active deformation to the north of the altyn tagh fault constraints on the northward growth of the northern tibetan plateau abstract sinistral transpressive deformation occurs in the region north of the altyn tagh fault due to the indo eurasian collision in this region several late cenozoic faults have developed and the sanweishan fault is the key feature with clear landforms in this study slip rate measurements combined with several dating methods imply that the sanweishan fault has been active with sinistral strike slip rates of 0 33 0 04 mm a since 14 ka bp and 0 28 0 03 mm a since 20 ka bp which are more than an order of magnitude smaller than that of the atf to the south the horizontal displacements are 1 7 5 5 m in the eastern segment and 25 0 76 0 m in the middle and western segments of the sanweishan fault the increment of horizontal displacement along the main sanweishan fault is 3 0 4 0 m between paleoearthquakes and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to m 7 2 7 5 the whole length of the sanweishan fault is 360 km or longer which include active faults in the yangguan and danghe reservoirs in the west more components of thrusting occur on the western and eastern segments of the sanweishan fault the growth of the sanweishan fault is similar to that of the atf but the former fault is younger and its slip rate is much smaller the differential slip rates on the sanweishan fault and atf may result in the clockwise rotation and eastward movement of the intervening block which compresses regions to the northeast

the late quaternary slip rate of the har us nuur fault mongolian altai from cosmogenic 10be and luminescence dating the altai range western mongolia accommodates nne ssw shortening across the northern india eurasia collision zone by dextral slip on faults trending nnw sse and anticlockwise vertical axis rotations of fault bounded blocks however fault slip rates and the way in which faulting evolves over time are poorly understood and form the motivation for this study we focussed on the har us nuur fault a major transpressional fault bounding the eastern margin of the altai three abandoned alluvial fan surfaces each displaced right laterally by the fault were targeted for dating with cosmogenic 10be and quartz optically stimulated luminescence osl the first surface a2 shows an exponential decrease in 10be with increasing depth with a significant inherited component modelling this profile yielded a minimum age of 74 1 ka material from the same sampling pit was dated at 19 ka with osl but we consider this younger age to be incorrect possibly due to feldspar contamination or abnormal quartz osl characteristics the a2 surface is displaced by 175 m implying a maximum dextral slip rate of 2 4 0 4 mm yr 1 a second fan surface f1 was dated at 6 ka with osl and shows little variation in 10be with depth consistent with this young age the inherited component is higher than for a2 indicating contrasting levels of inheritance for different periods of fan aggradation a final surface f2 shows scattered 10be concentrations and lacks material suitable for osl so cannot be dated precisely using the total vertical displacement across the fault we place the initiation of movement on the fault at 2 ma significantly later than the late oligocene to miocene 28 5 ma onset of shortening in the altai region this suggests that deformation in the altai has widened over time to incorporate new faults at the range margins such as har us nuur possibly because older faults in the range interior have rotated about vertical axes into orientations that require work to be done against gravity

aridification of central asia and uplift of the altai and hangay mountains mongolia stable isotope evidence central asia has become increasingly arid during the cenozoic though the mechanisms behind this aridification remain unresolved much attention has focused on the influence and uplift history of the tibetan plateau however the role of ranges linked to india asia convergence but well north of the plateau including the altai sayan and hangay in creating the arid climate of central asia is poorly understood today these ranges create a prominent rain shadow effectively separating the boreal forest to the north from the deserts of central asia to explore the role of these mountains in modifying climate since the late eocene we measured carbon and oxygen stable isotopes in paleosol carbonates from three basins along a 650 km long transect at the northern edge of the gobi desert in mongolia and in the lee of the altai and hangay mountains we combine these data with modern air parcel back trajectory modeling to understand regional moisture transport pathways at each basin in all basins 13c increases with the largest increase in western mongolia the first 13c increase occurs in central and southwestern mongolia in the oligocene 13c again increases from the upper miocene to the quaternary in western and southwestern mongolia we use a 1 d soil diffusion model to demonstrate that these 13c increases are linked to declines in soil respiration driven by dramatic increases in aridity using modern day empirical relations between mean annual precipitation and soil respiration we estimate that precipitation has likely more than halved over the neogene given the importance of the hangay and altai in steering moisture in mongolia we attribute these changes to differential surface uplift of the hangay and altai surface uplift in the hangay began by the early oligocene blocking siberian moisture and aridifying the northern gobi in contrast surface uplift of the altai began in the late miocene blocking moisture from reaching western mongolia thus the northern gobi became increasingly arid east to west since the late eocene likely driven by orographic development in the hangay during the oligocene and the altai in the late miocene through pliocene

tectonometamorphic evolution of an intracontinental orogeny inferred from p t t d paths of the metapelites from the rehamna massif morocco new petrographic and microstructural observations mineral equilibria modelling and u pb monazite geochronological studies were carried out to investigate relationship between deformation and metamorphism across the rehamna massif moroccan variscan belt in this area typical barrovian muscovite to staurolite zones developed in cambrian to carboniferous metasedimentary rocks that are distributed around a dome like structure first assemblages are characterized by the presence of locally preserved andalusite followed by prograde evolution culminating at 6 kbar and 620 c in the structurally deepest staurolite zone rocks this barrovian sequence was subsequently uplifted to supracrustal levels heterogeneously reworked at greenschist facies conditions which was followed locally by static growth of andalusite indicating heating to 2 5 4 kbar and 530 570 c the 206pb 238u monazite age of 298 3 4 1 ma is interpreted as minimum age of peak metamorphic conditions whereas the ages of 275 8 1 7 ma and 277 0 1 1 ma date decompression and heating at low pressure in agreement with previous dating of permian granitoids intruding the rehamna massif the prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust s1 horizontal schistosity the horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing n s compression the re heating of the massif follows late massive e w shortening refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of permian granitoids we argue that metamorphic evolution of the rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental gondwanan plate the tectonometamorphic history of the rehamna massif is put into palaeozoic plate tectonic perspective and late carboniferous reactivation of devonian early carboniferous basins formed during stretching of the north gondwana margin and formation of the palaeotethys ocean the inherited heat budget of these magma rich basins plays a role in the preferential location of this intracontinental orogen it is shown that rapid transition from lithospheric stretching to compression is characterized by specific ht type of barrovian metamorphism which markedly differs from similar barrovian sequences along palaeozoic plate boundaries reported from variscan europe this article is protected by copyright all rights reserved

progressive development of the buyuk menderes graben based on new data western turkey oblique and normal fault systems exposed in the buyuk menderes graben bmg region record two successive and independent complex tectonic events the first group tectonic event is defined by an e w extension related to n s contraction and transpression this group is responsible for the development of nw and ne trending conjugate pairs of oblique faults which controlled early middle miocene basin formation between the early middle miocene and plio quaternary strata exists an unconformity indicating a period of folding uplift and severe erosion associated with n s shortening the second group of events was the change in tectonic regime from e w extension to n s extension which controlled the formation of the buyuk menderes graben by three progressive pulses of deformation the first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the menderes massif mm with the development of the e trending buyuk menderes detachment fault bmdf the minimum age of this pulse is constrained by the older plio quaternary fluviatile deposits of the buyuk menderes graben that range in age from the plio pleistocene boundary interval to late pleistocene the second pulse which is marked by the rapid deposition of alluvial deposits initiated the formation of approximately e w trending high angle normal faults synthetic and antithetic to the buyuk menderes detachment fault on the northern margin during holocene times these faults are interpreted as secondary steeper listric faults that merge with the main buyuk menderes detachment fault at depth the third pulse was the migration of the buyuk menderes graben depocentre to the present day position by diachronous activity of secondary steeper listric faults these steeper faults are the most seismically active tectonic elements in western turkey according to the stratigraphic and structural data the n s extension in the buyuk menderes graben region produced a progressive deformation phase with different pulses during its plio quaternary evolution with migration of deformation from the master fault to the hangingwall the formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the buyuk menderes detachment fault hence the southward migration of the deformation and of the buyuk menderes graben depocentre should be related to the evolution of detachment in the region the presence of the seismically active splays of secondary faults implies an active detachment system in the region this young plio quaternary n s extension in the buyuk menderes graben may be attributed to the combined effects of the two continuing processes in aegean region the first process is back arc spreading or probably the roll back of african slab below the south aegean arc which seems to be responsible for the change in the stress tensor from e w extension to n s extension the second and later event is the southwestward escape of the anatolian block along its boundary fault that is the north anatolian fault naf

palaeomagnetism and 40ar 39ar geochronology of upper palaeogene volcanic rocks from central tibet implications for the central asia inclination anomaly the palaeolatitude of tibet and post 50 ma shortening within asia summary palaeomagnetic results from upper palaeogene volcanics from three localities in the qiangtang terrane of central tibet record a maximum likelihood palaeolatitude of 28 7 3 7 n these are the first volcanic based palaeomagnetic results from the plateau interior that appear to average secular variation well enough to yield a reliable palaeolatitude estimate this palaeolatitude estimate is significantly lower than the 36 3 n predicted for central tibet by late palaeogene eurasia reference poles consistent with the so called central asia inclination anomaly but it is consistent with values predicted from upper palaeogene reference poles for mongolia the mean inclination of coeval sedimentary rocks from central tibet is 15 5 shallower than our volcanic results similar to the magnitude of sedimentary inclination shallowing estimated from elongation inclination analysis of remanent directions in clastic rocks from the same region we conclude that most of the inclination anomaly observed in volcanic rocks and that which remains after removal of sedimentary flattening in clastic rocks probably is due to the combined effect of reference poles that are not representative of stable asia and by cenozoic intracontinental shortening within central asia on the order of several hundred not more than 1000 kilometers our compilation of palaeomagnetic data from the qiangtang terrane further suggest that the southern margin of the lhasa terrane the southern margin of pre india asia was located as far south as 20 n throughout eocene time these palaeolatitudes in conjunction with the upper crustal shortening record for asia indicate that only approximately one third of the post 50 ma india asia convergence is partitioned in asian lithosphere low latitudes also imply that much of the proto tibetan plateau occupied southerly tropical to subtropical latitudes which has important implications for the weathering and erosion of the tibetan plateau palaeoaltimetry proxies and early cenozoic climate dynamics

the oyut ulaan volcanic group stratigraphy magmatic evolution and timing of carboniferous arc development in se mongolia abstract the palaeozoic mesozoic tectonic evolution of central asia including the vast terrane collage that makes up mongolia has been a topic of considerable debate the oyut ulaan volcanic group is a sequence of volcanic and sedimentary rocks in se mongolia that forms the southern part of the devonian permian saykhandulaan inlier fieldwork traverses and mapping have established four distinct formations in the oyut ulaan volcanic group that record the nature of arc activity in part of the central asian orogenic belt during the carboniferous physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles 1 periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps 2 highly effusive plateau andesite volcanism 3 explosive rhyolitic effusion geochemical analyses of volcanic lithologies suggest that the group represents subduction related mature continental arc volcanism geochemical results document an evolving magma system to which surface processes of the volcano sedimentary model may be linked magma pulses and replenishments are identified from variations in chemostratigraphy newly obtained zircon ages from the volcanic succession fix its emplacement eruption at 323 0 0 7 ma mid carboniferous or late mississippian a granite cobble from the lower part of the oyut ulaan volcanic group gives a u pb zircon age of 338 9 0 4 ma indicating that arc plutons were emplaced 10 ma prior to the oyut ulaan volcanism and were eroded soon after our work provides timing constraints for final accretion and continental assembly in se mongolia and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen

interference of lithospheric folding in western central asia by simultaneous indian and arabian plate indentation abstract large scale intraplate deformation of the crust and the lithosphere in central asia as a result of the indentation of india has been extensively documented in contrast the impact of continental collision between arabia and eurasia on lithosphere tectonics in front of the main suture zone has received much less attention the resulting neogene shortening and uplift of the external zagros alborz kopeh dagh and caucasus mountain belts in iran and surrounding areas is characterised by a simultaneous onset of major topography growth at ca 5 ma at the same time subsidence accelerated in the adjacent caspian turan and amu darya basins we present evidence for interference of lithospheric folding patterns induced by the arabian and indian collision with eurasia wavelengths and spatial patterns are inferred from satellite derived topography and gravity models the observed interference of the patterns of folding appears to be primarily the result of spatial orientation of the two indenters differences in their convergence velocities and the thermo mechanical structure of the lithosphere west and east of the kugitang tunka line

gps measurements of crustal deformation in the baikal mongolia area 1994 2002 implications for current kinematics of asia 1 we present new geodetic results of crustal velocities over a large part of northern asia based on gps measurements in the baikal rift zone and mongolia spanning the 1994 2002 period we combine our results with the gps velocity field for china of wang et al 2001 and derive a consistent velocity field for most of asia we find contrasted kinematic and strain regimes in mongolia with northward velocities and n s shortening in westernmost mongolia but eastward to southeastward motion and left lateral shear for central and eastern mongolia this eastward to southeastward motion of central and eastern mongolia is accommodated by left lateral slip on the e w trending tunka bolnay and gobi altay faults 2 1 2 mm yr 1 2 6 1 0 mm yr 1 and 1 2 mm yr 1 respectively and by about 4 mm yr 1 of extension across the baikal rift zone consequently 15 of the india eurasia convergence is accommodated north of the tien shan by n s shortening combined with dextral shear in the mongolian altay and by eastward displacements along major left lateral strike slip faults in central and eastern mongolia we find a counterclockwise rotation of north and south china as a quasi rigid block around a pole north of the stanovoy belt which rules out the existence of an amurian plate as previously defined and implies 2 mm yr 1 of left lateral slip on the qinling shan fault zone

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

persistently low asian paleolatitudes implications for the india asia collision history 1 paleomagnetism provides independent paleolatitude constraints on the india asia convergence however implied cenozoic latitudinal convergence within asia thousands of km largely exceeds geologic estimates of tectonic shortening hundreds of km this discrepancy may result from a notoriously low bias in paleomagnetically determined cenozoic paleolatitudes in asia we provide here new paleomagnetic data from cenozoic mongolian volcanic rocks and from chinese paleogene sediments corrected from the depositional bias of inclination shallowing these results combined with similar asian data sets confirm that paleolatitudes are still 5 10 lower than predicted by the paleomagnetic apparent polar wander path apwp for asia between 50 and 20 ma inclination shallowing being excluded from the selected data sets we investigate the likeliness of other proposed mechanisms for this discrepancy 1 more southerly positions of asia than expected by the apwp due to apwp inaccuracies rather than eurasian non rigidity or 2 non dipolar geomagnetic field contributions fully explaining this discrepancy by only one of these mechanisms would imply either unrealistically large 10 apwp inaccuracies or unrealistically large octupolar field contributions up to 16 a combination of these mechanisms is found more likely to have produced the observed latitudinal discrepancy but their respective contributions cannot be quantified given the still relatively low amount and poor quality of cenozoic paleomagnetic data from stable cratons of asia india and europe by allowing for reasonable time dependant non dipolar contributions and a slight 5 apwp bias the latitudinal discrepancy can be resolved and the excessive amounts of intra asian shortening decrease to values in line with tectonic shortening from structural studies

mechanics of v shaped conjugate strike slip faults and the corresponding continuum mode of continental deformation v shaped conjugate strike slip faults occur widely on earth venus and mars in the solar system they commonly lie at 60 75 in map view from the maximum compressive stress 1 direction this fault pattern cannot be explained directly by the coulomb fracture criterion which predicts the formation of x shaped shear fractures at 30 from the 1 direction possible explanations of this odd fault geometry include rotation of early formed coulomb fractures or reactivation of preexisting weakness here we show that none of these mechanisms is feasible for the formation of a late cenozoic conjugate strike slip fault system in central tibet instead its initiation can be best explained by distributed deformation during the formation of two parallel and adjoining shear zones that have opposing senses of shear our suggestion is based on the current global positioning system gps velocity field in tibet which can be divided into two east trending shear zones a northern left slip zone consisting of active ene striking left slip faults and a southern right slip zone consisting of active wnw striking right slip faults the correlation between the gps strain field and the fault pattern suggests that the central tibet conjugate faults may have initiated as two sets of riedel shears in the two parallel but separate shear zones because the two east trending shear zones also experience north south contraction we refer to this mechanism of conjugate fault formation as paired general shear pgs deformation assuming a newtonian fluid the observed tibetan gps velocity field requires the paired shear zones to have formed either by gravitational spreading of the tibetan lithosphere or a horizontal shear at the base of the upper crust or mantle lithosphere we demonstrate the feasibility of the two inferred mechanisms for the formation of v shaped conjugate faults using simple sandbox experiments our paired general shear pgs model implies that the combined effect of the state of strain and the state of stress favors only one set i e riedel shear of coulomb conjugate shear fractures under general shear flow it also requires continuum deformation rather than discrete extrusion tectonics as the most dominant mode of deformation during the late cenozoic development of the central tibetan plateau

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

a mid cretaceous change from fast to slow exhumation of the western chinese altai mountains a climate driven exhumation signal abstract the chinese altai mountains in western china are bound by cenozoic transpressional strike slip faults many of which show quaternary activity to better understand how mesozoic cenozoic deformation has affected the history of exhumation and uplift of the chinese altai mountains we collected paleozoic granitoid samples for apatite fission track and apatite u th sm he thermochronology central apatite fission track ages for n 6 samples range from 68 to 104 ma whereas apatite u th sm he ages range from 56 to 272 ma for n 23 samples n 80 individual analyses across four transects in the western chinese altai our results indicate fast cooling during the late early cretaceous followed by slow cooling since thermal modeling results suggests

a low frequency airborne gpr system for wide area geophysical surveys the case study of morocco desert abstract the paper deals with development and validation of a vhf band airborne radar designed for subsurface exploration the radar system is a pulsed one and transmits a chirp pulse at the central frequency of 165 mhz with 40 mhz bandwidth a preliminary system validation has been performed by means of flight trials over morocco desert in may 2018 an ad hoc signal processing technique has been developed to produce focused images of the scene under investigation starting from raw and motion uncompensated data in particular the data processing technique is based on a microwave tomographic approach that has the novel feature to compensate the distortion effects produced by the non rectilinear motion of the aircraft based on navigation data the analysis and interpretation of the data is supported by comparison with electromagnetic simulations of the scene

neoproterozoic to paleozoic geology of the altai orogen nw china new zircon age data and tectonic evolution abstract we present a synthesis and a new account of the geological and tectonic history of the terranes of the chinese paleozoic altai orogen together with new single zircon ages for granitic and rhyodacitic rocks a central terrane consists of neoproterozoic to silurian amphibolite facies metasedimentary rocks and abundant devonian carboniferous granites the presence of precambrian basement is indicated by sinian fossils our xenocryst ages and published nd mean crustal residence ages of granites felsic arc type lavas on the southern margin of the terrane have a mean 207pb 206pb zircon age of 505 ma reflecting the time of arc volcanism and the presence of xenocysts with ages between 614 and 921 ma suggests derivation by intracrustal melting accordingly we suggest that a cambro ordovician continental magmatic arc was built on the southern margin of the central terrane by northward subduction a low grade ordovician andean type arc with a continental basement is situated above a normal fault on

revisiting the irtish tectonic belt implications for the paleozoic tectonic evolution of the altai orogen abstract the irtish tectonic belt is one of the most important suture zones in the central asian orogenic belt caob the various models invoked to explain the tectonic evolution of this belt in relation to paleozoic continental growth include 1 syn subduction strike slip duplication of a single long lived arc and 2 collision of many arcs and micro continents here we report new results from detailed field studies geochemistry and zircon u pb geochronology on the major rock units along the irtish belt both in kazakhstan and in the chinese altay our new results together with information from published data suggest that the altai mongolia terrain witnessed several episodes of subduction the junggar terrain which formed by multiple collisions of intra oceanic arcs seamounts and ophiolite suites prior to 330 ma subsequently amalgamated with the altai mongolia terrain at around 320 ma along the irtish suture zone following the clockwise rotation of the siberian craton and the n directed movement of the junggar terrain the sinistral strike slip motion along the irtish suture zone resulted in ductile shearing partial melting of the crustal material and the formation of mylonites syn tectonic migmatite and gneissic granites the sinistral strike slip deformation of the irtish suture zone culminated at ca 275 ma the diverse 275 250 ma magmatism mafic ultramafic complexes bimodal intrusives mafic and silicic dykes a type and i a type granites is related to magma pulses generated by the permian tarim mantle plume our model of multiple episodes of subduction below the altai arc is different from previous models and proposes that the subduction continued until triassic with the permian subduction under the altai arc and a late permian large scale south directed thrusting

combining insar and seismology to study the 2003 siberian altai earthquakes dextral strike slip and anticlockwise rotations in the northern india eurasia collision zone summary the 2003 september 27 m w 7 2 siberian altai earthquake was the largest to have struck the altai mountains in more than seventy years and was closely followed by two m w 6 2 and 6 6 aftershocks we use radar interferometry seismic bodywaves and field investigations to examine the source processes of these earthquakes the main shock of the initial earthquake ruptured a subvertical nw se striking dextral strike slip fault the fault was previously unrecognised although it approximately follows the southwestern boundaries of two intermontane depressions within the interior northwestern altai it has very little topographic expression a ne dipping m w 6 7 reverse subevent possibly triggered by shear waves from the main shock occurred ten seconds afterwards strike to the southeast the later m w 6 2 and 6 6 aftershocks were dextral strike slip events which contributed further to deformation in the northwest part of the fault zone however interferometric and bodywave models disagree significantly on the source parameters of the earthquakes in particular the total moment released and the dip of the fault planes trade offs of fault dip with moment and centroid depth in the bodywave modelling can account for some but not all of these discrepancies the interferometric data is unevenly distributed containing many more data points on one side of the fault zone than the other however on the basis of calculations with synthetic data we rule this out as a reason for the discrepancies in fault parameters the lower moment predicted by interferometry could be explained by the lack of coherent data close to the faulting if slip was concentrated at very shallow depths the dip yielded by the interferometric modelling might be influenced by lateral changes in elastic properties although these would also affect the bodywave solutions the earthquake sequence occurred close to recent palaeomagnetic measurements of late cenozoic anticlockwise rotations these suggest that the right lateral strike slip faulting that ruptured in the 2003 earthquakes accommodates regional nne ssw shortening by rotating anticlockwise over time the reverse subevent is a rare case of pure shortening perpendicular to the trend of the altai range

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

space geodetic investigation of the coseismic and postseismic deformation due to the 2003 mw7 2 altai earthquake implications for the local lithospheric rheology 1 we use envisat advanced synthetic aperture radar data and spot optical imagery to investigate the coseismic and postseismic deformation due to the 27 september 2003 mw7 2 altai earthquake which occurred in the chuya basin near the russia china mongolia border on the basis of the synthetic aperture radar sar and spot data we determined the rupture location and developed a coseismic slip model for the altai earthquake the inferred rupture location is in a good agreement with field observations and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data while the epicentral area of the altai earthquake is not optimal for radar interferometry in particular due to temporal decorrelation we were able to detect a transient signal over a time period of 3 years following the earthquake the signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation we find that the postearthquake interferometric sar data do not warrant poroelastic rebound in the upper crust the observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 pa s the data can be explained in terms of fault slip within the seismogenic zone on the periphery of areas with high coseismic slip most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks some shallow slip may have also occurred aseismically therefore the observed postseismic deformation due to the altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes in particular the landers and hector mine earthquakes in the mojave desert southern california the observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas

vertical axis rotation or lack thereof of the eastern mongolian altay mountains implications for far field transpressional mountain building abstract the altay mountains of western mongolia accommodate 10 20 of the current shortening of the india asia collision in a transpressive regime kinematic models of the altay require faults to rotate anticlockwise about a vertical axis in order to accommodate compressional deformation on the major strike slip faults that cross the region such rotations should be detectable by palaeomagnetic data previous estimates from the one existing palaeomagnetic study from the altay on oligocene and younger sediments from the chuya basin in the siberian altay indicate that at least some parts of the altay have experienced up to 39 8 of anticlockwise rotation here we present new palaeomagnetic results from samples collected in cretaceous and younger sediments in the zereg basin along the har us nuur fault in the eastern altay mountains mongolia our new palaeomagnetic results from the zereg basin provide reliable declinations with palaeomagnetic directions from 10 sites that pass a fold test and include magnetic reversals the declinations are not significantly rotated with respect to the directions expected from cretaceous and younger virtual geomagnetic poles suggesting that faults in the eastern altay have not experienced a large degree of vertical axis rotation and cannot have rotated 7 in the past 5 m y the lack of rotation along the har us nuur fault combined with a large amount of rotation in the northern altay fits with a kinematic model for transpressional deformation in which faults in the altay have rotated to an orientation that favours the development of flower structures and building of mountainous topography while at the same time the range widens at the edges as strain is transferred to better oriented structures thus the har us nuur fault is a relatively young fault in the altay and has not yet accommodated significant rotation

uhp metamorphism recorded by coesite bearing metapelite in the east kunlun orogen nw china the east kunlun orogen eko is the nw part of the central china orogenic belt which records the evolutionary history of the proto and palaeo tethys oceans from the cambrian to the triassic an early palaeozoic eclogite belt has been recognized in recent years which extends discontinuously for 500 km as three eclogite bearing terranes in this study we report an integrated study of zircon grains from mica schists accompanying the eclogites in terms of mineral inclusions u pb age systematics and p t conditions the presence of coesite is identified as inclusions within the metamorphic domain of zircons which provides unambiguous evidence for subducted terrigenous clastic rocks of the proto tethys ocean exhumed from coesite forming depths u pb dating of the metamorphic zircons yields a concordia age of 426 5 0 88 ma which is likely to be the time of ultrahigh pressure metamorphism in the kehete terrane p t calculations suggest that metapelite may have experienced a clockwise p t path with peak p t conditions of 685 41 c and 28 kbar and equilibrated at 482 566 c and 5 6 8 9 kbar during subsequent exhumation the high pressure ultrahigh pressure hp uhp metamorphic belt within the eko may have formed by collision between the qaidam block and the south kunlun block as a consequence of the closure of the proto tethys ocean

paleomagnetic study of cenozoic sediments from the zaisan basin se kazakhstan and the chuya depression siberian altai tectonic implications for central asia abstract this paper presents new paleomagnetic results on cenozoic rocks from northern central asia eighteen sites were sampled in pliocene to miocene clays and sandy clays of the zaisan basin southeastern kazakhstan and 12 sites in the upper oligocene to pleistocene clays and sandstones of the chuya depression siberian altai thermal demagnetization of isothermal remanent magnetization irm showed that hematite and magnetite are the main ferromagnetic minerals in the deposits of the zaisan basin stepwise thermal demagnetization up to 640 660 c isolated a characteristic chrm component of either normal or reverse polarity at nine sites at two other sites the great circles convergence method yielded a definite direction measurements of the anisotropy of magnetic susceptibility showed that the hematite bearing sediments preserved their depositional fabric these results suggest a primary origin of the chrm and were substantiated by positive fold and reversal tests the mean paleomagnetic direction for the zaisan basin d 9 i 59 k 19 95 11 is close to the expected direction derived from the apw path of eurasia j geophys res 96 1991 4029 and shows that the basin did not rotated relative to stable asia during the tertiary in the upper pliocene pleistocene sandstones of the chuya depression a very stable chrm carried by hematite was found its mean direction d 9 i 46 k 25 95 7 is characterized by declination close to the one excepted for early quaternary whereas inclination is lower in the middle miocene to lower pliocene clays and sandstones a stable chrm of both normal and reverse polarities carried by magnetite was isolated its mean direction d 332 i 63 k 31 95 4 is deviated with respect to the reference direction and implies a neogene 39 8 counterclockwise rotation of the chuya depression relative to stable asia these results and those from the literature suggest that the different amount of rotation found in the two basins is related to a sharp variation in their tectonic style predominantly compressive in the zaisan basin and transpressive in the siberian altai at a larger scale the pattern of vertical axis rotations deduced from paleomagnetic data in northern central asia is consistent with the hypothesis of a large left lateral shear zone running from the pamirs to the baikal heterogeneous rotations however indicate changes in style of faulting along the shear zone and local effect for the domains with the largest rotations

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

structural framework of a major intracontinental orogenic termination zone the easternmost tien shan china the barkol tagh and karlik tagh ranges of the easternmost tien shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range barkol and karlik tagh and lesser ranges to the north are bounded by active thrust faults that locally deform quaternary sediments major thrusts in karlik tagh connect along strike to the east with the left lateral gobi tien shan fault system in sw mongolia from a mongolian perspective karlik tagh represents a large restraining bend for this regional strike slip fault system and the entire system of thrusts and strike slip faults in the karlik tagh region defines a horsetail splay fault geometry regionally there appears to be a kinematic transition from thrust dominated deformation in the central tien shan to left lateral transpressional deformation in the easternmost tien shan this transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the nne directed maximum horizontal stress in the region and the pre existing basement structural grain which is northwesterly in the central tien shan orthogonal to sh max but more east west in the eastern tien shan acute angular relationship with sh max ar ar ages indicate that major range bounding thrusts in barkol and karlik tagh are latest permian triassic ductile thrust zones that underwent brittle reactivation in the late cenozoic it is estimated that the modern mountain ranges of the extreme easternmost tien shan could have been constructed by only 10 15 km of late cenozoic horizontal shortening

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

kilometer scale refolded folds caused by strike slip reversal and intraplate shortening in the beishan region china 1 spectacular refolded folds clearly visible from space deform permian turbidite successions in a 180 km2 fault bounded compartment within the beishan region of northwestern china the folds formed after final terrane amalgamation of the central asian orogenic belt and record an important sequence of intraplate deformation events in central asia during the late permian jurassic the fold interference patterns are dominantly type 2 refolds with kilometer scale wavelengths they are bounded to the north and south by regional e w faults with multiple displacement histories as revealed by crosscutting ductile and brittle fabrics and kinematic indicators indicating opposing senses of motion the proximity of the refolded folds to the main bounding faults strongly suggests that the fold interference structures were caused by strike slip fault reactivation and shear related bending of f1 folds combined with components of n s compression across the compartment faulting within the folded compartment is limited to an array of right lateral strike slip faults which appear to have helped accommodate room problems during the refolding event the driving force for the deformation was likely to be distant including regional block collision to the south large scale rotations between the siberian and north china cratons and plate boundary convergence along the eastern chinese margin our study demonstrates that continental interior regions characterized by terrane collages are susceptible to reactivation by distant plate margin effects and that polyphase reactivation of major strike slip and oblique slip faults can generate refolding within upper crustal basinal compartments in addition the fault bounded basin containing the refolded folds in the beishan region is surrounded by older more complexly deformed crystalline basement therefore the deformed basin sequence represents a unique compartmental archive of the permian triassic history of intraplate deformation north of tibet

devonian alaskan type ultramafic mafic intrusions and silicic igneous rocks along the southern altai orogen implications on the phanerozoic continental growth of the altai orogen of the central asian orogenic belt abstract in this contribution we have carried out an integrated study of the petrography geochronology geochemistry and mineral chemistry for the devonian alaskan type ultramafic mafic complexes and granitoids widely distributed along the southern altai orogen in order to provide a better understanding of the continental growth process and the regional tectonic evolution la icpms zircon u pb dating of three mafic samples one acidic volcanic rock sample and one granitic sample yielded the concordia ages of ca 400 ma olivine chemical compositions indicate these mafic intrusions crystallized from evolved mafic magmas and compositions of the clinopyroxene and hornblende show typical arc affinities whole rock compositions reveal their tholeiitic signature with enriched lrees and liles and intensive depleted hfses nb ta zr and hf leading to low hfse lree ratios nb la 0 1 0 4 isotopically these mafic intrusions have positive zircon e hf t 7 6 to 14 3 mostly 10 and positive whole rock e nd t 0 8 to 5 3 values which suggest that their parental magmas were derived from a time integrated depleted mantle source these features together with the presence of primary water bearing minerals biotite and or hornblende suggest that their primitive magmas were derived from a time integrated depleted lithosphere mantle which were metasomatized by fluids released from subduction slab these findings in combination with coeval voluminous granitoids and arc signature volcanic rocks indicate that the underplating of mafic magmas at the continental arc root leads to the partial melting of the continental crust it is inferred that mafic magmatic underplating in the altai orogenic belt significantly contributed to the phanerozoic vertical continental crust growth in the altai orogen

comment on tectono metamorphic evolution of the central ribeira belt brazil a case of late neoproterozoic intracontinental orogeny and flow of partially molten deep crust during the assembly of west by meira et al

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

late pleistocene slip rate of the hoh serh tsagaan salaa fault system mongolian altai and intracontinental deformation in central asia summary the mongolian altai is an intracontinental oblique contractional orogen related to the far field effects of the indo asian collision global positioning system gps data suggest that 10 15 per cent of total indo asia convergence is accommodated across this orogen the hoh serh tsagaan salaa fault system is one of several nnw sse trending oblique contractional faults acting to partition strain and accommodate shortening and dextral shear in the mongolian altai this fault zone displaces late pleistocene alluvium along the southwest piedmont of the hoh serh range in western mongolia along the central third of the fault zone strain is partitioned onto two separate strands one that accommodates nearly pure dextral shear and one that accommodates thrust motion we determined late pleistocene rates of deformation along each of the hoh serh tsagaan salaa fault strands based on differential gps surveys and cosmogenic nuclide 10be geochronology combining the measured offsets and 10be dates yields a minimum right lateral slip rate of 0 9 0 2 0 1 mm a 1 the minimum shortening rate is 0 3 0 1 mm a 1 with uplift of at least 0 1 0 1 mm a 1 resolving the shortening and dextral components of deformation yields a slip vector of 0 8 0 2 0 1 mm a 1 toward 336 this long term deformation vector is consistent with the short term strain field determined by gps in the region and indicates that 20 per cent of indo asian deformation in the mongolian altai 2 per cent of the total indo asia strain accumulation occurs along the hoh serh tsagaan salaa fault zone although rate data for other active faults in the mongolian altai are sparse our results suggest that strain may be accommodated almost exclusively on discrete structures in this intraplate tectonic setting

mongolian coal bearing basins geological settings coal characteristics distribution and resources abstract this paper presents geological settings stratigraphy coal quality petrography reserves and the tectonic history of the mongolian coal bearing basins this is based on a synthesis of the data from nearly 50 coal deposits the results of ultimate and proximate analyses and calorific value maceral composition and vitrinite reflectance data is given the coal deposits of mongolia tend to become younger from west to east and can be subdivided into two provinces twelve basins and three areas main controlling factor of coal rank is the age of the coal bearing sequences western mongolian coal bearing province contains mostly high rank bituminous coal in strata from late carboniferous the basins in southern mongolia and the western part of central mongolia have low rank bituminous coal in strata from the permian the northern and central mongolian basins contain mainly jurassic subbituminous coal whereas the eastern mongolian province has lower cretaceous lignite the carboniferous permian and jurassic coal bearing sequences were mainly deposited in foreland basins by compressional tectonic event whereas cretaceous coal measures were deposited in rift valleys caused by extensional tectonic event petrographically mongolian coals are classified as humic type vitrinite huminite groups of carboniferous permian and cretaceous coal range from 44 9 to 82 9 inertinite group varies between 15 0 and 53 3 but liptinite group does not exceed more than 7 jurassic coals are characterized by high percentages of vitrinite 87 3 to 96 6 and liptinite groups up to 11 7 this might be explained by paleoclimatic conditions mongolian coal reserves have been estimated to be 10 2 billion tons of which a predominant portion is lignite in the eastern mongolian province and coking coal in the south gobi basin

active intracontinental transpressional mountain building in the mongolian altai defining a new class of orogen abstract mountain ranges that are actively forming around the western and northern perimeter of the indo eurasia collisional deformational field such as the mongolian altai comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens late cenozoic uplift and mountain building in the mongolian altai is dominated by regional scale dextral strike slip faults that link with thrust and oblique slip faults within a 300 km wide deforming belt sandwiched between the more rigid junggar basin block and hangay precambrian craton dominant orogenic elements in the mongolian altai include double restraining bends terminal restraining bends partial restraining bends single thrust ridges thrust ridges linked by strike slip faults and triangular block uplifts in areas of conjugate strike slip faults the overall pattern is similar to a regional strike slip duplex array however the significant amount of contractional and oblique slip displacement within the range and large number of historical oblique slip seismic events renders the term transpressional duplex more accurate intramontane and range flanking basins can be classified as ramp basins half ramp basins open sided thrust basins pull apart basins and strike slip basins neither a classic fold and thrust orogenic wedge geometry nor a bounding foredeep exists the manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown however crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late cenozoic regional epeirogenic uplift in the russian altai and sayan regions

metacraton nature genesis and behavior article i nfo in this paper we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events leading to the transformation of their margins in some cases craton interiors can also be shaped by intense collisional processes leading to the generation of intra cratonic orogenic belts we propose to call these events metacratonization and the resulting lithospheric tract metacraton metacratons can appear similar to typical orogenic belts i e active margin transformed by collisional processes but are actually sharply different their main distinctive characteristics not all are present in each metacraton are 1 absence of pre collisional events 2 absence of lithospheric thickening high pressure metamorphism being generated by subduction leading to high gradient in strain and meta morphic intensity 3 preservation of allochthonous pre collisional oceanic terranes 4 abundant post collisional magmatism associated with shear zones but not with lithospheric thickening 5 presence of high temperature low pressure metamorphism associated with post collisional magmatism 6 intraconti nental orogenic belts unrelated to subduction and oceanic basin closures reactivation of the rigid but fractured metacratonic lithosphere will cause doming asthenospheric volcanism emplacement and mineral izations due to repetitive mineral enrichments this paper provides several geological cases exemplifying these different metacratonic features in scandinavia sahara central africa and elsewhere a special focus is given to the saharan metacraton because it is where the term metacraton originated and it is a vastly ex panded tract of continental crust 5 000 000 km 2

the role of intracontinental deformation in supercontinent assembly insights from the ribeira belt southeastern brazil neoproterozoic west gondwana in this study we challenge the multiple collision model for the tectonic evolution of the neoproterozoic ribeira belt in southeastern brazil new u pb shrimp data reveal palaeoproterozoic 2153 15 ma and cryogenian 783 6 and 768 8 ma granitic rocks in the embu domain and detrital zircon data of metasedimentary units from the embu and costeiro domains suggest a coherent tectonic evolution for the whole ribeira belt rather than by multiple collisions these data are best explained by a simpler tectonic model involving continent craton volcanic arc collisions in the dom feliciano and brasilia belts that led to intracontinental crustal thickening of the adjacent thinned hinterland ribeira belt at 640 610 ma followed by widespread post collisional magmatism and rift related sedimentation at 600 540 ma we suggest that intracontinental orogeny is a relevant process during supercontinent assembly as illustrated here by the evolution of significant parts of the brasiliano orogen

repeated large magnitude earthquakes in a tectonically active low strain continental interior the northern tien shan kyrgyzstan the northern tien shan of kyrgyzstan and kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries to assess the significance of such a pulse of strain release in a continental interior it is important to analyze and quantify strain release over multiple time scales we have undertaken paleoseismological investigations at two geomorphically distinct sites panfilovkoe and rot front near the kyrgyz capital bishkek although located near the historic epicenters both sites were not affected by these earthquakes trenching was accompanied by dating stratigraphy and offset surfaces using luminescence radiocarbon and 10be terrestrial cosmogenic nuclide methods at rot front trenching of a small scarp did not reveal evidence for surface rupture during the last 5000 years the scarp rather resembles an extensive debris flow lobe at panfilovkoe we estimate a late pleistocene minimum slip rate of 0 2 0 1 mm a averaged over at least two probably three earthquake cycles dip slip reverse motion along segmented moderately steep faults resulted in hanging wall collapse scarps during different events the most recent earthquake occurred around 3 6 1 3 kyr ago 1 with dip slip offsets between 1 2 and 1 4 m we calculate a probabilistic paleomagnitude to be between 6 7 and 7 2 which is in agreement with regional data from the kyrgyz range the morphotectonic signals in the northern tien shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer term coevolution of topography and seismogenic processes in similar structural settings worldwide

seismic anisotropy and mantle flow beneath the baikal rift zone seismic studies have shown that continental rifts such as lake baikal and the great rift valley of east africa are like mid ocean rifts in that they lie above broad regions of asthenospheric upvvarp of much greater extent than the surface expression of rifting1 4 the direction of mantle flow in such regions can be investigated using the seismic anisotropy created by flow induced orientation of mantle olivine crystals5 8 seismic studies of the mid atlantic ridge have revealed upwelling mantle flow beneath the ridge and flow normal to the ridge axis on either side8 10 here we present results from an array of seismic stations across the baikal rift zone in southern siberia the splitting in arrival times of sks seismic waves indicates that the upper mantle beneath the rift zone is anisotropic with the fast direction which reflects the direction of mantle flow being horizontal and normal to the rift axis this suggests that the broad upwarp associated with this continental rift is caused by similar mantle flow to that at mid ocean rifts this may help to elucidate the processes involved in continental rifting

upper mantle flow beneath and around the hangay dome central mongolia mongolia represents the northernmost area affected by the india asia collision and it is actively deformed along transpressive belts closely associated with large scale strike slip faults the active and past mantle flow beneath this region is however poorly known in order to investigate deep mantle deformation beneath central mongolia and its relation with the surrounding major structures such as the siberian craton the gobi altay belt and the baikal rift a ns trending profile of broadband seismic stations has been deployed in the summer 2003 from the southern siberian craton to the gobi altay range crossing the entire hangay dome mantle flow is deduced from the splitting of teleseismic shear waves such as sks phases in eastern mongolia the permanent station uln in ulaanbaatar reveals the presence of two anisotropic layers the upper one being oriented ne sw close to the trend of lithospheric structures and the lower one nw se close to the trend of eurasia absolute plate motion along the ns profile in central mongolia seismic anisotropy deduced from sks splitting reveals a homogeneous nw se trending structure fully consistent with the observations made in the altay sayan in western mongolia the observed delay times of 1 5 to more than 2 0 s favor consistent mantle flow over large mantle thicknesses since the lithosphere is less than 100 km thick beneath central mongolia and since the observed fast directions are parallel to the trend of the lithospheric structures but also close to the trend of the absolute plate motion we propose that both the lithosphere and the asthenosphere may join their anisotropic effects beneath central mongolia to explain the large delay times although gps vectors represent the instantaneous displacement of the earth s surface and sks splitting the time and vertical integration of finite strain at depth we use the opportunity of the dense geodetic measurements available in this region to discuss the anisotropy pattern in term of present day deformation in the eurasia fixed reference frame gps and sks both depict a similar trend beneath central mongolia suggesting a lithospheric block escaping toward the east that could orient olivine a axes in the upper mantle within a transpressive tectonic regime a different behaviour is observed in western mongolia the gps vectors trend ns close to the regional compression direction whereas the fast sks directions trend ew suggesting a tectonic regime close to a mode of axial shortening generating the development of an ew trending foliation at depth we therefore propose that mongolia is a place where active and frozen lithospheric deformation may add their effects together with the sublithospheric flow in the three sources of anisotropy inferred a fundamental role is played by the siberian craton that acted as an undeformable core of the continent through time the frozen paleozoic and mesozoic structures wrap around the craton building up the fast anisotropic direction pattern the present day sublithospheric flow induced by the plate motion is likely deflecting around its deep roots finally the present day tectonic regime appears to be controlled by the presence of the craton to the north

the intraplate character of supercontinent tectonics abstract for several decades geoscientists have recognised intraplate tectonic activity far from plate margins both from modern and ancient examples this apparent disconnect with the drivers of plate tectonics does not necessarily imply unconnected processes but rather an uncertainty in understanding exactly how these systems operate are the driving forces derived locally or do they propagate from plate margins how do these forces interact with a complex tectonic inheritance to generate the observed tectonism furthermore what novel approaches have been applied to understand these processes here we review the general literature and the contents of this special issue to develop some partial answers to these questions key observations include the critical importance of local lithospheric heterogeneities as a control on the mode of orogenesis and also the role of locally derived forces from mantle upwelling or from depositing thick piles of magmatic or sedimentary rocks these processes happen within the overarching tectonic setting provided by far field plate margins which show intimate links in both time and observed processes with many intraplate regions these insights would not be possible without a growing arsenal of geological geophysical and numerical methods that can be applied to intraplate regions and this is reflected in the varied approaches within the issue we envisage that this special issue will provide a stimulus for further progress in understanding intraplate tectonics

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

strain indicators and magnetic fabric in intraplate fault zones case study of daroca thrust iberian chain spain abstract anisotropy of magnetic susceptibility ams has been applied to the study of shallow fault zones although interpretation of the results requires establishing clear relationships between petrofabric and magnetic features magnetic behaviour of fault rocks and an extensive knowledge of p t conditions in this work we demonstrate that magnetic methods can be applied to the study of heterogeneous fault zones provided that a series of requisites are met a major fault zone within the iberian plate daroca thrust showing transpressional movements during cenozoic time was chosen for this purpose because of the exceptional outcrops of fault gouge and microbreccia and its relevance within the context of the northeastern iberian plate magnetic fabrics were analysed and the results were compared with foliation and s c structures measured within the fault zone clay mineral assemblages suggest maximum burial depths shallower than 2 km

evidences for a noachian hesperian orogeny in mars a number of tectonic structures have been located at the thaumasia plateau daedalia planum and aonia terra mars they include isolated folds with axial traces up to 200 km long trains of tightly folded structures tens of km long and thrusts their size and geometry are similar to those on earth and the direction of compression seems to have varied amply with time suggesting a complex tectonic evolution crater counts on the deformed terrain point to noachian to early hesperian ages on the basis of the geometry and geological relations of these structures we propose that they form part of an old martian orogen the thaumasia aonia orogen which embraced not only the thaumasia plateau but areas of daedalia planum aonia terra and nereidum montes as well a regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere

uplift age and rates of the gurvan bogd system gobi altay by apatite fission track analysis abstract the dating of the uplift onset of the mongolian mountain ranges the northernmost relief associated with the india eurasia convergence is a fundamental issue to better understand the mechanisms of propagation of the cenozoic transpressive deformation in central asia using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the gurvan bogd system in the gobi altay since the middle mesozoic to the late cenozoic the region was firstly affected by a lower middle jurassic tectonic phase characterized by a vertical crustal movement larger than 2 km then followed a protracted period without major crustal vertical movements until the last uplift phase the peneplanation of the jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 ma this same surface corresponds to the present summit plateaux of the massifs standing about 2000 m above the surrounding region which corresponds to the vertical movement produced by the ongoing uplift modelling of fission track data from the massifs of ih bogd and baga bogd shows that this uplift phase probably started at 5 3 ma the gobi altay mountain range appears therefore as one of the youngest mountain ranges in central asia which is consistent with the idea of a northward propagation of the transpressional deformation from the himalayan front to the siberian craton the cenozoic uplift rate of the massifs is estimated to be between 0 25 and 1 mm yr which is slightly higher than the upper pleistocene vertical slip rates of the bordering faults this suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

strike slip deformation reflects complex partitioning of strain in the nankai accretionary prism se japan abstract previous studies have suggested predominant extensional tectonics acting at present on the nankai accretionary prism nap and following a parallel direction to the convergence vector between the philippine sea and amur plates however a complex set of thrusts pop up structures thrust anticlines and strike slip faults is observed on seismic data in the outer wedge of the nap hinting at a complex strain distribution across se japan three dimensional 3d seismic data reveal three main families of faults 1 ne trending thrusts and back thrusts 2 nnw to n trending left lateral strike slip faults and 3 wnw trending to e w right lateral strike slip faults such a fault pattern suggests that lateral slip together with thrusting are the two major styles of deformation operating in the outer wedge of the nap both styles of deformation reflect a transpressional tectonic regime in which the maximum horizontal stress is geometrically close to the convergence vector this work is relevant because it shows a progressive change from faults trending perpendicularly to the convergence vector to a broader partitioning of strain in the form of thrusts and conjugate strike slip faults we suggest that similar families of faults exist within the inner wedge of the nap below the kumano basin and control stress accumulation and strain accommodation in this latter region

cenozoic detachment folding in the southern tianshan foreland nw china shortening distances and rates abstract intracontinental foreland basins with fold and thrust belts on the southern periphery of the tianshan orogenic belt in china resulted from still active contractional deformation ultimately cased by the india asia collision to quantify the amounts of shortening distance and the rates of deformation and to decipher the architectural framework we mapped the stratigraphy and structure of four anticlines in the kuqa and baicheng foreland thrust belts in the central southern tianshan in the baicheng foreland thrust belts lower cretaceous baxigai and bashijiqike formations located in the core of the kumugeliemu anticline are overlain by the paleocene to eocene kumugeliemu formation above which are conformable oligocene through pleistocene sediments a disharmonic transition from parallel to unconformable bedding at the boundary of the miocene kangcun and pliocene kuqa formations suggests a change from pre detachment folded strata to beds deposited on top of a growing anticline most of the anticlines have steep limbs 70 90 and are box to isoclinal folds suggestive of detachment folding or faulted detachment folding faults that transect a fold core or limb shortening estimates calculated from the cross sections by the excess area method indicate that the total shortening for the kelasu kuchetawu kezile and yaken sections are 6 3 km 6 4 km 5 8 km and 0 6 km respectively and the respective depths of the detachment zones are 2 3 km and 6 9 km 2 3 km 2 5 km and 3 4 km time estimates derived from a paleomagnetic study indicate that the transition to syn folding strata occurred at 6 5 ma at the kuchetawu section along the kuqa river in addition according to our field observations and previous sedimentary rate studies the initial time of folding of the yaken anticline was at 0 15 0 21 ma therefore the average shortening rate that began at 6 ma was 2 mm a for the kelasu kuchetawu and kezile sections at 0 15 0 21 ma the average shortening rate increased to 3 4 mm a in the yaken section combined with the recent gps data the shortening rate in the central southern tianshan area increased to 4 7 1 5 mm a at present we suggest that there was a linear increase in shortening rate in the southern tianshan foreland basin which also indicates that the far field stress increased considerably from the late miocene to present in response to the india asia collision

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

acceleration and deceleration of india asia convergence since the cretaceous roles of mantle plumes and continental collision 1 a strong 50 35 ma decrease in india asia convergence is generally ascribed to continent continent collision however a convergence rate increase of similar magnitude occurred between 65 50 ma an earlier increase occurred at 90 ma both episodes of accelerated convergence followed upon arrival of a mantle plume below and emplacement of a large igneous province lip on the indian plate we here first confirm these convergence rate trends reassessing the indo atlantic plate circuits then using two different numerical models we assess whether plume head arrival and its lateral asthenospheric flow may explain the plate velocity increases and whether decreased plume flux and increasing continent plume distance may explain deceleration even without continental collision the results show that plume head arrival can indeed lead to absolute indian plate motion accelerations on the order of several cm yr followed by decelerations on timescales similar to the reconstructed fluctuations the 90 ma increase could potentially be explained as response to the morondova mantle plume alone the 65 50 ma convergence rate increase however is larger than can be explained by plume head spreading alone we concur with previous hypotheses that plume induced weakening of the indian continental lithosphere asthenosphere coupling and an increased slab pull and ridge push efficiency are the most likely explanations for the large convergence rate increase the post 50 ma decrease is best explained by orogeny related increased trench resistivity decreased slab pull due to continental subduction and possibly restrengthening of lithosphere asthenosphere coupling upon plume demise

horizontal surface slip distribution through several seismic cycles the eastern bogd fault gobi altai mongolia abstract the 1957 mw 8 1 gobi altai earthquake southern mongolia produced a 360 km long surface rupture along the eastern bogd fault cumulative offsets of geomorphic features suggest that the eastern bogd fault might produce characteristic slip over the last seismic cycles using orthophotographs derived from a dataset of historical aerial photographs acquired in 1958 we measured horizontal offsets along two thirds 170 km of the 1957 left lateral strike slip surface rupture we propose a new empirical methodology to extract the average slip for each past earthquake that could be recognized along successive fault segments to determine the slip distribution associated with successive past earthquakes our results suggest that the horizontal slip distribution of the 1957 gobi altai earthquake is fairly flat with an average offset of 3 5 m 1 3 m a combination of our lateral measurements with vertical displacements derived from the literature allows us to re assess the magnitude of the gobi altai earthquake to be between mw 7 8 and mw 8 2 depending on the depth of the rupture and related value of the shear modulus when comparing this magnitude to magnitudes derived from seismic data it suggests that the rupture may have extended deeper than the 15 km to 20 km usually considered for the seismogenic crust we observe that some fault segments are more likely than others to record seismic deformation through several seismic cycles depending on the local rupture complexity and geomorphology additionally our results allow us to model the horizontal slip function for the 1957 gobi altai earthquake and for three previous paleoseismic events along 70 of the studied area along about 50 of the fault sections where we could recognize three past earthquakes our results suggest that the slip per event was similar for each earthquake

precambrian crystalline basement in southern mongolia as revealed by shrimp zircon dating single zircon ages determined by ion microprobe shrimp ii for granitoid gneisses from the southern slope of the baga bogd massif gobi altai southern mongolia reveal several episodes of zircon growth ranging from late palaeoproterozoic to late cambrian the oldest events are documented by a zircon crystallization age for a gneiss protolith at 1519 11 ma and by a xenocrystic zircon from a dark grey augen gneiss yielding an age of c 1701 ma discrete igneous events are recorded in granite gneisses with protolith emplacement ages of 983 6 956 3 and 954 8 ma these ages provide the first record of early neoproterozoic magmatic activity in this region a much younger and discrete magmatic event is recorded by several dioritic to granitic orthogneisses which are tectonically interlayered with the older gneisses and have protolith emplacement ages between 502 and 498 ma these late cambrian granitoids of calc alkaline affinity are likely to have been emplaced along an active continental margin and suggest that the baga bogd precambrian crustal fragment was either docked against the southward present day coordinates growing margin of the caob or was a large enough crustal entity to develop an arc along its margin we speculate that the precambrian gneisses of this massif may be part of a crustal fragment rifted off the tarim craton

late holocene meghalayan palaeoenvironmental evolution inferred from multi proxy studies of lacustrine sediments from the dayan nuur region of mongolia abstract the altai tavan bogd national park located between 2000 m and 4000 m a s l in the north western part of the mongolian altai is a forest steppe ecosystem in central asia which is noticeable because of its extreme continental and high altitude conditions its vegetation is very sensitive to environmental changes and impact by nomadic people to reconstruct the dynamics of this forest steppe ecosystem a broad approach was taken employing multi proxy analyses including the analysis of pollen spores non pollen palynomorphs charcoal and diatoms as well as xrf scanning of a lacustrine sediment core of a small and shallow lake located south of dayan nuur five radiocarbon dates indicate a record spanning the last 4375 years between 4310 and 1040 cal yr bp the vegetation was characterized by a mixture of alpine meadow and moist true steppe communities as well as forested areas with larix sibirica pinus sibirica and picea obovata stands starting around 2350 cal yr bp a substantially greater and or denser forest occurrence can be inferred a marked forest decline after 1040 cal yr bp and the loss of pinus sibirica and picea obovata near the study area proceeded in accordance with a significantly higher abundance of large herbivores and a strong indication of nomadic people in the area as inferred from coprophilous fungi one period of markedly increased fire activity is found from 640 to 550 cal yr bp for the latest holocene period the records of non pollen palynomorphs and diatoms suggest a rise of the lake water level these contrasting trends of forest decline despite higher water availability may reflect the considerable human impact of the nomadic population and their cattle on the ecosystem in the altai tavan bogd national park and central asia in general

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

active faulting geometry and stress pattern near complex strike slip systems along the maghreb region constraints on active convergence in the western mediterranean the maghreb region from tunisia to gibraltar is a key area in the western mediterranean to study the active tectonics and stress pattern across the africa eurasia convergent plate boundary in the present study we compile comprehensive data set of well constrained crustal stress indicators from single focal mechanism solutions formal inversion of focal mechanism solutions and young geologic fault slip data based on our and published data analyses stress inversion of focal mechanisms reveals a first order transpression compatible stress field and a second order spatial variation of tectonic regime across the maghreb region with a relatively stable s hmax orientation from east to west therefore the present day active contraction of the western africa eurasia plate boundary is accommodated by 1 e w strike slip faulting with reverse component along the eastern tell and saharan tunisian atlas 2 a predominantly ne trending thrust faulting with strike slip component in the western tell part and 3 a conjugate strike slip faulting regime with normal component in the alboran rif domain this spatial variation of the present day stress field and faulting regime is relatively in agreement with the inferred stress information from neotectonic features according to existing and newly proposed structural models we highlight the role of main geometrically complex shear zones in the present day stress pattern of the maghreb region then different geometries of these major inherited strike slip faults and its related fractures v shaped conjugate fractures horsetail splays faults and riedel fractures impose their component on the second and third order stress regimes neotectonic and smoothed present day stress map mean s hmax orientation reveal that plate boundary forces acting on the africa eurasia collisional plates control the long wavelength of the stress field pattern in the maghreb the current tectonic deformations and the upper crustal stress field in the study area are governed by the interplay of the oblique plate convergence i e africa eurasia lithosphere mantle interaction and preexisting tectonic weakness zones

effects of fault weakening processes on oblique intracontinental rifting and subsequent tectonic inversion financial support was provided by the swiss national science foundation grant 2 77297 15

field examples of strike slip fault terminations in mongolia and their tectonic significance deformation at the ends of large intracontinental strike slip faults that do not simply link other major structures often involves rotations about a vertical axis we use earthquake slip vectors surface rupture in earthquakes and geomorphology to examine the ends of three major strike slip faults in mongolia in these places a simple pattern is seen consisting of a thrust fault on one side with a displacement that decreases away from the strike slip fault consistent with local rotational deformation strike slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area for example from dominantly strike slip to dominantly dip slip while still accommodating the overall deformation required by larger scale regional motions such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis which may be detected paleomagnetically the kind of strike slip fault termination described here may have consequences for how large strike slip fxaults evolve and grow and for the variation in displacement along their length