evolution of mesozoic sandstone compositions southern junggar northern tarim and western turpan basins northwest china a detrital record of the ancestral tian shan abstract sandstone compositional data can be a powerful tool in the interpretation of tectonic and climatologic influences on sedimentary basin fill in addition to yielding important information about porosity in sandstone petroleum reservoirs in order to explore these relationships a modified gazzi dickinson point counting technique was used to analyze the composition of 143 mesozoic sandstone samples from the southern junggar northern tarim and western turpan basins of northwestern china results indicate that a mesozoic ancestral version of the tian shan physiographically separated the junggar and tarim basins and provided sand of very different composition to each basin mesozoic sandstone from the northern tarim basin is diverse in composition and lithic rich qm41f14l45 qp42lvm26lsm32 is locally micaceous and contains common radiolarian chert grains and few dense accessory minerals inferred source rocks include upper paleozoic alkali granite and metamorphic complexes thick silurian bedded chert sequences and lower paleozoic strata of a passive continental margin in contrast sandstone from the southern junggar and western turpan basins is uniformly volcanic rich qm21f21lt58 qp13lvm68lsm19 and contains abundant dense accessory minerals and only local radiolarian chert and mica inferred principal source rocks are devonian carboniferous andesitic arc volcanics the effect of sampling scale on sandstone composition outweighs that of plate tectonic setting samples were derived mostly from medium and coarse grained fluvial systems that likely drained only portions of the ancestral tian shan and hence preserve local source rock signatures rather than an integrated compositional signal that can be directly compared to plate tectonic petrofacies models in addition though mesozoic basins of western china were most akin to broken foreland basins mesozoic sandstone is considerably more compositionally diverse and lithic rich than that of modern or ancient broken foreland basins because of the variety of accreted terranes constituting the ancestral tian shan temporal changes in sandstone composition are consistent with episodes of mesozoic deformation in the tian shan each deformational episode increased physiographic relief of the ancestral range produced renewed downcutting and erosion of source rocks and resulted in the deposition of compositionally very immature sandstone in adjacent basins although a regional early mesozoic megamonsoon and an early cretaceous rain shadow cast across the northern tarim basin are interpreted from regional facies and paleontologic data neither paleoclimatic phenomenon appears to have significantly modified sandstone composition in the study area calculations of intergranular volume porosity cement indicate that porosity in sandstone from the tarim and junggar basin depocenters was reduced principally by burial compaction and that the rate of porosity reduction was highest for lithic rich samples

formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

active tectonics of an apparently aseismic region distributed active strike slip faulting in the hangay mountains of central mongolia summary we identify and describe a series of east west left lateral strike slip faults named the songinomargats the hag nuur the uliastay and the south hangay fault systems in the hangay mountains of central mongolia an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the india eurasia collision zone the strikeslip faults of central mongolia constitute a previously unrecognized hazard in this part of mongolia each of the strike slip faults show indications of late quaternary activity in the form of aligned sequences of sag ponds and pressure ridges developed in alluvial deposits total bed rock displacements of 3 km are measured on both the songino margats and south hangay fault systems bed rock displacements of 11 km are observed across the hag nuur fault cumulative offset across the uliastay fault systems are unknown but are unlikely to be large we have no quantitative constraint on the age of faulting in the hangay the 20 km of cumulative slip on the hangay faults might at least in part be inherited from earlier tectonic movements our observations show that despite the almost complete absence of instrumentally recorded seismicity in the hangay this part of mongolia is cut through by numerous distributed strike slip faults that accommodate regional left lateral shear between siberia and china central mongolia is thus an important component of the india eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity we suggest that active faults such as those identified in the hangay of mongolia might exist in other apparently aseismic regions within continental collision zones

the thermo tectonic history of the song kul plateau kyrgyz tien shan constraints by apatite and titanite thermochronometry and zircon u pb dating abstract the song kul basin sits on a plateau at the northern and middle kyrgyz tien shan junction it is a lacustrine basin occupied by lake song kul and predominantly developed on igneous basement this basement was targeted for a multi method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present day morphology zircon u pb dating by la icp ms revealed four different magmatic episodes a late cambrian 500 ma island arc system a late ordovician 450 ma subduction related intrusion an early permian 290 ma collisional stage and a middle to late permian 260 ma post collisional magmatic pulse middle to late triassic 200 230 ma titanite fission track ages and late triassic early jurassic 180 210 ma apatite fission track ages and thermal history modeling indicate the song kul basement was already emplaced in the shallow crust at that time an exhumed fossil apatite fission track partial annealing zone is recognized in the bordering song kul mountain ranges the area experienced only minor post early mesozoic denudation the igneous basement was slowly brought to apatite u th he retention temperatures in the late cretaceous palaeogene miocene to present reactivation of the tien shan does not manifestly affect this part of the orogen

denudation and cooling of the lake teletskoye region in the altai mountains south siberia as revealed by apatite fission track thermochronology abstract lake teletskoye occupies a narrow graben located in the northwestern sector of the altai fold belt in south siberia the lake basin is thought to have formed during the pleistocene as a distant result of the cenozoic collision of india and eurasia that caused a tectonic reactivation of the palaeozoic gorny altai ga and west sayan ws blocks the present work reports of a pilot fission track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake the age length data and aft thermochronological modelling reveal two important phases of cooling in the altai mountains a first one during the late jurassic early cretaceous and a second one that started in the miocene pliocene and that persists until today the first event is interpreted to result from uplift induced denudation probably related to the closure of the mongol okhotsk ocean the second event can be linked to the young cenozoic movements that lie at the origin of the formation of the lake teletskoye basin

early cretaceous denudation related to convergent tectonics in the baikal region se siberia we present 24 new apatite fission track aft ages and 18 track length measurements from the baikal region se siberia most samples have aft ages between 140 and 100 ma with relatively high mean track lengths c 13 2 m the relationship between aft ages elevation and mean track lengths indicate that the samples record rapid cooling during the early cretaceous 140 120 ma as also shown by thermal history inversion of track length distributions cooling took place during a late jurassic early cretaceous orogenic phase related to closure of the mongol okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting basin inversion and large vertical motions the variation in aft ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role minimum amounts of early cretaceous denudation are estimated at 2 3 km

tectonic history of the kyrgyz south tien shan atbashi inylchek suture zone the role of inherited structures during deformation propagation 1 multimethod chronology was applied on intrusives bordering the kyrgyz south tien shan suture stss to decipher the timing of 1 formation and amalgamation of the suturing units and 2 intracontinental deformation that built the bordering mountain ranges zircon u pb data indicate similarities between the tien shan and tarim precambrian crust caledonian 440 410 ma and hercynian 310 280 ma zircon u pb ages were found at the edge of the stss related to subduction and closure of the turkestan ocean and the formation of the suture itself permian triassic 280 210 ma titanite fission track and zircon u th he data record the first signs of exhumation when the stss evolved into a shear zone and the adjacent tarim basin started to subside low temperature thermochronological apatite fission track zircon and apatite u th he analyses reveal three distinct cooling phases becoming younger toward the stss center 1 jurassic cretaceous cooling ages provide evidence that a mesozoic south tien shan orogen formed as a response to the cimmerian orogeny 2 early paleogene 60 45 ma data indicate a renewed pulse of stss reactivation during the early cenozoic 3 neogene ages constrain the onset of the modern tien shan mountain building to the late oligocene 30 25 ma which intensified during the miocene 10 8 ma and pliocene 3 2 ma the cenozoic signals may reflect renewed responses to collisions at the southern eurasian border i e the kohistan dras and india eurasia collisions this progressive rejuvenation of the stss demonstrates that deformation has not migrated steadily into the forelands but was focused on pre existing basement structures

water quality assessment and the investigation of the relationship between the river delice and the aquifer systems in the vicinity of yerkoy yozgat turkey the aim of this study was to investigate the pollution parameters relating to surface and groundwaters and to establish an interaction between these for the area near yerkoy three characteristic facies were determined based on the results of hydrochemical analyses 1 na cl facies were greater the deeper the aquifer 2 na so42 facies were the greater portion of the shallow alluvium aquifer and 3 na hco3 so42 facies represented the western portion of the shallow alluvium aquifer based on field and laboratory observations it was found that the water of the river delice is suitable for irrigation and domestic use whereas the water from the shallow aquifer is extremely saline and considered to have been polluted by local lithological units active groundwater circulation and dilution between the alluvium aquifer and the river delice was observed because of the short residence time of the groundwater in this area the hydrogeochemical concentration and the salinity were found to be low the other portions of the alluvium aquifer bear higher concentrations of soluble ions

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

meso cenozoic building of the northern central asian orogenic belt thermotectonic history of the tuva region abstract the tuvinian and west sayan mountain ranges form part of the central asian orogenic belt caob more specifically they align along the altai sayan hangay zone its precambrian paleozoic basement has been subjected to mesozoic and cenozoic tectonic reactivation two north south transects across the mountain belts and intervening basins of tuva were sampled for apatite fission track aft thermochronology in order to elucidate the thermal history of the tuvinian basement in relation to the mesozoic and cenozoic reactivation of the caob most aft ages are late cretaceous and range between 55 and 115 ma mean lengths of confined fission tracks are relatively long with most values between 13 and 14 m thermal history modeling shows a rapid late jurassic cretaceous cooling for the sampled tuvinian crystalline rocks related to exhumation of the paleozoic basement this exhumation is possibly related to the building and subsequent orogenic collapse of the mongol okhotsk orogen that formed between the siberian and north china mongolian sino korean or amurian continental blocks during the late mesozoic far field effects of this orogeny and its collapse might have affected the baikal altai and sayan units of the central asian orogenic belt including the tuvinian basement also at the mesozoic southern eurasian margin growth of the asian continent continued and several collision accretion events asserted distal tectonic influence into the caob after a paleogene period of stability thermal history models for some samples hint at a renewed period of basement cooling during the neogene in support of this neogene event a single sample from the main west sayan fault zone contains an apatite population with 2 ma reset aft ages this is interpreted in the framework of ongoing building of the modern central asian orogens and associated fault movements and exhumation of the basement presumably related with the ongoing india eurasia convergence

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

tertiary strike slip faulting in southeastern mongolia and implications for asian tectonics abstract geologic maps have long portrayed the late cretaceous recent geologic history of southeastern mongolia as tectonically quiescent we present new data based on outcrop observations that indicate the northeast trending east gobi fault zone egfz was reactivated in the cenozoic as a sinistral strike slip fault system inversions of cenozoic fault slip data imply that faulting was associated with north northwest subhorizontal shortening and east northeast subhorizontal extension we propose that faulting is tertiary in age based on published interpretations of seismic reflection data which reveal that the mid cretaceous 100 95 ma unconformity is deformed by strike slip faults and based on field observation of strike slip faults and fracture sets that cut upper cretaceous and cenozoic strata but lack evidence for neotectonic activity published seismicity maps also appear to argue against significant quaternary faulting within the egfz these new data may lend credence to published models proposing a middle miocene or older kinematic linkage between the egfz and the altyn tagh fault in china the recognition that the egfz has a history of left lateral displacement in both the early mesozoic and cenozoic means that currently available estimates of offset based on displaced paleozoic rocks constrain total offset only this reactivation history supports the notion that inherited lithospheric structures are important in controlling the location and thus modes of intracontinental deformation in asia as a function of collisional far field effects and evolving boundary conditions of the pacific margin

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

deposition in the kuznetsk basin siberia insights into the permian triassic transition and the mesozoic evolution of central asia abstract this paper describes the permian mesozoic stratigraphy of the kuznetsk basin southern siberia which is adjacent to the vast and hydrocarbon rich west siberian basin and on the edge of the siberian flood basalts the basin fill is permian to cretaceous in age and is dominated by non marine siliciclastics up to 7 km thick palaeocurrent indicators show dominant flow to the north northeast during the permian to jurassic fourteen lithofacies are grouped in three facies associations fluvial channel belt overbank and floodplain floodplain pond coal bearing permian siliciclastics are interpreted as meandering river deposits in a foreland basin with subsidence generated by thrust sheet loading from at least three basin margins these sediments pass abruptly but conformably upwards into coal barren sandstones and conglomerates and siltstones interpreted as braided river deposits two basalt flows occur within the coal barren succession a recently published precise ar ar age of 250 3 0 7 ma for the lower of these basalts

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

inventory of landslides and susceptibility mapping in the dessie area northern ethiopia abstract a comprehensive study of landslide processes was carried out in the city of dessie and its environs in northern ethiopia the study area consists of a graben bounded by steep fault scarps and characterized by highly weathered tertiary basaltic rocks covered with quaternary deposits a method of landslide susceptibility mapping that adapts to the area of the hillside about 16 km2 is presented first a preliminary zoning was made by dividing the area into a discrete number of smaller units having similar susceptibility to sliding followed by semi quantitative field investigation of the geological geotechnical geomorphological hydrogeological and anthropogenic factors that contribute to the susceptibility of the units to landslide activity the final landslide susceptibility map was accomplished by using classical overlay procedures of established maps representing the different influencing factors the validity of the method was checked by means of a landslide hazard map that showed the actual distribution of landslide episodes that have occurred in the past finally four broad landslide susceptibility zones and 22 specific active landslide sites were identified the most important landslide types were complex earth and debris slides and flows in silty clay soils associated with alluvial and colluvial deposits overlying highly weathered basalts intact basaltic rocks experienced rock fall and toppling in steep slope areas large scale landslides have been initiated mostly by surface water and groundwater during the wet season

geomorphic mesozoic and cenozoic evolution in the oka jombolok region east sayan ranges siberia the east sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far field effects of the india asia collision and the extension linked to the opening of the baikal rift system the active deformation that affects this range is very recent around 5 ma but occurs in a very complex morphotectonic setting and the understanding of the tertiary deformation relies entirely on a detailed knowledge of the pre deformation situation using apatite fission track thermochronology cosmogenic 10be and morphological study on tertiary lava flows we demonstrate that prior to the oligocene the morphology of the east sayan area was characterized by a wide constantly rejuvenated erosion surface apatite fission track thermal modelling indicates that this surface started to form at least in late jurassic early cretaceous 140 120 ma the long term exhumation rates several tens of million years derived from apatite fission track data 17 5 m ma and the short term erosion rates over a few hundred thousand years derived from cosmogenic 10be data 12 20 m ma are coherent implying a near constant mean erosion rate since late jurassic this constant slow erosion prevented the formation of a lateritic kaolinic weathering crust on the planation surface by oligocene early miocene times a long wavelength uplift that remains to be explained induced incision that created shallow valleys later filled by basaltic lava flows finally the present short wavelength topography initiated during the pliocene

early middle paleozoic granitoids in gorny altai russia implications for continental crust history and magma sources abstract major element and trace element compositions as well as nd isotope ratios and protolith model ages of early to middle paleozoic granitoids from the russian gorny altai are summarized and discussed in terms of the compositions and tectonic settings the observed geographic variations of compositions in the granitoid assemblages correlate with three groups of late neoproterozoic to middle paleozoic terranes corresponding to oceanic island arc and turbidite basin settings plutonic rocks in the oceanic and island arc terranes are commonly low alkali metaluminous tonalite and trondhjemite that formed by melting of oceanic crust the island arc terranes also contain tonalite trondjemite granodioritic and tonalite granodiorite granitic rocks with higher alkali and potassium contents which result from anatectic melting of volcanics and sediments granitoids in the turbidite basins are potassic peraluminous monzogranite produced by anatectic melting of upper crustal turbidites as well as subalkaline tonalite granodiorite and granite derived from upper crustal metasediments and metamorphosed mafic oceanic crust underlying the turbidite basins alkaline granitoids emplaced during two major tectonomogamatic events early and late devonian and are present in terranes of all three settings their source is of crustal origin like in other groups of granitoids but it was a mixture of crustal and mantle material thus the compositional trends of early and middle paleozoic granitoids in the gorny altai record the history of continental crust

stratigraphic and structural evolution of the selenga delta accommodation zone lake baikal rift siberia seismic reflection profiles from the lake baikal rift reveal extensive details about the sediment thickness structural geometry and history of extensional deformation and syn rift sedimentation in this classic continental rift the selenga river is the largest single source of terrigenous input into lake baikal and its large delta sits astride the major accommodation zone between the central and south basins of the lake incorporating one of the world s largest lacustrine deltas this depositional system is a classic example of the influence of rift basin structural segmentation on a major continental drainage more than 3700 km of deep basin scale multi channel seismic reflection mcs data were acquired during the 1989 russian and the 1992 russian american field programs the seismic data image most of the sedimentary section including pre rift basement in several localities the mcs data reveal that the broad bathymetric saddle between these two major half graben basins is underlain by a complex of severely deformed basement blocks and is not simply a consequence of long term deltaic deposition maximum sediment thickness is estimated to be more than 9 km in some areas around the selenga delta detailed stratigraphic analyses of the selenga area mcs data suggest that modes of deposition have shifted markedly during the history of the delta the present mode of gravity and mass flow sedimentation that dominates the northern and southern parts of the modern delta as well as the pronounced bathymetric relief in the area are relatively recent developments in the history of the lake baikal rift several episodes of major delta progradation each extending far across the modern rift can be documented in the mcs data the stratigraphic framework defined by these prograding deltaic sequences can be used to constrain the structural as well as depositional evolution of this part of the baikal rift an age model has been established for this stratigraphy by tying the delta sequences to the site of the baikal drilling project 1993 drill hole although the drill hole is only 100 m deep and the base of the cores is only 670 ka in age ages were extrapolated to deeper stratigraphic intervals using the reflection seismic radiocarbon method of cohen et al 1993 the deep prograding delta sequences now observed in the mcs data probably formed in response to major fluctuations in sediment supply rather than in response to shifts in lake level this stratigraphic framework and age model suggest that the deep delta packages developed at intervals of approximately 400 ka and may have formed as a consequence of climate changes affiliated with the northern hemisphere glaciations the stratigraphic analysis also suggests that the selenga basin and syncline developed as a distinct depocentre only during the past 2 3 ma

multi method chronometry of the teletskoye graben and its basement siberian altai mountains new insights on its thermo tectonic evolution

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

pliocene to quaternary deformation in south east sayan siberia initiation of the tertiary compressive phase in the southern termination of the baikal rift system the south east sayan area wof the lake baikal is subjected to a very complex tectonic setting where the extensional stress field of the baikal rift system meets the compressional stress field generated by the india asia collision further south using satellite images aerial photographs srtm dem field mapping of geomorphological structures and published neotectonics and geological data we show that most of the relief in the se sayan initiated during late pliocene pleistocene through compressive reactivation of inherited structures by late quaternary clockwise rotation of the compressive field generated strike slip faulting and local secondary extension still within a general compressional stress field we demonstrate that the formation of the small scale extensional basins within the east sayan range is not linked to general the extension in the baikal rift system nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history ii application to the french western alps abstract thermochronologic data collected along age elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates however thermochronologic age elevation relationships are known to be perturbed by topographic effects and potential changes in relief which are neglected in the inherently 1 d interpretation commonly applied such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging in a companion paper we develop a methodology for rigorously interpreting thermochronologic age elevation profiles in terms of exhumation rates and relief development through time and to independently quantify the resolution of these constraints here we test this approach using a thermochronological dataset consisting of apatite and zircon fission track and u th he data collected at la meije peak in the pelvoux ecrins massif french western alps our data and models suggest a three phase exhumation history in the pelvoux ecrins massif including a pulse of rapid exhumation at 6 5 5 ma preceded and followed by more moderate rates of denudation in the order of 0 3 0 4 km myr 1 this rapid exhumation event appears to occur coevally in other external crystalline massifs in the alps but is not detected by qualitative inspection of the age elevation relationships both our synthetic results and inversion of the la meije data strongly suggest that apatite fission track age elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required combining apatite fission track and u th he ages and particularly including fission track length data greatly improves the resolution of the inferred exhumation histories although denudation rates through time and the timing of rate changes are generally well resolved our data have insufficient resolution to satisfactorily constrain the relief history synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data

age and evolution of late mesozoic metamorphic core complexes in southern siberia and northern mongolia numerous cretaceous metamorphic core complexes mccs extend from transbaikalia in russia to northern mongolia within the central asian orogenic belt we investigated the buteel and zagan mccs in detail shear sense indicators in mylonitized rocks show footwall to the nw tectonic transport single zircon dating of footwall rocks in the buteel mcc establishes the emplacement of granitoid orthogneiss precursors at 240 211 ma a felsic metavolcanic rock at 265 0 1 2 ma a syenite at 265 5 1 2 ma and a metarhyolite of the pre granitoid basement at 553 6 2 9 ma a peralkaline granite intruding orthogneisses of the zagan mcc has a new u pb zircon age of 151 6 0 7 ma 40 ar 39 ar ages of 133 5 1 8 ma of hornblende from amphibolite and 122 6 1 8 ma of biotite from mylonitized gabbro dolerite of the buteel mcc are interpreted as cooling ages representing the time of deformation in the footwall geological data suggest that the mccs in transbaikalia and northern mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc alkaline magmatism in an andean type setting on the border of the closing mongol okhotsk ocean by widespread collisional to post collisional thrusting and by extensive alkaline peralkaline magmatism

competing processes of clastic deposition and compartmentalized inversion in an actively evolving transpressional basin western mongolia the dariv basin is an actively evolving intracontinental transpressional basin located on the eastern flank of the mongolian altai the basin occupies a complex tectonic position between a restraining bend a thrusted basement block and two major conjugate strike slip fault systems structures and sedimentary strata exposed within the dariv basin suggest a mesozoic and cenozoic two stage evolution jurassic cretaceous strata fine upward and record alluvial fan fluvial and lacustrine depositional environments the distribution of mesozoic sedimentary rocks and the presence of a suspected jurassic normal fault array suggest that the dariv basin initially formed as an extensional basin following palaeogene tectonic quiescence oligocene recent basin fill is dominated by alluvial fan sediments derived from basin flanking ranges the modern basin is deforming by thrusting normal fault inversion and folding along discrete belts expressed as intrabasinal ridges and domes these belts define a rhomboid of active deformation that compartmentalizes the basin sediments derived from these discrete deforming belts and from basin flanking ranges continue to accumulate in the basin centre thus modern fans contain reworked older basin fill and competing processes of sedimentation deformation erosion and resedimentation can be observed the dariv basin is an excellent example of a transpressional piggyback basin in the early stages of basin inversion and destruction

tectonic history of the irtysh shear zone ne kazakhstan new constraints from zircon u pb dating apatite fission track dating and palaeostress analysis abstract the irtysh shear zone isz is an important structure in the framework of the central asian orogenic belt caob it represents the site of final collision of kazakhstan with siberia during hercynian times and records up to 1000 km of lateral displacement during subsequent reorganization in the caob edifice we present new zircon u pb apatite fission track and fault kinematic data along the isz and consequently derived its tectonic history with emphasis on its formation and reactivation episodes carboniferous 340 320 ma zircon u pb ages were obtained for the syn and post collisional kalba narym intrusives dating their emplacement in the framework of the siberia kazakhstan collision during this period the isz experienced an early brittle left lateral mainly transtensional stress regime late carboniferous early permian post collisional intrusives were emplaced and the stress regime changed to a late brittle regime characterized by more compressional conditions indicating rheological strengthening as a response to cessation of ductile shearing and cooling of the isz crust apatite fission track data and thermal history modeling reveal late cretaceous 100 70 ma cooling of the isz basement rocks as a response to denudation of a bordering late mesozoic altai orogen after this denudation event the tectonic activity ceased during the late mesozoic early cenozoic a final step of cooling from 25 ma exhibited by some of the thermal history models may reflect reactivation of the isz and initiation of cenozoic altai mountain building the late plio pleistocene phase of mountain building coincides with a new change in the palaeostress field characterized by minor transpressional right lateral shear conditions

the mongol okhotsk belt in mongolia an appraisal of the geodynamic development by the study of sandstone provenance and detrital zircons abstract the mongol okhotsk belt formed in a late stage of jurassic orogeny in the composite central asian orogenic belt the present paper investigates the late palaeozoic mesozoic sandstones associated with the belt in mongolia aimed at reconstructing the time and mode of ocean formation subduction and collision we apply provenance analysis including 1 heavy mineral and sandstone framework grain analysis 2 u pb laser ablation icp ms dating of detrital zircons for identifying contemporaneous volcanic arc activity and the recycling of older crustal material and 3 on dated zircon grains we analyze trace element contents and hf isotopic ratios in order to characterize the rock types in which they crystallized and the magma sources respectively the investigated samples are derived from 1 the adaatsag and doschgol terranes which represent the suture zone 2 the hangai hentei belt to the northwest and 3 the ereendavaa terrane and the middle gobi volcanic belt to the southeast of the suture the latter two are concurrent with the northern and southern margins of the mongol okhotsk ocean tectono stratigraphic arguments suggest that the mongol okhotsk ocean opened during the silurian within the early palaeozoic collage in the suture zone permian syn sedimentary zircon trace element contents confirm mafic rock sources and the mantle involvement in the magmatism epsilon hf t from 13 up to 20 n and s directed bi vergent subduction developed as revealed by contemporaneous zircons 1 along the northern margin hangai hentei from silurian early carboniferous subduction and accretion prevailed epsilon hf t from 3 up to 12 in associated zircons which was re initiated during the permian and 2 the contemporaneous silurian devonian southern margin ereendavaa middle gobi still represented an extensional continental margin showing reworking of neoproterozoic early palaeozoic zircons from the basement it turned into an active continental margin with starting arc magmatism in the carboniferous zircon mean epsilon hf t 5 75

age of palaeozoic granites and metamorphism in the tuvino mongolian massif of the central asian mobile belt loss of a precambrian microcontinent abstract the tuvino mongolian massif tmm was previously interpreted as a precambrian block within the central asian mobile belt according to this idea it consists of tectonic slices composed of metamorphic rocks of pre mesoproterozoic basement that experienced two episodes of regional metamorphism and mesoproterozoic cover rocks that were reworked together with the basement during high grade metamorphism zircon u pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536 6 ma significantly later than the deposition of the cover rocks regional upper amphibolite facies metamorphism which affected all metasedimentary units of the tmm occurred in the short time interval of 497 4 to 489 3 ma we propose that there is no simple basement cover relationship in the tuvino mongolian massif instead the massif consists of tectonic domains composed of heterogeneous metasedimentary successions with distinct pre metamorphic and pre tectonic histories that were juxtaposed by thrusting prior to 497 ma and then metamorphosed under upper amphibolite facies conditions we suggest that this thrusting event was associated with early palaeozoic collisional processes related to amalgamation of the central asian mobile belt our new model for the evolution of the tmm implies derivation of neoproterozoic terrigeneous metasediments from 800 900 ma granitoids formed in an andean type active continental margin setting

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

late jurassic early cretaceous closure of the mongol okhotsk ocean demonstrated by new mesozoic palaeomagnetic results from the trans baikal area se siberia summary we present new palaeomagnetic results from the transba ikal area se siberia from the mongol okhotsk suture zone the boundary between the amuria and siberia blocks in order to better constrain the time of closure of the mongol okhotsk ocean in the mesozoic we col lected 532 rock samples at 68 sites in six localities of basalts trachy basalts and andesites from both sides of the mongol okhotsk suture at unda river j 3 51 7 n 117 4 e kremljevka peak k1 51 8 n 117 5 e and torey lakes k 1 50 1 n 115 9 e on the southern side of the suture and at monostoy river j 1 51 1 n 106 8 e ingoda river k 1 51 2 n 112 2 e and bichura town k 1 50 6 n 107 6 e on the northern side progressive thermal demagnetization enabled us to resolve low ltc and high htc temperature components of magnetization at most sites jurassic palaeopoles computed from the htcs show a large discrepancy with respect to the apparent polar wander path of eurasia which we interpret in terms of 1700 2700 km of post late jurassic northward movement of amuria with respect to siberia although ge ological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data give evidence of a large remaining palaeolatitude difference between the amuria and siberia blocks in contrast early cretaceous sites cluster remarkably well along a small circle which is centred on the average site location this implies the absence of post early cretaceous northward motion of amuria relative to siberia and demonstrates the pre early cretaceous closure of the mongol okhotsk ocean finally we interpret the very large tectonic rotations about local vertical axes evidenced by the small circle distribution of poles as arising both from collision processes and from left lateral shear movement along the suture zone due to the eastward extrusion of amuria under the effect of the collision of india into asia

thermo tectonic history of the issyk kul basement kyrgyz northern tien shan central asia abstract lake issyk kul occupies a large late mesozoic cenozoic intramontane basin between the mountain ranges of the northern kyrgyz tien shan these ranges are often composed of granitoid basement that forms part of a complex mosaic assemblage of microcontinents and volcanic arcs several granites from the terskey kungey trans ili and zhetyzhol ranges were dated with the zircon u pb method shrimp la icp ms and yield concordant late ordovician silurian 456 420 ma emplacement ages these constrain the caledonian accretion history of the northern kyrgyz tien shan in the amalgamated palaeo kazakhstan continent the ancestral tien shan orogen assembled in the early permian when final closure of the turkestan ocean ensued collision of palaeo kazakhstan and tarim a late palaeozoic structural basement fabric formed and middle late permian post collisional magmatism added to crustal growth of the tien shan permo triassic cooling 300 220 ma of the ancestral tien shan was unraveled using 40 ar 39 ar k feldspar and titanite fission track ft thermochronology on the issyk kul granitoids apatite thermochronology ft and u th sm he applied to the broader issyk kul region elucidates the meso cenozoic thermo tectonic evolution and constrains several tectonic reactivation episodes in the jurassic cretaceous and cenozoic exhumation of the studied units occurred during a protracted period of intracontinental orogenesis linked to far field effects of late jurassic cretaceous accretion of peri gondwanan blocks from the tethyan realm to eurasian following a subsequent period of stability and peneplanation incipient building of the modern tien shan orogen in northern kyrgyzstan started in the oligocene according to our data intense basement cooling in distinct reactivated and fault controlled sections of the trans ili and terskey ranges finally pinpoint important miocene pliocene 22 5 ma exhumation of the issyk kul basement late cenozoic formation of the tien shan is associated with ongoing indentation of india into eurasia and is a quintessential driving force for the reactivation of the entire central asian orogenic belt

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

timing of exhumation of the ereendavaa metamorphic core complex north eastern mongolia u pb and 40ar 39ar constraints abstract the occurrence of numerous ne sw trending rift basins that locally bound metamorphic core complexes in transbaikalia northern mongolia and north eastern china indicates that the eastern domain of the central asian orogenic belt was affected by a large scale nw se extensional tectonic event during late jurassic to early cretaceous times available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in transbaikalia 134 121 ma and north china 136 110 ma suggesting dome exhumation during the early cretaceous in north eastern mongolia the ereendavaa range lined by the onon shear zone was recently interpreted as one of these metamorphic core complexes of late jurassic to early cretaceous age on the basis of u pb zircons data from two synkinematic pegmatite dykes however this wide time range remains to be discussed the present work constrains the tectono thermal evolution of the range by providing new mc icp ms u pb zircons ages from pegmatite dykes and metamorphic igneous rocks and mica and amphibole 40 ar 39 ar laser step heating ages from metamorphic and magmatic rocks that crop out within the range the results show that 1 the ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late jurassic times 2 cooling of the range began at least at 137 9 0 3 ma as revealed by a 40 ar 39 ar plateau ages obtained from an hornblende sampled within the range core and 3 exhumation along the onon shear zone occurred from 130 3 1 9 ma down to 124 8 0 3 ma as shown by ages of most of micas and amphiboles from the shear zone these more accurate ages are consistent with metamorphic core complex ages from adjacent areas furthermore they argue for an extensional dynamic paroxysm at the scale of eastern asia during a narrow time range in the early cretaceous between ca 130 ma and ca 120 ma

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

emplacement and exhumation of the kuznetsk alatau basement siberia implications for the tectonic evolution of the central asian orogenic belt and sediment supply to the kuznetsk minusa and west siberian basins terra nova 23 248 256 2011 abstract new geochronological data zircon u pb titanite fission track tft and apatite fission track aft dating and apatite u th sm he thermochronology and thermal history modelling yield constraints on the development of the granitoid basement of the kuznetsk alatau mountains southern siberia the final stages of magmatism in the kuznetsk alatau palaeo island arc are late cambrian and collision of the arc with siberia occurred in the early ordovician the basement was exhumed by the early devonian continuous devonian early triassic sedimentation filled the adjoining kuznetsk and minusa basins and buried and re heated the kuznetsk alatau basement after initial pangaea break up and siberian flood basalt magmatism the basement reached tft and aft retention temperatures in the middle triassic and early cretaceous respectively during denudation induced cooling terra nova 00 1 9 2011

structural evolution of the teletsk graben russian altai abstract lake teletskoye in the northeastern part of the altai mountain range has attracted the attention of geo scientists for a long time because it fills an impressive tectonic depression the lake is 77 km long and 4 km wide and it has a maximum water depth of 325 m the vertical offset of the basement surface is up to 3000 m a multidisciplinary study of the teletsk graben was carried out during the last few years including satellite image and air photo analysis bathymetric structural and geomorphological mapping high resolution seismic profiling and seismic refraction the structural study revealed that reactivation of preexisting weak basement zones is important in controlling the basin formation these zones separate different tectonic terranes at the contact of which the teletsk graben developed this study identifies the significance of the basin in the regional neotectonic context it shows that the major vertical movements are restricted to the basin itself but do not characterize the whole region outside of the basin recent tectonic structures have the same pattern as adjacent areas of northeast altai and west sayan quaternary glaciations have had no major influence on the basin formation two stages of faulting are identified first transpressive movements restricted to discrete reactivated fault zones controlled the opening of the basin in the second stage normal faulting is dominant and is responsible for the modern basin outline an echo sounding survey led to the recognition of several morphological characteristics of the lake bottom in the southern part the uppermost sediments seem slightly disturbed whereas further north transverse ridges and slope breaks are increasingly common the deepest part of the lake is located in a highly disturbed zone of normal fault bounded blocks the structural difference between the southern and northern subbasins is supported by the interpretation of a deep seismic refraction profile which indicates a substantial increase of basement isochores in the area where the reactivated teletsk paleozoic shear zone crosses the lake correlation of high resolution seismic profiles suggests that the teletsk graben started to evolve during the pleistocene and that its present shape was formed in two stages the first stage was responsible for the opening of the southern basin it probably started in the middle pleistocene a second kinematic stage induced by a sinistral reactivation of the ne striking west sayan fault initiated the opening of the different segments of the northern subbasin due to opposite movements between the reactivated teletsk and west sayan faults this second stage was active after the end of late pleistocene glaciations and during the holocene the recent lateral extension and the related n s trending normal faults result from a change in tectonic regime with related extensional movements along the main reactivated fault zones these recent movements result in the lateral escape of the lake borders and the collapse of the area between them

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

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

structural control on meso cenozoic tectonic reactivation and denudation in the siberian altai insights from multi method thermochronometry abstract the siberian altai forms part of the central asian orogenic belt and currently is an active intracontinental mountain belt this siberian altai orogen was shaped during multiple phases of intense mountain building and associated denudation throughout the mesozoic and cenozoic we performed a multi method thermochronometric study on the altai basement in siberia in order to distinguish these denudation episodes and to place them in an absolute time frame our data shows that inherited suture zones such as the charysh terekta ulagan sayan suture played a dominant role during this episodic deformation in the altai titanite fission track results reveal late triassic early jurassic cooling which is best expressed in intrusions close to the suture zone apatite fission track aft results reveal a second phase of steady basement cooling during the late jurassic and cretaceous in the suture aft and additional apatite u th sm he ahe data reveal a consistent late cretaceous early palaeogene phase of fast cooling we interpret the mesozoic cooling signals as far field effects of the mongol okhotsk orogeny the intense late cretaceous palaeogene basement cooling signal in the suture zone can be explained as a result of fault reactivation during the collapse of this orogen and the subsequent re organization of crustal blocks during most of the palaeogene and early neogene basement cooling stagnated indicating tectonic quiescence neogene ahe ages for the kurai range directly adjacent to the suture may reflect renewed rapid cooling as a result of denudation of the present day altai mountains we interpret this most recent cooling as an indirect consequence of stress propagation from the india eurasia collision into the caob interior which thus reached as far as southern siberia this study further demonstrates the importance of thermochrological studies on intrusions along major fault zones in order to date and distinguish fault reactivation episodes

evolution of mesozoic fluvial systems along the se flank of the west siberian basin russia abstract the mesozoic stratigraphy in the subsurface of the west siberian basin contains prolific hydrocarbon accumulations and thus the depositional environments of marine and marginal marine jurassic and cretaceous age sediments are well established however no information is currently available on strata of equivalent age that crop out along the se basin margin in the mariinsk krasnoyarsk region despite the potential of these exposures to supply important information on the sediment supply routes into the main basin detailed sedimentological analysis of jurassic cretaceous clastic sediments in conjunction with palaeo botanical data reveals five facies associations that reflect deposition in a range of continental environments these include sediments that were deposited in braided river systems which were best developed in the early jurassic these early river systems infilled the relics of a topography that was possibly inherited from earlier triassic rifting more mature fluvial land systems evolved in the mid to late jurassic by the mid jurassic well defined overbank areas had become established channel abandonment was commonplace and mudrocks were deposited on floodplains coal deposition occurred in mires which were subject to periodic incursions by crevasse splay processes cretaceous sedimentation saw a renewed influx of sand grade sediment into the region it is proposed that landscape evolution throughout the jurassic was driven simply by peneplanation rather than tectonic processes by contrast the influx of sandstones in the cretaceous is tentatively linked to hinterland rejuvenation tectonic uplift possibly coeval with the growth of large deltaic clinoform complexes of the neocomian in the basin subsurface