blocks and the predominant deformation was through displacement across various boundary sutures and faults

cretaceous deformation history of the middle tan lu fault zone in shandong province eastern china abstract based on field analysis of fault slip data from different rock units of the cretaceous basins along the middle part of the tan lu fault zone shandong province eastern china we document polyphase tectonic stress fields and address the changes in sense of motion of the tan lu fault zone during the cretaceous the cretaceous deformation history of the tan lu fault zone can be divided into four main stages the first stage during the earliest cretaceous was dominated by n s extension responsible for the formation of the jiaolai basin we interpret this extension to be related to dextral strike slip pull apart opening guided by the tan lu fault zone the second stage during the middle early cretaceous was overwhelmingly rift dominated and characterized by widespread silicic to intermediate volcanism normal faulting and basin subsidence it was at this stage that the tan lu parallel yi shu rift was initiated by e w to wnw ese extension the tectonic regime then changed during the late early cretaceous to nw se oriented transpression causing inversion of the early cretaceous rift basin and sinistral slip along the tan lu fault zone during the late cretaceous dextral activation of the tan lu fault zone resulted in pull apart opening of the zhucheng basin which was subsequently deformed by ne sw compression this deformation chronology of the tan lu fault zone and the associated cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of asia or related to collision in the tibet region

a monochromatic earthquake suggesting deep seated magmatic activity beneath the izu ooshima volcano japan after a quiescence of 12 years the izu ooshima volcano located about 30 km east of the izu peninsula in central japan erupted on november 15 1986 on august 27 1985 about 1 year before the eruption a peculiar earthquake of magnitude 2 7 took place near the moho boundary just beneath the izu ooshima volcano where seismic activity is otherwise absent analysis of digital data obtained by the telemetered seismic network of the national research center for disaster prevention reveals the following distinctive features of the seismic waves 1 the main part of the wave train is composed of s waves and a small p phase precedes it 2 the spectral density has a sharp peak at 1 0 hz which is independent of the epicentral distance azimuth and time indicating a monochromatic spectrum at the source 3 ground motion for the initial part of the s wave is polarized in the n s direction at almost all the stations the amplitude ratios of s to p waves and the polarization pattern of s waves suggest that a traction force caused by magma flow is a more probable source than a double couple mechanism free oscillation of the magma reservoir or opening of a tensile crack we propose a traction force model for this earthquake in which magma flow through a conduit produces unidirectional viscous force on the conduit walls the observations imply a n s force direction and a maximum force of about 2 8 1010 n the pressure difference between the ends of the conduit is estimated as 6 1 107 pa 610 bar under the assumption of conduit dimensions of 2 km 1 km the monochromatic nature of the source spectrum is difficult to account for by the free oscillation of a magma reservoir we tentatively suggest the intermittent opening of a barrier in the conduit as a plausible mechanism of the periodic oscillation

paleomagnetism of eocene red beds in the eastern part of the qiangtang terrane and its implications for uplift and southward crustal extrusion in the southeastern edge of the tibetan plateau abstract a primary magnetic component with the acquisition time of 56 0 43 2 ma was isolated between 580 c and 685 c from the eocene gonjo and ranmugou formations in the eastern part of the qiangtang terrane tibetan plateau the tilt corrected site mean direction is d s 35 5 i s 29 3 k 45 9 95 3 2 the site mean inclination increased from 29 3 to 41 6 after multiple inclination shallowing corrections giving a paleopole of 57 9 n 192 1 e a 95 2 9 comparison of the paleogene paleomagnetic data for the qiangtang terrane and lhasa terrane reveals that both terranes experienced latitudinal crustal shortening before 54 43 ma indicating the uplift of southern and central tibet in the early eocene subsequently since 35 4 2 4 ma the north of the qiangtang terrane experienced 1300 410 km of crustal shortening indicating the uplift of the northern tibetan plateau the lhasa terrane and qiangtang terrane have not experienced further crustal shortening since the late eocene and the southeastern part of tibet cannot have provided abundant crustal material to accommodate the significant crustal southward extrusion in the southeastern edge of the tibetan plateau the crust of the tengchong terrane and shan thai block did not experience significant southward extrusion since the late oligocene early miocene the indochina block was situated in the north of the qiangtang terrane before the oligocene and since the early oligocene the indochina block began to experience southward extrusion from the north of the qiangtang terrane which absorbed part of the crustal shortening in the north of the qiangtang terrane

the 2016 kumamoto mw 7 0 earthquake a significant event in a fault volcano system the 2016 kumamoto earthquake sequence occurred on the futagawa hinagu fault zone near the aso volcano on kyushu island the sequence was initiated with two major m w 6 0 foreshocks and the mainshock m w 7 0 occurred 25 h after the second major foreshock we combine gps strong motion synthetic aperture radar images and surface offset data in a joint inversion to resolve the kinematic rupture process of the mainshock and coseismic displacement of the foreshocks the joint inversion results reveal a unilateral rupture process for the mainshock involving sequential rupture of four major asperities the slip area of the foreshocks and mainshock and the aftershock loci form a detailed complementary pattern the mainshock rupture terminates near the rim of the caldera leaving a 10 km long gap of aftershocks this area is characterized by high temperature and low shear wave velocity density and resistivity which may be related to the partially melted geothermal condition ductile material property near the volcano may act as a material barrier to the dynamic rupture topographic weight of the caldera increases compressional normal stress on the fault plane which may behave as a stress barrier long term seismic hazard and deformation behaviors related to these two types of barriers are discussed in terms of the associated frictional mechanism significant postseismic creeps observed near the volcano area indicates a velocity strengthening frictional behavior near the rupture termination which confirms that the material barrier mechanism is likely the dominant rupture termination mechanism

late jurassic early cretaceous continental convergence and intracontinental orogenesis in east asia a synthesis of the yanshan revolution abstract the basic tectonic framework of continental east asia was produced by a series of nearly contemporaneous orogenic events in the late middle jurassic to early cretaceous commonly the late mesozoic orogenic processes were characterized by continent continent collision large scale thrusting strike slip faulting and intense crustal shortening crustal thickening regional anatexis and metamorphism followed by large scale lithospheric extension rifting and magmatism to better understand the geological processes this paper reviews and synthesizes existing multi disciplinary geologic data related to sedimentation tectonics magmatism metamorphism and geochemistry and proposes a two stage tectono thermal evolutionary history of east asia during the late middle jurassic to early cretaceous ca 170 120 ma in the first stage three orogenic belts along the continental margins were formed coevally at ca 170 135 ma i e the north mongol okhotsk orogen the east paleo pacific coastal orogen and the west bangong nujiang orogen tectonism related to the coastal orogen caused extensive intracontinental folding and thrusting that resulted in a depositional hiatus in the late jurassic as well as crustal anatexis that generated syn kinematic granites adakites and migmatites the lithosphere of the east asian continent was thickened reaching a maximum during the latest jurassic or the earliest cretaceous in the second stage ca 135 120 ma delamination of the thickened lithosphere resulted in a remarkable 120 km lithospheric thinning and the development of mantle derived magmatism mineralization metamorphic core complexes and rift basins the middle jurassic early cretaceous subduction of oceanic plates paleo pacific meso tethys and mongol okhotsk and continent continent collision e g lhasa and qiangtang along the east asian continental margins produced broad coastal and intracontinental orogens these significant tectonic activities marked by widespread intracontinental orogeny and continental reconstruction are commonly termed the yanshan revolution movement in the chinese literature

repeated large scale eruptions from a single compositionally stratified magma chamber an example from aso volcano southwest japan abstract aso volcano has the largest caldera 18 25 km in the southwestern japan island arc which was formed as a result of four gigantic pyroclastic eruption cycles the latest eruption cycle aso 4 cycle 90 ka produced the most voluminous deposits 600 km3 among the four eruption cycles we investigated pre eruptive magma chamber configurations and processes in compositionally stratified aso 4 pyroclastic eruptions based on whole rock chemical phenocryst mineralogical and sr isotope analyses of juvenile clasts previous stratigraphical studies have suggested that the aso 4 cycle is divided into two subcycles in both of which eruption of voluminous silicic is followed by eruption of mafic magma geochemical and mineralogical results indicate that the pre eruptive magma chamber was composed of three layers silicic hybrid and mafic magma layers from the top to the bottom the silicic magma layer was relatively homogenous whereas the mafic magma layer was compositionally zoned where magma became more silicic with height the hybrid magma was generated by mixing the silicic magma and the silicic end of the zoned mafic magma layer i e the uppermost part of the mafic magma layer the first subcycle began with evacuation of the upper silicic magma and successively proceeded to tap the lower hybrid and mafic magmas the eruption of the first subcycle stopped before the whole magma chamber evacuated during this subcycle the hybrid magma and the upper part of the mafic magmas layer were selectively withdrawn and mixed with the overlying silicic magma the second subcycle eruption started with the new hybrid magma and followed by eruption of the mafic magma

segmentation and inversion of the hangjinqi fault zone the northern ordos basin north china abstract this paper deals with the segmentation and inversion of the hangjinqi fault zone hfz which is the dominant structure in the northern part of the ordos basin in north china hfz was reactivated during the late triassic and obliquely inverted during the middle jurassic shortening subsurface geological mapping and structural analysis were carried out to determine the segmentation and kinematic history of the deformation the hfz was a left stepping fault zone and was made up of three segments the porjianghaizi fault pf wulanjilinmiao fault wf and sanyanjing fault sf which are separated by two relay ramps two distinct phases can be identified in its structural evolution 1 during the late triassic compressional deformation the hfz was characterized by shortening and thrusting to the north and 2 during the middle jurassic phase the hfz was oblique to the extensional fault trends the reverse faults were reactivated as dextral strike slip faults as a result of transtensional inversion the inversion ratio of the hfz indicates an increase in deformational degree from east to west over the whole region the first deformation stage resulted from the n s compression between the south china and north china plates during the late triassic the second deformation stage of compression was related to the west northwestward subduction of the paleo pacific plate during the middle jurassic in the jurassic deformation framework the hfz may be interpreted as an accommodation structure parallel to the yanshan yinshan orogenic belt developed in the northern ordos area

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

crustal magma pathway beneath aso caldera inferred from three dimensional electrical resistivity structure at naka dake cone aso caldera japan volcanic activity is raised cyclically an example of which was a phreatomagmatic eruption in september 2015 using a three dimensional model of electrical resistivity we identify a magma pathway from a series of northward dipping conductive anomalies in the upper crust beneath the caldera our resistivity model was created from magnetotelluric measurements conducted in november december 2015 thus it provides the latest information about magma reservoir geometry beneath the caldera the center of the conductive anomalies shifts from the north of naka dake at depths 10 km toward naka dake along with a decrease in anomaly depths the melt fraction is estimated at 13 15 at 2 km depth moreover these anomalies are spatially correlated with the locations of earthquake clusters which are distributed within resistive blocks on the conductive anomalies in the northwest of naka dake but distributed at the resistive sides of resistivity boundaries in the northeast

shear wave velocity variation across the taupo volcanic zone new zealand from receiver function inversion summary the taupo volcanic zone tvz new zealand is a region characterized by very high magma eruption rates and extremely high heat flow which is manifest in high temperature geothermal waters the shear wave velocity structure across the region is inferred using non linear inversion of receiver functions which were derived from teleseismic earthquake data results from the non linear inversion and from forward synthetic modelling indicate low s velocities at 6 16 km depth near the rotorua and reporoa calderas we infer these low velocity layers to represent the presence of high level bodies of partial melt associated with the volcanism receiver functions at other stations are complicated by reverberations associated with near surface sedimentary layers the receiver function data also indicate that the moho lies between 25 and 30 km deeper than the 15 2 km depth previously inferred for the crust mantle boundary beneath the tvz

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

shear wave splitting vp vs and gps during a time of enhanced activity at aso caldera kyushu 1 we performed shear wave splitting analyses and calculated vp vs ratios on local earthquakes recorded at seven stations around aso volcano japan between 2001 and 2008 the mean vp vs of 1 61 0 01 from all stations is among the lowest average values found anywhere in the world a temporal change of shear wave splitting fast polarization is observed at one station additionally spatial variations of shear wave splitting delay times and vp vs ratios show a correlation at three stations we suggest that stress controlled anisotropy dominates at these stations gps baselines and 2d strain reveal extension in the caldera in 2003 and compression before and after 2003 strain shortening axes indicate either a variation in regional stress or a local stress source that overprints the regional field in 2003 baseline changes correlate with periods of increased low frequency seismic activity located deeper than 15 km compaction and degassing of a previously reported sill at approximately 15 km depth could lead to constantly high pressure of volcanic gases over a wide area and explain the generally low vp vs ratios and the observed compression in the caldera we propose that a small volume of magma intruded into the sill in 2003 caused extension at the surface and triggered ash eruptions between 2003 and 2005 associated localized migration of gases in overpressured cracks with aspect ratios potentially 0 5 in the upper crust with porosities 0 1 could be the source of changes in seismic anisotropy and explain the slight variations observed in vp vs

cretaceous and cenozoic cooling history of the eastern qilian shan north eastern margin of the tibetan plateau evidence from apatite fission track analysis the exhumation history and tectonic evolution of the qilian shan at the north eastern margin of the tibetan plateau has been widely debated here we present apatite fission track aft data for 12 ordovician granodiorite samples along a vertical transect in the eastern qilian shan these thermochronometry data indicate that the eastern qilian shan experienced a three stage cooling history including i rapid initial cooling in the late cretaceous ii a stage of quasi isothermal quiescence from similar to 80 to 24ma and iii rapid subsequent cooling beginning in the early miocene the inferred cooling rates for the three stages are 6 8 4 9 degrees cma 1 0 6 0 2 degrees cma 1 and 2 7 0 9 degrees cma 1 respectively 1 sigma assuming a geothermal gradient of 25 degrees ckm 1 the exhumation rates for the three stages are 0 27 0 20mma 1 0 017 0 007mma 1 and 0 11 0 04mma 1 respectively 1 sigma we suggest that the late cretaceous cooling records collision of the lhasa block with the eurasian continent and that the miocene cooling represents uplift exhumation of the qilian shan

apatite fission track evidence for neogene uplift in the eastern kunlun mountains northern qinghai tibet plateau china abstract forty one apatite fission track ages aft were determined on samples collected along a n s section of the eastern kunlun mountains across the middle and south kunlun faults between buqingshan and dulan measured aft ages lie between 25 2 and 130 10 ma and all are significantly younger than their host rock formation or sediment deposition ages modelling the aft data identifies a two stage regional cooling history that spans the last 100 myrs the earliest cooling phase occurred between the late jurassic and early tertiary and involved a moderate level of cooling between 20 and 40 c equivalent to average exhumation rates of 15 m myr the second phase of cooling took place from 20 ma with cooling rates increasing tenfold average exhumation rates for this period are estimated to be in the range of 100 150 m myr the first stage of protracted cooling is consistent with regional evidence from the qiantang and lhasa terrans where previous studies have noted low rates of denudation in relation to a back arc extensional setting the more recent acceleration in cooling seen in the kunlun data coincides with an increase in sedimentation rates in the adjacent qaidam basin this points to a phase of neogene uplift and increased erosion of the kunlun range although contemporaneous monsoon strengthening may also have had a role

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

superposed deformation in the helanshan structural belt implications for mesozoic intracontinental deformation of the north china plate abstract the north china plate ncp underwent multi phase intracontinental deformation during the mesozoic which is a much debated research subject here we present a case study of this deformation inferred from regional scale helanshan superposed folds in the west of the ncp new structural analyses and fault kinematic analyses in the helanshan structural belt hsb indicate a two stage syn folding paleo stress field comprising early nne ssw compression with mean orientations 190 01 plunge direction plunge for 1 283 26 for 2 and 100 63 for 3 and later wnw ese compression with mean orientations of 1 2 and 3 at 124 07 213 04 and 001 75 respectively these results combined with geochronological analysis indicate two episodes of shortening in this belt during the mesozoic late triassic early jurassic nne ssw shortening which produced 8 1 km of horizontal shortening led to the development of open wnw trending fold structures subsequent late jurassic early cretaceous wnw ese shortening which produced 18 7 km of horizontal shortening reshaped the early wnw trending structures and generated close overprinting nne trending folds that resulted in the development of the regional scale superposed folds in this area in terms of geodynamics the early nne ssw shortening is likely to be related to indosinian intercontinental convergence between the north china plate and the yangtze plate and the later wnw ese shortening is likely to have been related to subduction of the paleo pacific plate the regional structural analysis indicates that the whole of the western north china plate experienced two phase contractional deformation during the mesozoic as manifest by the early nne ssw and the late wnw ese shortening that characterized mesozoic intracontinental deformation in the western ncp

possible southwestward extrusion of the ordos block in the late paleoproterozoic constraints from kinematic and geochronologic analysis of peripheral ductile shear zones abstract the paleoproterozoic is a pivotal period of the tectonic evolution of the north china craton ncc various models have been postulated by previous researchers through the study of petrology and metamorphism but the lack of structural analyses has hampered further understanding of the tectonic evolution of the ncc a series of well exposed ductile shear zones developed on the northern northwestern and eastern edges of the ordos block in the western part of the ncc we carried out detailed field studies along with isotopic dating focused on the kinematics and geochronology of the ductile shear zones on the north margin of the ordos block the wulashan daqingshan ductile shear zone is characterized by an e w trending shearing foliation that steeply dips 75 80 to the north or south with subhorizontal stretching lineation plunging 10 15 toward the east or west and dextral strike slip shearing kinematics on the west margin of the ordos block is the zongbieli ductile shear zone with top to the nw thrusting kinematics on the east margin of the ordos block is the xueling ductile shear zone with top to the se thrusting accompanied by sinistral strike slip shearing kinematics the 40ar 39ar ages of deformed minerals from mylonitic high grade metamorphic rocks and la icp ms u pb dating results of zircons from syn tectonic anatectic granites reflect that the ductile shear zones surrounding the ordos block deformed between 1 85 and 1 81 ga the similar deformation ages indicate that the ductile shear zones might be genetically correlated the geometry kinematics and geochronology characteristics of the wulashan daqingshan ductile shear zone on the north margin the zongbieli ductile shear zone on the west margin and the xueling ductile shear zone combined with the zhujiafang sinistral ductile shear zone on the east margin defined the possible southwestward extrusion of the ordos block in the late paleoproterozoic which might have resulted from the westward subduction collision of the eastern block under the western block at approximately 1 85 ga and which is correlated with the amalgamation of the columbia supercontinent

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and its bearing on the evolution of the yinshan yanshan orogenic belt part i structural analyses and geochronological constraints abstract with a cratonic nucleus the north china craton ncc experienced a complex tectonic evolution with multiphase compressional and extensional events during mesozoic times along the northern part of the ncc the yinshan yanshan fold and thrust belt was a typical intraplate orogen jurassic and cretaceous continental sedimentation magmatism widespread intraplate characterize the yinshan yanshan orogenic belt the geodynamic significance of these tectonic events is still in dispute in the western part of the liaoning province the yiwulushan massif crops out at the eastern end of the yinshan yanshan orogenic belt the yiwulushan massif presents an elliptical domal shape with a ne sw striking long axis the structural evolution of this massif brings new insights for the understanding of the mesozoic plutonic tectonic history of the ncc a multidisciplinary study involving structural geology geochronology anisotropy of magnetic susceptibility ams and gravity modeling have been carried out the presentation of the new results splits into two parts part i this paper deals with field and laboratory structural observations and presents the main geochronological results the ams gravity modeling data will be provided in a companion paper part ii the early compressional deformation d1 corresponds to a late jurassic to early cretaceous southward thrusting the subsequent deformation is related to the early cretaceous exhumation of the yiwulushan massif a detailed structural analysis allows us to distinguish several deformation events d2 d3 and d4 the cretaceous extensional structures such as syntectonic plutons bounded by ductile normal faults metamorphic core complexes and half graben basins are recognized in many places in east asia these new data from the yiwulushan massif constitute a link between transbaikalia mongolia north china and south china indicating that nw se extensional mesozoic tectonics occurred throughout the entire region

on the detection and identification of converted and reflected phases from receiver functions summary we develop a simple methodology to extract information related to crustal structure such as the mean vp vs ratio the magnitude of lateral variations and the presence of discontinuities from a selection of receiver functions we show that crustal phases can be detected and exploited on individual receiver functions two filtering techniques based on singular value decomposition and spectral matrix filtering are proposed to enhance the coherent phases in receiver functions additionally the relative traveltimes and slownesses between the different phases are utilized for a more reliable phase identification we apply these methods to data of station pru czech republic and compare the results with a classical time domain waveform inversion we find a good qualitative agreement between the simple crustal models inferred from the two approaches waveform modelling suggests that the identification of converted phases can still be ambiguous and other geophysical or geological constraints are needed

three dimensional seismic velocity structure beneath aso volcano kyushu japan tomographic results for p and s wave velocity structure beneath the active aso volcano kyushu japan using 800 well recorded earthquakes and ten shots recorded by an eight station seismic network are presented a 68 variance reduction was achieved upon simultaneous inversion for hypocenter and velocity structure well resolved velocity anomalies associated with the active crater reveal heterogeneity up to 26 slower and 18 faster in p velocity and up to 31 slower and 22 faster in s velocity than the one dimensional model the largest anomaly is seen over the upper 11 km in the central and northern parts beneath the central cones two low velocity regions are imaged the first region a 10 15 km region encompassing the upper 3 km centered near the caldera wall at tateno valley is characterized by p velocities up to 19 slower 20 for s the second low velocity region is associated with the central cones and active magma conduit system at 6 km depth velocities as low as 4 3 km s up to 26 in p and 2 km s 31 slower in s characterize the 7 km wide volume the magma chamber is roughly spherical in shape centered at 6 km depth flattens at 10 km depth and is located between mt kishima mt eboshi and mt naka the present focus of magmatism a sharp velocity contrast at the depth of 3 km with high velocities to the southwest and lower velocities to the northeast characterizes different abutting structures associated with the oita kumamoto tectonic line

late mesozoic and cenozoic thermotectonic evolution along a transect from the north china craton through the qinling orogen into the yangtze craton central china 1 cretaceous and cenozoic reactivation of the triassic qinling dabie orogen between the north china and yangtze cratons resulted from the combined effects of pacific subduction back arc extension in east china and collisions in west china we report new apatite fission track and apatite and zircon u th he data from east qinling along a 400 km long n s transect from huashan through the qinling orogen to huangling the ages show a general pattern of younging northward three major cooling phases are defined by modeling the multiple thermochronologic data sets the first phase occurred locally in the north and south qinling during the late triassic to early jurassic following heating associated with the triassic yangtze subduction and exhumation of the wudang metamorphic core complex on the cratonal edge a second phase represents regional exhumation between 100 and 60 ma coeval with rifting marked by the late cretaceous eocene k2 e red bed deposition in eastern china and possibly indicating a link with pacific subduction back arc extension in eastern china however it may also have been superimposed by eastward tectonic escape resulting from the lhasa west burma qiangtang indochina collision the third cooling phase was initiated at 45 ma exclusively in the north qinling and in the footwall of the graben bounding normal fault of the weihe graben in the lesser qinling we suggest the third phase was related to reactivation of the qinling fault system as a result of eastward tectonic escape imposed by the india asia collision at 50 ma

seismic velocity structure in the source region of the 2016 kumamoto earthquake sequence japan we investigate seismic wave velocity structure and spatial distribution of the seismicity in the source region of the 2016 kumamoto earthquake sequence a one dimensional mean velocity shows that the seismogenic zone has a high velocity and low vp vs ratio relative to the average velocity structure of kyushu island this indicates that the crust is relatively strong capable of sustaining sufficiently high strain energy to facilitate two large mj 6 5 earthquakes in close proximity to one another in rapid succession three dimensional tomography of the seismogenic zone around the source of the 2016 kumamoto earthquake sequence yields vp 6 km s and vs 3 5 km s most large displacement areas asperities of the mj 7 3 event overlap with the seismogenic zone and the overlying surface layer aftershock seismicity is distributed deeper than the conventional seismogenic zone which suggests decreased strength due to fluids or increased stress both caused by coseismic slip

steady subsidence of a repeatedly erupting caldera through insar observations aso japan the relation between unrest and eruption at calderas is still poorly understood aso caldera japan shows minor episodic phreatomagmatic eruptions associated with steady subsidence we analyse the deformation of aso using sar images from 1993 to 2011 and compare it with the eruptive activity although the dataset suffers from limitations e g atmospheric effects coherence loss low signal to noise ratio we observe a steady subsidence signal from 1996 to 1998 which suggests an overall contraction of a magmatic source below the caldera centre from 4 to 5 km depth we propose that the observed contraction may have been induced by the release of the magmatic fluids feeding the eruptions if confirmed by further data this hypothesis suggests that degassing processes play a crucial role in triggering minor eruptions within open conduit calderas such as at aso our study underlines the importance of defining any eruptive potential also from deflating magmatic systems with open conduit

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

crustal structure along the aleutian island arc new insights from receiver functions constrained by active source data 1 moho depth and vp vs estimates from stacking phases of receiver functions along the aleutian island arc give new constraints on its composition and structure they expand on the current understanding of island arcs and their relationship to continental crust production we also present an approach for including constraints from active source data in receiver function analysis in a region with sparse data coverage to complement this analysis moho depth averages 37 5 km with an average uncertainty of 2 5 km along the entire arc excluding the westernmost island of attu yields an average crustal thickness of 38 5 2 9 km the vp vs ratio decreases moving eastward along the arc with an average value of 1 80 in the western and central portion of the arc built on oceanic crust but 1 63 in the eastern section built on continental crust this may reflect tectonic and compositional changes along the arc however overall the arc appears more mafic than continental crust near constant crustal thickness despite significant compositional changes may indicate that nonmagmatic processes such as erosion and isostasy act to regulate arc thickness additionally strong conversions from an upper crustal magma chamber are observed beneath akutan island confirming and clarifying the geometry of the magma body inferred from other techniques they indicate a volcanic body much larger than the eruptive edifice a feature that must persist between eruptive cycles

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

sedimentary record of triassic intraplate extension in north china evidence from the nonmarine nw ordos basin helan shan and zhuozi shan abstract the helan shan and zhuozi shan of the nw ordos basin china contain thick up to 4 km sequences of nonmarine triassic strata these rocks represent a major intraplate sedimentary basin the paleogeography tectonic setting and provenance of which are poorly understood and controversial studies of the sedimentary geology of the basin supported by new palinspastic reconstruction of younger deformation demonstrate that the basin filled from three sides by fluvial lacustrine deltaic and alluvial fan depositional systems the basin forms a westward thickening wedge that reaches its maximum thickness along the western margin of the helan shan and thins to a relatively constant 600 800 m east of the zhuozi shan the stratigraphy of the basin is strongly asymmetric alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section much of the eastern part of the basin is dominated by west flowing meandering river and deltaic systems large structures of triassic age have not been identified in the helan shan or zhuozi shan but small triassic normal faults have been documented in the western and central helan shan these characteristics most strongly support an extensional origin for the triassic basin in nw ordos the basin is interpreted to have been a north trending half graben bound along its western margin by an east dipping normal fault presently concealed beneath quaternary cover west of the helan shan the eastern margin now found in the zhuozi shan has simple ramp margin geometry driving mechanisms for this extension are not obvious due to limited documentation of triassic structure throughout the region but probably relate to far field stresses from the qinling or jinsha active margins interacting with the stable ordos block

neogene exhumation in the outer western carpathians terra nova 23 283 291 2011 abstract apatite fission track analysis was used to investigate the cenozoic tectonic evolution of the polish sector of the outer western carpathians where thrusting was overlapped by extension in the last 10 ma the results show a general decrease of burial degree towards the european foreland and a range of cooling ages between 26 and 7 ma younger ages 10 7 ma are confined to the eastern region whereas exhumation in the central western region is about 10 ma older and is characterized by no major age differences among structural units therefore exhumation of the chain is inferred to have occurred since the early miocene when it appears to have been essentially coeval with thrusting whereas extensional tectonics is likely to have played an important role during late miocene exhumation

fine crustal and uppermost mantle s wave velocity structure beneath the tengchong volcanic area inferred from receiver function and surface wave dispersion constraints on magma chamber distribution the tengchong volcanic area is located in the southeastern margin of the collision zone between the indian and eurasian plates it is one of the youngest intraplate volcano groups in mainland china imaging the s wave velocity structure of the crustal and uppermost mantle beneath the tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity in this study we analyze teleseismic data from nine broadband seismic stations in the tengchong earthquake monitoring network we then image the crustal and uppermost mantle s wave velocity structure by joint analysis of receiver functions and surface wave dispersion the results reveal widely distributed low velocity zones we find four possible magma chambers in the upper to middle crust and one in the uppermost mantle the chamber in the uppermost mantle locates in the depth range from 55 to 70 km the four magma chambers in the crust occur at different depths ranging from the depth of 7 to 25 km in general they may be the heat sources for the high geothermal activity at the surface based on the fine crustal and uppermost mantle s wave velocity structure we propose a model for the distribution of the magma chambers

inversion of the erlian basin ne china in the early late cretaceous implications for the collision of the okhotomorsk block with east asia abstract a significant transition in tectonic regime from extension to compression occurred throughout east asia during the mid cretaceous and has stimulated much attention however the timing and driving mechanisms of the transition remain disputed the erlian basin a giant late mesozoic intracontinental petroliferous basin located in the inner mongolia northeast china contains important sedimentary and structural records related to the mid cretaceous compressional event the stratigraphical sedimentological and structural analyses reveal that a nw se compressional inversion occurred in the erlian basin between the depositions of the lower cretaceous saihan and upper cretaceous erlian formations causing intense folding of the saihan formation and underlying strata and the northwestward migration of the depocenters of the erlian formation based on the newly obtained detrital zircon u pb data and previously published paleomagnetism and fossil based ages the saihan and erlian formations are suggested as latest aptian albian and post early cenomanian in age respectively implying that the inversion in the erlian basin occurred in the early late cretaceous cenomanian time apatite fission track thermochronological data record an early late cretaceous cooling exhuming event in the basin corresponding well with the aforementioned sedimentary structural and chronological analyses combining with the tectono sedimentary evolutions of the neighboring basins of the erlian basin we suggest that the early late cretaceous inversional event in the erlian basin and the large scale tectonic transition in east asia shared the common driving mechanism probably resulting from the okhotomorsk block east asia collisional event at about 100 89 ma

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and their bearing on the yinshan yanshan orogenic belt part ii anisotropy of magnetic susceptibility and gravity modeling abstract granitoids play an important role in deciphering both crustal growth and tectonic evolution of earth in the eastern end of the yinshan yanshan belt of north china craton the yiwulushan massif is a typical region that presents the tectonic evolution features of this belt our field work on the host rocks has demonstrated two phases of opposite tectonics compressional and extensional however the deformation is almost invisible in the intrusive rocks to improve the understanding of the tectonic evolution of the yiwulushan massif and the late mesozoic tectonics of east asia a multidisciplinary study has been carried out in this study anisotropy of magnetic susceptibility ams and gravity modeling have been applied on these jurassic plutons lushan jishilazi and guanyindong which intrude into the yiwulushan massif according to laboratory measurements and microscopic observations on thin sections the ams of the yiwulushan massif is characterized by secondary fabrics indicating that the intensive post solidus deformation has reset the primary magmatic magnetic fabrics a relatively gentle nw dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of n34 e and n335 e orientations namely lm1 and lm2 relatively gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif integrating all results from structural observation geochronological investigation ams measurement and gravity modeling two tectonic phases have been identified in the yiwulushan massif posterior to the jurassic 180 160 ma magmatism in the yinshan yanshan area the early one concerns a late jurassic early cretaceous 141 ma compressional event with a top to the south to southwest sense of shear the second one shows an early cretaceous 126 ma nw se ductile extensional shearing at that time sedimentary basins widened and jurassic plutons started to be deformed under post solidus conditions in fact the nw se trend of the maximum stretching direction is a general feature of east asian continent during late mesozoic

early jurassic extensional basin formation in the daqing shan segment of the yinshan belt northern north china block inner mongolia abstract structural and stratigraphic studies of the western daqing shan segment of the yinshan belt have recognized an early jurassic extensional episode supported by several lines of evidence first normal faults cut the lowermost jurassic sequence and are overlapped by younger lower jurassic rocks second lower jurassic rocks include growth strata in small scale graben at the base of the jurassic basin third rapid lateral facies changes are mapped from boulder conglomerates along the basin bounding faults to lacustrine and meandering fluvial rocks in the basin center fourth paleodrainage systems provided sediment input from three sides of the basin two transverse and one axial finally there is a strongly asymmetric distribution of coarse proximal and fine distal facies within the basin the early jurassic extensional episode was responsible for formation of an east trending half graben basin in the western daqing shan in which at least 1800 m of syn extensional nonmarine sediments accumulated and are preserved previous studies in the triassic and jurassic of other parts of northwest and north central china have concluded that the early mesozoic was a time of continental amalgamation and contractile deformation the recognition of an early jurassic extensional episode along the northern margin of the north china block is problematic in this context at least superficially we propose two possible explanations for the early jurassic extension transtension associated with strike slip tectonics or gravitational collapse of a pre existing late paleozoic early mesozoic contractile orogenic belt the first possibility transtensional deformation is problematic because specific strike slip faults have not been identified that could control extension in the western daqing shan however several lines of evidence allow the possibility of such a driving mechanism including documented early jurassic transtensional systems in the southwestern north china block several candidate strike slip faults along the china mongolia border region structural discontinuity between the daqing shan and southern mongolia and along strike changes in structural style within the yinshan belt the second possibility orogenic collapse is similarly difficult to establish because of the limited amount of data concerning the regional distribution and orientation of pre jurassic contractile structures and early jurassic extensional structures however documented late paleozoic triassic contractile deformation as well as the close temporal and spatial association and parallelism between early jurassic extensional structures and older contractile structures in the western daqing shan requires consideration of gravitational collapse as a driving mechanism for early jurassic extension in the yinshan belt

vp and vs tomography of kyushu japan new insight into arc magmatism and forearc seismotectonics high resolution 3d tomographic images of the crust and upper mantle are determined under the entire arc region of kyushu by inverting a large number of arrival time data of p wave s wave and sp depth phases the hypocenters of the offshore earthquakes are accurately located by applying a combined method that makes use of sp depth phases and double difference of the p wave and s wave arrival times our tomographic results confirmed the major features delineated by previous studies and revealed some new features of structural heterogeneity related to arc magmatism beneath the kyushu arc high velocity anomalies correspond to the subducting philippine sea slab whilst low velocity zones in the mantle wedge are clearly imaged coinciding well with the velocity heterogeneities determined by previous studies strong low velocity anomalies are distributed extensively along the volcanic front and extend to the back arc side in the crust and upper mantle our present seismic images together with the previous results suggest that the fluids supplied by the dehydration processes of the descending philippine sea slab and the hot upwelling materials related to the opening of the okinawa trough might have contributed to the unzen volcanism under the forearc region of the kyushu subduction zone prominent low velocity anomalies are visible at depths of 10 40 km along the upper boundary of the subducting philippine sea slab and large interplate earthquakes are located around the low velocity zones which is similar to the features revealed in the northeast japan subduction zone the spatial distribution of large thrust earthquakes below the offshore region reflects the existence of weak coupled or decoupled portions on the interface of the subducting philippine sea slab

tomographic evidence for the subducting oceanic crust and forearc mantle serpentinization under kyushu japan we determined high resolution three dimensional p and s wave velocity vp vs structures beneath kyushu in southwest japan using 177 500 p and 174 025 s wave arrival times from 8515 local earthquakes a poisson s ratio structure was derived from the obtained vp and vs values our results show that significant low vp low vs and high poisson s ratio zones are extensively distributed along the volcanic front in the uppermost mantle which extend and dip toward the back arc side in the mantle wedge in the crust low vp low vs and high poisson s ratio anomalies exist beneath the active volcanoes the subducting philippine sea slab is clearly imaged as a high vp high vs and low poisson s ratio zone from the nankai trough to the back arc a thin low velocity zone is detected above the subducting philippine sea slab in the mantle wedge and earthquakes in the upper mantle are distributed along the transition zone between this thin low velocity zone and the high velocity philippine sea slab which may imply that oceanic crust exists on the top of the slab and the forearc mantle wedge is serpentinized due to the slab dehydration the seismic velocity of the subducting oceanic crust with basaltic or gabbroic composition is lower than that of the mantle according to the previous studies the serpentinization process could also dramatically reduce the seismic velocity in the forearc mantle wedge c 2008 elsevier b v all rights reserved

mesozoic cenozoic evolution and mechanism of tectonic geomorphology in the central north china block constraint from apatite fission track thermochronology abstract during the mesozoic cenozoic the central north china block underwent complex tectonic transition and significant changes of tectonic geomorphology this apatite fission track study shows that the west part of the taihang mountains experienced a rapid event which commenced before 160 ma and lasted until 135 ma together with the extensive development of folds and thrusts indicating this area experienced intense compression and uplift combined with the petrological and geological characteristics the exhumation event represents the uplift of the yanshanian north china plateau and the taihang mountains inside it during the cenozoic two episodes of rapid cooling events took place during 65 55 ma and after 25 ma respectively the former one corresponds with the formation of the bohai bay basin bbb which led to the extensional denudation of the taihang mountains the formation of the bohai bay basin disrupted the yanshanian north china plateau caused the negative inversion of the tectonic geomorphology in the central north china block the thermal models indicates that the formation of north and south parts of the bbb commenced simultaneously in the south and north parts of the taihang mountains implying the dynamics should be derived from the west or the east rather than the north or the south the latter cooling event took place earlier in the north part of the taihang mountains than the south part corresponding with the miocene thermal subsidence of the bbb

is the jurassic yanshanian intraplate tectonics of north china due to westward indentation of the north china block terra nova 24 333 338 2012 abstract the northern mountains of beijing are the type locality of the mesozoic yanshanian orogen our structural study emphasizes the importance of dextral strike slip for the formation of this intracontinental belt the south and north directed thrusts are positive flower structures rooted in strike slip faults this transpressional tectonics developed from late triassic to late jurassic early cretaceous through three deformation phases coeval with syntectonic sedimentation separated by two transtensional episodes coeval with magmatism the late jurassic early cretaceous tectonic event is also recognized in several places of north china strike slip faulting controls the deformation of the northern border of the north china block in the yanshan yinshan belt simultaneously east directed thrusts and folds develop along n s elongated ranges in helanshan shanxi highlands and taihangshan the jurassic tectonics of the north china block is interpreted in a unitary way as the result of the westward underthrusting of the north china block below the alashan block

multiple layers of seismic anisotropy and a low velocity region in the mantle wedge beneath japan evidence from teleseismic receiver functions 1 a complete characterization of seismic anisotropy can yield powerful constraints on mantle flow and deformation this is particularly important for the mantle wedge above subducting slabs where the geometry of mantle flow remains poorly understood we seek to better characterize the geometry and strength of anisotropy in the mantle wedge beneath northeast honshu and hokkaido both of which overlie the subducting pacific plate previous studies indicate that upper mantle anisotropy in the japan subduction zone is highly complex and exhibits dramatic spatial variations to provide complementary constraints on the along strike variations in anisotropy we analyze teleseismic receiver functions from stations of the broadband f net array using the multitaper correlation receiver function estimator backazimuthal variations in p to sh converted energy provide clear evidence for complicated anisotropic structure in the mantle wedge beneath northeast honshu and hokkaido in northeast honshu forward modeling of receiver functions using synthetic seismograms suggests the presence of an anisotropic layer in the forearc mantle wedge above the subducting slab and a second anisotropic layer beneath the crust of the overriding plate we also see evidence for a region of low isotropic velocity in the central part of the wedge beneath ne honshu comparisons between transverse component receiver functions at stations located in ne honshu and hokkaido reveal striking differences providing further evidence for along strike variation in anisotropic structure in the mantle wedge beneath japan

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

direct dating of eocene reverse faulting in northeastern tibet using ar dating of fault clays and low temperature thermochronometry abstract paired together fault gouge dating and low temperature thermochronometry overcome the limitations and assumptions inherent in each independent technique here we establish timing of brittle faulting along the west qinling fault of northeastern tibet by dating several size fractions of fault gouge clay that represent variable populations of illite polytypes results show that the authigenic or fault generated component of illite formed at 50 8 ma and that the detrital component formed at 236 7 ma indicating a middle eocene age of faulting and a middle triassic age of the wall rocks comparing this dataset with published thermochronology from hanging wall rocks supports the interpretation that the west qinling fault initiated at 50 ma and continued until at least middle miocene time and that authigenic clay growth occurred at ambient temperatures of 110 c lack of overprinting of younger clay ages at this site may indicate that rocks were out of the thermal window for authigenic clay formation during later faulting episodes the potential for temperature to control illite growth has implications for interpretation of authigenic illite ages and their relationship to deformation episodes within fault zones

sedimentary record and tectonic implications of mesozoic rifting in southeast mongolia the east gobi basin of mongolia is a poorly described late jurassic early cretaceous extensional province that holds great importance for reconstructions of mesozoic tectonics and paleogeography of eastern asia extension is especially well recorded in the structure and stratigraphy of the unegt and zuunbayan subbasins southwest of saynshand mongolia where outcrop and subsurface relationships permit recognition of prerift synrift and postrift mesozoic stratigraphic megasequences within the synrift megasequence three sequences developed in response to climatic and rift related structural controls on sedimentation where best exposed along the northern margin of the unegt subbasin each of the synrift sequences is bounded by unconformities and generally fines upward from basal alluvial and fluvial conglomerate to fluvial and lacustrine sandstone and mudstone resedimented ashes and basalt flows punctuate the synrift megasequence rifting began in the unegt subbasin prior to 155 ma with coarse alluvial filling of local fault depressions subsidence generally outstripped sediment supply and fresh to saline lacustrine environments expanding southward with time dominated the unegt zuunbayan landscape for much of latest jurassic early cretaceous time episodic faulting and volcanism characterized the basin system for the balance of the early cretaceous a brief period of compressional and or transpressional basin inversion occurred at the end of the early cretaceous prior to deposition of a widespread upper cretaceous overlap sequence the driver s of late jurassic early cretaceous extension remain uncertain because southeast mongolia occupied an intraplate position by the beginning of the cretaceous extension in the east gobi basin was coeval with collapse and extension of early mesozoic contractional orogenic belts along the northern and southern borders of mongolia and probably was a linked phenomenon strike slip faulting associated with collisions on the southern asian and mongol okhotsk margins likely also played a role in late mesozoic deformation of the east gobi region perhaps partitioning the gobi from apparently coeval large magnitude contractional deformation in the yinshan yanshan orogenic belt south of the study area in inner mongolia

low velocity zones in the crust beneath aso caldera kyushu japan derived from receiver function analyses aso volcano in central kyushu island in southwest japan has a large caldera 18 25 km that formed by the ejection of more than 600 km3 of deposits 89 thousand years ago we calculated receiver functions from teleseismic waveform data obtained from densely distributed stations in and around the caldera we estimated the crustal s wave velocity structure from the receiver functions by using genetic algorithm inversion we detected a low velocity zone vs 2 2 km s at a depth of 8 15 km beneath the eastern flank of the central cones a sill like deformation source has been detected at a depth of 15 5 km by analyses of gps data and a swarm of low frequency earthquakes exists at depths of 15 25 km just beneath this low velocity zone magma may be newly generated and accumulated in this low velocity zone as a result of hot intrusions coming from beneath it except for the region beneath the eastern flank of the central cones a second low velocity zone vs 1 9 km s extends in and around the caldera at a depth of 15 23 km although phenomena representing intrusions have not been detected below it from the estimated velocity structure these low velocity zones are interpreted to contain a maximum of 15 melt or 30 water

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

accommodating large scale intracontinental extension and compression in a single stress field a key example from the baikal rift system the baikal rift system in southern siberia is one of the main intracontinental extensional features on earth the rift system represents the northwestern boundary of the amuria plate and in that respect can be considered as an evolving plate boundary the baikal rift system has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution however the age of the initiation of deformation and the mechanism driving this deformation are still largely debated while major extension has occurred since the late miocene pliocene the onset of extension seems older than the india asia collision implying that several driving mechanisms may have acted together or in relay through time in this work we review the available data and models for deformation in an area encompassing the baikal rift system the sayan ranges to the west and the transbaikal to the east using a synthesis of this data and our own field and mapping observations we show that the baikal rift system along with transpressional deformation in the sayan ranges and transtension in the transbaikal area can be explained through major left lateral strike slip systems the deformation is strongly controlled by inherited crustal and lithospheric structures and is distributed over a wide area within the western amuria plate that consequently cannot be considered as a rigid block such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

mesozoic contractional deformation in the middle of the asian tectonic collage the intraplate western ordos fold thrust belt china abstract intraplate deformation can occur at great distances from synchronous plate boundaries and is most likely the result of strain concentrations into weak zones these weak zones may be pre existing crustal heterogeneities such as faults thermally weakened zones due to magmatism and or the effects of a thick sedimentary cover or mechanical contrasts between adjacent crustal blocks intraplate deformation is not exclusively related to continent continent collision it can be the result of a change in subduction dynamics or the interaction of two convergent plate boundaries asia has many examples of active intraplate deformation that are thought to be related to the cenozoic indo asian collision although much attention is placed on active examples discerning controls on pre cenozoic asian intraplate deformation will lead to not only a better understanding of the processes involved in intraplate orogens but also the tectonic evolution of asia situated on either side of the yellow river along the western margin of the ordos plateau the intraplate western ordos fold thrust belt involves units as old as archean basement and as young as late jurassic the fold thrust belt is spectacularly exposed in two ranges the helan shan and the zhuozi shan cross sections drawn through the north trending fold thrust belt suggest 30 minimum shortening a paleocurrent reversal within the lower middle jurassic section is interpreted to mark the onset of contraction and mountain building a late jurassic synorogenic boulder conglomerate records the final deformation in the fold thrust belt synchronous with contraction and cutting across the fold thrust belt is an e w striking strike slip fault that displays right lateral drag and sub horizontal striae we interpret this fault as an accommodation structure in the thrust belt following e w contraction the thrust belt was dismembered by an n15 w trending left lateral strike slip fault the left lateral fault displaces the frontal portion of the thrust belt the zhuozi shan 62 km to the north relative to a more internal portion the helan shan we propose that the anomalous orientation and intraplate location of the western ordos fold thrust belt is a function of mechanical contrasts between a previously deformed area and a stable crustal block ordos to the east pre existing crustal weakness or anisotropy along the western margin of the ordos block is most likely related to either a late proterozoic early paleozoic aulacogen a triassic fault system or to both although its intraplate location and the complexities of mesozoic asian plate interactions make it difficult to relate deformation in the western ordos fold thrust belt to a specific contemporaneous plate boundary its n s trend may suggest a link with paleo pacific subduction along the eastern margin of asia