relief and drainage evolution during the exhumation of the sierra nevada se spain is denudation keeping pace with uplift abstract we have performed a geomorphic analysis of the sierra nevada the highest range of the betic cordillera se spain with the aim to elucidate its late miocene to present day exhumation history the qualitative and quantitative analysis is based on filtered topography local relief swath profile analysis anomalies on stream orientation bulk erosion volume hypsometry and steepness index k sn all these parameters are intimately linked to river incision and development of drainage pattern having been calculated to assess the role of folding and faulting on the evolution of the sierra nevada moreover uplift rates in the core of the sierra nevada have been deduced from an extrapolation of the position of late tortonian to pliocene coastline deposits these data have been compared to apatite u th he fission track and 10 be cosmogenic data from se spain in order to evaluate the consistency among uplift thermal histories and denudation rates our preferred tectonic scenario is one that favors fast exhumation of the western sierra nevada in a nw se overall compressive setting produced by the convergence between the nubia and africa plates sub perpendicular to this compression a westward 4 mm year extensional hanging wall displacement promotes uplift and unroofing of the western part of sierra nevada

asymmetrical valleys created by the geomorphic response of rivers to strike slip fault abstract offset fluvial valleys including rivers beheaded and deflected by strike slip faults have long been used to estimate horizontal displacements on the faults larger rivers crossing such faults however sometimes show either no offset or only a small amount of offset compared to smaller rivers crossing the same faults the larger rivers with higher erosional rates may widen their valleys asymmetrically downstream of strike slip faults rather than being beheaded or deflected examples are described from the yellow river near the ne margin of the tibetan plateau river beheading and asymmetrical widening are two end members of a fluvial valley s response to strike slip faulting whereas deflection is a combination of both recognition of the formation of such asymmetrical valleys related to strike slip faulting will help to understand fault activity better over longer time spans and enable a re evaluation of many fault histories worldwide

tectonic geomorphology of the southeastern mississippi embayment in northern mississippi usa we analyzed drainage basin geometry in part of the southeastern mississippi embayment near the new madrid seismic zone in order to detect areas of lateral stream migration that could indicate recent tectonism toward this goal a field of drainage basin asymmetry vectors was generated from a digital terrain model and compared to geologic structure lithofacies seismicity remotely sensed lineaments and major drainage divides transverse topographical drainage basin asymmetry t index results define geomorphic domains in northern mississippi 33 to 35 n 88 5 to 90 25 w that may reflect deep crustal blocks bounded by active faults or flexures t index measurements a proxy for lateral stream migration of more than 4500 second order drainage basins produced a two dimensional field of 282 spatially averaged vectors from which we interpreted 12 domains some domain boundaries correspond to mapped faults of two paleozoic fault systems in our study area the northeast striking mississippi valley graben system and the northwest striking ouachita thrust belt and foreland faults several other prominent domain boundaries may be previously unmapped faults flexures parallel to these systems this interpretation is supported by satellite image analysis of the northeastern study area which reveals lineaments consistent with our domain boundaries that have strikes that reflect the regional subsurface structural grain

the implications of geology soils and vegetation on landscape morphology inferences from semi arid basins with complex vegetation patterns in central new mexico usa abstract this paper examines the relationship between land surface properties e g soil vegetation and lithology and landscape morphology quantified by the catchment descriptors the slope area s a relation curvature area c a relation and the cumulative area distribution cad in two semi arid basins in central new mexico the first site is composed of several basins located in today s desert elevations with mesic north facing and xeric south facing hillslopes underlain by different lithological formations the second site is a mountainous basin exhibiting vegetation gradients from shrublands in the lower elevations to grasslands and forests at higher elevations all three land surface properties were found to have significant influences on the s a and c a relations while the power law exponents of the cads for these properties did not show any significant deviations from the narrow range of universal scaling exponents reported in the literature among the three different surface properties we investigated vegetation had the most profound impact on the catchment descriptors in the s a diagrams of the aspect controlled ecosystems we found steeper slopes in north facing aspects than south facing aspects for a given drainage area in elevation controlled ecosystems forested landscapes exhibited the steepest slopes for the range of drainage areas examined followed by shrublands and grasslands in all soil textures and lithologies in the c a diagrams steeper slopes led to a higher degree of divergence on hillslopes and a higher degree of convergence in the valleys than shallower slopes the influence of functional types of vegetation detected on observed topography provided some initial understanding of the potential impacts of life on the organization of topography this finding also emphasizes the critical role of climate in catchment development we suggest that climatic fluctuations that are capable of replacing vegetation communities could lead to highly amplified hydrological and geomorphic responses

river terrace systems in north west europe an archive of environmental change uplift and early human occupation abstract staircases of large scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes particularly in areas beyond the reach of the erosive activities of pleistocene ice sheets it is now recognized that the cyclic fluctuations of climate during the quaternary have driven the generation of terraces through the direct and indirect influence of both temperature and precipitation on fluviatile activity where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record thus providing an important framework for the evidence of environmental change on land middle and late pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial interglacial cycles or with longer periodicity megacycles climatic forcing alone is insufficient to cause terraces to form however uplift is also necessary so that terrace sequences can provide a useful record of crustal movement in northwest europe where some of the best known studies of river terrace sequences have been carried out the fluviatile deposits are also an important repository for palaeolithic artefacts from which a record of early human occupation can be reconstructed

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

the role of vapor in volcanic activity abstract a thermodynamic model for a magma intrusion is presented a mechanism for volcanic eruptions is discussed in view of the fact that vapor is sometimes formed inside the magma chamber the vapor is exsoluted from an ascending magma parcel rich in volatiles the ascent of this parcel causes volume creation pressurization of the chamber and possible eruption the model leads to the development of a differential equation which governs the dynamic process of the chamber pressurization it is found that very high internal pressures may be created by this mechanism which may lead to violent eruptions even in the absence of any other corroborating mechanism

degassing of stratified magma by compositional convection abstract a new model is proposed for passive degassing from sub volcanic magma chambers the water content in stably stratified shallow magma chamber will be equated to its solubility at the upper boundary by convection water from a lower layer high in water content can enrich the contact zone of the upper layer and lead to further convective overturn of this boundary layer a complete set of equations describing convection with bubble formation and dissolution is reduced to a simplified form by assuming a small bubble content the development and pattern of flow driven by vesiculation is modeled numerically in a 2d magma chamber for relatively low raleigh numbers 5 105 bubbles rising from the magma will collect near the roof in a layer of 8 10 vol and then escape upward to fumaroles the stokes flux of bubbles escaping from an andesitic magma with viscosity 104 p and a top surface of about 500 500 m corresponds with observed total magmatic water fluxes of 35 kg s pressure within the chamber is buffered by elastic and local visco elastic deformations in the solid rocks bounding the chamber to the range between ambient and close to lithostatic values in a chamber closed to fresh magma inputs the decrease in volume due to such gentle volatile escape lowers the reference pressure bubbles flux from the lower layer induced by variation of the saturation level around stratification boundary may be efficient mechanism for the water transport between layers

active tectonics in the sierra nevada betic cordillera se spain insights from geomorphic indexes and drainage pattern analysis article i nfo the sierra nevada of the central betic cordillera is a 3000 m high mountain range surrounded by neogene quaternary sedimentary basins having been uplifted since late miocene times the southern and western mountain fronts of the sierra nevada are fault bounded while the northern one is an unconformity between the neogene quaternary sediments of the guadix baza basin and the metamorphic rocks of the nevado filabride complex we have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift mountain front sinuosity smf area altitude relations hypsometric curves and valley floor entrenchment differ significantly between the northern western and southern mountain fronts the lack of important faults along the northern sierra nevada mountain front together with the elevated topographic position of the guadix baza basin average altitude is around 1100 m points to similar uplift of both geomorphic units sierra and basin in a single large scale crustal block the asymmetry factors show systematic asymmetries at both sides of the lanjaron river probably due to the presence of an active nne ssw oriented antiform in the western sierra nevada finally river profiles indicate maximal river entrenchment in the western part of the sierra nevada probably related to the uplift of the footwall of the padul niguelas fault system therefore our geomorphic analysis suggests that the western part of the sierra nevada is tectonically active by means of a combination of normal faults along the mountain front and nne ssw oriented active folds which in turn likely have a gravitational origin related to the exhumation of the footwall of the normal fault system

active faulting and tectonics of the ningxia hui autonomous region china strike slip thrust and normal faulting all seem to play an active role in the tectonics of ningxia in the southernmost part of the region a major left lateral strike slip fault enters the region from the neighboring gansu province to the west and trends about s65 e this fault is very clear on landsat imagery and on aerial photos and the portion in eastern gansu and ningxia broke in the haiyuan earthquake of december 16 1920 displacements of 5 10 m caused by that earthquake are clear in numerous localities and accord with a revised value of the seismic moment of 1 2 1021n m the eastern end of the haiyuan fault terminates in a narrow south trending fold and thrust zone several other similar north to northwest trending fold and thrust belts are present in the area about 50 200 km northeast of the haiyuan fault and divide it into small apparently relatively undeformed blocks 10 40 km in dimensions the geometry of the structures in the fold and thrust zones and the apparently shallow depths at the time of deformation suggest that current deformation is similar to that that occurred in the fold and thrust belt of the idaho wyoming rocky mountains north of this area both the helan shan a horst and the yinchuan graben are bounded by clear active northerly trending normal faults in some cases with right lateral strike slip components the overall deformation hence seems to include dominant components of east west left lateral strike slip movement northeast southwest crustal shortening and northwest southeast extension we interpret the extension as a response to a northeast directed force applied to the ordos block and both this northeast directed force and the left lateral slip on the haiyuan fault to the eastward displacement of material on the northeast edge of the tibetan plateau with respect to eurasia north of it

geology of the haiyuan fault zone ningxia hui autonomous region china and its relation to the evolution of the northeastern margin of the tibetan plateau the haiyuan area located along the northeastern margin of the tibetan plateau in north central china provides a laboratory for studying how the plateau has grown in late cenozoic time rocks in the area range from pre silurian precambrian to recent the pre silurian and cenozoic rocks form the most extensive outcrops the pre silurian rocks consist of amphibolite and greenschist grade metasedimentary and metaigneous rocks unconformably overlain by silurian and devonian red beds all of these rocks are intruded by granodiorite of unknown age cenozoic rocks consist of 2 6 3 0 km of eocene to miocene red beds that were deposited over an extensive area in this part of china pliocene conglomerate contains clasts from all older formations and is interpreted to have been derived from highlands developed during the beginning of cenozoic deformation in the haiyuan area except for the widespread loess deposits quaternary rocks reflect deposition in local tectonic environments the oldest cenozoic structures in the haiyuan area are folds and small thrust faults that generally strike n30 45 w and involve mostly pre quaternary rocks these structures and all the quaternary rocks are cut by the haiyuan left lateral strike slip left slip fault zone that generally trends n60 65 w and is nearly vertical at the western end of the mapped area a fault zone which strikes n75 90 w forms a left stepping transfer zone that connects with another segment of the haiyuan fault zone which continues n60 65 w west into gansu province a small basin the salt lake basin is marked by active faults in the area of the transfer zone and is interpreted as a pull apart basin along the left slip haiyuan fault zone at its eastern end the haiyuan fault zone has an irregular surface trace east of luzigou an active fault striking n35 45 w branches to the south this southern branch appears to be a younger fault and now accommodates most of the left slip deformation that formerly occurred on the easternmost part of the haiyuan fault zone this younger fault connects through a left stepping transfer zone to a parallel fault the xiaokou fault that can be traced into the liupan shan about 60 km to the southeast the laohuyaoxian basin is interpreted as a very young pull apart basin in the area of the transfer zone matching different geological features across the haiyuan fault zone yields a total left slip offset of between 10 5 and 15 5 km and the best constrained offsets yield 12 9 14 8 km if left slip began near the end of the pliocene time or earliest pleistocene time it indicates an average slip rate between 5 and 10 mm yr progressively smaller offsets can be determined on progressively younger geological features but dates for these younger features are too imprecise to constrain slip rates through time surface ruptures that formed during the 1920 haiyuan earthquake m 8 7 show mostly left slip displacement with magnitudes of more than 10 m in some places active faulting in the region suggests the tibetan plateau may be extending to the northeast in time in the haiyuan area deformation probably began in pliocene time compared with a likely earlier initiation to the southwest thus deformation began about 40 45 m y after collision between india and asia formation of the low ranges to the northeast of the haiyuan area however may have developed at different times and deformation may not have propagated regularly to the northeast a total displacement of 10 5 15 5 km on the haiyuan fault zone indicates that this fault zone does not accommodate large scale eastward lateral transfer of continental fragments in the northern tibetan plateau

structure and tectonic geomorphology of the qujiang fault at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system china abstract the northwest striking qujiang fault is located at the southeastern tip of the sichuan yunnan block which is bounded by the ailao shan red river fault and the xianshuihe xiaojiang fault system the qujiang fault is one of the most seismically active faults in western yunnan china and is considered to be the seismogenic fault of the 1970 ms 7 7 tonghai earthquake in this study we examine the geometry kinematics and geomorphology of this fault through field observations satellite images and dems it is a holocene active fault characterized by dextral strike slip movements with dip slip components it can be divided into northwest and southeast segments depending on different kinematics the northwest segment from baiyizhai to wujie shows right lateral strike slip with normal components whereas it is characterized by dextral movements with the northeast wall thrusting over the opposite in the southeast segment from wujie to miaobeishan the geophysical data combined with our investigations indicate that the fault dips steeply to the ne at depth while secondary faults with different dip directions developed at shallow surface owing to fault bifurcation during the tonghai earthquake a blind fault may have developed on the southwest wall resulting in aftershocks concentrated to the southwest of the surface raptures multiple tectonic landforms are developed along the fault the right lateral holocene slip rate was determined to be 2 84 3 27 mm year based on radiometrically dated offset gullies our analyses show that the present deformation at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system is partitioned into a shortening distributed over a region 150 km wide and a right lateral strike slip localized on the qujiang and jianshui faults since the late pleistocene the qujiang fault has been playing an important role in accommodating the ongoing se directed movements of the sichuan yunnan block creating strong earthquakes to release strain energy

the uncertainty of 2d models along wide angle seismic profiles the estimation of uncertainty for any geophysical model is important for determining how reliable the model is it is especially important for subjective trial and error modelling techniques like forward ray tracing modelling of wide angle seismic data when the final result is very dependent on the interpreter s knowledge of the area and experience in this kind of modelling it is common to encounter over interpretation of the seismic data without checking the uncertainty of the result especially in the deep parts that are not constrained with other a priori knowledge in this paper we propose a method of estimating the uncertainty of the final models based on a one dimensional method of small error propagation generalized for 2d profiles with a simple approximation we estimate the uncertainty for published interpretative models of selected profiles from seismic experiments in the central europe we conclude that for typical wide angle seismic profiles we can reliably interpret four layered models of the earth s crust based on traveltimes fitting we also show how the number of layers influence obtained uncertainties estimated uncertainties for both the velocity fields and the boundaries between layers are important for future tectonic and geodynamic interpretation of those profiles

tectonic controls of the north anatolian fault system nafs on the geomorphic evolution of the alluvial fans and fan catchments in erzincan pull apart basin turkey abstract the erzincan pull apart basin is located in the eastern section of the north anatolian fault system nafs the tectonic evolution of this basin is mostly controlled by strike slip master faults of the nafs this study examines the topography structure relationships in an effort to evaluate the tectonic signatures in the landscape paying special attention to recent tectonic activity in the study the main focus is on the tectonic controls of the nafs on the geomorphic evolution of alluvial fans and fan catchments in the erzincan pull apart basin the observations of the amount of tilting of the alluvial fans and its relation with morphometric asymmetry factor af hypsometric integral hi fractal analysis of drainage networks d properties of the fan catchments provide valuable information about the tectonic evolution of the basin area the results of the analyses showed that the alluvial fan and fan catchment morphology in the pull apart basin are mainly controlled by the ongoing tectonic activity of the nafs the fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin and aggradation processes by causing channel migration channel incision and tilting the alluvial fans

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

late miocene pliocene geomorphological evolution of the xiaoshuizi peneplain in the maxian mountains and its tectonic significance for the northeastern tibetan plateau as a remnant elevated peneplain the tangxian planation surface is widely distributed in north china and the ordos plateau further into the tibetan plateau tp the main planation surface can also be traced across this the highest plateau on the earth s surface what the relation is between these two planation surfaces and whether they represent the remnants of a unique planation surface remains open to question as the intermediate region between the low altitude north china and the high altitude tp the maxian mountains and such bilateral basins located in the northeastern tp margin retain a series of well preserved geomorphic features such as planation surfaces pediment surface and the fluvial terraces of the yellow river when and how the xiaoshuizi peneplain was formed are crucial questions to elucidate the geomorphic evolution of the northeastern tp and infer the tectonic history of the tp here we present two parallel red clay loess drill cores from the uplifted xiaoshuizi bedrock peneplain in the maxian mountains which document both the upper formation age of the planation surface and the evolution of asian aridification based on the integration of high resolution magnetostratigraphy analysis and pliocene mammal fossils we demonstrate that the red clay loess succession deposited on the xiaoshuizi peneplain probably began to accumulate at similar to 6 9 ma implying that the xiaoshuizi peneplain had begun to form before this these results support the hypothesis that the xiaoshuizi planation surface is equivalent to tangxian planation surface of north china and main planation surface of the tp furthermore the onset of red clay sequence may indicate that the xiaoshuizi peneplain was ultimately destroyed by the intensive tectonic uplift of the northeastern tp before 6 9 ma taking into account the synchronous late miocene red clay deposition between the xiaoshuizi peneplain and central chinese loess plateau clp we propose that the onset of interior asian aridification occurred in the late miocene and was principally triggered by the rapid uplift of tp

tilting neotectonics of the guadiamar drainage basin sw spain the guadiamar river ows from the southern iberian massif to the guadalquivir foreland basin sw spain its drainage basin displays asymmetries in the stream network the arrangement of alluvial terraces and the con guration of the trunk river valley the stream network asymmetry was studied using morphometric measures of transverse topographic sym metry asymmetry factor and drainage basin shape the alluvial terraces were studied through the lithologic logs of more than a hundred boreholes and eld mapping the morphometric methods demonstrate a regional tectonic tilting toward the sse causing both the migration of the guadiamar river toward the east and the migration of the guadiamar tributaries toward the southwest as a consequence of the guadiamar river migration an asymmetric valley developed with a steep eastern margin caused by river dissection and a gentle western margin where the main alluvial deposits are found the ages obtained using the 14c analysis of samples from several alluvial deposits show that the river migration and thus tilting has occurred during the holocene as well as earlier in the quaternary this interpretation revises the guadiamar longitudinal fault assumed by previous studies copyright 2003 john wiley sons ltd

identification of possible quaternary deformation in the northeastern mississippi embayment using quantitative geomorphic analysis of drainage basin asymmetry to investigate neotectonism in the mississippi embayment east of the new madrid seismic zone we identified geomorphic domains that show evidence of ground tilting during quaternary time transverse basin profiles were converted to two dimensional vectors that denote channel position with respect to basin divides these basin asymmetry vectors record the net direction and degree of lateral migration of trunk streams more than 2500 vectors were measured and spatially averaged within 400 km 2 bins this field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting the timing of stream migration was interpreted using across valley distributions of quaternary alluvial terraces comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults late quaternary activity is suggested for two northeast striking faults of the southeastern reelfoot rift margin we acquired two seismic profiles showing near surface faulting beneath scarps that follow the domain boundary associated with one of these northeast striking faults big creek fault zone reelfoot thrust seismicity ends on the south against this fault suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall our vector field also suggests late quaternary movement on the reelfoot thrust and on two other northwest striking faults here termed the hatchie river fault and the wolf river fault several other weak domains may imply minor elements of neotectonism our results demonstrate that morphometric analysis of drainage basin asymmetry can be an effective reconnaissance tool within neotectonic settings

dating of erosion surface and terraces in the eastern qilian shan northwest china the actively deformed foreland of eastern qilian shan mountains contains well preserved geomorphic features such as erosion surfaces river terraces and tectonically uplifted alluvial fans providing suitable archives for research on regional tectonic activities and palaeoclimatic changes these geomorphic surfaces are well dated by using a combination of magnetostratigraphy electron spin resonance thermoluminescence infra red stimulated luminescence radiocarbon dating and correlation with the well established loess palaeosol sequences of china our results show that the erosion surface formed about 1 4 ma ago and the age of river terraces is 1 24 ma 820 860 ka 780 ka 420 440 ka 230 250 ka 140 ka 60 ka and 10 ka respectively valley incision rates of e 0 09 0 25 m ka 1 have been identified the repetitive stratigraphic and geomorphic pattern of these terraces indicates the fluvial sedimentation incision cycles are tightly associated with the 100 ka glacial interglacial climatic cycles copyright c 2006 john wiley sons ltd

tilting of active folds and drainage asymmetry on the manawatu anticlines new zealand a preliminary investigation the apparent southward tilting of five anticlines in the manawatu north island new zealand is investigated using two drainage basin analysis techniques the transverse topographic symmetry factor t and the asymmetry factor af the techniques are used to determine whether westward flowing trunk streams on the gentle western limbs of five anticlines are migrating southwards across their drainage basins concomitant with down tilting of the fold axes while results show potential for the techniques to be applied in such a tectonic setting our findings are inconclusive this could be due to the incipient nature of the folds c 0 5 ma in age and it would seem more appropriate to apply the techniques in concert with detailed field analyses of river migration patterns copyright 2008 john wiley sons ltd

asymmetrical river valleys and their tectonic significance in the maxianshan area ne tibetan plateau abstract the geometry of river networks is particularly sensitive to active tectonic deformation morphotectonic analyses conducted using geomorphic indices and numerical models are useful methods with which to identify such deformation the northeastern ne margin of the tibetan plateau is characterized by active tectonics easily erodible bedrock and well developed valleys and is thus an ideal region for studying the effects of tectonics on the landscape evolution here we firstly identify the systemic asymmetrical valleys in the maxianshan area ne tibetan plateau to quantitatively analyze the asymmetrical characteristics of these valleys identified in the southern maxianshan 33 parallel streams were investigated by using two drainage basin analytical techniques namely the transverse topographic symmetry factor t and asymmetry factor af our results show that the mean t value is 0 14 magnitude and 319 08 direction and the majority of the af results are

coupled degassing and crystallization experimental study at continuous pressure drop with application to volcanic bombs experiments on degassing of water saturated granite melts with a pressure drop from 100 and 450 mpa to 40 and 120 mpa respectively at temperatures close to feldspar liquidus 750 700 c were carried out to determine the modality of water exsolution and vesicle formation at the liquidus temperature pressure drop rates as small as approximately 100 bar day were used uniform space distributions of bubbles of exsolved water were obtained with starting glass containing a small fraction 0 5 vol of trapped air bubbles volume crystallization of feldspar was observed in degassed melts supplied with seeds bubble size distributions bsd measured in granite glasses after degassing are presented data on vesicle characteristics number radius area elongation were acquired on images digitized with standard software while the reconstruction of size distributions was performed with the schwartz saltikov unfolding procedure bubble size distributions of size classes in the range 5 1000 m were acquired with proper magnification and satisfactory statistical reliability of determined number densities the bsds of the experimental samples are compared with the results of measurements of rapidly degassed products of mt etna and vulcano island many particular features of the bubble nucleation and growth can be distinguished in an individual bsd however the general bsd of the whole data set including natural ones can be relatively well described with linear regression in bilogarithmic coordinates the slope of this regression is approximately 2 8 0 1 this dependence is in striking contrast with distributions theoretically predicted with classical nucleation models based on homogeneous nucleation of vesicles the theoretical distribution requires the occurrence of strong maxima that are not observed in our experimental and natural samples thus arguing for heterogeneous nucleation mechanisms

late quaternary left lateral slip rate of the haiyuan fault northeastern margin of the tibetan plateau 1 slip rates of major active strike slip faults within and around the tibetan plateau provide constraints for understanding the dynamics of continental deformation in general because large slip rates can be taken to imply localized deformation between rigid blocks and low slip rates on faults are more consistent with distributed deformation several major strike slip faults have been studied during the last 3 decades as one of important active strike slip faults in and around the tibetan plateau the slip rate of the haiyuan fault has been discrepantly estimated to be high by proponents of escape tectonics or low by others and gps observations to better constrain its slip rate and then to better understand the mechanics of intracontinental deformation we try to more carefully consider offset geomorphic features and age constraints along the haiyuan fault in this paper we select three sites where both upper and lower bounds of slip rate can be obtained we find that slip rates are 4 2 0 8 mm yr at the shaomayin 4 5 0 7 mm yr at gaowanzi and 5 0 2 5 mm yr at huangliangtan site combinations of these rates with those published previously yield an average slip rate of 4 5 1 0 mm yr on the haiyuan fault this rate agrees with the present day slip rate of 4 3 1 5 mm yr measured by gps 4 2 8 mm yr by interferometric synthetic aperture radar and 5 mm yr through paleoseismological studies the temporal consistency suggests a steady state process of strain accumulation and release along the haiyuan fault the low slip rate suggests that the haiyuan fault similar to the altyn tagh fault does not transfer a significant portion of the convergence between india and asia out of india s path into eurasia but merely redistributes crustal thickening

asymmetrical river valleys in response to tectonic tilting and strike slip faulting northeast margin of tibetan plateau the northeast margin of the tibetan plateau a particularly important area to understand the mechanism of plateau formation is characterized by large transpressional arcuate faults there is debate on the amount of quaternary sinistral displacement on the major haiyuan fault previously unrecognized systemic asymmetrical valleys have developed between the haiyuan and xiangshan faults southeast tilting and sinistral displacement on the northeast side of the haiyuan fault resulted in southeast migration of large rivers and asymmetrical widening of their valleys leaving a systematic distribution of tilted strath terraces along their northwest sides where asymmetrical widening created by tilting kept pace with sinistral displacement rivers have not been deflected and the increase in valley width downstream from the fault should equate to total lateral displacement since river formation e g yuan river a 7 km asymmetrical valley with a c 2 2 ma paleomagnetic age where river deflection and asymmetrical valley growth are coeval valley width is less than total horizontal displacement e g hebao river a c 2 1 km asymmetrical valley with c 2 km deflection all rivers north of the haiyuan fault converge to cut across the xiangshan mountains as a gorge northeast thrusting of the upthrown side of the xiangshan fault has resulted in degradation and related strath terrace formation as the valleys asymmetrically widened a probable earthquake induced landslide caused by movement on the xiangshan fault in latest pleistocene blocked the gorge causing aggradation along all rivers and their tributaries deposition terraces were formed after the landslide dam was breached together with previous research on the xiangshan fault it is concluded that there has been c 7 km of quaternary sinistral displacement on the haiyuan and xiangshan faults along the northeast margin of the tibetan plateau since the formation of rivers that intersect them copyright 2014 john wiley sons ltd

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

valley asymmetry and glacial versus nonglacial erosion in the bitterroot range montana usa theories that propose feedbacks among climate tectonics and surface processes commonly assume that erosion is enhanced by glacial activity indeed studies have shown that glaciers appear to limit the elevation of mountain ranges however comparisons between rates of glacial and nonglacial erosion are difficult to make ideally such comparisons must hold precipitation and lithology constant while only varying the erosional regime located in a climatic transition zone during the pleistocene the east west trending valleys of the bitterroot range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north facing sides of the valleys were glaciated whereas the south facing slopes were not the different erosional regimes operating on either side of the valleys created strongly asymmetric ridges ridgelines separating the east west trending valleys have been pushed southward by glacial headwall retreat such that ridge to valley distances are 50 greater on the north facing slopes than on the south facing slopes in addition mean hillslope angles are 6 lower on the glaciated slopes than on the unglaciated slopes and calculations of geophysical relief suggest that on average glaciers have removed nearly twice as much rock as nonglacial processes finally we conclude that although rates of vertical incision by glacial processes in the bitterroot range were more rapid than nonglacial processes the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat

geomorphic constraints on the active tectonics of southern taiwan summary taiwan is a region of rapid active tectonics yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation we use digital topography to look for indications of active deformation preserved in the local geomorphology in particular anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity the apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left lateral shear running down the southeastern side of taiwan asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern taiwan with the most rapid uplift close to taitung at the indentation point of the luzon arc with the chinese continental margin our interpretations though based predominantly on remote sensing observations are consistent with the available field evidence this study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift which may have wider applicability in other deforming parts of the world

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

gypsum scarps and asymmetric fluvial valleys in evaporitic terrains the role of river migration landslides karstification and lithology ebro river ne spain abstract most of the spanish fluvial systems excavated in tertiary evaporitic gypsum formations show asymmetric valleys characterized by a stepped sequence of fluvial terraces on one valley flank and kilometric long and 100 m high prominent river scarp on the opposite side of the valley scarp undermining by the continuous preferential lateral migration of the river channel toward the valley margin leads to vertical to overhanging unstable slopes affected by a large number of slope failures that become the main geological hazard for villages located at the toe of the scarps detailed mapping of the gypsum scarps along the ebro and huerva rivers gypsum scarps demonstrates that landslides and lateral spreading processes are predominant when claystones crop out at the base of the scarp while rockfalls and topples become the dominant movement in those reaches where the rock mass is mainly constituted by evaporites the dissolution of gypsum nodules seasonal swelling and shrinking and dispersion processes contribute to a decrease in the mechanical strength of claystones the existence of dissolution enlarged joints sinkholes and severely damaged buildings at the toe of the scarp from karstic subsidence demonstrates that the interstratal karstification of evaporites becomes a triggering factor in the instability of the rock mass the genesis of asymmetric valleys and river gypsum scarps in the study area seem to be caused by the random migration of the river channel in the absence of lateral tilting related to tectonics or dissolution induced subsidence once the scarp is developed its preservation depends on the physicochemical properties of the substratum the ratio between bedrock erosion and river incision rates and climatic conditions that favour runoff erosion versus dissolution

analyzing the drainage system anomaly of zagros basins implications for active tectonics abstract morphometric analysis of hierarchical arrangement of drainage networks allows to evaluate the effects of external controls especially tectonics on basin development in this study a quantitative method for calculation of stream s hierarchical anomaly number is introduced morphometric parameters such as hierarchal anomaly index a percent of asymmetry factor paf basin shape bs basin length to mean width ratio bl bmw stream s bifurcation ratio rb bifurcation index r drainage density dd drainage frequency df and anticline s hinge spacing hs of 15 basins in zagros mountains were examined results show that the strong correlations exist between pairs a paf r 0 844 a bs r 0 732 a bl bmw r 0 775 a r r 0 517 paf bl bmw r 0 519 bs r r 0 659 bl bmw r r 0 703 hs a r 0 708 hs paf r 0 529 and hs bs r 0 516 the variations in trend of anticlines control the shape of basins so that where anticlines hinges become closer to each other in the downstream direction basin become narrower downward and hence the a increases the more uplifted northeastern anticlines cause the trunk river of the basins to migrate toward the younger anticlines in southwest and hence a increases because the trunk river receives a lot of first order streams data reveal that the rate of a is higher in elongated synclinal basins due to the decrease in the intensity of deformation from northeast toward southwest of zagros the hinge spacing of anticlines increases southwestwards data reveal that the variation in hinge spacing of anticlines strongly controls the basin s shape and tilting as well as the hierarchical anomaly of drainage system since the elongation and tilting of basins are associated with the variations in rates of folding uplift and hinge spacing of anticlines it can be concluded that the hierarchical anomaly of drainages in studied basins is controlled by the intensity of zagros tectonic activities

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

drainage and valley asymmetry in the tertiary hills of lower bavaria germany abstract valley asymmetry with steeper west facing valley sides is a common feature in the tertiary hills of lower bavaria several previous studies have attributed these forms to microclimatic differences under periglacial conditions during the pleistocene glacials however little attention has been given to the pattern of drainage networks in this area as a means of explaining valley asymmetry drainage networks show asymmetry both in length and number of tributaries on either side of the main stream drainage asymmetry is very likely primarily the reason of a drainage development in competitive situations four possible causes have been identified 1 the position of an initial channel in relation to its adjacent parallel or subparallel drainage lines 2 different rates of headward erosion of tributaries on either side of an inter stream divide 3 drainage development oblique to an initial terrain slope and 4 tilting of a landsurface and the resulting preferential headward erosion of consequent running streams thus asymmetric drainage development causes differences in slope dimensions and an imbalance in run off and sediment yield on opposite valley sides leading to the development of asymmetric valleys

plio quaternary uplift of the iberian chain central eastern spain from landscape evolution experiments and river profile modeling abstract the iberian chain central eastern spain is characterized by a dome shaped topography with poorly incised and relatively flat landscape in its interior at an elevation of 1300 m a recent regional tectonic event started during or after the late pliocene inducing deep valley incision on the flanks of the iberian chain the rate and timing of this deformation as well as the magnitude of the uplift induced erosion processes still lack a quantitative validation we used 3d signum and 1 d river profile numerical models to investigate the landscape evolution of the iberian chain from the late pliocene to the present and to study the response of topography and rivers to tectonically induced base level lowering our model results are supported by geological geomorphological and geochronological data the results of the signum experiments show that the iberian chain topography has experienced regional uplift since ca 3 ma with rates between 0 25 and 0 55 mm y 1 in response to this uplift rivers have incised at an average long term incision rate of about 0 22 mm y 1 and have progressively captured drainage areas from the chain interior to further validate the results of landscape evolution modeling we use a 1 d river incision model to explore the incision history of several rivers draining the iberian chain the results constrain the range of values of bedrock erodibility from 5 8 10 5 to 5 0 10 4 m 0 4 y 1 and predict long term incision rates similar to those from the signum experiments

two phase natural convection implications for crystal settling in magma chambers abstract crystal settling is no longer thought to be the most likely mechanism operating in the formation of layered igneous intrusions the main objection raised against its feasibility is the prediction that crystal settling velocities are likely to be orders of magnitude smaller than convective velocities and that vigorous convection would therefore keep crystals well mixed within the interior of a magma chamber in previous theoretical and numerical investigations of crystal settling no account has been taken of compositional buoyancy gradients created by the interpenetration of crystals and melt this paper includes these effects the results of two dimensional numerical simulations show that parameter regimes exist in which effective crystal settling occurs in infinite prandtl number thermally convecting two phase fluids even for small ratios of settling to convective velocity