wind driven flow dynamics off the northwestern arabian gulf coast abstract this study investigates the wind driven hydrodynamics and their influence on the water properties temperature and salinity in the northwestern arabian persian gulf off the kuwaiti coast understanding the effects of wind driven hydrodynamics on the abrupt changes in water properties and offshore transport is key in determining the fate of the gulf s environmental sensitive species and distribution of coastal contaminants offshore observational meteorological and hydrographical data were collected from mid october 2013 to mid january 2014 at two locations using time series of the observed water current profiles we show that three wind events order of 2 3 days with wind directions parallel to the coast generated significant volume transports 1 96 m2 s in the upper layer directed perpendicular to the coast the ensuing upwelling downwelling effects appear to be generally confined to the near coast region 16 km offshore with cooler waters observed during upwelling and warmer waters during downwelling further offshore qarooh island 44 km offshore the thermal structure was found to be strongly influenced by a warm tongue that extended across the northern gulf the progression and retreat of the tongue was found to be in close response to the general wind direction during two wind events numerical simulations of the thermal structure at qarooh using a one dimensional model based on the two equation k e turbulence model showed an overall good agreement between the observations and simulations during the three wind events in particular the along shore volume transports which followed the general wind direction were captured well in the simulation however the inability of the model to reproduce effects related to the coastal boundary resulted in a poor matching of simulated and observed cross shore transports

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

a numerical investigation of circulation in the arabian gulf a three dimensional hydrodynamic model is developed to study the circulation in the arabian gulf the model contains realistic basin geometries and bathymetries of the arabian gulf and a good portion of the gulf of oman and is driven by monthly climatological winds evaporation and net ocean heat gain in both gulfs and the shatt al arab discharge it is found that the cyclonic circulation in the southern portion of the gulf is primarily driven by the evaporation induced freshening from the strait of hormuz in the northwestern corner of the gulf the shatt al arab discharge maintains the cyclonic circulation which would otherwise be anticyclonic the northwestward intrusion of fresher water along the iranian coast is weakened by northwesterly winds in winter but strengthens and extends almost to the head of the gulf in summer owing to the warming of the gulf of oman waters the development of the summer thermocline in the arabian gulf and diminishing winds the southward coastal current along the arabian coast is most prominent between the head of the gulf and qatar the model also predicts a strong southward coastal jet east of qatar which is primarily wind driven no similar coastal jet can be developed in the gulf of salwa west of qatar

a prolonged high salinity event in the northern arabian sea during 2014 17 abstracta prolonged high salinity event in the northern arabian sea to the east of the gulf of oman during 2014 17 was identified based on argo datasets the prolonged event was manifested as enh

qinling gneiss domes and implications for tectonic evolution of the early paleozoic orogen in central china abstract the qinling arc terrane qat at the southern margin of the north qinling early paleozoic orogen central china is composed of gneiss domes overridden by cold allochthon nappes the gneiss domes are characterized by migmatitic and plutonic cores of granite or gabbro and overlying upper amphibolite to granulite facies metamorphic sequences with pervasive injection of leucogranitic veins the gneiss domes display a high temperature domal foliation dipping radially away the core and a down dipping stretching lineation cascading folds occur in the mantling metamorphic rocks the new data of zircon monazite u pb dating suggest that the gabbroic and granitic plutons formed at 514 476 ma and 495 441 ma respectively whereas the high grade metamorphism of the mantling rocks took place at 469 412 ma and the leucogranitic veins formed at two main episodes 472 440 ma and 416 413 ma mica 40ar 39ar dating yields 402 328 ma for the cooling ages of the leucogranitic veins and gneissic rocks the basaltic magma underplated into the qat lower crust resulted in partial melting producing granitic magma at the late cambrian to middle ordovician during northward subduction of the shangdan proto tethyan oceanic slab buoyant upwelling of the migmatitic and plutonic core was promoted by constriction in the lower crust and decompression extension in the upper crust during the silurian since the closure of the shangdan ocean and the collision between the north china block and south china block 400 ma the qinling gneiss domes experienced rapid uplift and were finally overthrust by the upper allochthon transported from the north qinling

a hycom modeling study of the persian gulf 1 model configurations and surface circulation 1 the circulation and water mass transformation processes in the persian gulf and the water exchange with the indian ocean through the strait of hormuz are studied using the hybrid coordinate ocean model hycom model results show that the indian ocean surface water iosw propagates in two branches into the gulf one along the iranian coast toward the northern gulf and the other one onto the southern banks driven by the ekman drift due to the prevailing northwesterly winds these two branches of inflow form two cyclonic gyres in the northern and in the southern gulf a salinity front separates the fresher intruding iosw from the saltier waters in the gulf eddies with size of about 100 km are fully developed along the salinity front in summer the intrusion of the iosw in the model extends much farther into the gulf in summer than in winter by analyzing the salt balance in the basin and conducting sensitivity experiments we show that it is the balance between the advection of iosw and vertical salt flux induced by mixing that mainly controls the seasonal variation of the surface salinity surface wind stress plays a secondary role in modulating the seasonal intrusion of the iosw high frequency atmospheric forcing produces more realistic surface temperatures than obtained from climatological forcing as a result of increased heat loss in winter however the high frequency forcing does not change significantly the general features of the circulation

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 1 strait of hormuz in october and early november 1999 the gogp99 experiment collected hydrological currentmeter tide recorder thermistor and drifting buoy data near the strait of hormuz data analysis provides the water mass structure in the strait persian gulf water pgw core is banked against the omani coast while indian ocean surface water iosw lies near the iranian coast these water masses are most often covered by a homogeneous surface layer thermohaline characteristics of the pgw core decrease substantially downstream from the persian arabian gulf to the gulf of oman pgw and iosw thermohaline characteristics and distribution also exhibit notable changes at periods shorter than a month as shown by repeated hydrological sections the tidal signal measured south of the strait by moored adcp and thermistor chains has predominant semi diurnal m2 and s2 and diurnal k1 components and possesses a complex vertical structure tidal intensification near the surface pycnocline is associated with noticeable internal waves at subtidal timescale mooring recordings confirm the water mass variability observed in the repeated hydrological sections the mixed layer also deepens substantially during the 1 month period finally trajectories of surface buoys drogued at 15 m exhibit reversals over periods characteristic of changes in wind direction

modeling of circulation in the arabian gulf and the sea of oman skill assessment and seasonal thermohaline structure hindcast simulations of the arabian gulf and the sea of oman using the regional ocean modeling system roms are quantitatively evaluated with basin wide hydrographic data and time series measurements the model shows comparable skill in reproducing moored observations of current velocities structure in upper and bottom depths the skill in simulating observed temperature is higher of 0 93 scale 0 1 in upper depths compared to 0 52 in bottom depths model results are sensitive to parameterization of water clarity a lower sensitivity was noticed to kpp gls and my2 5 turbulence closures when coastal turbid water parameterization is used accuracy of the model in reproducing seasonal and spatial variations of temperature and salinity increased by 25 compared to the clear water case whereas only 10 increase was noticed when applying kpp turbulent closure the model reproduces well anticlockwise circulation in the gulf a stronger surface inflow of fresher water to the arabian gulf through the strait of hormuz is simulated in summer compared to winter conditions mainly due to upper layer horizontal gradient of density between the arabian gulf and the sea of oman less seasonal variability of outflow between 0 15 and 0 20 m s 1 at 50 m to bottom depth around the strait of hormuz was noticed in the model results modeled surface layer stratification is stronger in summer than winter and varies spatially in the arabian gulf with highest stratification near the strait of hormuz overall the stratification in shallow water area of the arabian gulf remains low throughout the year

evolution of the qinling orogenic belt detailed field mapping geophysics and geochemistry show that the qinling orogenic belt is a southward vergent tectonic wedge consisting of six regional thrust sheets the lushan luanchun qinling douling wudang and zhuqi thrust sheets these regional thrusts underwent displacement at the end of the mid triassic and the end of the late jurassic due to the collision between the north and south china blocks and subsequent detachment the qinling orogenic belt is thus an indosinian yanshanian collision detachment zone the so called caledonian orogeny in the qinling orogenic belt records a succession of extensional and partial melting events in the continental crust the basic lavas in the lower paleozoic were erupted into rifting zones both in the northern qinling subzone and southern qinling subzone at the same time local melting of the transitional continental crust occurred and resulted in formation of s type granites

observations of seasonal exchange through the straits of hormuz and the inferred heat and freshwater budgets of the persian gulf the exchange between the persian arabian gulf and the indian ocean is investigated using hydrographic and moored acoustic doppler current profiler data from the straits of hormuz during the period december 1996 to march 1998 the moored time series records show a relatively steady deep outflow through the strait from 40 m to the bottom with a mean speed of approximately 20 cm s a variable flow is found in the upper layer with frequent reversals on timescales of several days to weeks the annual mean flow in the near surface layer is found to be northeastward out of the persian gulf in the southern part of the strait suggesting a mean horizontal exchange with the indian ocean that is superimposed on the vertical overturning exchange driven by evaporation over the gulf the salinity of the deep outflow varies from 39 3 to 40 8 psu with highest outflow salinities occurring in the winter months december march the annual mean deep outflow through the strait is estimated to be 0 15 0 03 sv calculation of the associated heat and freshwater fluxes through the strait yields estimates for the annual heat loss over the surface of the gulf of 7 4 w m2 and an annual water loss e p r of 1 68 0 39 m yr these values are shown to be in relatively good agreement with climatological surface fluxes derived from the southampton oceanography centre global flux climatology after known regional biases in the radiative budget are taken into account

a comparison of mechanisms generating vertical transport in the brazilian coastal upwelling regions 1 several mechanisms can drive vertical velocities in the coastal ocean including wind forcing and through gradients in the vorticity field generated by flow topography interactions a two layer steady wind driven analytical model is applied to the major upwelling systems of brazil cabo frio cf and cabo de santa marta csm regions comparisons are made between the relative roles of wind and flow topography interaction in inducing upwelling over these regions ekman pumping is the weakest mechanism over the shelf but does influence the along shelf temperature in the cf area away from coastline irregularities wind driven upwelling ekman transport dominates over all mechanisms however in the vicinity of capes and coastal features topographically driven upwelling plays a significant role and its transports may vary from 43 to 94 of wind driven upwelling upstream of capes topographically driven vertical motions are downwelling favorable and act against the wind driven coastal upwelling while downstream of capes they are upwelling favorable where all mechanisms add up to create strong upwelling peaks in total upwelling in the cf region are about twice as large as those in the csm area because the cf region has stronger winds and larger coastline perturbations than in the csm region observed sea surface temperatures sst agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast results suggest that on larger scales the sst variability along the coast is mainly controlled by wind driven upwelling while upwelling due to flow topography interaction is responsible for the smaller scale sst variability

p t conditions of crystallization and origin of plagioclase mantled alkali feldspar megacrysts in the mesozoic granitoids in the qinling orogen china abstract the qinling orogen between the north china and south china cratons was intruded at 211 217 ma by calc alkaline quartz monzonitic to monzogranitic plutons characterized by i to a type geochemistry and in many places contain plagioclase mantled alkali feldspar megacrysts rapakivi texture sensu lato the felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas the p t conditions of crystallization have been determined for early mineral assemblages inner parts of alkali feldspar megacrysts and their plagioclase quartz amphibole and biotite inclusions and late assemblages matrix minerals of the rapakivi textured granitoids al contents in amphibole from the early and late mineral assemblages yield pressures of 1 2 3 0 and 0 7 3 0 kbar respectively and indicate only minor pressure change between the crystallization of the early and late assemblages amphibole plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 c for both the early and late assemblages indicating nearly isothermal conditions feldspar thermometers yield lower temperatures relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in mgo na 2 o and cao than the early assemblages rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts

injection of oxygenated persian gulf water into the southern bay of bengal persian gulf water pgw is an oxygenated high salinity water mass that has recently been detected in the bay of bengal bob however little is known about the transport pathways of pgw into the bob ocean glider observations presented here demonstrate the presence of pgw in the southwestern bob output from an ocean reanalysis product shows that this pgw signal is associated with a northward flowing filament of high salinity water particle tracking experiments reveal two pathways one in the eastern arabian sea that takes a minimum of 2 years and another in the western arabian sea that takes a minimum of 3 years the western pathway connects to the bob via equatorial currents the greatest influx of pgw occurs between 82 and 87 e during the southwest monsoon we propose that injection of pgw to the bob oxygen minimum zone omz contributes to keeping oxygen concentrations in the bob above the level at which denitrification occurs

a hycom modeling study of the persian gulf 2 formation and export of persian gulf water 1 the circulation and water mass transformation processes in the persian gulf and the water exchange with the indian ocean through the strait of hormuz are studied using the hybrid coordinate ocean model hycom model results suggest that intruding indian ocean surface water iosw is transformed into hypersaline waters with salinity 41 practical salinity unit by the fresh water loss in the northern end of the gulf and in the southern shallow banks during wintertime intense heat loss from sea to air leads to the formation of cold and saline waters both in the northern gulf and in the southern gulf dense waters formed in the southern gulf have higher salinity and spill into the axial deep trough of the gulf as a sporadic bottom outflow in winter which leads to high salinity pulses in the strait as observed whereas in summer their buoyancy is increased due to heating and they are exported as a warm yet salty intermediate depth flow through the strait dense waters formed in the northern gulf propagate toward the strait along the axial trough throughout the year correspondingly there are two branches of seasonal overturning circulation in density classes the northern branch peaking in august with strength of 0 13 sv and the southern branch peaking in february and december with strength of 0 08 sv these two branches outflow together feed a seasonally varying deep outflow through the strait with an annual mean volume transport of 0 12 sv

orogen parallel westward oblique uplift of the qinling basement complex in the core of the qinling orogen china an example of oblique extrusion of deep seated metamorphic rocks in a collisional orogen abstract both vertical uplift and lateral extrusion of rocks in convergent orogens have been widely documented this article using the basement core of the qinling orogen as an example demonstrates orogen parallel westward uplift with both vertical and horizontal displacement components the qinling complex of the qinling orogen is a tectonic slice of a precambrian crystalline basement it is an elongate lens between younger terranes bounded by the shangdan suture to the south and by the zhuxia zone to the north during the middle paleozoic the complex underwent large scale orogen parallel westward oblique ductile uplift supporting evidence for this includes the following 1 opposite shear senses of the two bounding shear zones i e the thrust sinistral shear on the south and thrust dextral shear on the north 2 well developed eastward plunging orogen parallel a type structures in the complex such as stretching lineation and sheath folds 3 strong decompression metamorphism of the complex f

significant and vertically coherent seismic anisotropy beneath eastern tibet 1 shear wave splitting measurements using teleseismic sks and skks phases recorded by the indepth iv arrays has revealed a strong upper mantle anisotropic fabric in northeastern tibet with large delay times of up to 2 2 s suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle the coherence among fast polarization orientations of split core phases and the left lateral slip on eastern striking southern striking faults in eastern tibet and the surface deformation fields calculated from both gps observations and quaternary fault slip rates support the idea that left lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics we suggest the bending of the eastern himalayan syntaxis around the foundering burma andaman sumatra slab also contributes to the observed seismic anisotropy in the eastern himalayan syntaxis region two plausible competing processes are proposed for the flow of asthenosphere in eastern tibet in the first the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle in the second the asthenosphere beneath northeastern tibet is squeezed between the advancing indian continental lithosphere and the thick tarim and qaidam lithospheric blocks to the north a westward retreat of the burma slab from eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab the rotation of fast orientations for stations in the eastern himalayan syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere

character and dynamics of the red sea and persian gulf outflows historical hydrographic data and a numerical plume model are used to investigate the initial transformation dynamics and spreading pathways of red sea and persian gulf outflow waters where they enter the indian ocean the annual mean transport of these outflows is relatively small 0 4 sv but they have a major impact on the hydrographic properties of the indian ocean at the thermocline level because of their high salinity they are different from other outflows in that they flow over very shallow sills depth 200 m into a highly stratified upper ocean environment and they are located at relatively low latitudes 12 n and 26 n furthermore the red sea outflow exhibits strong seasonal variability in transport the four main results of this study are as follows first on the basis of observed temperature salinity t s characteristics of the outflow source and product waters we estimate that the red sea and persian gulf outflows are diluted by factors of 2 5 and 4 respectively as they descend from sill depth to their depth of neutral buoyancy the high dilution factor for the persian gulf outflow results from the combined effects of large initial density difference between the outflow source water and oceanic water and low outflow transport second the combination of low latitude and low outflow transport and associated low outflow thickness results in ekman numbers for both outflows that are o 1 this indicates that they should be thought of as frictional density currents modified by rotation rather than geostrophic density currents modified by friction third different mixing histories along the two channels that direct red sea outflow water into the open ocean result in product waters with significantly different densities which probably contributes to the multilayered structure of the red sea product waters in both outflows seasonal variations in source water and oceanic properties have some effect on the t s of the product waters but they have only a minor impact on equilibrium depth fourth product waters from both outflows are advected away from the sill region in narrow boundary currents at least during part of the year at other times the product water appears more in isolated patches

on the mechanisms of episodic salinity outflow events in the strait of hormuz abstract observations in the strait of hormuz 26 26 n 56 08 e during 1997 98 showed substantial velocity fluctuations accompanied by episodic changes in the salinity outflow events with amplitude varying between 1 and 2 psu on time scales of several days to a few weeks these events are characterized by a rapid increase in salinity followed by an abrupt decline the mechanisms behind these strong pulses of salinity events are investigated with a high resolution 1 km hybrid coordinate ocean model hycom with particular reference to the year 2005 in accordance with the observations the simulated salinity events are characterized by strong coherence between the enhanced flows in zonal and meridional directions it is inferred that most of the simulated and observed outflow variability is associated with the continuous formation of strong mesoscale cyclonic eddies whose origin can be traced upstream to around 26 n 55 5 e these cyclonic eddies have a diameter of about 63 km and have a remnant of p

seasonal spreading of the persian gulf water mass in the arabian sea the characteristics of the subsurface salinity maximum associated with the persian gulf water mass pgw are used to quantify the spreading and mixing of pgw in the thermocline of the arabian sea based on a bimonthly climatology of temperature and salinity examination of the seasonal cycles of heat and freshwater fluxes in the persian gulf region indicates that pgw forms as a result of elevated evaporative cooling in conjunction with reduced insolation during winter maps are presented of the distributions of depth salinity and geostrophic flow on 26 5 which nearly coincides with the core of the pgw after intense mixing in the strait of hormuz the property fields suggest that warm 17 c and high salinity 36 2 psu pgw enters the arabian sea to form a subsurface salinity extremum between 200 and 300 m we have found variability in the distribution of pgw in the arabian sea associated with monsoonal changes in the arabian sea circulation during the winter monsoon there is southward spreading of pgw along the western boundary during summer it is not present lateral mixing with low salinity water from the bay of bengal in the region south of 10 n and along the west coast of india during winter accounts for changes in the characteristics of pgw along these paths associated with the findlater jet during summer the entire thermohaline structure is vertically displaced along the coasts of somalia and arabia ekman convergence in the central arabian sea accounts for deepening of the pgw either lateral or vertical mixing would cause changes in pgw properties in these regions during this time pgw spreads predominantly southward along the central arabian sea as indicated by a tongue of high salinity

triassic granitoids of the qinling orogen central china genetic relationship of enclaves and rapakivi textured rocks abstract granitoids varying in composition from biotite amphibole granodiorite to monzogranite with rapakivi textures have recently been recognized in the qinling orogen central china the granitoids are magnesian calc alkalic and metaluminous a cnk 0 71 0 95 they contain many mafic to intermediate microgranular enclaves the enclaves are quenched mafic melts in granitic host magma as evidenced by fine grained sinuous margins against or transitional contacts with the host granitoids as well as disequilibrium textures and mineral assemblages u pb zircon dating of the granitoids yields 209 2 ma and 212 2 ma and the enclaves 210 2 ma and 211 2 ma respectively the host granitoids and enclaves show obvious silica gap but similar ree and trace element patterns the whole rock 87sr 86sr t end t and zircon ehf t values for the granitoids vary from 0 70516 to 0 70634 2 3 to 4 4 and 0 7 to 7 6 and for the enclaves from 0 70467 to 0 70600 1 1 to 4 0 and 1 2 to 8 8 respectively showing overlapped end t and zircon ehf t values all these suggest that the two magmatic systems represented by the host rock and enclave are probably derived from distinct sources with sufficient interaction or common origin but underwent different degrees of crustal contamination mineralogical and geochemical data point to enclave dissolution in silicic magma as a major process accounting for the origin of the rapakivi texture the possible bimodal magmatism suggested by the coeval granitoids and lamprophyre dykes combined with the structural pattern geochemical features and regional tectonics suggest a post collision setting for the qinling rapakivi textured granitoid plutons

metamorphic history and tectonic evolution of the qinling complex eastern qinling mountains china abstract the metamorphic history and tectonic evolution of the qinling complex is divided into formation and modification stages during the proterozoic formation stage three deformational sequences are recognized andalusite muscovite sillimanite muscovite and sillimanite k feldspar zones of amphibolite facies regional metamorphism are earlier than or synchronous with the first or second phase of folding ductile shear zones were formed and caledonian granites were emplaced during the modification stage the granites superimposed contact aureoles garnet k feldspar zone on the regional metamorphic fabric metamorphic reactions p t conditions of metamorphism and p t t paths were estimated by analysis of mineral textures and standard thermobarometric techniques the p t t path of the proterozoic tectonometamorphic cycle shows prominent clockwise decompression the p t t path of the caledonian tectonometamorphic cycle is characterized by an early rise of pressure and temperature followed by isothermal decompression rapid uplift and finally with isobaric cooling the p t t paths of the two tectonometamorphic cycles reflect two major stages of collision and uplift in the evolution of the qinling orogenic belt during the proterozoic and caledonian hercynian periods respectively

chemical oceanography of the persian gulf abstract measurements of basic hydrographic properties nutrient elements alkalinity and total carbon dioxide were made in the persian gulf in february and march 1977 on r v atlantis ii cruise 93 the results show clearly the penetration into the gulf of surface indian ocean water initially of 36 5 salinity which is carried northwards along the iranian coast gradually increasing in salinity to more than 40 the inflowing surface water is high in phosphate 1 0 0 5 moles kg 1 due to upwelling induced by the north east monsoon however nitrate levels are at or below the detection limit and nitrogenous nutrients appear to be limiting the seawater carbonate system is greatly perturbed by the precipitation of large quantities of calcium carbonate the alkalinity salinity relationship shows that the greatest carbonate loss occurs in the shallow waters of the trucial coast where up to 125 moles kg 1 of caco3 have been lost from the water dense saline low specific alkalinity water formed in the shallows appears to migrate down slope to augment the outflowing waters in the deeper part of the gulf the outflow of the tigris euphrates and karun rivers to the north provides an intense but low capacity signal of low salinity high specific alkalinity waters large amounts of co2 are also fixed by photosynthetic processes the classical mediterranean type of circulation is plainly revealed the residence time of water within the persian gulf is approximately 2 5 yr

early paleozoic tectonic evolution of the north qinling orogenic belt in central china insights on continental deep subduction and multiphase exhumation abstract the north qinling orogenic belt is an important component of qinling composite orogen in central china high pressure and ultra high pressure hp uhp rocks occur as lenses or layers surrounded by gneissic rocks in the northern central and southern qinling complex of the north qinling belt considered to have formed through deep continental subduction the magmatic protoliths of the hp uhp metamorphic rocks show formation ages ca 800 ma geochemical characteristics and pb nd isotopic compositions similar to those of the neoproterozoic igneous rocks of the south qinling belt continental materials of the south qinling belt were dragged down to mantle depths by the shangdan oceanic crust subducted and subjected to hp uhp metamorphism at ca 500 ma the erlangping and kuanping backarc basin formed in response to subduction of the shangdan ocean and might have developed into a limited small ocean basin at ca 500 ma the hp uhp rocks yielded retrograde metamorphic ages of ca 470 450 ma and ca 420 400 ma these ages are identical to the age of magmatic events in the north qinling hp uhp belt at 500 ma 450 ma and 420 ma related to deep subduction collision slab breakoff and crustal thinning during post collisional extension the dominant ca 500 400 ma ages of detrital zircons from the liuling group of the south qinling belt match well with those from the three stages of magmatic rocks and hp uhp rocks in the qinling complex this correlation suggests that the magmatic rocks and hp uhp metamorphic rocks in the north qinling belt initially exhumed to the surface eroded and were then deposited in the liuling basin in a post orogenic extensional setting during middle to late devonian new evidence suggests that the qinling complex is a tectonic complex rather than a uniform stratigraphic unit or a microcontinent as previously believed and is mainly composed of the exhumed hp uhp metamorphic rocks deep subduction exhumation related magmatic rocks and the early neoproterozoic granites together with the host rocks from the over riding plate at an active continental margin the early paleozoic tectonic history of the nqb includes oceanic slab subduction and formation of arc backarc spreading continental deep subduction arc continent collision break off and multi stage exhumation of the deep subducted slab as well as extension and thinning and associated erosion and deposition

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

formation and circulation of dense water in the persian arabian gulf 1 the nature and circulation of water masses in the persian arabian gulf hereinafter referred to as the gulf is investigated by examination of a historic database of hydrographic observations the densest water forms in winter at the northern end of the gulf rather than along the warmer southern and western coasts with the exception of small amounts of water directly above the seafloor most water flowing out of the gulf mixes across a density front that separates gulf deep water within the gulf from the indian ocean surface water iosw contrary to previous inferences the seasonally variable incursion of iosw into the gulf peaks in late spring this timing may be due to seasonal changes in sea surface slope driven by variations in evaporation rate in order to explain mooring results published elsewhere that show relatively small seasonal changes in the volume flux through the strait of hormuz hereinafter referred to as the strait we suggest that this flux is driven by the difference between the density of gulf deep water in the interior of the basin and water at comparable depths outside the gulf this density difference varies less than 15 during the year high rates of vertical mixing in the strait extend about 200 km westward in response to topographic constriction of tidal flows by islands and shoals