etude petro structurale des chevauchements ductiles himalayens sur la transversale de l everest makalu nepal oriental tectonic and microtectonic data in eastern nepal indicate that the major observed thrusting 100 km on the main central thrust mct postdates the barrovian metamorphism of the high himalaya gneisses this result at variance with the famous reverse metamorphism model better explains the abnormal metamorphic superpositions in the himalayas and accounts for the lack of high pressure assemblages under the thick allochtonous high himalaya tibetan slab pressure and temperature estimates by microprobe analysis on plagioclase biotite garnet kyanite sillimanite and cordierite assemblages are presented for samples collected along the mct shear zone and across the gneiss slab in the everest makalu area since there is very little difference in pressure at the front of the slab kathmandu klippe and its root these estimates support the existence of important late metamorphic thrusting the decrease of pressure towards the top of the gneiss pile combined with a small temperature increase explains the k

megathrust splay faults at the focus of the prince william sound asperity alaska 1 high resolution sparker and crustal scale air gun seismic reflection data coupled with repeat bathymetric surveys document a region of repeated coseismic uplift on the portion of the alaska subduction zone that ruptured in 1964 this area defines the western limit of prince william sound differencing of vintage and modern bathymetric surveys shows that the region of greatest uplift related to the 1964 great alaska earthquake was focused along a series of subparallel faults beneath prince william sound and the adjacent gulf of alaska shelf bathymetric differencing indicates that 12 m of coseismic uplift occurred along two faults that reached the seafloor as submarine terraces on the cape cleare bank southwest of montague island sparker seismic reflection data provide cumulative holocene slip estimates as high as 9 mm yr along a series of splay thrust faults within both the inner wedge and transition zone of the accretionary prism crustal seismic data show that these megathrust splay faults root separately into the subduction zone decollement splay fault divergence from this megathrust correlates with changes in midcrustal seismic velocity and magnetic susceptibility values best explained by duplexing of the subducted yakutat terrane rocks above pacific plate rocks along the trailing edge of the yakutat terrane although each splay fault is capable of independent motion we conclude that the identified splay faults rupture in a similar pattern during successive megathrust earthquakes and that the region of greatest seismic coupling has remained consistent throughout the holocene

two dimensional modeling of the p t t paths of regional metamorphism in simple overthrust terrains quantitative modeling of metamorphic p t t paths in thrust belts has so far been limited to one dimensional simplification we have developed a two dimensional time dependent finite element procedure capable of tracing and updating fault and strata boundaries during faulting for modeling thermal evolution of overthrust terrains we show that the two dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the p t t paths of rocks in orogenic belts the results suggest that petrological studies of p t paths of rocks from different lateral positions in an orogenic belt along with two dimensional modeling procedure can put strong constraints on models of regional tectonic processes

alaska megathrust 1 seismicity 43 years after the great 1964 alaska megathrust earthquake 1 the largest moment release during the 1964 mw 9 2 alaska earthquake was on the portion of the megathrust under the eastern kenai peninsula and the prince william sound the area is currently locked geodetically and corresponds to where the yakutat terrane is subducting in 2006 2009 a seismic array consisting of 34 broadband seismometers was deployed in the region an automatic algorithm was used to detect 12 563 local earthquakes using 13 months of data from the experiment of these 9427 good quality earthquakes could be relocated in a joint inversion for hypocenters and velocity structure they were then relocated by double difference to generate a final catalog of 8308 hypocenters these microearthquakes delineate a deeper steeply dipping wadati benioff zone contiguous with an 11 km wide seismic zone dipping at 3 between 20 km and 40 km depth along the 1964 earthquake s rupture zone focal mechanisms do not show interplate thrust faulting events but mostly normal faulting events with t axes generally parallel the slab dip direction indicating them to be intraslab seismicity the shallow narrow band of seismicity lies within the subducting yakutat terrane and right below the thrust zone possibly thrust faulting has not yet resumed yet in this early phase of the earthquake cycle thick subducted sediments overlying the yakutat terrane could also form a large strong contact zone on a relatively smooth plate boundary which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes

mine drainage water from coal mines of kerman region iran two types of mine drainage water were recognized in kerman coalfield namely neutral to alkaline and acid amd both types contain a high level of trace metal concentrations with a higher level in amd trace metals from the coal mine waters of kerman coalfield are mainly present as adsorption on fe and mn oxide and hydroxide particles and to a lesser extent as sulfate simple metal ions and as metal sorption on clay particles and hydrous aluminum oxides

late cretaceous emplacement of the indus suture zone ophiolitic melanges and an eocene oligocene magmatic arc on the northern edge of the indian plate we report three40ar 39ar dates on stratigraphically located samples of 82 6ma from a syenite cutting the indus suture zone ophiolitic melange and about 39 and about 45 ma from granodiorite intrusions north of the suture zone sedimentological observations indicate eocene to miocene deposition of coarse clastics by very large braided and meandering streams in a continental back arc setting these observations suggest that the ophiolitic melanges of the indus suture zone were emplaced in the late cretaceous shortly after a major change in plate motions in the indian ocean they further suggest that an andean type magmatic arc developed on the northern edge of the indian plate during the eocene and oligocene

geochemistry of rare earth elements in a neutral mine drainage environment anjir tangeh northern iran abstract this study investigates the geochemical characteristics of rare earth elements and yttrium ree y in the neutral mine drainage nmd and river water in the vicinity of the anjir tangeh coal washing plant mazandaran province northern iran the nmd water had a neutral ph along with high sulphate and bicarbonate concentrations the total concentrations of ree in the nmd water were lower than in the river water according to the north american shale composite nasc normalised concentrations the patterns of nmd showed heavy ree hree enrichment while the river water represented middle ree mree enhancement both negative europium eu and positive gadolinium gd anomalies were observed in the drainage and river water within the study area the sum of ree concentration increased gradually downstream of the discharging point of the plant reject water in contrast to decreasing of al fe mn and cu pb zn concentrations the river sediment with high fe concentrations was enriched with lanthanum la and cerium ce the overall ree pattern of the nmd approximates those of coal except for the depletion in light ree lree and the enrichment of eu dominant inorganic ree species in the river water included ln co3 2 and lnco3 while lnco3 ln co3 2 and ln so4 were the main complexes in the nmd the saturation index indicated that al and fe were both oversaturated in the drainage and river water which can control the fractionation of ree by the sorption process according to both hierarchical cluster analysis hca and principal component analysis pca ph al and p were the significant parameters in the ree distribution

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

metamorphic reactions related to decompression and synkinematic intrusion of leucogranite high himalayan crystallines bhutan the high himalayan crystallines hhc of bhutan were penetratively deformed intruded by leucogranite and metamorphosed during the collision of the indian and asian plates metamorphic reaction textures in the hhc show that it experienced decompression while maintaining a laterally heterogeneous and locally inverted internal temperature range of c 600 750c this thermal structure was produced by thrusting hot migmatitic rocks over lower grade rocks within the hhc and by the advection of heat from the intrusion of leucogranite dykes and sills during decompression a variable velocity field within the hhc during exhumation and extrusion between india and tibet caused the inversion of top to the south sense of shear present throughout most of the hhc to top down to the north shear near its top

overturned marble layers evidence for upward extrusion of the backbone range of taiwan abstract the backbone range is part of the taiwan mountain belt which was formed due to the oblique collision between the luzon arc and the eurasian passive continental margin from plio pleistocene to the present stable isotope compositional profiles of thin marble layers from this mountain range show that marble layers from rock sections with an inverted metamorphic zonation were all overturned after the peak metamorphism and that marble layers from rock sections with a normal metamorphic zonation were not overturned exhumation folding seems to be the responsible process an upward extrusion exhumation model is therefore postulated as the probable mechanism for the mountain building process this model can well explain the fanning orientation of rock cleavage s dipping in a regional scale as well as the metamorphic characteristics across the mountain range the model also shows that the recorded stretching lineation is secondary in nature meaning the exact direction of rock movement during the initial exhumation stage in response to the oblique collision cannot be deduced

accretion in the wake of terrane collision the neogene accretionary wedge off kenai peninsula alaska subduction accretion and repeated terrane collision shaped the alaskan convergent margin the yakutat terrane is currently colliding with the continental margin below the central gulf of alaska during the neogene the terrane s western part was subducted after which a sediment wedge accreted along the northeast aleutian trench this wedge incorporates sediment eroded from the continental margin and marine sediments carried into the subduction zone on the pacific plate prestack depth migration was performed on six seismic reflection lines to resolve the structure within this accretionary wedge and its backstop the lateral extent of the structures is constrained by high resolution swath bathymetry and seismic lines collected along strike accretionary structure consists of variably sized thrust slices that were deformed against a backstop during frontal accretion and underplating toward the northeast the lower slope steepens the wedge narrows and the accreted volume decreases notwithstanding a doubling of sediment thickness in the trench in the northeasternmost transect near the area where the terrane s trailing edge subducts no frontal accretion is observed and the slope is eroded the structures imaged along the seismic lines discussed here most likely result from progressive evolution from erosion to accretion as the trailing edge of the yakutat terrane is subducting

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

landslides and megathrust splay faults captured by the late holocene sediment record of eastern prince william sound alaska abstract we present new marine seismic reflection profiles and bathymetric maps to characterize holocene depositional patterns submarine landslides and active faults beneath eastern and central prince william sound pws alaska which is the eastern rupture patch of the 1964 m w 9 2 earthquake we show evidence that submarine landslides many of which are likely earthquake triggered repeatedly released along the southern margin of orca bay in eastern pws we document motion on reverse faults during the 1964 great alaska earthquake and estimate late holocene slip rates for these growth faults which splay from the subduction zone megathrust regional bathymetric lineations help define the faults that extend 40 70 km in length some of which show slip rates as great as 3 75 mm yr we infer that faults mapped below eastern pws connect to faults mapped beneath central pws and possibly onto the alaska mainland via an en echelon style of faulting moderate m w 4 upper plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate m w 7 8 earthquakes and that these earthquakes could damage local infrastructure from ground shaking submarine landslides regardless of the source of initiation could generate local tsunamis to produce large run ups along nearby shorelines in a more general sense the pws area shows that faults that splay from the underlying plate boundary present proximal perhaps independent seismic sources within the accretionary prism creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches

the four plutonic belts of the transhimalaya himalaya a chemical mineralogical isotopic and chronological synthesis along a tibet nepal section

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

contrasting p t paths in the eastern himalaya nepal inverted isograds in a paired metamorphic mountain belt petrology and phase equilibria of rocks from two profiles in eastern d f matrix assemblages are overprinted by decompression reaction textures and in zones f and g progress into the sillimanite field nepal from the lesser himalayan sequences across the main central thrust zone and into the greater himalayan sequences the two terranes were brought into juxtaposition during formation of sillimanite biotite gedrite foliation seams s3 formed at reveal a paired metamorphic mountain belt pmmb composed of two thrust bound metamorphic terranes of contrasting metamorphic conditions of 674 33 c and 5 7 1 1 kbar the contrasting average geothermal gradients and p t paths of these two metastyle at the higher structural level the greater himalayan sequences experienced high t moderate p metamorphism with an anmorphic terranes suggest they make up a pmmb the upperplate position of the greater himalayan sequences produced an ticlockwise p t path low p inclusion assemblages of quartz hercynitic spinel sillimanite have been overgrown by peak anticlockwise p t path with the high average geothermal gradient being possibly due to high radiogenic element content in this terrane metamorphic garnet cordierite sillimanite assemblages that equilibrated at 837 59 c and 6 7 1 0 kbar matrix in contrast the lower plate lesser himalayan sequences were deeply buried metamorphosed in a clockwise p t path and display minerals are overprinted by numerous metamorphic reaction textures that document isobaric cooling and re equilibrated samples preserve inverted isograds as a result of progressive ductile overthrusting of the hot greater himalayan sequences during prograde metamorphism evidence of cooling to 600 45 c at 5 7 1 1 kbar below the main central thrust the lesser himalayan sequences are a continuous though inverted barrovian sequence of high p moderate t metamorphic rocks metamorphic zones upwards from the

timing of late cenozoic tidewater glaciation in the far north pacific the onset of late cenozoic glacial events in the far north pacific ocean is recorded by ice rafted debris in the yakataga formation in the gulf of alaska the dating of these events is controversial ages based on molluscs suggest that initial late cenozoic tidewater glaciation occurred in the early middle miocene 15 16 ma previous work on planktic foraminifera indicates that this event is no older than late miocene probably latest miocene 5 6 ma resolution of this problem is important because the yakataga formation is the thickest most complete and best exposed repository of late cenozoic glaciomarine rocks in the northern hemisphere investigation of this record has broader implications for global temperature gradients paleoceanographic development of the far north pacific and northern hemisphere glacial history new planktic foraminiferal data from onshore and offshore yakataga formation sections in the gulf of alaska are compared to a regional depositional and chronostratigraphic framework in order to test whether the yakataga record is anomalous or consistent with the paleoclimatic record of the north pacific this comparison reconfirms that initial glaciomarine rocks of the yakataga formation are no older than late miocene new paleomagnetic data suggest that the base of the yakataga formation is within the lower gilbert polarity chron consistent with the planktic foraminiferal dating and k ar dates on glauconite correlation of the yakataga record to key offshore sections in the far north pacific deep sea drilling project dsdp sites 178 183 192 provides additional insights into the paleoclimatic significance of these rocks uplift of the alaska coastal ranges a necessary prelude to alpine glaciation occurred during late miocene time diatom biofacies dsdp sites 183 192 indicate warm middle miocene conditions climatic deterioration during the late middle and early late miocene time and initial tidewater glaciation between 5 0 and 6 7 ma a relatively warm mid pliocene interval succeeded this initial glaciation which was in turn followed by hemisphere scale glaciation beginning at 2 5 ma this second phase of yakataga glaciation may have begun as early as 3 0 3 5 ma glaciomarine rocks in the basal yakataga formation mark an important climatic event in the north pacific ocean they are latest miocene in age consistent with regional climatic information and not a middle miocene climatic anomaly

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

structure and tectonics of the himalaya constraints and implications of geophysical data the himalayan range is a product of continental collision between india and eurasia and for several reasons it is a logical place to examine the physical causes and mechanisms of mountain building the exceptionally high mountains and the great length of the range alone single the himalaya out as a major structural feature the convergence rate between india and eurasia of about 50 mm yr 1 minster jordan 1978 requires rapid rates of slip and the occurrence of four major earthquakes with magnitudes in excess of 8 4 in the last 100 years attests to a high level of seismicity and a rapid rate of active deformation e g richter 1958 seeber armbruster 1981 the exposures of high grade metamorphic rocks in the greater himalaya may suggest large vertical transport of lower crustal rocks e g valdiya 1980a b and the occurrences of young postcollision granites imply recent large perturbations of the temperature structure of the range e g lefort 1981 moreover as sediments derived from the himalaya fill the broad ganga basin south of the range the mountain belt simul taneously seems to override the basin e g g d johnson et al 1979 n m johnson et al 1982 as such the processes occurring now and since the collision began in the early tertiary as well as the present structure of the himalayan belt are probably similar to those at different stages of collision and mountain building in other older orogenic belts such as the appalachians the scottish and scandinavian caledonides the alps and

mid proterozoic pb pb ages for some himalayan base metal deposits and comparison to deposits in rajasthan nw india abstract lead isotope ratios from three base metal deposits rangpo gorubathan in the eastern lesser himalaya and bageswar in the lesser himalaya of kumaun have been studied the first two deposits generally stratiform and stratabound occur within pelitic psammopelitic wacke type metasediments which are locally carbonaceous the bageswar deposit is hosted by silicified dolomitic carbonate rocks the pb isotope ratios appear to be homogenous in two and heterogenous in one of the deposits model pb pb ages obtained for the rangpo and gorubathan deposits are 1800 ma and for the bageswar deposit 1550 1700 ma dispersion in isotopic ratios reflect the geochemical heterogeneity particularly with respect to larger variation in the composition of pb isotope ratios in the bageswar deposit may be explained by the participation of pb from heterogenous sources pb isotope characteristics of the himalayan deposits are compared with those of a number of base metal deposits in the delhi aravalli belt in rajasthan nw india ore lead from the deposits of both the himalaya and of rajasthan are enriched in 206pb and 207pb however lead in all cases plots on the evolution lines corresponding to sources with higher u pb ratios but the sources of lead in the himalayan deposits had a lower th u ratio the geologic observations as well as the pb isotope compositions are consistent with a sedimentary diagenetic origin of the himalayan base metal deposits

changes in crustal seismic deformation rates associated with the 1964 great alaska earthquake we calculated seismic moment rates from crustal earthquake information for the upper cook inlet region including anchorage alaska for the 30 yr prior to and 36 yr following the 1964 great alaska earthquake our results suggest over a factor of 1000 decrease in seismic moment rate in units of dyne centimeters per year following the 1964 mainshock we used geologic information on structures within the cook inlet basin to estimate a regional geologic moment rate assuming the structures extend to 30 km depth and have near vertical dips the geologic moment rates could underestimate the true rates by up to 70 since it is difficult determine the amount of horizontal offset that has occurred along many structures within the basin nevertheless the geologic moment rate is only 3 7 times lower than the pre 1964 seismic moment rate suggesting the 1964 mainshock has significantly slowed regional crustal deformation if we compare the geologic moment rate to the post 1964 seismic moment rate the moment rate deficit over the past 36 yr is equivalent to a moment magnitude 6 6 7 0 earthquake these observed differences in moment rates highlight the difficulty in using seismicity in the decades following a large megathrust earthquake to adequately characterize long term crustal deformation

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

early and late holocene glacial fluctuations and tephrostratigraphy cabin lake alaska marked changes in sediment types deposited in cabin lake near cordova alaska represent environmental shifts during the early and late holocene including fluctuations in the terminal position of sheridan glacier cabin lake is situated to receive meltwater during periods when the outwash plain of the advancing sheridan glacier had aggraded a brief early holocene advance from 11 2 to 11 0 cal ka is represented by glacial rock flour near the base of the sediment core non glacial lake conditions were restored for about 1000 years before the water level in cabin lake lowered and the core site became a fen the fen indicates drier than present conditions leading up to the holocene thermal maximum an unconformity spanning 5400 years during the mid holocene is overlain by peat until 1110 ce when meltwater from sheridan glacier returned to the basin three intervals of an advanced sheridan glacier are recorded in the cabin lake sediments during the late holocene 1110 1180 1260 1540 and 1610 1780 ce the sedimentary sequence also contains the first five reported tephra deposits from the copper river delta region and their geochemical signatures suggest that the sources are the cook inlet volcanoes redoubt augustine and crater peak and possibly mt churchill in the wrangell volcanic field copyright 2013 john wiley sons ltd

geometry of isograds in metamorphic terrains abstract a simple mathematical relation among the dip of isograd surface dip of isotherm surface temperature gradient t g pressure gradient p g and t gdp of reaction is given by 1 sin ga t p p g 1 t g cos cot p g is taken to be constant at 0 3 kb km four major theoretical models for shapes and orientations of isograds are formulated on the basis of the parameters t g and t p this offers a rational basis for studying the geometry of isograds normal reverse metamorphism and determination of temperature gradient two examples have been studied in the light of these models in one case the domed shape of the isograd is best explained by a downwardly directed t g in the other case reverse metamorphism is best explained as the result of a horizontal t g of 18 c km

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

tectonic controls on the uplift of the nanga parbat massif pakistan himalayas cenozoic mountain belts like the himalayas contain regions that experienced rapid uplift in comparison with the areas around them1 whether this uplift occurred by buoyant rebound of previously thickened crust2 or during the crustal thickening process itself is uncertain3 4 here we show however that the 7 mm yr 1 recent uplift5 of the nanga parbat massif pakistan himalayas was accomplished during nw directed thrusting located along its western margin this 3 km wide liachar thrust zone operated from amphibolite facies to the present topographic surface and accommodates substantial crustal shortening the adjacent indus river valley itself cut by seismogenic faulting completely transects the massif showing that erosion keeps pace with geologically rapid thrust uplift6

metamorphism and tectonics of the himalaya metamorphism connected with the main growth and deformation stages of the himalaya ranges from mid cretaceous to the quaternary northward subduction gave rise in the early to mid cretaceous to an island are complex with greenschists amphibolites granulites and blueschists in the w kohistan ladakh and an andean type margin with greenschist amphibolite grade metamorphism in the e india and tibet ophiolitic nappes were thrust southwards over the indian continental margin in the palaeogene during the final stages of closure of the southern arm of tethys the indus zangbo suture bifurcates westwards and between the two sutures lies the kohistan ladakh island arc which was converted to an andean type arc in the palaeocene eocene the karakorum range underwent northward subduction at least during the late cretaceous to give rise to a complex and prominent calc alkaline batholith post collisional southward thrusting of crustal slabs over the indian continental margin took place in the early miocene with production of high grade metamorphism inverted isograds and crustal melt granites later southward thrusting in the pliocene to quaternary gave rise to localized low grade recrystallization against the thrusts

some secondary ore formation features of the sar cheshmeh porphyry copper molybdenum deposit kerman iran new secondary mineral features and the control of secondary molybdenum enrichment have now been recognized at the sar cheshmeh copper deposit in part of the deposit copper is locally concentrated within a subvolcanic unit the so called late fine porphyry in amounts that seem too great to have come from the primary phase of the same unit clay minerals are believed to have influenced the deposition of copper by through flowing oxidized zone solutions within this otherwise subeconomic unit these solutions have caused argillic alteration and copper concentration within the plagioclase phenocrysts fractures are filled with chrysocolla but little chrysocolla was observed within the altered plagioclase phenocrysts the scattered layers of sedimentary unroofing breccia horizontal layers of quaternary age accumulated within the depressions at the top of the deposit contain minor amounts of native copper the breccia consists of angular to subangular clasts of local derivation cemented by a matrix of hematite limonite geothite and small rock fragments native copper the only copper mineral associated with the breccia mainly adhers to the cavity walls in the cementing materials the amount of molybdenum within the leached capping of the sar cheshmeh deposit is generally controlled by the amount of pyrite abundant pyrite has caused the retention of molybdenum within the leached capping of the pyritic halo as a result of the more acidic solution during weathering in contrast to the leached zone of the pyrite poor stock where molybdenum is partially mobile

a study of historic earthquakes of the prince william sound alaska region we have investigated the character of seismicity that occurred in the prince william sound cook inlet region during 40 years prior to the 1964 great alaskan earthquake we have relocated all events of magnitude 5 5 focal mechanisms have been determined from body waveform modeling and first motion analysis for the larger generally magnitude 6 3 events the results suggest a number of similarities and differences between pre and post 1964 mainshock seismicity similarities include the persistence of normal faulting at depths of 40 to 60 km within the subducted slab in both the tazlina glacier and columbia bay regions north of prince william sound and among deeper events within northern cook inlet differences include a higher level of shallow seismicity 40 km depth in the upper cook inlet region and north of cook inlet prior to 1964 higher levels of seismicity within the subducting plate in the south central and eastern kenai peninsula prior to 1964 and a lower level of seismicity in the offshore prince william sound region prior to 1964 much of the lower plate seismicity for the past 70 years appears to cluster immediately downdip of the 1964 asperity two of the events in this study caused notable damage modified mercalli intensity vii to viii in the anchorage area the first in 1933 m w 6 9 appears to have occurred at 9 km depth along a strike slip fault within northern cook inlet the second in 1954 m w 6 7 occurred within the subducting plate at 60 km depth beneath the northern kenai peninsula analysis of these events as well as smaller events we have studied will greatly improve models of seismic hazard for the anchorage region manuscript received 18 september 2000

thrust tectonics and the deep structure of the pakistan himalaya the systematic restoration of thrust systems provides a powerful constraint on the deep structure of orogenic belts a balanced cross section through the imbricated upper crust of the indian plate in the footwall to the main mantle thrust of the western himalaya restores to a minimum width of 730 km the implicit shortening being in excess of 470 km this requires the himalaya and southern tibetan region to be underlain by a wedge of indian crust however a full appraisal of gross crustal structure awaits deep seismic control

structural evolution and sequence of thrusting in the high himalayan tibetan tethys and indus suture zones of zanskar and ladakh western himalaya reply abstract the timing of motion on major thrusts in the western himalaya shows an extremely complex sequence that spans approximately 70 ma from the latest cretaceous throughout the tertiary three major phases of thrusting can be distinguished the earliest phase t1 is associated with emplacement of tethyan basin thrust sheets lamayuru sediments and spontang ophiolite south and south westwards onto the submerged northern passive margin of india 75 60 ma collision between india and asia occurred at 50 36 ma and was followed immediately by the major phase t2 of crustal shortening involving large scale south and south westward directed thrusting of the complete palaeozoic mesozoic and late tertiary tibetan tethys zone rocks preliminary balanced cross sections show a minimum shortening of 126 km of these rocks across the zanskar range the late collision phase t3 involved re thrusting of the previously stacked pile breaching or leap frog thrusting reversing the earlier stacking order in places and widespread steepening overturning and backthrusting along the whole northern margin of the tibetan tethys zone and throughout the indus suture zone

the tectonic history of kohistan and its implications for himalayan structure the tectonic history of kohistan northern pakistan involves two collisional events cleavage and folding developed at 90 100 ma along the northern suture between the kohistan island arc and the asian plate at the same time there was major folding and shearing of the lower part of the kohistan arc approximately 100 km south of the suture this deformation was followed by ocean subduction south of the kohistan arc generating the kohistan calc alkaline batholith with subsequent ocean closure during the eocene and obduction of the kohistan arc together with the adjacent part of the asian plate over the indian continental crust the construction of balanced cross sections through the imbricated upper part of the indian continental crust in the footwall to this southern suture indicates a minimum displacement of 470 km requiring the western himalayan hinterland to be underlain by a large wedge of indian middle to lower crust there is some shortening of the overriding kohistan and asian plates by thrusts and shear zones but it is insufficient to satisfy the palaeomagnetic data there must be major crustal shortening involving thrusts in the hindu kush and pamirs north of kohistan the post eocene thrust direction which for most of pakistan is towards 160 is almost perpendicular to that immediately to the east in the himalayan belt generating complex refolded thrust patterns in the hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the nanga parbat syntaxis these different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics cannot always be related to plate movement vectors but are modified by or develop from complex rotations during place collision or from the gravitational spreading of a thickened crust a regional approach is required to recognize and correctly attribute the various components in thrust displacements

high p t polymetamorphism dehydration melting and generation of migmatites and granites in the higher himalayan crystalline complex sikkim india the higher himalayan crystalline complex hhc in sikkim india consists of pelitic migmatites interlayered with calc silicate rocks and minor metabasites microstructural relationships between the mineral phases and deformational fabric elements and zoning characteristics of garnet indicate a prolonged and complex polymetamorphic history for the hhc the pelitic rocks in the upper part of the hhc contain the assemblage plagioclase quartz garnet k feldspar biotite sillimanite and are devoid of muscovite most of the mineral phases grew syn to post tectonically mineral growth coincided with development of a pervasive fabric s 2 during prograde metamorphism m 2 in the early stages of the collisional event some garnet grains display texturally distinct cores and rims which are separated by calcic plagioclase this texture suggests an earlier metamorphic episode m l m may represent pre himalayan metamorphism and decompression of the hhc later the collisional event led to renewed burial of the hhc and m 2 reactions m 2 is reflected by dehydration melting of muscovite and biotite to form granitic melts which either crystallized in situ to form leucosomes or migrated from their source regions to form larger granitic bodies geothermobarometric estimates for peak m 2 conditions indicate p 10 12 kbar t 800 850 c a subsequent metamorphic event m 3 occurred because of 5 kbar of decompression m 3 is recorded by the breakdown of porphyroblastic garnet in all hhc lithologies higher temperature and pressure estimates come from progressively higher structural levels of the complex the thermal gradient of 5 5 c km is anomalous and may be a consequence of thermal buffering during melting however the pressure gradient of 0 25 kbar km resembles a normal lithostatic gradient which suggests that the hhc in sikkim represents an inverted barrovian sequence this inverted zonation of the hhc is probably the result of large scale structural inversion and or tectonic juxtaposition because of ductile shearing

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another

late holocene great earthquakes in the eastern part of the aleutian megathrust abstract the great earthquake mw 9 2 of ad 1964 may not be typical of other megathrust earthquakes in the region during the last 4000 years we present new field data from three sites copper river delta the lower katalla river valley and puffy slough to enhance the temporal and spatial resolutions of the paleoseismic records of multiple great earthquakes differences in the spatial patterns of coseismic uplift and subsidence suggest different rupture combinations of the kodiak prince william sound and western yakutat segments of the plate boundary the longest and most comprehensive records all come from the prince william sound segment most sites here reveal net subsidence over multiple earthquake cycles except where probable upper plate faulting contributes locally to net uplift with measurable differences between sites only a few kilometres apart we identify the katalla area as a source of local seismic hazard similar to other locations in the western part of the yakutat microplate including the two mw8 ruptures in ad 1899 we use a bayesian radiocarbon modelling approach to estimate the age and recurrence intervals of multiple great earthquakes for the prince william sound segment of the megathrust the long interval 883 34 2 years between the penultimate earthquake and ad 1964 contrasts with the older earthquakes that have intervals ranging from 420 to 610 years with a mean of 535 years