giant iron ore deposits of the hamersley province related to the breakup of paleoproterozoic australia new insights from in situ shrimp dating of baddeleyite from mafic intrusions comment and reply comment muller et al 2005 1 have presented important new age data for mafic intrusions in the hamersley province of western australia which they use to constrain the ages of the ophthalmian orogeny and giant iron ore deposits their 2208 10 ma age for dolerite sills intruded into the turee creek

the uplift history of the haiyuan liupan shan region northeast of the present tibetan plateau integrated constraint from stratigraphy and thermochronology abstractthe haiyuan liupan shan delimits the northeastern margin of the tibetan plateau we present the integrated results of new stratigraphic investigations apatite fission track analyses and related thermal history modeling tied to the structural fabric of this region these constraints provide insight into the timing of northward propagation of the plateau with 1 local relief creation and enhanced erosion in the latest jurassic to earliest cretaceous representing the local element of a complex regional far field deformation response to the lhasa qiangtang collision with the south asian margin 2 evidence for likely late cretaceous exhumation but this is uncertain given the regional sedimentary gap that exists across this interval 3 eocene relief generation as a first likely response to far field effects of the india asia collision and related to wider regional events recognized in this part of northwestern china and 4 the latest deformation episode propagating strongly into the haiyuan

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

rapid exhumation at 8 ma on the liupan shan thrust fault from apatite fission track thermochronology implications for growth of the northeastern tibetan plateau margin abstract the liupan shan mountain is one of the outermost ranges in northeastern tibetan plateau the onset of its uplift provides insight on whether the plateau grew sequentially outward or broad areas of the plateau deformed simultaneously the apatite fission track method can be used to date rapid cooling as the result of unroofing of rocks in response to tectonically induced vertical motion fission track data from apatite in early cretaceous sedimentary strata exposed on the hanging wall of liupan shan thrust fault in northeastern tibet suggest that a late cenozoic rapid cooling events occurred at 7 3 8 2 ma or 8 ma this age apparently dates fault activity of the liupan shan thrust in response to northeastward growth of the tibetan plateau uplift and lateral growth which continues today numerous studies of the tibetan plateau suggest that the onset of deformation in eastern and northern margin of tibetan plateau occurred in the latest miocene

range front fault scarps of the sierra el mayor baja california formed above an active low angle normal fault the canada david detachment a west dipping low angle normal fault juxtaposes pliocene and pleistocene sedimentary units over sheared bedrock in the sierra el mayor baja california along the west central range front the detachment is overlapped by quaternary alluvial fans that are in turn cut by fault scarps up to 7 m high map relationships suggest that scarp forming faults may sole into the detachment at very shallow depth 200 300 m palinspastic restoration of a topographic profile across 15 north striking scarps suggests that the ratio of net heave to net throw along scarp forming faults is 2 consistent with them soling into a low angle 30 fault these 15 scarps may have all formed in one earthquake with rupture propagation from depth to the near surface aided by clay gouge along the detachment the detachment is abandoned in the footwall east of the scarps

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

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

upper neogene stratigraphy and tectonics of death valley a review abstract new tephrochronologic soil stratigraphic and radiometric dating studies over the last 10 years have generated a robust numerical stratigraphy for upper neogene sedimentary deposits throughout death valley critical to this improved stratigraphy are correlated or radiometrically dated tephra beds and tuffs that range in age from 3 58 ma to

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

a revised chronology for tertiary sedimentation in the sikouzi basin implications for the tectonic evolution of the northeastern corner of the tibetan plateau abstract the space time pattern of development of high topography associated with the tibetan plateau remains incomplete due in large part to sparse proxy data that allow estimates of the growth of individual mountain ranges here we present the results of a stratigraphic investigation of a 3100 m section of tertiary fluvio lacustrine strata in the sikouzi basin located at the northeastern most corner of the tibetan plateau results of magnetostratigraphic analysis coupled with a newly discovered miocene in situ fossil assemblage suggest that the section preserves a nearly complete record extending from initial basin formation at 29 myr until 0 5 myr sediment accumulation rates increase from relatively slow accumulation during the oligocene miocene 9 cm kyr to rapid accumulation in the pliocene 22 cm kyr apparently occurring in two sustained pulses at 10 5 ma and 5 ma respectively the increase in accumulation rates starting at 10 5 ma is interpreted as heralding the initial uplift of the liupan shan consistent with cooling and exhumation of the range zheng et al 2006 the pliocene increase in accumulation rate is accompanied by a distinct change in lithofacies the appearance of coarse detritus with provenance from the madong shan and up section changes in bedding orientation that are interpreted as growth strata collectively our data suggest that the generation of relief in the madong shan began at 5 4 ma moreover analysis of paleomagnetic declinations from the sikouzi section reveals a clockwise rotation of the sikouzi basin during the time period 24 5 4 ma that was followed by a subsequent counterclockwise rotation 5 4 0 5 ma our study suggests that activity along the liupan shan haiyuan fault system probably initiated at 10 5 ma but that the present day configuration of the fault system and associated ranges near the fault tip dates to pliocene time

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

luminescence ages for alluvial fan deposits in southern death valley implications for climate driven sedimentation along a tectonically active mountain front abstract controversy exists over whether alluvial fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause alluvial fan deposits in death valley and throughout the arid southwestern united states have long been the subjects of study but their ages have generally eluded researchers until recently most mapping efforts have recognized at least four major relative age groupings q1 oldest q2 q3 and q4 youngest using observed changes in surface soils and morphology relation to the drainage net and development of desert pavement obtaining numerical age determinations for these morphologic stages has proven challenging we report the first optically stimulated luminescence osl ages for three of these four stages deposited within alluvial fans along the tectonically active black mountains of death valley deposits showing distinct remnant bar and swale topography q3b have osl ages from 7 to 4 ka whereas those with moderate to poorly developed desert pavement and located farther above the active channel q3a have osl ages from 17 to 11 ka geomorphically older deposits with well developed desert pavement q2d have osl ages 25 ka using this osl based chronology we note that alluvial fan deposition along this tectonically active mountain front corresponds to both wet to dry and dry to wet climate changes recorded globally and regionally these findings underscore the influence of climate change on alluvial fan deposition in arid and semi arid regions

commencing uplift of the liupan shan since 9 5 ma evidences from the sikouzi section at its east side abstract the cenozoic evolution of the liupan shan situated at the northeast of the tibetan plateau will provide constraints to test the models and mechanisms of the evolution of the plateau in this contribution the sikouzi section at the east of the liupan shan has been selected to study liupan shan s uplift history at around 9 5 ma constrained by the magnetostratigraphy the sediment and depositing architecture characteristics obviously changed synchronously flow direction changed from e w to w e and accumulation rate increased to more than double all these evidences suggest that the liupan shan initiated uplifting at around 9 5 ma subsequently a stage of intense uplift happened during 8 2 7 3 ma indicated by the apatite fission track aft data across the liupan shan regional comparison indicates that this stage of uplift is not only with local but also regional significance the miocene uplift of the tibetan plateau triggered the intensification of the east asian monsoon and asian intercontinental aridity which has been implied by the pollen results of the sikouzi section

dissipation of fast strike slip faulting within and beyond northeastern tibet structural patterns global positioning system gps velocities and quaternary fault slip rates in northeastern tibet indicate a transfer of left lateral slip from the kunlun fault northeast to the haiyuan fault and minor crustal shortening and rotation within a 200 km wide stepover zone related deformation also continues at least a few hundred kilometers north of the haiyuan fault into a region of diffuse extensional shear or rotation underlain by average thickness crust fast localized slip along the central kunlun fault transforms into distributed deformation across a 500 km wide zone where the lower crust is weak the distribution of fault parallel gps velocities across this region suggests a decrease in fault slip toward eastern fault tips and progressive dissipation of slip to the north rather than east of the tibetan plateau as previously suggested

holocene slip rates along the owens valley fault california implications for the recent evolution of the eastern california shear zone one of the largest historical earthquakes in california occurred in 1872 along the owens valley fault located along the western margin of the eastern california shear zone new paleoseismic and optically stimulated luminescence data are the first to bracket the timing of the pre 1872 rupture to between 3 3 0 3 and 3 8 0 3 ka these data yield an earthquake recurrence interval between 4100 and 3000 yr under the assumption of uniform return and indicate a holocene slip rate between 1 8 0 3 and 3 6 0 2 mm yr our data are broadly consistent with a model proposed for the space time evolution of the eastern california shear zone our holocene slip rate estimates for the owens valley fault are slower than present day slip rates determined from elastic half space models of geodetic data this discrepancy is reduced by using the recurrence interval estimated here and a viscoelastic model of geodetic data or by including geologic slip rates from adjacent faults

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

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

dating fluvial sediments by optically stimulated luminescence selection of equivalent doses for age calculation fluvial sediments are not an ideal material for optical dating because of insufficient or and uneven exposure to daylight prior to burial the equivalent doses for a sample obtained using the single aliquot regenerative dose method usually show a large scatter which may be attributed to many factors here we developed a technique to evaluate the contributions from each factor using this technique relatively well bleached aliquots were identified and the average of their equivalent doses was taken for age calculation

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

quaternary alluvial fan development climate and morphologic dating of fault scarps in laguna salada baja california mexico article i nfo late quaternary slip across the canada david detachment has produced an extensive array of quaternary scarps cutting alluvial fans along nearly the entire length 60 km of the range bounding detachment eight regional alluvial fan surfaces q1 youngest to q8 oldest are defined and mapped along the entire sierra el mayor range front terrestrial cosmogenic nuclide 10 be concentrations from individual boulders on alluvial fan surfaces q4 and q7 yield surface exposure ages of 15 5 2 2 ka and 204 11 ka respectively formation of the fans is probably tectonic but their evolution is strongly moderated by climate with surfaces developing as the hydrological conditions have changed in response to climate change on milankovitch timescales systematic mapping reveals that the fault scarp array along active range bounding faults in sierras cucapa and el mayor can be divided into individual rupture zones based on cross cutting relationships with alluvial fans quantitative morphological ages of the laguna salada fault scarps derived from linear diffusive degradation modeling are consistent with the age of the scarps based on cross cutting relationships the weighted means of the maximum mass diffusivity constant for all scarps with offsets b 4 m is 0 051 and 0 066 m 2 ka for the infinite and finite slope solutions of the diffusion equation respectively this estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of laguna salada

thermochronological constraints on the meso cenozoic tectonic evolution of the haiyuan liupanshan region northeastern tibetan plateau abstract the cenozoic outward growth of the tibetan plateau is traditionally considered to be responsible for the arcuate structures in the northeastern tibetan plateau however it is still unclear how pre cenozoic tectonics contributed to this unique geomorphic setting to decipher the meso cenozoic tectonic evolution we systematically summarize the published thermochronological data and perform a low temperature thermochronology study on paleozoic mesozoic samples from the haiyuan liupanshan region apatite fission track ages from the new samples vary widely ranging from 158 4 ma to 34 4 ma apatite fission track and u th sm he thermal history modeling constrained by zircon fission track data and geological evidence indicate that this area experienced multiple stages of cooling from the late triassic to the cenozoic these cooling events include i late triassic early jurassic ii late jurassic early cretaceous iii late cretaceous early cenozoic and iv late cenozoic 7 ma late triassic early jurassic cooling was driven by the collision of the nouth china plate and the sorth china plate the late jurassic early cretaceous tectonothermal event is interpreted as a record of the intracontinental orogeny in east asia it is possible that late cretaceous early cenozoic exhumation was the far field response to the neo tethyan subduction under the lhasa terrane in addition late cenozoic 7 ma rapid cooling in the yueliangshan range southern part of the haiyuan liupanshan region was a result of the intense activation of the easternmost haiyuan fault in response to the outward growth of the tibetan plateau these findings suggest that pre cenozoic tectonics played an important role in the growth of the present day northeastern tibetan plateau edifice

strain accumulation along the laguna salada fault baja california mexico strain accumulation observed over the 1978 1991 interval in a 30 100 km aperture trilateration network spanning the laguna salada fault is described by the principal strain rates 0 101 0 012 strain yr n80 e 2 and 0 021 0 012 strain yr n10 w 2 extension reckoned positive these strain accumulation rates have been corrected to remove coseismic effects of the nearby 1979 imperial valley m 6 5 1980 victoria baja california m 6 4 1987 superstition hills m 6 5 and 1987 elmore ranch m 5 9 earthquakes the observed strain rates indicate extension at a rate of about 0 08 strain yr perpendicular to the trend n35 w of the salton trough as well as a right lateral tensor shear strain rate 0 05 strain yr across it the extension perpendicular to the trough is observed neither farther north near the salton sea nor farther south across the gulf of california however holocene slip on the laguna salada fault about equal parts right lateral and normal slip is consistent with the observed strain accumulation a simple dislocation model intended to explain the observed strain accumulation as a product of slip at depth on the laguna salada fault would require that the fault be listric

late quaternary activity of the laguna salada fault in northern baja california mexico faulted alluvial fans and bajadas along the central laguna salada fault zone in northernbajacaliforniarecordarecurrent history of oblique slip holocene earthquakes alluvialsurfaces whichrangefrom late pleistocene to historic in age have been progressively displaced along the base of the crystalline rangefront as well as along more basinward fault splays in alluvium the recurrence interval determined from displacedalluvialdepositsthataredatedby soil profile development is in the range of 1 2 ka with a corresponding right lateral slip rate of 2 3 mm yr similar to that of thesouthernelsinorefaultinsoutherncalifornia the most recent event along the fault zone is probably the widely felt earthquake of february 23 1892 at least 22 km ofthefaultzonerupturedduringthisevent along both an oblique dextral section of the northwest strikinglagunasaladafaultand

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

late pleistocene holocene alluvial stratigraphy of southern baja california mexico abstract a late pleistocene to holocene alluvial stratigraphy has been established for the basins of la paz and san jose del cabo in the southern tip of the baja california peninsula mexico six discrete alluvial units qt1 through qt6 were differentiated across the region using a combination of geomorphologic mapping sedimentological analysis and soil development these criteria were supported using radiocarbon optically stimulated luminescence and cosmogenic depth profile geochronology major aggradation started shortly after 70 ka qt2 and buildup of the main depositional units ended at 10 ka qt4 after deposition of qt4 increasing regional incision of older units and the progressive development of a channelized alluvial landscape coincide with deposition of qt5 and qt6 units in a second incisional phase all units consist of multiple 1 3 m thick alluvial packages deposited as upper flow stage beds that represent individual storms main aggradational units qt2 qt4 occurred across broad 2 km channels in the form of sheetflood deposition while incisional stage deposits are confined to channels of 0 5 2 km width continuous deposition inside the thicker 10 m pre qt5 units is demonstrated by closely spaced dates in vertical profiles in a few places disconformities between these major units are nevertheless evident and indicated by partly eroded buried soils the described units feature sedimentological traits similar to historical deposits formed by large tropical cyclone events but also include characteristics of upper regime flow sedimentation not shown by historical sediments like long 10 m wavelength antidunes and transverse ribs we interpret the whole sequence as indicating discrete periods during the late pleistocene and holocene when climatic conditions allowed larger and more frequent tropical cyclone events than those observed historically these discrete periods are associated with times when insolation at the tropics was higher than the present day conditions determined by precessional cycles and modulated by the presence of el nino like conditions along the tropical and northeastern pacific the southern baja california alluvial record is the first to document a precession driven alluvial chronology for the region and it constitutes a strong benchmark for discrimination of direct tropical influence on any other alluvial record in southwestern north america

cosmogenic 10be and 36cl geochronology of offset alluvial fans along the northern death valley fault zone implications for transient strain in the eastern california shear zone the northern death valley fault zone ndvfz has long been recognized as a major right lateral strike slip fault in the eastern california shear zone ecsz however its geologic slip rate has been difficult to determine using high resolution digital topographic imagery and terrestrial cosmogenic nuclide dating we present the first geochronologically determined slip rate for the ndvfz our study focuses on the red wall canyon alluvial fan which exposes clean dextral offsets of seven channels analysis of airborne laser swath mapping data indicates 297 9 m of right lateral displacement on the fault system since the late pleistocene in situ terrestrial cosmogenic 10 be and 36 cl geochronology was used to date the red wall canyon fan and a second correlative fan also cut by the fault beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 22 20 ka for the offset landforms the minimum age of the alluvial fan deposits based on 36 cl depth profiles is 63 8 ka combining the offset measurement with the cosmogenic 10 be date yields a geologic fault slip rate of 4 2 1 9 1 1 mm yr 1 whereas the 36 cl data indicate 4 7 0 9 0 6 mm yr 1 of slip summing these slip rates with known rates on the owens valley hunter mountain and stateline faults at similar latitudes suggests a total geologic slip rate across the northern ecsz of 8 5 to 10 mm yr 1 this rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the mojave section of the ecsz does not extend north of the garlock fault although the overall geodetic rates are similar the best estimates based on geology predict higher strain rates in the eastern part of the ecsz than to the west whereas the observed geodetic strain is relatively constant

thermal evolution of monte blanco dome low angle normal faulting during gulf of california rifting and late eocene denudation of the eastern peninsular ranges footwall rocks of the canada david detachment fault northeastern baja california record late eocene earliest oligocene and late neogene cooling events previously unrecognized in the region biotite 40 ar 39 ar ages of 65 ma reflect slow cooling through 350 c 5 to 10 m y later than is typical in the region multiple diffusion domain modeling of k feldspar 40 ar 39 ar release spectra shows very slow cooling 1 c m y from 65 to 45 ma accelerated cooling from 315 c to 215 c between 45 and 33 ma records at least 3 4 km of denudation that we relate to east side up reactivation of late cretaceous structures that generally follow the oceanic continental suture previously established rivers flowing west from mainland mexico apparently became further entrenched during this uplift and continued to supply distinctive rhyolitic detritus to the coast ultimately surface uplift disrupted and rerouted the extraregional rivers some 2 to 6 m y before the cooling event ended footwall rocks remained nearly isothermal from 30 to 15 10 ma when renewed rapid cooling 33 17 c m y began in response to footwall exhumation by top to the west low angle normal faulting that accommodated rift related extension in what finally became the gulf of california apatite fission track and u th he ages of 5 ma and 4 ma respectively record final detachment related cooling through 110 c to 70 c thermal kinematic modeling suggests that 5 7 km of late neogene tectonic denudation and 10 12 km of horizontal extension were necessary in order to unroof the samples by 2 ma additional extension of unknown magnitude has probably occurred subsequently geodetically measured horizontal extension rates are considerably higher than the long term extension rate that can be attributed to detachment faulting

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

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

seismically induced mass movements and volumetric fluxes resulting from the 2010 mw 7 2 earthquake in the sierra cucapah mexico the observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building to better constrain the role of high magnitude earthquakes in orogenesis high resolution data of earthquake induced mass wasting is required for areas of differing tectonic morphological and climatic settings here we compare the erosional flux to the tectonic flux associated with the 2010 mw 7 2 sierra el mayor earthquake in mexico and examine the landslide patterning of coseismic mass movements associated with this event the ruptured fault system has a significant strike slip component with subsidence along the eastern flank and uplift on the western flank of the range peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation this result suggests that strike slip systems experience very different landslide patterning to thrust faults during earthquakes based on interferometric analysis of synthetic aperture radar images the earthquake resulted in a total uplifted volume of 41 6 106 m3 and a loss of 95 2 106 m3 due to subsidence this suggests a net tectonic volumetric flux of 53 6 106 m3 sediment mobilisation by coseismic landslides is estimated at 2 7 106 m3 derived from a manually mapped inventory using spot 5 multispectral imagery thus the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux which was only marginally enhanced by mass wasting

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

beryllium 10 terrestrial cosmogenic nuclide surface exposure dating of quaternary landforms in death valley quaternary alluvial fans and shorelines spits and beach bars were dated using 10 be terrestrial cosmogenic nuclide tcn surface exposure dating in death valley the 10 be tcn ages show considerable variance on individual surfaces samples collected in the active channels date from 6 ka to 93 ka showing that there is significant inheritance of 10 be tcn within cobbles and boulders that were dated which suggests that slopes erode and sediment is transferred very slowly in most regions within death valley comparisons of 10 be tcn ages on alluvial fan surfaces with chronostratigraphies based on soil development and optically stimulated luminescence dating show that minimum 10 be tcn ages within sample sets on individual surfaces most closely approximate to the age of landforms that are younger than 70 ka alluvial fan surfaces older than 70 ka have begun to undergo significant erosion so that the majority of 10 be tcn ages for data sets on individual surfaces underestimate the true age of the surface due to erosion and exhumation of fresh cobbles and boulders the spread of 10 be tcn ages for beach bars near beatty junction and shorelines 8 km south of furnace creek is large ranging from 119 ka to 385 ka and 109 ka to 465 ka respectively however new and previously published luminescence ages soil development and geomorphic context suggest that these landforms formed during high lake level stands in marine isotope stage 2 22 18 ka but these younger ages my reflect soil development and material elluviated into the bar deposit long after deposition this suggests that the cobbles and boulders dated with 10 be methods have inherited 10 be tcns which have been derived from older shorelines or associated landforms these results highlight the problems associated with using surface cobbles and boulders to date quaternary surfaces in death valley and other similar dryland settings moreover this study emphasizes the need to combine multiple different dating methods to accurately date landforms in death valley and similar settings

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

luminescence chronology of incision and channel pattern changes in the river ganga india the river ganga in the central gangetic plain shows the incision of 20 m of late quaternary sediments that form a vast upland terrace t2 the incised ganga river valley shows two terraces namely the river valley terrace t1 and the present day flood plain terrace t0 terrace t1 shows the presence of meander scars oxbow lakes scroll plains which suggests that a meandering river system prevailed in the past the present day river channel flows on terrace t0 and is braided sensu stricto it is thus inferred that the river ganga experienced at least two phases of tectonic adjustments 1 incision and 2 channel metamorphosis from meandering to braided optical dating of samples from three different terraces has bracketed the phase of incision to be 6 and 4 ka different ages of the top of terrace t2 show that this surface experienced differential erosion due to tectonic upwarping in the region which also caused the river incision river metamorphosis occurred some time during 4 and 0 5 ka

dating offset fans along the mojave section of the san andreas fault using cosmogenic 26al and 10be analysis of cosmogenic 1 0 be and 2 6 al in samples collected from exposed boulders n 20 and from buried sediment n 3 from offset fans along the san andreas fault near little rock california yielded ages ranging from 16 to 413 ka which increase with dis lance from their source at the mouth of little rock creek in order to determine the age of the relatively younger fans the erosion rate of the boulders and the cosmogenic nuclide inheritance from exposure prior to deposition in the fan were established cosmogenic nuclide inheritance values that range between 8 5 x 10 3 and 196 10 3 atoms 1 0 be g 1 quartz were determined by measuring the concentrations and ratios of 1 0 be and 2 6 al in boulders n 10 and fine sediment n 7 at the outlet of the present active stream boulder erosion rate ranging between 17 and 160 mm k y 1 was estimated by measuring 1 0 be and 2 6 al concentrations in nearby bedrock outcrops n 8 since the boulders on the fans represent the most resistant rocks in this environment we used the lowest rate for the age calculations monte carlo simulations were used to determine ages of 16 5 and 29 7 ka for the two younger fan surfaces older fans older than 100 ka were dated by analyzing 1 0 be and 2 6 al concentrations in buried sand samples the ages of the three oldest fans range between 227 242 and 413 185 ka although fan age determinations are accompanied by large uncertainties the results of this study show a clear trend of increasing fan ages with increasing distance from the source near little rock creek and provide a long term slip rate along this section of the san andreas fault slip rate along the mojave section of the san andreas fault for the past 413 k y can be determined in several ways the average slip rate calculated from the individual fan ages is 4 2 0 9 cm yr 1 a linear regression through the data points implies a slip rate of 3 7 1 0 cm yr 1 a most probable slip rate of 3 0 1 0 cm yr 1 is determined by using a 2 test these rates suggest that the average slip along the mojave section of the san andreas fault has been relatively constant over this time period the slip rate along the mojave section of the san andreas fault determined in this study agrees well with previous slip rate calculations for the quaternary

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

millennial scale varnish microlamination dating of late pleistocene geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a climate based correlative age determination technique used to correlate and date various geomorphic features in deserts in this study we establish a generalized late pleistocene 18 74 ka millennial scale microlamination sequence in fine grained fast accumulating rock varnish for the drylands of western usa radiometrically calibrate the sequence and correlate it with the 18 o record in the gisp2 greenland ice core we then use this climate correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late pleistocene geomorphic features in the study region the vml dating of debris flow deposits on the sehoo recessional shorelines of lake lahontan at the jessup embayment of central nevada yields a minimum limiting age of 14 95 15 95 ka in good agreement with a calibrated 14 c age of 15 22 0 12 ka for the timing of the lake recession the vml dating of a giant ejecta block on the rim of meteor crater in northern arizona yields a minimum limiting age of 49 15 ka closely matching a thermoluminescence tl age of 49 3 ka and slightly younger than a recently updated cosmogenic 36 cl age of 56 0 2 4 ka for the meteor impact event the vml dating of distal q2c fan surfaces on hanaupah canyon alluvial fan in death valley california yields a minimum limiting age of 73 55 ka in accord with cosmogenic 36 cl depth profile ages of 66 22 14 ka and 72 24 20 ka for the same fan deposits the close agreement between the vml age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial scale vml dating to further assess its potential in desert geomorphological research we use the vml method to study alluvial fan responses to millennial scale climatic changes the vml dating of a small tributary fan in death valley reveals two episodes of fan aggradation one ceasing at 73 55 86 75 ka during the dry period of the last interglacial mis 5a and the other finishing at 66 15 ka during the wet period of the last glacial mis 4 the vml and 36 cl dating of the distal q2c fan surfaces on hanaupah canyon fan reveal two episodes of large scale fan aggradation ended at 72 24 20 ka and 73 55 ka during the wet period of mis 4 fanhead incision and associated within channel or fantoe aggradation are found to take place during the relatively dry period of the glacial to interglacial climatic transition 12 24 ka and the holocene interglacial dry period 0 12 ka these data indicate that on the millennial to sub milankovitch timescale 10 3 10 4 years fan aggradation is a discrete sedimentational process under various climatic conditions because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events which in turn are modulated by major climatic oscillations such as heinrich events dansgaard oeschger do events and glacial interglacial shifts these major climatic changes could be the pacemaker of regionally contemporaneous large area fan segmentation

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

the age and extent of tropical alpine glaciation in the cordillera blanca peru based on new 10 be data for moraines in the cordillera blanca of central peru we have calculated model ages of three sets of pleistocene glacial moraines in order of decreasing age these are the cojup rurec and laguna baja moraines the oldest moraines occur at the lowest elevations and yield dates of 400 ka pre dating the last interglacial and demonstrating that maximum ice volumes occurred during previous glacial periods and not at the end of the last glacial our new data from the younger moraines indicate that the end of the last glacial cycle comprised two separate advances at ca 29 ka and ca 16 5 ka each reflecting significant 4 c tropical of cooling at 10 s these data combined with published records from the laurentide ice sheet indicate that climate instabilities associated with the close of the last glacial were likely global and synchronous in nature copyright 2005 john wiley sons ltd

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

episodic late quaternary slopewash deposition as recorded in colluvial aprons southeastern wyoming abstract colluvial aprons found along fluvial terraces of the laramie river and sybille creek in southeastern wyoming are interpreted as late quaternary slopewash deposits each apron studied contained multiple buried soils interpreted to indicate that slopewash activity was episodic and short lived and was followed by relatively long periods of landscape stability and soil development apron deposits were described and subsequently correlated based on their internal stratigraphy and their relative degree of soil development optical dating was used to chronologically constrain periods of slopewash deposition and based on 17 optical ages taken from five aprons aggradation occurred at 65 56 16 0 12 9 11 8 8 1 7 3 5 0 and 1 7 ka several of these events correspond with climatic transitions such as the termination of heinrich event 1 the onset and termination of the younger dryas and the 8 2 ka event suggesting that apron aggradation was driven by changes in climatic regime although either increased aridity or a change in precipitation regime could result in increased erosion of terrace scarps apron aggradation events do not correlate with regional records of aridity instead periods of increased precipitation intensity and or frequency that occur during climatic transitions most likely drive apron aggradation events

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

luminescence dating applications in geomorphological research abstract chronological control remains critical to the interpretation of environmental change and to establishing long term rates of geomorphological processes radiocarbon dating will continue to be the central technique for age assessment of carbon bearing sediments deposited in the last ca 40 ka but alternative absolute dating strategies are required for older or non carbon bearing sediments they include uranium series dating of precipitated sediments k ar and ar ar dating of primary volcanic materials and cosmogenic isotopic dating of surface exposure ages an additional family of methods collectively termed luminescence techniques is increasingly providing a basis for the age assessment of detrital sedimentary deposits these methods directly date the deposition of detrital mineral grains typically quartz and feldspar and have been demonstrated to provide accurate deposition chronologies for up to 800 ka although 150 ka is more typical in the past decade a subset of luminescence techniques which employ optical sample stimulation methods called optical dating has made it possible to date samples from a much wider range of depositional systems given that the methods directly date sedimentation they allow direct assessment of depositional dynamism in numerous terrestrial and subaqueous including marine sedimentary systems and have demonstrated particular potential in the elucidation of chronologies from aeolian dune and loess fluvial colluvial coastal and volcaniclastic environments this paper provides a summary of the principles of the luminescence especially optical dating methods and shows how recent developments specifically single aliquot dating procedures have dramatically enhanced the scope and potential of the method the luminescence techniques are increasingly being incorporated into a wide range of geomorphological studies which seek to establish the nature of landscape changes over the past interglacial glacial cycle and beyond

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

eocene to pliocene exhumation history of the tianshui huicheng region determined by apatite fission track thermochronology implications for evolution of the northeastern tibetan plateau margin abstract this study presents new apatite fission track aft data from the tianshui huicheng region which is situated in the northeastern margin of the tibetan plateau aft results including 19 detrital and 13 bedrock samples show that deposition in the tianshui huicheng basin range from early eocene to late miocene pliocene and most of the apatites derived from the western qinling orogenic belt reflecting one rapid exhumation episode at 34 29 ma and two phases of volcanism at 23 18 ma and ca 13 ma the exhumation history of the tianshui huicheng region is likely related to episodic tectonic activity and directly linked to the kinematics of active deformation of the tibetan plateau active processes deciphered from the detritus indicate that deformation reached the northeastern tibetan plateau margin as early as ca 49 ma which is manifested by the initiation of the tianshui huicheng basin the 23 18 ma event linked to the lithosphere deformation of the western qinling and the neogene basin formation along the tianshui huicheng region by modeling the bedrock samples an 8 4 ma event was revealed which resulted from the intense deformation of the tianshui huicheng region

amount and style of late cenozoic deformation in the liupan shan area ningxia autonomous region china the structures of the liupan shan area are characterized by numerous active thrust and strike slip faults that suggest thin skinned deformation the structural history of this area can be divided into three phases that probably overlap one another in time and are parts of a single protracted deformation the oldest cenozoic deformational phase occurred probably between late pliocene and early quaternary time and produced some of the folds and thrust faults in the liupan shan and yueliang shan during this phase deformation was the result of approximately n50 e shortening and the amount of shortening seems to have been about 1 2 km the second phase of deformation was dominated by left lateral strike slip faulting left slip on the n60 w striking haiyuan fault zone and shortening on north south trending structures shortening was associated with a transfer of the left slip displacement on the haiyuan fault zone to shortening in areas farther east shortening occurred by thrust faulting in the liupan shan and xiaoquan shan and by folding in the madong shan during this phase the orientation of shortening changed to n60 w the average amount of shortening on the north south trending folds in the madong shan is about 6 3 7 8 km most of the shortening on the liupan shan and xiaoguan shan thrust faults also occurred during this phase and amounted to a minimum of 4 8 6 3 km and 6 6 7 6 km respectively also with an orientation of n60 w during the third phase of deformation about 1 1 5 km of late pleistocene to recent left slip occurred on the xiaokou fault which was transferred into oblique left slip thrusting in the liupan shan at this time deformation in the madong shan and xiaoguan shan ceased or was reduced to a very slow rate the present active left slip on the haiyuan fault zone is accommodated by shortening in the liupan shan area the total displacement along the haiyuan fault is essentially the same as the total amount of shortening in the liupan shan area the sequence and interaction of strike slip and thrust faults in the liupan shan area seem to apply to the folds and thrust faults farther north in the southern ningxia region thus the northeastern margin of the tibetan plateau appears to grow by shortening oriented northeast and by left slip faulting that transfers material from farther to the west the total left slip in the entire southern ningxia region probably is less than 20 25 km and may be absorbed by shortening within this region thus the eastward translation of crustal fragments in the northern part of the tibetan plateau may not extend east of southern ningxia and if large scale eastward displacement has occurred it must lie farther south

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

late quaternary alluvial fans at the eastern end of the san bernardino mountains southern california abstract alluvial fans at the eastern end of the san bernardino mountains in southern california provide a record of climate modulated sediment transfer and erosion and are deformed and displaced in places by active faults alluvial fans within two study areas the mission creek and the whitewater river drainages were examined using geomorphic sedimentological and 10be terrestrial cosmogenic nuclide tcn surface exposure methods to define the timing of alluvial fan formation and erosion and to examine the role of climatic tectonic and autocyclic processes these alluvial fan complexes were studied because they are amongst the best preserved successions of alluvial fans in southern california and they are located at the mouths of two of the largest drainages whitewater river and mission creek in the san bernardino mountains and traverse major faults the mission creek and banning the alluvial fans comprise bouldery debris deposits that represent deposition dominated by flash flood and debris flow events tcn surface exposure dating indicates that abandonment incision of alluvial fan surfaces date to early in the last glacial or more likely the penultimate glacial cycle to marine isotope stage mis 4 and to the holocene the lack of alluvial fan ages during the latter part of the last glacial mis 2 and 3 suggests that there has been little alluvial fan lobe deposition incision during that time this is similar to findings for many other alluvial fans throughout the american southwest and supports the view that there is a strong climatic control on alluvial fan formation throughout this region furthermore the oldest alluvial fan surfaces in the mission creek region are beheaded by the whitewater river drainage showing that the oldest alluvial fans in the mission creek region underwent significant capture by the whitewater river drainage this shows the autocyclic controls are also important on alluvial fan evolution in this region but the importance of these processes to alluvial fan development in other regions of the american southwest needs to be more fully assessed the alluvial fans in the mission creek area traverse the mission creek fault but are not deformed by it which suggests that there may have been little if any movement along this fault since at least mis 4 in contrast alluvial fans in the whitewater river study are displaced by active faults highlighting the influence of tectonism on alluvial fan development in this region in addition to illustrating the importance of climatic controls on the development of alluvial fans in the american southwest a classic region for alluvial fan studies this study illustrates the complex mixture of autocyclic and allocyclic factors that force alluvial fan development in tectonically active settings

isotopic insights into smoothening of abandoned fan surfaces southern california cosmogenic nuclide concentrations measured on abandoned fan surfaces along the mojave section of the san andreas fault suggest that sediment is generated transported and removed from the fans on the order of 30 40 kyr we measured in situ produced cosmogenic 10 be and in some cases 26 al in boulders n 15 surface sediment n 15 and one depth profile n 9 nuclide concentrations in surface sediments and boulders underestimate fan ages suggesting that 10 be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages field observations grain size distribution and cosmogenic nuclide data suggest that over time boulders weather into grus and the bar sediments diffuse into the adjacent swales as fans grow older the relief between bars and swales decreases the sediment transport rate from bars to swales decreases and the surface processes that erode the fan become uniform over the entire fan surface the nuclide data therefore suggest that over time the difference in 10 be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized resulting in a common surface lowering rate and common 10 be concentrations across the fan during this phase the entire fan is lowered homogeneously at a rate of 10 15 mm kyr 1

active faults and magnitudes of left lateral displacement along the northern margin of the tibetan plateau abstract the northern margin of the tibetan plateau nmtp is a major intracontinental cenozoic transpressional zone that comprises a series of active strike slip faults and thrust faults it is important to document cumulative horizontal displacements along the nmtp in order to understand quantitatively strain partitioning in east asia since the india eurasia collision based on an analysis of horizontal slip along major active faults the total amount of horizontal displacements is estimated up to 700 km between the tibetan plateau and the tarim basin since the convergence of india and eurasia along the western and middle segment of the altyn tagh fault to the northern margin of the qaidam basin there are abundant evidence that show that the net displacement is 400 km since 40 35 ma and along the shulenan shan and southeast of middle qilian shan since 25 17 ma the amount of offset is 150 km the largest horizontal slip in qilian shan hexi corridor to the northeast of the altyn tagh fault is also 150 km since late oligocene to early miocene it decreases to only 60 km along the haiyuan fault since late miocene and to 25 km along the zhongwei tongxin fault since the pliocene about 5 3 3 4 ma at the northeast margin of the tibetan plateau this clearly implies northeastward diminishing of the total horizontal displacement and temporal getting younger of the fault slip along the nmtp however this tendency is very complicated at different times and different segments as a result of the uplift growth and rotation of different segments of the nmtp at different stages during the convergence of india and eurasia

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

right lateral shear and rotation as the explanation for strike slip faulting in eastern tibet the convergence of two continents can be accommodated by crustal thickening and by lateral transport of crust out of the path of the converging continents1 3 the principal features suggesting that lateral transport is important are major strike slip faults striking roughly orthogonally to the orientation of convergence between the continents displacement on such faults is imagined to allow lateral transport of material with respect to the converging continents possibly accounting for a large fraction of the convergence between the two continents the most spectacular example of such strike slip faulting is in the eastern part of the tibetan plateau where three major left lateral faults with slip rates of 10 mm yr 1 and several smaller roughly parallel faults dominate the regional strain field2 3 cobbold and davy4 suggested that these faults may be rotating in a clockwise fashion here we put bounds on that rate of rotation and conclude that the image of lateral transport on such faults2 known also as continental escape extrusion or expulsion is an illusion and that instead the left lateral slip on east striking planes in eastern tibet is a manifestation of north striking right lateral simple shear if this conclusion is correct the east striking left lateral faults and the crustal blocks between them are rotating clockwise at 1 2 myr 1 the east west dimension of eastern tibet is shortening at 10 20 mm yr 1 and little material is moving eastward out of india s path into eurasia by left lateral simple shear

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

late neogene stratigraphy and tectonic control on facies evolution in the laguna salada basin northern baja california mexico abstract the laguna salada basin lsb in northeastern baja california records late neogene marine incursions in the salton trough and progradation of the colorado river delta early subsidence and subsequent tectonic erosion are related to evolution of the sierra el mayor detachment fault during late miocene time

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

timing and controls on late quaternary landscape development along the eastern sierra el mayor range front in northern baja california mexico abstract the sierra el mayor sierra cucapa mountain range in northern baja separates the colorado river delta from the laguna salada basin and is important in terms of understanding the structural transition from the northern gulf extensional province to the san andreas system one of the principal quaternary landscape features of the eastern sierra el mayor sierra cucapa is a prominent surface that slopes 1 2 eastward towards the colorado river delta along the eastern side of the sierra el mayor and facing the colorado river delta but not along other piedmont mountain fronts that face the delta this surface is terminated by a series of stepped terrace surfaces the terrace surfaces are cut into fluvial deltaic deposits from the colorado river delta system and are capped by 1 m thick gravels optically stimulated luminescence ages from interbedded coarse sands in the capping gravels of the upper surface and two of the inset terraces range from 17 to 31 ka average 24 3 ka but lack a systematic age trend from upper to lower surface the underlying fluvial deltaic deposits have older optically stimulated luminescence ages of 31 to 39 ka and suggest colorado river delta deposition during the relatively stable interstadial of the middle wisconsinan substage marine isotope stage 3 when sea level was ca 60 to 80 m samples from depth profiles in the capping gravels and from the top of the upper surface have a mean 10 be terrestrial cosmogenic nuclide age of 59 5 ka when corrected for inheritance an average age of 21 ka is computed for exposure of the capping gravels on the upper surface and inset terraces which is in the range of the optically stimulated luminescence burial ages both the upper surface and inset terraces formed 17 30 ka at a transition time from dry to relatively wet climate when increased aggradation caused alluvial fan development on the upper surface regionally these surfaces correlate with the q2c q3a age deposits of the southwestern north america alluvial fan and terrace deposits sea level was also falling rapidly at this time which may have caused the colorado river to become entrenched near the range front thus allowing rapid response and down cutting to form the inset terraces on the east side of the sierra el mayor facing the delta assuming the 34 ka delta deposits graded to a base level that was 60 to 80 m during marine isotope stage 3 the computed surface uplift rate for the eastern side of the sierra el mayor is 2 1 2 7 mm yr this uplift may be accommodated on a fault or fault system that is a southward extension of the mexicali spreading and seismic zone that is buried beneath the colorado river delta east of the sierra el mayor the uplift rates from this study are consistent with geologic and geodetic data for the sierra el mayor and sierra cucapa and account for much of the missing extensional strain across the area

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

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete