tectonic control on 10 be derived erosion rates in the garhwal himalaya india erosion in the himalaya is responsible for one of the greatest mass redistributions on earth and has fueled models of feedback loops between climate and tectonics although the general trends of erosion across the himalaya are reasonably well known the relative importance of factors controlling erosion is less well constrained here we present 25 10 be derived catchment averaged erosion rates from the yamuna catchment in the garhwal himalaya northern india tributary erosion rates range between 0 1 and 0 5 mm yr 1 in the lesser himalaya and 1 and 2 mm yr 1 in the high himalaya despite uniform hillslope angles the erosion rate data correlate with catchment averaged values of 5 km radius relief channel steepness indices and specific stream power but to varying degrees of nonlinearity similar nonlinear relationships and coefficients of determination suggest that topographic steepness is the major control on the spatial variability of erosion and that twofold to threefold differences in annual runoff are of minor importance in this area instead the spatial distribution of erosion in the study area is consistent with a tectonic model in which the rock uplift pattern is largely controlled by the shortening rate and the geometry of the main himalayan thrust fault mht our data support a shallow dip of the mht underneath the lesser himalaya followed by a midcrustal ramp underneath the high himalaya as indicated by geophysical data finally analysis of sample results from larger main stem rivers indicates significant variability of 10 be derived erosion rates possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

higher himalaya in the bhagirathi section nw himalaya india its structures backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms the higher himalayan crystalline hhc in the bhagirathi river section india on fieldwork reveals two extensional ductile top to n ne shear sub zones the south tibetan detachment system and the basal detachment besides a preceding top to s sw ductile shear a top to n ne brittle shear was identified as backthrusts from the hhc except its northern portion that occur repeatedly adjacent to numerous top to s sw brittle shears as fore thrusts the northern portion of the hhc the gangotri granite exhibits infrequent total six extensional and compressional brittle shear senses the backthrusts could be due to a low friction between the lower boundary of the hhc i e the main central thrust zone and the partially molten hot rock materials of the hhc subduction of the eurasian plate towards s sw below the indian plate more extensively in the garhwal sector could be the second possible reason presence of two ductile extensional shear sub zones may indicate channel flow or several exhumation mechanisms of the hhc in a shifting mode similar to mukherjee et al in int j earth sci 101 253 272 2012 the top to s sw extensional brittle shear exclusively within the upper northern portion of the hhc and a top to s sw brittle shear within the remainder of it is a possible indicator of critical taper deformation mechanism thus this work provides the field evidences of possibly both channel flow and critical taper conditions from a higher himalayan section besides that by larson et al geol soc am bull 122 1116 1134 2010

was himalayan normal faulting triggered by initiation of the ramgarh munsiari thrust and development of the lesser himalayan duplex the ramgarh munsiari thrust is a major orogen scale fault that extends for more than 1 500 km along strike in the himalayan fold thrust belt the fault can be traced along the himalayan arc from himachal pradesh india in the west to eastern bhutan the fault is located within the lesser himalayan tectonostratigraphic zone and it translated paleoproterozoic lesser himalayan rocks more than 100 km toward the foreland the ramgarh munsiari thrust is always located in the proximal footwall of the main central thrust northern exposures toward the hinterland of the thrust sheet occur in the footwall of the main central thrust at the base of the high himalaya and southern exposures toward the foreland occur between the main boundary thrust and greater himalayan klippen although the metamorphic grade of rocks within the ramgarh munsiari thrust sheet is not significantly different from that of greater himalayan rock in the hanging wall of the overlying main central thrust sheet the tectonostratigraphic origin of the two different thrust sheets is markedly different the ramgarh munsiari thrust became active in early miocene time and acted as the roof thrust for a duplex system within lesser himalayan rocks the process of slip transfer from the main central thrust to the ramgarh munsiari thrust in early miocene time and subsequent development of the lesser himalayan duplex may have played a role in triggering normal faulting along the south tibetan detachment system

middle late miocene 10 ma formation of the main boundary thrust in the western himalaya three independent data sets from northwestern india and pakistan suggest initial displacement along 1000 km of the main boundary thrust prior to 10 ma at least 5 m y earlier than previously reported regionally extensive changes in the depositional characteristics and rates of the foreland basinfill between 11 and 9 5 ma are interpreted to reflect new hinterland loading due to the formation of the main boundary thrust sediment accumulation rates sandstone siltstone ratios and thickness and amalgamation of individual sandstone bodies all substantially increase after 11 ma in well dated stratigraphic sections from pakistan to nepal across the indo gangetic foreland basin in the himachal pradesh reentrant of northwestern india a newly discovered 8 7 ma conglomerate derived from the hanging wall of the main boundary thrust indicates that source area uplift and denudation must have occurred prior to 9 ma and probably prior to 10 ma assuming a gravelprogradationrateof3cm yr threeapatitefission trackages fromstructuresattheleadingedgeofthemainboundarythrustin the kohat region of northwest pakistan indicate that rapid cooling below 105 c1 2 m y earlier these data indicate that the main boundary thrust in the western himalaya formed synchronously along strike in the middle late miocene has a displacement rate of 10 mm yr and has a displacement history that is coeval with late displacement on the main central thrust

discovery of a natural co2 seep in the german north sea implications for shallow dissolved gas and seep detection a natural carbon dioxide co2 seep was discovered during an expedition to the southern german north sea october 2008 elevated co2 levels of 10 20 times above background were detected in seawater above a natural salt dome 30 km north of the east frisian island juist a single elevated value 53 times higher than background was measured indicating a possible co2 point source from the seafloor measured ph values of around 6 8 support modeled ph values for the observed high co2 concentration these results are presented in the context of co2 seepage detection in light of proposed subsurface co2 sequestering and growing concern of ocean acidification we explore the boundary conditions of co2 bubble and plume seepage and potential flux paths to the atmosphere shallow bubble release experiments conducted in a lake combined with discrete bubble modeling suggest that shallow co2 outgassing will be difficult to detect as bubbles dissolve very rapidly within meters bubble plume modeling further shows that a co2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly co2 enriched water tends to sink toward the seabed results suggest that released co2 will tend to stay near the bottom in shallow systems 200 m and will vent to the atmosphere only during deep water convection water column turnover while isotope signatures point to a biogenic source the exact origin is inconclusive because of dilution this site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor

intense ch4 plumes generated by serpentinization of ultramafic rocks at the intersection of the 15 20 n fracture zone and the mid atlantic ridge abstract as part of the fara french us program designed to study the mid atlantic ridge mar between 15 n and the azores twenty three dives with the submersible nautile were conducted during the french us faranaut 15n cruise on the eastern and western parts of the 15 20 n fracture zone ridge axis intersection south of the eastern ridge transform fault intersection nine nautile dives were made within the rift valley and along the western rift valley wall ch4 concentrations in the bottom waters reach 53 2 nmol kg along faulted zones on top and on the east flank of the ultramafic inner corner high 15 05 n 44 59 w where serpentinized rocks outcrop no 3he anomaly is associated with methane ruling out any primary mantle component fourteen dives were also made in the rift valley to the north close to the western intersection of the 15 20 n transform high ch4 anomalies up to 22 nmol kg are also present in the bottom waters of the rift valley northern segment on both the western and eastern valley walls and on the inner high adjacent to the eastern wall where ultramafic rocks outcrop seven vertical hydrocasts carried out in the axial valley 4500 m deep show an intense ch4 anomaly with a maximum 35 8 nmol kg at 3200 m depth this ch4 concentration is among the highest found along the mid atlantic ridge charlou and donval 1993 charlou et al 1997 ch4 concentrations of 9 9 14 9 nmol kg are also present on the western wall along the 3200 m isobath the high ch4 concentrations correspond to only weak 3he anomalies this ch4 rich plume is also associated with active fault zones that expose peridotite rocks ch4 output from ultramafic outcrops on the western and eastern intersections of the 15 20 n fracture zone with the mar is believed to reflect ongoing serpentinization these results associated with many other ch4 anomalies measured in the water column above ultramafic outcrops found between 12 n and the azores most likely reflect serpentinization processes extending along the whole slow spreading mid atlantic ridge

microseismicity of the bearn range reactivation of inversion and collision structures at the northern edge of the iberian plate the bearn range located to the north of the axial zone in the western pyrenees is affected by numerous small magnitude seismic events these events overlap an area characterised by specific geological structures which are interpreted to have resulted from multistage extensional and compressional deformation an analysis of surface geology draped over dem together with field investigations allow identification of two main shortening episodes with differing direction of contraction d1 represents the inversion of the north pyrenean basin whose mesozoic infill was detached from highly extended crust and transported southwards over the necking zone and the northern margin of the iberian plate d2 corresponds to the collision stage and is characterised in the study area by backfolding and backthrusting deformation coeval with uplift in the axial part of the chain due to thickening of the iberian plate the microseismicity appears to concentrate along the basal part of the inverted basin units d1 where this initially low angle thrust has been tilted and steepened during collision d2 we propose that local steepening of this ancient inversion structure which should not be named north pyrenean fault provided the suitable dip for extensional solicitation in association with the present uplift of the axial zone whatever the driving mechanism of this uplift could be

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

helium isotopes at the rainbow hydrothermal site mid atlantic ridge 36 14 n the 3he 4he ratio and helium concentration have been measured in the vent fluids and the dispersing plume of the rainbow hydrothermal site on the mid atlantic ridge mar the 3he 4he ratio 7 51 ra and 3he end member concentration 25 pmol kg are in the range of observed values elsewhere on mid ocean ridges pointing to the relative homogeneity of the upper mantle with respect to helium isotope geochemistry 3he is linearly correlated with methane and manganese throughout the plume with ch4 3he and mn 3he ratios identical to those measured in the hot fluids the bulk residence time of the plume in the rift valley estimated from the plume 3he budget is v20 days the 3he flux transported by the plume calculated from current meter data is 12 3 3 nmol s requiring a flux of 490 kg s of high temperature fluid the scaling of the heat flux emitted by the rainbow site to that of 3he using the 3he heat ratio measured in the hydrothermal fluids 9 3 2u10318 mol j indicates a heat output of 1320 mw with a regional spreading rate of v25 mm year we calculate that the annual 3he flux for this section of the mar is of the order of 0 5 0 2 mmol per kilometre of ridge per millimetre of newly formed crust this figure compares well with the flux calculated for the neighbouring lucky strike segment although the uncertainties remain large both fluxes are v40 50 above the world average 0 33 mmol km mm thus supporting earlier suggestions that the intensity of the hydrothermal activity south of the azores is higher than expected from the regional spreading rate

zircon u pb ages and hf isotopes of the askot klippe kumaun northwest india implications for paleoproterozoic tectonics basin evolution and associated metallogeny of the northern indian cratonic margin

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

superposed folding of a blind thrust and formation of klippen results of anisotropic magnetic susceptibility studies from the lesser himalaya abstract the rocks of the garhwal lesser himalaya have undergone a weak superimposed deformation hence linear and planar structures are either absent or poorly developed this puts a severe limitation on application of conventional methods of finite strain determination in understanding the deformation pattern however the geometry orientation and distribution of magnetic susceptibility strain ellipses clearly reveal the effects of early and superposed deformations in the area the orientation patterns of the ellipses also help to identify reversal of displacement along an oblique fault ramp during the superposed deformation the hrouda double plot reveals a combination of lateral shortening and simple shear thereby suggesting a small translation along the klippe detachment thrust the study has important implications for understanding the structural evolution of the lesser himalayan klippen because the earlier models in the absence of the relevant data are based on assumptions concerning thrust displacement the present field studies and the ams data favour an alternate model for the structural evolution of the lesser himalayan klippen that lie in the core of the mussoorie syncline the model explains structural features and outcrop patterns as due to a combination of fault bifurcation back thrusts pop up and subsequent superposed deformation the klippen lie over their roots and are described as pop up klippen

tracking basement cross strike discontinuities in the indian crust beneath the himalayan orogen using gravity data relationship to upper crustal faults the himalaya is the result of the on going convergence and collision of india and asia two plates with complex and protracted geological evolutions the internal configuration and processes that govern the rise of the himalaya and tibetan plateau are crucial to understand continental collision zones however knowledge of the prior configuration of the colliding plates is equally important since inherited preorogenic basement structures can undeniably influence the development of the orogenic architecture throughout the orogen s cycle of collision and eventual collapse three northeast trending palaeotopographic ridges of faulted precambrian indian basement underlie the ganga basin south of the himalaya oil and natural gas commission 1968 valdiya 1976 gahalaut kundu 2012 our study godin harris 2014 illustrates a crustal scale fault origin for these ridges and succeeds in determining how far north beneath the himalayan system they extend and how they ultimately govern the location of upper crustal faults in southern tibet spectrally filtered egm2008 bouguer gravity data and edges in its horizontal gradient at different source depths gravity worms over northern peninsular india the himalaya and southern tibet reveal several continuous himalayan cross strike discontinuities interpreted to represent crustal faults fig 1 gravity lineaments in peninsular india coincide with edges of the precambrian basement ridges and megakinks up to 100 km wide develop in foreland cover sequences between the interpreted basement faults the interpreted basement faults project northward beneath the himalayan system and southern tibet our results suggest that several active himalayan cross strike faults such as the ones related to many graben in southern tibet are rooted in the underplated indian lower crust or step en echelon along interpreted basement faults our interpretation thus suggests that south tibet graben are spatially related to deepseated crustal scale faults rooted in the underplated indian crust these major discontinuities partition the himalayan range into distinct zones and could ultimately contribute to lateral variability in tectonic evolution along the orogen s strike

the break back thrust splay of the main dun thrust himalayas of western nepal evidence of an intermediate displacement scale between earthquake slip and finite geometry of thrust systems abstract numerous studies have shown that development of a forward breaking sequence in a thrust belt is accompanied by reactivation of inner faults and development of break back thrusts the partitioning of shortening in the outer and lesser himalayan thrust belt follows these rules tectonic and sedimentary relationships in this thrust belt exemplify out of sequence thrusts in the lesser himalayas and break back imbricate fans close to the mbt main boundary thrust and mdt main dun thrust which are transported during their development above the himalayan basal detachment the displacement along a single splay of the imbricate fan of the mdt was 40 m before abandonment and nucleation of a new inner splay the development of the break back imbricate fan is discontinuous in time furthermore superimposition of ultracataclasite pressure solution cleavage extensional crenulation cleavage and tension gashes in the fault zones suggests that the 40 m displacement occurred by discrete slip events or most probably by a succession of several seismic aseismic deformations these data require several scales of sequential displacement in the outer and lesser himalayas consisting of forward propagation of the thrust system out of sequence reactivation break back nucleation of thrust splays and seismic aseismic fault slip our findings require an intermediate period of tectonism between the 500 ka deformation of the accretionary sediments of the himalayas

interplay of thrust back thrust strike slip and salt tectonics in a fold and thrust belt system an example from zakynthos island greece the southwestern flank of the hellenic fold and thrust belt situated along the southern edge of the dinarides albanides hellenides continental convergent zone was examined for reconstructing the tectonic deformation this investigation presents an integrated study of onshore sedimentological and structural analyses as well as offshore seismic lines across the pliocene pleistocene sedimentary succession in zakynthos island back thrust faults using the triassic evaporites as decollement surface during the pliocene and coeval diapiric intrusions formed three sub basins on the hangingwall of the kalamaki back thrust fault this interaction is responsible for the growth of the skopos mountain and the soft sediment deformation that formed synclines and slumps respectively back thrust and strike slip faults were active during the early pleistocene and diapiric intrusions modified the bathymetry on the sea floor giving rise to slumps and recumbent folds at least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons during the holocene the diapiric intrusions between the kalamaki back thrust and the vrachionas anticline could be either related to normal faults or gravitationally driven

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

analysis of simultaneous gravity and tremor anomalies observed during the 2002 2003 etna eruption abstract in this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002 2003 eruption of etna volcano italy seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0 5 5 hz frequency band on three different occasions 12 november 19 20 november and 8 9 december 2002 we observed marked increases of the tremor amplitude up to a factor of 4 which occurred simultaneously with gravity decreases up to 30 gal the three concurrent gravity tremor anomalies last 6 to 12 hours and terminate with rapid up to 2 hours changes after which the signals return back to their original levels based on volcanological observations encompassing the simultaneous anomalies we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source this study highlights the potential of joint gravity seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment

seismotectonics of the 20 october 1991 uttarkashi earthquake in garhwal himalaya north india the 20 october 1991 uttarkashi earthquake killed over a thousand people and caused extensive damage to property in the garhwal himalaya region the body wave magnitude of the earthquake was 6 6 and the fault plane solution indicates reverse faulting the hypocenrre was located at a focal depth of about 12 km between the chail and jutogh thrusts but movement propagated southward along the jamak gangori fault jgf and dunda fault df which are developed as blind faults related to the growing uttarkashi antiform

the origin of changes in structural style across the bandar abbas syntaxis se zagros iran abstract the bandar abbas syntaxis marks the transition between the zagros collisional belt and the makran subduction related prism and constitutes a major structural feature within the alpine himalayan mountain belt within the foreland part of the zagros the zagros fold thrust belt zftb the transition is marked by a sudden change in structural trends and style and a rapid decrease in seismicity and salt diapirism from west to east of the syntaxis the depth to decollement and lithology affect the geometry and size of the folds on each side of the syntaxis while different mechanical coupling along the basal decollement affects the degree of internal rock deformation thus the short and broad folds of the western side of the syntaxis are decoupled along the 8 km deep hormuz evaporites visible at surface in numerous salt diapirs strong seismicity in this area suggests that the basement is involved in the deformation by contrast the long and narrow folds of the eastern side of the syntaxis appear to be controlled by frictional slip along a 6 km deep detachment the absence of seismicity suggests that the basement is not involved in the deformation in this area we propose that the basal decollement for these structures corresponds to the eroded top of the nne ssw trending oman mesozoic nappes resulting from late cretaceous obduction of tethys on the arabian margin these structures are visible onshore in the northern tip of the oman peninsula and seen in offshore seismic profiles continuing northward beneath the strait of hormuz finally map view observations show that the main zagros thrust and the zendan fault separating the zftb from the internal zones of the orogen are shallow low angle thrust faults rather than steeply dipping faults

review of flanking structures in meso and micro scales a variety of host fabric elements he cut by cross cutting elements ce in rocks defines flanking structures fs on mesoscopic and microscopic scales there has been renewed interest in studying and classifying the fs for their morphologies useful as shear sense indicators and geneses existing non genetic morphologic parameters for the fs are reviewed and two new classification schemes are presented one of these is based on the nature of the ce and whether he penetrates it the other scheme takes account of all the potential combinations of drag no drag and slip no slip of the he deciphering the shear sense of the rock body from fs is complicated because the angular relationship between the ce and the primary shear planes might be opposite to what is found between s and c ductile shear fabrics further single ces can curve and several similar fs occur in reverse forms as with mineral fish the shape asymmetries of microscopic ces indicate the shear sense conjugate fs with non parallel ces with interfering perturbation fields around the ces are more reliable shear sense indicators than fs with single ce during low but increasing bulk strains fs may evolve from one type to another e g from a to s type at high strain fs can resemble intrafolial or sheath fold whether the drag is normal or reverse depends fundamentally on the initial angle between the he and the ce and the relative magnitudes of throw and vertical separation

methane in the northern atlantic controlled by microbial oxidation and atmospheric history during may august 1997 the distributions of dissolved methane and ccl3f cfc11 were measured in the atlantic between 50 and 60 n in surface waters throughout the region methane was observed to be close to equilibrium with the atmospheric mixing ratio implying that surface ocean methane is tracking its atmospheric history in regions of north atlantic deep water formation despite the different atmospheric history and ocean chemistry of ch4 and cfc11 their spatial distribution patterns in the water column are remarkably similar one dimensional distributions have been simulated with an advection diffusion model forced by the atmospheric histories the results suggest that the similar patterns result from the increasing input of ch4 and cfc11 to newly formed deep waters over time combined with the effect of horizontal mixing and the oxidation of methane on a 50 year time scale

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

flow and mixing in the rift valley of the mid atlantic ridge high levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation in topographically confined areas such as the deep median valleys of slow spreading ridges these fluxes strongly influence the local hydrography and dynamics data from a segment scale hydrographic survey of the rift valley of the mid atlantic ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment scale gradients the rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional alongsegment flow into a cul de sac therefore most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity 1025 ms 21 the observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column hydrographic budgets in the rift valley yield diffusivity values of order 5 3 1023 m2 s 21 consistent with estimates derived from statically unstable overturns the largest of which were observed downstream of topographic obstacles in the path of the along segment flow this suggests vertical shear associated with cross sill flows as the dominant contributor to the mechanical mixing in the rift valley

fold accommodation faults fold accommodation faults are secondary faults that accommodate strain variations related to structural and stratigraphic position during fold evolution four main types of fold accommodation faults are commonly found out of syncline and into anticline thrusts form primarily because of an increase in bed curvature within fold cores although differential layer parallel strain at different scales also contributes to fault slip depending on the kinematic evolution of the major fold the thrusts may propagate along the steep or gentle limb of an asymmetric fold or along the hinge of symmetric folds wedge thrusts are primarily formed in competent units because of variations in penetrative layer parallel strain between adjacent units limb wedges occur as hanging wall and or footwall fault bend and fault tip folds whereas hinge wedges occur as multiple nested faults that tend to thicken the more competent units forelimb and backlimb thrusts form by a variety of mechanisms forelimb space accommodation thrusts are low displacement thrusts that resolve strain discontinuities resulting from increased curvature in fold cores forelimb shear thrusts form in the late stages of folding because of rotation and layer parallel extension on the steep forelimbs of folds most backlimb thrusts originate as out of syncline thrusts they may eventually link with forelimb thrusts to form forelimb backlimb thrusts back thrusts accommodate hanging wall strain during the formation of fault related folds they either form selectively in competent units or propagate through the section at the same rate as the main thrust although fold accommodation faults are secondary features they are important elements that define the geometry and size of structural traps in fold thrust structures accurate mapping of these structures is therefore critical in interpreting the structural geometry of fold and thrust belts shankar mitra holds the monnett chair and professorship of energy resources at the university of oklahoma he received his ph d in structural geology from johns hopkins university in 1977 he spent 19 years at arco research and exploration as senior and principal research geologist director of structural geology manager of geological research and senior exploration research advisor his primary research interests are in the development of structural concepts and methods and their application to exploration and production problems he is a recipient of aapg s wallace pratt and cam sproule awards

recent movements along the main boundary thrust of the himalayas normal faulting in an over critical thrust wedge abstract the main boundary thrust mbt is one of the major himalayan thrusts occurring during the cainozoic and it is presently incorporated within the himalayan thrust wedge lesser and outer himalayas displaced above the indian lithosphere nonetheless the mbt shows recent normal displacement along most of its length we suggest that the orientation of the major principal stress within the himalayan thrust wedge deviates significantly from the horizontal and when this deviation exceeds the dip of the vectors normal to back tilted thrusts the normal component of displacement may act along these faults steep north dipping segments of the mbt therefore show a normal component of displacement if a geometrical definition is used but they are faults in a compressional regime where the major principal stress axis has deviated from the horizontal micro structural data recorded along the surkhet ghorahi segment of the mbt are consistent with a strong deviation of the state of stress the presence of such peculiar normal faulting along the mbt is used to calibrate the mechanical characteristics of the belt considered as a coulomb wedge the following characteristics are suggested a very poor strength contrast between basal decollement and rocks in the wedge body b a high pore fluid pressure ratio probably close to 0 8 0 9 and a higher fluid pressure ratio close to 1 0 along the active normal faults if a high internal friction angle close to the byerlee value is considered the strong deviation in principal stress direction may have recently increased due to a taper of the himalayan wedge exceeding the stability boundary and may be controlled by erosion and isostatic uplift rebound of the himalayan range

ongoing methane discharge at well site 22 4b north sea and discovery of a spiral vortex bubble plume motion highlights mega ebullition of biogenic methane from an abandoned offshore gas well north sea evidence for midwater bubble plume intrusion fallback and short circuiting of the plume effective trapping of seabed released methane underneath the thermocline first observation of a spiral vortex methane plume and marginal turbulences megaplumes appear less efficient in terms of vertical methane transport than previously thought abstract first direct evidence for ongoing gas seepage activity on the abandoned well site 22 4b northern north sea 57 55 n 01 38 e and discovery of neighboring seepage activity is provided from observations since 2005 a manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor capture and isotope chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90 vol with 13c ch4 values around 74 vpdb indicating a biogenic origin bulk methane concentrations throughout the water column were assessed by 120 niskin water samples showing up to 400 000 nm ch4 in the crater at depth in contrast concentrations above the thermocline were orders of magnitude lower with a median value of 20 nm a dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to 1 ms 1 determined near the seabed however the dissolved dye did not pass the thermocline but returned down to the seabed measurements of direct bubble mediated atmospheric flux revealed low values of 0 7 0 3 kty 1 much less than current state of the art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths i e 100 m acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer a partly downward orientated bubble plume motion is also visible in the acoustic data with potential short circuiting in accordance to the dye experiment this observation could partly explain the observed trapping of most of the released gas below the well established thermocline in the north sea moreover 3d analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics dissolution behavior gas escape to the atmosphere and is considered very important for respective modeling approaches

carbon isotopic distribution of methane in deep sea hydrothermal plume myojin knoll caldera izu bonin arc implications for microbial methane oxidation in the oceans and applications to heat flux estimation the concentration and stable carbon isotopic composition 13c of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the myojin knoll caldera izu bonin arc in the western north pacific the hydrothermal end member concentrations and 13c of methane show near homogeneity among vents 41 2 mol kg and 16 3 0 8 pdb respectively while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation 2 1 11 nmol kg and 29 0 to 11 3 pdb respectively comparison of concentration and 13c data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume assuming steady state emission of methane from the vents 1 kinetic isotope effect due to the microbial oxidation k12 k13 2 methane flux from the vents fvents 3 heat flux from the vents q and 4 average turnover time of hydrothermal methane tall are estimated to be k12 k13 1 005 0 001 fvents 90 340 mol d q 30 110 mw and tall 60 240 d respectively the estimated turnover times however are not uniform within the water column around the vents a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean while those at the distant points correspond to values more typical for deep ocean water

methane seepage along the hikurangi margin of new zealand geochemical and physical data from the water column sea surface and atmosphere the concentration and carbon isotope values of dissolved methane were measured in the water column at rock garden omakere ridge and wairarapa areas in the first dedicated cold seep investigation along the hikurangi margin of new zealand these measurements provide a high resolution impression of the methane distribution in the water column and show that these seep sites are actively venting methane with varying intensity the highest concentrations up to 3500 nm measured in water samples obtained from conductivity temperature depth ctd operations were at faure site of rock garden here seafloor bubble release was observed by rov the omakere ridge area is actively venting over almost its entire length not vert similar 25 km in particular at bear s paw a newly discovered seep site in the wairarapa area another new seep site called tui was discovered where methane measurements often exceeded 500 nm no evidence was obtained from water column or sea surface measurements along the hikurangi margin to indicate that methane from seeps is reaching the sea surface in fact a consistent upper boundary was observed at a density of 26 85 kg m3 which occurs at about 500 m below sea surface above which methane decreased to background concentrations no obvious oceanographic feature is associated with this 500 m ch4 boundary bubble dissolution calculations show that about 500 m was also the model derived maximum bubble rise height a wide range of 13cch4 values from 71 to 19 vpdb were measured with the highest ch4 concentrations having the lowest 13cch4 values of about 71 to 68 simple mixing and isotope fractionation calculations show that changes of 13cch4 values are predominantly caused by the dilution of seep fluids with the seawater with some anaerobic oxidation also occurring

sources and fluxes of hydrothermal heat chemicals and biology within a segment of the mid atlantic ridge we have conducted a segment wide study of the chemical biological and thermal effects of hydrothermal activity in a bathymetrically enclosed 50 km long segment of the mid atlantic ridge at 29 n our study involved long term monitoring of bottom current speeds and temperatures coupled with snap shot surveys of the concentrations of hydrothermal shrimp manganese and particulate plumes occupying the water column enclosed by the axial valley these data are combined with the calculated volume transport rates for the segment and the results compared with the heat and manganese flux from the broken spur vent field located in the center of the segment our current meter data show that the basin like bathymetry acts to restrict and control flow of water warm and shallow water exported from the segment is replaced by colder and deeper water water column profiles showed an increase in temperature of the water within the broken spur segment compared with background stations located outside the ridge axis the average refresh rate for the water column enclosed by the segment was found to be about 262 days from these data we calculate that the segment wide flux of juvenile shrimp is 20 106 individuals per year we show that the flux of manganese exported at a rate of 5 6 mol s is matched by input from high temperature effluent discharge at the broken spur vent field we also calculate that the minimum average heat flux exported from the segment is about 275 mw of this more than 90 is pervasively dissipated throughout the segment floor by conductively heated sea water or simple thermal conduction that carries little or no manganese to the water column the remaining 10 or less of the heat flux results from localized manganese rich high temperature hydrothermal venting

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

diapycnal mixing associated with an overflow in a deep submarine canyon abstract in order to close the global overturning circulation the buoyancy loss to the atmosphere associated with the formation of deep and bottom water at high latitudes must be balanced by buoyancy gain elsewhere in case of water that is not in contact with the atmosphere except in its formation region the required buoyancy gain is accomplished primarily by diapycnal mixing recent observations suggest that a significant portion of the diapycnal buoyancy fluxes in the abyss is associated with overflows in submarine valleys or canyons especially on the flanks of slow spreading mid ocean ridges in the present study hydrographic and velocity data from an overflow across a sill rising 1000 m above the floor of the rift valley of the mid atlantic ridge near 36 n were used to infer the associated diapycnal mixing the cross sill density gradients are characterized by a vertical dipole with an upper layer of streamwise density increase overlying a lower layer where the density decreases along the flow this is qualitatively consistent with the effects of diapycnal mixing transferring buoyancy from the upper into the lower layer hydrographic and velocity profiles provide evidence for strong mixing associated with the overflow across the sill in addition to thick layers that are susceptible to shear instability there are numerous density overturns indicating a spatially averaged diffusivity of order 10 2 m 2 s 1 inversions of the density equation reveal that the cross sill gradients can be accounted for either by adiabatic vertical advection or by vertical eddy diffusion although the adiabatic solutions are considered energetically implausible because they require upwelling in the layer of cross sill density increase eddy diffusive solutions both with and without adiabatic downwelling are characterized by diffusivity profiles attaining local maxima of order 10 2 m 2 s 1 250 m above the sill depth the vertical structure of the inversion derived diffusivities is consistent with the thorpe scale based estimates and with observations from overflows in major ocean passages which also are often characterized by local diffusivity maxima of order 10 2 m 2 s 1 a few 100 m above sill depth combining the diffusivity profiles near the sill with budget derived bulk estimates for 150 km of rift valley implies that 50 of the mixing in the rift valley is associated with overflows while the remainder is caused by other processes including the breaking of tidally forced internal waves

flux and dispersion of gases from the drachenschlund hydrothermal vent at 8 18 s 13 30 w on the mid atlantic ridge hydrothermal emission of mantle helium appears to be directly related to magma production rate but other processes can generate methane and hydrogen on mid ocean ridges in an on going effort to characterize these processes in the south atlantic the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8 17 9 s 13 30 4 w the vent lies on the shoulder of an oblique offset in the mid atlantic ridge and discharges high concentrations of methane and hydrogen measurements during expeditions in 2004 and 2006 show that the ratio of ch4 to 3he in the neutrally buoyant plume is quite high 4 108 the ctd stations were accompanied by velocity measurements with lowered acoustic doppler current profilers ladcp and from these data we estimate the methane transport to have been 0 5 mol s 1 in a wsw trending plume that seems to develop during the ebb tidal phase this transport is an order of magnitude greater than the source of ch4 calculated from its concentration in the vent fluid and the rise height of the plume from this range of methane fluxes the source of 3he is estimated to be between 0 14 and 1 2 nmol s 1 in either case the 3he source is significantly lower than expected from the spreading rate of the mid atlantic ridge from the inventory of methane in the rift valley adjacent to the vent it appears that the average specific rate of oxidation is 2 6 to 23 yr 1 corresponding to a turnover time between 140 and 16 days vertical profiles of methane in the surrounding region often exhibited gaussian like distributions and the variances appear to increase with distance from the vent using a gaussian plume model we obtained a range of vertical eddy diffusivities between 0 009 and 0 08 m2m2 s 1 these high values may be due to tidally driven internal waves across the promontory on which the vent is located

methane in aging hydrothermal plumes methane concentration and the stable carbon isotopic composition 13 c ch4 were measured in aging hydrothermal plume waters originating at the endeavour segment juan de fuca ridge ch4 concen trations decreased systematically from 600 nm at on axis stations to 11 nm at a distal station 15 km off axis background ch4 concentrations are 2 nm ch4 behaves nonconservatively in plume waters and does not correlate with conservative parameters such as temperature anomaly but is highly correlated with nh4 and total dissolvable mn 13 c ch4 values for plume depth samples varies inversely and significantly r 2 0 89 with methane concentrations normalized to some 13 c ch4 values 1 8 and 10 9 measured at the 15 km off axis station are among the heaviest yet reported from a natural marine environment less than 5 of original hydrothermal methane remains in the plume at this station the data are consistent with extensive microbial methane oxidation a narrow range of fractionation factors rc 1 0072 to 1 0077 was calculated for the endeavour samples these fractionation factors are less than those reported by coleman et al 1981 but fall near the trend line of their rc versus temperature data when extrapolated to plume water temperature 2 c copyright 2002 elsevier science ltd

carbon cycling fed by methane seepage at the shallow cumberland bay south georgia sub antarctic recent studies have suggested that the marine contribution of methane from shallow regions and melting marine terminating glaciers may have been underestimated here we report on methane sources and potential sinks associated with methane seeps in cumberland bay south georgia s largest fjord system the average organic carbon content in the upper 8 m of the sediment is around 0 65 wt this observation combined with parasound data suggest that the methane gas accumulations probably originate from peat bearing sediments currently located several tens of meters below the seafloor only one of our cores indicates upward advection instead most of the methane is transported via diffusion sulfate and methane flux estimates indicate that a large fraction of methane is consumed by anaerobic oxidation of methane aom carbon cycling at the sulfate methane transition smt results in a marked fractionation of the 13c ch4 from an estimated source value of 65 to a value as low as 96 just below the smt methane concentrations in sediments are high especially close to the seepage sites 40 mm however concentrations in the water column are relatively low max 58 nm and can be observed only close to the seafloor methane is trapped in the lowermost water mass however measured microbial oxidation rates reveal very low activity with an average turnover of 3 1 years we therefore infer that methane must be transported out of the bay in the bottom water layer a mean sea air flux of only 0 005 nm m2 s confirms that almost no methane reaches the atmosphere

fluid and gas fluxes from the logatchev hydrothermal vent area the logatchev hydrothermal field at 14 45 n on the mar is characterized by gas plumes that are enriched in methane and helium compared to the oceanic background we investigated ch4 concentration and 13c together with 3he in the water column of that region these data and turbidity measurements indicate that apart from the known vent fields another vent site exists northeast of the vent field logatchev 1 the distribution of methane and 3he concentrations along two sections were used in combination with current measurements from lowered acoustic doppler current profilers ladcp to calculate the horizontal plume fluxes of these gases according to these examinations 0 02 mol s 1 of 3he and 0 21 mol s 1 of methane are transported in a plume that flows into a southward direction in the central part of the valley based on 3he measurements of vent fluid 22 6 pm we estimate a total vent flux in this region of about 900 l s 1 and a total flux of ch4 of 3 2 mol s 1

short term variations in the distribution of hydrothermal plumes along a superfast spreading center east pacific rise 27 30 32 20 s 1 a multidisciplinary expedition to the southern east pacific rise 27 30 32 20 s provided an opportunity to compare the efficiency and effectiveness of two methods for mapping hydrothermal plumes the standard conductivity temperature depth optical ctdo tow yo method and a towed fixed array of hydrographic and optical sensors miniature autonomous plume recorders maprs six second order segments were mapped twice once with ctdo tow yos and then again with a fixed array of maprs attached to the cable of a deep towed side scan sonar we found a high degree of overall agreement between the two methods in both the distribution and optical intensity of hydrothermal plumes between survey differences increased as time between surveys increased from 6 days presumably because of advection of the plumes by local currents plume locations changed by as much as 10 km implying a confidence limit in predicting vent site location using segment scale hydrothermal plume surveys towed mapr arrays proved an efficient and effective method for acquiring coregistered geological and hydrothermal plume data

the kumaun and garwhal lesser himalaya india part 1 structure and stratigraphy our understanding of the geologic evolution of the himalaya remains incomplete particularly in regard to structural and geochronologic details of the proterozoic paleozoic lesser himalayan sequence we conducted an integrated field mapping geochronological study and geochemical analysis of the lesser himalayan sequence strata in the kumaun and garwhal himalaya of nw india 78 00 80 30 e structural observations reveal a systematic change in deformation styles from lower to higher structural levels in the main central thrust footwall in the south and at lower structural levels the main central thrust footwall is characterized by parallel folding and sparse development of axial cleavage quartz microstructures indicate that deformation occurred at temperatures below 350 c in contrast in the north and at higher structural levels close to the main central thrust deformation is characterized by replacement of original bedding the development of penetrative cleavage and schistosity locally folds are tight in places isoclinal and overturned the corresponding quartz microstructures indicate that deformation occurred above 350 c dating of detrital zircons from lesser himalayan sequence metasedimentary units and igneous zircons from schistose gneisses throughout the lesser himalayan sequence allow refinements to the stratigraphic framework first unlike has been observed in western nepal immediately west of our study area u pb zircon dating suggests the absence of paleoproterozoic strata in the ramgarh thrust hanging wall this suggests that the thrust cuts upsection laterally along strike second u pb detrital zircon dating suggests that metasedimentary strata in the ramgarh thrust hanging wall are correlative with basal units of the outer lesser himalayan sequence removing the necessity that the ramgarh thrust hanging wall was allochthonous with respect to its footwall lesser himalayan sequence units schistose gneisses with u pb ages of ca 1850 ma are older than lesser himalayan sequence units in the area suggesting that they are thrust emplaced lesser himalayan sequence basement we conclude that the ramgarh thrust is an out of sequence thrust postdating a folding event in its footwall the earlier proposal that neoproterozoic cambrian lesser himalayan sequence strata are the southern extension of the tethyan himalayan sequence requires that the tons thrust which separates the distal and proximal facies of the lesser himalayan sequence be a major south directed structure with a slip magnitude of 50 100 km

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

transpressive ductile flow and oblique ramping of lower crust in a two sided orogen insight from quartz grain shape fabrics near the alpine fault new zealand 1 the three dimensional 3 d grain shape fabric gsf of deformed quartz veins was measured in 30 samples from the hanging wall of the oblique slip alpine fault in the central southern alps new zealand these record aspects of the neotectonic strain experienced by lower crustal rocks in the pacific plate as they were transported through a two sided orogen deformation was nonsteady state transpression was followed by near vertical shearing as the rocks negotiated the oblique footwall ramp of the alpine fault at the brittle ductile transition ramping up was accommodated by an escalator like back shearing process this thinned the transpressed crust and boosted dip slip rate on the alpine fault mechanically this suggests a sharp step in the footwall ramp adjacent to which differential stresses were transiently high margin parallel motion was partitioned onto these shears fabric development is simulated using a 3 d kinematic model into which we input constraints on plate motion fault slip rates crustal structure fabrics and geodetic strain in the southern alps this model can explain many aspects of the southern alps fabrics including their nonvertical foliation and lineation similarities between the model predictions and the observed fabrics suggest that lower crustal flow in the pacific plate mimicked the geodetic velocity pattern at the surface today with obliquely convergent deformation being distributed across a wide region to the east of the alpine fault the model shows that the timescale for an exhumational steady state with respect to deformational fabrics is slow 107 years a condition which the 6 m y old southern alps have probably not yet achieved

triggered slip on a back reverse fault in the mw6 8 2013 lushan china earthquake revealed by joint inversion of local strong motion accelerograms and geodetic measurements abstract the 2013 mw6 8 lushan china earthquake occurred in the southwestern end of the longmenshan fault zone we jointly invert local strong motion data and geodetic measurements of coseismic surface deformation including gps and insar to obtain a robust model of the rupture process of the 2013 lushan earthquake our joint inversion best model involves the rupture of two opposing faults during the lushan earthquake a main fault and a secondary fault it is only when the secondary fault is included that both the gps and insar measurements are fit along with the near field strong motion over 75 of the computed moment was released in slip on the main fault segment a northwest dipping listric thrust fault with buried thrust and dextral strike slip at hypocenter depths and with only minor slip closer to the surface the secondary fault mainly involved oblique thrust slip or pure dextral strike slip at shallower depths and accounts for just under 24 of the moment released in the lushan earthquake coulomb stress changes of about 0 5 mpa on the secondary fault segment at the time coseismic slip initiated on that fault indicate that slip was likely triggered by the coseismic slip on the main blind thrust fault our coseismic slip model is consistent with a sub horizontal and east west to southeast northwest trending most compressive stress our inferred coseismic slip model is also consistent with previous gps derived models of strain accumulation on the longmenshan fault system

origin of methane in serpentinite hosted hydrothermal systems the ch4 h2 h2o hydrogen isotope systematics of the hakuba happo hot spring abstract serpentinite hosted hydrothermal systems have attracted considerable attention as sites of abiotic organic synthesis and as habitats for the earliest microbial communities here we report a systematic isotopic study of a new serpentinite hosted system the hakuba happo hot spring in the shiroumadake area japan 36 42 n 137 48 e we collected water directly from the hot spring from two drilling wells more than 500 m deep all water samples were strongly alkaline ph 10 and rich in h2 201 664 mol l and ch4 124 201 mol l despite the relatively low temperatures 50 60 c thermodynamic calculations suggest that the h2 was likely derived from serpentinization reactions hydrogen isotope compositions for happo 1 happo 3 were found to be as follows d h 2 700 710 d ch 4 210 300 and d h 2 o 85 84 the carbon isotope compositions of methane from happo 1 and 3 were found to be c 13 34 5 and 33 9 respectively the ch4 h2 h2o hydrogen isotope systematics indicate that at least two different mechanisms were responsible for methane formation happo 1 has a similar hydrogen isotope compositions to other serpentinite hosted systems reported previously the elevated d ch 4 with respect to the equilibrium relationship suggests that the hydrogen of the happo 1 methane was not sourced from molecular hydrogen but was derived directly from water this implies that the methane may not have been produced via the fischer tropsch type ftt synthesis but possibly by the hydration of olivine conversely the depleted d ch 4 with respect to the equilibrium relationship in happo 3 suggests the incorporation of biological methane based on a comparison of the hydrogen isotope systematics of our results with those of other serpentinite hosted hydrothermal systems we suggest that abiotic ch4 production directly from h2o without mediation by h2 may be more common in serpentinite hosted systems hydration of olivine may play a more significant role in abiotic methane production than previously thought

a balanced cross section across the himalayan frontal fold thrust belt subathu area himachal pradesh india thrust sequence structural evolution and shortening abstract the structural evolution of the frontal fold thrust belt in the nw himalayas has been deciphered through the construction of a balanced cross section which incorporates all the tertiary and the precambrian sedimentary rock units belonging to the sub himalaya zone and the lesser himalaya zone respectively towards the foreland the structural geometry is rather simple with widely spaced thrust ramps and simple fault bend folds in the hangingwall in the central sector the structural geometry seen at the surface is essentially controlled by a thrust system that can be approximately described as a buried hinterland dipping duplex the structural geometry becomes extremely complex in the northeastern sector i e towards the hinterland owing to out of sequence thrusting low ramp spacing leading to dislocation of older thrusts and related structures by younger thrusts folded thrusts and breached horses stacked up horses occupied by lesser himalaya zone formations dominate the structural geometry in this sector an in sequence thrusting event followed by out of sequence thrusting in an approximately break back style best describe the structural evolution of the fold thrust belt in this area a total slip of about 96 km occurred along the detachment and the shortening partitioned within the fold thrust belt is about 72 km or about 71

isotope fractionation and mixing in methane plumes from the logatchev hydrothermal field as methane is consumed in the deep sea its 13c 12c ratio progressively increases because of kinetic isotope fractionation many submarine hydrothermal vents emit methane with carbon isotope ratios that are higher than those of background methane in the surrounding ocean since the latter exists at low concentrations mixing of background methane with vent fluid tends to decrease the 13c 12c ratio as concentration decreases opposite to the trend produced by consumption we investigated ch4 concentration and 13c together with 3he in plumes from the logatchev hydrothermal field lhf located at 14 45 n 45 w which generates relatively heavy methane 13c 13 by serpentinization of ultramafic rock the measured methane and 3he were well correlated at high concentrations indicating a ch4 3he ratio of 1 108 in the vent fluids these tracer distributions were also simulated with an advection diffusion model in which methane consumption only occurs above a certain threshold concentration we utilized 3he to calculate the methane remaining in solution after oxidation f and the deviation of 13c from the value expected from mixing alone 13c both in the model and in the data the entire set of 13c values are not correlated with log f which is due to continuous oxidation within the plume while mixing with background seawater a linear relationship however is found in the model for methane at concentrations sufficiently above background and many of the samples with elevated ch4 north of lhf exhibit a linear trend of 13c versus log f as well from this trend the kinetic isotope fractionation factor in the lhf plumes appears to be about 1 015 this value is somewhat higher than found in some other deep sea studies but it is lower than found in laboratory incubation experiments

geochemical and physical structure of the hydrothermal plume at the ultramafic hosted logatchev hydrothermal field at 14 45 n on the mid atlantic ridge abstract the hydrothermal plume generated in deep waters above the logatchev hydrothermal field lhf about 15 n on the mid atlantic ridge was investigated and mapped for its 3d distributions using a combination of in situ optical light scattering data temperature and salinity data as well as concentrations of hydrogen methane total dissolvable fe and total dissolvable mn based on the results obtained for these meaningful parameters we report the geochemical and physical characteristics of the fluids expelled from the ultramafic lhf and the chemical structure of its hydrothermal plume in the water column the hydrothermal plume is sourced by at least seven distinct vent sites and possibly additional diffusive fluid and gas discharge it comprises a water body characterized by strong nephelometric anomalies expressed as ntu nephelometric turbidity units and high concentrations of fe and mn 5 times seawater concentration and the gas plume with several times the h 2 and ch 4 concentrations of normal seawater up to three plume levels with a total vertical extension of about 350 m from the seafloor were classified in the hydrothermal plume the ntu plume could be followed to approximately 2 5 km to the north and to the south from the vent site while the gas plume spread several km farther from the hydrothermal source high concentrations of h 2 up to 1598 nmol l 1 and ch 4 up to 323 nmol l 1 accompanied by relatively low dissolvable fe concentrations up to 270 nmol l 1 as well as low concentrations of dissolvable mn 112 nmol l 1 compared to basaltic hydrothermal systems are the characteristics of the plume the low metal gas ratios showed a decrease with increasing distance from the vent site our data demonstrate that ultramafic systems such as the lhf serve both as sources and sinks for elements with respect to metal and gas inputs into the oceanic water column the relevance of such systems is underlined by the discovery and postulated frequency of further ultramafic hosted hydrothermal systems on slow spreading ridges

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

late quaternary holocene evolution of dun structure and the himalayan frontal fault zone of the garhwal sub himalaya nw india abstract dun structures are common in the sub himalayan zone of the himalaya bounded by the main boundary thrust mbt and the himalayan frontal thrust hft they are broad synclinal longitudinal valleys formed as a consequence of the exhumation of the range front of the himalaya in the garhwal sub himalaya these structures have grown since 0 5 ma with the peak activity postdating 100 ka a series of out of sequence deformation structures have been identified within the mbt hft bounded dun structures they are identified on the basis of geomorphic post 100 ka stratigraphic and structural expressions with activity as young as the early holocene to the south of the range front of the himalaya uplift has been observed in the piedmont zone with peculiar active tectonic geomorphic expressions piedmont sediments of 15 5 ka determined by optically simulated luminescence osl have been affected by the above uplift the complete tectonic scenario has been analyzed and an attempt has been made to delineate the sequential evolution of these structures during the post 100 ka period late quaternary holocene in the himalayan range front

initiation of a thrust fault revealed by analog experiments abstract to reveal in detail the process of initiation of a thrust fault we conducted analog experiments with dry quartz sand using a high resolution digital image correlation technique to identify minor shear strain patterns for every 27 m of shortening with an absolute displacement accuracy of 0 5 m the experimental results identified a number of weak shear bands and minor uplift prior to the initiation of a thrust in cross section view the observations suggest that the process is closely linked to the activity of an adjacent existing thrust and can be divided into three stages stage 1 is characterized by a series of abrupt and short lived weak shear bands at the location where the thrust will subsequently be generated the area that will eventually be the hanging wall starts to uplift before the fault forms the shear strain along the existing thrust decreases linearly during this stage stage 2 is defined by the generation of the new thrust and active displacements along it identified by the shear strain along the thrust the location of the new thrust may be constrained by its back thrust generally produced at the foot of the surface slope the activity of the existing thrust falls to zero once the new thrust is generated although these two events are not synchronous stage 3 of the thrust is characterized by a constant displacement that corresponds to the shortening applied to the model similar minor shear bands have been reported in the toe area of the nankai accretionary prism sw japan by comparing several transects across this subduction margin we can classify the lateral variations in the structural geometry into the same stages of deformation identified in our experiments our findings may also be applied to the evaluation of fracture distributions in thrust belts during unconventional hydrocarbon exploration and production

a note on the fluxes of abiogenic methane and hydrogen from mid ocean ridges the concentrations of methane and hydrogen in hydrothermal vent fluids issuing from mid ocean ridges tend to fall into two groups one with high concentrations of these gases in ultramafic hosted vent fields and a second group with relatively lower concentrations in basalt hosted vent fluids ultramafic hosted systems however appear to be restricted to slow spreading ridges and constitute only a fraction of the hydrothermal systems found there in this note the hydrothermal fluxes of methane and hydrogen have been calculated by estimating the percentages of the total subsurface hydrothermal circulation that circulate through each type of host rock even though the percentage of the total subsurface flow that is affected by serpentinization appears to be rather small 8 it still appears that this process produces about 70 of the total mid ocean flux of these gases the total production of methane and hydrogen is calculated to be about 20 x 10 9 mol yr 1 and 190 x 10 9 mol yr 1 respectively the hydrogen flux is comparable to that most recently calculated on the basis of the rate of hydration of mantle rock in newly formed crust and the stoichiometry of the serpentinization reaction this suggests that except for the production of methane a major portion of the hydrogen produced in the subsurface is not consumed before venting

propagation of the thrust system and erosion in the lesser himalaya geochemical and sedimentological evidence centre de recherches pe trographiques et ge ochimiques bp 20 54501 vandoeuvre les nancy franceabstractsedimentological and nd isotope data of two sections of the sub himalaya of westernnepal are used as new constraints for understanding the erosion history of the himalaya throughout the deposition of the middle and upper members of the siwalik group thelesser himalaya contribution to the total detrital input progressively increased from lessthan 20 to 40 the increasing proportion of lesser himalaya sediments started at ca 10 8 ma and is associated with a coarsening of the maximum grain size at both micro scopic and macroscopic scales thin skinned tectonics of the lesser himalaya thrust sys tem would have controlled the exhumation of the lesser himalaya rocks and would havebegun at 12 10 ma taking into account the delay for denudation together with otherstudies these data restrict the onset of movement on the lesser himalaya thrust systemto less than 3 m y along more than 1750 km this short time frame implies a ratio oflateral propagation rate to shortening rate far too high for the propagation of a singlecrustal thrust thus we suggest instead the simultaneous initiation of several thrusts aheadof the main central thrust at ca 12 ma we suggest that a rapid rise of the tibetanplateau at this time has transformed the himalaya to an overcritical thrust wedge thathas propagated forward to return to a stable state this regional rising could be the primecause of the increase of sediment in ux at ca 11 ma around the himalaya keywords siwalik formations neodymium grain size erosion thrust sheets himalaya

structure of hydrothermal plumes at the logatchev vent field 14 45 n mid atlantic ridge evidence from geochemical and geophysical data abstract in the seventh cruise of r v professor logatchev anomalies of natural electric field ef eh and ps were discovered using a towed instrument package rift at 14 45 n on the mar logatchev hydrothermal field the anomalous zone az is situated close 10 35 m to two low temperature venting areas of degrading sulphides and a black smoker irina microsmoke forming a distinct buoyant plume over or close to the main area of high temperature venting situated to the south east from the az no ef or eh anomalies were observed according to the results of mir dives the highly mineralised solutions from smoking craters at the main mound mostly form non buoyant plumes reverse plumes the buoyant plume structure shows the differentiation of the electrical and eh fields within the plume maxima of the ef eh and e h 2 s anomalies were revealed in the lower part 15 m of the plume the negative redox potential plume coupled with a sulphide anomaly is more localized in comparison with the ef this observation indicates a distinct change in the composition of buoyant plume water which may be due to the formation and fallout of early formed fe sulphide particles soon after venting

extrusion vs duplexing models of himalayan mountain building 1 discovery of the pabbar thrust confirms duplex dominated growth of the northwestern indian himalaya since mid miocene ongoing himalayan growth is generally thought to be dominated by duplexing and or extrusion processes these models may be tested by reconstructing himalayan fold thrust belt growth since the middle miocene however our knowledge of basic structural geometry remains too fragmentary to resolve the issue even in areas with rich stratigraphic diversity such as the northwestern indian himalaya in this region a primary outstanding question involves the uncertain relationship of the berinag thrust and the tons thrust structures with displacements of 80 km and 40 km respectively the uncertain geometry and kinematics allow for the complete range of duplexing or extrusion processes for the integrated kinematic history since the middle miocene to address this issue field mapping and kinematic analysis were performed to reconstruct the deformation of the lesser himalayan sequence in the northwest indian himalaya our results reveal a new discovery a 450 m thick top to southwest shear zone termed the pabbar thrust the pabbar thrust placed the outer lesser himalayan sequence the tons thrust hanging wall directly on the berinag group the berinag thrust hanging wall this discovery requires that the berinag thrust and tons thrust are in fact the same structure and discrete duplexing processes dominated growth of the northwest indian himalaya for the past 10 15 million years along strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the india west nepal border where prior work suggests that structures are continuous but stratigraphy does not match

stable isotopic compositions of methane and carbon monoxide in the suiyo hydrothermal plume izu bonin arc tracers for microbial consumption production abstract effluent hydrothermal water samples in and around the water column of the suiyo seamount caldera ca 2 km diameter izu bonin arc were taken to determine concentrations and stable carbon isotopic compositions 13c of methane ch4 and carbon monoxide co in the plume venting fluids on the caldera floor ca 1370 m depth were also examined using the manned submersible shinkai 2000 to compare the chemical composition and isotopic composition of ch4 and co with those in the hydrothermal plume strong ch4 enrichment was detected not only in the water column within the caldera but also on those outside the caldera at the depth of ca 1100 m the sill depth of the caldera wall within the plume we also detected significant co enrichment the 13c of co in the plume however exhibited highly 13c depleted values 110 vpdb to 60 vpdb compared with those in seafloor venting hydrothermal fluids around 31 vpdb besides the plume samples exhibited higher co ch4 ratios depending on the distance from the seafloor venting site we conclude that in situ microbial activity in the plume causes the co enrichment in the hydrothermal plume the present results suggest that co enrichment in deep sea water could act as a new tracer for unidentified seafloor hydrothermal activities especially for detecting plumes distant from venting sites as well as for quantifying in situ microbial activity related to co production in hydrothermal plumes

evidence for a far traveled thrust sheet in the greater himalayan thrust system and an alternative model to building the himalaya the galchhi shear zone underlies the kathmandu klippe in central nepal and has emerged as a key structure for discriminating competing models for the formation of the himalayan orogenic wedge new chronologic data from the galchhi area suggest a new structural and orogenic interpretation zircons from quartzites and an orthogneiss restrict protolith deposition to between 467 7 10 ma and 570 ma with metamorphic zircon growth at 23 29 ma comparable data from the greater himalayan sequence ghs at the intra ghs langtang thrust north of galchhi similarly restrict ghs deposition to between 475 7 3 and 660 ma undeformed pegmatites near galchhi constrain movement of the galchhi shear zone to 22 5 2 3 ma long before slip of the main central thrust in the region 17 ma shear sense indicators in the galchhi area indicate both top to the south and top to the north shears the old age of movement neoproterozoic youngest detrital zircons occurrence of top to the south shear sense indicators and intrusive paleozoic granites all suggest that the galchhi shear zone is an intra ghs top to the south thrust rather than either a thrust involving lesser himalayan rocks or a top to the north shear zone that juxtaposed tethyan and ghs rocks during coeval movement of the main central thrust the ghs in nepal was not emplaced as a single body of rock but consists of at least two ductile thrust sheets present in both the hinterland at langtang and toward the foreland at galchhi ghs thrust sheets sequentially underplated during southward propagation of the thrust belt

distribution of methane in the water column of the baltic sea the distribution of dissolved methane in the water column of the baltic sea was extensively investigated a strong correlation between the vertical density stratification the distribution of oxygen hydrogen sulfide and methane has been identified a widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth the deep basins in the central baltic sea show the strongest methane enrichments in stagnant anoxic water bodies max 1086 nm and 504 nm respectively with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations saturation values of 206 and 120 respectively in general the more limnic basins in the northern part of the baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium between 106 and 116 in contrast the shallow western baltic sea is characterized by high saturation values up to 746

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

stable carbon isotopic evidence for methane oxidation in plumes above hydrate ridge cascadia oregon margin 1 the transport and consumption of methane in the water column in the vicinity of the cold seeps of hydrate ridge on the cascadia oregon margin were characterized using measurements of the stable carbon isotope composition of methane the 13c ch4 values measured in the water column ranged from approximately 65 to 16 pdb the combination of measured methane concentration data and the stable carbon isotope values from the same depths support the hypothesis of biogenically produced methane which enters the water column from dissolving bubbles released from cold seepages likely as a consequence of destabilized methane hydrate 13c ch4 65 pdb kinetic fractionation factors associated with aerobic bacterial methane oxidation in the water column were calculated using a rayleigh distillation equation applied to a subset of the data fractionation factors ranged from 1 002 to 1 013 mean 1 008 and were in the lower end of the range of those reported in the literature a result likely due to the influence of temperature and mixing in plume waters the fraction of methane remaining after oxidation calculated using the same rayleigh model approach suggests that the aerobic oxidation of methane in the water column over hydrate ridge is nearly quantitative

hydrothermal methane venting between 12 n and 26 n along the mid atlantic ridge hydrographic surveys along the mid atlantic ridge mar between 12 n and 26 n carried out from 1984 to 1990 show a variable pattern of ch4 rich water column plumes the vertical distribution of ch4 at stations located every 20 40 km is presented along this 1200 km long section of the mar ch4 venting is clearly demonstrated ch4 enriched fluids rise from vents as plumes spreading is confined to the axial valley due to the topography of the mar ch4 contents from 45 nmol to 675 nmol kg are measured in the buoyant plumes above the two active hydrothermal sites mark 23 n tag 26 n known at present whereas ch4 anomalies up to 3 6 nmol kg are typically observed in plumes emitted either on the inner floor on the walls and or at the top of the rift mountains along the studied ridge section ch4 concentrations 45 mol to 144 mol kg in mark and tag vent fluids are of the same order of magnitude as those found in the east pacific rise fluids even though ch4 is known to be unstable with respect to oxidation by dissolved oxygen and in spite of its microbial oxidation in plumes these results confirm ch4 to be a good indicator to track hydrothermal plumes and to map the variation of hydrothermal activity along mid oceanic ridges moreover between 12 and 26 n along the mar ch4 results show that while hydrothermal activity is present everywhere along the ridge it is predominant near fracture zones fz kane fz 15 20 n fz comparison of ch4 tracer with total dissolvable manganese tdm tracer in plumes allows us to differentiate subseafloor hydrothermal processes the high tdm ch4 found above tag and mark areas is indicative of basalt seawater interaction while at 15 n the low tdm ch4 provides evidence of fluid circulation in ultrabasic rocks ch4 data confirm the association between mantle degassing hydrothermal activity and serpentinization along this 12 26 n section of the mid atlantic ridge

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

dissolved hydrogen and methane in the oceanic basaltic biosphere abstract the oceanic basaltic crust is the largest aquifer on earth and has the potential to harbor substantial subsurface microbial ecosystems which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats within the sediment buried 3 5 myr old basaltic crust of the eastern juan de fuca ridge flank the circulating basement fluids have moderate temperature 65 c and low to undetectable dissolved oxygen and nitrate concentrations sulfate present in high concentrations is therefore expected to serve as the major electron acceptor in this subsurface environment this study focused on the availability and potential sources of two important electron donors methane ch4 and hydrogen h2 for the subseafloor biosphere high integrity basement fluids were collected via fluid delivery lines associated with integrated ocean drilling program iodp circulation obviation retrofit kits corks that extend from basement depths to outlet ports at the seafloor two new corks installed during iodp 327 in 2010 1362a and 1362b were sampled in 2011 and 2013 the two corks are superior than earlier style corks in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines reducing the interaction between casing materials with the environment additional samples were collected from an earlier style cork at borehole 1301a the basement fluids are enriched in h2 0 05 1 8 mol kg suggesting that the ocean basaltic aquifer can support h2 driven metabolism the basement fluids also contain significant amount of ch4 5 32 mol kg revealing ch4 as an available substrate for subseafloor basaltic habitats the 13c values of ch4 from the three boreholes ranged from 22 5 to 58 while the 2h values ranged from 316 to 57 the isotopic compositions of ch4 and the molecular compositions of hydrocarbons suggest that ch4 in the basement fluids is of both biogenic and abiotic origins varying among sites and sampling times the 2h values of ch4 in cork 1301a fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic ch4 in conclusion our study shows that ch4 and h2 are persistently available to fuel the deep biosphere and that ch4 is both produced and potentially consumed by microorganisms in the oceanic basement