early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

late permian early triassic orogeny in japan piling up of nappes transverse lineation and continental subduction of the honshu block abstract field surveys in the oga atetsu and yamaguchi areas of southwest japan have been conducted in order to precise the structure of the permian orogen a stack of nappes is recognized comprising from top to bottom 1 the oga nappe which is considered to be a seamount complex 2 hp sangun metamorphics 3 the permian yakuno ophiolite and 4 the permian detrital maizuru group which is interpreted as the sedimentary cover of a continental block called here the honshu block outcropping as the older granite this stack of nappes is overthrust by the paleozoic hida basement consisting of ht gneisses granites and late carboniferous shallow water sediments microtectonic analysis of the sangun schists shows that the subhorizontal schistosity bearing a submeridian lineation was formed during the synmetamorphic phase asymmetric pressure shadows shear bands and sigmoidal minerals show that the synmetamorphic deformation corresponds to a ductile shear from north to south the permian early triassic orogeny is interpreted as the result of a collision between the hida gneiss or south china block and the honshu block the intervening oceanic area gave rise to southward directed nappes the permian orogenic belt extends at least from taiwan to central japan

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

mercury evidence from the sino korean block for emeishan volcanism during the capitanian mass extinction a prominent large negative 13 c org excursion and a coeval notable spike in mercury hg total organic carbon ratio are observed in the middle upper permian gohan formation in central korea located in the eastern sino korean block skb which may represent the capitanian mass extinction event the skb was separated from the south china block by the eastern palaeo tethys ocean this finding from the skb supports the widespread hg loading to the environment emitted from the emeishan volcanic eruptions in sw china this study demonstrates that the hg cycle was globally perturbed in association with global carbon cycle perturbation that occurred during the capitanian extinction

new gas geothermometers for geothermal exploration calibration and application calibration of five gas geothermometers is presented three of which used co2 h2s and h2 concentrations in fumarole steam respectively the remaining two use co2h2 and h2sh2 ratios the calibration is based on the relation between gas content of drillhole discharges and measured aquifer temperatures after establishing the gas content in the aquifer gas concentrations were calculated in steam formed by adiabatic boiling of this water to atmospheric pressure to obtain the gas geothermometry functions it is shown that the concentrations of co2 h2s and h2 in geothermal reservoir waters are fixed through equilibria with mineral buffers at temperatures above 230 c epidote prehnite calcite quartz are considered to buffer co2 two buffers are involved for h2s and h2 and two functions are therefore presented for the geothermometers involving these gases for waters containing less than about 500 ppm chloride and in the range 230 300 c pyrite pyrrholite epidote prehnite seem to be involved but pyrite epidote prehnite magnetite or chlorite for waters above 300 c and waters in the range 230 300 c if containing over about 500 ppm the gas geothermometers are useful for predicting subsurface temperatures in high temperature geothermal systems they are applicable to systems in basaltic to acidic rocks and in sediments with similar composition but should be used with reservation for systems located in rocks which differ much in composition from the basaltic to acidic ones the geothermometry results may be used to obtain information on steam condensation in upflow zones or phase separation at elevated pressures measured aquifer temperatures in drillholes and gas geothermometry temperatures based on data from nearby fumaroles compare well in the five fields in iceland considered specifically for the present study as well as in several fields in other countries for which data were inspected the results of the gas geothermometers also compare well with the results of solute geothermometers and mixing models in three undrilled icelandic fields

the geochemistry of trace elements in geothermal fluids iceland abstract trace element geochemistry was studied in geothermal fluids in iceland the major and trace element compositions of hot springs sub boiling and two phase liquid and vapor wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth aquifer fluid temperatures ranged from 4 to 300 c ph values between 4 5 and 9 3 and fluids typically contained total dissolved solids

provenance derived from the geochemistry of late paleozoic early mesozoic mudrocks of the pyeongan supergroup korea late carboniferous early triassic pyeongan supergroup korea was deposited in paralic to nonmarine environments developed disconformably on a lower paleozoic platformal sequence pyeongan supergroup mudrocks show progressive upsection changes in major trace and rare earth element compositions mudrocks in the lower and middle parts of the pyeongan supergroup are strongly depleted in cao and na2o while those in the upper part are enriched in these elements in parallel with cao and na2o the ratio of k2o al2o3 in the lower and middle sections is less than 0 3 while uppermost strata are enriched in k2o having k2o al2o3 ratios greater than 0 3 the index of compositional variability a measure of compositional maturity is less than 0 6 in the lower to middle section whereas in the uppermost strata it is greater than 0 7 similar trends are reflected in a cn k space compared to paas mudrocks of the pyeongan supergroup except for those in uppermost units they are depleted in mn ca and na and are slightly depleted in mg and p contrasting major oxide trends between the lower and middle parts of the pyeongan and the uppermost units are due to decreasing proportions of clay minerals and a concomitant increase in the proportion of nonclay silicate minerals due to increasing input of first cycle detritus excursions marked by increases in mgo na2o and cao reflect large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift incompatible elements are generally enriched in mudrocks of the pyeongan supergroup relative to paas while transition metals co ni cr and v are progressively depleted in younger parts of the section total rare earth element concentrations are higher than paas but chondrite normalized patterns display the typical lree enriched pattern of paas eu anomalies for most mudrocks are close to that of paas the youngest mudrocks in the pyeongan supergroup have the most negative values these trends can be explained by a sedimentary system dominated by detritus derived from recycled highly weathered granitic materials in the lower to middle pyeongan section with an increased proportion of less weathered detritus derived from fractionated granitic materials in uppermost strata such an interpretation is consistent with the results of studies on coarse grained sediments of the pyeongan supergroup

circulation induced by isolated dense water formation over closed topographic contours abstractthe problem of localized dense water formation over a sloping bottom is considered for the general case in which the topography forms a closed contour this class of problems is motivated by topography around islands or shallow shoals in which convection resulting from brine rejection or surface heat loss reaches the bottom the focus of this study is on the large scale circulation that is forced far from the region of surface forcing the authors find that a cyclonic current is generated around the topography in the opposite sense to the propagation of the dense water plume in physical terms this current results from the propagation of low sea surface height from the region of dense water formation anticyclonically along the topographic contours back to the formation region this pressure gradient is then balanced by a cyclonic geostrophic flow this basic structure is well predicted by a linear quasigeostrophic theory a primitive equation model and in rotating tank experiments for sufficie

origin and history of hydrothermal fluids of the reykjanes and krafla geothermal fields iceland the reykjanes and krafla geothermal fields are both examples of active high temperature systems and show similar assemblages of alteration minerals but the fluid at reykjanes is dominantly sea water whereas that at krafla is meteoric oxygen isotope analyses of surface rock and of drill chip samples from different depths are presented together with results for the krafla fluid which is close to local precipitation 18o 11 9 d 86 8

opaque minerals in geothermal well no 7 krafla northern iceland abstract study of the opaque minerals from well no 7 krafla indicates two mineral assemblages 1 hydrothermally altered igneous minerals and 2 secondary minerals that have precipitated from the geothermal fluid at depths down to 2140 m and at temperatures up to more than 340 c chief amongst the chemically precipitated minerals are pyrite pyrrhotite and goethite which is described here for the first time in an icelandic geothermal drill hole the geothermal system at krafla has been periodically disturbed by the influx of volcanic emanations this article attempts to interpret by use of thermochemical calculations the processes affecting the precipitated mineral assemblage

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

sandstone detrital modes central utah foreland region stratigraphic record of cretaceous paleogene tectonic evolution abstract within a sedimentary basin the analysis of sandstone petrofacies defined by detrital modes of framework grains is a powerful means to detect areal or temporal changes in provenance related to evolving paleotectonics and paleogeography in the central utah foreland the regional tectonic transition from thin skinned sevier thrusting during the late cretaceous to deep seated laramide deformation during the paleogene is recorded by four contrasting petrofacies in uppermost cretaceous and paleogene sandstones of fluvial and deltaic facies coeval subaqueous environments were marine during the cretaceous and lacustrine during the paleogene the cretaceous quartzose petrofacies qm93 f1 lt6 of mainly campanian age was derived from sedime tary sources in the active sevier thrust belt and transported into a broad adjacent foreland basin by transverse paleocurrents the heterogeneous cretaceous quartzolithic petrofacies qm40 70 f5 20 lt25 40 of uppermost campanian age was derived from the sevier orogenic belt during the waning phases of sevier tectonism and was distributed by longitudinal paleocurrents within a foreland basin whose floor had begun to be deformed by incipient laramide tectonism the paleogene feldspathic petrofacies qm50 f35 lt15 in paleocene and eocene strata is composed of arkosic detritus that was derived principally from basement rocks then exposed in the extensive san luis uplift of laramide age in south central colorado the feldspathic sand was transported to the laramide uinta basin and vicinity in utah by a trunk river which flowed generally northwestward between monoclinal laramide uplifts of the colorado plateau the paleogene quartzolithic petrofacies qm75 f2 lt23 of dominantly eocene age was derived mainly from sedimentary sources in the laramide uinta uplift to the north but also in part from similar sources in the dormant sevier thrust belt to the west in the rocky mountain and intermountain regions more widespread and systematic use of petrofacies analysis in combination with standard paleocurrent and lithofacies analyses could lead to better definition of the timing of laramide uplift and improved understandi g of the evolution of complex laramide paleogeography

late palaeozoic to early mesozoic geodynamic evolution of the circum pacific orogenic belt in south korea and southwest japan abstract a review of the overall features of the late palaeozoic early mesozoic orogen of southwest japan and its korean hinterland allows a new geodynamic model for the building of the east asian margin to be proposed during middle carboniferous to early permian times an oceanic basin formed in a passive margin environment at a moderate spreading rate as the honshu continental block drifted away from the sino korean continent during that period paralic platform conditions and extensional synsedimentary tectonics prevailed in korea in middle permian times the closure of the oceanic area was responsible for yakuno ophiolite obduction and high pressure metamorphism while highly subsiding coal basins developed in the emerged korean hinterland thereafter in late permian times when the honshu block collided with the asian margin akiyoshi orogeny locally derived terrestrial clastic sedimentation in korea has succeeded coal measure deposition with local unconformity in early triassic times the collision was completed and regional uplift of the thickened crust resulted in the deposition of thick distal siliciclastic rocks in rapidly subsiding hinterland troughs korea and flyschoid deposition in the tamba foreland basin outer zone of southwest japan middle to late triassic medium to low pressure metamorphism large scale transcurrent tectonics and associated calc alkaline synkinematic plutonism in the hida and ogcheon belts represent a post collisional feature of the akiyoshi orogenic event post tectonic intrusives and terrestrial deposits post date intracratonic tectonics at ca 200 ma thus the akiyoshi orogeny of southwest japan is a result of continental drift and ensuing collisional rewelding of a fragment of sino korea the honshu microcontinent

tectonometamorphic evolution of the permo triassic songrim indosinian orogeny evidence from the late paleozoic pyeongan supergroup in the northeastern taebaeksan basin south korea the deformed and metamorphosed middle pennsylvanian to early triassic rocks of the pyeongan supergroup occurring in northeastern flank of the paleozoic taebaeksan basin east central south korea record the impact of the late permian triassic songrim indosinian collisional orogeny in the eastern eurasia margin analysis of meso and microstructures and their relationship with porphyroblast growth has revealed that these metasedimentary rocks were affected by four deformation events d1 d4 during the polyphase deformations successive foliations with alternately steep s1 and s3 and flat lying s2 and s4 orientations were produced with growth of chloritoid andalusite and kyanite porphyroblasts during d1 and d2 and growth of garnet staurolite and andalusite porphyroblasts during d3 and d4 shrimp u pb detrital zircon ages 330 310 ma from metapelites in the oldest unit of the pyeongan supergroup in the study area combined with the previous data on sandstone compositions indicate magmatic activity that was contemporaneous with the initial deposition of the pyeongan supergroup this also suggests that the pyeongan supergroup was deposited in an arc related foreland basin at an active continental margin during the late carboniferous and permian time two contractional deformation events d1 and d3 and two events related to gravitational flattening d2 and d4 along with barrovian type medium pressure regional metamorphism may have resulted from the late permian triassic songrim orogeny related to collision between the north and south china blocks and or collision between the eastern eurasia margin and the proto japan terrane

sandstone composition of the upper jurassic emuerhe formation from the mohe basin china the sandstone composition analysis carried out on the samples from three different sections western section middle section and eastern section of the upper jurassic emuerhe formation in the mohe basin northeastern china reveals that the okhotsk orogenic belt and the ergun massif basement are the source areas for the emuerhe formation the source area of the western section and the a segment of the middle section is the okhotsk orogenic belt the tectonic attributes of the okhotsk orogenic belt are those of a dissected arc the transportation distance of clastic rocks from these sections gradually lengthened and the uplift rate of the okhotsk orogenic belt gradually increased the source area of the eastern section and the b segment of the middle section is the ergun massif basement compared with the okhotsk orogenic belt the tectonic attributes and uplift rate of the ergun massif basement are different from the former the attributes of the ergun massif basement are those of basement uplift the transportation distance of clastic rocks from the eastern section and the b segment of the middle section gradually shortened and the uplift rate of the ergun massif basement gradually decreased these conclusions are consistent with the characteristics of a foreland basin thus we can draw the conclusion that the mohe basin belongs to the foreland basin

detrital modes of the pyeongan supergroup late carboniferous early triassic sandstones in the samcheog coalfield korea implications for provenance and tectonic setting abstract medium to coarse sandstones of the carboniferous to early triassic pyeongan supergroup in the samcheog coalfield korea were studied to infer the provenance and tectonic settings of the source areas sandstone detrital modes change upwards stratigraphically sandstone types from the manhang to dosagog formations low to middle in the sequence are quartzarenite and sublitharenite to litharenite whereas sandstones of the gohan and donggo formations high in the sequence are feldspathic litharenite and arkose respectively using various ternary diagrams the provenance of the manhang to gohan formations is suggested to be a recycled orogen setting some gohan formation sandstones plot within the arc related setting field and the donggo formation sandstones plot within both continental block and recycled orogen fields results of quartz grain petrography are consistent with those of detrital modes quartz in sandstones of all units except the donggo formation indicates derivation from low rank metamorphic sources quartz in donggo sandstones was derived from medium to high rank metamorphic and plutonic source rocks considering the sandstone composition and palaeocurrent data the pyeongan supergroup probably was deposited in a molasse foreland basin and was derived from a synbasinal orogenic belt probably the akiyoshi orogen located in southwest japan

multiple sulfur isotope systematics of icelandic geothermal fluids and the source and reactions of sulfur in volcanic geothermal systems at divergent plate boundaries abstract multiple sulfur isotope systematics of geothermal fluids at krafla northeast iceland were studied in order to determine the source and reactions of sulfur in this system as an example of a geothermal system hosted on a divergent plate boundary fluid temperatures ranged from 192 to 437 c and the fluids have low cl concentration between 10 and 150 ppm with liquid water and vapor being present in the reservoir dissolved sulfide s ii and sulfate svi predominated in the water phase with trace concentrations of thiosulfate s 2 o 3 2 whereas sulfide s ii was the only species observed in the vapor phase the reconstructed sulfur isotope ratios of the reservoir fluids based on samples collected at surface from two phase and vapor only well discharges indicated that 34s and 33s of sulfide in the reservoir fluid ranged from 1 5 to 1 1 and 0 001 to 0 017 respectively whereas 34s and 33s of sulfate were significantly different and ranged from 3 4 to 13 4 and 0 000 to 0 036 respectively depressurization boiling upon fluid ascent coupled with progressive fluid rock interaction and sulfide mineral pyrite formation results in the liquid phase becoming progressively isotopically lighter with respect to both 34s and 33s in contrast h2s in the vapor phase and pyrite become isotopically heavier the observed 33s and 34s systematics for geothermal fluids at krafla suggest that the source of sulfide in the reservoir fluids is the basaltic magma either through degassing or upon dissolution of unaltered basalts at high temperatures insignificant so4 was observed in the fluids but below 230 c significant concentrations of so4 were observed the source inferred to be h2s oxidation the two key factors controlling the multiple sulfur isotope systematics of geothermal fluids are 1 the isotopic composition of the source material and 2 the isotope fractionation associated with aqueous and vapor speciation and how these change as a function of processes occurring in the system including boiling oxidation and fluid rock interaction

provenance evolution and unroofing history of a modern arc continent collision evidence from petrography of plio pleistocene sandstones eastern taiwan abstract plio pleistocene sandstones from the coastal range of eastern taiwan provide a record of shifting source areas and unroofing events in adjacent arc and accretionary wedge terranes during the early stages of are continent collision in latest miocene and early pliocene time arc derived sediments were deposited in a precollisional forearc basin between the luzon volcanic arc and the manila trench sandstones of this age are rich in zoned plagioclase volcanic lithic fragments and pelagic foraminifera and contain only minor quartz and sedimentary metasedimentary lithic fragments in contrast lower pliocene to lower pleistocene sandstones are poor in feldspar and volcanic fragments and contain abundant sedimentary and metasedimentary lithic fragments this reflects a provenance shift f om the volcanic arc to the uplifted meta sedimentary accretionary wedge of proto taiwan which resulted from the early pliocene onset of arc continent collision a refined classification of sedimentary and metasedimentary lithic fragments is introduced here and used to interpret the early evolution of the collisional orogen lithic fragments are rich in pelitic minerals and are divided into 1 sedimentary ls mudstone shale siltstone chert and argillite 2 low grade metamorphic lm1 slate slatey siltstone and quartzite and 3 medium grade metamorphic lm2 phyllite schist phyllitic quartzite and quartz mica albite aggregate a good correlation is observed between these lithic fragment types and bedrock lithologies exposed in the present day central range of taiwan based on this correlation the change in relative abundance of sedimentary and metasedimentary lithic fragments through time has been used to interpret an unroofing sequence for the collisional fold and thrust belt lower pliocene taiwan derived sandstones are rich in sedimentary lithic fragments ls which were shed from the accretionary wedge during the earliest stages of arc continent collision from early pliocene to early pleistocene time sandstones became progressively depleted in ls lithic fragments and enriched first in lm1 and later in lm2 fragments as deeper levels in the metamorphic complex were uplifted and exposed to erosion regional metamorphism of biotite grade rocks lm2 occurred at about 4 5 ma at depths of 12 15 km ernst 1983 and were uplifted to the surface by about 1 4 ma this study these ages give an uplift rate of 4 to 5 km m y which is in good agreement with independent estimates based on fission track studies raised coral reefs quaternary elevation changes and present day denudation rates thus it appears that sandstone detrital modes of clastic orogenic sequences can be used to interpret specific aspects of unroofing and tectonic evolution in nearby active mountain belts

dense water formation around islands 1 basic constraints on the dense water formation rate and circulation resulting from cooling around an island are discussed the domain under consideration consists of an island surrounded by a shelf a continental slope and a stratified ocean atmospheric cooling over the shelf forms a dense water that penetrates down the sloping bottom into the stratified basin strong azimuthal flows are generated over the sloping bottom as a result of thermal wind thermally direct and indirect mean overturning cells are also forced over the slope as a result of bands of convergent and divergent reynolds stresses associated with the jets the coriolis force associated with the net mass flux into the downwelling region over the slope is balanced by these nonlinear terms giving rise to a fundamentally different momentum budget than arises in semienclosed marginal seas subject to cooling a similar momentum balance is found for cases with canyons and ridges around the island provided that the terms are considered in a coordinate system that follows the topography both eddy fluxes and the mean overturning cells are important for the radial heat flux although the eddy fluxes typically dominate the properties of the dense water formed over the shelf temperature diapycnal mass flux are predicted well by application of baroclinic instability theory and simple heat and mass budgets it is shown that each of these quantities depends only on a nondimensional number derived from environmental parameters such as the shelf depth coriolis parameter offshore temperature field and atmospheric forcing

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

petrology of late paleozoic early mesozoic pyeongan group sandstones gohan area south korea and its provenance and tectonic implications abstract carboniferous to triassic strata of the pyeongan group crop out in the gohan area northeastern south korea these strata consist in ascending order of the hongjeom sadong gobangsan and nogam formations sandstones in these formations comprise three distinct framework mineral suites suite 1 sandstones hongjeom formation through the middle member of gobangsan formation are quartz and quartzose arenites wackes that contain abundant quartz little or no feldspar and few acid volcanic clasts heavy minerals are mainly tourmaline rutile and zircon suite 2 sandstones upper member of gobangsan formation are lithic arenites wackes characterized by moderate quartz content low amounts of feldspar and moderate to abundant volcanic clasts sphene is the predominant heavy mineral suite 3 sandstones nogam formation are feldspathic arenites wackes distinguished by low quartz content moderate to abundant feldspar and low amounts of acid volcanic clasts the heavy mineral assemblage of the nogam formation is characterized particularly by epidote and sphene feldspar poor suite 1 sandstones were derived from a source terrain rich in quartzite and quartzose sandstone abundant quartz and stable heavy minerals were supplied initially during late carboniferous time to a shallow marine shelf which changed gradually near the end of carboniferous time to a nonmarine paralic platform setting electron probe microanalysis shows that suite 1 tourmaline was derived originally from li poor granitoids pegmatites and ca poor aplite and metapsammite petrographic evidence demonstrates that the scarcity of feldspars in suite 1 sandstones is not the result of diagenetic intrastratal solution major changes in mineralogy from suite 1 into suite 2 and suite 3 sandstone indicate changes in provenance suite 2 sandstones were derived from diorite granodiorite acid volcanic rocks and possibly some metamorphic rocks which furnished feldspars and sphene the appearance of feldspars and volcanic rock fragments in these sandstones reflects orogenic changes and uplift resulting from incipient collision of the asian mainland and the honshu block of southwest japan compositionally immature suite 3 sandstones were derived mainly from granite granodiorite and granitic gneiss indicating continuing uplift these source rocks provided quartz k feldspar plagioclase epidote and sphene acid volcanic rocks supplied minor amounts of rock fragments

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

composition of geothermal minerals from saline and dilute fluids krafla and reykjanes iceland abstract in high temperature geothermal areas t 200 c in iceland the alteration minerals formed show a regular zoning with increasing temperature i e smectite chlorite epidote and actinolite to test the effect of varying composition of the hydrothermal circulation fluid drillhole chips from two contrasting areas were analyzed in detail the reykjanes area is fed with sea water while krafla is fed with meteoric water and has a cl concentration of 28 ppm both areas have tholeiitic basalts lavas and hyaloclastites as original reservoir rocks although both systems have the same sequence of alteration minerals the actual composition of the minerals differs between systems reflecting the different chemical composition of the circulating waters in reykjanes with its brine fluid the composition of the original rock appears not to affect the composition of the alteration minerals while the reverse appears to be the case in krafla

magnetization of the la palma seamount series implications for seamount paleopoles paleopoles determined from seamount magnetic anomalies constitute the major data source for the pacific apparent polar wander path but relatively little is known about the processes of remanence acquisition in seamounts since magnetic anomalies reflect both natural remanence nrm and the induced field it is important first to assess whether the nrm is likely to represent an original field direction and second to constrain the magnitude of the induced component to this end we present paleomagnetic data from an uplifted subaerially exposed section through a seamount on la palma canary islands the pliocene seamount series of la palma comprises a 6 km sequence of alkalic extrusives and intrusives which includes all lithologies likely to be volumetrically important in seamounts the structural tilt of the seamount series allows separation of early thermal or chemical remanence from magnetization components acquired after tilting e g viscous remanence the nrm provides a poor indication of the original magnetization direction although the characteristic magnetization of many la palma samples is compatible with the original pretilt direction hydrothermal alteration has resulted in the production of ti poor magnetite and an increasing contribution of hematite with increasing degree of alteration more importantly well defined magnetization directions which deviate from any reasonable geomagnetic direction at la palma can be attributed to hydrothermal alteration in a different polarity than prevalent during the original magnetization based on a comparison of the magnitude of low stability components of magnetization and laboratory acquisition of viscous remanence and previous estimates of the induced magnetization we conclude that viscous and induced magnetization probably account for 15 25 of the total magnetization of seamounts the resulting paleopole bias is a function of the polarity and paleolatitude of the seamount and ranges from 4o to 16 o for cretaceous seamounts in the pacific

the tectonic setting of the eastern margin of the sino korean block inferred from detrital zircon u pb age and nd isotope composition of the pyeongan supergroup upper palaeozoic lower triassic korea the upper palaeozoic succession pyeongan supergroup in central eastern korea is well correlated with the equivalent successions distributed in north china suggestive of the korean upper palaeozoic being part of the sino korean block detrital zircon u pb ages and sm nd isotope compositions of the pyeongan supergroup in the samcheok coalfield of the taebaeksan basin were analysed a single predominant zircon age peak at c 1 9 ga 70 is marked in all sedimentary units followed by varying amounts of minor late palaeozoic grains up to 30 the rarity of meso to neoproterozoic and silurian aged zircons confirms that sediment influx from the south china and qinling blocks was insignificant the 2 0 1 8 ga dominated zircon age pattern and the nd isotope composition average end 0 15 5 4 0 of the pyeongan supergroup most closely reflect the signature of the yeongnam massif basements which supports a previous hypothesis that the pyeongan supergroup was mostly derived from a palaeo orogen located to the east southeast relatively higher end 0 values 10 1 in the lowermost and the upper parts of the succession are closely matched by the increased occurrence of syn depositional aged zircons which indicates considerable mixing of juvenile materials at c 320 ma and 260 ma both arc related magmatic events are interpreted to have been related to oceanic subduction suggesting that the eastern margin of the sino korean block was an active continental margin during late palaeozoic times

elastic deformation models of krafla volcano iceland for the decade 1975 through 1985 the dynamics of the shallow magma reservoir at krafla volcano in ne iceland have been analyzed with three types of elastic models based on over 70 surveys of tilt and displacement made from 1975 to 1985 a period of continuous volcano tectonic activity modeling results are integrated with geophysical and geological information to estimate the position geometry and volume change of magma reservoir domains subjected to periodic inflation and deflation dominating influences on magma reservoir dynamics are examined in the context of activity in krafla s associated rift system and the deformation of its caldera from 1975 1985 rather than the fluid filled cavity concept of mogi 1958 and most recent workers our models are idealized as strained regions with spherical double spherical or general ellipsoidal symmetry the models are mathematically generalized from that of mogi 1958 and are derived by inversion of displacements model results from different displacement components are remarkably consistent although models based on vertical displacements typically have errors of fit much closer to expected measurement errors than those based on tilt or horizontal displacements about one half of the double sphere and ellipsoid models have significantly better fits than single sphere models double sphere model results are consistent with a 2 to 3 km center to center separation of magma storage zones from at least 2 km to 4 km depth by portions of the fissure system as implied by s wave attenuation patterns for 1976 1977 however all models suggest pressurization zones of more limited extent than possible domains of storage inferred from s wave attenuation ellipsoid models typically implied unrealistically shallow depths of magma storage caldera inflation rates decreased after january 1978 when the caldera periodically reinflated to its level prior to the initial december 1975 deflation event from 1975 1980 the volume and duration of inflation between deflation events was strongly correlated with the volume of the previous deflation after 1980 there was a significant increase in the duration of inflation periods and a decrease in rates of caldera inflation and fissure system widening consistent with these results the magma reservoir is conceptualized as a hot rock mass containing numerous magma chambers and pressure sensitive conduits connecting the chambers and deep magma sources magma is injected into the fissure system at critical pressures determined by the confining stress and rock mass strength the duration and volume of inflation required to reach a critical pressure threshold is largely dependent on the volume of magma released in the previous deflation reduction of the extension rate across the krafla fissure system after 1980 suggests that extensional forces were also reduced a resultant rise of confining pressure on the magma reservoir and a reduced capacity of the fissure system to accommodate dike injection in combination would have increased critical stress levels for reservoir deflation and reduced the pressure gradient driving magma supply from deep sources

lithostratigraphy and depositional environments of the pyeongan supergroup carboniferous permian in the taebaek area mid east korea abstract the pyeongan supergroup carboniferous permian consists of a thick siliciclastic sequence 1700 m thick recent sedimentological work in the taebaek area has refined the lithostratigraphic units manhang geumcheon jangseong hambaeksan dosagok gohan and donggo formations in ascending order the entire sequence is represented by thirteen sedimentary facies which can be organized into seven facies associations fa the lower part of the manhang formation fa 1 moscovian consists of crudely cross stratified conglomerate massive sandstone and gray homogeneous siltstone formed in shoreface off river mouth whereas purple siltstone and grainstone of the upper part fa 2 probably formed in a coastal plain environment the geumcheon jangseong formation moscovian artinskian consists of dark gray sandstone dark gray shale coal and bioturbated wackestone fa 3 formed in a lagoonal environment the hambaeksan formation kungurian comprises milky white crudely stratified conglomerate gray coarse sandstone and partly laminated black shale fa 4 representing a shoreface progradation the dosagok formation late permian is characterized by an alternation of purple fine sandstone and conglomerate fa 5 formed in a bedload dominated fluvial system the gohan formation late permian is mostly composed of upward fining units massive sandstone to dark gray siltstone fa 6 suggesting a restricted inter distributary bay environment the donggo formation late permian consists of cross stratified coarse sandstone and purple sandstone fa 7 interpreted as deposits of perennial sandy braided river system

is the ogcheon metamorphic belt of korea the eastward continuation of the nanhua basin of china abstract the ogcheon metamorphic belt in central korea has been interpreted to be the eastward extension of the nanhua basin aulacogen of southeast china in this paper comparisons are made between the two regions based on stratigraphic thermal tectonic and other considerations from this comparison correlation of geological events between the nanhua basin and ogcheon metamorphic belt are at best equivocal the closest similarity is the presence in both regions of two major diamictite units of glacial origin and neoproterozoic age 750 690 ma range in china but of controversial origin and uncertain age in korea volcanic rocks in both regions appear to have similar petrological and geochemical traits and are interpreted to be rift related however their ages are different mostly 795 780 ma in the nanhua basin and c 750 ma in central korea so correlation remains uncertain more isotopic data from both regions may shed light on this comparison correlation between other pre carboniferous stratigraphic units in the two regions is hampered by the uncertainty about the stratigraphic age and succession in the ogcheon metamorphic belt stemming mainly from the absence of fossils and the strong tectonic metamorphic overprint both regions appear to have undergone deformation and metamorphism during the middle triassic indosinian songrim in some uncertain way related to the collision between the north and south china plates in the ogcheon metamorphic belt there has been no confirmation of a mid palaeozoic event but in the nanhua basin that event is recorded by stratigraphic and palaeogeographic evidence in the nanhua basin there is no evidence for an early permian metamorphic event that appears on isotopic grounds to have affected the ogcheon metamorphic belt this apparent difference has been interpreted as a result of diachronous deformation during late palaeozoic early mesozoic plate collisions that took place earlier in the east in korea than in the west in china

the dispersal of dense water formed in an idealized coastal polynya on a shallow sloping shelf abstractthis study examines the dispersal of dense water formed in an idealized coastal polynya on a sloping shelf in the absence of ambient circulation and stratification both numerical and laboratory experiments reveal two separate bottom pathways for the dense water an offshore plume moving downslope into deeper ambient water and a coastal current flowing in the direction of kelvin wave propagation scaling analysis shows that the velocity of the offshore plume is proportional not only to the reduced gravity bottom slope and inverse of the coriolis parameter but also to the ratio of the dense water depth to total water depth the dense water coastal current is generated by the along shelf baroclinic pressure gradient its dynamics can be separated into two stages i near the source region where viscous terms are negligible its speed is proportional to the reduced gravity wave speed and ii in the far field where bottom drag becomes important and balances the pressure gradient the velocity i

the pyeongan supergroup upper paleozoic lower triassic in the okcheon belt korea a review of stratigraphy and detrital zircon provenance and its implications for the tectonic setting of the eastern sino korean block abstract the tectonic setting of the okcheon belt in the korean peninsula has long been regarded as one of the important topics in discussing east asian tectonics the controversial tectonic setting of the okcheon belt before the triassic collision between north and south china limits proper understanding of the late paleozoic tectonics of east asia focusing on the upper paleozoic to lower triassic pyeongan supergroup coeval sedimentary records in different parts of the okcheon belt are reviewed this study has a clear advantage over previous assessments that build upon comparison between meta sedimentary units of unknown age in the region the pyeongan supergroup sediments show high similarity in both stratigraphy and detrital zircon u pb ages throughout the okcheon belt they are distinct from their age equivalents in south china while sharing characteristics with those in north korea and north china critical criteria include marine influence and enrichment of organic materials at each time period and relative proportion of mesoproterozoic silurian components in detrital zircon age population the combined results agree with the view that the entire okcheon belt was a single tectonic unit at least by the late carboniferous the results of this study favor the idea of the sino korean block encompassing the whole korean peninsula and cast doubts on the tectonic models that attribute the southern part of the korean peninsula to the south china block a retroarc foreland basin setting of the okcheon belt with detritus mainly provided from a subduction related orogen in the continent sided japan is inferred from the provenance characteristics of the detrital zircons

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

exceptions to the relationship between plate tectonics and sandstone composition abstract routine use of qfl qplsmlvm and lmlslv plate tectonic provenance diagrams has led to the recognition of error populations for these sandstones the interpretation of tectonic setting based on data exclusive of petrography does not coincide with the interpretation of tectonic setting based on their location on compositional diagrams the anomalous sandstones can be separated into at least four categories i sandstones deposited during the transition between tectonic regimes may be derived in part from relict source rocks ii the relative enrichment of sandstones in detrital quartz by weathering and or depositional reworking may lead to an inaccurate interpretation of tectonic setting from compositional data iii sandstones deposited in tectonic settings as yet unrepresented on he provenance diagrams may plot between the provenance fields or overlap existing fields iv the role of detrital carbonate rock fragments directly affects the location of data points on provenance diagrams and is an unresolved problem the first two categories represent permanent problems in the use of sandstone composition as an indicator of plate tectonic setting whereas the last two may only be temporary problems that can be solved by more data and a consensus on determining detrital modes recognition of anomalous sandstones in the rock record will reduce the probability of erroneous interpretations of tectonic setting and enhance the use of sandstone petrology as an indicator of plate tectonic setting

quartz grain types in holocene deposits from the spanish central system some problems in provenance analysis holocene sands of the spanish central system were exclusively derived from plutonic middle upper grade and low grade metamorphic rocks modal composition of studied sands is mostly controlled by grain size and source area lithology thus sands derived from slates and schists plot near the qr edge on the qfr diagram for ali grain size fractions sands derived from granitic or gneissic rocks have a wide dispersion on the qfr diagram from the r pole to the qf edge depending on sand grain size percentages of quartz types in granitic derived sands are qnu42 qu40 qp2 314 and qp 34 sands of gneissic origin have qnu 51 qu 1 5 qp2 323 and qp 311 sands derived from slates and schists have qnu 20 qu 1 2 qp2 35 and qp 363 quartz types easily discrimina te sands of low grade origin but distinction of sands derived from plutonic rocks from those derived from middle upper grade metamorphic rocks is difficult because of the highly variable qu content of plutonic rocks related to strain history and crystallization conditions thus quartz types mus be used with caution in source discrimination if plutonic rocks are present in the source area

petrology of holocene sand peninsular ranges california and baja norte mexico implications for provenance discrimination models abstract the peninsular ranges of southern california and baja california norte mexico represent an uplifted and variably dissected mesozoic magmatic arc they are composed mostly of cretaceous plutonic rocks and mesozoic greenschist to amphibolite facies metasedimentary and metavolcanic rocks in order to evaluate the reliability of the diamond shaped qnuquqp provenance discrimination diagram developed by basu et al 1975 and the qfl provenance discrimination diagram developed by dickinson et al 1983 we collected 62 samples of holocene sand from four drainage basins along the west side of the peninsular ranges the qfl composition of each specimen was determined by the gazzi dickinson point counting method the relative percentages of med um grained fragments of qnu qu and qp were determined by counting 100 grains in each specimen the results of our study indicate that holocene sands derived from the peninsular ranges have the following average petrological characteristics 1 sands derived mostly or exclusively from plutonic rocks are composed of 16 46 percent q 54 83 percent f and 0 2 0 5 percent l the medium grained quartz population produced by erosion of mostly or exclusively plutonic rocks consists of 61 77 percent qnu 4 17 percent qu and 13 27 percent qp 2 sands originating from the erosion of metasedimentary rocks are composed of 63 percent q 13 percent f and 24 percent l the medium grained quartz population derived from a metasedimentary source is made up of 25 percent qnu 9 percent qu and 66 percent qp 3 sands produced by the erosion of mostly or exclusively metavolcanic rocks are composed of 19 percent q 39 44 percent f and 38 43 percent l the medium grained quartz population originating from a mostly or exclusively metavolcanic source consists of 48 74 percent qnu 6 percent qu and 20 46 percent qp petrological data obtained during this study indicate that the qfl provenance discrimination model generally yields a correct interpretation of tectonic setting when applied to holocene sand from the peninsular ranges data however also show that local source areas produce sands that when interpreted on the basis of their position on the qfl provenance discrimination diagram yield an erroneous interpretation of tectonic setting data obtained from counting varieties of medium grained quartz show that detrital quartz populations produced by plutonic rocks are discriminated from those derived from metasedimentary rocks by the qnuquqp provenance discrimination diagram in contrast quartz populations originating from a mostly or exclusively metavolcanic source are difficult to interpret on the qnuquqp diagram therefore we recommend that the qfl provenance discrimination model be used with caution when sand or sandstone samples are from a limited geographic area and that the qnuquqp provenance discrimination diagram be used with prudence when metavolcanics are suspected in the provenance

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

provenance of the qingshuijian formation late carboniferous ne china implications for tectonic processes in the northern margin of the north china block the upper carboniferous qingshuijian formation in the western hill ne china was deposited disconformably on a lower paleozoic platformal carbonate sequence the provenance and the tectonic setting of the source area of the qingshuijian formation were studied using sandstone petrography and mudstone geochemistry sandstones consist mainly of quartz and meta sedimentary lithic fragments and are classified as litharenite feldspar is lacking in sandstones and negative eu anomalies similar to those displayed by post archean australian shale paas along with depleted ca na cs and rb and low k2o al2o3 ratios in mudstones all suggest that feldspar was scarce in the source terrane abundant sedimentary lithic fragments in sandstones low values of the index of compositional variability 1 values of chemical index of alteration higher than paas depleted transition metals higher total ree abundances and more fractionated ree patterns than paas all indicate that the source area was dominated by sedimentary rocks geochemical and sandstone tectonic discrimination diagrams suggest that the provenance of the qingshuijian formation was a recycled orogen composed of quartzose to lithic sedimentary rocks that were deposited originally in a passive margin setting the yinshan uplift located in the northern margin of the north china block that formed as a result of the collision between the north china block and the mongolian continent is interpreted to be the provenance for the qingshuijian formation during collision the intervening sea floor was subducted northward and an accretionary prism was elevated forming a barrier to arc derived sediments

modification of the magnetic mineralogy in basalts due to fluid rock interactions in a high temperature geothermal system krafla iceland summary active high temperature 150 c geothermal areas like the krafla caldera ne iceland often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity the main alteration processes in such an environment are low temperature oxidation 350 c maghemitization and fluid rock interactions we investigated the rock magnetic properties natural remanent magnetization nrm magnetic susceptibility and their temperature and field variation and the mineralogy using x ray diffraction microscopic methods and electron microprobe analyses of two drill cores kh1 and kh3 from the rim of the krafla caldera the drill cores have distinctly lower nrm values average 3 a m 1 compared to younger surface basalts average 20 a m 1 along with a large variation in magnetic susceptibility 1 3 10 7 4 9 10 5 m3 kg 1 the secondary mineral assemblage sulphides sphene rutile and chlorite indicates an alteration within the chlorite smectite zone for both cores without depth zoning optical miscroscopy in combination with the bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite 1 titanomaghemite with intermediate titanium concentration and probably high vacancy concentration and 2 titanomaghemite with low titanium concentration and low vacancy concentration the mineral assemblages textures and magnetic properties deduced from the mentioned magnetic measurements indicate two stage transformation mechanism 1 dissolution of titanium at low ph under oxidizing conditions the ulvospinel component of titanomagnetite and ilmenite forms rutile or sphene and fe2 migrates out of the spinel lattice forming titanomaghemite 2 formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions the latter mechanism produces ghost textures all titanomaghemite is transformed and only their former grain shapes are preserved with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved this mechanism could explain the significant magnetization loss which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like iceland or hawaii the production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of krafla

the emergence of the north icelandic jet and its evolution from northeast iceland to denmark strait abstractthe north icelandic jet nij is an important source of dense water to the overflow plume passing through denmark strait the properties structure and transport of the nij are investigate

petrography and major element geochemistry of the permo triassic sandstones central india implications for provenance in an intracratonic pull apart basin abstract detrital mode composition of feldspars and heavy minerals and major element chemistry of sandstones from the permo triassic succession in the intracratonic satpura gondwana basin central india have been used to investigate provenance the talchir formation the lowermost unit of the succession comprises glacio marine and glacio fluvial deposits the rest of the succession base to top comprising the barakar motur bijori pachmarhi and denwa formations largely represent variety of fluvial depositional systems with minor fluvio deltaic and fluvio lacustrine sedimentation under a variety of climatic conditions including cold warm arid sub humid and semi arid qfl compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault bounded basement uplift tectonic setting compositional maturity of sandstones gradually increases upwards from the early permian talchir to the middle triassic denwa but is punctuated by a sharp peak of increased maturity in the barakar sandstones this temporal change in maturity was primarily controlled by temporal variation in fault induced basement uplift in the craton and was also influenced by climatic factors plots of different quartz types suggest plutonic source rocks for the talchir sandstones and medium to high rank metamorphic plus plutonic source rocks for the younger sandstones composition of alkali feldspars in the permo triassic sandstones and in different precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks compositions of plagioclase in the talchir and bijori sandstones are comparable with those of granite acid volcanic and metasedimentary rocks of the precambrian basement suggesting the latter as possible source rare presence of high k plagioclase in the talchir sandstones however indicates minor contribution from volcanic source rock exclusively plagioclase bearing metasedimentary rock tonalite gneiss and mafic rocks are the probable sources of plagioclase in the upper denwa sandstones quartz rich nature of the sandstones predominance of k feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic pull apart basin like the satpura gondwana basin composition of garnet and its comparison with that from the precambrian basement rocks suggests mica schist and amphibolite as possible sources predominance of dravite variety of tourmaline in the permian sandstones suggests sediment supply from metasedimentary rocks presence of both dravite and schorl variety of tourmaline in subequal amount in the triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks however schorl bearing rocks are absent in the basement complex of the study area a cn k plot suggests granites acid volcanic rock and meta sediments of the basement as possible sources of the talchir sandstones and metasedimentary rocks for the barakar to pachmarhi sandstones the denwa sandstones were possibly derived from k feldspar free plagioclase bearing metasediments mafic rocks and tonalite gneiss chemical index of alteration cia values suggest low intensity source rock weathering for the talchir sandstones and higher intensity source rock weathering for the others various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples

observations of hydrography and downflow of brine enriched shelf water in the storfjorden polynya svalbard 1 observations of hydrography and currents in the active storfjorden polynya during fieldwork in april 2004 and 2006 are presented the polynya adds salt from its efficient ice production usually increasing the density 0 15 kg m 3 downflow of dense water from the coastal polynya to the deeper basin enclosed by the storfjorden sill was captured in both years april 2006 had a period of strong heat loss and intense frazil ice growth in the polynya this created downflow of brine enriched shelf water bsw with a maximum salinity of 35 25 i e an increased density 0 4 kg m 3 above that of the source water in april 2004 the salinity remained lower than bsw s 34 8 reflecting the fresh source water in fall 2003 due to the heavy ice conditions in the western barents sea that year a portion 0 05 sv of such source water probably enters storfjorden through freemansundet where the mean current transports less saline and warmer water from the northwestern barents sea freemansundet has additionally a strong tidal current peaking at 53 cm s 1 dominated by the m2 component the tidal wave propagates through the narrow sound producing shallow water components and a locally well mixed water column the estimated ice production in winter 2004 twice as large as that of winter 2006 could not overcome this less saline well mixed source water bsw downflow within storfjorden was both observed and modeled to occur in areas with steep bathymetry our observations show that high resolution hydrographical data spacing less than 0 5 km are necessary to resolve such downflow consistent with the observed polynya water salinity current data at the sill showed weaker overflow in 2004 than in 2006 overflow of bsw was observed on the eastern part of the storfjorden sill in april 2006 indicating that overflow occurs across the entire sill width during the freezing period current temperature and salinity data from the overflow indicate a time lag of 12 18 days between the bsw production and the sill this downflow overflow link is confirmed by a numerical experiment and analytical scaling making results applicable to other polynyas

monitoring of fumarole discharge during the 1975 1982 rifting in krafla volcanic center north iceland abstract fumarole discharge chemistry in the krafla geothermal field changed regionally during the 1975 1982 rifting activity the discharge chemistry previously encountered in the krafla fumarole grounds was masked by a carbon dioxide rich gas during the first weeks of rifting the new discharge composition remained unchanged until 1983 when the first signs of recovery of the previous equilibrium composition appeared at the margins of the area the outgassing carbon dioxide is released from the deep aquifers beneath the area by the interaction of magmatic gas with the hydrothermal system in addition to juvenile magmatic carbon the outgassing contains carbon released from the hydrothermal systed upon reaction with acid magmatic gases increased boiling of the hydrothermal fumaroles was induced by the lowering of the partial pressure of steam due to increased gas content in the fumarole conduits at the center of rifting activity above the magma chamber the fumarole discharge was temporarily mixed with magmatic gases during local effusive activity hydrogen was the dominating magmatic gas in that discharge due to the preferred degassing of hydrogen from magma at shallow levels these hydrogen pulses increased in magnitude and duration towards the end of rifting in 1982 the discharge chemistry correlates with the expansion of the magma reservoir of the volcano regional change of long duration and local volcanism short lived change hydrogen pulses the chemical monitoring of fumaroles in krafla shows that the chemical surveillance of volcanos needs rapid methods for sampling and complete chemical analysis which can be interpreted in terms of reactions and magmatic processes

geology of the fuding inlier in southeastern china implication for late paleozoic cathaysian paleogeography abstract the age and composition of the basement rocks underlying the mesozoic volcanic rocks in southeastern china have been long debated new field investigation stratigraphical and sedimentological studies of the fuding inlier in eastern cathaysian block have identified the presence of three stratigraphic units the upper carboniferous carbonate unit composed of silicified limestone deposited on carbonate platform in a continental shelf environment the lower permian siliciclastic unit consisting of slate and phyllite with minor arenites deposited on shallow semi restricted shelf the third unit is a suite of jurassic conglomerates and sandstones deposited in alluvial fan environment provenance data indicate that the fuding inlier was part of the wuyishan terrane in the eastern cathaysian block the u pb age and hf isotope of detrital zircons indicate that extensive magmatic activity happened during 280 360 ma in the source area the e hf values of detrital zircons point to magmatic mixing of juvenile material and precambrian crust the similarities in rock compositions and detrital zircon ages among the yeongnam massif in the korean peninsula the tananao complex in taiwan and the fuding inlier have led to the conclusion that these three regions most likely belonged to the wuyishan terrane eastern cathaysia during the late paleozoic

sandstone petrofacies expressions of multiphase basinal tectonics and arc magmatism permian triassic north bowen basin australia abstract modal analyses of 209 sandstone samples from the permian triassic succession of the northern bowen basin eastern australia identify two stratigraphically and compositionally distinct petrofacies the lower to mid upper permian back creek group is characterised by petrofacies a which is quartz rich q82f8l10 it was sourced primarily from cratonic basement terranes to the west where relief was subdued and the quartz content of the sandstones may also reflect some reworking in the marine realm with a consequent loss of labile grains petrofacies b is volcanolithic and characterises alluvial sediments of the upper permian blackwater and lower triassic rewan groups it was sourced from an undissected to transitional magmatic arc provenance located in the contemporary new england orogen to the east which supplied abundant pyroclastic debris to the depositional complex petrofacies b of the northern bowen basin was derived primarily from felsic volcanics compared to an intermediate association recorded for the southern basinal sector indicating significant along arc variation in volcanic style as a consequence its framework grain population is enriched in quartz and is not readily accommodated in the schemes of provenance interpretation currently in use the consistency of framework detrital modes for sandstones distributed throughout the blackwater group q24f10l66 allows the recognition of subpetrofacies b1 and shows that the volcanism associated with the magmatic arc system was remarkably uniform in character and activity during deposition of the entire group the magmatic arc delivered almost identical sedimentary debris over a period of some 9 my in the late permian relative enrichment of quartz within the early triassic rewan group q49f6l45 relative to the blackwater group discriminates subpetrofacies b2 and is attributed to a climatic change and shift in palaeotemperature at the permian triassic boundary the contact between the marine back creek group petrofacies a and the coal bearing blackwater group petrofacies b represents an abrupt switch in provenance with little or no evidence of source mixing the boundary marks the onset of volcanism and associated tectonic uplift in the northern part of the new england orogen to the east sediment from the new source prograded rapidly westwards across the basin coincident with regression direct evidence of contemporaneous volcanism is widespread in the blackwater group as shown by tuffs and tonsteins which are distributed throughout the entire late permian succession