cyclostratigraphy of lower triassic terrestrial successions in the junggar basin northwestern china abstract the astrochronology for the early triassic has been constructed from well preserved marine successions however astronomical analyses of terrestrial strata have continued to be rare and problematic physical logs natural gamma ray logging data from two wells in the junggar basin northwestern china cover the entire lower triassic terrestrial baikouquan formation and have been shown to be a powerful tool in cycle analysis therefore these logs offer an excellent opportunity to detect astronomically forced sedimentation in a terrestrial setting from mid to high latitudes power spectral analysis revealed that the sedimentary cycles had wavelengths of 31 3 35 9 m 8 4 10 0 m 4 0 4 6 m and 4 0 m these are interpreted to correspond to the orbital eccentricity cycles of 405 kyr and 100 kyr and to the obliquity cycles of 51 kyr and 34 kyr respectively we thus established an astronomical time scale for the studied interval assuming that the 31 3 35 9 m cycles represent the 405 kyr eccentricity cycles this astrochronology indicated that the duration of the baikouquan formation was 2 0 0 1 myr statistical evaluations of optimal sediment accumulation rates using the correlation coefficient approach showed that the rates of the investigated successions were approximately 6 0 12 0 cm kyr orbitally controlled climate change was the major dynamic mechanism for the formation of early triassic fan delta successions in the junggar basin

a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

mountains and arid climates of middle latitudes simulations from a global climate model with and without orography have been used to investigate the role of mountains in maintaining extensive arid climates in middle latitudes of the northern hemisphere dry climates similar to those observed were simulated over central asia and western interior north america in the experiment with mountains whereas relatively moist climates were simulated in these areas in the absence of orography the experiments suggest that these interior regions are dry because general subsidence and relatively infrequent storm development occur upstream of orographically induced stationary wave troughs downstream of these troughs precipitation bearing storms develop frequently in association with strong jet streams in contrast both atmospheric circulation and precipitation were more zonally symmetric in the experiment without mountains in addition orography reduces the moisture transport into the continental interiors from nearby oceanic sources the relative soil wetness of these regions in the experiment without mountains is consistent with paleoclimatic evidence of less aridity during the late tertiary before substantial uplift of the rocky mountains and tibetan plateau is believed to have occurred

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

origin and recharge model of the late cretaceous evaporites in the khorat plateau abstract evaporites commonly occur in the mesozoic cenozoic tethyan domain which characterized by extensive late cretaceous potash deposits in the lanping simao basin lsb in southwestern china and in the khorat plateau kp in thailand and laos the lsb and the kp are located in the eastern tethyan tectonic belt the origin of the late cretaceous evaporites in these basins is controversial possibilities include marine continental or hydrothermal origins in addition the recharge model for the major solutes into these evaporitic basins is inadequate whether it is from the kp to the lsb or from the qiangtang to the lsb to the kp in this study 34 gypsum anhydrite and halite samples from two sediment cores collected from the kp were analyzed to determine their stable b sr s isotopic compositions this is the first time that 11b values have been reported for the anhydrite in the study area the origin and evolutionary relationships of these evaporitic basins were investigated based on the geochemical data sedimentary features mineral sequences and stratigraphic ages of the evaporites in the lsb and kp the tectonic evolution and stratigraphic comparisons during the triassic cretaceous in the eastern tethyan domain were systematically reviewed and summarized in order to determine a preferred recharge model for the evaporites in the kp the following conclusions were reached 1 the reconstructed 11b values 38 20 to 51 23 of the parent solution which were based on those of the anhydrite 8 20 to 21 23 and the isotopic fractionation levels 30 2 to 32 7 87sr 86sr ratios 0 70743 0 70846 and 34s values 14 39 to 15 94 of the anhydrite and halite in the kp overlap with those of late cretaceous seawater suggesting a marine origin 2 the similar mineral sequences and b sr s isotopic signatures and the comparable sedimentary features and inherited ore forming ages indicate that evaporites in the lsb and kp have similar solute sources and evolutionary relationships 3 the tectonic evolution and stratigraphy demonstrate that during the late cretaceous paleoseawater from the shan boundary ocean the eastern segment of the meso tethys ocean most likely passed through the southwestern part tengchong baoshan block of sibumasu and preferably recharged marine solutes into the lsb and kp

high resolution clay mineral and major elemental characterization of a permian triassic terrestrial succession in southwestern china diagenetic and paleoclimatic paleoenvironmental significance abstract relatively high resolution clay mineralogical and chemical index of alteration cia analyses were conducted on the terrestrial lubei section in southwestern china to gain a better understanding of the paleoclimatic paleoenvironmental evolution on land during the permian triassic transition p tr transition clay mineral species include illite smectite mixed layers i s illite irregular chlorite expandable mixed layers c e chlorite kaolinite vermiculite hydroxyl interlayered mineral him and corrensite cia values are as high as approaching 100 in the permian and show a gradual and subtle decrease towards the lowermost triassic where a sudden decrease to persistently

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

a possible model for large preseismic slip on a deeper extension of a seismic rupture plane abstract i develop a numerical model for preseismic slip and episodic aseismic slip events slow earthquakes on a deeper extension of a seismogenic plate interface using a rate and state dependent friction law the deep preseismic slip and episodic slow slip were indicated by models based on geodetic observations though they cannot be explained by common rate and state dependent laws i investigate whether this incongruity can be removed by including use of additional known constraints on the frictional property the steady state friction on a model fault is taken to be velocity weakening at low velocities and velocity strengthening at high velocities the transition velocity from velocity weakening friction to velocity strengthening is assumed to be the seismic slip velocity at shallow seismic depths and decreases with depth at deeper parts simulation results for a 2d model of interplate earthquakes at a subduction zone are as follows 1 during an interseismic period between successive large earthquakes at shallow seismogenic depths some episodic aseismic slip events with durations of a few years occur on the plate interface just below the seismogenic depths 2 preseismic slip occurs at nearly the same location where the episodic aseismic slip events occur these may explain some characteristics of observed preseismic slip of the 1944 tonankai earthquake m 7 9 along the nankai trough central japan and episodic aseismic slip events in the same area

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

sanjiang tethyan metallogenesis in s w china tectonic setting metallogenic epochs and deposit types abstract tectonically the sanjiang tethyan metallogenic domain stmd is located within the eastern himalayan tibetan orogen in the sanjiang tethys southwestern china although this metallogenic domain was initiated in the early palaeozoic extensive metallogenesis occurred in the late palaeozoic late triassic and himalayan tertiary epochs corresponding tectonic settings and environments in the domain are an arc basin system related to the subduction of the palaeo tethyan oceanic slabs a post collision crustal extension setting caused by the lithospheric delamination or slab breakoff underneath the sanjiang tethys during the late triassic large scale strike slip faulting and thrusting systems due to the indo asian continent collision since the palaeocene in this metallogenic domain important gold copper base metals rare metals and tin ore belts incorporating a large number of giant deposits were developed the main types of deposits include 1 porphyry copper deposits controlled by a large scale strike slip fault system 2 vhms deposits mainly occurring in intra arc rift basins and post collision crustal extensional basins 3 shear zone type gold deposits in the ophiolitic melange zone along the thrusting shearing system 4 hydrothermal silver polymetallic deposits in the triassic intra continental rift basins and tertiary strike slip pull apart basins and 5 himalayan granite related greisen type tin and rare metallic deposits within the metallogenic epochs of the late palaeozoic to cenozoic the styles and types of the ore deposits changed from vhms types in the late palaeozoic through exhalative sedimentary type deposits in the late triassic to porphyry type copper deposits shear zone type gold deposits hydrothermal vein type silver polymetallic deposits greisen type tin and rare metal deposits in the cenozoic correspondingly ore forming metals also changed from a pb zn cu ag association through ag cu pb zn fe ag pb and ag au hg associations to ag cu pb zn cu mo au sn and li rb cs nb zr hf y ce sc associations

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

mid cretaceous aeolian desert systems in the yunlong area of the lanping basin china implications for palaeoatmosphere dynamics and paleoclimatic change in east asia abstract the mid cretaceous constitutes a period of worldwide atmospheric and oceanic change associated with slower thermohaline circulation and ocean anoxic events possible polar glaciations and by a changing climate pattern becoming controlled by a zonal planetary wind system and an equatorial humid belt during the mid cretaceous the subtropical high pressure arid climate belt of the planetary wind system controlled the palaeolatitude distribution of humid belts in asia as well as the spatial distribution of rain belts over the massive continental blocks at mid low latitudes in the southern and northern hemispheres additionally the orographic effect of the andean type active continental margin in east asia hindered the transportation of ocean moisture to inland regions with rising temperatures and palaeoatmospheric conditions dominated by high pressure systems desert climate environments expanded at the inland areas of east asia including those accumulated in the mid cretaceous of the simao basin the sichuan basin and the thailand s khorat basin and leading the late cretaceous erg systems in the xinjiang basin and jianghan basin this manuscript presents evidences that allow to reinterpret previously considered water laid sediments to be accumulated as windblown deposits forming part of extensive erg sandy desert systems using a multidisciplinary approach including petrological sedimentological and architectural observations the mid cretaceous albian turonian nanxin formation from the yunlong region of lanping basin formerly considered to aqueous deposits is here interpreted as representing aeolian deposits showing local aeolian fluvial interaction deposits the palaeowind directions obtained from the analysis of aeolian dune cross beddings indicates that inland deserts were compatible with a high pressure cell hpc existing in the mid low latitudes of east asia during the mid cretaceous compared with the early cretaceous the mid cretaceous had extremely lower temperatures and pressure gradients more arid climate which is in accordance with the existing morphology of hpc and the hpc was stable with little movement simultaneously the deserts controlled by the mid cretaceous hpc were closer to the equator indicating the shrinkage of the hadley cell relative to the early cretaceous

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

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

the disappearance of a late jurassic remnant sea in the southern qiangtang block shamuluo formation najiangco area implications for the tectonic uplift of central tibet abstract located between the bangong nujiang suture zone and the qiangtang block in central tibet the najiangco area 5 km to the north of nima selinco contains an upper jurassic lower cretaceous sedimentary succession deposited during a period of marine regression the youngest marine sedimentary unit in the najiangco area is the upper jurassic shamuluo formation which consists of sandstone limestone siltstone and shale sedimentary facies analysis shows that tidal flat and subtidal lagoonal facies characterized the northern margin of the basin while delta front and prodelta facies dominated the middle part and carbonate shoal and patch reef facies prevailed along the southern margin provenance analysis including petrographic modal analysis of sandstones and u pb dating of detrital zircons shows that a recycled orogen in the central qiangtang to the north of najiangco area was the source of the sandstones in the shamuluo formation biostratigraphy and u pb zircon dating of a porphyritic granitoid dike 151 2 ma indicate that the shamuluo formation was deposited during the late jurassic oxfordian to kimmeridgian during middle jurassic time the southern qiangtang basin was dominated by shallow marine environments later during the late jurassic oxfordian to kimmeridgian the shallow marine facies retreated to the southern margin of the basin combined with regional paleogeographic data from central tibet two stages of southward retreat of the qiangtang remnant sea and three stages of topographic uplift of the qiangtang block can be recognized during late middle jurassic to early cretaceous time

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

preliminary conclusions of the royal society and academia sinica 1985 geotraverse of tibet the 1985 chinese british expedition to the tibetan plateau attempted to solve the question of the origin of the very thick crustal rocks in this region continuing northwards movement of the indian plate over the past 38 myr has given rise to severe folding and thrust faulting causing crustal thickening by internal deformation previous collisions of microplate terranes derived from gondwanaland occurred during mesozoic times but the kun lun terrane of northern tibet was already part of laurasia by the carboniferous

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

palaeoceanographic and palaeoclimatic reorganization around the middle late jurassic transition abstract a middle to upper jurassic succession of submarine hardgrounds overlain by nodular limestones is exposed in the jura mountains and in the helvetic of the swiss alps these sediments were accumulated along the northern shelf of the east west trending tethys seaway submarine hardgrounds and nodular limestones were also formed on the brianconnais high today outcropping in the middle penninic nappe pile of the alps hardgrounds record strong and persistent current activity along the northern tethys shelf and on the brianconnais high during the callovian and early oxfordian the transition from hardgrounds to nodular limestones corresponds to a major reorganization of tethys oceanography the change occurred in plicatilis ammonite zone middle oxfordian carbon isotope stratigraphy calibrated against an ammonite dated reference section in the french subalpine basin serves as a correlation tool between ammonite dated sections and successions with poor biostratigraphic resolution correlation demonstrates that the end of hardground formation was synchronous over wide parts of the northern tethys the change in shelf sedimentation coincides with a positive carbon isotope excursion with an amplitude of 1 5 the change in c isotope stratigraphy indicates that observed reorganization of current patterns along the northern tethys shelf was coupled with global change in oceanography and climate we propose that the change in northern tethys sedimentation was caused by opening of new seaways at a time of progressive collapse of pangaea

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

global paleobiogeography of brachiopods during the mississippian response to the global tectonic reconfiguration ocean circulation and climate changes abstract changes in mississippian global paleogeography derived from the reconfiguration of the continents a reversal in ocean currents and global cooling although the tectonic and climatic changes are well documented their effects on the distribution of brachiopod fauna are poorly documented here we present systematic quantitative analyses on global paleobiogeography based on a global brachiopod database from the mississippian i e tournaisian visean and serpukhovian the dataset consists of 2123 species of 344 brachiopod genera from 1156 localities our results reveal that global provincialism was not evident during the tournaisian and visean stages two realms i e the gondwanan and paleoequatorial realms are recognized during the tournaisian the paleoequatorial realm dominates during the visean stage whereas the gondwanan realm is not documented due to the absence of data points in contrast to the early and middle mississippian stages faunal provincialism is greatly enhanced in the serpukhovian stage with paleotethyan and north american realms easily distinguished this indicates that the rheic ocean was closed before the serpukhovian due to the collision between gondwana and laurussia that disrupted faunal interchange between the paleotethys and north america in addition the paleolatitude related thermal gradient was enhanced and the boreal realm was distinguished from the paleotethyan realm during the onset of the late palaeozoic ice age lpia in the serpukhovian the paleolatitude diversity gradient pattern further shows a distinct shift of diversity center from the southern tropic zone in the tournaisian and visean to the northern tropic zone in the serpukhovian

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

summertime quadruplet heating pattern in the subtropics and the associated atmospheric circulation 1 a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer based on data diagnosis the ocean region to the west is characterized by strong longwave radiative cooling lo the western and eastern portions of the continent are dominated by sensible heating se and condensation heating co respectively and the ocean region to the east is characterized by double dominant heating d with lo prevailing co these compose a losecod heating quadruplet its general feature is heating over the continent and cooling over the oceans a distinct circulation pattern accompanies this heating pattern in the upper troposphere anticyclonic circulation over the continent is accompanied by cyclonic circulations over the oceans on its western and eastern sides near the surface cyclonic circulation over the continent is accompanied by anticyclonic circulations over the oceans on both sides this circulation feature is interpreted as the atmospheric thermal adaptation to the quadruplet heating it is further demonstrated that the global summer subtropical heating and circulation may be viewed as mosaics of such a quadruplet heating and circulation patterns respectively

stress transfer and strain rate variations during the seismic cycle 1 the balance of forces implies stress transfers during the seismic cycle between the elastobrittle upper crust and the viscoelastic lower crust this could induce observable time variations of crustal straining in the interseismic period we simulate these variations using a one dimensional system of springs sliders and dashpot loaded by a constant force the seismogenic zone and the zone of afterslip below are modeled from rate and state friction the ductile deeper fault zone is modeled from a viscous slider with newtonian viscosity n the force per unit length f must exceed a critical value fc to overcome friction resistance of the fault system this simple system produces periodic earthquakes the recurrence period tcycle and the duration of the postseismic relaxation phase which is driven dominantly by afterslip then both scale linearly with n between two earthquakes interseismic strain buildup across the whole system is nonstationary with the convergence rates vi just after each earthquake being systematically higher than the value vf at the end of the interseismic period we show

the mesozoic cenozoic tectonic settings paleogeography and evaporitic sedimentation of tethyan blocks within china implications for potash formation abstract potash deposits are common in the mesozoic cenozoic tethyan domain which features the giant potash deposits in the late jurassic central asian basin and the late cretaceous khorat basin of thailand laos widespread evaporitic sequences from these intervals have been found in some marine and transitional basins within the chinese continental blocks such as the yangtze simao and tarim blocks in which only one small scale potash deposit had been found in the late cretaceous simao basin these evaporites are commonly characterized by depositional cycles that are more frequent than those of other potash basins around the world it remains debated whether large or giant potash deposits could be formed in chinese blocks of tethyan domain and if so what mechanism was responsible for the potash formation to address these issues we comprehensively review the meso cenozoic drift history and collision dynamics of these chinese blocks and summarize the formation mechanism depositional characteristics and paleoclimate of the evaporite basins in these blocks these blocks drifted from the southern hemisphere and collided and welded together in the beginning of the late permian in the northern hemisphere the collisions often commenced in the east and gradually spread to the west of these blocks resulting in 1 westward seawater retreat 2 differential topographic uplift with high topography in the east and low topography in the west and 3 increasingly closed depositional environments in these basins in addition these collisions often exerted nearly n s oriented principal compressive stress which resulted in nearly e w oriented extension these forces induced a series of faulted bounded subsidence belts with n s striking extensional sub basins arranged in an e w oriented chain in these blocks in this chain like sub basins system as sea level rose and seawater flowed from west to east the western sub basins proximal to the open sea would have precipitated calcium carbonates and calcium sulfates resulting in a high degree of concentration by the time the brines reached the distal end i e eastern sub basins ultimately potash minerals were commonly deposited in the easternmost sub basins based on the above model of potash formation we predict that potash deposits may be formed in certain sub basins in the eastern part of these basins in chinese tethyan blocks which maybe lay a theoretical foundation for china s future exploration of potash deposits

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

large dry humid fluctuations in asia during the late cretaceous due to orbital forcing a modeling study abstract cretaceous stratigraphy in the mid to low latitude asia indicates that the climate was overall dry with large variations in aridity in timescales of 1 100 ka different from the present day monsoonal humid climate to identify the possible mechanism for such variation we modeled the late cretaceous climate using a fully coupled atmosphere ocean general circulation model aogcm community earth system model version 1 2 cesm1 2 under different co2 concentrations and orbital configurations the simulation results show that the mid to low latitude asia was generally dry during that time consistent with reconstructions the arid area decreases and the semi arid area increases with the increase of co2 concentration but the change in total area is small even when co2 is increased by 8 folds in contrast the area of dryland can increase by 67 or 500 depending on how dryness is defined when the orbital configuration changes from one in which the northern hemispheric summer receives the most solar insolation to one in which it receives the least solar insolation therefore the mid to low latitude asia was likely going through dramatic dry humid cycles at orbital timescale during the late cretaceous similar to the saharan region during the late miocene pleistocene

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

morphological drainage and eolian controls on the microtidal patara beach sediments eastern mediterranean textural geochemical and mineralogical investigations abstract the effects of dominant hydrodynamic morphological fluvial and hinterland geological source conditions on the texture and composition of the microtidal and dissipative patara beach mediterranean coast of sw turkey sediments were investigated at 47 locations patara beach sediments are composed entirely of sand fine sand 5 94 was more abundant in the northwestern section while medium sand contents 2 94 increased in the central and southeastern sections moderately to well sorted mostly 0 3 0 7 o sediments tend to show overall better sorting towards the southeast in the net longshore current direction terrigenous carbonate grains derived from the hinterland constituted 6 50 as caco3 with varying tendencies to increase or decrease within sections alongshore total heavy mineral concentrations in bulk sediments 1 17 mostly

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

gps constraints on 34 slow slip events within the cascadia subduction zone 1997 2005 1 refinements to gps analyses in which we factor geodetic time series to better estimate both reference frames and transient deformation resolve 34 slow slip events located throughout the cascadia subduction zone from 1997 through 2005 timing of transient onset is determined with wavelet transformation of geodetic time series thirty continuous stations are included in this study ranging from northern california to southwestern british columbia our improvements in analysis better resolve the largest creep events and also identify many smaller events at 48 5 n latitude a 14 month average recurrence interval has been observed over eight events since 1997 farther north along vancouver island a host of smaller events with a distinct 14 month periodicity also occurs in southern washington state some of the largest transient displacements are observed but lack any obvious periodicity in their recurrence along central oregon an 18 month recurrence is evident while in northern california an 11 month periodicity continues through 2005 we invert gps offsets of the 12 best recorded events for thrust slip along the plate interface using a cross validation scheme to derive optimal smoothing parameters these 12 events have equivalent moment magnitudes between 6 3 and 6 8 and have 2 3 cm of slip unlike other subduction zones no long duration events are observed and cumulative surface deformation is consistently less than 0 6 cm the many newly resolved smaller transient events in cascadia show that slow slip events occur frequently with gps best capturing only the largest events it is likely that slow slip events occur more frequently at levels not detectable with gps

land sea geometry and its effect on monsoon circulations the role of land sea geometry in determining the existence and character of monsoon circulations is examined using an atmospheric general circulation model with land surface properties represented by the simplified simple biosphere model idealized land sea distributions are used to examine the effects of the latitude of continental coastlines the meridional and zonal extent of continents the shape of continents and the presence of orography on circulation in the tropics and subtropics it is found that the latitude of the continent is critical to the establishment of a distinct seasonality of precipitation and a summer monsoon circulation low latitude positions of the continent lead to landlocked precipitation maxima and poleward positions lead to a mediterranean winter monsoon climate in every case the subsiding branch of the hadley cell at continental longitudes locks over some part of the land variations in the meridional extent of land affect the strength of the hadley cell and the degree of seasonality in the climate over land the extension of a subtropical continent into the tropics is critical for establishing heavy convective rainfall over land in the summer when tropical peninsulas are added to a subtropical continent the distribution of moisture and rain over semi arid and arid regions of the original continent are affected when a broad mountain of 1200 m maximum elevation is present on the idealized continent there is a band of increased precipitation to the south and east of the mountain with a systematic decrease to the south north and west of the band

sensitivity of east asian monsoon climate to the uplift of the tibetan plateau abstract using the cola center for ocean land atmosphere studies general circulation model a series of numerical experiments were conducted to examine the impact of uplift of the tibetan plateau on the evolution of the monsoon climate in east asia an attempt was made to isolate the effect of the plateau uplift from the changes in other forcing mechanisms we examined the spatial and temporal variation patterns of a variety of climatic variables and indices including monsoon intensity sea level pressure surface and upper air winds temperature at different levels precipitation air humidity and soil moisture our results suggest that the evolution of the east asia monsoon may be more sensitive to the uplift of the tibetan plateau than that of the south asia monsoon moreover the effect of the plateau uplift on the east asia winter monsoon is more significant than that on the summer monsoon in the northern part of east asia north china the formation of the monsoon climate is marked mainly by the establishment of the northerly winds in winter or the winter monsoon system corresponding to the uplift of the plateau when the height reaches approximately 50 of its current elevation on the other hand the establishment of the monsoon climate in the southern part of east asia the yangtze river valley and the area south of it may be much earlier than that in the northern part

the evolution of the seismic aseismic transition during the earthquake cycle constraints from the time dependent depth distribution of aftershocks 1 using the example of the 1992 m 7 3 landers earthquake we show that in the aftermath of a large earthquake the depth extent of aftershocks shows an immediate deepening from pre earthquake levels followed by a time dependent postseismic shallowing we use these seismic data to constrain the change in the depth of the seismic aseismic transition with time throughout the earthquake cycle most studies of the seismic aseismic transition have focussed on the effects of temperature and or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding a strain rate dependent transient deepening of the brittle ductile transition following a major earthquake is predicted by geological and laboratory observations by analyzing the time dependent depth distributions of aftershocks we identify and quantify the temporal evolution of this transition in the example of the landers earthquake its depth changes by as much as 3 km over the course of 4 years

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

early paleozoic paleomagnetic poles from the western part of the north china block and their implications abstract we collected 917 oriented drill core samples 124 sites from 22 units spanning the early cambrian to middle ordovician formations of the north china block ncb to construct an apparent polar wander path apwp of the early paleozoic for the ncb sampling areas are located in the helanshan tongchuan hancheng and yuncheng luliang regions along the margin of the ordos basin characteristic remanent magnetizations for five periods between the cambrian and ordovician are isolated from 281 samples by careful demagnetization directions cluster around northwesterly direction with upward shallow inclination and its antipode after tilt correction reliability of these five directions is ascertained through positive fold and reversal tests the five cambrian and ordovician paleopoles plot in the present atlantic ocean which is consistent with previously reported paleomagnetic poles a newly constructed apwp between the cambrian and ordovician indicates that the ncb was located in the southern hemisphere around 15 s during cambro ordovician time motion of the ncb between the early and middle cambrian comprised a counterclockwise rotation of 22 3 7 0 and a northward latitudinal displacement of 7 2 6 8 combining the paleobiogeographic and paleoclimatic data with the paleomagnetic implies that the ncb was probably located in east gondwana in the early cambrian and may have separated from gondwana in post early cambrian time the ncb is also inferred to have been located close to siberia and north america during the middle ordovician

strengths of serpentinite gouges at elevated temperatures serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones to test these hypotheses we have measured the strength of chrysotile lizardite and antigorite rich serpentinite gouges under hydrothermal conditions with emphasis on chrysotile which has thus far received little attention at 25 c the coefficient of friction of chrysotile gouge is roughly 0 2 whereas the lizardite and antigorite rich gouges are at least twice as strong the very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content when the adsorbed water is removed chrysotile is as strong as pure antigorite gouge at room temperature heating to 200 c causes the frictional strengths of all three gouges to increase limited data suggest that different polytypes of a given serpentine mineral have similar strengths thus deformation induced changes in polytype should not affect fault strength at 25 c the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities consistent with previous studies at temperatures up to 200 c however chrysotile strength is essentially independent of velocity at low velocities overall chrysotile has a restricted range of velocity strengthening behavior that migrates to higher velocities with increasing temperature less information on velocity dependence is available for the lizardite and antigorite gouges but their behavior is consistent with that outlined for chrysotile the marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth the velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip but in the presence of a hydrostatic fluid pressure gradient all varieties of serpentine are too strong to explain the apparent weakness of faults such as the san andreas

a jackknife for magnetostratigraphy we investigate the problem of evaluating the reliability of a magnetostratigraphic section using a jackknife resampling scheme we define a parameter j as the slope relating the percentage of polarity zones of a sampled section remaining after random deletion of sites increasing in proportion to a total of 20 of the initial collection so defined j quantifies the dependence of a magnetostratigraphic record on the distribution of sampling sites based on simulated magnetostratigraphic sections j was found to be an indicator of the approximate percentage of polarity zones present in the original reference sections that were recovered in the sampled section j will perhaps be most helpful as a guide to investigators as to whether further sampling would provide useful information as well as to the non paleomagnetist user of black and white interpretive polarity logs as an estimate of the reliability of a given section

magnetostratigraphy of the middle upper jurassic sedimentary sequences at yanshiping qiangtang basin china a series of important geological events occurred in the tibetan plateau area during the jurassic such as the collision of the lhasa and qiangtang terranes the closure of the meso tethyan ocean the opening of the neo tethyan ocean and the cessation of the mega monsoon the similar to 3000 m thick jurassic sedimentary sequence in the qiangtang basin on the central tibetan plateau which is called the yanshiping ysp group recorded these geological events however the chronology of the sequence is surprisingly poorly constrained here we perform a detailed palaeomagnetic analysis on the similar to 1060 m thick middle and upper portions of the ysp group the xiali and suowa formations in the ysp section of the eastern qiangtang basin three bivalve zones at stratigraphic intervals of similar to 40 140 640 800 and 940 1040 m are identified which yield a bathonian callovian age for the lower xiali fm a callovian oxfordian age for the lower suowa fm and an oxfordian kimmeridgian age for the upper suowa fm a total of 544 oriented palaeomagnetic samples were collected from the section by combining thermal and alternating field demagnetizations clear characteristic remanent magnetization chrm directions are isolated for most of the samples the robust chrm directions pass fold and reversals tests which support the primary nature of the chrms and yield a palaeopole at 76 8a degrees n 297 2a degrees e dp 2 2a degrees dm 3 7a degrees a total of 27 normal and 26 reversed polarity zones were successfully recorded in the section combined with fossil age constraints results suggest that the section is plausibly composed of a callovian early kimmeridgian age sedimentary sequence

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

new mesozoic apparent polar wander path for south china tectonic consequences a new paleomagnetic study in the south sichuan basin south china block has been carried out on sediments of early triassic to middle jurassic age detailed stepwise thermal and alternating field demagnetizations allowed us to isolate two to three components a low temperature component component a falls close to the local present earth field direction a middle temperature component component b is found both in limestone and red beds of early triassic age in limestones of middle triassic age and finally in red beds of jurassic age the component b directions failed the fold test but show a significant increase of the ks kg ratio at 60 when a progressive stepwise unfolding is applied the directions obtained at 60 unfolding are grouped best and yield a pole position at 76 5 n 174 1 e a95 3 7 that is close to the late cretaceous pole of the south china block scb or the early tertiary pole of the eurasian plate characteristic directions are finally obtained component c for early triassic and early to middle jurassic sediments only both with reversal and fold tests they yield pole positions at 44 1 n and 217 2 e a95 4 9 and 79 n and 227 e a95 4 5 respectively the early triassic result well fits other data of the same age from the scb the revised late permian to cretaceous paleopole data provide a new mesozoic apparent polar wander path for south china the successive pole positions from late permian to early triassic indicate motion of the south china block as a whole rather than local rotations linked to important strain within the block the early to middle jurassic pole is statistically indistinguishable from the compiled north china block ncb poles and indicates that final suturation between the two blocks occurred by the end of the triassic which is coherent with the age of ultra high pressure metamorphism in the dabie sulu areas of eastern china the asian plate including the mongol central asian block ncb and scb however was probably separated from siberia by the mongol okhotsk ocean during jurassic time

paleomagnetism of cretaceous rocks from eastern qiangtang terrane of tibet thermal demagnetization has successfully isolated high unblocking temperature characteristic directions from paleomagnetic samples of lower and middle cretaceous redbed formations from eastern qiangtang terrane tibet the tilt corrected mean direction for the lower cretaceous is d i 57 7 50 2 with 95 10 9 and n 12 sites and that for the middle cretaceous is d i 39 7 51 6 with 95 8 5 and n 11 sites both formations pass the fold test and the latter possesses two polarities the magnetization predates the eocene and was probably acquired during cretaceous time comparison of the mean directions with expected directions from the stable interior of eurasia indicates significant clockwise rotation but little paleolatitudinal change for the sampling area deformation and rotation of these rocks are presumably related to the collision of india with asia and its subsequent northward indentation into asia existing paleomagnetic data from tibet and its environs seems to be compatible with a crustal shortening thickening model dewey et al 1988 in that the continental crust directly north of the indian indenter was substantially shortened north south whereas in the vicinity of the western and eastern syntaxes latitudinal displacement was minimal but tectonic rotation was very important more data are needed to further differentiate between this model and the lateral eastward crustal extrusion model molnar and tapponier 1975

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

late mesozoic tectonic evolution and growth of the tibetan plateau prior to the indo asian collision abstract the elevation of the tibetan plateau is a revolutionary event in the earth history which resulted in change not only of cenozoic regional and global climate but also of monsoon intensity a critical aspect for the development of the tibetan plateau that remains open to intense debate is whether the collision among the tibetan continental blocks or the subduction of the tethys prior to the indo asian collision in the cenozoic contributed to the plateau growth we propose here that an andean type orogen could have been present in southern tibet from the jurassic to early cretaceous but collapsed during the middle cretaceous based on a synthesis of existing structural sedimentary geochronological and geochemical data the orogeny is marked by north verging jurassic early cretaceous thrusting in the lhasa block a result of flat subduction of the yarlung zangpo neo tethys that is recorded by a narrow belt of 205 174 ma adakitic rocks along the southernmost margin of the lhasa block denudation of the orogen produced a thick up to 15 km sequence of jurassic turbidites and molasse type sediments on the northern lhasa block widespread middle cretaceous 135 100 ma postorogenic strongly peraluminous to calc alkaline magmatism and extensional deformation in the lhasa block and an extensive marine transgression in tibet indicate that the orogen broke down due to extension resulting from lithosphere delamination and asthenosphere upwelling meanwhile the north dipping subduction of the bangong meso tethys produced a wide jurassic middle cretaceous magmatic arc along the southern margin of the qiangtang block findings of 132 108 ma aged ophiolites rich with middle cretaceous radiolarians in central tibet indicate that the bangong meso tethys did not close until the late cretaceous repeated flat slab subduction of the yarlung zangpo neo tethys occurred during the late cretaceous 90 78 ma as indicated by the adakites in the southernmost lhasa block which together with the ongoing qiangtang lhasa collision could have contributed to the growth of the tibetan plateau

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

mid cretaceous desert system in the simao basin southwestern china and its implications for sea level change during a greenhouse climate abstract paleoclimatic indicators suggest that the mid cretaceous was one of the warmest intervals of the phanerozoic the period of the mid cretaceous super greenhouse also experienced an equator to pole temperature gradient much lower than that of the present day implying greater meridional heat transport by the atmosphere and or oceans however reconstructions of cretaceous atmospheric circulation have been hindered by a lack of relevant datasets based on reliable proxies or direct geological evidence aeolian deposits provide direct information about paleoclimate as well as the direction and intensity of paleo wind in the interiors of continents using petrologic and sedimentologic observations this study reassesses the terrestrial deposits of the mid cretaceous mangang formation in the simao basin of southwestern china originally considered to be aqueous deposits we reinterpret these strata as representing aeolian transport in a desert environment we suggest that the development of aeolian deposits in the mangang formation and coeval strata in adjacent basins was a local response to the prevailing desert climate in the mid to low latitudes of the northern hemisphere during the mid cretaceous which were dominated by subtropical high pressure systems on a planetary scale in addition with the closure of the mesotethys ocean the intermontane basins of the south china simao and indochina blocks became more isolated from atmospheric circulation bidirectional subduction of the bangong nujiang oceanic crust and the izanagi plate beneath east asia led to the development of andean type margins which created a rain shadow effect in continental east asia these factors caused the development of a tropical desert climate characterized by aeolian dunes and evaporite deposition we speculate that the severe depletion of groundwater reservoirs via the desertification of east asia may represent a previously unrecognized trigger for short term sea level changes during the ice free cretaceous greenhouse interval

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

mesozoic litho and magneto stratigraphic evidence from the central tibetan plateau for megamonsoon evolution and potential evaporites the megamonsoon was a striking event that profoundly impacted the climatic environment and related mineral sources salts coals and oil gases in the mesozoic how this event impacted asia is unknown here we firstly reported a mesozoic stratigraphic sequence in the northern qiangtang basin in the central tibetan plateau based on lithofacies and chronologies of paleontology and magnetostratigraphy hpw the planetary and megamonsoon circulations controlled the asian climate with time has been recorded using the basic principles of physical geography present analogs and a newly developed model the evolution of the stratigraphic sequence was interpreted to demonstrate that the qiangtang basin has been subjected to a megamonsoon climate with heavy precipitation during its northward movement since the latest permian but has been subjected to a dry environment due to moving into the northern hemisphere subtropic high zone in the middle triassic and monsoonal retreat in the early late jurassic early oxfordian approximately 161 ma the coupling of the hot dry climate and the close of the meso tethys along with sea retreat in the late jurassic ensured a large potential time window for evaporite potash formation in the qiangtang basin while the tropic megamonsoon rain forest in the late permian to the early triassic and in the late triassic to middle jurassic favored the formation of coal and hydrocarbon source rocks c 2016 international association for gondwana research published by elsevier b v all rights reserved

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

magnetostratigraphic study of the potash bearing strata from drilling core zk2893 in the sakhon nakhon basin eastern khorat plateau abstract the khorat plateau holds one of the world s largest potash deposits although many attempts have been made the age of the potash bearing strata remains poorly determined here we report a high resolution magnetostratigraphic study of a 595 4 m deep potash bearing borehole zk2893 in the southeast sakhon nakhon basin in central laos this borehole penetrated the whole potash bearing nong boua formation and reached the underlying sandstone beds of the nam noy formation a total of 500 383 level cubic paleomagnetic samples were collected k t curves and hysteresis loops revealed that hematite and magnetite were the main magnetic carriers and were likely of detrital origin as indicated by microscopic and electron microprobe analysis empa examinations progressive thermal and alternating field af demagnetization isolated 229 valid characteristic remnant magnetizations chrms which showed a normal and antipodal distribution of the inclination data both the microscopic and empa examinations and inclination only analysis suggest primary magnetizations of the chrms yielding nine normal and seven reversed polarity zones combined with regional palynological isotopic and sedimentologic evidence the obtained polarity zones were best correlated to the geomagnetic polarity time scale of gradstein et al 2012 gpts2012 yielding magnetostratigraphic ages of 63 5 ma to 92 ma for the potash bearing nong boua formation and 85 ma for the potash bed in its lower salt unit

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

stabilizing effect of high pore fluid pressure on slip behaviors of gouge bearing faults this work is supported by the department of energy office of science the office of basic energy sciences chemical sciences geosciences biosciences division under award no de fg 0207er15916 and by the national science foundation under grant no ear 1761912

a review of permian stratigraphy palaeobiogeography and palaeogeography of the qinghai tibet plateau the permian marine lithostratigraphy biostratigraphy and faunal compositions among all the major tectonic blocks in the qinghai tibet plateau are synthesised based on published literature authors unpublished data and field observations palaeobiogeographically the permian marine faunas in the qinghai tibet plateau can be assigned to four biotic provinces cathaysian indoralian cimmerian and himalayan provinces as well as a broad south transitional zone for parts of the permian the qamdo block clearly belongs to the cathaysian province as it is characterised by a lack of glacial deposits and a dominance of warm water faunas during the whole permian the qiangtang block lhasa block and the himalaya tethys zone in southern tibet can be grouped into the south transitional zone during the cisuralian which is characterised by the combination of the bivalve eurydesma the brachiopods cimmeriella bandoproductus and the fusuline monodiexodina the south transitional zone gave birth to the cimmerian province as shown in the qiangtang and lhasa blocks from roadian to capitanian during which its faunas were characterised by an admixture of cold and warm water elements supplemented by a limited number of endemic taxa such as the fusuline eopolydiexodina the non fusuline foraminifer shanita hemigordiopsis assemblage and the coral thomasiphyllum the formation and development of the south transitional zone and the cimmerian province is interpreted to be closely linked to and driven by the northward drift of the cimmerian continent superimposed with a gradual global warming in the wake of gondwanan deglaciation the consequently combined effects of these events forced the climate of the drifting peri gondwana blocks to ameliorate and its marine faunas to transform from an essentially cold water gondwanan type in the early cisuralian through a transitional stage to a predominantly warm water cathaysian type by the lopingian the himayala tethys zone in southern tibet is assigned to the himalayan province from late guadalupian to lopingian and identified by persistent occurrences and dominance of cold water brachiopods and corals both the permian sedimentary sequences and faunal successions are strongly different between the qamdo block and the qiangtang block this is taken to suggest that the longmu co shuanghu lancangjiang suture between the two blocks most likely represents the main branch of the palaeotethys suture in tibet a comparison and correlation of permian sequences and faunas between tibetan blocks and adjacent blocks in western yunnan indicates that the qiangtang block should be aligned with the baoshan block whereas the lhasa block more closely related to the tengchong block further comparison and correlations of permian stratigraphy and faunas of all major peri gondwana blocks suggest that they probably constituted three different continental slices rather than one as perceived in some previous literature the first slice is composed of central pamir the qiangtang block and the baoshan block the second slice consists of south pamir karakorum south afghanistan central iran and turkey these two continental slices are both characterised by a continuously active rifting event from artinskian to guadalupian by contrast the third slice is interpreted to consist of the lhasa block the tengchong block and the sibumasu block none of which has late cisuralian rift related basalts the baoshan block and the lhasa block are thought to have initially early cisuralian intersected probably at a triple junction point close to western australia and were then rifted off from gondwana at different times during the permian

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

complementary slip distributions of the largest earthquakes in the 2012 brawley swarm imperial valley california we investigate the finite rupture processes of two m 5 earthquakes in the 2012 brawley swarm by joint inversion of nearby strong motion and high rate gps data waveform inversions up to 3 hz were made possible by using a small event m w3 9 for path calibration of the velocity structure our results indicate that the first m w5 3 event ruptured a strong concentrated asperity with offsets of 20 cm centered at a depth of 5 km the subsequent m w5 4 event occurred 1 5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event the second event has a longer rise time and weaker high frequency energy release compared to the m w5 3 event both events display strong rupture directivity toward the southwest and lack of very shallow 2 km coseismic slip the hypocenters for these events appear to be near or in the bedrock but most of the slip is distributed at shallower depths 6 km and can explain a large part of the gps offsets for the swarm the complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets

late jurassic climate and its impact on carbon cycling abstract the climate of the late jurassic has been characterized by high atmospheric co2 levels and by a monsoonal rainfall pattern in this study we traced the evolution of the global carbon cycle through the late jurassic with the help of carbonate carbon isotope stratigraphy the oxfordian tithonian 13c curve is marked by one major positive carbon isotope excursion with an amplitude 13 c 1 0 middle to late oxfordian and a second minor positive excursion with an amplitude 13 c late kimmeridgian the early kimmeridgian and early tithonian 13c values fluctuate around 13 c 2 0 3 and contrast with the less positive 13c values of early oxfordian and late tithonian age 13 c 1 0 5 a comparison of the late jurassic carbonate carbon isotope curve with the occurrence of organic rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the c isotope record the oxfordian c isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level however episodes of enhanced organic carbon burial during the kimmeridgian and early tithonian are not reflected by prominent spikes in the c isotope record favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the c org c carb burial ratio and hence maintained the 13c record at steady but relatively positive values the middle and late tithonian c isotope values drop below 13 c 1 5 a similar shift to less positive c isotope values was recognized in other c isotope records from the tethys and atlantic oceans and reflects a decrease in the c org c carb burial ratio possibly related to a reorganisation of the global climate system globally widespread marine black shale mature quartzose sandstone assemblages suggest that the relative efficiency of the late jurassic carbon pumps was controlled by weathering erosion and runoff causing widespread marine eutrophication eutrophication favoured the organic carbon pump but it diminished the carbonate platform growth potential the monsoonal rainfall distribution pattern may explain why late jurassic carbonate platforms experienced less severe growth crises than early cretaceous carbonate platforms

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

spatiotemporal evolution of slow slip events in a nonplanar fault model for northern cascadia subduction zone slow slip events sses are identified as the quasi stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones in the well instrumented cascadia margin a class of mw6 0 slow slip events arise beneath port angeles every 14 months as inferred from two decades of continuous geodetic monitoring the along strike bending of the incoming oceanic plate beneath north washington is a unique geometric feature whose influence on slow slip processes is still unknown here we incorporate a realistic fault geometry of northern cascadia in the framework of rate and state dependent friction law to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault the modeled sses capture the major characteristics revealed by gps observations the central 150 km long fault segment beneath port angeles acts as a repetitive slip patch where sses appear every 1 5 years with a maximum slip of 2 5 cm two minor slip patches with smaller areas and cumulative slips straddle this central slip patch the along strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone suggesting strong geometrical control on the slow slip process this correlation holds even after removing the effect of w h ratio between velocity weakening sse fault width and characteristic nucleation size besides the gps detectable fast spreading phase we find that each sse cycle consists of deep pre sse preparation and post sse relaxation phases which may be the driving mechanism for the deep tremor activity between major sse episodes discovered in cascadia

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

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

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses