paleoseismic study on active normal faults in the southeastern weihe graben central china abstract field investigations and trench excavations can provide direct and indirect geological evidence for the occurrence of paleo earthquakes in this study we present geological and topographical evidence for the occurrence of great paleo earthquakes produced by active normal faults in the southeastern weihe graben central china field and trench observations in combination with radiocarbon ages reveal that i four surface faulting events occurred in the past 4000 years with an average recurrence interval of 1000 years which is in contrast with the previously estimated interval of 2000 2900 years ii the most recent fault event is correlated to the 1556 m 8 5 huaxian earthquake iii an alluvial terrace riser that formed at 5300 yr b p has been vertically offset by 9 11 m indicating an average vertical slip rate of 1 7 2 1 mm yr in the late holocene our results confirm that normal faults in the southeastern weihe graben have been active in the late holocene as source seismogenic faults and that these faults have the potential to trigger large earthquakes of m 7 in the future therefore it is important to urgently reevaluate the seismic potential and seismic hazard in the densely populated weihe graben region

eocene onset and late miocene acceleration of cenozoic intracontinental extension in the north qinling range weihe graben insights from apatite fission track thermochronology abstract intracontinental extension in central china is accommodated by cenozoic grabens flanking the ordos block such as the weihe graben which accommodate 5 6 mm yr of extension to define the onset and evolution of major cenozoic extension we examine the cooling history of exhumed footwall rocks in the north qinling range adjacent to the weihe graben we present results from 47 new apatite fission track aft samples primarily from two vertical transects of 1 5 2 5 km relief located on the northern flank of the north qinling footwall aft ages that get progressively older with increasing distance from the active range bounding normal fault suggest that cenozoic uplift and southward tilting was a response to range parallel extension correlations between aft ages and both elevation and track lengths combined with thermal modeling of representative samples reveal that the north qinling experienced two major stages of cenozoic exhumation 1 relatively slow exhumation in response to a small magnitude of extension that initiated at 50 ma 2 relatively rapid exhumation in response to a large magnitude of accelerated extension that initiated at 10 ma in addition small changes in cooling rate at 35 ma and 25 ma may reflect minor changes in faulting rate we interpret initial extensional at 50 ma to be a far field effect of initial india asia continental collision in contrast accelerated extension after 10 ma along the qinling is likely linked to the upward and outward growth of the tibetan plateau alternatively lower crustal flow beneath the qinling may have progressively accelerated exhumation in late miocene time

tectonic geomorphology of a large normal fault aksehir fault sw turkey abstract in order to better understand the activity of the aksehir normal fault in sw turkey and the associated seismic hazard we investigated the tectonic geomorphology of a 60 km stretch of the 100 km long aksehir fault block the fault can be separated into seven geomorphic segments 1 to 7 from nw to se along the mountain front segment length varies from about 9 to 14 km and relief of the horst block varies from about 0 6 km in the se to 1 0 km in the nw analysis of the tectonic geomorphology of 32 drainage basins and mountain front facets using a combination of geomorphic indices reveals a general pattern of high slip rates in the northern and central segments and low slip rates in the southern probably older segments we show that mountain front sinuosity varies from about 1 1 to 1 4 on segments s1 s6 to 2 4 on segment s7 suggesting that the six northern segments are more active than the southernmost segment similarly analysis and slope area analysis of streams reveal a pattern of steepest channels draining the central and northern segments of the horst the ratio of valley floor width to valley height varies from 0 2 to 0 6 which are typical values for tectonically active mountain fronts and alluvial fans along segments s1 s2 and s4 are back tilted finally we show that 1 shapes of the 100 900m high mountain front facets are mostly triangular 80 and partly trapezoidal 20 2 facet slopes range from 6 to 22 3 facets at the nw and se segment ends are larger than the intervening facets and 4 steepest facets occur along the central segments uplift rates estimated from the slope of mountain front facets range from about 0 06 m ky on the southernmost fault segment s7 to 0 23 m ky on the more central s5 and 0 16 m ky on the northern segment s1 the estimated pattern of uplift is consistent with the pattern of geomorphic indices the vertical relief of the facets suggests that uplift of the mountain front initiated in the late miocene early pliocene and continues to the present with the earliest surface rupturing faults on the southernmost fault segment s7 large normal faults with a similar slip rate of 0 2 0 3 m ky typically have strong earthquakes every few thousand years therefore the many moderate to strong earthquakes on the aksehir fault in the past few hundred years may be misleading a paleoseismic evaluation could answer questions concerning the area s earthquake hazard the tectonic geomorphology suggests that the aksehir fault is active and larger earthquakes than those of the historic period are a potential threat

controls on marine carbonate cement mineralogy review and reassessment abstract commonly cited models for controls on variations in carbonate mineralogy are only partly successful in accounting for natural mineralogical trends this limited success may result in part from a failure to recognize or address the ramifications of assumptions inherent to such models in general changes from calcite to aragonite or vice versa and variations in mgco3 incorporation in calcite are interpreted as resulting from 1 kinetic rather than thermodynamic effects 2 the effects of fluid chemistry rather than hydrologic biological or substrate effects 3 the effects of single parameters of fluid chemistry rather than the interactive or aggregate effects of several components and or 4 inorganic rather than organic parameters of fluid chemistry recent laboratory data suggest the necessity of a new approach to modeling controls on mineralogy these data indicate that no single fluid parameter is likely to be a sole or dominant control on carbonate mineralogy in natural environments in some cases thermodynamic stability differences may be as important as kinetic factors in determining mineralogy furthermore the effects of substrate hydrologic and biological factors and of organic compounds cannot be ruled out for most natural situations although at present reliable data are lacking to quantify the influence of these factors on mineralogy future models of controls on carbonate mineralogy need to consider the aggregate and interdependent effects of all of these factors

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

calcium isotope fractionation in ikaite and vaterite abstract we investigated the isotopic composition of calcium in the metastable calcium carbonate polymorphs vaterite and ikaite the synthetic vaterite precipitates show a smaller degree of ca isotope fractionation than calcite or aragonite at comparable temperatures and revealed no significant temperature sensitivity between 10 and 50 c ikaite the water bearing ca carbonate modification caco 3 6h 2 o was precipitated at 2 c in controlled laboratory experiments and in addition recovered from marine sediments and sea ice synthetic and natural ikaites show similar values of ca isotope fractionation in general ikaite is less depleted in heavy isotopes compared to calcite or aragonite at low temperatures the observed offset of vaterite and ikaite to calcite or aragonite precipitated at similar temperatures is presumably mainly related to differences in precipitation rates and regimes which seem however to be typical for the growth of these carbonate minerals small differences in ca isotope ratios of naturally formed ikaites from different locations seem to be related to different geochemical conditions in the respective sediment settings

rapid subsidence and sedimentation from oblique slip near a bend on the north anatolian transform fault in the marmara sea turkey several basins are developing near bends on strands of the north anatolian transform fault in northwest turkey oblique slip on these faults rather than strain partitioning accounts for trans tension and subsidence these basins are asymmetric and tilt and subside most rapidly at their narrow ends near the bends the turbidite surface marking the floor of the cinarcik basin eastern marmara sea was mostly abandoned at a sudden drop in sedi mentation which was likely coincident with the 14 ka lake sea transition and is now a warped reference surface from which we can measure strain and sedimentation subsidence and tilt are rap id but do not require late quaternary changes in regime they are linked to transcurrent motion by slip parallel to an oblique bend on the north anatolian fault and suggest tsunamogenic ver tical motion in large marmara sea earthquakes

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

gallium germanium indium and other trace and minor elements in sphalerite as a function of deposit type a meta analysis abstract while a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades no meta analysis of this data has ever been conducted in this study the results of such an analysis are presented while the study focusses on ga ge and in data for six other elements ag cd co cu fe and mn was also included the results show that there are systematic statistically significant differences in the mean concentrations of fe ga ge in and mn in sphalerite from different deposit types while cd and cu concentrations show no such differences and ag and co concentrations are only significantly different for vein type deposits a principal component analysis demonstrates that the differences between deposit types are approximately one dimensional being expressible in terms of a single number this number correlates strongly with the homogenisation temperature of fluid inclusions r 2 0 82 p 16 it may be expressed as follows pc 1 ln c ga 0 22 c ge 0 22 c fe 0 37 c mn 0 20 c in 0 11 with ga ge in and mn concentrations in ppm and fe concentration in wt the relationship is sufficiently strong to be used as a geothermometer ggimfis the empirical relationship between pc 1 and the homogenisation temperature t is t c 54 4 7 3 pc 1 208 10 our results indicate a strong control of sphalerite chemistry by fluid temperature particularly for the concentrations of ga r 2 0 40 ge r 2 0 65 fe r 2 0 30 and mn r 2 0 60 and to a lesser degree in r 2 0 10 the concentrations of ag cd co and cu appear to be independent of temperature as a consequence of the strong temperature control on pc 1 metamorphic overprinting of pb zn deposits even by lower greenschist facies events may lead to significant changes in sphalerite composition namely a relative decrease in ga and ge concentrations and increase in fe mn and to a lesser degree in concentrations the closure temperature of sphalerite in regional metamorphic events appears to be around 310 50 c such that higher grade events will not be reflected in its composition factors other than temperature such as differences in fluid salinity or source rock composition do not appear to be responsible for differences between deposit types but rather appear to cause differences between individual deposits particularly the cu activity in ore forming systems appears to have a strong influence on in concentrations in sphalerite the observed trends in sphalerite compositions provide a useful tool for future studies of different types of pb zn deposits as well as for mineral exploration they should be particularly relevant for the identification of new resources of ga ge and in

the fenwei rift and its recent periodic activity the fenwei rift on the southern sector of the jin shaan rift system of china is marked by a crescent shaped valley 600 km in length and 30 90 km in width depressed up to 10 km and filled with about 7000 m of cenozoic deposits bounded on both northern and southern sides by majestic mountain ranges the geometry of the rift valley is characterized by six branch depressions and five intervening swells extending east northeastward in a dextral en echelon pattern and bounded on both sides by abrupt topographic slopes reflecting the underlying faults these are typically a system of growth faults having downthrows ranging from 800 m to 10 km and dipping toward the centre of the valley forming an asymmetric graben structure the geometry kinematics and evolution of these faults have had controlling influences on the neotectonic movement of the rift and its recent periodic activity as the present overall form of the rift valley estimates of the amount of extension across the rift for various recent geological periods were obtained from calculations made on the fault separation of corresponding stratigraphie horizons the total amount of extension in response to tensile stresses acting in a direction varying from 25 nw on the west to 70 nw on the northeast is estimated to be 9065 m since the beginning of the rift formation in the eocene whereas the rate of extension in the recent is 4 5 mm yr and in modern times it is 8 24 mm yr the amount of left lateral displacement across the rift during various stages of its development was also calculated from the observed effects of strike slip movement on the drainage system the left lateral offset since the mid pleistocene is approximately 7170 m and the offset rate in modern times is 6 mm yr these estimates suggest that the fenwei rift has been a place of intense neotectonic activity details of more recent activity of the rift were investigated in terms of the various rift related phenomena such as seismic events ground fissuring epeirogenic movement shifting of streams or lakes and climatic changes which have occurred in the historic period seven highly periodic cycles of seismicity are recognized from available historic records of the earthquakes that have occurred in the rift region during the last 4000 yrs each cycle appears to begin with a period of intense seismicity consisting of a series of violent shocks chiefly of m6 8 and lasting approximately 200 yrs and then passes on to a prolonged period of quiescence of about 600 yrs during which only minor seismic events occur the 22 events of ground fissuring recorded in the historic annals are also concentrated in several distinctive periods of intense activity which coincide with seven corresponding periods of active seismicity suggesting that seismic events and ground fissures resulted from the same cause both being indications of periodic tectonic activity of the rift moreover periodic and coincident with periods of tectonic activity are the occurrences of the natural phenomena related to rifting such as the appearance and disappearance of lakes the shifting of streams and changes of river water from clear to turbid

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

authigenic carbonates at cold seeps in the marmara sea turkey a lipid biomarker and stable carbon and oxygen isotope investigation abstract cold seeps along the north anatolian fault in the marmara sea turkey have been recently explored during international expeditions through submersible surveys seafloor mapping and extensive sampling of sediments biota carbonates and pore waters in this study we investigated the main mineralogy carbon and oxygen isotopic compositions and lipid biomarkers in authigenic carbonates retrieved from active seepage areas in the marmara sea abundant microbial lipid biomarkers with light 13 c values as low as 113 as well as light 13 c caco 3 values of bulk carbonate 34 to 21 provided evidence that anaerobic oxidation of methane aom mediated by methanotrophic archaea anme and their bacterial partners is the major process leading to sequestration of methane derived carbon diagnostic lipid distributions indicated that anme 2 archaea and associated sulphate reducing bacteria srb as the prevalent aom mediating microbes diverse non isoprenoid dialkyl glycerol ethers dages including tentatively identified novel compounds were identified with similar 13 c values as lipid biomarkers of srb 105 to 68 though dages are often assigned to srb other unknown bacteria closely involved in aom are likely as source organisms as well despite dominant aom related lipid biomarker patterns the stable carbon isotopic composition of bulk carbonates in two samples from south cinarcik basin and central high in combination with higher hydrocarbon signatures and environmental parameters suggested that oxidation of non methane hydrocarbons including oil may be a contributor to the dissolved inorganic carbon pool and may also be involved in carbonate authigenesis at hydrocarbon seepage settings as previously proposed in the gulf of mexico

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

estimation of slip rates in the southern tien shan using cosmic ray exposure dates of abandoned alluvial fans cosmic ray exposure dates based on in situ produced 10 be in combination with measured heights of fault scarps that cut three abandoned fans imply a slip rate of less than 2 mm yr on the bounding thrust fault along a segment of the southern flank of the tien shan of central asia this rate somewhat lower than those for the segment farther west and for the northern margin of the belt implies that the distribution of shortening across the tien shan must change markedly along the belt the date of abandonment of the smallest of the three fans is consistent with fan formation since the last glacial maximum but the other two fans appear to have been formed and abandoned prior to that time these and other results suggest that advances and retreats of alpine glaciers may not be synchronized with continental ice sheets and that not all prominent geomorphological features in arid asian regions have formed since the last glacial maximum in this study we have assessed the relationship between cosmogenic nuclide content of individual clasts and the time since their deposition on a surface cosmogenic nuclide accumulation represents the integrated total surface exposure of rocks in source regions during transport and since deposition postdepositional processes erosion burial bioturbation and cryoturbation all of which decrease the quantity of cosmogenic nuclides produced in a rock in a given time and hence the apparent exposure age also cause significant scatter among apparent ages of samples from the surfaces very low 10 be concentrations in material from active streambeds and at depth below one of the fan surfaces indicate that exposure prior to deposition onto fan surfaces was minimal

use of small unmanned aerial vehicle suav acquired topography for identifying and characterizing active normal faults along the seerteng shan north china abstract high resolution topographic datasets are being increasingly applied in studies of active tectonics for precise quantification of lateral and vertical offsets of landforms digital elevation models dem acquired by airborne light detection and ranging lidar have also been used for morphological analysis of tectonic scarps to infer the seismic slip history of active faults however the high cost of conducting lidar studies limits its widespread application in contrast the potential applicability of the low cost and portable small unmanned aerial vehicles suav combined with structure from motion sfm techniques to investigate morphological features of fault generated scarps and their paleoseismic implications has not been fully explored here based on suav acquired dems and field observations we present a case study of the morphological features of fault scarps along the seertengshan piedmont fault spf a major boundary fault of the hetao graben north china and discuss their paleoseismic implications the results demonstrate that low angle 2000 years ago the observed 1 8 2 5 m high fault scarps with single slope sections probably represent the most recent incremental displacements associated with surface rupturing earthquake s topographic data acquired by suav are suitable for quantitative morphological analyses of fault generated scarps in actively deforming regions and can contribute to assessments of seismic hazard

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

tectonic activity and structural features of active intracontinental normal faults in the weihe graben central china abstract this study examines the tectonic activity and structural features of active normal faults in the weihe graben central china the weihe graben is an area with a high level of historic seismicity and it is one of the intracontinental systems that developed since tertiary in the extensional environment around the ordos block analysis of high resolution remote sensing imagery data field observations and radiocarbon dating results reveal the following i active normal faults are mainly developed within a zone

dem based morphometry of range front escarpments in attica central greece and its relation to fault slip rates in this paper we apply current geological knowledge on faulting processes to digital processing of digital elevation models dem in order to pinpoint locations of active faults the analysis is based on semiautomatic interpretation of 20 and 60 m dem and their products slope shaded relief in northern eastern attica five normal fault segments were recognized on the 20 m dem all faults strike wnw ese the faults are from west to east thriassion thfs fili fifs afidnai affs avlon avfs and pendeli pefs and range in length from 10 to 20 km all of them show geomorphic evidence for recent activity such as prominent range front escarpments v shaped valleys triangular facets and tilted footwall areas however escarpment morphometry and footwall geometry reveal systematic differences between the bexternalq segments pefs thfs and avfs and the binternalq segments affs and fifs which may be due to mechanical interaction among segments and or preexisting topography in addition transects across all five escarpments show mean scarp slope angles of 22 18f0 78 for both carbonate and metamorphic bedrock the slope angle equation for the external segments shows asymptotic behaviour with increasing height we make an empirical suggestion that slope angle is a function of the long term fault slip rate which ranges between 0 13 and 0 3 mm yr the identified faults may rupture up to magnitude 6 4 6 6 earthquakes the analysis of the 60 m dem shows a difference in fault patterns between western and northern attica which is related to crustal rheology variations d 2004 elsevier b v all rights reserved

a microseismic study in the western part of the gulf of corinth greece implications for large scale normal faulting mechanisms summary we present the results of a dense seismological experiment in the western part of the gulf of corinth psathopyrgos aigion area one of the most active rifts in the aegean region for which we have precise tectonic information the network included 51 digital stations that operated during july and august 1991 covering a surface of 40 x 40 km2 among the 5000 recorded events with ml ranging between 1 0 and 3 0 we precisely located 774 events we obtained 148 well constrained focal mechanisms using p wave first motions of these 60 also have mechanisms obtained by combining the p wave first motions with the s wave polarization directions the observed seismicity is mainly located between 6 and 11 km depth most of the fault plane solutions correspond to e w striking normal faulting in agreement with the geological evidence most of the well determined mechanisms indicate a nodal plane dipping 10 25 due north and a steep south dipping plane a similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the corinth rift we discuss this evidence and the inference of a deep detachment zone a structure where the major faults seen at the surface appear to root a large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone this feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes

a study of the chemistry of pore fluids and authigenic carbonates in methane seep environments kodiak trench hydrate ridge monterey bay and eel river basin analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the kodiak trench hydrate ridge monterey bay clam flats and the eel river basin coupled with the studies of the chemistry of the pore fluids have shown that these carbonates have grown within the sediment column geochemical profiles of pore fluids show that in deep water seeps kodiak trench 4450 m monterey bay 1000 m hydrate ridge 650 m 13c dic values are low isotopically light whereas in the eel river area 350 500 m 13c dic values are much higher isotopically heavier in all cases the 13c values indicate that processes of methane oxidation associated with sulfate reduction are dominant in the shallow sediments data on the isotopic composition of authigenic carbonates found at sites in kodiak trench eel river basin south and eel river basin north indicate a variable composition and origin in different geochemical environments some of the authigenic carbonates from the study sites show a trend in their 13c values similar to those of the pore fluids obtained in their vicinity suggesting formation at relatively shallow depths but others indicate formation at greater sediment depths the latter usually consist of high magnesium calcite or dolomite which from their high values of 13c up to 23 and 18o up to 7 5 suggest formation in the deeper horizons of the sediments in the zone of methanogenesis these observations are in agreement with observations by other workers at hydrate ridge in monterey bay and in the eel river basin

freshening of the marmara sea prior to its post glacial reconnection to the mediterranean sea during the last glaciation the marmara sea was isolated from the mediterranean sea because global sea level was below the depth of the dardanelles sill prior to the postglacial reconnection to the mediterranean sea 14 7 cal kyr bp the surface waters of the marmara sea were brackish marmara lake freshening of a previously saline marmara sea could have happened via spill out of brackish to fresh water from the surface water of the black sea through the bosphorus strait this hypothesis has not been tested against alternative possibilities salt flushing by river run off and precipitation here we use the dissolved cl and stable isotope composition o18 and d of marmara sea sediment pore water to estimate the salinity and stable isotope composition of marmara lake bottom water and to evaluate possible freshening scenarios we use a transport model to simulate pore water cl o18 and d in marmara sea sediments in the past 130 kyr which includes the last interglacial 130 75 cal kyr bp the last glacial 75 14 cal kyr bp and the current postglacial period our results show that the bottom waters of the marmara lake were brackish 4 salinity and isotopically depleted o18 10 2 and d 70 respectively compared to modern seawater their salinity and stable isotope ratios show that they are a mixture of mediterranean waters and danube like waters implying that the freshening took place via spill out of freshwater through the bosphorus our modelling approach indicates that the transit of fresh water from glacial eurasia to the mediterranean via the marmara sea started at least 50 cal kyr bp was continuous throughout most of the last glaciation and persisted up to the post glacial reconnection to the mediterranean through the dardanelles sill 14 7 cal kyr bp these results are consistent with previously published micropaleontological and geochemical investigations of sediment cores that indicate lacustrine conditions in the marmara sea from about 75 to 14 7 cal kyr bp

structural analysis of the right lateral strike slip qingchuan fault northeastern segment of the longmen shan thrust belt central china abstract the eastern margin of the tibetan plateau is marked by the longmen shan thrust belt lstb which is dominated by thrust faults and thrust related fold structures that is home to the 2008 mw 7 9 thrusting type wenchuan earthquake although previous works demonstrated that the seismogenic fault for the earthquake changed coseismic slip sense from thrust dominated slip in the central and southeastern segments of the lstb to right lateral strike slip dominated displacement along the qingchuan fault northeastern segment of the lstb the related structures and current activity of the qingchuan fault remains unclear topographic analyses of 0 5 m resolution worldview imagery and digital elevation model dem data field investigations and structural analysis of the fault zone reveal that i stream channels and late pleistocene holocene terrace risers and alluvial fans are systematically offset dextrally along the qingchuan fault ii foliations developed in the fault zone indicate a right lateral strike slip dominated displacement and iii geological evidence and seismic data show that the qingchuan fault is currently active as the main seismogenic fault dominated by a right lateral strike slip with an average slip rate of ca 3 5 mm yr our results demonstrate that the spatial change in slip sense along the lstb from thrust dominated in the central and southwestern sectors to right lateral strike slip dominated in the northeastern sector is mainly caused by a change in the orientation of fault geometry from ne sw to ene wsw along the lstb

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

controls on calcium isotope fractionation in sedimentary porewaters abstract the calcium isotopic composition of porewaters and authigenic carbonates in the anoxic sediments of a convergent continental margin drilled during ocean drilling program odp provides first insight into the different processes that control ca geochemistry in clastic marine organic rich sedimentary environments in 4 sites drilled during leg 204 at hydrate ridge cascadia margin offshore oregon usa sulfate is consumed during anaerobic oxidation of methane and of organic matter via sulfate reduction within the upper meters of the sedimentary section these reactions promote the precipitation of authigenic carbonates through the generation of bicarbonate which is reflected in a pronounced decrease in calcium concentration although ca isotope fractionation is observed during carbonate precipitation ca concentration in the pore fluids from odp leg 204 is decoupled from ca isotopy which seems to be mainly controlled by the release of light ca isotopes that completely overprint the carbonate formation effect different processes such as the release of organically bound ca ion exchange and ion pair formation may be responsible for the released light ca deeper within the sedimentary section additional processes such as ash alteration influence the ca isotopic composition of the porewater two sites drilled into the deeper core of the accretionary prism reveal the nature of fluids which have reacted with the oceanic basement these deep fluids are characterized by relatively high ca concentrations and low 44 40ca ratios

bedded jaspers of the ordovician lokken ophiolite norway seafloor deposition and diagenetic maturation of hydrothermal plume derived silica iron gels sedimentary beds of jasper red hematitic chert in the ordovician lokken ophiolite of norway are closely associated with volcanogenic massive sulphide vms deposits the jaspers occur in the immediate hangingwall and laterally peripheral to the large lokken 25 30 mt and small hoydal 0 1 mt vms deposits and are exposed discontinuously for several kilometres along strike massive or laminated types predominate jasper sulphide debris flow deposits are also abundant near vms deposits the jaspers contain hematite rich laminae showing soft sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels early textures include 1 straight or curved chains of hematitic filaments 3 10 m in diameter and 20 100 m long 2 branching networks of 15 25 m thick tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite 3 small up to 10 m spherules composed of cryptocrystalline hematite and silica and 4 up to 50 m silica spherules with hematitic cores the small filaments seem to have been deposited in varying proportions in the primary laminae possibly together with hematitic and siliceous microspheroids diagenetic changes are represented by polygonal syneresis cracks and the presence of cryptocrystalline originally opaline silica chalcedony quartz carbonate and cryptocrystalline hematite and or goethite forming botryoidal masses and spheroids 10 m to 5 mm in diameter coarser euhedral grains of quartz carbonate and hematite are integral parts of these textures bleached silica rich jaspers preserve only small relics of fine grained hematite rich domains and locally contain sparse pockets composed of coarse euhedral hematite epidote

evolution of the late cenozoic tectonic stress regime in the shanxi rift central north china plate inferred from new fault kinematic analysis abstract the shanxi rift an intracontinental belt along the eastern margin of the ordos block north china plate has undergone multi stage extensional deformation during the late cenozoic in this study new fault kinematic analysis of boundary faults in the shanxi rift constrained by geochronological data defines a three stage tectonic stress regime since the late miocene providing new structural evidence for deciphering the northeastward growth of the tibetan plateau the earliest stage involved a transtensional stress regime of nw se extension and ne sw compression in the late miocene early pleistocene ca 10 1 8 ma and characterized by mean principal stress axes of 1 at 344 7 87 2 2 at 217 6 01 1 and 3 at 128 1 01 0 the early transtensional stress regime was responsible for the opening of the shanxi rift and was very likely associated with intensive right lateral pull apart activity in the eastern ordos block due to the northeastward growth of the tibetan plateau during the second stage the stress regime changed to less intense ne sw extension with mean stress orientations of 323 3 85 2 for 1 127 5 02 9 for 2 and 214 9 02 6 for 3 in the early late pleistocene ca 1 8 0 11 ma this stage is marked by a distinct shift from fluvio lacustrine to fluvio piedmont sedimentary facies at the end of the early pleistocene and the widespread eruption of basalt in the datong basin north of the shanxi rift this short lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the tibetan plateau the third stage was transtensional characterized by nnw sse extension and wnw ese compression 1 at 060 88 9 2 at 074 9 03 9 and 3 at 164 00 since the late pleistocene ca 0 11 ma causing dextral shear deformation in the shanxi rift and the disappearance of its paleo lake this stage resulted from regional ene wsw shortening due to northeastward growth of the tibetan plateau

intraplate seismotectonic features of north china abstract intraplate earthquakes in north china are characterized by shallow depth large magnitude and high frequency obviously the zonal distribution of earthquakes is closely related to recent active faults and cenozoic graben and rift systems the active faults are mainly oriented nne with right lateral movements and partially oriented nw with left lateral movements the hetao yinchuan graben fenhe weihe graben and north china plain rift systems often reflect crustal thinning and mantle uplift according to the data concerning crustal deformation particularly the movement patterns of faulting crustal taphrogenesis and earthquake surface rupture it is suggested that a shearing extension mechanism could be considered as a cause of the formation of seismotectonic structures in north china since the early cenozoic era graben and rift systems also developed in northeast and south china they formed earlier than the graben and rift systems in north china however and their activity has decreased during the quaternary period it is reasonable that the seismicity in northeast and south china is not as strong as that in north china

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

using the aster global dem to derive empirical relationships among triangular facet slope facet height and slip rates along active normal faults abstract the advent of global dems provided a uniform elevation dataset for studying geomorphic parameters in a variety of settings in this paper aster dem data 30 m pixel size are used to derive empirical relationships between triangular facet attributes and slip rates along active normal faults we sampled 232 triangular facets along 10 normal faults in greece and bulgaria that slip with rates from 0 1 mm yr up to 1 3 mm yr the studied normal faults accumulate quaternary tectonic strain in well known extensional provinces such as central greece crete and sw bulgaria the normal fault footwalls analyzed herein have been developed under similar long term climatic conditions it is suggested that two key geometrical features of the youngest generation of triangular facets slope angle and height can provide useful metrics to assess rates of deformation when seismological and geodetic data are lacking or not found in sufficient quantity to make reasonable assessments our derived empirical relation between slip rate and facet slope angle is y 0 057 x 1 where y is the fault slip rate mm yr and x is the facet slope angle degrees with an r 2 0 728 it is envisaged that our analysis may be helpful in assessing seismic hazard along normal faults with similar facet characteristics in other extensional settings

quaternary rate of folding of the ventura avenue anticline western transverse ranges southern california upper quaternary terraces of the ventura river california are uplifted tilted and folded over the ventura avenue anticline rates of uplift and tilting have decreased since inception of the structure over the past 200 ka assuming that the chronology based on amino acid racemization 14c dates and soils correlation is approximately correct then the minimum possible average rate of uplift in the axial region of the fold has decreased from 14 mm yr to 2 mm yr during the past 200 ka interval rates of uplift for the periods 200 ka to 80 or 105 ka 80 or 105 ka to 30 ka and 30 ka to present are respectively about 20 mm yr 9 mm yr and 5 mm yr the rate of tilting shows a similar trend decreasing from 5 8 urad yr 2 5 urad yr and 1 2 urad yr for the same time intervals respectively based on the mechanics of flexural slip folds in stratified sedimentary rocks these data suggest that the rootless ventura avenue anticline is a fold that has been shortening at a relatively constant rate of about 9 mm yr since its inception

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

neotectonic activity along the shanxi rift system china abstract the shanxi rift system is one of the most outstanding pliocene quaternary continental rift systems and strong earthquake belts in china it extends as a series of en echelon left stepping asymmetrical half graben basins on the shanxi highlands over a distance of more than 1200 km it describes a sinous s shaped curve with a nne trending transtensional segment in the middle and ne ene trending extensional domains on both terminal segments the latter are characterized by apparently synchronous high angle normal faulting accommodating large vertical and relatively smaller lateral strains 3 5 8 5 which produces the modern basin and range structure the rift system has been intermittently active since the pliocene geomorphological neotectonic and seismic studies indicate that the rift system is at present still developing as demonstrated by the occurrence of strong destructive historical earthquakes of magnitudes 7 8 and the large slip rates on the nne trending transtensional faults in the middle segment the slip rates of these faults reached 4 9 6 4 mm per year during the holocene geophysical studies show that the rifting occurred in a thickened crust and no compelling evidence exists for the major thermal event in the mantle uniquely associated with the rifting the development of the shanxi rift system is consistent with the regional brittle strain pattern of a right lateral shear belt and a regional stress field of ene wsw compression and nnw sse extension of the north china subplate this structural setting corroborates the hypothesis that the deformation is in response to the escape tectonics caused by the himalayan indenter from the southwest and at the same time by the counter clockwise rotation of the intervening crustal blocks this provides the mode of formation of the shanxi rift system

stratigraphy and alteration of the host rocks united verde massive sulfide deposit jerome arizona the early proterozoic volcanogenic united verde massive sulfide orebody is situated within the cleopatra member of the deception rhyolite the cleopatra member a porphyritic rhyodacite has been subdivided into an upper unit and a lower unit the united verde orebody previously interpreted to lie at the top of the cleopatra member is now recognized as lying within the basal section of the upper unit of the cleopatra member the upper unit and lower unit are differentiated on the basis of alteration mineralogy mineral and rock geochemistry and lithologic peculiarities the contact between the two units is marked by sediments at the base of the upper unit including a distinct green calcitebearing feldspar tuff chert and hematitic chert layers and a quartz porphyry conglomerate the cleopatra member contains six distinct alteration types five alteration types characterize the lower unit and include two types of moderate chloritic and sericitic alteration designated b1 and b2 two spatially distinct types of sericitic and silicic alteration designated s1 and s2 and an area of intense chloritic alteration designated c these five alteration types record the effects of hydrothermal alteration by the massive sulfide ore forming system and of a regional greenschist facies metamorphic event the upper unit contains the least altered rocks of the cleopatra member and the bulk of the sixth alteration type designated h the rocks included within h type alteration have disseminated hematite and or hematitic chert veining whole rock and mineral geochemistry of the lower unit may be used to establish position within the palcohydrothermal system the distal area of moderate alteration b1 contains samples enriched in mgo slightly depleted in alkalies and having ratios of fe 2 o sub 3 sub total fe 2 o sub 3 sub total mgo for whole rocks and fe sub total fe sub total mg for chlorites that are low relative to other cleopatra member samples these attributes are suggestive of the low temperature seawater rock interaction expected in the domain of fluid recharge rocks of alteration type c experienced significant additions of iron and magnesium and losses of cao na 2 o and k 2 o presumed to reflect alteration in the main discharge conduit for the hydrothermal fluid chlorite and whole rock iron to iron plus magnesium ratios decrease within the area of alteration type c toward the sediment water interface this is consistent with mixing of an evolved ore forming fluid with seawater in the upper levels of the area of alteration type c samples from the area of alteration type b2 which is intermediate between the recharge b1 and discharge areas c are greatly depleted in cao and na 2 o and are enriched in iron alteration types s1 and s2 are interpreted to reflect localized sites of fluid discharge where sio 2 and k 2 o have been added and other major elements except for al 2 o 3 have been removed whole rock and mineral chemistry of the alteration types record progressive changes in the hydrothermal fluid from seawater to an ore forming fluid the fluid that was discharging and depositing ore apparently had a log a sub o 2 between 41 7 and 35 5 a log a sub h 2 s between 5 and 2 6 and was saturated with respect to iron sulfides magnesium silicates and ore forming metals

clustering of offsets on the haiyuan fault and their relationship to paleoearthquakes we used airborne light detection and ranging lidar data to reevaluate the single event offsets of the 1920 haiyuan ms 8 5 earthquake and the cumulative offsets along the western and middle segments of the coseismic surface rupture zone our lidar data indicate that the offset observations along both the western and middle segments fall into groups the group with the minimum slip amount is associated with the 1920 haiyuan ms 8 5 earthquake which ruptured both the western and middle segments our research highlights two new interpretations first the previously reported maximum displacement of the 1920 earthquake was likely due to at least two earthquakes second our results reveal that the cumulative offset probability density copd peaks of the same offset amounts on the western and middle segments do not correspond to one another one to one we suggest that any discussion of the rupture pattern of a certain fault based on the offset data should also consider fault segmentation and paleoseismological data therefore the copd peaks should be computed and analyzed on fault subsections and not entire fault zones to study the number of paleoearthquakes and their rupture patterns

beware of slowly slipping faults the fault zone that hosted the devastating wenchuan earthquake in 2008 had been assigned a moderate to low seismic hazard rating because it slips slowly in hindsight it seems that this type of fault is not necessarily innocuous

tectonic uplift of the northern qinling mountains central china during the late cenozoic evidence from dem based geomorphological analysis abstract the qinling mountains which stretch from east to west in central china represent an important geological and geographical boundary between north china and south china because of the northeastward growth of the tibetan plateau since the late cenozoic the northern qinling mountains have been strongly reactivated and uplifted to investigate the landscape response to the tectonic uplift the geomorphic indices of the northern qinling mountains including the hypsometry mathematical function of the longitudinal profile channel longitudinal profile and steepness index were analyzed the topographic analysis reveals that the landscape evolution of the heihe river basin is in a transient state the upstream of the heihe river basin has undergone a long period of erosion and represents relict landscape in contrast the downstream represents adjusting landscape which formed by river incision in response to the rapid uplift of the northern qinling mountains this is a result of the extension of the weihe graben which has formed due to the northeastward growth of the tibetan plateau during the late cenozoic the spatial distribution of the geomorphic indices reveals that the ne striking taibai fault has experienced strong tectonic activity since the late cenozoic and is a secondary fault that accelerated the uplift rate of the northern qinling mountains the tectonic stress due to the northeastward growth of the tibetan plateau has been transmitted to the northern qinling mountains along the taibai fault therefore we proposed that the uplift of the northern qinling mountains is due to the combined effects of the weihe graben extension and taibai fault activity forming the highest peak taibai mountain of the northern qinling mountains near the intersection of the qinling piedmont fault and taibai fault

geochemical constraints on the origin of the pore fluids and gas hydrate distribution at atwater valley and keathley canyon northern gulf of mexico abstract pore fluids from atwater valley at 13 14 and keathley canyon kc 151 in the northern gulf of mexico are surprisingly similar with respect to ionic concentrations and oxygen and strontium isotope values as well as hydrocarbon geochemistry suggesting that these widely separated localities share common deep subsurface fluid origins seafloor mounds with focused fluid migration pathways and inferred near seafloor gas hydrates characterize the at 13 14 region whereas the kc 151 region has a bottom simulating reflector bsr at 310 mbsf which is rather uncommon in the gulf of mexico gom at these sites seafloor gas hydrates were not observed but the sediment surface in the vicinity and particularly at the mounds is populated with chemosynthetic communities that are commonly associated with seafloor gas emission the geochemical results together with the pressure core data suggest that at the at region methane hydrate mostly occurs in near surface sediments at mounds consistent with focused migration pathways in the kc region methane hydrate mostly occurs deeper in the section in highly fractured silty clayey sediments from 220 to 300 mbsf the pore fluids at the at mounds and kc 151 are characterized by higher than seawater salinity the more saline pore fluids at the at mound and at kc151 sites located 350 km apart are almost chemically indistinct ionic ratios indicate that this distinct high salinity fluid is not from in situ salt dome halite dissolution rather this fluid is a subsurface brine derived from jurassic or cenozoic evaporite formation modified by fluid sediment reactions and migrated to the two sites analyzed despite porewater salinities elevated above that of seawater the sediment temperatures are within the range of methane hydrate stability for each of the sites based on cl dilutions the maximum gas hydrate pore volume occupancy at the at mound sites would be 9 at kc cl concentrations in pressure cores imply that in situ hydrate is unevenly distributed with pore volume occupancy of 1 12 significant variations in sulfate gradients were observed with the sulfate to methane transition zone smtz at or near the seafloor at the at mound sites at at 13 2 the well defined smtz is at 8 mbsf and at kc 151 3 it is at 9 mbsf there is no coincidence between the steepness of the sulfate gradients and the presence or depth of a bsr suggesting that the smtz interfaces are measuring different aspects of the subsurface methane hydrology at both at and kc the 13 c dic values clearly indicate that anaerobic oxidation of methane aom is the dominant reaction responsible for sulfate reduction and the increased alkalinities observed the most negative 13 c dic values obtained are 46 3 and 49 6 at the smtzs at at 13 2 and kc 151 3 respectively

sulfate dependent anaerobic oxidation of methane at a highly dynamic bubbling site in the eastern sea of marmara cinarcik basin abstract during the marsitecruise expedition in november 2014 on board the rv pourquoi pas multidisciplinary sampling was carried out with the rov victor 6000 in order to investigate biogeochemical processes taking place at cold seep environments in the sea of marmara pore water bottom water sediment and authigenic carbonate samples were collected from two short push cores mrs dv5 pc04 8 cm mrs dv5 pc01 12 5 cm at an active methane bubbling site in the southeastern part of the cinarcik basin sulfate sulfur and oxygen isotope data as well as sulfide isotope data indicate that sulfate dependent anaerobic oxidation of methane is the dominant process in the sediments this is confirmed by archaeal lipids diagnostic for anaerobic methane oxidizers detected with strong 13c depletions the available data even allows to distinguish the dominant aom assemblages specific lipid patterns are consistent with a dominance of anme 2 archaea within the microbial community abundant authigenic carbonates mostly aragonite found at all depths show a narrow range in 13c values between 27 69 and 33 40 the carbon isotopic composition of the dissolved inorganic carbon as well as strontium and calcium isotopes confirm that the current reaction zone sulfate methane transition zone starts at the bottom of the core all shallower carbonates are witnesses of paleo seepage activity u th dating of four pure aragonite samples show the short time span that is preserved in core mrs dv5 pc01 235 60 yr b p two major earthquakes of 1766 ce and 1754 ce in the cinarcik basin might potentially have triggered the increased seepage of methane at this location

geomorphological observations of active faults in the epicentral region of the huaxian large earthquake in 1556 in shaanxi province china abstract the huaxian magnitude 8 great earthquake of january 23 1556 is the largest one recorded in the weihe basin shaanxi province china and caused 830 000 people either injury or death the epicenter is located in the southeastern part of the weihe basin around huaxian city earthquakes are closely related to active faults and active faults are well developed in the epicentral area of the huaxian large earthquake thus we will discuss the activity of the major faults in the epicentral area by geomorphological observations there are three major fault sets in the study area striking approximately east west northeast and northwest these are inhomogeneous in spatial distribution rates and manners of faulting as shown by geomorphological observations such as faulted fluvial terraces and alluvial fans the ages of the second and first terraces are around 20 000 and 5 000 years b p by thermoluminescent dating carbon 14 dating and archeology the terraces were faulted by the north huashan fault f1 the main boundary fault of weihe basin and the piedmont fault f2 after the second and the first terraces formed the distribution of the displacement shows that the intersections of the north huashan fault and the chishui fault f4 striking northwest and the western margin fault f5 of tongguan loess tableland have the largest in offsets in the area perhaps the huanxian great earthquake in 1556 a d had a close relation to the north huashan fault the weihe fault f3 striking east west is also an active fault by analysis of the flood plain structure thus we should pay attention to the activities of the faults to take precautions against another possible large earthquake in this region

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

controls on δ 34 s and δ 18 o of dissolved sulfate in aquifers of the murray basin australia and their use as indicators of flow processes the usefulness of stable isotopes of dissolved so4 34s and 18o to study recharge processes and to identify areas of significant inter aquifer mixing was evaluated in a large semi arid groundwater basin in south eastern australia the murray basin the distinct isotopic signatures in the oxidizing unconfined murray group aquifer and the deeper reducing renmark group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections 34s values in the unconfined murray group aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20 8 to 0 3 the concomitant increasing so4 cl ratios as well as relatively low 18oso4 values suggest that vertical input of biogenically derived so4 via diffuse recharge is the predominant source of dissolved so4 to the aquifer further along the hydraulic gradient towards the discharge area near the river murray 34s values in the unconfined murray group aquifer increase and so4 cl ratios decrease due to upward leakage of waters from the confined renmark group aquifer which has a distinctly low so4 cl and high 34s 14 9 56 4 relatively positive 34s and 18oso4 values and low so4 cl in the renmark group aquifer is typical of so4 removal by bacterial reduction the s isotope fractionation between so4 and hs of 24 estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation 70 even though the confined groundwater residence time is 300 ka years mapping the spatial distribution of 34s and so4 cl of the unconfined murray group aquifer provides an indicative tool for identifying the approximate extent of mixing however the poorly defined end member isotopic signatures precludes quantitative estimates of mixing fractions

composition and origin of authigenic carbonates in the krishna godavari and mahanadi basins eastern continental margin of india abstract the mineralogical and stable isotopic composition of authigenic carbonates from the krishna godavari kg and mahanadi basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of india in the bay of bengal authigenic carbonate cements micro nodules bioturbation casts and tubes from 12 core locations drilled during the indian national gas hydrate program nghp expedition 01 were investigated for this study three main processes responsible for authigenic carbonate precipitation are identified organoclastic sulfate reduction anaerobic oxidation of methane and methanogenesis evidence of vigorous methane seepage is indicated in carbonates recovered at sites 7 10 12 kg basin and 19 mahanadi basin these methane derived carbonates display typical paragenetic carbonate mineralogies aragonite high mg calcite with 15 mol mgco 3 ca rich dolomite two separate horizons of methane derived carbonates are correlated between 4 drill holes up to 16 km apart the upper horizon has been dated with 14 c 40 100 51 600 a bp 1950 and clearly indicates that methane seepage has been much more vigorous in the past possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin

spatial variations in late quaternary slip rates along the doruneh fault system central iran the doruneh fault system dfs is one of the major active strike slip faults in the arabia eurasia collision zone despite its geological activity no large m 6 5 historical or instrumental earthquakes have been recorded along it to date the rate and distribution of slip as well as the seismic behavior of the dfs have been unknown we reconstructed 67 geomorphic offsets recorded by three successive alluvial abandonment surfaces q1 q2 and q3 displaced along the western wfz and central cfz fault zones the determined ages of 12 36 and 120 ka using in situ produced 10 be and 36 cl cosmogenic nuclides for theses surfaces allowed to estimate three sets of individual left lateral slip rates and consequently to describe the spatiotemporal distribution of slip along the cfz and wfz the slip rates averaged over time intervals of 36 and 120 ka reveal variable slip rates along length but similar slip rates at a point with a maximum rate of 8 2 mm yr during the holocene however the fault slip behavior appears more complex with a maximum rate of 5 3 mm yr the cfz is divided into two 4 km apart segments with symmetrical slip distributions relative to a persistent boundary which has not been ruptured over the last 12 ka the maximum length of seismic fault segments varies from 70 to 100 km which could produce earthquakes with a magnitude of m w 7 2 7 4 this emphasizes the necessity of segmentation models for long strike slip faults that may not necessarily rupture along their whole length during a single earthquake

microseismicity and faulting geometry in the gulf of corinth greece summary during the summer of 1993 a network of seismological stations was installed over a period of 7 weeks around the eastern gulf of corinth where a sequence of strong earthquakes occurred during 1981 seismicity lies between the alepohori fault dipping north and the kaparelli fault dipping south and is related to both of these antithetic faults focal mechanisms show normal faulting with the active fault plane dipping at about 45 for both faults the aftershocks of the 1981 earthquake sequence recorded by king et al 1985 were processed again and show similar results in contrast the observations collected near the western end of the gulf of corinth during an experiment conducted in 1991 rigo et al 1996 and during the aftershock studies of the 1992 galaxidi and the 1995 aigion earthquakes hatzfeld et al 1996 bernard et al 1997 show seismicity dipping at a very low angle about 15 northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30 we suggest that the 8 12 km deep seismicity in the west is probably related to the seismic aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed the diverence in the seismicity and focal mechanisms between east and west of the gulf could be related to the diverence in the recent extension rate between the western gulf of corinth and the eastern gulf of corinth which rotated the faults dipping originally at 45 as in the east of the gulf to 30 as in the west of the gulf

late quaternary slip rate along the central bangong chaxikang segment of the karakorum fault western tibet insight into the spatial and temporal changes of slip rate is essential to understand the kinematic role of large strike slip faults in continental collision zones geodetic and geologic rates from present to several million years ago along the karakorum fault range from 0 to 11 mm yr here we determine the first late quaternary slip rate at the southern end of the linear bangong chaxikang segment of the karakorum fault using cumulative offsets 20 200 m of fans and terraces at three sites as well as 74 new 10 be surface exposure ages to constrain the age of these offset geomorphic markers the rate is 3 mm yr at sites gun and chaxikang and it is 1 7 2 2 mm yr at the gar fan site together with rates obtained along the southernmost menshi kailas segment the karakorum fault slip rate seems to increase southeastward from south of bangong lake to kailas from 3 to 8 mm yr these karakorum fault slip rate data 3 8 mm yr together with the total length of the fault 1000 km and its initiation age 13 23 ma confirm that the karakorum fault is the major fault accommodating dextral strike slip motion ne of the western himalayas the dextral karakorum fault in the south and the conjugate left lateral longmu co altyn tagh fault system in the north are thus the major strike slip faults of western tibet which contribute to eastward extrusion of tibet

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

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

dolomite formation in the dynamic deep biosphere results from the peru margin early diagenetic dolomite beds were sampled during the ocean drilling programme odp leg 201 at four reoccupied odp leg 112 sites on the peru continental margin sites 1227 684 1228 680 1229 681 and 1230 685 and analysed for petrography mineralogy 13c 18o and 87sr 86sr values the results are compared with the chemistry and 13c and 87sr 86sr values of the associated porewater petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate dolomite precipitation often pre dates the formation of framboidal pyrite most dolomite layers show 87sr 86sr ratios similar to the composition of quaternary seawater and do not indicate a contribution from the hypersaline brine which is present at a greater burial depth also the 13c values of the dolomite are not in equilibrium with the 13c values of the dissolved inorganic carbon in the associated modern porewater both petrography and 87sr 86sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment 30 m below the seafloor a significant depletion in the dissolved mg and ca in the porewater constrains the present site of dolomite precipitation which co occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate methane interface it has been hypothesized that microbial hot spots such as the sulphate methane interface may act as focused sites of dolomite precipitation varying 13c values from 15 to 15 for the dolomite are consistent with precipitation at a dynamic sulphate methane interface where 13c of the dissolved inorganic carbon would likewise be variable a dynamic deep biosphere with upward and downward migration of the sulphate methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter thus the study of dolomite layers in ancient organic carbon rich sedimentary sequences can provide a useful window into the palaeo dynamics of the deep biosphere

geology and volcanic stratigraphy of the canatuan and malusok volcanogenic massive sulfide deposits southwestern mindanao philippines the canatuan and malusok massive sulfide deposits are located near siocon zamboanga del norte in southwestern mindanao philippines the canatuan malusok area is underlain by the jurassic cretaceous tungauan schists which form much of the zamboanga peninsula the volcanic strata at canatuan and malusok can be traced for 7 km along strike and is host to at least three discrete massive sulfide bodies canatuan malusok and se malusok basal basaltic andesite volcanic rocks are generally chemically uniform and show only moderate alteration the massive sulfide deposits occur in overlying rhyolitic to rhyodacitic volcanic rocks that are altered to a schistose assemblage of quartz sericite chlorite and pyrite the alteration is texturally destructive but graded clastic beds are locally observed despite tropical saprolitic weathering four lithogeochemical subunits of the felsic package are identified stratigraphic interleaving however has made correlation of these units over any significant distance difficult the sulfide lenses are overlain by a few metres of felsic schists which locally contain manganese bearing silicates and oxides that serve as a stratigraphic marker hangingwall andesitic volcaniclastic rocks are discontinuously preserved although where present they consist of regularly bedded mafic volcanic sandstones the lateral continuity of a manganese bearing marker and flanking felsic volcaniclastic intervals indicate that locally the volcanic strata form a homoclinal sequence the canatuan au ag cu zn deposit consists of a gossan overlying a massive sulfide lens the sulfides and gossan are flat lying and hosted within felsic volcanic rocks the gossan is gold silver rich and was formed by a combination of oxidation and volume collapse of the original sulfide lens the sulfide minerals present below the current water table are auriferous massive pyrite with base metal sulfides with some supergene chalcocite the transition from gossan to sulfides is very sharp occurring at the water table massive sulfide deposits at malusok are hosted in the same felsic sequence as canatuan and they have similar base and precious metal contents only limited gossan has been found at malusok the bimodal nature of the volcanic rocks at canatuan together with their low hfse contents near flat ree patterns and tholeiitic affinities suggest that they formed in an intra oceanic arc setting above a depleted mantle source mafic and felsic volcanic rocks of similar composition have been recovered from the tonga kermadec and izu bonin marianas island arc systems in the western pacific mafic rocks at canatuan show no evidence for lile enrichment that characterizes melts derived from metasomatized mantle under more mature arcs suggesting that they are the product of a nascent rather than a mature arc there is no evidence from the ree or other incompatible trace elements that continental crust or evolved arc crust was involved in the generation of the canatuan malusok volcanic rocks although it has been proposed that the zamboanga metamorphic complex comprises microcontinental fragments of eurasian affinity our data do not support an evolved crustal setting for the canatuan malusok volcanic rocks which we suggest were derived from an intra oceanic arc and subsequently accreted to the eastern mindanao terrane

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

hydrology in the sea of marmara during the last 23 ka implications for timing of black sea connections and sapropel deposition 1 sediments deposited under lacustrine and marine conditions in the sea of marmara hold a late quaternary record for water exchange between the black sea and the mediterranean sea here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells major and trace elements and specific organic biomarker measurements as well as a micropaleontological study from a 14c dated sediment core retrieved from the sea of marmara pronounced changes occurred in 18o and 87sr 86sr values at the fresh and marine water transition providing additional information in relation to micropaleontological data organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event when compared with the black sea record the results suggest that the black sea was outflowing to the sea of marmara from the last glacial maximum until the warmer bolling allerod the first marine incursion in the sea of marmara occurred at 14 7 cal ka b p however salinification of the basin was gradual indicating that black sea freshwaters were still contributing to the marmara seawater budget after the younger dryas which is associated with a high input of organic matter of terrestrial origin both basins were disconnected resulting in a salinity increase in the sea of marmara the deposition of organic rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population

a combined fluid inclusion and s pb isotope study of the neoproterozoic pingshui volcanogenic massive sulfide cu zn deposit southeast china abstract the pingshui cu zn deposit is located in the jiangshan shaoxing fault zone which marks the neoproterozoic suture zone between the yangtze block and cathaysia block in south china it contains 0 45 million tons of proven ore reserves with grades of 1 03 wt cu and 1 83 wt zn this deposit is composed of stratiform massive sulfide ore bodies which contain more than 60 vol sulfide minerals these ore bodies are hosted in altered mafic and felsic rocks spilites and keratophyres of the bimodal volcanic suite that makes up the neoproterozoic pingshui formation metallic minerals include pyrite chalcopyrite sphalerite tennantite tetrahedrite and magnetite with minor galena gangue minerals are quartz sericite chlorite calcite gypsum barite and jasper three distinct mineralogical zones are recognized in these massive sulfide ore bodies a distal zone composed of sphalerite pyrite barite zone i an intermediate zone characterized by a pyrite sphalerite chalcopyrite assemblages zone ii and a proximal zone containing chalcopyrite pyrite magnetite zone iii a thin layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone the volcanic rocks of the pingshui formation are all highly altered spilites and keratophyres but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 c and their salinities range from 3 2 to 5 7 wt nacl equivalent raman spectroscopy of the fluid inclusions showed that water is the dominant component with no other volatile components fluid inclusion data suggest that the ore forming fluids were derived from circulating seawater the 34 s values of pyrite from the massive sulfide ores range from 3 6 to 3 4 indicating that the sulfur was primarily leached from the arc volcanic rocks of the pingshui formation both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions implying that the lead was also derived from the pingshui formation the low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many vms cu zn deposits in canada e g noranda and thus can be classified as belonging to the bimodal mafic subtype the presence of magnetite and the absence of jaspilite and barite at the 505 m level in the pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies if this interpretation is correct the deep part of the pingshui cu zn deposit may have significant exploration potential

quaternary deformation at the southeastern margin of the ordos block north china inferred from structural analysis of basin bounding faults abstract the southeastern margin of the ordos block semob is located at the juncture of the north china block the ordos block and the qinling orogen a series of faulted basins has developed in this area since the cenozoic the latest focal mechanism solution and stress field analyses indicate that the semob is located at the adjacent regions of present different stress field although the structural activity and internal mechanisms of this changing remain unclear in this paper we describe the results of a study into the fault systems and quaternary deformation between the linfen and weihe basins on the semob based on the deformation sequences kinematic analyses and activity timing we found that the strain field in semob underwent three evolutionary stages during the quaternary nw se extension in the early pleistocene ne sw extension in the middle pleistocene and ca n s oblique extension from the late pleistocene to the holocene this evolution of the strain field affected both the geomorphic patterns and the activity of paleo earthquake events along the semob during the quaternary quaternary extensional deformation in the upper crust along the semob possibly resulted from crust mantle decoupling which may be related to eastward expansion of the tibetan plateau and subduction of the pacific and philippine sea plates

characteristics of late quaternary activity along the southern border fault zone of weihe graben basin abstract the weihe graben basin located in the centre of shaanxi china is a tectonic depression on the southern border of ordos massif a subtectonic unit in the sino korean paraplatform in the light of new information exhibited from geological mapping on the scale of 1 50 000 the active history and the feature of the southern border fault zone of weihe graben basin have been researched the fault zone may be subdivided into two segments the piedmont fault of huashan mt in the east sector and the northern border fault of qinling mts in the west sector the research shows that new activity of the piedmont fault of huashan mt is obvious since the late quaternary a great number of relics of earthquake deformation such as the newest fault scarps bedrock fractures loess crevices landslides and mountain creep are distributed along this fault and its two flanks this fault is most likely the causative fault zone of the huaxian great earthquake in 1556 m 8 the analysis of two palaeoseismic profiles shows the earthquake recurrence interval is 2000 2500 years for the huashan mt piedmont fault whereas 2000 4000 years for the northern border fault of qinling mts

isotope fractionation during ca exchange on clay minerals in a marine environment abstract in order to interpret marine porewater profiles it is mandatory to understand the behavior of calcium ca and its isotopes during cation exchange in marine sediments it has been proposed that the exchange of adsorbed ca 2 for ammonium which is a product of organic matter decomposition results in the releases of light ca from clay minerals into the porewater teichert et al 2009 in order to investigate the effect of ammonium on ca isotope fractionation experiments with clay mineral separates illites montmorillonite kaolinite and natural marine sediments from the north atlantic integrated ocean drilling project site u1306a in artificial seawater were carried out at different temperatures 4 14 21 c and ammonium concentrations 100 140 180 mm the results of the adsorption experiments carried out in artificial seawater show that during adsorption of ca 2 the light ca isotopes are favored over the heavier ca isotopes this effect is most prominent for the illite samples 1000ln 0 82 to 1 15 and kaolinite sample 1000ln 1 23 to 2 76 whereas montmorillonite and the natural marine sediments show smaller degrees of fractionation from the fluid in the range of 0 46 to 0 06 determination of the desorbed ca 2 is based on the adsorbed ca 2 left on the exchanger and reveals that the desorbed ca 2 has a significantly different isotopic signature from the surrounding fluid in general the degree of ca isotope fractionation is dependent on the ammonium concentration and does not show significant influence of temperature modeling the ca 2 desorption induced by ammonium adsorption demonstrates that according to the prevailing mineralogy and porewater sediment ratio desorbed ca 2 has the potential to shift the porewater isotopy by up to 2 5 and needs to be considered when interpreting ca isotope porewater profiles

tectonic characteristics of the lishan piedmont fault in the se weihe graben central china as revealed by the geomorphological and structural analyses abstract the fault kinematics slip rate and paleoseismicity along the approximate ew trending lishan piedmont fault lpf in the se weihe graben central china have been determined the results of geomorphological analysis field investigations and radiocarbon 14 c age dating indicate that i slope angles of the observed triangular facets cluster around 20 ii empirical correlations yield a vertical slip rate throw rate of 0 11 0 25 mm yr 1 which is lower than the neighboring active faults iii the lpf is characterized by almost purely normal slip and was active within the past 18 000 yr these findings can provide a basis for the assessment of seismic risk in and around the densely populated city of xi an an old capital of china however we suggest more precise constraints on the fault slip rate and detailed paleoseismological studies on the timing of the most recent earthquake and the repeat time of paleo earthquakes are needed in order to better understand the seismogenic behaviors of the active lpf

mineralogy and geochemistry of the masa valverde blind massive sulphide deposit iberian pyrite belt spain abstract masa valverde is a blind volcanic hosted massive sulphide deposit recently discovered in the spanish sector of the iberian pyrite belt ipb the deposit is more than 1 km long and is located at depths between 400 and 850 m in direct spatial association with a residual gravimetric anomaly the ore body is concealed beneath culm sedimentary rocks which cover the western extension of a hercynian age anticline a few kilometers west of an area where older massive sulphide workings existed the masa valverde deposit consists of two main ore bodies composed dominantly of massive and banded pyrite which are hosted by a volcano sedimentary sequence made up of felsic tuffs interlayered with shale siliceous exhalite and radiolarian chert the abundance of sedimentary host rocks to the deposit is a feature shared by other large massive sulphide deposits in the eastern sector of the ipb and is interpreted as significant with respect to the origin of the deposit a break in volcanic activity the thickness of the upper massive sulphide orebody varies between a few meters and 70 m and it consists of lenses and blankets of massive sulphides with interbedded tuff and shale and occasionally stockwork zones the lower orebody is smaller and thinner than the upper one but this may be due to incomplete drilling two types of stockwork occur beneath the massive sulphide bodies the more common type consists of irregular and anastomosing sulphide veinlets and irregular blebs formed by replacement stockwork with cross cutting generally straight sided sulphide veins is by contrast suggestive of formation by hydraulic fracturing the mineralogy and alteration processes of the ore and host rocks at masa valverde are analogous to those of other ipb massive sulphides the average temperature of formation of the components of the ore zones estimated on the basis of chlorite thermometry are as follows siliceous exhalites 290 c massive sulphides 325 c and stockworks 305 c rare earth element measurements indicate that the lowest metal concentrations occur in chloritites which occasionally host cu rich stockwork and are characterised by a strongly negative eu anomaly by contrast rocks hosting the sulphide lenses where silicification sericitization and carbonatization are more intense are enriched in lree two main stages of hydrothermal activity are suggested for the masa valverde deposit during an early stage ore fluids would have discharged onto the sea floor resulting in the deposition of pyrite with sphalerite and galena later on with continued input of high temperature fluids 290 to 315 c chalcopirite precipitated especially in the stockworks and at the base of the sulphide lenses at masa valverde this late cu rich hydrothermal event would have produced an ascending cu front which overpassed the stockwork zone and reached a higher temperature 325 c at the base of the massive sulphide lenses the combination of geological mineralogical and geochemical features of the masa valverde deposit provide guidelines for exploration for new blind orebodies in this part of the ipb where tuffs and sedimentary rocks are the dominant host lithologies the masa valverde deposit can be considered as a vhms subtype transitional to shms

geomorphological and structural characterization of the southern weihe graben central china implications for fault segmentation abstract the cenozoic graben systems around the tectonically stable ordos block central china have been considered as ideal places for investigating active deformation within continental rifts such as the weihe graben at the southern margin with high historical seismicity e g 1556 m 8 5 huaxian great earthquake however previous investigations have mostly focused on the active structures in the eastern and northern parts of this graben by contrast in the southwest tectonic activity along the northern margin of the qinling mountains has not been systematically investigated yet in this study based on digital elevation models dems we carried out geomorphological analysis to evaluate the relative tectonic activity along the whole south border fault sbf on the basis of field observations high resolution dems acquired by small unmanned aerial vehicles suva using structure for motion techniques radiocarbon 14c age dating we demonstrate that 1 tectonic activity along the sbf changes along strike being higher in the eastern sector 2 seven major segment boundaries have been assigned where the fault changes its strike and has lower tectonic activity 3 the fault segment between the cities of huaxian and huayin characterized by almost pure normal slip has been active during the holocene we suggest that these findings would provide a basis for further investigating on the seismic risk in densely populated weihe graben

height of faceted spurs a proxy for determining long term throw rates on normal faults evidence from the north baikal rift system siberia 1 we present new results on the long term throw rates of active normal faults in the north baikal rift nbr eastern siberia based on a statistical analysis of triangular faceted scarps fault bounded ridges in the nbr display typical morphologies with several contiguous facets separated by fault perpendicular catchments over a range of 20 fault segments analyzed triangular facet heights vary from 200 to 900 m as fault scarps have been developing under similar long term climatic conditions we infer that the scatter in mean facet height arises from long term differences in fault throw rate we compare the morphology of nbr facets with results obtained in a previously published numerical model of facet growth using facet height as an input model results provide estimates of the long term fault throw rate nbr throw rates vary between 0 2 and 1 2 mm yr 1 the throw rates are then compared with the cumulated throw which has been constrained by geophysical and stratigraphic data in the basins this provides an estimate of the age of fault and basin initiation we show that the modern stage of basin development started circa 3 myr ago except for the north baikal basin 8 ma our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage

late pleistocene holocene activity of the zemuhe fault on the southeastern margin of the tibetan plateau abstract a n s trending active fault zone which includes the anninghe zemuhe and xiaojiang faults forms the tectonic boundary of the tibetan plateau on its southeastern margin marking the limit of the eastward extrusion of the tibetan plateau in this paper we document the late pleistocene holocene activity of the zemuhe fault which is the central segment of the fault zone we have been able to determine slip rate and the average recurrence interval of large earthquakes upon the fault based on aerial photograph interpretations field investigations trench excavations and radiocarbon age data the zemuhe fault is mainly characterized by left lateral offsets with a horizontal slip rate of 10 12 mm yr and a vertical slip component of 2 0 2 4 mm yr trench investigations and 14 c ages reveal that at least four large earthquakes occurred during the last 1100 1500 years indicating an average recurrence interval of 300 400 years for m 7 0 7 5 earthquakes consistent with the documented history of the region our results confirm that the zehume fault plays an important role as a tectonic boundary in releasing the strain energy caused by the southeastwards motion of the tibetan plateau the energy is released in the form of repeated large earthquakes

seismic assessment of the weihe graben central china insights from geomorphological analyses and 10be derived catchment denudation rates abstract the tectonic activity and potential for linkage of adjacent active faults are crucial for seismic assessment as the two largest faults that bound the weihe graben central china the qinling northern piedmont fault qnf 200 km and the huashan piedmont fault hpf 150 km are mainly responsible for seismic risk in this densely populated area where the 1556 m 8 5 huaxian earthquake occurred with 830 000 fatalities however their tectonic activity and the degree of interaction remain poorly constrained hampering an adequate seismic risk assessment of the weihe graben here we integrate 23 new 10be derived catchment averaged denudation rates of 0 06 0 32 mm yr with topographic metrics to evaluate the seismic risk the results demonstrate that the landscape of the qinling and huashan mountains is in transient state in response to the tectonic perturbations of the qnf and the hpf with tectonic knickpoints formed along main streams and tributaries and widespread unstable drainage divides these two faults have comparable tectonic activity and are potentially capable of generating earthquakes with the maximum magnitude of mw 7 7 7 9 moreover they have likely started linking posing a greater seismic risk than previously estimated

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

tectonic and sedimentary controls on widespread gas emissions in the sea of marmara results from systematic shipborne multibeam echo sounder water column imaging understanding of the evolution of fluid fault interactions during earthquake cycles is a challenge that acoustic gas emission studies can contribute a survey of the sea of marmara using a shipborne multibeam echo sounder with water column records provided an accurate spatial distribution of offshore seeps gas emissions are spatially controlled by a combination of factors including fault and fracture networks in connection to the main marmara fault system and inherited faults the nature and thickness of sediments e g occurrence of impermeable or gas bearing sediments and landslides and the connectivity between the seafloor and gas sources particularly in relation to the eocene thrace basin the relationship between seepage and fault activity is not linear as active faults do not necessarily conduct gas and scarps corresponding to deactivated fault strands may continue to channel fluids within sedimentary basins gas is not expelled at the seafloor unless faulting deformation or erosional processes affect the sediments on topographic highs gas flares occur along the main fault scarps but are also associated with sediment deformation the occurrence of gas emissions appears to be correlated with the distribution of microseismicity the relative absence of earthquake induced ground shaking along parts of the istanbul silivri and princes islands segments is likely the primary factor responsible for the comparative lack of gas emissions along these fault segments the spatiotemporal distribution of gas seeps may thus provide a complementary way to constrain earthquake geohazards by focusing the study on some key fault segments e g the northern part of the locked princes islands segment

late pleistocene regional extension rate derived from earthquake geology of late quaternary faults across the great basin nevada between 38 5 n and 40 n latitude maps showing quaternary deposits and active fault traces paleoseismic trenches scarp diffusion analyses and soil characteristics in displaced alluvial surfaces are combined with previous paleoseismic studies to examine the character of late pleistocene earthquake recurrence and estimate the net extension rate across the interior of the great basin of the western united states at the latitude of 39 n the study area includes faults bounding the desatoya toiyabe monitor simpson park toquima antelope fish creek butte egan and schell creek ranges the rate of earthquake recurrence is documented to be significantly less than observed within the walker lane central nevada seismic belt and along the wasatch which respectively define the western and eastern boundaries of the interior of the great basin late pleistocene extension across the interior of the great basin is calculated to equal 1 mm yr across the 450 km transect and is consistent with rates defined by recent geodetic studies the agreement in extension rate estimates over different time scales indicates that tectonic deformation in the great basin has been characterized by relatively slow and consistent extension through the late pleistocene to the present the internal deformation of the great basin and the pattern of strain release may reflect a broad transition zone from northwest directed shear in the west to extension along the eastern edge of the pacific north american plate boundary

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

chemoherms on hydrate ridge unique microbially mediated carbonate build ups growing into the water column two active chemoherm build ups growing freely up into the oceanic water column the pinnacle and the south east knoll chemoherms have been discovered at hydrate ridge on the cascadia continental margin these microbially mediated carbonate formations rise above the seafloor by several tens of meters and display a pinnacle shaped morphology with steep flanks the recovered rocks are pure carbonates dominated by aragonite based on fabric and mineralogic composition different varieties of authigenic aragonite can be distinguished detailed visual and petrographic investigations unambiguously reveal the involvement of microbes during the formation of the carbonates the fabric of the cryptocrystalline and fibrous aragonite can be described as thrombolitic fossilized microbial filaments in the microcrystalline aragonite indicate the intimate relationship between microbes and carbonates the strongly 13c depleted carbon isotope values of the samples as low as 48 1 pdb are characteristic of methane as the major carbon source for the carbonate formation the methane rich fluids from which the carbonates are precipitated originate most probably from a gas reservoir below the bottom simulating reflector bsr and rise through fault systems the 18o values of the aragonitic chemoherm carbonates are substantially higher as high as 5 0 pdb than the expected equilibrium value for an aragonite forming from ambient seawater 3 5 pdb as a first approximation this indicates formation from glacial ocean water but other factors are considered as well a conceptual model is presented for the precipitation of these chemoherm carbonates based on in situ observations and the detailed petrographic investigation of the carbonates this model explains the function of the consortium of archaea and sulfate reducing bacteria that grows on the carbonates performing anaerobic oxidation of methane aom and enabling the precipitation of the chemoherms above the seafloor surrounded by oxic seawater beggiatoa mats growing on the surface of the chemoherms oxidize the sulfide provided by sulfate dependent anaerobic oxidation of methane within an oxic environment the contact between beggiatoa and the underlying microbial consortium represents the interface between the overlying oxic water column and an anoxic micro environment where carbonate formation takes place

tracing the paleo sulfate methane transition zones and h2s seepage events in marine sediments an application of c s mo systematics 1 microbially mediated anaebic oxidation of methane aom coupled with sulfate consumption within the sulfate methane transition zone smtz in marine sediments is a widely recorded biogeochemical reaction and has profound influence on the atmospheric ch4budget marine carbon cycle and composition of sediment pore fluids recognizing the paleo smtzs in the marine sediments rock records can throw light on the variation of paleo methane fluxes and occurrences of cold seep h2s ch4 events through geologic time here we present results from carbonate carbon pyrite sulfur and molybdenum analyses for two sediment cores overlying the methane hydrate deposits in the bay of bengal the results show intimate association of isotopically depleted carbonate carbon and enriched pyrite sulfur constraining the paleo smtz within the sediment column in addition anomalous enrichments of mo concentrations indicate hydrogen sulfide seepage events here we propose a geochemical tool using c s mo sytematics to decipher the paleo smtzs in marine sediments and rocks