structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

three dimensional aspects of the seasonal heat balance in the gulf of california previously unresolved three dimensional aspects of the time mean as well as the annual and semiannual cycles of the heat transport are studied in the gulf of california using a minimal box model suggested by the hydrographic data at the very least three horizontal domains are needed for the model a shallow region north of the big islands a deep region identifiable with the ballenas channel and another deep region spanning the rest of the gulf south of the archipelago only one vertical layer is considered in the northern region whereas two layers are taken into account in the other two regions out of all of the possible heat exchanges among the various boxes of the model the least flux variance solution is considered the annual mean heat entering the surface in the northern region is exported in almost equal amounts to the ballenas channel and the southern region ballenas channel in turn exports heat to the southern region mainly through the lower layer producing a transversal asymmetry of the mouthward flux into the upper layer at the mouth the heat is exported to the pacific ocean largely through the upper layer both the annual and semiannual amplitude of the exchanges between all regions are as important as the annual average except at the mouth of the gulf where the semiannual component is not statistically relevant the pacific ocean fluxes estimates at the annual frequency agree well with those produced by a baroclinic wave which has been shown to explain a big deal of the thermodynamics of the gulf the annual mean vertical flux per unit horizontal area in the ballenas channel is much larger than that in the southern region this reinforces previous speculations that mixing processes in this region are very important a depth independent eddy diffusivity parameterization suggests that diffusion might not be invoked to explain the annual mean vertical flux in the ballenas channel

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

a three dimensional model of the mean and seasonal circulation of the gulf of california 1 the mean and seasonal circulation of the gulf of california is simulated with a three dimensional numerical model forced by the pacific ocean through specifying the sea level the temperature and the salinity fields at its entrance at the sea surface the wind and the heat and freshwater fluxes are specified the model reproduces the observed mean and seasonal variability of sea level of heat and salt balances and the sea surface temperature sst climatology it also reproduces the general surface circulation of the northern gulf which consists of a seasonally reversing basin wide gyre it is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the sst tides provide the mixing to upwell the cooler subsurface waters in the large islands area and the heating from the surface raises the sst the general circulation of the southern part of the gulf is due to the wind and the pacific forcing in the ekman layer two periods of anticyclonic circulation and one cyclonic per year occur below this layer two cyclonic periods develop in the northern part the tides play an important role in producing mean residual currents and both tides and winds compete against the pacific forcing to produce a cyclonic and anticyclonic circulation once a year contrary to conclusions of previous studies the thermohaline circulation is found to be unimportant in the gulf

seasonal gyres in the northern gulf of california abstract the circulation pattern in the northern gulf of california based on drifting buoys and hydrographic observations can be explained using the results of a linear two layer primitive equations model forced at the annual frequency by the pacific ocean wind stress and heat flux through the surface the modeled surface circulation consists of a cyclonic gyre from june to october and an anticyclonic gyre from december to april both located in the central region of the northern gulf of california which includes angel de la guarda island the maximum intensities of the gyres occur in august and february respectively with values of surface velocities of 65 cm s 1 in agreement with the observations and very low opposite velocities in the bottom layers may and november are transition months in which both gyres can be observed finally in june july or december january the growing gyre is still connected with the rest of the gulf of california through the narrows between tiburon island san este

internal structure of sst features in the central gulf of california abstract closely spaced xbt and ctd data were used to study the sub surface structure of features observed in satellite avhrr sea surface temperature sst images of the gulf of california gc such as fronts jets and gyres the lowest ssts in the gc are found around the midriff islands and especially over the sills because of strong mixing from tidal currents and breaking internal waves this minimum sst area is limited to the south and north by sharp sst fronts which frequently show convolutions gyres and filaments a vertical section of temperature along the gulf length shows that about 300 km south of the sills the isotherms begin to spread out in the vertical reducing stratification the thermocline isotherms begin surfacing about 100 km south of the sill forming the sst minimum area which has a maximum temperature difference of 6 c with waters to the south and a horizontal sst gradient of 0 05 c km 1 the evolution and subsurface structure of a cool filament apparently originated as an instability of the sst front was intensely sampled satellite images show that its head advanced due south at about 0 5 ms 1 along the edge of a pool of warm surface water about 110 km in diameter the thermocline below the warm pool was raised at its edge and some isotherms reached the surface producing the cool filament the tilt of the temperature salinity and density isolines at the edge of the warm pool produced a geostrophic jet adjacent to the cool filament and just inside the warm pool with maximum speed 0 5 ms 1 and extending down to 80 m the filament lasted about 10 days its width was 30 km and it reached a maximum length of 120 km the volume transport of the jet in the top 100 m was around 0 7 sv

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

thermohaline circulation in the gulf of california the gulf of california a narrow semienclosed sea is the only evaporative basin of the pacific ocean as a result of evaporative forcing salinities in the gulf are 1 to 2 higher than in the adjacent pacific at the same latitude this paper examines the thermohaline structure of the gulf and the means by which thermohaline exchange between the pacific and the gulf occurs over time scales of months to years in addition to evaporative forcing air sea heat fluxes and momentum fluxes are important to thermohaline circulation in the gulf from observations presented here it appears that the gulf gains heat from the atmosphere on an annual average unlike the mediterranean and red seas which have comparable evaporative forcing as a result outflow from the gulf tends to be less dense than inflow from the pacific winds over the gulf change direction with season blowing northward in summer and southward in winter this same seasonal pattern appears in near surface transports averaged across the gulf the thermohaline circulation then consists of outflow mostly between about 50 m and 250 m inflow mostly between 250 m and 500 m and a surface layer in which the direction of transport changes with seasonal changes in the large scale winds using hydrographic observations from a section across the central gulf total transport in or out of the northern gulf is estimated to be 0 9 sv heat gain from the atmosphere is estimated to be 20 to 50 w m 2 and evaporation is estimated to be 0 95 m yr 1 these estimates are annual averages based on cruises from several years seasonal variations in thermohaline structure in the gulf are also examined and found to dominate the variance in temperature and density in the top 500 m of the water column salinity has little seasonal variability but does exhibit more horizontal variablility than temperature or density major year to year variations in thermohaline structure may be attributable to el nino southern oscillation events

ar ar and fission track ages in the song chay massif early triassic and cenozoic tectonics in northern vietnam the song chay massif is the northeasternmost metamorphic complex in vietnam to the east of the red river shear zone it shows a large antiformal structure involving orthogneisses and migmatites overlain on its northern flank by muscovite bearing marbles an e w striking fault bounds the dome to the south kinematic indicators along a s n section reveal top to the n shear sense along the interface between the orthogneissic core and the overlying metasediments radiometric ages were obtained by the 40ar 39ar method using purified mica separates across the dome ages range from 236 ma at the southern edge to 160 ma in the core attesting to a strong imprint in the early triassic time a clear difference is seen between these mesozoic ages and the eocene to miocene ages from 40 to 24 ma that obtained in the nearby red river shear zone using the same method these data show that the song chay massif was already high in the crust when the high temperature deformation of the red river shear zone took place the final exhumation of the song chay orthogneiss constrained by fission track analysis on samples along the same transect occurred during the early miocene and could be interpreted as the consequence of a first normal sense of motion along the fault which bounds the massif to the south timing is similar to that of exhumation in the red river shear zone

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

a numerical simulation of the two and three dimensional lagrangian circulation in the northern gulf of california the surface circulation in the northern gulf of california is dominated by a cyclonic gyre during summer and an anticyclonic gyre during winter the associated 3d lagrangian circulation is calculated and compared with that detected by surface floats by inhibiting vertical advection in a three dimensional 3d numerical model in general the 3d circulation follows the same horizontal paths as in the two dimensional 2d case but with vertical excursions along the trajectories however in some areas especially those close to the coasts which represents 20 of the study area the vertical displacements cause the paths of both cases with and without vertical advection to differ considerably thus resulting in different destinations for the particles this finding is of relevance for the fate of larvae or contaminants in the area which so far had been studied on the basis of 2d results alone

peat formation in the context of the development of the mkuze floodplain on the coastal plain of maputaland south africa this paper examines the geomorphological and sedimentological development of blocked valley lakes in the mkuze floodplain on the coastal plain of maputaland northern kwazulu natal south africa b

structural doming tectonics intracontinental deformation of the sw margin of the yangtze block china the southwest margin of the yangtze block underwent multiple tectonic events including the collision between the yangtze and the south china plate caledonian folding and uplift of south china subduction of the western pacific plate and cenozoic continental escape during the indo asia collision the structural framework and tectonic evolution of the area are currently unclear through field petrologic and structural studies microstructures within the deformed units and estimates of the temperature of deformation we constrain the conditions of deformation and further classify at least four stage deformation the first stage involved northeastward thrusting that produced folds mylonites and dynamically recrystallized quartz and calcite electron backscatter diffraction data indicate that deformation during this event occurred at 400 c corresponding to a depth of 10 km the second stage of deformation involved uplift extension and the generation of a domal structure during the third event high angle normal faults formed within the cover sequence that surrounds the dome the fourth stage of deformation occurred in the cenozoic and involved motion along sinistral and dextral strike slip faults which cut structures that formed during the previous stages of deformation the first deformation event was related to triassic n s collision with the indochina block the second and third stages resulted from far field compression related to westward subduction of the paleo pacific plate and the fourth event was related to displacement along the ailaoshan red river strike slip fault the dome in the study area represents a transitional structure between a metamorphic core complex and a gneissic dome which we refer to as structural doming

the 40ar 39ar dating of biotite in ore veins and zircon u pb dating of porphyrtic granite dyke in the nanyangtian tungsten deposit in se yunnan china abstract the nanyangtian tungsten deposit is located in the laojunshan sn w polymetallic metallogenic province in se yunnan china tectonically it is located in the conjunction of the cathaysia and indochina blocks the orebodies primarily hosted within the stratiform like skarn and marble in the paleoproterozoic nanyangtian formation three ore forming stages have been identified based on mineral assemblages and on the intercalated relationships between the veins they include skarn scheelite stage quartz scheelite vein stage and carbonate scheelite vein stage in this paper we present 40ar 39ar laser incremental heating analyses of hydrothermal biotite intergrowth with scheelite from quartz scheelite vein with two yielded well defined 40ar 39ar plateau ages of 97 49 0 97 ma and 99 48 0 97 ma and two isochronal ages of 97 01 1 39 ma and 99 58 0 98 ma respectively representing the age of second mineralization stage of the nanyangtian tungsten deposit the ages are well consistent with the emplacement age of the laojunshan granite 96 ma to 117 ma u pb geochronological data for magmatic zircons separated from porphyritic granite dyke in the mine pit indicate that the granite body was emplaced in the post ore stage 89 88 0 53 ma integrated with previously high resolution diagenetic and metallogenic geochronological data two significant magmatic mineralization events are presented in se yunnan china and north vietnam the first event took place from 97 ma to 124 ma which is closely related to the tungsten mineralization the second event occurred from 75 ma to 95 ma which is closely related to the sn cu ag zn mineralization according to the exhibited data we preliminarily conclude that the late cretaceous magmatic mineralization activity in se yunnan and north vietnam is the product of post collision of the cathaysia and indochina blocks and should have formed under a same geodynamic setting

summer generation of the southern gulf of california eddy train 1 ocean color and sea surface temperature satellite observations show the existence of a series of anticyclonic eddies along the axis of the southern gulf of california sgoc to investigate the summer generation of these eddies a regional version of the hybrid coordinate ocean model hycom has been configured for the goc and has been nested inside the global model a suite of experiments using the nested goc model was developed and used to isolate the effects of the local wind and the effects of the oceanic remote forcing on the generation of the sgoc eddies the results indicate that the local wind is not essential for the generation of these eddies rather it is the oceanic remote forcing in the sgoc the monthly variability of the currents and sea surface height is mainly due to the deterministic near coastal poleward eastern boundary currents pebc the interaction of the pebc with the topographic irregularities the capes at topolobampo and cabo lobos and the ridges extending offshore from the entrance of the san lorenzo and sinaloa rivers generates the sgoc eddies the northward upper ocean transport induced by the pebc includes two maximums one in may june and the other in december during the summers of 1999 and 2004 the pebc were intensified by the arrival of equatorially originated downwelling coastally trapped waves ctws which contributed to the generation of the sgoc eddies the summer 2004 ctw increased the northward upper ocean transport by 2 sv this particular ctw was measured by several tide gauges located along the coast

a group of papers on fluid inclusion research applied to ore deposits an introduction the group of six papers and one scientific contribution that follow this brief introduction illustrate the application of fluid inclusion research to ore deposits a field pioneered by edwin woods roedder july 30 1919 august 1 2006 fig 1 who contributed nearly 400 published works during a career that spanned more than three quarters of a century his first paper was published in 1935 roedder 1935 on the topic of black sulfur at hillborn new york his final posthumous publication in 2008 was as a coauthor on the thermal history of yucca mountain nevada whelan et al 2008 many readers of this journal will know that ed roedder was the leader in the field of fluid and melt inclusions roedder 1984b but some may not realize that he also made significant contributions in other areas including experimental petrology of the k2o feo al2o3 sio2 system roedder 1951 the geologic storage of radioactive waste roedder 1957 and lunar petrology roedder and weiblen 1970 ed s most significant contributions were related to the critical role that fluids and related processes play in ore formation a large number of his publications were related to mineral deposits and ore genesis with 25 of these published in economic geology between 1962 roedder 1962 and 1989 anderson et al 1989 a compilation and summary of much of ed s work up until the early 1980s is included in his well known publication fluid inclusions roedder 1984b a complete listing of ed roedder s publications is available at the edwin woods roedder memorial virtual library at the following location some lithium salts exhibit high solubilities in aqueous solutions leading to high concentrations in continental brines postmagmatic hydrothermal systems and rare element pegmatites despite lithium being a trace element in

surface heat flux in the northern gulf of california recent coastal meteorological data 1979 1986 are used to evaluate the seasonal cycle of surface heat fluxes in the northern gulf of california although net heat loss occurs from october to january the annual mean of the net surface heat flux was found to be into the sea 69 w m 2 near the coast and 83 w m 2 offshore with a mean evaporation rate 0 9 m yr 1 these results require an oceanic export of heat and salt out of the northern gulf to achieve a balance and imply that the annual mean thermohaline circulation must have an inflowing component at depth thus enriching the central and northern parts of the gulf these results differ from previous meteorological estimates which suggested a net surface heat loss but confirm those based on hydrographic data

residual circulation and tidal stress in the gulf of california 1 results of a three dimensional nonlinear barotropic shelf model are used to study the effect of the m2 tidal stress on the residual current in the gulf of california the tidal stress summarizes the nonlinear interactions and forces the residual circulation it is calculated following the method developed by nihoul and ronday 1975 the vertical structure of the tidal stress reveals clearly the zones where the interaction between tidal currents and the basin geometry is strong the highest values of tidal stress were found over the salsipuedes sill and in the ballenas channel in the central archipelago and in the colorado river delta relatively high values of tidal stress were also found in deeper layers in the southern part the high tidal stress values coincide well with the anomalous cold water patches observed in the archipelago area attributed to tidal mixing the calculated residual currents show a maximum of about 15 cm s 1 in the upper layers in the archipelago area at subsurface layers an anticyclonic circulation is observed divergence patterns in the upper layers suggest that m2 tide residuals contribute to significant upward movements of water on the west side of tiburon island this barotropic process may contribute to the generation of the observed cold patches

pressure temperature and fluid conditions during emerald precipitation southeastern yukon canada fluid inclusion and stable isotope evidence abstract the crown emerald veins are somewhat enigmatic displaying characteristics that are common to emerald deposits of tectonic hydrothermal origin and of igneous origin the veins cut the fire lake mafic meta volcanic rocks occurring within 600 m of an outcrop of cretaceous s type granite field work and vein petrography are consistent with a polythermal origin for the veins the primary vein mineralogy is quartz and tourmaline with variable sized alteration haloes consisting of tourmaline quartz muscovite chlorite and emerald the veins weather a buff brown colour due to jarosite scheelite and minor lepidocrocite which were precipitated during the waning stages of vein formation microthermometic studies of primary fluid inclusions within emerald growth zones are consistent with emerald precipitation from h 2 o co 2 ch 4 n 2 h 2 s bearing saline brines the estimated fluid composition is approximately 0 9391 mol h 2 o 0 0473 mol co 2 0 0077 mol ch 4 and 0 0059 mol nacl 2 wt nacl eq fluid inclusion and stable isotope studies are consistent with vein formation in the temperature range 365 498 c with corresponding pressures along fluid inclusion isochore paths ranging from 700 to 2250 bars these data correlate with a very slow uplift rate for the region of 0 02 0 07 mm year emerald deposits are generally formed when geological conditions bring together cr v and be cr and v are presumed to have been derived locally from the mafic and ultramafic rocks during hydrothermal alteration the be is most likely derived from the nearby cretaceous granite intrusion

oxygen isotope systematics of emerald relevance for its origin and geological significance oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in 18o smow between 6 2 and 24 7 the 18o values for each deposit are restricted and can be used to determine the origin of emerald from the world s most important producers the 18o value of emerald appears to be a fingerprint of its origin especially for gems of exceptional quality from colombia eastern emerald zone 18o 16 8 0 1 western emerald zone 18o 21 2 0 5 afghanistan 18o 13 5 0 1 pakistan swat mingora districts 18o 15 7 0 1 brazil santa terezinha de goias 18o 12 2 0 1 quadrilatero ferrifero 18o 6 9 0 4 and zimbabwe sandawana 18o 7 5 0 5 furthermore the 18o composition of emerald appears to be a good marker of its geological environment because the data suggest that host rock buffering of fluid 18o is considerable during fluid rock interaction

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

surface circulation in the gulf of california in summer from surface drifters and satellite images 2004 2006 surface drifters released in the gulf of california between june 2004 and august 2006 are used to describe the surface circulation in late spring and summer in the june to september mean there was a poleward coastal current on the shelf and slope of the mainland side of the gulf with mean speed 0 3 m s it reached the northern gulf and joined the cyclonic circulation typical of this zone in summer in the western half of the southern gulf the drifters presented recirculating currents that are due to mesoscale eddies that appear to dominate the surface circulation in summer in june 2004 the coastal current presented an enhancement event with mean speed around 0 60 m s and maximum 0 80 m s it took 20 days for a particular drifter to travel the 1000 km from the gulf entrance to the head this strengthening of the coastal current was apparent in chlorophyll a and sst satellite images the drifters following closely the intrusion of warm chlorophyll poor surface water from outside the gulf the drifters and the satellite images suggest that the current enhancement event lasted less than a month this mesoscale event was linked with a mesoscale remote forcing in the tropical pacific coast and with a mesoscale local forcing of the wind these events seem to occur every year and are probably important in carrying organisms and properties from the entrance to the whole length of the gulf

surface dispersion in the gulf of california abstract surface dispersion is measured in the gulf of california by means of argos drifters released along this semi enclosed elongated basin first basic one particle statistics lagrangian scales absolute dispersion and diffusion coefficients are estimated along and across the gulf absolute dispersion shows a nearly ballistic regime during the lagrangian time scale t 2 where t is time during the subsequent 30 days absolute dispersion enters a random walk regime t along the gulf while being saturated across the basin due to the lateral boundaries secondly the analysis is extended to two particle statistics relative dispersion between pairs of drifters and finite scale lyapunov exponents fsle relative dispersion is nearly exponential in both directions during the first few days though evidence is not conclusive during the subsequent 30 days it grows as t 1 5 along the gulf while being saturated across the basin again it is shown that relative dispersion along the gulf is proportional to t 3 where t represents a shifted time that depends on the initial separation of the particles this form of the richardson regime is consistently measured for particles that are sufficiently separated 30 km or more the richardson regime is verified with the fsle for particle separations ranging from 30 to 140 km approximately the obtained dispersion properties are discussed in terms of the main circulation features within the basin such as mesoscale vortices that occupy the width of the gulf these structures might retain buoys during days or weeks thus preventing or delaying further displacements and therefore affecting the particle dispersion the vortices are also an important mechanism to translate particles across the gulf between the peninsula and the continent thus promoting the saturation of dispersion along this direction

sources of the nanwenhe song chay granitic complex sw china ne vietnam and its tectonic significance abstract the nanwenhe song chay complex nscc is a large early paleozoic pluton straddling the border between sw china and ne vietnam it is located at the tectonic junction of the yangtze cathaysia and indochina blocks so that the source of the complex is still enigmatic the rocks from the complex are high k calc alkaline and peraluminous s type granite la icp ms u pb dating of zircons from twelve granitic samples in the complex gives crystallization ages in the range of 436 423 ma zircon u pb hf isotopes and geochemical data show that the nanwenhe granites in the northern part of the nscc probably were mainly derived from neoproterozoic metamorphic pelites analogous to those in the xiajiang and danzhou groups in contrast the song chay granites in the southern part of the nscc were probably derived from neoproterozoic metamorphic psammites analogous to those in the fanjingshan and sibao groups in the southwestern yangtze block the granites from the complex contain abundant inherited zircons with a main peak at 836 808 ma and subordinate peaks at 734 ma and 528 665 ma the inherited zircons have age distribution patterns and hf isotopic compositions similar to those for the detrital zircons from neoproterozoic to early paleozoic sedimentary rocks in the southwestern part of the yangtze block but different from those of the cathaysia block and indochina block therefore the basement of the nscc is equivalent to the yangtze block and the complex may represent the westernmost tip of the early paleozoic orogenic belt in the scb we thus assume that the boundaries between the yangtze block and the cathaysia block and between the scb and icb should be located to the southeast and southwest of the nanwenhe song chay area respectively

modeling the seasonal and interannual variability of the northern gulf of california salinity 1 the 7 years 2003 2009 of output from a regional version of the hybrid coordinate ocean model hycom nested in global hycom are used to study the seasonal and interannual variability of the salinity in the northern gulf of california ngoc previous studies illustrate that the ngoc is characterized by an annual evaporation of 0 9 m yr this evaporation generates high sea surface salinity sss water which reaches a maxima in the ngoc 37 and decreases to 35 toward the entrance of the gulf of california the ngoc surface water is interannually modulated by fluctuations in evaporation and by fluctuations in the low salinity water transported into the region by poleward eastern boundary currents the fluctuations in the transport of low salinity water are linked to the arrival of equatorially originated coastally trapped waves the crucial role of the transport of low salinity water for the interannual variability of sss is illustrated by the 2006 and 2008 fall seasons which include the lowest simulated salinity of the period 2003 2009 the lowest salinity in 2006 and 2008 cannot be explained solely by evaporation because 2006 was characterized by the largest evaporation of the period 2003 2009 however the presence of the lowest salinity environment can be attributed to the evaporation in conjunction with the largest upper ocean transport of low salinity water carried to the ngoc by the 2006 and 2008 coastally trapped waves intensified poleward eastern boundary currents

conditions for early cretaceous emerald formation at dyakou china fluid inclusion ar ar and stable isotope studies the dyakou emerald occurrence is located in malipo county in the province of yunnan southern china the occurrence lies in the northern part of the laojunshan song chay metamorphic core complex which is exposed in an area of approximately 2 000 km2 and extends across the border between china and vietnam emerald mineralization is hosted by pegmatite and associated quartz veins that intrude deformed proterozoic biotite muscovite granofels and schist hydrogen and oxygen isotope results from the emerald channel waters and emerald respectively are consistent with an igneous fluid source the 18o fractionation between emerald and quartz yields vein temperatures of 365 to 420 c fluid inclusions indicate that the emerald precipitated from saline brines ranging from almost pure water to 10 5 mass percent nacl equiv fluid inclusion isochores intersected with 18o data yield pressures changing along the geothermal gradient from 1 500 to 3 300 bars ar ar geochronology of biotite and muscovite from the emerald veins yields consistent ages of 124 1 ma these constraints combined with field observations indicate that the dyakou emerald deposit is consistent with the igneous related model for emerald formation

ocean color observations of eddies during the summer in the gulf of california 1 using seawifs ocean color satellite images collected during 1997 2001 a series of eddies have been observed in the gulf of california these eddies are not clearly seen in the summertime sea surface temperature images the surface circulation between the midriff islands and the mouth of the gulf appears to be dominated by this series of eddies that have an alternating sense of rotation an eddy pair is observed to extend from cabo lobos in each of the three years suggesting that the eddies are topographically locked the formation mechanism of the eddies remains unknown however we suspect the most likely mechanism includes baroclinic instabilities along the coast produced by interactions between coastally trapped waves and local wind driven currents

long and complex thermal history of the song chay metamorphic dome northern vietnam by multi system geochronology multi system geochronology was used to unravel the long and complex thermal history of the song chay range northern vietnam a high grade granitic and metamorphic dome in the vicinity of the cenozoic ailao shan red river fault zone it was considered to be proterozoic south china basement but its geological history was basically unknown scattered field observations suggest three episodes of high temperature deformation firstly at the time of granite emplacement secondly a decollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages p t estimates suggest that metamorphism coeval with the second deformation phase culminated at 580 ca nd 4 5 kbar 16 km depth multi system geochronology is applied to a two micas granite sample slightly deformed within the decollement u pb dating of zircon yields an age of 428 5m a 2s interpreted as the time of granite crystallization within the south china caledonian belt rb sr on white micas and biotite yields ages of 206 10 ma and 176 5 3 ma respectively 2s whereas 39ar 40 ar ages of the same minerals are 210 9a nd 190 8m a 2s these ages suggest an upper triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the decollement the k feldspar irregular 39ar 40ar age spectrum can to the first order be explained by a cooling history with two episodes of rapid cooling one at 140 ma and a second around 41 to 25 ma apatite fission tracks central age 33 6 3 6 ma 1s confirms a tertiary rapid cooling event interpreted as the final exhumation of the song chay dome 2000 elsevier science b v all rights reserved

equilibria within the mineral assemblage quartz muscovite biotite garnet plagioclase and implications for the mixing properties of octahedrally coordinated cations in muscovite and biotite interaction parameters derived using empirical calibration methods indicate strong non ideality in the mixing of octahedrally coordinated cations in muscovite and biotite the data set used for calibration comprises mineral compositions from 49 samples containing quartz muscovite biotite garnet plagioclase and al2sio5 kyanite or sillimanite pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet biotite femg1 exchange equilibrium and geobarometry based on the anorthite breakdown equilibrium two equilibria yielded simple expressions from which binary interaction parameters for octahedrally coordinated cations in biotite could be directly determined a four component fe2 mg al ti regular symmetric mixing model was assumed for biotite one equilibrium yielded a simple expression from which an interaction parameter for the mixing of the mgal celadonite component in muscovite could be directly determined two sets of calculations were performed utilizing different calibrations of the garnet biotite geothermometer and the anothite breakdown geobarometer and different garnet activity models both placed samples within or near the stability field of the al2sio5 phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties indicating that the values are insensitive to differences in the underlying methods using the derived interaction parameters activity models were formulated for the annite phlogopite eastonite and siderophyllite components of biotite and for the mgal celadonite component of muscovite these were utilized for the empirical calibration of 45 fluid independent equilibria involving unique combinations of phase components from the mineral assemblage garnet plagioclase biotite muscovite quartz forty three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz muscovite biotite garnet plagioclase when care is taken to insure that applications are restricted to valid compositional ranges for these the calibrations yielded multiple correlation coefficients ranging from 0 953 to 0 998 and standard deviations of the residuals ranging from 597 to 118 bars