intersections between wind regimes topography and sediment supply perspectives from aeolian landforms in central asia abstract the widespread aeolian deposits of the central asian steppes and piedmonts offer potential to better understand the dynamics of the major eurasian climate subsystems over quaternary timescales however current assumptions linking climate processes with aeolian activity remain poorly substantiated and potentially problematic emerging datasets suggest that loess accumulation rates and the timing of peak dust flux along the tien shan piedmont are highly variable between sites the degree to which desert dunes reflect wind regimes and therefore provide records of climate circulation is unknown and the presumed genetic link between the region s desert dunes and piedmont loess deposits remains hypothetical these uncertainties raise questions as to the nature of the relationship between aeolian flux deposition and palaeo climate here we investigate the relationship between wind regimes and the distribution morphology and timing of two aeolian landform types dunes and loess in the topographically diverse ili basin of southeast kazakhstan and western china we establish late holocene ages for three dune sites and one loess profile and infer that the location and morphology of these landforms can be used to test their genetic link with recent wind regimes we assess the morphologic characteristics of linear dunes at four sites using a semi automated mapping approach and analyse the variability in dune orientations with respect to sand shifting wind trajectories identified from meteorological reanalysis data for each site the most frequently occurring wind direction appears to be responsible for sediment supply while the strongest winds drive dune orientation wind orientations are strongly influenced by topography back trajectories incorporating dust transport and deposition potential to the loess site suggest both westerly and northerly delivery of fine grained material to the piedmont and that the most common source areas lie in regions where surface sediment contains a mixture of coarse and fine grained material to facilitate entrainment into suspension

kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

intracontinental subduction and palaeozoic inheritance of the lithosphere suggested by a teleseismic experiment across the chinese tien shan teleseismic tomography across the chinese tien shan shows that seismic wave speeds in the lithosphere beneath central tien shan are high and therefore the lithosphere is not weaker than that beneath the adjacent undeformed tarim and junggar basins there is evidence for significant velocity contrasts within the lithosphere that are presumably inherited from the palaeozoic collision history the high velocity thick yili block observed underneath the northern tien shan is a clue for shortening by a intracontinental subduction the observed geometry is consistent with a simple model of intracontinental subduction and suggests that during orogeny the lithosphere has remained heterogeneous and has deformed along existing planes of weakness rather than by homogeneous thickening of a particularly weak lithosphere

a miocene coarse volcaniclastic mass flow deposit in the shimane peninsula sw japan product of a deep submarine eruption a subaqueous volcaniclastic mass flow deposit in the miocene josoji formation shimane peninsula is 15 16 m thick and comprises mainly blocks and lapilli of rhyolite and andesite pumices and non to poorly vesiculated rhyolite it can be divided into four layers in ascending order layer 1 is an inversely to normally graded and poorly sorted lithic breccia 0 3 6 m thick layer 2 is an inversely to normally graded tuff breccia to lapilli tuff 6 11 m thick this layer bifurcates laterally into minor depositional units individually composed of a massive lithic rich lower part and a diffusely stratified pumice rich upper part with inverse to normal grading of both lithic and pumice clasts layer 3 is 2 5 3 m thick and consists of interbedded fines depleted pumice rich and pumice poor layers a few centimeters thick layer 4 is a well stratified and well sorted coarse ash bed 1 5 2 m thick the volcaniclastic deposit shows internal features of high density turbidites and contains no evidence for emplacement at a high temperature the mass flow deposit is extremely coarse grained dominated by traction structures and is interpreted as the product of a deep submarine explosive eruption of vesicular magma or explosive collapse of lava

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

evaluating fluvial terrace riser degradation using lidar derived topography an example from the northern tian shan china abstract the morphological degradation of fluvial terrace risers provides a constraint to terrace chronology in this study we morphologically date the terrace risers along the kuitun river on the north flank of the tian shan china and subsequently discuss possible relationships between terrace formation and the past regional climate changes and tectonic activity of the dushanzi fault related fold to do this 159 topographic profile swaths of terrace risers were extracted from lidar derived dem and were analysed to determine a range of best fitting morphological ages through monte carlo simulation a locally applicable sediment transport coefficient diffusivity was calibrated as 5 5 1 6 m 2 ky given the morphological age of the t1 t2 riser and its independently known age taking this calibrated coefficient we estimate age ranges of 11 6 3 4 ka 6 5 1 4 ka 5 3 1 1 ka and 4 2 1 2 ka for terraces t3 t4 t5 and t6 respectively under the assumption that the age of the riser is close to the abandonment age of the lower surface these new terrace ages combining climate proxy records from the oxygen isotope curve from the guliya ice cap and paleoearthquake events in the dushanzi fault related fold suggest that tectonic activity may be an important factor in the formation of lower terraces within the growing anticlines while in more extensive areas beyond anticlines climate changes controlled the main deposition and incision events in the present study area and thus terrace formation of t1 t3

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

the rio caliente ignimbrite analysis of a compound intraplinian ignimbrite from a major late quaternary mexican eruption the rio caliente ignimbrite is a multi flow unit orcompound ignimbrite formed during a major late quaternary explosive rhyolitic eruption of la primavera volcano mexico the eruption sequence of the ignimbrite is complex and it occurs between lower and upper plinian air fall deposits it is therefore anintraplinian ignimbrite air fall layers pyroclastic surge mudflow and fluviatile reworked pumice deposits also occur interbedded between ignimbrite flow units a chaotic near vent facies of the ignimbrite includes co ignimbrite lag breccias segregated from proximal pumice flows the facies locates a central vent but one which could not have been associated with a well defined edifice many of the lithics in the exposed lag breccias and near vent facies of the ignimbrite appear to be fragments of welded rio caliente ignimbrite and indicate considerable vent widening or migration during the eruption nearer vent the ignimbrite is thickest and composed of the largest number of flow units here it is welded and is a simple cooling unit evidence suggests that it was only the larger thicker pumice flows that escaped to the outer parts of the sheet detailed analysis of four flow units indicates that the pumice flows were generally poorly expanded less mobile flows which would be produced by collapse of low eruption columns the analogy of a compound ignimbrite with a compound lava flow is therefore good a compound lava flow forms instead of a simple one when the volumetric discharge rate or intensity is low and in explosive eruptions this predicts lower eruption column heights a corollary is that the ignimbrite has a high aspect ratio

active thrust sheet deformation over multiple rupture cycles a quantitative basis for relating terrace folds to fault slip rates many recent thrust fault earthquakes have involved coseismic surface faulting and folding revealing the multifaceted nature of active thrust sheet deformation we integrate records of surface deformation subsurface structure and geochronology to investigate active surface deformation over multiple rupture cycles across the southern junggar thrust sjt in the southern junggar basin nw china fluvial terrace geometries extracted from a 1 m digital elevation model reveal records of surface faulting across a prominent fault scarp in addition terraces exhibit progressive folding across fold scarps fault and fold scarps are spatially coincident with a surface emergent sjt splay and subsurface fault bends along the sjt respectively constrained by seismic reflection data we quantify the magnitude of fault slip at depth implied by fold scarps along holocene aged terraces our method yields results consistent with independent estimates of slip implied by fault scarp relief for the same terraces four late quaternary terrace records are less continuous preserved only as fold scarps that suggest folding kinematics involving a component of limb rotation we develop a new method for quantifying fault slip at depth from terrace folds using a mechanical forward modeling approach our analysis yields quantitative relations between fold dip and fault slip allowing us to quantify sjt fault slip from terrace folds from 250 ka present sjt fault slip rate has decelerated from 7 0 mm yr in the late quaternary to 1 3 mm yr throughout the holocene these results provide new insight into the kinematics of fault bend folding for natural structures and define new methods to accurately estimate fault slip and slip rates from terrace folds in active thrust sheets

structure of la primavera caldera jalisco mexico deduced from gravity anomalies and drilling results abstract previous studies of la primavera caldera have mostly been based on surface geology and topography since 1980 many wells exploring for geothermal energy have reached depths of about 2 to 3 km at the center of the caldera the results of the drillings together with those of the gravity surveys provide information about the subsurface structure of the caldera and shed light on its formation the drilling results and gravity anomalies at la primavera caldera and san marcos located at about 40 km distance from the caldera suggest that regional gravity anomalies can be interpreted in terms of depths of the granitic basements the basement beneath la primavera caldera is about 3 km deep and consists of roughly the same horizon as that beneath san marcos the drilling results within the caldera reveal that the depth of the caldera fills ranges from 0 3 to 1 km at the drilling sites the andesite basement about 1 km deep remains approximately horizontal and the granitic basement has a depth of about 3 km the surface topographies such as the postcaldera domes scarcely disturb the subsurface strata the local gravity anomalies show two lows within the caldera reflecting the configuration of caldera bottom two funnel shaped depressions one of which corresponds to a vent of the tala tuff deduced from geological observations the mass deficiency within the caldera estimated from the gravity anomaly satisfies the general relationship that the mass deficiency is proportional to the caldera diameter cubed this means that caldera structure is three dimensional the larger the diameter the deeper the funnel shape at present this argument may be limited to funnel shaped calderas

the saturation behaviour of pumice and some sedimentological implications abstract caldera forming explosive eruptions from rhyolitic volcanoes typically produce huge quantities of pyroclastic material blanketing the landscape and triggering long term voluminous and widespread sedimentary responses pumice is a major component of such eruptions but its behaviour in the sedimentary environment is little understood its most notable feature is its very low density which frequently enables pumice to float on water for long periods of time before eventually waterlogging enough to sink once fully saturated pumice behaves in a broadly similar way to normal clastic material in terms of its hydrodynamic behaviour modified by its lower density however relatively little is known about its earlier behaviour in the sedimentary environment and in particular the manner and rate by which initially dry pumice absorbs water in this paper we develop a mathematical model which predicts that the time required for a pumice clast to saturate is proportional to the square of its radius tests on samples of real pumice accord with predicted trends and match lacustrine pumiceous facies observed in the field the ability to predict the time required for large pumice clasts to sink may provide a tool for estimating the timescales over which certain rapid post eruptive sedimentary processes operate

a new shortening rate across the dushanzi anticline in the northern tian shan mountains china from lidar data and a seismic reflection profile abstract in the northern foreland basin of the tian shan mountains strata have been intensively deformed as a result of the ongoing cenozoic indian eurasian collision the dushanzi anticline lies in the northernmost deformation belt of the tian shan mountains understanding the shortening rate and paleoseismicity of the dushanzi anticline is important for both understanding the propagation of the thrust front of the tian shan mountains and for assessing seismic hazards in this highly populated area here we integrate lidar derived topographic data a high quality seismic reflection profile and field observations across the dushanzi anticline to resolve the holocene deformation history of the anticline a reconstructed longitudinal profile along the kuitun river that flows across the dushanzi anticline demonstrates a holocene history of both folding and faulting the total shortening from faulting is 4 4 0 1 m while the shortening accommodated by folding is 12 6 1 1 m since 7 5 10 ka b p a total of 17 0 1 1 m of shortening has occurred across the dushanzi anticline in the holocene at a rate of 2 0 0 2 mm a this shortening represents up to 18 of the 11 mm a total shortening rate across the entire eastern tian shan mountains at this longitude the holocene shortening rate of the dushanzi anticline is 6 times greater than its long term average shortening rate 0 3 0 1 mm a since 4 8 ma furthermore we analyzed a displaced terrace sequence at a site along the dushanzi frontal fault and found that the average coseismic dip slip displacement is 2 5 0 1 m with an average recurrence interval of 2 8 0 3 ka

crustal and upper mantle structure under the tien shan from surface wave dispersion long period seismograms of nuclear explosions and natural earthquakes in central asia recorded at three digital stations of the laboratoire de detection geophysique ldg network in france attest to a significant propagation effect in the tien shan area this allows for an investigation of the deep structures under the range which has been the site of particularly intense intracontinental deformation since about the middle miocene group velocity curves have been obtained by regionalization for pure paths across either the central or eastern tien shan they indicate a crust of approximately 50 55 km in thickness and particularly low shear wave velocities under the central tien shan our study suggests lateral variation of the deep structures under the range which could be related to a westward increase along the range of cumulative amount and rate of shortening

the submarine eruption of the bombarda volcano milos island cyclades greece the milos volcanic field includes a well exposed volcaniclastic succession which records a long history of submarine explosive volcanism the bombarda volcano a rhyolitic monogenetic center erupted 1 7 ma at a depth 200 m below sea level the aphyric products are represented by a volcaniclastic apron up to 50 m thick and a lava dome the apron is composed of pale gray juvenile fragments and accessory lithic clasts ranging from ash to blocks the juvenile clasts are highly vesicular to non vesicular the vesicles are dominantly tube vesicles the volcaniclastic apron is made up of three fades massive to normally graded pumice lithic breccia stratified pumice lithic breccia and laminated ash with pumice blocks we interpret the apron beds to be the result of water supported volcaniclastic mass how emplacement derived directly from the collapse of a small volume subaqueous eruption column and from syn eruptive down slope resedimentation of volcaniclastic debris during this eruptive phase the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion the lava dome emplaced later in the source area is made up of flow banded lava and separated from the apron by an obsidian carapace a few meters thick the near vertical orientation of the carapace suggests that the dome was intruded within the apron remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement

subaqueous eruption and emplacement of ot2 in the middle miocene iizuka formation noto peninsula japan abstract ot2 okada tuff 2 is one of six rhyolitic tuff beds that occur in a middle miocene marine diatomite lower iizuka formation and are known as the okada tuff ot2 is well sorted and thins and thickens infilling channels 1 3 m across and 0 30 cm deep with a thickness up to 30 cm small channels 10 30 cm across and 1 10 cm deep are commonly superimposed within wider channels a thin diatomite layer is ripped from the substrate up to a level immediately above the small channels the basal part beneath the ripped up diatomite layer is dominated by ash components with vague wavy stratifications above the ripped up diatomite layer diatomite clasts are dispersed and pumice lapilli increase upward in amount and size with local interruption at a middle lower level by a poorly defined pumice lapilli poor thin layer many glass and pumice shards are blocky with curviplanar surfaces and jigsaw cracks presumably produced by phreatomagmatic explosions the poorly defined two layers of ot2 are interpreted to be ash turbidites individually produced by discrete phreatomagmatic explosions lenticular bedforms and channels indicate that the currents were fully turbulent and unsteady fed by the submarine eruptions upward coarsening of pumice probably represents settling lag of hot pumice ot2 perhaps provides potential diagnostic features to identify eruption fed turbidites

effects of water depth on pumice formation in submarine domes at sumisu izu bonin arc western pacific domes of the sumisu volcanic complex western pacific having summits at ocean depths of 1100 600 245 and 95 m are mantled with compositionally identical rhyolitic pumice that has similar vesicularity but that varies systematically in distribution size and surface texture suggesting that facies and morphology can serve as useful indicators of eruption depth at depths 500 m the pumice formed a thick carapace on dense rhyolite and disintegrated by quench fracture and mechanical failure into a jumble of giant meters to tens of meters polyhedral blocks with smooth curviplanar surfaces that display a single quenched margin vesiculation was arrested on eruption in seawater in all but the interior of the thickest carapace at 500 m depths the pumice occurs as an apron of blocky giant and smaller rough textured clasts enclosed by quenched margins and pockmarked by coarse cm vesicles no carapace pumice occurs and the summit is composed of craggy dense dome rock these shallower water pumice clasts resemble those spalled from historic submarine dome forming eruptions that buoyed to the sea surface we interpret spalling to result from vent derived weak volatile driven explosions that take place at water depths 500 m our study shows that an increase in hydrostatic pressures over a range of 12 mpa reduces volatile driven explosivity for subaqueous rhyolitic dome forming eruptions but does not affect vesicularity we conclude that meter size highly vesicular pumice is diagnostic of subaqueous dome eruptions in water depths of at least 1300 m and its morphology can be used to distinguish between explosive and effusive origins

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

late oligocene miocene intra continental mountain building of the harke mountains southern chinese tian shan evidence from detrital aft and ahe analysis abstract as the largest intra continental mountain belt in central asia the tian shan mountain range underwent a diachronous uplift history in different regions the present crustal shortening rate of this mountain range is also characterized by an along strike variation and decreases from west to east the harke mountains located in the middle part of the southern tian shan accommodate a relatively lower crustal shortening rate but host the highest topography of this mountain range this study aims to restore the cenozoic mountain building history of the harke mountains detrital aft and ahe analyses were conducted for paleocene pliocene sediments and modern moraines in the kuqa depression an abrupt increase in the lag time of the detrital aft young age components at 26 23 ma indicates that the uplift of the southern tian shan initiated in the late oligocene early miocene which is consistent with the regional tectonic activation of the tian shan mountain range in the late miocene the basement of the harke mountains underwent rapid exhumation from 10 to 6 ma comparing our result with previously published tectonic data we infer that the intense exhumation in our study area corresponds to the intensified deformation of the whole tian shan mountain range in the late miocene which was probably driven by the accelerated convergence between the tarim and tian shan

reply to a discussion of the rio caliente ignimbrite analysis of a compound intraplinian ignimbrite from a major late quaternary mexican eruption by g a mahood the discussion by mahood 1983 concerning my paper on the rio caliente ignimbrites is most welcome even though one would have to admit somewhat tardy and a tittle over vehement in places my work on the rio caliente ignimbrite formed part of a larger study on la primavera from imperial college london during the mid and late 70s and mahood s criticism also concerns other papers and theses published by the group wright 1979 clough 1981 clough et al 1981 walker et al 1981 it is a pity that some of the points raised here could not have been considered in some of mahood s previous papers on la primavera her review paper on the geology and geochemistry of la primavera mahood 1981 would have been an ideal forum but unforhmately in this paper the study carded out by imperial college was ignored this cannot be an oversight because as early as 1976 mahood pers comm was well aware of our work on the volcano which began with a reconnaissance study in 1973

morphologic dating of scarps formed by repeated slip events along the san andreas fault carrizo plain california morphologic dating of fault scarps determines late cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model we postulate that the material transport rate along the profile is a function only of local slope and is transport limited morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant the time since the downdrop was initiated or the fault began to slip we calibrated the hillslope development model on the southwest facing scarp southeast of wallace creek along the san andreas fault saf in the carrizo plain california the scarp has been exposed by right lateral offset of a southeast sloping shutter ridge located on the southwest side of the saf and by vertical offset related to secondary deformation we assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge forward modeling of profile development yielded a mass diffusivity of 8 6 0 8 m2 kyr 1 normal fault slip rates were determined for two graben bounding faults in the northern elkhorn hills in the southeastern carrizo plain by applying the calibrated to the degradation of the scarps to determine the scarp age one fault scarp began to form about 12 kyr ago and the other about 63 kyr ago those ages and estimates of the dip slip along the faults result in slip rates of 1 2 mm yr 1

application of in situ produced cosmogenic 10be and 26al to the study of lateritic soil development in tropical forest theory and examples from cameroon and gabon abstract depth profiles of in situ produced cosmogenic nuclides including 10 be t 1 2 1 5 10 6 years and 26 al t 1 2 0 73 10 6 years in the upper few meters of the earth s crust may be used to study surficial processes quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations in this paper we discuss the fundamentals of the method and apply it to two lateritic sequences located in african tropical forests

late pleistocene acceleration of deformation across the northern tianshan piedmont china evidenced from the morpho tectonic evolution of the dushanzi anticline we document the temporal evolution of deformation in the northern tianshan piedmont where the deformation is partitioned across several thrusts and folds we focus on the dushanzi anticline where abandoned terraces and growth strata allow us to constrain the history of folding since the miocene based on subsurface seismic imaging structural measurements and morphological analysis we show that this anticline is associated with two decollement levels we use kink band migration in growth strata dated by paleomagnetism to constrain the shortening from the mio pliocene to the holocene our results show that the dushanzi anticline has been active since at least 8 ma and that the fold grew at a steady shortening rate of 0 6 0 1 mm yr from 8 to 1 5 ma with possible variations from 2 5 to 1 5 ma then it accelerated rapidly to a rate of 4 3 1 0 mm yr over at least the last 100 ka these results together with similar temporal shortening evolutions across other structures suggest that the deformation rate across the eastern tianshan piedmont increased relatively recently this may reflect either a redistribution of the deformation from the internal structures toward the borders or a general acceleration of the deformation across the entire range

late miocene to quaternary slip history across the qiulitag anticline in the southern tianshan piedmont in this study we reconstruct the miocene to quaternary shortening history across the qiultag anticline a complex fault bend fold located in southern tianshan we studied the yaha and kuche sections where we combined surface structural measurements and seismic imaging to model the stratigraphic horizons the history of folding was reconstructed based on magnetostratigraphic analyses and eight cosmogenic burial ages in kuche pleistocene deformation rates were also quantified in yaha based on a deformed fluvial terrace that we dated to 67 ka using a cosmogenic depth profile our results suggest that the fold grew at a mean slip rate of 0 9 1 3 mm a in both sections but accelerated to 2 5 mm a during the pleistocene in kuche these results support a migration of the deformation toward the basin during the pleistocene and suggest that most of the present deformation of the tianshan is accommodated across the external structures of the range

post collapse volcanic history of calderas on a composite volcano an example from roccamonfina southern italy roccamonfina part of the roman potassic volcanic province is an example of a composite volcano with a complex history of caldera development the main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the brown leucitic tuff blt around 385 000 yr bp the campagnola tuff the youngest ignimbrite of the blt however drapes the caldera margin and must postdate at least the initial stages of collapse during the subsequent history of the caldera there were several major explosive eruptions the largest of these was that of the galluccio tuff at about 300 000 yr bp it is likely that there was further collapse within the main caldera associated with these eruptions it is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr bp early in the history of roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera one of the youngest major events on roccamonfina occurred at the head of this northern caldera with explosive activity producing the conca ignimbrite and associated caldera there is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

geometry and kinematics of mykonos detachment cyclades greece evidence for slip at shallow dip 1 the eastern part of mykonos island cyclades greece shows the detailed internal structure of a two branch shallow dipping extensional detachment system of miocene age this paper shows that the last stage of slip along the detachment during the deposition of syn rift sediments occurred with a very low dip and proposes that this geometry prevailed since the initiation of extension extensional deformation during and after a 13 ma old granite intrusion is taken up by two main shallow dipping shear zones 1 the lower livada detachment which extends laterally across tinos island is a ductile structure located at the interface between the granite and the upper cycladic nappe metabasites a pervasive top to the ne shearing deformation is observed throughout the granite in this island with a strong gradient toward the intrusive contact later brittle faults shallowly and steeply dipping rework the ductile deformation with the same overall shear sense 2 the upper mykonos detachment is brittle and separates the metabasites from late miocene sandstones and conglomerates the detachment fault dips 12 15 toward the nne and its sense of shear is consistent with that of the livada detachment soft sediment deformation during the time of detachment faulting and the presence of steep normal faults that root into the detachment gouge indicate a shallow depth of deformation rotations about vertical and horizontal axes can be reconstructed within and below the detachment zone indicating that the overall direction of extension is nne ssw with a sense of shear toward the nne and the dip of the fault is throughout very low the two detachments have accommodated several tens of kilometers of horizontal extension during the formation of the aegean sea which emphasizes the importance of low angle extensional faults and shear zones in extensional tectonics

denudation intensity and control in the chinese tian shan new constraints from mass balance on catchment alluvial fan systems tectonics and climate are usually seen as the main controlling factors of denudation rates which seem to rise with the tectonic activity and to decrease when the climate becomes drier however the low denudation rates observed in semi arid to arid contexts are generally measured on orogenic plateaus where the respective influence of the flat relief and the dry climate cannot really be unravelled the chinese tian shan was chosen as a case study in the northern piedmont of this mountain range a series of well preserved quaternary alluvial fans offer the opportunity to perform a mass balance study at the scale of several catchment areas and several hundreds of thousands of years based on a geometrical reconstruction of these fans the volumes of sediments exported out of 10 drainage basins during the middle late pleistocene from 300 to 12 kyr and the holocene from 12 kyr to present have been estimated from these volumes an average denudation rate of 135 m myr was determined in the tian shan range for the last 300 kyr in agreement with other mass balances performed in the same area the typical denudation intensity of the northern tian shan is thus of a few hundred meters per million years at most regardless of the space and time scales considered from a comparison with denudation rates in other mountain ranges throughout the world we suggest that a dry climate can dramatically limit the denudation intensity even in active orogenic systems with a high topographic gradient like the tian shan as a result the time required to reach equilibrium between denudation and rock uplift in these systems could be extremely long i e of more than several million years copyright 2016 john wiley sons ltd

enclaves in the cadillac mountain granite coastal maine samples of hybrid magma from the base of the chamber the cadillac mountain intrusive complex is dominated by the introduction cadillac mountain granite and a 2 3 km thick section of interlayered enclaves occur in nearly all granites and have recently gabbroic dioritic and granitic rocks which occurs near the base of been the focus of many studies see reviews by vernon the granite the layered rocks record hundreds of injections of basaltic 1983 and didier barbarin 1991 although enclaves magma that ponded on the chamber floor and variably interacted may have originated in many different ways and from with the overlying silicic magma magmatic enclaves ranging in different sources there has been a growing consensus composition from 55 to 78 wt sio2 are abundant in granite that there are textural criteria to recognize a class of above the layered mafic rocks the most mafic enclaves are highly enclaves that formed from different magmas that were enriched in incompatible elements and depleted in compatible elemingled into the granitic magma while it was still mobile ments their compositions can be best explained by periodic vernon 1984 1990 these can appropriately be termed replenishment mixing and fractional crystallization of basaltic magmatic enclaves their compositions are commonly magma at the base of the chamber the intermediate to silicic intermediate but can vary from basaltic to highly silicic enclaves formed by hybridization between the evolved basaltic magma magmatic enclaves occur in all types of granite and are and resident silicic magma there is little evidence for significant probably the dominant type of enclave in most calcexchange between enclaves and the enclosing granite instead alkaline i type granites in spite of partial reequilibration hybridization apparently occurred between stratified mafic and silicic enclaves of this type commonly have nd isotopic commagmas at the base of the chamber enclaves in a restricted area positions that are distinct from the enclosing granite and commonly show distinctive compositional characteristics suggesting support their formation from mantle derived magmas they were derived from a discrete batch of hybrid magma enclaves holden et al 1987 were probably dispersed into a localized portion of the granitic the compositions of magmatic enclaves can vary magma when replenishment or eruption disrupted the intermediate widely even within a single pluton and they can only layer rarely be interpreted as simple mixtures between an original basaltic magma and the host granitic magma there is ample petrographic and chemical evidence in many enclaves for hybridization mixing of liquids and

late cenozoic tectono geomorphologic evolution of the northern tian shan mountain range insight from u pb ages of detrital zircon grains from the upper oligocene quaternary sediments of the southern junggar basin abstract being one of the largest intra continental orogens of the world the tian shan orogenic belt was uplifted to its present elevation due to the far field effect of the india asia convergence in this study we performed a systematic study on the upper oligocene quaternary sedimentary rocks from the southern junggar basin including conglomerate clast counting and detrital zircon u pb dating to reconstruct the late cenozoic uplift history of the northern tian shan mountain range the new detrital zircon u pb data provide new constrains on the late cenozoic intra continental deformation of the borohoro range the yili central tian shan and north tian shan were the major sources for the junggar basin during the latest cretaceous paleogene period at that time the borohoro range was characterized by low topography and wide drainage pattern as the uplift of the north tian shan commenced at 25 23 ma the high topography of the northern borohoro range blocked the transport of sediments from the yili central tian shan to the north the north tian shan became the primary provenance area of the southern junggar basin according to sedimentary provenance analysis and geomorphologic survey we infer that the yili central tian shan started to uplift at 12 9 ma combined with previously published data our results suggest that the middle miocene uplift event most likely occurred in both the hinterland and foreland regions along the whole tian shan mountain range

uplift shortening and steady state topography in active mountain belts we present a tectonic surface process model used to investigate the role of horizontal shortening in convergent orogens and the effects on steady state topography the tectonic model consists of a specified velocity field for the earth9s surface and includes a constant uplift rate and a constant horizontal strain rate which varies to reflect the relative importance of frontal accretion and underplating in an orogenic wedge the surface process model includes incision of a network of rivers formed by collection of applied precipitation and diffusive hillslope mass transfer three non dimensional parameters describe this model a ratio of the maximum horizontal velocity to the vertical velocity a peclet number expressing the efficiency of the hillslope diffusion relative to the uplift rate and a fluvial erosion number reflecting the fluvial incision efficiency relative to the uplift rate a series of models are presented demonstrating the resultant steady state landforms parameterized by these three numbers a finite velocity ratio results in an asymmetric form to the model mountain range although the magnitude of the asymmetry also depends on the peclet number topographic steady state is achieved faster for models with no horizontal component to the velocity field with finite horizontal velocity topographic steady state is achieved only at the scale of the entire mountain range even the first order drainage basins are unstable with time in the presence of horizontal shortening we compare our model results to topographic profiles from active mountain ranges in taiwan new zealand and the olympic mountains of washington state all these examples exhibit asymmetric topographic form with the asymmetry consistent with the polarity of subduction suggesting that horizontal tectonic motion is affecting the macro geomorphic form of these ranges

limited impact of quaternary glaciations on denudation rates in central asia because of its essential role in coupling climate and tectonics denudation is a key parameter when constraining the history of earth s surface this is particularly true at the pliocene pleistocene transition and the potential impact of the onset of quaternary glaciations remains strongly debated in the present study we measured in situ cosmogenic 10be within continuous late cenozoic sedimentary sections that had already been dated using magnetostratigraphy the new data were obtained from four sedimentary basins in the northern and southern tianshan range central asia we first thoroughly discuss how in situ cosmogenic 10be concentrations can be corrected for radioactive decay and for the contribution of postdepositional cosmogenic accumulation to derive the paleo denudation rates our analysis shows that in the four sedimentary records the potential bias remains low enough to consider the derived denudation rates reliable the four records although likely influenced by local particularities due to lithological heterogeneity and local tectonics display similar trends of continuously increasing denudation between ca 9 ma and the present these rates have remained relatively high but steady since 4 ma 1 5 m y before the onset of the quaternary glacial cycles though the rejuvenation of the tianshan range since 11 ma may explain most of the progressive increase 5 in denudation our data suggest that the quaternary glaciations had only a limited impact on denudation in the tianshan our data however indicate an increase in the spatial and high frequency variability 1 m y of the denudation rates between 3 and 1 ma this may correspond to a transient readjustment of the landscape in response to the onset of quaternary glacial cycles

grain size distribution of volcaniclastic rocks 2 characterizing grain size and hydraulic sorting quantification of the grain size distribution of sediments allows interpretation of processes of transport and deposition jutzeler et al 2012 developed a technique to determine grain size distribution of consolidated clastic rocks using functional stereology allowing direct comparison between unconsolidated sediments and rocks here we develop this technique to characterize hydraulic sorting and infer transport and deposition processes we compare computed grain size and sorting of volcaniclastic rocks with field based characteristics of volcaniclastic facies for which transport and depositional mechanisms have been inferred we studied pumice rich subaqueous facies of volcaniclastic rocks from the oligocene ohanapecosh formation ancestral cascades washington usa pliocene dogashima formation izu peninsula honshu japan miocene manukau subgroup northland new zealand and the quaternary sierra la primavera caldera jalisco state mexico these sequences differ in bed thickness grading and abundance of matrix we propose to evaluate grain size and sorting of volcaniclastic deposits by values of their modes matrix proportion 2 mm f 1 and d16 instead of median diameter d50 and standard deviation parameters f 1 and d16 can be uniformly used to characterize and compare sieving and functional stereology data volcaniclastic deposits typically consist of mixtures of particles that vary greatly in density and porosity hydraulic sorting ratios can be used to test whether inferred density of mixed clast populations of pumice and dense clasts are hydraulically sorted with each other considering various types of transport under water evaluation of this ratio for our samples shows that most studied volcaniclastic facies are deposited by settling from density currents and that basal dense clast breccia are emplaced by shear rolling these hydraulic sorting ratios can be applied to any type of clastic rocks and indifferently on consolidated and unconsolidated samples

luminescence dating of the stratzing loess profile austria testing the potential of an elevated temperature post ir irsl protocol abstract feldspar infrared stimulated luminescence irsl signals saturate at 2000 gy i e 500 700 ka assuming a dose rate of 3 4 gy ka typical for loess and it is therefore theoretically possible to date middle pleistocene loess however the accuracy of age estimates is hampered by anomalous fading which leads to significant age underestimation fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses as the growth curve approaches saturation recent studies have identified a post ir irsl signal that shows less fading and is thus less dependent on accurate fading corrections this study builds upon these investigations and applies a post ir irsl sar dating protocol to polymineral fine grain samples of the loess palaeosol sequence in stratzing lower austria after a preheat at 320 c 60 s and an ir bleach at 50 c 200 s irsl was measured at 290 c for 200 s the same set of conditions were used to measure the response to a test dose recycling ratios recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation although finite residual doses of up to 20 gy are observed for the oldest samples the natural signal is in or close to saturation indicating that fading is negligible in nature this observation is inconsistent with the measured laboratory fading rates of 1 1 5 decade and needs further investigation

new constraints on the late quaternary landscape evolution of the eastern tibetan plateau from 10be and 26al in situ cosmogenic nuclides abstract based on terrestrial cosmogenic nuclide tcn constraints from depth profiles of one granitic regolith from wumingshan and five fluvial terraces from xianshuihe and zagunao rivers we discuss the timing of the last deglaciation the landscape scale denudation and fluvial incision rates across the eastern tibetan plateau in relation to previous work we present a three dimensional graph visualization approach and corresponding constraints to better assess the feasibility and applicability of cosmogenic nuclides depth profile dating the exposure age older than 19 4 ka of the wumingshan regolith corresponds to the retreat of the palaeo daocheng ice cap which covered the yidun terrane during the last glacial maximum lgm most basin wide denudation rate data in the eastern tibetan plateau are lower than 130 mm ka 47 n 90 which is consistent with the wumingshan regolith denudation rate lower than 52 8 mm ka and thus indicate that the landscape scale denudation has been stabilized after the last deglaciation considering the reduction of integrated bulk density due to the accumulation of lower density loess we estimate mean exposure ages of xianshuihe and zagunao river terraces of 4 0 0 7 ka 5 9 0 3 ka 13 4 2 0 ka and 16 6 1 4 ka the observed increase in incision rate from 0 39 mm yr over long timescale 600 ka to 5 88 mm yr over the last 15 ka at the xianshuihe river site is probably due to the transition from glacial to interglacial climatic conditions the fewer abandoned terraces along the zagunao river after the heinrich event 1 h1 indicates that the climate change during the latest glacial interglacial transition impacted less the landscape evolution in a relatively lower elevation area comparison with previously reported fluvial incision rates elsewhere across the eastern margin of the tibetan plateau indicates that incision rates are mainly influenced by abrupt climate change or intensified summer monsoon since the early holocene but probably controlled by regional tectonic uplift or fluvial headward retreat as the timescale increases overall we propose a synthetic pattern of landscape evolution mainly dominated by long term tectonic uplift together with fluvial headward erosion episodically influenced by climatic change throughout the late quaternary

paleo erosion rates in central asia since 9 ma a transient increase at the onset of quaternary glaciations erosion is a fundamental player of the interactions existing between internal geodynamics and climate in particular through its influence on the carbon dioxide budget however long term 1 ma erosion rates estimated indirectly from sediment budget remain poorly constrained while some studies suggest that worldwide erosion rates increased at the plio pleistocene climatic transition 4 2 ma the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins in the present study we estimate erosion rates over the last 9 ma using in situ produced cosmogenic 10be concentrations measured in magnetostratigraphically dated continental sediments we focus on an intracontinental endorheic watershed draining the northern tianshan in central asia a key region regarding the ongoing debate while erosion rates between 0 1 and 1 mm yr 1 are derived from most of our record they reach values as high as 2 5 mm yr 1 from 2 5 to 1 7 ma then after 1 7 ma recent and modern erosion rates fell below 1 mm yr 1 this temporary increase is correlated with the onset of quaternary ice ages and suggests that global climate had a significant and transient impact on erosion

planation surfaces of the tian shan range central asia insight on several 100 million years of topographic evolution abstract in central asia numerous fragments of planation surfaces are visible within the present day topography however their precise timing of formations is still poorly constrained and it is not clear if they are remnants of a single extensive planation surface or if they represent different planation episodes by reconstructing the landscape evolution of the tian shan region and by analyzing the relations between the planation surfaces preserved within the eastern tarim basin and the sedimentary record we demonstrate that the numerous erosional surfaces preserved within the tian shan range represent different episodes of surfaces genesis these erosion events span from the late paleozoic to the early cenozoic the widespread preservation of large fragments of these surfaces within the tian shan range implies that this region did not undergo strong relief building during most of its mesozoic evolution but was dominated by plains associated to small hills along episodically active discrete tectonic structures finally the preservation of these surfaces within the active tian shan range implies a long term strong non equilibrium state of the topography during its cenozoic evolution this was probably promoted by the arid to semi arid climate prevailing since the late paleogene onset of relief building

active tectonics in southern xinjiang china analysis of terrace riser and normal fault scarp degradation along the hotan qira fault system the northern piedmont of the western kunlun mountains xinjiang china is marked at its easternmost extremity south of the hotan qira oases by a set of normal faults trending n50e for nearly 70 km conspicuous on landsat and spot images these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the tarim platform loaded by the western kunlun northward overthrust the hotan qira normal fault system vertically offsets the piedmont slope by 70 m highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high successive stream entrenchments in uplifted footwalls have formed inset terraces we have leveled topographic profiles across fault scarps and transverse abandoned terrace risers the state of degradation of each terrace edge has been characterized by a degradation coefficient derived by comparison with analytical erosion models edges of highest abandoned terraces yield a degradation coefficient of 33 4 m 2 profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model the analysis shows that 1 rate of fault slip remained essentially constant since the aggradation of the piedmont surface and 2 the occurrence of inset terraces was synchronous at all studied sites suggesting a climate driven terrace formation observation of glacial and periglacial geomorphic features along the northern front of the western kunlun range indicates that the qira glaciofluvial fan emplaced after the last glacial maximum during the retreat of the kunlun glaciers 12 22 ka the age of the most developed inset terrace in uplifted valleys is inferred to be 10 3 ka coeval with humid climate pulses of the last deglaciation the mass diffusivity constant k t being time b p in the hotan region is determined to be 3 3 1 4 m 2 10 3 years consistent with other estimates in similar climatic and geologic environments of western china these results imply a minimum rate for the tarim subsidence of 3 5 2 mm yr if western kunlun overthrusts the tarim platform on a crustal ramp dipping 40 45 to the south it would absorb at least 4 5 3 mm yr of convergence between western tibet and tarim

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

major temporal variations in shortening rate absorbed along a large active fold of the southeastern tianshan piedmont china the investigation of deformation rates on a mountain piedmont can provide key information for improving our understanding of the overall dynamics of a mountain range here we estimate the shortening rate absorbed by a quaternary emergent detachment fold on the southeastern piedmont of the tianshan china our work is primarily based on new 10be cosmogenic exposure dating of deformed alluvial surfaces the method we have developed combines depth profiling with sampling of surface cobbles thereby allowing exposure time erosion rate and inheritance to be simultaneously constrained the exposure ages of the uppermost uplifted alluvial surfaces are around 140 17 ka140 17 ka 130 9 ka130 9 ka and 47 9 ka47 9 ka from west to east a terrace lying below the 140 ka surface is dated at 65 5 ka65 5 ka the ages of the uplifted and folded alluvial surfaces were then combined with estimates of shortening obtained using two distinct methods 1 the excess area method where sedimentation rates extracted from magnetostratigraphic studies are used to determine the amount of sedimentation after the abandonment of the river and 2 a folding model derived from sandbox experiments the late pleistocene shortening rates are shown to be between 0 4 0 1 mm yr0 4 0 1 mm yr and 0 8 0 5 mm yr0 8 0 5 mm yr on the western part of the fold and 2 1 0 4 mm yr2 1 0 4 mm yr along its central part the central part of the frontal yakeng anticline therefore accommodates up to 25 of the total shortening currently absorbed across the whole eastern tianshan range 8 mm yr however this situation seems to have prevailed for only the last 150 ka as the shortening rate absorbed by this nascent fold was previously ten times slower while the initiation of folding of the yakeng anticline can be traced back to 5 5 ma ago the basinward migration of the active deformation front onto the yakeng fold is a relatively recent phenomenon and appears to be diachronous from west to east probably in relation to the tectonic activity of the folds in the hinterland

initial incision of the jinshan gorge of the yellow river china constrained by terrestrial in situ cosmogenic nuclides chronology abstract how post burial terrestrial in situ cosmogenic nuclides tcn production is build up in slow burial condition remains uncertain in this study we dated high fluvial terrace sediments that overlain by loess with a slow deposition rate that is based on the assumption of steady accumulation rate via 26al 10be burial dating method for sample in deep and rapid buried condition prior to slow overlying post burial production shows low component 4 6 in measured concentration however post burial production occupied 39 79 of measured 26al and 10be concentrations which suggests approximately 0 2 0 3 ma underestimation in simple burial dating mode if post burial production is neglected corrected by post burial production we yielded burial ages of two top terraces ca 1 7 2 5 ma and 1 5 ma respectively below the tangxian planation surface along the jinshan gorge of the yellow river implying that the jinshan gorge initially incised at ca 1 7 2 5 ma corresponding well to regional tectonic activities such as extension in the fenwei graben accelerative uplift of the tangxian planation surface vigorous dissection of north china and significant tectonic deformation in northeastern tibetan plateau the slow burial mode is probably a potential method for plateau paleo elevation estimation taking advantage of height sensitivity of tcn production rate if overlying loess magnetostratigraphic age is known

an upper pliocene coarse pumice breccia generated by a shallow submarine explosive eruption milos greece the filakopi pumice breccia fpb is a very well exposed pliocene volcaniclastic unit on milos greece and has a minimum bulk volume of 1 km3 it consists of three main units a basal lithic breccia 4 8 m mainly composed of angular to subangular andesitic and dacitic clasts up to 2 6 m in diameter b very thickly bedded poorly sorted pumice breccia 16 17 m and c very thick reversely graded grain supported coarse pumice breccia 6 5 20 m at the top the depositional setting is well constrained as shallow marine up to a few hundred metres by overlying fossiliferous and bioturbated mudstone this large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because 1 pumice clasts are the dominant component 2 the coarse pumice clasts 64 mm have complete quenched margins 3 very large 1 m pumice clasts are common 4 overall the formation shows good hydraulic sorting and 5 a significant volume of ash was deposited together with the coarsest pyroclasts

an unusual bed of giant pumice in mexico we report here that a remarkable bed of giant sized pumice blocks occurs within an old caldera of the major late quaternary rhyolitic volcano of sierra la primavera mexico fig 1a the bed lies within a 100 m thick sedimentary sequence distributed over a near circular area 10km across the margin of this circular area closely parallels an incomplete ring of prophyritic comendite lava domes fig 1b some of which may be shallow intrusions emplaced into the sediments the vents of these domes are believed to lie on a ring fault fig 1b the sedimentary sequence now gently updomed fig 1c is believed to have accumulated in a caldera lake the shoreline of which lay up to 1 km outside the ring fault

contrasting pyroclast density spectra from subaerial and submarine silicic eruptions in the kermadec arc implications for eruption processes and dredge sampling pyroclastic deposits from four caldera volcanoes in the kermadec arc have been sampled from subaerial sections raoul and macauley and by dredging from the submerged volcano flanks macauley healy and the newly discovered raoul sw suites of 16 32 mm sized clasts have been analyzed for density and shape and larger clasts have been analyzed for major element compositions density spectra for subaerial dry type eruptions on raoul island have narrow unimodal distributions peaking at vesicularities of 80 85 whereas ingress of external water wet type eruption or extended timescales for degassing generate broader distributions including denser clasts submarine erupted pyroclasts show two different patterns healy and raoul sw dredge samples and macauley island subaerial emplaced samples are dominated by modes at 80 85 implying that submarine explosive volcanism at high eruption rates can generate clasts with similar vesicularities to their subaerial counterparts a minor proportion of healy and raoul sw clasts also show a pink oxidation color suggesting that hot clasts met air despite 0 5 to 1 km of intervening water in contrast macauley dredged samples have a bimodal density spectrum dominated by clasts formed in a submarine eruptive style that is not highly explosive macauley dredged pyroclasts are also the mixed products of multiple eruptions as shown by pumice major element chemistry and the sea floor deposits reflect complex volcanic and sedimentation histories the kermadec calderas are composite features and wide dispersal of pumice does not require large single eruptions when coupled with chemical constraints and textural observations density spectra are useful for interpreting both eruptive style and the diversity of samples collected from the submarine environment

stratigraphy chronology and sedimentology of ignimbrites from the white trachytic tuff roccamonfina volcano italy abstract we describe the stratigraphy chronology and grain size characteristics of the white trachytic tuff wtt of roccamonfina volcano italy the pyroclastic rock was emplaced between 317 and 230 ma bp during seven major eruptive events units a to g and three minor events units bc cd and de these units are separated by paleosol layers and compositionally well differentiated pyroclastic successions stratigraphic control is favored by the occurrence at the base of major units of marker layers four wtt units 1 to 4 occur within the central caldera these are not positively correlated with specific extracaldera units the source of most of the wtt units was the central caldera units b and c were controlled by the western wall of the caldera whereas units d and e were able to overcome this barrier spreading symmetrically along the flanks of mc the maximum pumice size mp of units increases with distance from the caldera whereas the maximum lithic size ml decreases mp and ml of the marker layer of unit d mkda mkdp do not show any systematic variations with respect to the central caldera in contrast the thickness of surge mkda decreases with distance from the source and mkdp accumulates to the north of mc probably controlled respectively by mobility transport power and by wind blowing northwards the grain size characteristics of the wtt deposits are used for classifying the units there is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units large variation of components in subunit e1 with repetitive alternation of pyroclastic flow to surge through fallout vs surge deposits suggests that the process of eruption took place in a complex or piecemeal fashion pumice concentration zones pcz occur at all wtt levels on the volcano but they are much thicker and pumice clasts are much larger within the central caldera these were probably originated by the disruption of lava flow or dome to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava local basal pcz are in some cases similar to the lapilli rich layer 1p that has been described elsewhere and may have been deposited from currents transitional between pyroclastic surge and flow other basal pcz formed in response to small undulations in the substrate or can be originated by fallout lenticular pcz within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts some of which were buried by subsequant pyroclastic flows lithic concentration zones lcz also occur at various stratigraphic height within the extracaldera ignimbrites whereas intracaldera lcz are absent probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent lcz at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients a segregation process coarse lcz and coarse lithic breccias lb that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas are interpreted to be the result of slugs of lithic rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths these lcz become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows desegregation processes

giant rafted pumice blocks from the most recent eruption of taupo volcano new zealand insights from palaeomagnetic and textural data abstract giant blocks of pumice lie strewn along a former shoreline of intracaldera lake taupo new zealand and are the sole subaerial evidence of the most recent volcanism at the taupo supervolcano geochemically they are identical to material erupted during the complex and multiphase 1 8 ka taupo eruption which they post date by one to two decades the blocks some of which are 10 m long show complex jointing patterns indicative of both surface chilling and continued interior expansion as well as heterogeneous vesicularity with dense rims mean density 917 kg m3 grading via an intervening transition zone mean density 844 kg m3 into a more highly vesicular interior mean density 815 kg m3 analysis of thermal demagnetisation data indicates significant reorientation of the blocks as they cooled through a series of blocking temperatures some parts of block rims cooled to below 580 c well before emplacement on the shore whereas other parts in the interior and transition zones which cooled more slowly acquired different orientations before stranding some block interiors cooled after blocks were finally deposited and record the direction of the 1 8 ka field the blocks are believed to be derived from one or both of a pair of rhyolitic lava domes that developed on the bed of lake taupo several decades after the climactic taupo eruption over the inferred vent area these and similar giant rafted pumice blocks in other marine and lacustrine settings raise a number of questions about how volatile rich felsic magma can be erupted underwater with only limited thermal fragmentation furthermore the prolonged flotation of out sized fragments of vesiculated magma formed during subaqueous dome growth contrasts with the rapid sinking of smaller pieces of hot plinian pumice under laboratory conditions the genesis of pumice forming the blocks is not entirely clear most simply the blocks may represent part of a vesiculated carapace of a growing lava dome broken loose as the dome grew and deformed then rising buoyantly to the surface parts of the carapace could also be released by local magma water explosions some textures of the pumice however suggest fresher magma released from beneath the carapace this may suggest that silicic dikes and pillows pods intruded into a growing mound of silicic hyaloclastite itself formed by quench fragmentation and thermal granulation of the dike margins this fragmental cover would have inhibited cooling of a still hot and actively vesiculating interior which was then released to float to the surface by gravitational destabilisation and collapse of the growing pile following their formation the large fragments of pumice floated to the lake s surface where they were blown ashore to become embedded in accumulating transgressive shoreface sediments and continue cooling

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation 1 we present a methodology to derive the growth history of a fault tip fold above a basal detachment our approach is based on modeling the stratigraphic and geomorphic records of deformation as well as the finite structure of the fold constrained from seismic profiles we parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments assuming a stationary spatial pattern of deformation we simulate the gradual warping and uplift of stratigraphic and geomorphic markers which provides an estimate of the cumulative amounts of shortening they have recorded this approach allows modeling of isolated terraces or growth strata we apply this method to the study of two fault tip folds in the tien shan the yakeng and anjihai anticlines documenting their deformation history over the past 6 7 myr we show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation rate is known yielding respective rates of 2 15 and 1 12 mm yr across yakeng and anjihai consistent with the deformation recorded by fluvial and alluvial terraces this study demonstrates that the shortening rates across both folds accelerated significantly since the onset of folding it also illustrates the usefulness of a simple geometric folding model and highlights the importance of considering local interactions between tectonic deformation sedimentation and erosion

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

chemical and isotopic evidence for major mass transfer between mafic enclaves and felsic magma abstract in both the strontian and criffell zoned granitoid plutons certain chemical elements notably k rb ca sr and pb display a correlation between their concentration in microdiorite enclaves and their concentration in the immediately enclosing host granitic rock this appears to represent the effects of post incorporation mixing and exchange between the enclave and its host magma enclave initial 87 sr 86 sr ratios are indistinguishable from those of the host while enclave initial 143 nd 144 nd ratios are systematically more radiogenic establishing that these enclaves are not melt segregations nor restite the isotopic data are in agreement with the chemical data in indicating that sr is almost entirely derived from the host despite clear evidence of major mass transfer of alkali metals alkali earths and transition metals a comparison of the concentrations and ratios of hfse and ree and nd isotopic ratios with those of a number of potential starting protoliths allows the enclave precursors to be positively discriminated in this regard enclave hfse and ree compositions may allow for models of granitoid production by the injection of hot mantle derived magmas into the crust to be tested

erosion as a driving mechanism of intracontinental mountain growth in nature mountains can grow and remain as localized tectonic features over long periods of time 10 m y by contrast according to current knowledge of lithospheric rheology and neglecting surface processes any intracontinental range with a width that exceeds that which can be supported by the strength of the lithosphere should collapse within a few tens of millions of years for example assuming a quartz dominated crustal rheology the relief of a range initially 3 km high and 300 400 km wide is reduced by half in about 15 m y as a result of lateral spreading of its crustal root we suggest that surface processes might actually prevent such a subsurface collapse removal of material from topographic heights and deposition in the foreland oppose spreading of the crustal root and could eventually drive a net influx of material toward the orogeny we performed a set of numerical experiments in order to validate this hypothesis a section of a lithosphere with a brittle elasto ductile rheology initially loaded by a mountain range is submitted to horizontal shortening and to surface processes if erosion is intense material is removed more rapidly than it can be supplied by crustal thickening below the range and the topography is rapidly smoothed for example a feature 3 km high and 300 400 km wide is halved in height in about 15 m y for an erosion coefficient k 10 3 m 2 yr the erosion rate is of the order of a few 0 1 mm yr this regime might be called erosional collapse if erosion is not active enough the crustal root spreads out laterally and subsurface collapse occurs in the third intermediate regime removal of the material by erosion is dynamically compensated by isostatic rebound and inward flow in the lower crust so that the range can grow in this mountain growth regime the range evolves toward a characteristic graded shape that primarily depends on the erosion law the erosion rate may be high e g 0 5 0 9 mm yr close to the rate of tectonic uplift e g 0 7 1 1 mm yr and few times higher than the rate of topographic uplift 0 15 0 2 mm yr these experiments show that surface processes can favor localized crustal shortening and participate in the development of an intracontinental mountain surface processes must therefore be taken into account in the interpretation and modeling of long term deformation of continental lithosphere conversely the mechanical response of the lithosphere must be accounted for when large scale topographic features are interpreted and modeled in terms of geomorphologic processes

morphology and dimensions of the young comendite lavas of la primavera volcano mexico quantitative data on the rhyolitic lavas of the quaternary la primavera volcano mexico are presented lavas vary in form from domes and mesa lavas to short coulees average thickness is 100 m average surface area is 2 7 km2 and aspect ratios vary from 1 7 to 1 25 two petrological lava types are distinguished porphyritic and aphyric porphyritic lavas occur on or within an inner ring fracture and are associated with an area of caldera lake deposits many features suggest that these porphyritic lavas were emplaced into the wet sediments or water of the caldera lake aphyric lavas are largely found to the south of this region and form large polygenetic structures extruded on dry land the porphyritic lavas generally are smaller and have higher aspect ratios than the aphyric which are attributed to their special environment of emplacement some porphyritic lavas extruded on dry land outside the region occupied by the caldera lake are however the thinnest on the volcano

pumiceous peperite in a submarine volcanic succession at mount chalmers queensland australia pumiceous peperite comprising irregularly shaped apophyses of feldspar phyric rhyolitic tube pumice and siltstone occurs within well bedded volcaniclastic sandstone and siltstone facies of the early permian berserker beds at mount chalmers australia the tube pumice structure is preserved where sericite or silica have replaced the glass of vesicle walls and vesicles have been infilled by silica in some instances the peperite occurs gradationally above or below intervals of coherent feldspar phyric rhyolite that are also predominantly pumiceous the siltstone in the pumiceous peperite is texturally homogeneous locally vesicular and contains shards and crystals derived from disintegration of the pumiceous rhyolite pumiceous rhyolite and peperite occur at various positions in the stratigraphy and may represent interconnected intrusive digits or lobes intrusion of the lobes was accommodated by expansion of the pore water and possible fluidisation of the host sediment resulting in local destruction of bedding the lobes developed chilled margins at contacts with wet sediment and inflated in response to vesiculation and the supply of new magma cooling of the lobes was possibly accompanied by development of microfractures in the glassy vesicle walls rupture of the chilled margin and propagation of fractures into the interior could have temporarily and locally depressurised the lobes resulting in failure disintegration and mixing with the adjacent wet and or steam rich sediment hot pumiceous rhyolite in lobe interiors may have interacted directly with the wet sediment and been dismembered by quench fragmentation and or steam explosions bubbles of magmatic gas and or steam were trapped in the sediment that mixed with the pumiceous rhyolite the development of pumiceous texture in the sills was favoured by emplacement beneath a thin cover of wet sediment in a relatively shallow submarine shelf setting in which the confining pressure was sufficiently low to permit vesiculation this setting was also important in limiting the extent of degassing of the pumiceous rhyolite during cooling

spatiotemporal patterns of the late quaternary deformation across the northern chinese tian shan foreland abstract the investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt here we focus on the spatiotemporal patterns of the late quaternary deformation along the north piedmont of the chinese tian shan a mountain range formed by the ongoing india asia collision by using a terrace as the reference and applying the area conservation method the holocene shortening rate of the halaande anticline a fold of the distal structure belt iii in the foreland is estimated to 2 14 0 24 mm yr for the first time similarly we re calculate the holocene shortening rates of the other anticlines of belt ii iii using the magnitude of shortening documented by river terraces and the terrace formation ages published previously the summed holocene 103 year timescale shortening rates of individual anticlines along n s transects are 2 4 mm yr consistent with the late pleistocene 104 year timescale shortening rate but about 2 6 times higher than the long term 106 year timescale average shortening rate of 1 mm yr during the past several million years together with the shortening rates of individual anticlines at the 103 year 104 year and 106 year scales these observations imply that the deformation across the northern chinese tian shan foreland has accelerated since at least late pleistocene by summing the late quaternary rates of shortening in the southern chinese tian shan foreland 4 5 mm yr and the intermontane basins in the hinterland of the tian shan 2 mm yr the late quaternary rate of shortening across the tian shan range between longitude 83 e and 87 e amounts to 9 0 1 0 mm yr approximately matching the modern shortening rate of 8 mm yr derived from the gps measurements these results imply i that the deformation across the tian shan range and its foreland basins between longitude 83 e and 87 e could have not been changed significantly since at least late pleistocene ii that in the northern chinese tian shan foreland the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the holocene or even geodetic rate of deformation

geophysical modeling of la primavera caldera and its relation to volcanology activity based on 3d susceptibility inversion and potential data analysis abstract la primavera lp is a rhyolitic caldera located in the western sector of the trans mexican volcanic belt tmvb lp is located close to the triple point junction of the chapala colima and tepic zacoalco rifts to understand the internal structure of the lp and its relationship with the tepic zacoalco rift we carried out a geophysical study with different techniques satellite gravity airborne data followed by ground based gravity and magnetic surveys were used to performed semi quantitative analysis to understand the structure of the lp residual gravity anomalies 22 15 mgal occuring on the entire volcanic structure are attributed to its rhyolitic nature aeromagnetic anomalies 125 nt occur on the south and western portions of lp analyzed lineaments in the area tilt derivative algorithm follow predominantly regional nw se and w e trends modeled werner anomalies identify the presence of numerous contacts and dikes especially along main faults such as rio caliente la gotera mesa nejahuete and the caldera ring fracture strikinlgy the higher parts of intrusive bodies and dikes appear at variable depths 7 3 km beneath san miguel and las planillas domes these results were replicated by using an euler s solution map the deepest parts of these bodies occur at around 7 8 km south of las planillas and el tajo domes we developed a 3d smooth model of the magnetic susceptibility isosurfaces with five magnetized bodies beneath the lp structure depth and geometry of surface volcanic structures were determinate thus providing a preliminary visualization of the main isosurface of 0 0343 si located in the southern area of the caldera additionally the upper part of the magnetic source is 5 5 km in depth the present study therefore reveals the presence of various intrusive bodies existing at different depths inside the caldera further structures and lineaments within the caldera provide evidence for understanding the presence of intrusive bodies geological structures associated with the caldera structure and geothermal activity

dry early holocene revealed by sand dune accumulation chronology in bayanbulak basin xinjiang nw china understanding the holocene climate changes especially moisture variation and their mechanisms in the semiarid arid central asia sca is very important as water availability is crucial for sustainable developments in this area this study presents chronostratigraphy of an aeolian sedimentary sequence from bayanbulak basin xinjiang nw china aiming to infer the holocene moisture history in the sca luminescence dating technique was selected to construct the age framework of the study section since the luminescence signal intensity of quartz from the samples was too low to be detected feldspar was used as an alternative dosimeter a newly developed post infrared ir ir stimulated luminescence irsl pirir dating protocol on k feldspar was applied to determine the ages of samples a set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable combined with the stratigraphic investigation on the sand dune palaeosol section the results imply a very dry climatic condition characterized by sand dune accumulation at similar to 9 8 kyr and a wet interval of 5 1 6 kyr when a soil layer was formed this moisture variation pattern is consistent with that inferred from many lacustrine records in the sca suggesting a widespread dry period at 11 8 kyr the present results appear to challenge a new stalagmite delta o 18 sequence located nearby to bayanbulak basin which instead suggested a humid early holocene

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

pyroclastic geology of the rhyolitic volcano of la primavera mexico explosive eruptions of this large quaternary rhyolitic volcano have produced voluminous pumice fall deposits and ignimbrites a stratigraphie study reveals more than 30 fall deposits totalling more than 90 km3 which have come from many different vents some are of plinian type and one is among the largest known in the world the main ignimbrite rio caliente is of intra plinian type in all 140 km3 of rhyolitic material were erupted during the past 105 years of which 50 km5 are dispersed well outside the volcano the dense rock equivalent volume is 60 km3 of which fall deposits ignimbrites and lava bodies comprise 45 25 and 30 respectively the average output rate of 0 06 km3 per century is nearly an order of magnitude less than for the most productive rhyolitic volcanoes known a circular area 10 km across in the centre of la primavera contains updomed lacustrine ashes and associated sediments including a remarkable giant pumice bed which probably accumulated in a caldera lake la primavera has no record of historical eruptions and hot springs are the only signs of present activity but the updoming is thought to be due to the uprise of a new acid pluton beneath the volcano and future eruptions are probable

late cretaceous palaeogene topography of the chinese tian shan new insights from geomorphology and sedimentology abstract the cenozoic growth of the intra continental tian shan range initiated during the late eocene oligocene and led to a tectonic reactivation of the complex palaeozoic and mesozoic lithospheric structure due to the very low erosion rates linked to the semi arid climate that characterised the tian shan region during most of the cenozoic the topography of the range is not at equilibrium with deformation fragments of pre orogenic low relief surfaces are preserved among the late cenozoic alpine type topography using field observations and satellite image mapping of those fragments as well as sedimentology and biostratigraphic analysis we show that the pre oligocene topography of the tian shan region was indeed complex combining hundreds of metres to one and a half kilometre high reliefs with a multi phased mesozoic planation surface incised by late mesozoic paleo valleys the occurrence of several metres thick late cretaceous palaeogene calcareous paleosols in the basins surrounding the range further implies a semi arid climate very low subsidence rates and no uplift at that time late cretaceous and early miocene fossil records in the northern tian shan suggest a possible connection even if episodic between the drainage system of the south junggar foreland basin and the proto paratethys sea to the west a renewed late eocene early oligocene sedimentation probably marks the onset of the tian shan uplift we argue that in addition to the growth of the pamir and western kunlun ranges this incipient uplift was one of the driving mechanisms for the final retreat of the proto paratethys sea from the tarim basin this regression apparently did not change the climate in the studied area because semi arid conditions seem to prevail at least since the late cretaceous finally the tian shan uplift remained very limited up to the miocene as revealed by the occurrence of burdigalian lake deposits preserved in the paleo valleys inside the present day range in contrast post early miocene deformation of the northern tian shan has produced 4000 to 5000 m of differential vertical movement between the uplifted range and the subsiding proximal foreland basin

climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the tian shan nw china abstract combined tectonic uplift and quaternary climate variability control the deposition and abandonment of terraces along the southern tian shan in northwest china several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern tian shan we combine geomorphic mapping topographic surveys of the deformed terrace surfaces 10be terrestrial cosmogenic nuclide tcn depth profile dating and optically stimulated luminescence osl dating to develop a new chronology for the terraces along the huangshui he since 550 ka our in situ 10be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle late pleistocene these data indicate that the formation of the four terraces occurred at 550 430 350 and 60 ka we suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods followed by subsequent incision that led to abandonment of these terraces during deglaciation we also estimate that tectonically induced river incision may account for about 60 70 of the total incision however during the intervening time between 350 ka and present only one terrace was formed and preserved we suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces therefore our results demonstrate the utility of chronologic records from southern tian shan for deconvolving the effects of tectonics and climate on fluvial incision

miocene to present kinematics of fault bend folding across the huerguosi anticline northern tianshan china derived from structural seismic and magnetostratigraphic data we combine surface structural measurements subsurface seismic imaging and magnetostratigraphic dating to retrieve through geometric modeling the detailed history of fold growth and sedimentation across the huerguosi anticline on the northern tianshan piedmont taking advantage of a beautifully exposed section of growth strata the model assumes a fault bend folding mechanism consistent with subsurface fold geometry the shortening history is obtained by least squares fi tting of the measured dip angles of the growth strata the shortening rate across the anticline is shown to have been remarkably constant it increased only slightly from 0 84 0 04 mm yr between 10 and 4 ma to 1 14 0 02 mm yr over the past 4 m y this approach also allows correcting syntectonic sedimentation rates for the effect of the fold growth and shows that the sedimentation rates in the piggyback basin increased abruptly from 0 4 to 0 7 mm yr ca 4 ma

denudation outpaced by crustal thickening in the eastern tianshan the modern high topography of the tianshan resulted from the reactivation of a paleozoic orogenic belt by the india asia collision today the range exhibits tectonically active forelands and intermontane basins based on quantitative morphotectonic observations and age constraints derived from cosmogenic 10be dating single grain post infrared infrared stimulated luminescence p ir irsl dating and modeling of fault scarp degradation we quantify the deformation in the nalati and bayanbulak intermontane basins in the central eastern tianshan our results indicate that at least 1 4 mm yr of horizontal crustal shortening is accommodated within these two basins this shortening represents over 15 of the 8 5 0 5 mm yr total shortening rate across the entire range at this longitude this shortening rate implies that the eastern central tianshan is thickening at a mean rate of 1 4 mm yr a rate that is significantly higher than the average denudation rate of 0 14 mm yr derived from our cosmogenic analysis this discrepancy suggests that the tianshan range has not yet reached a steady state topography and remains in a transient state of topographic growth most likely due to limited denudation rates driven by the arid climate of central asia

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

bubble development in explosive silicic eruptions insights from pyroclast vesicularity textures from raoul volcano kermadec arc critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation here we present data on densities and vesicle size and number characteristics for representative pyroclasts from six silicic eruptions of contrasting size and style from raoul volcano kermadec arc we use these data to evaluate histories of bubble nucleation coalescence and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material density vesicularity distributions show a scarcity of pyroclasts with 65 75 vesicularity however pyroclasts closest to this vesicularity range have the highest bubble number density bnd values regardless of eruptive intensity or style clasts with vesicularities greater than this 65 75 pivotal vesicularity range have decreasing bnds with increasing vesicularities interpreted to reflect continuing bubble growth and coalescence clasts with vesicularities less than the pivotal range have bnds that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite rich magma or vesiculation during slow ascent of degassing magma bubble size distributions bsds and bnds show variations consistent with 65 75 representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation consistent with the closest packing of spheres we consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit these processes can act in concert with multiple nucleation events generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed fragmentation preserves the range in vesicularity seen as well as any post fragmentation pre quenching expansion which may have occurred we demonstrate that differing density pyroclasts from a single eruption interval can have widely varying bnd values corresponding to the degree of bubble maturation that has occurred the modal density clasts the usual targets for vesicularity studies have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

calculation of the cosmogenic nuclide production topographic shielding scaling factor for large areas using dems the recent surge of applications using terrestrial cosmogenic nuclides tcns to calculate catchment averaged erosion rates from isotopic concentrations in fluvial sediment and the prospect of coupling tcn production functions with numerical surface process models spms necessitate a fast and accurate algorithm for the calculation of topographic shielding topographic shielding refers to the proportion of the incoming cosmic radiation that is shielded by the surrounding topography the scaling factor being defined as the ratio of the unshielded total minus shielded to the total or maximum cosmic ray flux i e the flux received by a horizontal unobstructed surface topography contributes to the reduction of tcn production by obstructing a certain proportion of the incoming flux and by modifying the angle of incidence available algorithms calculate the proportion of obstructed radiation by dividing the horizon as seen by the sample a grid cell in the case of a dem into arc segments usually of equal length for which the average obstruction heights expressed as zenith angles are calculated the use of these methods is feasible only when dealing with a small number of isolated samples since the identification of obstructions when dealing with an entire area is computationally very intensive this paper describes a method that uses a relief shadow modelling technique to identify those areas of a dem that are under shadow i e shielded and thus to account for the obstructed radiation this method produces results that are very similar to those obtained using a direct implementation of available methods maximum difference between results of c 0 1 the method based on relief shadow modelling is also faster than a direct implementation of any available method and can be readily implemented in any gis system with raster capabilities copyright 2006 john wiley sons ltd

the interplay between crystallization replenishment and hybridization in large felsic magma chambers abstract while hybridized granitoid magmas are readily identifiable the mechanisms of hybridization in large crustal magma chambers are so not clearly understood characteristic features of hybrid granitoids are 1 both the granitoid and included enclaves are commonly hybrids as shown by mineralogy geochemistry and isotopes 2 mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early 3 zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution 4 mafic end members in hybrids are commonly fractionated magmas and 5 stratification in subvolcanic granitoid magma chambers is not uncommon and stratification has been identified in some deeper level plutons hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma experimental work with magma analogues and theoretical considerations reveal very severe thermal rheological and dynamical limitations on mixing only very similar composition temperature magmas are likely to mix to homogeneity and only moderately silicic hybrids are likely to be produced however impossibly silicic hybrids do exist synchronous interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas in the following manner a mafic magma intrudes into the base of a stratified felsic magma and is cooled against it crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber subsequently melt released by crystallization pf this now hybrid zone mixes with adjacent more felsic zones thus a suite of hybrid magmas are progressively formed density inhibitions are overcome by the generation of relatively low density residual melts as crystallization proceeds later injections are preserved as dykes and enclaves composed of hybrid magma in this process only physically adjacent and dynamically thermally similar magmas directly interact and so may mix to homogeneity finally not simply felsic and mafic endmembers mix but a whole suite of intermediate endmembers participate ranging from relatively mafic through to felsic pairs of magmas direct mixing between the primary magmas only occurs at the beginning