on the summer poleward coastal current off sw mexico 1 for the first time on the basis of direct observations june 2003 and june 2005 the characteristics of the summer time coastal poleward current off sw mexico are reported only the surface evidence of this coastal current has previously been described from ship drift compilations in june 2003 the current was 90 180 km wide 400 m deep with speed 0 3 ms 1 and transport 4 sv 1 sv 106 m3 s 1 in june 2005 its width was 90 km it was 250 300 m deep with mean speed 0 15 m s 1 and transport 2 5 sv california current water ccw and equatorward flow were found further offshore mesoscale eddies significantly affected the coastal current and transported ccw into the coastal zone

fluid rock interactions during uhp metamorphism a review of the dabie sulu orogen east central china comprehensive review on the characteristics of petrology oxygen isotope fluid inclusion and nominally anhydrous minerals nams for many dabie sulu ultrahigh pressure uhp metamorphic rocks including drill hole core samples reveals that fluid has played important and multiple roles during complicated fluid rock interactions attending the subduction and exhumation of supracrustal rocks we have identified several distinct stages of fluid rock interactions as follows 1 the neoproterozoic supercrustal protoliths of uhp rocks experienced variable degrees of hydration through interactions with cold meteoric water with extremely low oxygen isotope compositions during neoproterozoic snow ball earth time 2 a series of dehydration reactions took place during triassic subduction of the yangtze plate beneath the sino korean plate the released fluid entered mainly into volatile bearing high pressure hp and uhp minerals such as phengite zoisite epidote talc lawsonite and magnesite as well as into uhp nams such as garnet omphacite and rutile 3 silicate rich supercritical fluid hydrous melt existed during the uhp metamorphism at mantle depths 100 km which mobilized many normally fluid immobile elements and caused unusual element fractionation 4 the fluid exsolved from the nams during the early exhumation of the dabie sulu terrane was the main source for hp hydrate retrogression and generation of hp veins 5 local amphibolite facies retrogression at crustal depths took place by infiltration of aqueous fluid of various salinities possibly derived from an external source 6 the greenschist facies overprinting and low pressure lp quartz veins were generated by fluid flow along ductile shear zones and brittle faults during late stage uplift of the uhp terrane

seasonality of the transitional region of the california current system off baja california hydrographic data collected over the period 1997 2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the baja california peninsula the upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn in the first case the system typically shows relatively low temperature and salinity waters which give it a subarctic character in the second only the region north of punta eugenia 28 n maintains subarctic characteristics while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds which allows the poleward advection of surface waters also during this period a positive wind stress curl promotes the zonal advection of north pacific s eastern edge waters into the coast and to the north as a surface coastal flow average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth with two clearly defined cyclonic structures in summer and autumn both separated at the latitude of punta eugenia the analyses conducted also showed a clear continuity of the california undercurrent along the shelf break with more diffuse currents in the winter poleward flows were observed throughout the water column especially in summer and autumn although the origin of the surface flow does not necessarily involve a surfacing of the california undercurrent

alpine and pacific styles of phanerozoic mountain building subduction zone petrogenesis of continental crust a broad continuum exists between two distinct end member types of mountain building alpine type orogenic belts develop during subduction of an ocean basin between two continental blocks resulting in collision they are characterized by an imbricate sequence of oceanward verging nappes some alpine belts exhibit superimposed late stage backthrusting sediments are chiefly platform carbonates and siliciclastics in some cases associated with minor amounts of bimodal volcanics pre existing granitic gneisses and related continental rocks constitute an autochthonous parautochthonous basement metamorphism of deeply subducted portions of the orogen ranges from relatively high pressure hp to ultrahigh pressure uhp calcalkaline volcanic plutonic rocks are rare and have peraluminous s type bulk compositions in contrast pacific type orogens develop within and landward from long sustained oceanic subduction zones they consist of an outboard oceanic trench accretionary prism and an inboard continental margin island arc the oceanic assemblage consists of first cycle in part melanged volcaniclastics and minor but widespread cherts deep water carbonates intimately mixed with disaggregated ophiolites the section recrystallized under hp conditions recumbent fold vergence is oceanward a massive slightly older to coeval calcalkaline arc is sited landward from the trench complex on the stable non subducted plate it consists of abundant dominantly intermediate metaluminous i type volcanics resting on old crust both assemblages are thrown into open folds intruded by comagmatic i type granitoids and metamorphosed locally to regionally under high t low p conditions in the subduction channel of collisional and outboard circumpacific terranes combined extension above and subduction below allows buoyancy driven ascent of ductile thin aspect ratio slices of hp uhp complexes to midcrustal levels where most closely approached neutral buoyancy exposure of rising sheets caused by erosion and gravitational collapse results in moderate amounts of sedimentary debris because exhumed sialic slivers are of modest volume at massive sialic buildups associated with convergent plate cusps syntaxes tectonic aneurysms may help transport hp uhp complexes from mid to upper crustal levels the closure of relatively small ocean basins that typify many intracratonic suture zones provides only limited production of intermediate and silicic melts so volcanic plutonic belts are poorly developed in alpine orogens compared with circumpacific convergent plate junctions generation of a calcalkaline arc mainly depends on volatile evolution at the depth of magma generation phase equilibrium studies show that under typical subduction zone p t trajectories clinoamphibole ca al hydrous silicates constitute the major hydroxyl bearing phases in deep seated metamorphic rocks of morb composition other hydrous minerals are of minor abundance ca and na clinoamphiboles dehydrate at pressures of above approximately 2 gpa but low temperature devolatilization may be delayed by pressure overstepping thus metabasaltic blueschists and amphibolites expel h2o at melt generation depths and commonly achieve stable eclogitic assemblages partly serpentinized mantle beneath the oceanic crust dehydrates at roughly comparable conditions for reasonable subduction zone geothermal gradients however white micas biotites remain stable to pressures 3 gpa accordingly attending descent to depths of 100 km mica rich quartzofeldspathic lithologies that constitute much of the continental crust fail to evolve substantial amounts of h2o and transform incompletely to stable eclogite facies assemblages underflow of amphibolitized oceanic lithosphere thus generates most of the deep seated volatile flux and the consequent partial melting to produce the calcalkaline suite along and above a subduction zone where large volumes of micaceous intermediate and felsic crustal materials are carried down to great depths volatile flux severely diminishes thus continental collision in general does not produce a volcanic plutonic arc whereas in contrast the long continued contemporaneous underflow of oceanic lithosphere does

volume imaging lidar observations of the convective structure surrounding the flight path of a flux measuring aircraft the university of wisconsin volume imaging lidar has been used to portray images of the three dimensional structure of clear air convective plumes in the atmosphere surrounding the flight path of the instrumented twin otter aircraft operated by the national aeronautical establishment nae of canada lidar images provide a context for interpretation of the aircraft measurements the position of data points within a convective element can be determined and the temporal development of the plume can be observed to time the observation with respect to the life cycle of the plume plots of the vertical flux of water vapor q w superimposed on lidar images clearly demonstrate the well known sampling difficulties encountered when attempting to measure fluxes near the top of the convective layer when loran was used to determine average aircraft velocity flight leg averaged horizontal winds measured by the aircraft and area averaged winds measured by lidar agree to within 0 2 m s 1 in speed and 1 in direction

carbon concentrations and isotopic ratios of eclogites from the dabie and sulu terranes in china abstract both concentration and isotope composition of bulk carbon in apatite and host eclogites from the dabie sulu ultrahigh pressure uhp terranes in china have been determined along with their oxygen isotope composition the results show significant 13 c depletion in the apatite 13 c 27 7 to 20 8 with the carbon concentrations of 0 59 to 1 65 wt co 2 despite a large variation in 18 o 6 5 to 9 5 the bulk carbon in 21 of the 24 eclogites has low 13 c values of 26 1 to 17 9 with low carbon content of 500 to 1000 ppm whereas the other three samples show high 13 c values of 7 1 to 2 8 with high carbon contents of 2400 to 4300 ppm noncarbonate carbon was measured by treating the all eclogites with 5 n hcl solution yielding uniformly low 13 c values of 27 9 to 24 2 and carbon contents of 200 to 300 ppm carbonate carbon is thus calculated by mass balance to have also low 13 c values of 25 6 to 15 1 for the 21 samples but high 13 c values of 4 3 to 1 2 for the remaining three samples secondary carbonate was identified in the three eclogites that are also depleted in 13 c primarily but subjected to overprint of 13 c rich co 2 bearing fluid subsequent to the uhp metamorphism the isotopically light carbon in both eclogite and apatite is interpreted to represent the isotope composition of carbon in eclogite precursors before plate subduction and thus has an origin of organic carbon from the earth s surface the uniformly low 13 c values of apatite suggest that the co 2 of metamorphic fluid in equilibrium with the host eclogites would be derived from the oxidation of organic carbon rather than the decarbonation of underthrust carbonates during progressive metamorphism protoliths of the eclogites are inferred to be of igneous origin which underwent more extensive interaction with organic matter than with meteoric hydrothermal fluid on the subsurface of the continental crust the break off of the subducted plate containing the isotopically light carbon and subsequent interactions with the surrounding mantle could produce the mafic and or silicic magmas that are significantly depleted in 13 c relative to the primary mantle carbon this may provide evidence for a linkage of the 13 c depleted mantle carbon to a surficial source via plate subduction

ultra high pressure metamorphism of carbonate rocks in the dabie mountains central china abstract widespread ultra high p assemblages including coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite in marble gneiss and phengite schist are present in the dabie mountains eclogite terrane these assemblages indicate that the ultra high p metamorphic event occurred on a regional scale during triassic collision between the sino korean and yangtze cratons marble in the dabie mountains is interlayered with coesite bearing eclogite and gneiss and as blocks of various size within gneiss discontinuous boudins of eclogite occur within marble layers marble contains an ultra high p assemblage of calcite aragonite dolomite clinopyroxene garnet phengite epidote rutile and quartz coesite coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite occur as fine grained inclusions in garnet and omphacite phengites contain about 3 6 si atoms per formula unit based on 11 oxygens similar to the coesite bearing eclogite marble exhibits retrograde recrystallization under amphibolite greenschist facies conditions generated during uplift of the ultra high p metamorphic terrane retrograde minerals are fine grained and replace coarse grained peak metamorphic phases the most typical replacements are symplectic pargasitic hornblende epidote after garnet diopside plagioclase an18 after omphacite and fibrous phlogopite after phengite ferroan pargasite plagioclase and actinolite formed along grain boundaries between garnet and calcite and calcite and quartz respectively the estimated peak p t conditions for marble are comparable to those for eclogite garnet clinopyroxene geothermometry yields temperatures of 630 760 c the garnet phengite thermometer gives somewhat lower temperatures the minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite such estimates of ultra high p conditions are consistent with the coexistence of grossular rich garnet rutile and the high jadeite content of omphacite in marble the fluid for the peak metamorphism was calculated to have a very low xco2 0 03 the p t conditions for retrograde metamorphism were estimated to be 475 550 c at 7 kbar

convective boundary layer evolution to 4 km asl over high alpine terrain airborne lidar observations in the alps mountain ranges have important influences on the structure and composition of the convective boundary layer cbl and free troposphere ft evolution of the summer cbl measured over the european alps using airborne lidar was clearly observed to attain a near uniform height up to 4 2 km asl by early afternoon a climatology of in situ high alpine aerosol measurements suggests that such substantial growth corresponding to 0 3 of the mid latitude tropopause height often occurs during summer months subsequent nocturnal collapse of the cbl was estimated to result in the venting of 0 8 0 3 so44 gg day 1 into a ft residual layer leeward of the alps

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

sst thermohaline structure and circulation in the southern gulf of california in june 2004 during the north american monsoon experiment 1 the thermohaline structure circulation and heat fluxes in the gulf of california entrance during june 2004 are described based on conductivity temperature depth and lowering acoustic doppler current profiler data collected in a 14 day survey supported by satellite data the avhrr images show extensive mesoscale structures in the region the most striking being 1 a cool filament extending from the california current domain and 2 a warm intrusion along the mainland shelf on the warm side of the thermal front created by the cool filament there was a strong current flowing into the gulf with speeds up to 0 70 ms 1 in the surface this current which the sst images suggest was associated with a decaying eddy carried 6 sv into the gulf associated with the second structure there was an ingoing coastal current on the mainland shelf with weak surface currents but with speeds 0 25 ms 1 at its core between 70 and 200 m this coastal current transported 2 sv into the gulf the two ingoing currents appear to join inside the gulf forming a very strong speeds 0 40 0 80 ms 1 narrow 30 km coastal current between the surface and 500 m depth changes in the thermohaline structure of the upper layers observed by repeat sampling of three cross sections were dominated by advection however it was found that the advective heat flux is very variable in space and time for the period of observation it was estimated that the lateral heat input was 4 8 3 0 105 wm 2 as estimated with ladcp currents and 5 7 2 20 105 wm 2 with geostrophic velocities

geochemistry and geochronology of eclogites from the northern dabie mountains central china abstract recent discoveries of uhp eclogites from the northern dabie complex ndc in central china provide an opportunity to improve our understanding of the tectonic setting of the ndc and exhumation mechanism of uhpm rocks the petrology geochemistry sr nd o isotopic compositions and sm nd isotopic chronology of some eclogites from the ndc were obtained in this study the major elemental compositions and relatively low nd t of about 10 for the eclogites suggest that the protoliths of most eclogites were ancient basaltic rocks developed in continental crust and thus these eclogites were produced by subduction of the yangtze continental crust however some of the eclogites within foliated peridotites with relatively high nd t values up to 2 4 are interpreted as pieces of lithospheric mantle scraped off the overlying mantle by subducting continental crust and then subducted together into mantle depths therefore the metamorphosed mafic ultramafic belt containing eclogite and meta peridotite blocks along the southern part of the mozitan xiaotian fault zone may represent the tectonic melange produced by the subduction of the yangtze continental crust the sm nd age of 212 4 ma defined by garnet omphacite is interpreted to represent a cooling age corresponding to in the retrograde stage of granulite facies metamorphism during eclogite exhumation the relationship between the 18o values of the eclogitic minerals such as garnet and omphacite from an eclogite sample suggests oxygen isotope equilibrium pointing to sm nd isotope equilibrium between garnet and omphacite according to comparability between o and sm nd diffusivities however the sm nd isochrons defined by whole garnet or omphacite zonal garnet yield a large age range of 187 266 ma which may be produced by nd isotopic disequilibrium between garnet and retrograded minerals in whole rocks therefore the eclogites in the ndc also underwent triassic uhp metamorphism like the uhp eclogites in the southern dabie mountains the 18o values of whole rocks for the eclogites are 2 40 to 4 32 indicating that protolith of the eclogites in the ndc underwent hydrothermal alteration at high temperature by surface water before subduction of the yangtze continental crust during the triassic period in a manner similar to protoliths of uhp rocks in the southern dabie mountains

mesoscale eddies in the northeastern pacific tropical subtropical transition zone statistical characterization from satellite altimetry 1 mesoscale eddies in the northeastern pacific tropical subtropical transition zone 16 n 30 n 130 w 102 w are analyzed using nearly 18 years of satellite altimetry and an automated eddy identification algorithm eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories we found three near coastal eddy prolific areas 1 punta eugenia 2 cabo san lucas and 3 cabo corrientes these three areas are located in places where the coastal morphology changes abruptly and strong surface current intensification occurs at some phase of the seasonal cycle although mesoscale eddies in these areas have been previously reported this study provides their first statistically supported characterization punta eugenia showed the highest eddy production with more cyclones generated followed by cabo corrientes also with more cyclones and cabo san lucas with more anticyclones cabo corrientes eddies showed the highest mean values in propagation speed swirling speed and eddy kinetic energy whereas punta eugenia eddies showed the lowest values cyclonic eddies increased their distance traveled and duration from south to north in contrast anticyclonic eddies increased from north to south in average anticyclones tend to travel faster than cyclones in all the subregions these long lived eddies were mainly nonlinear and therefore can redistribute coastal waters relatively far into the open ocean the peaks in the seasonal signal of eddy generation can be associated with the peaks in the strength of the offshore currents and or in the coastal upwelling index no clear relationship could be established between el nino events and eddy generation

oxygen isotope systematics of the precambrian basement of alberta implications for paleoproterozoic and phanerozoic tectonics in northwestern alberta we have conducted a regional survey of the oxygen isotope compositions of drill core samples from the precambrian basement of the alberta sedimentary basin the majority of samples have whole rock 18o smow values between 7 and 11 as is typical of crustal rocks however there are also a significant number of samples with 18o values less than 5 in these samples high grade minerals such as pyroxene amphibole and biotite commonly show retrograde alteration to chlorite and or epidote the majority of low 18o samples are from a 250 x 50 km zone in northwestern alberta which we refer to as the kimiwan isotope anomaly the anomaly is significant in that the most reasonable explanation for generating such a laterally extensive zone of rocks with 18o values below 5 is through high temperature interaction with surface derived fluids in an extensional tectonic setting we propose therefore that the low 18o samples define a hitherto unrecognized extensional zone in the alberta basement avai

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

low δ18o zircons u pb dating and the age of the qinglongshan oxygen and hydrogen isotope anomaly near donghai in jiangsu province china zircons from metamorphosed granites exposed near qinglongshan have 18ovsmow values of 7 to 0 in both grain rims and cores the concordant 238u 206pb ages of zircon cores are 684 to 754 ma with rims at 221 ma discordant 238u 206pb ages range from 242 to 632 ma results demonstrate a neoproterozoic age for the origin of the qinglongshan oxygen and hydrogen isotope anomaly the low 18o values were imprinted on the rocks by a hydrothermal system charged with meteoric water from a cold climate groundwater circulation was driven by heat from cooling granitic magma the geologic age of the hydrothermal system correlates with that of the nantuo tillite in the sinian strata of the south china block suggesting that qinglongshan s cold climate may be a manifestation of neoproterozoic snowball earth

the stable isotopic evolution of a metamorphic complex naxos greece a detailed study of the stable isotope composition of pelites amphibolites and marbles from the m2 metamorphic complex on naxos is presented the low grade rocks of this metamorphic complex have isotopic compositions typical of metasedimentary rocks whilst those at high grades have values typical of igneous rocks the isotopic compositions of rocks at intermediate grades vary smoothly between these two end members this variation is shown to result from the superimposition of at least two fluid flow events on a pre existing isotopic gradient the contrast between the observed seemingly simple mixing trend and the complexity of the isotopic history of these rocks has important implications for quantitative studies of fluidrock interactions

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project ii oxygen isotope and fluid inclusion distributions through vertical sections in order to reconstruct the formation and exhumation mechanisms of uhp metamorphic terrains the chinese continental scientific drilling program ccsd has been carried out in donghai of the dabie sulu ultrahigh pressure uhp metamorphic belt east china eclogite gneiss amphibolite retrograded from eclogite ultramafic rocks and minor schist and quartzite have been drilled aiming to reveal the fluid behaviour in a vertical sequence of an uhp slab we investigated fluid inclusion and oxygen isotope characteristics of selected drillcores from the main hole and the pilot holes pp2 and zk 703 of the ccsd more than 540 laser ablation oxygen isotope analyses on garnet omphacite quartz kyanite amphibole phengite rutile epidote amphibole plagioclase and biotite from various rocks in the depth range of 0 3 000 m mainly eclogite and gneiss show that the investigated rocks can be divided into two groups 18o depleted rocks as low as 18o 7 4 for garnet indicate interaction with cold climate meteoric waters whereas 18o normal rocks with bulk 18o 5 6 have preserved the o isotopic compositions of their protoliths meteoric water rock interaction has reached depths of at least 2 700 m oxygen isotope equilibrium has generally been achieved isotopic compositions of mineral phases are homogeneous on a mm to cm scale regardless of lithology but heterogeneous on the scale of a few metres oxygen isotope distributions in the vertical sections favour an in situ origin of the uhp metamorphic rocks the very negative 18o eclogites usually have higher hydroxyl mineral contents than the normal 18o rocks indicating higher water content during uhp metamorphism fluid inclusion data suggest that rocks with depleted 18o compositions have had different fluid histories compared to those with normal 18o values rocks with depleted 18o mainly have primary medium to high salinity inclusions in omphacite kyanite and quartz and abundant secondary low salinity or pure water inclusions in quartz indicating a high salinity brine dominated fluid system during peak uhp metamorphism no carbonic inclusions have been identified in these rocks by contrast primary very high density co2 inclusions are commonly found in the rocks with normal 18o values these observations suggest that fluid and oxygen isotope composition of minerals are related and reflect variable degrees of alterations of the dabie sulu uhp metamorphic rocks

fluid inclusions in granulites granulitized eclogites and garnet clinopyroxenites from the dabie sulu terranes eastern china minor granulites believed to be pre triassic surrounded by abundant amphibolite facies orthogneiss occur in the same region as the well documented triassic high and ultrahigh pressure hp and uhp eclogites in the dabie sulu terranes eastern china moreover some eclogites and garnet clinopyroxenites have been metamorphosed at granulite to amphibolite facies conditions during exhumation granulitized hp eclogites garnet clinopyroxenites at huangweihe and baizhangyan record estimated eclogite facies metamorphic conditions of 775 805 c and 15 kbar followed by granulite to amphibolite facies overprint of ca 750 800 c and 6 11 kbar the presence of na ca ba sr feldspars in garnet and omphacite corresponds to amphibolite facies conditions metamorphic mineral assemblages and p t estimates for felsic granulite at huangtuling and mafic granulite at huilanshan indicate peak conditions of 850 c and 12 kbar for the granulite facies metamorphism and 700 c and 6 kbar for amphibolite facies retrograde metamorphism cordierite orthopyroxene and ferropargasite plagioclase coronas and symplectites around garnet record a strong rapid decompression possibly contemporaneous with the uplift of neighbouring hp uhp eclogites carbonic fluid co2 rich inclusions are predominant in both hp granulites and granulitized hp uhp eclogites garnet clinopyroxenites they have low densities having been reset during decompression minor amounts of ch4 and or n2 as well as carbonate are present in the granulitized hp uhp eclogites garnet clinopyroxenites early fluids are high salinity brines with minor n2 whereas low salinity fluids formed during retrogression syn granulite facies carbonic fluid inclusions occur either in quartz rods in clinopyroxene granulitized hp garnet clinopyxeronite or in quartz blebs in garnet and quartz matrices uhp eclogite for hp granulites a limited number of primary co2 and mixed h2o co2 liquid inclusions have also been observed in undeformed quartz inclusions within garnet orthopyroxene and plagioclase which contain abundant low density co2 carbonate inclusions it is suggested that the primary fluid in the hp granulites was high density co2 mixed with a significant quantity of water the water was consumed by retrograde metamorphic mineral reactions and may also have been responsible for metasomatic reactions giant myrmekites occurring at quartz feldspar boundaries compared with the uhp eclogites in this region the granulites were exhumed in the presence of massive externally derived carbonic fluids and subsequently limited low salinity aqueous fluids probably derived from the surrounding gneisses

pre metamorphic 40ar 39ar and u pb ages in hp metagranitoids from the hercynian belt france in most orogenic belts the age of hp metamorphism and subsequent exhumation events still remain open to debate since geochronology can yield results which appear to conflict with the closure temperature concept dodson m h 1973 contrib mineral petrol 40 259 274 and because the behaviour of daughter radiogenic isotopes under hp to uhp conditions is poorly constrained to obtain new data on isotope migration under high pressure conditions two undeformed hp metagranites with partially preserved magmatic assemblages from the french variscan belt were investigated using the 40ar 39ar laser probe and u pb ion probe methods in both cases 40ar 39ar biotite and u pb zircon ages are consistent and could be related to the emplacement of pre orogenic granites despite petrological evidence of a strong metamorphic overprint during the variscan orogeny temperatures experienced by the granites during subduction and exhumation events were more than 400 c above that normally estimated for argon retention in biotite but failed to cause significant resetting of the mica 40ar 39ar chronometer only a weak intragrain redistribution of argon is evidenced with the laser probe up to the contact with metamorphic garnet fringing biotite by contrast a complete resetting of biotite ages occurs in gneisses enclosing the metagranites these results suggest that in these dry undeformed hp metagranites the thermally activated diffusion was relatively ineffective and that recrystallisation is the main process which controlled isotopic exchanges of ar and pb it is likely that the absence of pervasive deformation and fluid circulation has also exercised some control on the preservation of pre metamorphic isotopic signature in the studied rocks the possible influence of several other parameters is also discussed this example reveals that recovering thermochronological information in high pressure metamorphic rocks is not straightforward and that great caution must be paid in the use of ages for the reconstruction of p t t paths

refolded syn ultrahigh pressure thrust sheets in the south dabie complex china field evidence and tectonic implications the exhumation mechanisms of ultrahigh pressure uhp rocks have been a controversial issue ever since the discoveries of coesite and diamond in metamorphic rocks from several orogenic belts the lack of consensus principally reflects the limited number of combined structural petrologic and geochronologic studies that have been carried out in great detail within these terrains in this study we derive a complex structural history for the uhp south dabie terrain based on detailed 1 10000 mapping in the eastern dabie shan and use this to place new constraints on the exhumation process structural analysis demonstrates that syn uhp south vergent thrusting d 1 was followed by north vergent folding under amphibolite facies conditions d 2 and a third generation of folding at shallower level d 3 this supports a two stage exhumation model in which initially rapid exhumation from mantle depth to lower crustal levels is followed by slower exhumation from the lower crust level to the earth surface the remarkable structural concordance between lithological units containing uhp mineral assemblages and the enclosing gray gneiss units implies that the apparent difference in peak pressures recorded by different lithologies is not a consequence of tectonic juxtaposition but a result of differential reequilibration during decompression

altimeter derived surface circulation in the large scale ne pacific gyres part 1 seasonal variability abstract the seasonal variability of sea surface height ssh and currents are defined by analysis of altimeter data in the ne pacific ocean over the region from central america to the alaska gyre the results help to clarify questions about the timing of seasonal maxima in the boundary currents as explained below the long term temporal mean of the ssh values must be removed at each spatial point to remove the temporally invariant and large signal caused by the marine geoid we refer to the resulting ssh values which contain all of the temporal variations as the residual ssh our main findings are 1 the maximum surface velocities around the boundaries of the cyclonic alaska gyre the alaska current and the alaska stream occur in winter at the same time that the equatorward california current is weakest or reversed forming the poleward davidson current the maximum surface velocities in the california current occur in summer these seasonal maxima are coincident with the large scale atmospheric wind forcing over each region 2 most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the ne pacific basin directly connecting the boundaries of the subpolar gyre the subtropical gyre and the equatorial current system 3 seasonal variability in the surface velocities of the eastward north pacific current west wind drift is weak in comparison to seasonal changes in the surface currents along the boundaries 4 there is an initial appearance next to the coast and offshore migration of seasonal highs and lows in ssh alongshore velocity and eddy kinetic energy eke in the alaska gyre similar to the previously described seasonal offshore migration in the california current 5 the seasonal development of high ssh and poleward current residuals next to the coast appear first off central america and mainland mexico in may june prior to their appearance in the southern part of the california current in july august and their eventual spread around the entire basin in november december similarly low ssh and equatorward transport residuals appear first off central america and mexico in january february before spreading farther north in spring and summer 6 the maximum values of eke occur when each of the boundary currents are maximum

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

zircon u pb dating of water rock interaction during neoproterozoic rift magmatism in south china abstract a combined study of zircon u pb dating and mineral o isotope analysis was carried out for neoproterozoic granite gabbro and gabbrodiorite from the beihuaiyang zone that marks a rifted margin between the south china block and the supercontinent rodinia the results provide precise constraints on timing of water rock interaction resulting in unusual 18 o depletion in igneous minerals cl imaging reveals that zircons mostly show clear oscillatory and or sector zoning with or without thin alteration rims no metamorphic zircon occurs in the igneous intrusives although they suffered greenschist facies metamorphism during triassic continental collision la icpms zircon u pb dating yields consistent ages of 739 8 to 754 5 ma which are interpreted as timing of magma crystallization mineral separates have highly variable 18 o values of 0 6 to 6 8 for zircon 1 2 to 12 5 for quartz and 0 3 to 8 4 for plagioclase oxygen isotope heterogeneities exist within single intrusions and between different intrusions magmatic zircons with low 18 o values and a weighted mean u pb age of 748 6 ma crystallized from low 18 o magmas that were derived from melting of hydrothermally altered low 18 o rocks both low and normal 18 o intrusives in the beihuaiyang zone are shown to form at the same time contemporaneous with the rodinia breakup thus tectonic evolution from supercontinental rift to breakup is proposed to create conditions for alternating processes of high t hydrothermal alteration and low 18 o magmatism such processes are a characteristic feature of high t water rock interaction in volcanic rift margins associated with localized water saturated melting while the occurrence of low 18 o magmas demonstrates penetration of meteoric water into the rift tectonic zone of crustal melting the existence of normal 18 o magmas indicates that their emplacement may serve as a thermal engine to drive the second stage of meteoric water rock interaction resulting in the unusual 18 o depletion in adjacent rocks the concurrent occurrence of both low and normal 18 o magmas appears to indicate highly heterogeneous high t water rock interaction during rift magmatism

regional ultrahigh pressure coesite bearing eclogitic terrane in central china evidence from country rocks gneiss marble and metapelite the dabie mountains represent a fault bounded coesite bearing eclogite gneissic terrane within the collisional belt between the sino korean and yangtze cratons the following geologic evidence indicates that this terrane has been subjected to regional ultrahigh pressure metamorphism 1 the country rocks have a metamorphic pressure temperature evolution compatible with that of the eclogites on the basis of the occurrence of quartz pseudomorphs after coesite calcite pseudomorphs after aragonite relict high pressure assemblages in different rock types of the country rocks and consistent comparable compositional zonations of garnets in both country rocks and eclogites 2 peak metamorphic pressure temperature conditions consistently decrease both from east to west in the collisional belt and from north to south in the dabie mountains and clockwise pressure temperature paths are common for eclogites over the region 3 layered eclogites interbedded with gneisses and amphibolites contain omphacite kyanite and garnet indicating a minimum pressure of 20 kbar at 600 c for formation of these rocks

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

fluid rock interactions during ultra high pressure metamorphism dabie shan china oxygen isotope analyses of garnet separates and whole rock samples of gneiss and marble hosted eclogites from the ultra high pressure uhp dabie shan terrain fall in the range 6 76 to 10 76 comparison of the isotopic compositions of the eclogites with those of their host rocks leads to the following conclusions 1 the basaltic protolith of the eclogites had isotopic compositions in the range 2 15 to 4 99 it is proposed that this is the result of contamination of the parent basaltic magma with hydrothermally altered18o depleted source materials 2 18o enriched eclogite compositions resulted from local scale 3 m interaction between this basaltic eclogite protolith and fluids produced by decarbonation of impure marble lithologies during uhp metamorphism 3 18o depleted eclogite and gneiss compositions resulted from regional scale meteoric hydrothermal alteration of the basalts and their host rocks prior to uhp metamorphism epidote separates and whole rocks from the cores and rims of mineralogically zoned eclogite boudins within amphibolite grade biotite gneisses show no distinct isotopic differences this suggests that the preferential recrystallisation of the gneisses and the associated amphibolite grade overprint of the rims of eclogite bodies could not have resulted from regional scale infiltration of significant volumes of fluid during the exhumation of the dabie shan terrain

in situ oxygen isotope major and trace element constraints on the metasomatic modification and crustal origin of a diamondiferous eclogite from roberts victor kaapvaal craton a subducted oceanic crustal origin for most eclogite xenoliths in kimberlites has long been a cornerstone of tectonic models for craton development however eclogite xenoliths often have protracted and complex histories involving multiple metasomatic events that could overprint some of the key geochemical indicators typically taken as evidence of a subducted origin e g garnet 18o values and mineral 87sr 86sr compositions to assess the potential for disturbance of oxygen isotopic compositions in mantle eclogites via diamond forming and other possible metasomatic fluids we have conducted a multi technique in situ study of a diamondiferous eclogite xenolith from the roberts victor kimberlite s africa using sims we provide the first texturally controlled in situ measurements of 18o values in eclogitic garnet in close proximity to diamond garnet and clinopyroxene modal proportions are heterogeneous in the xenolith and garnet compositions vary from mg 75 8 79 2 grossular proportions 8 05 10 14 mol and omphacitic pyroxene has jd13 24 and mg 86 6 90 0 rare earth element patterns of minerals across the xenolith including grains close to diamond are typical lree depleted garnets and markedly lree enriched pyroxenes these silicate minerals also record detectable intra and inter grain lree abundance variations clinopyroxenes of the studied xenoliths show hfse and sr abundance variations that are decoupled from lree contents and major element variations mineralogical constraints and bulk rock reconstructions indicate that the studied sample likely experienced selective incompatible element enrichment during small volume 0 03 wt infiltration of metasomatic fluid s potentially linked to ancient diamond evolution intra grain major element lree and hfse variations in clinopyroxene resulted from late stage metasomatism oxygen isotope compositions in garnet are decoupled from all major and trace element variations with garnet 18o values being uniform across the xenolith in a wide variety of textural settings garnet 18o values of 6 5 0 2 are higher than the mean 5 19 0 26 of the mantle garnet range 4 8 5 5 modelling of the buffering effect of mantle peridotite on co2 rich and h2o rich metasomatic fluids at temperatures within the diamond stability field indicates that the likelihood of a metasomatic fluid with exotic oxygen isotopic composition arriving at a mantle eclogite body with its isotopic composition unmodified after percolative flow through dominantly peridotitic mantle at great depth is very low as we find no evidence of metasomatically induced garnet oxygen isotope variations in the studied diamondiferous eclogite xenolith we conclude that the most likely origin for the elevated garnet 18o values is via inheritance from a crustal protolith altered at relatively low temperatures these results have broader relevance and support the hypothesis of a low pressure protolith for mantle eclogite xenoliths demonstrating the robust nature of garnet oxygen isotope compositions even in diamond bearing eclogites

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

petrogenesis of late mesozoic granitoids and coeval mafic rocks from the jiurui district in the middle lower yangtze metallogenic belt of eastern china geochemical and sr nd pb hf isotopic evidence abstract large scale cu au mineralization is associated with the late mesozoic granitoids in the jiurui district of the middle lower yangtze mineralization belt in eastern china to constrain the petrogenesis of these granitoids and coeval mafic rocks a detailed geochemical and sr nd pb hf isotopic study was performed the jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry these granitoids are characterized by sio 2 and k 2 o contents of 58 8 wt to 68 6 wt and 1 9 wt to 5 7 wt respectively these granitoids show relatively high mgo contents 1 0 wt to 3 1 wt average 2 1 wt and high mg values 39 to 70 average 54 the jiurui granitoids are enriched in light rare earth elements lree large ion lithophile elements lile and compatible trace elements cr ni and v but are relatively depleted in nb ta y and yb these rocks show a negligible negative eu anomaly eu eu 0 76 1 13 average 0 91 and nearly no negative sr anomaly the whole rock initial 87 sr 86 sr ratios range from 0 7060 to 0 7092 and the e nd t values vary from 5 4 to 2 0 the granitoids show radiogenic pb isotopic ratios with values of 206 pb 204 pb 17 93 18 21 207 pb 204 pb 15 55 15 58 and 208 pb 204 pb 38 16 38 56 for the plagioclases the zircon hf isotopic compositions show e hf t values from 11 8 to 2 4 the coeval mafic rocks consist of lamprophyre diabase and fine grained mafic dyke these rocks are characterized by sio 2 contents ranging from 47 6 wt to 54 8 wt with a negative eu anomaly and a positive to negative sr anomaly the whole rock initial 87 sr 86 sr ratios range from 0 7059 to 0 7071 and the e nd t values vary from 3 8 to 1 4 by comparing the geochemical and isotopic compositions of the jiurui granitoids and the coeval mafic rocks we conclude that the granitoids are similar to adakites that were likely related to the delamination processes and the coeval mafic rocks may have originated directly from enriched lithospheric mantle the thickened lower continental crust and underlying enriched lithospheric mantle may have been simultaneously delaminated into the asthenospheric mantle this process led to the partial melting of the thickened lower crust and the enriched lithospheric mantle and the melts experienced an interaction with the asthenospheric mantle during ascension mafic melts could be generated from the enriched lithospheric mantle which was heated by the upwelling asthenospheric mantle the geochemical and isotopic compositions of mafic rocks were most likely controlled by the afc process a geochemical and isotopic comparison of the granitoids in the jiurui district with those of two other districts e g angui and tongling in the same mineralization belt indicates that a significant crust mantle interaction played a crucial role in their petrogeneses and metallogeneses from the southwest to northeast in this metallogenic belt the proportion of mantle component that was involved in the granitic magma shows a decreasing trend from the jiurui to the angui and tongling districts it is suggested that the juirui district has the highest potential for a significant amount of cu au accumulation because the mantle is an important supply for these metals

high pressure blueschists and eclogites in hong an a framework for addressing the evolution of high and ultrahigh pressure rocks in central china the hong an region in the qinling dabie collisional zone in eastern china hosts a series of metamorphic rocks exposing a south to north distribution from blueschist blueschist greenschist amphibolite eclogite kyanite free and kyanite eclogite to coesite eclogite facies rocks that represent progressively deeper levels of the mesozoic subduction collision complex the hong an area is interesting for three reasons 1 it escaped the thermal and structural overprint imparted on much of the dabie mountains during early cretaceous intrusion of voluminous granites and granodiorites 2 the high pressure hp hong an eclogites are widely distributed often preserve prograde crystallization histories and can be directly linked in time and space to the blueschist blueschist greenschist rocks exposed to the south 3 the blueschist blueschist greenschist facies rocks are generally better exposed than their equivalents in the southeastern dabie mountains and offer some opportunity for simultaneous structural and metamorphic analysis the hong an area hp rocks offer perhaps the closest approximation to a preserved snapshot of mesozoic pressure temperature p t conditions attending early subduction exhumation in the region and are thus essential to generating a coherent picture of the dynamics attending both metamorphism and exposure of the coeval ultrahigh pressure uhp rocks the purpose of this contribution is twofold 1 to document previously unpublished metamorphic and structural data characterizing these hp sequences and their relative continuity in hong an 2 to incorporate these data with recent geochronologic structural and paleomagnetic information in the context of protracted late paleozoic through mesozoic subduction collision and exhumation metamorphism and exhumation of some of the southern hong an hp sequences appear to have occurred concomitant with oceanic subduction immediately to the west and thus may have preceded widespread continental subduction collision moreover all of the hp uhp sequences in the region were exhumed before the end of collision between the sino korean and yangtze cratons at ca 160 ma exhumation of hp uhp rocks both before and during continental plate collision is neither novel for central china nor for other hp uhp zones but is important to take into account when reconstructing the evolution of such orogens

unusually low δ18o ultra high pressure metamorphic rocks from the sulu terrain eastern china eclogite and quartzite interlayers containing ultra high pressure uhp metamorphic mineral assemblages occur at qinglongshan in the sulu terrain eastern china these rocks exhibit some of the most negative oxygen isotope compositions that have ever been reported for metamorphic rocks the 18 value of minerals in eclogite ranges from 10 4 to 9 0 o and in quartzite ranges from 10 2 to 7 3 near isotopic equilibrium between minerals and rocks suggests that these rocks must have acquired such low oxygen isotope compositions before the uhp metamorphism through near surface meteoric water rock interactions the rocks were then subducted to a great depth during continent continent collision forming uhp minerals with concomitant local oxygen isotope redistribution it is significant that the rocks have retained such negative oxygen isotope compositions despite subduction into the upper mantle

stable isotope geochemistry of marbles from the coesite uhp terrains of dabieshan and sulu china abstract marbles from dabieshan and sulu china suffered ultra high pressure uhp metamorphism in the coesite eclogite facies at approximately 700 c and 30 kbars during triassic continental collision and subduction the marbles range in isotopic composition from 7 to 25 18 o vsmow and from 0 to 6 13 c vpdb high 13 c values are representative of unmodified protoliths and are similar to those of 13 c enriched sinian carbonate rocks from the yangtze craton high oxygen isotope ratios reflect pristine protoliths but the low values may have been caused by infiltration of low 18 o meteoric water during diagenesis and dolomitization by fracture controlled infiltration of water during subduction by metamorphic mineral reactions or by a combination of these processes no evidence of regional isotopic transport during uhp metamorphism has been found sampling on scales of 1 to 100 m shows marbles to be inhomogeneous in both carbon and oxygen isotopes only samples separated by less than 10 cm have equilibrated oxygen and carbon isotope compositions limited isotopic equilibration between adjacent rocks is consistent with the preservation of unaltered uhp minerals and indicates that the metamorphic fluid rock system was rock dominated during and following peak metamorphism a freely flowing pervasive fluid phase was not present during uhp metamorphism there is no evidence of isotopic exchange between marble and the upper mantle into which it was subducted correlation of geochemical similarities of uhp marbles with sinian limestones implies that the subducted edge of the yangtze craton extends at least as far north as the coesite eclogite facies rocks of dabieshan deposition of protolith carbonates may have taken place in a cold climate either preceding or following but not coincident with neoproterozoic glaciation

fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe dabie shan china fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe in dabie shan east central china have preserved remnants of early prograde and or peak metamorphic fluids reset during post uhp ultrahigh pressure metamorphic uplift inclusions occur in several minerals e g omphacite epidote notably as isolated primary inclusions in quartz included in various host minerals two major fluid types have been identified non polar fluid species n2 or co2 and aqueous the latter is by far the most predominant aqueous fluids cover a wide range of salinity from halite bearing brines to low salinity fluids for non polar fluids few n2 inclusions occur in undeformed eclogite whereas a number of co2 rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences the primary character of n2 and high salinity aqueous inclusions indicates that they are remnants from uhp metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre metamorphic fluids this conclusion is supported by the preservation in some samples of microdomains containing synchronous inclusions of variable salinities which tend to relate to the chemical composition of the host crystal carbonic fluids may be derived from neighbouring rocks notably marble and carbonate bearing metasediments during post metamorphic uplift during post uhp exhumation a limited decrease of the fluid density has occurred with formation of new sets of fluid inclusions fluid movements however remained exceedingly limited at the scale of the enclosing crystal

mean three dimensional circulation in the northeast tropical pacific abstract historical xbt data are used to construct a mean climatology of the three dimensional geostrophic circulation in the northeast tropical pacific southwest of mexico and central america and are diagnosed based on linear dynamics forced with satellite scatterometer winds unlike the familiar central tropical pacific where the zonal scales are very large and the wind forcing nearly a function of latitude alone the north pacific east of about 120 w is strongly influenced by wind jets blowing through gaps in the central american cordillera the curl imposed by these wind jets imprints on the ocean producing a distinctive pattern of thermocline topography and geostrophic currents that are consistent with the sverdrup balance notably the weakening of the north equatorial countercurrent near 110 w is due to the wind forcing given the observed stratification and wind stress curl planetary vorticity conservation also determines the distribution of vertical velocity in the region with about 3 5 sv

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

structure of the atmosphere in an urban planetary boundary layer from lidar and radiosonde observations the planetary boundary layer pbl over mexico city was probed with a scanning backscatter lidar to characterize and evaluate the multidimensional structure of the atmosphere comparisons were made between radiosonde and lidar derived pbl heights which showed the two techniques to be in close agreement the spatial properties of the free atmosphere pbl interface were found to be approximately the same size as the entrainment zone thickness below the interface the lidar observed spatially resolved structures such as thermal plumes convective eddies low level jets and entrainment into the pbl these structures were spatially correlated with the local diabatic condition and wind stress one highly unstable atmosphere contains a lidar visualized convective structure rising to a height of 0 45 the inversion base which was predicted from earlier turbulence models other features such as low level jets were found to be associated with neutral atmospheres in the mixing layer the analysis indicates that the transport of pollutants is not a continuous and gradient driven process but low frequency and spatially discontinuous the high spatial and temporal resolution afforded by the scanning lidar depicts surface atmosphere interactions which are neither spatially homogeneous nor horizontally uniform

field occurrences and petrology of eclogites from the dabie mountains anhui central china four distinct types of eclogites are recognized according to their field occurrences and mineral parageneses in a gneiss terrane of the dabie mountains a collision zone between the sino korean and yangtze cratons in central china some eclogites contain coesite and its quartz pseudomorphs enclosed in garnet and omphacite type i eclogites occur as layers in serpentinites and contain garnet clinopyroxene orthopyroxene phengite rutile and coesite pseudomorph type ii eclogites occur as lenticular bodies inside serpentinites and contain garnet clinopyroxene quartz rutile and edenitic hornblende type iii eclogites occur as blocks of 2 cm to 20 m in size in a matrix of hornblende gneiss and biotite gneiss and type iv eclogites occur as thin layers interbedded with amphibolites p t estimates for these different eclogites indicate that they were formed under different physical conditions all the eclogites were affected by later regional metamorphism for which the p t conditions are estimated this paper provides an introduction to the abundant eclogites from central china which have not been reported previously in western literature specifically the mode of field occurrence petrography mineral chemistry and formation conditions of the four types of eclogites are described the paper is thus designed to establish a petrological framework for future detailed studies of the eclogites and their country rocks in an ancient zone of collision

the paleozoic metamorphic history of the central orogenic belt of china from 40ar 39ar geochronology of eclogite garnet fluid inclusions abstract the pressure temperature time evolution of the uhp eclogites of dabie sulu in the eastern sector of the central orogenic belt of china shows a complex pattern of predominantly triassic and to a lesser extent early paleozoic ages 40 ar 39 ar stepwise crushing analysis of eclogitic garnets yielded consistently paleozoic ages because our initial results from the bixiling eclogite were of limited areal extent their significance required further testing data for garnet bearing gneiss and eclogites from new locations in northern and southern dabieshan shuanghe ganghe and hongmiao confirm the paleozoic garnet results obtained from bixiling eclogite we also tested the technique on a garnet sample of known paleozoic age from altyn tagh in the western central orogenic belt these new results indicate that light colored garnets from dabieshan and altyn tagh yield concordant 40 ar 39 ar ages ranging from 445 465 ma by in vacuo crushing and confirm that a paleozoic u hp metamorphic event took place in the central orogenic belt from altyn tagh in western china to dabieshan in eastern china in contrast dark colored garnets from mafic metavolcanics do not yield 40 ar 39 ar plateaux or isochrons ages

u pb hf and o isotope evidence for two episodes of fluid assisted zircon growth in marble hosted eclogites from the dabie orogen abstract a combined study of internal structure u pb age and hf and o isotopes was carried out for metamorphic zircons from ultrahigh pressure eclogite boudins enclosed in marbles from the dabie orogen in china cl imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain respectively the metamorphic zircons have low th and u contents with low th u ratios yielding two groups of 206 pb 238 u age at 245 3 to 240 2 ma and 226 4 to 223 2 ma respectively anomalously high 18 o values were obtained for refractory minerals with 9 9 to 21 4 for garnet and 16 9 for zircon this indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction zone metamorphism most of the zircons are characterized by very low 176 lu 177 hf ratios of 0 000001 0 000028 indicating their growth in association with garnet recrystallization a few of them falling within the older age group have comparatively high 176 lu 177 hf ratios of 0 000192 0 000383 suggesting their growth prior to the formation of garnet in the late stage of subduction the variations in the lu hf ratios for zircons can thus be used to correlate with garnet growth during eclogite facies metamorphism in either case the zircons have variable e hf t values for individual samples suggesting that their protolith is heterogeneous in hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle nevertheless a positive correlation exists between 206 pb 238 u ages and lu hf isotope ratios for the metamorphically recrystallized zircons suggesting that eclogite facies metamorphism in the presence of fluid has the identical effect on zircon lu hf and u th pb isotopic systems we conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh pressure metamorphism whereas the younger zircons grew in the presence of fluid released during the initial exhumation toward high pressure eclogite facies regime

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

metamorphic evolution mineral chemistry and thermobarometry of schists and orthogneisses hosting ultra high pressure eclogites in the dabieshan of central china as is typical of ultra high pressure uhp terrains the regional extent of the uhp terrain in the dabieshan of central china is highly speculative since the volume of eclogites and paragneisses preserving unequivocal evidence of coesite and or diamond stability is very small by contrast the common garnet xmn 0 18 0 45 phengite si 3 2 3 35 zoned epidote ps38 97 biotite titanite two feldspars quartz assemblages in the more extensive orthogneisses have been previously thought to have formed under low p t conditions of ca 400 50 c at 4 kbar however certain orthogneiss samples preserve garnets with xca up to 0 50 rutile inclusions within titanite or epidote and relict phengite inclusions within epidote with si contents p f u of up to 3 49 overlapping with the highest values 3 49 3 62 recorded for phengites in samples of undoubted uhp schists these and other mineral composition features such as a site deficiencies in the highest si phengites na in garnets linked to y yb substitution and al f ti 1 o 1 substitution in titanites are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated uhp schists and eclogites re evaluated garnet phengite and garnet biotite fe mg exchange thermometry and calculated 5 rutile 3 grossular 2sio2 h2o 5 titanite 2 zoisite equilibria indicate that the orthogneisses may indeed have followed a common subduction related clockwise p t path with the uhp paragneisses and eclogites through conditions of pmax at ca 690 c 715 c and 36 kbar to tmax at ca 710 c 755 c and 18 kbar prior to extensive re crystallisation and re equilibration of these ductile orthogneisses at ca 400 c 450 c and 6 kbar the consequential conclusion that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these dabieshan orthogneisses with undoubted uhp lithologies has far reaching implications for the interpretation of controversial gneiss eclogite relationships in other uhp metamorphic terrains

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism

oxygen isotope geochemistry of ultrahigh pressure metamorphic rocks from 200 4000 m core samples of the chinese continental scientific drilling abstract oxygen isotope studies were carried out for ultrahigh pressure metamorphic rocks from the main hole of the chinese continental scientific drilling in the sulu orogen the samples of interest include various types of lithology mainly eclogite and gneiss in a depth of 200 to 4000 m containing five continuous core segments between contrasting lithologies the results show a large variation in 18o value from 10 41 to 9 63 for constituent minerals distinct 18o depletions are observed in the frequently alternated layers of eclogite and gneiss in which the variations of 18o values are gradual regardless of lithologies both equilibrium and disequilibrium o isotope fractionations are observed between quartz and the other minerals special attention was paid to the relationship between distance petrography and 18o value of adjacent samples the results show o isotope heterogeneities between the different and same lithologies on scales of about 20 to 50 cm corresponding to the maximum scales of fluid mobility during the continental collision amphibolite facies retrograde metamorphism during exhumation caused mineral reactions and o isotope disequilibria between some of the minerals considerable changes occur in 18o and petrography at the contact between eclogite and gneiss suggesting that the contact between different lithologies is the most favorable place for fluid activity despite the widespread retrogression retrograde fluid was internally buffered in the stable isotope compositions the retrograde fluid is of deuteric origin and thus was derived from the decompression exsolution of structural hydroxyl although locally external fluids became available along fault zones and lithological layers it still acted within the exhumed slabs with internal origins fluid flow also took place after the amphibolite facies retrogression but it only affects the o isotope compositions of feldspar and mica premetamorphic protoliths are deduced to have heterogeneous 18o values due to varying degrees of meteoric water rock interaction before continental collision minimum depth of the 18o depletion is up to 3300 m together with areal 18o depletion in surface outcropped rocks along the dabie sulu orogenic belt at least 66 000 km3 of supracrustal rocks were interacted with meteoric water along the northern margin of the south china block during the neoproterozoic

water masses and circulation in the tropical pacific off central mexico and surrounding areas abstractthe seasonal variations and the interactions of the water masses in the tropical pacific off central mexico tpcm and four surrounding areas were examined based on an extensive new hydrographic database the regional water masses were redefined in terms of absolute salinity sa and conservative temperature according to the thermodynamic equation of seawater 2010 teos 10 hydrographic data and the evaporation minus precipitation runoff balance were used to investigate the origin and seasonality of two salinity minima in the area the shallow 50 100 m salinity minimum originates with the california current system and becomes saltier as it extends southeastward and mixes with tropical subsurface waters while the surface salinity minimum extends farther north in the tpcm in summer and fall because of the northward advection of tropical surface waters the interactions between water masses allow a characterization of the seasonal pattern of circulation of the mexican coastal current mcc

u pb zircon and sm nd isotopic study of the huangtuling granulite dabie sulu belt china implication for the paleoproterozoic tectonic history of the yangtze craton sims data demonstrate archean 2 9 to 2 7 ga and paleoproterozoic 1991 43 ma ages for rounded detrital zircon cores and unzoned rims respectively in a graulite sample collected from huangtuling dabie sulu orogenic belt china the granulite rocks in this locality have pelitic compositions and represent an exposure of the northern margin of the yangtze craton the rounded zircon cores show oscillatory zoning and have th u ratios 0 17 0 78 systematically higher than those of the unzoned luminescent rims 0 005 0 03 the age of the detrital zircon cores and whole rock nd isotope model age suggest that the huangtuling granulite was possibly derived from a provenance dominated by archean rocks similar to the kongling complex exposed 200 km in the southwest multiple phases of metamorphism have been identified for the granulites with the dominant granulite facies mineral assemblage defining an early clock wise metamorphic p t path orthopyroxene plagioclase and whole rock material define a linear trend in a 147sm 144nd 143nd 144nd diagram corresponding to an age of 1926 146 ma this result and the u pb data for the zircon rims suggest that a collisional event may have occurred along the northern margin of the yangtze craton at 2 0 ga inviting further study on whether the yangtze craton was involved in the assembly of the recently proposed paleo mesoproterozoic supercontinent columbia

in situ zircon u pb oxygen and hafnium isotopic compositions of jurassic granites from the north china craton evidence for triassic subduction of continental crust and subsequent metamorphism related 18o depletion abstract six samples of the linglong granitic pluton from the southeastern margin of the north china craton yield similar jurassic magmatic zircon u pb ages and evolved whole rock sr nd isotopic compositions they are weakly peraluminous to strongly peraluminous with a cnk molar al 2 o 3 cao na 2 o k 2 o ratios of 1 05 to 1 3 except one sample with an a cnk of 0 98 however they have contrasting inherited zircon ages and magmatic zircon hf and o isotopic compositions two samples have 2 5 ga inherited zircons and high 18 o magmatic zircons and are interpreted to be derived dominantly from the lower crust of the north china craton another two samples with dominantly triassic inherited zircons and low 18 o magmatic zircons are considered to be derived mainly from the subducted continental crust of the south china craton and the source was considered to be significantly depleted in 18 o during triassic metamorphism the rest two samples have dominantly neoproterozoic inherited zircons and intermediate 18 o magmatic zircons and are also considered to be derived mainly from the subducted continental crust of the south china craton but the source was not significantly depleted in 18 o during triassic metamorphism the different lithologies whole rock e nd t and zircon e hf t between the samples also strongly support that they are derived from different sources although magmatic zircons from the six samples have variable 18 o from 0 7 to 8 5 and e hf t from 27 6 to 11 8 individual samples have more limited e hf t and 18 o the 18 o and e hf t of magmatic zircons from the samples indicate no contribution of mantle derived magmas to the linglong granites this is supported by the fact of no coeval mantle derived rocks in the region the results suggest that large variations of e hf t and 18 o do not necessarily indicate mixing between mantle and crustal derived magmas instead they may reflect heterogeneity in the source the granites are interpreted to result from partial melting of the thickened crust caused by triassic subduction of the south china craton continental crust beneath the north china craton subsequent lithospheric extension and orogenic collapse are the most likely mechanism for the granites

a review of eastern tropical pacific oceanography summary abstract the collection of articles in this volume reviewing eastern tropical pacific oceanography is briefly summarized and updated references are given the region is an unusual biological environment as a consequence of physical characteristics and patterns of forcing including a strong and shallow thermocline the itcz and coastal wind jets equatorial upwelling the costa rica dome eastern boundary and equatorial current systems low iron input inadequate ventilation of subthermocline waters and dominance of enso scale temporal variability remaining unanswered questions are presented

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

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

prograde mica 40ar 39ar growth ages recorded in high pressure rocks syros cyclades greece abstract phengites from the eclogite and blueschist facies sequences of the cycladic island of syros greece have been dated by the in situ uv laser ablation 40 ar 39 ar method a massive phengite rich eclogite and an omphacite rich metagabbro were investigated the phengites are euhedral and coarse grained several 100 m strain free and exhibit no evidence for late brittle deformation or recrystallization apparent ages in these samples range from 43 to 50 ma for the phengite rich eclogite and 42 to 52 ma for the omphacitic metagabbro this large spread of ages is visible at all scales within individual grains as well as in domains of several 100 m and across the entire sample ca 2 cm such variations have been traditionally attributed to metamorphic cooling or the incorporation of excess argon however the textural equilibrium between the phengites and other high pressure phases and the subtle compositional variations within the phengites especially the preservation of growth textures alternatively suggest that the observed range in ages may reflect variations of radiogenic argon acquired during phengite formation and subsequent growth thus dating a discrete event on the prograde path this implies that the oldest phengite 40 ar 39 ar ages provide the best estimate of a minimum crystallization age which is in agreement with recently reported u pb and lu hf geochronological data our results are consistent with available stable isotope data and further suggest that under fluid restricted conditions both stable and radiogenic isotopic systems can survive without significant isotopic exchange during subduction and exhumation from eclogite facies p t conditions

altimeter derived surface circulation in the large scale ne pacific gyres part 2 1997 1998 el nino anomalies abstract changes in the sea surface heights ssh and geostrophic transports in the ne pacific are examined during the 1997 1998 el nino using altimeter data sea level pressure slp fields proxy winds and satellite sea surface temperature sst most of the signal occurs along the boundaries of the basin from panama to the alaska peninsula changes in the ssh and alongshore transports along the boundaries are caused both by propagation of signals from the south stronger between the equator and the gulf of california and by local and basin scale winds stronger between the pacific northwest and the alaska peninsula two periods of high ssh occur at the equator may july 1997 and october 1997 january 1998 the first coastal ssh signal moved quickly polewards to approximately 24 n in early june then stalled and moved farther north during transient events in july september large scale wind forcing combined with the equatorial signals during the second period of high equatorial ssh fall 1997 to move the high ssh and poleward transports quickly around the alaska gyre a connection between the boundary currents and the interior north pacific developed as part of the large scale response to the basin scale winds after changes in the boundaries decreases in anomalies of ssh and poleward transports began in january 1998 south of 40 n and in february 1998 farther north

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

circulation at the entrance of the gulf of california from satellite altimeter and hydrographic observations 1 the surface circulation around the entrance to the gulf of california is described from satellite altimetry supported by 10 conductivity temperature depth ctd surveys the sea surface height calculated from the 1 4 world ocean database 2001 climatology plus the archiving validation and interpretation of satellite oceanographic altimeter data october 1992 to january 2008 were rms adjusted to the dynamic height calculated from ctd data the 27 0 kg m 3 isopycnal provided the optimum reference in the mean the surface circulation shows a branch of the california current heading landward toward the gulf of california entrance where it splits into two subbranches these are separated by a cyclonic circulation attached to the coast south of cabo corrientes this feature is produced by sverdrup dynamics and is the first observational indication that the mexican coastal current is generated locally by the wind stress curl as previously suggested by numerical models the global variance of the surface circulation can be separated into seasonal explained variance 35 interannual explained variance 35 and mesoscale explained variance 30 components the seasonal signal which shows the interplay of the poleward mexican coastal current and the equatorward branch of the california current can be explained by a long rossby wave model forced by the annual wind and by radiation from the coast the interannual component is dominated by the el nino southern oscillation which induces in the gulf entrance an anticyclonic cyclonic circulation during el nino la nina this circulation includes a poleward flowing branch during el nino parallel to the pacific coast of the baja california peninsula the mesoscale variability is caused by intense eddy activity

mesoscale eddies in the southern gulf of california during summer characteristics and interaction with the wind stress 1 the hydrodynamic characteristics of mesoscale eddies of the southern gulf of california are described from observations made in august 2004 vertical profiles to 1000 m were made with a conductivity temperature depth ctd probe with dissolved oxygen and fluorescence sensors and a lowered acoustic doppler profiler the four sampled eddies were aligned along the gulf axis and had alternating sense of rotation the okubo weiss parameter was used to calculate the eddy core radii and it also revealed that the current field of almost all the sampled area was eddy dominated the mean radii of the eddy cores varied between 32 and 36 km maximum surface velocities were 0 4 0 5 m s the anticyclonic eddies were 500 700 m deep while the cyclones were 450 500 m deep the depression of the isolines associated with the anticyclonic eddies was 100 m at depths between 200 and 400 m however the thermocline pycnocline which spanned from 20 to 75 m was domed by 10 m the cyclonic eddies lifted the isolines by 70 m at depths above 500 m but the isolines were flat above 60 m this suggests that different dynamics operate in the layer above the strong and shallow pycnocline in particular the wind stress curl can affect circulation and pycnocline topography and therefore the patterns that appear in chlorophyll satellite images in our case the eddies were detectable in those images because of the chlorophyll enhanced streamers along their edges and for anticyclones probably because the chlorophyll maximum found at 40 50 m depth was domed following the pycnocline

cluster of water molecules in garnet from ultrahigh pressure eclogite through the use of transmission electron microscopy and infrared spectroscopy hydrous components have been identified as hydroxyl and free water h 2 o in elongate garnet of ultrahigh pressure eclogite from the dabie mountains eastern china the h 2 o occurs as clusters of water molecules and as hydroxyl in garnet the clusters of water molecules are interpreted to have promoted elongation of garnet through hydrolytic weakening the presence of hydrous species in ultrahigh pressure garnet from continental crust protoliths indicates that such protoliths are able to carry water into the mantle during the subduction of continental lithosphere

hydrogen and oxygen isotope evidence for fluid rock interactions in the stages of pre and post uhp metamorphism in the dabie mountains abstract hydrogen and oxygen isotope studies were carried out on high and ultrahigh pressure metamorphic rocks in the eastern dabie mountains china the 18 o values of eclogites cover a wide range of 4 2 to 8 8 but the d values of micas from the eclogites fall within a narrow range of 87 to 71 both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals with reversed fractionations between omphacite and garnet in some eclogite samples the 18 o values of 4 to 1 for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water rock interaction before the high to ultrahigh pressure metamorphism heterogeneous 18 o values for the eclogite protoliths implies not only the varying degrees of the water rock interaction before the metamorphism at different localities but also the channelized flow of fluids during progressive metamorphism due to rapid plate subduction retrograde metamorphism caused oxygen and hydrogen isotope disequilibria between some of the minerals but the fluid for retrograde reactions was internally buffered in the stable isotope compositions and could be derived from structural hydroxyls dissolved in nominally anhydrous minerals

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

distribution of hydrous components in jadeite of the dabie mountains two kinds of jadeite occur in the jadeite quartzite from the dabie mountains eastern china associated either with weak or strong deformation the former shows a uniform composition while the latter shows both uniform and zoning composition these jadeites were examined with infrared ir spectroscopy all jadeite displays hydroxyl oh stretching bands implying that hydrous components commonly exist in jadeite the concentration of the hydrous components in the jadeite with weak deformation is homogenous whereas the concentration of the hydrous components in strongly deformed samples is variable the correlation between the intensity of oh band absorbance and compositional zoning of jadeite with strong deformation indicates that na rich jadeite can accommodate more oh than na poor jadeite its interpretation is that there is more na associated with greater oh availability in the initial crystallization environment our data of the comparatively high oh concentrations recorded in the core of the jadeite which contains relative high vacancies in m2 site imply that both oh content and the vacancies in m2 site could decrease during exhumation of the jadeite quartzite the decrease of oh solubility in jadeite would result in the formation of h2o fluid during the early exhumation of uhp metamorphic rocks the h2o fluid transformed from oh during exhumation could trigger and enhance the early retrograde metamorphism of the host rocks and facilitate plastic deformation of jadeite grain by dislocation creep and diffusion creep

origin of retrograde fluid in ultrahigh pressure metamorphic rocks constraints from mineral hydrogen isotope and water content changes in eclogite gneiss transitions in the sulu orogen abstract by taking advantage of having depth profiles between contrasting lithologies from core samples of the chinese continental scientific drilling ccsd project a combined study was carried out to examine changes in mineral h isotope total water and hydroxyl contents in garnet and omphacite across the contacts between ultrahigh pressure uhp eclogite and gneiss in the sulu orogen east central china the samples of interest were from two continuous core segments from the ccsd main hole at depths of 734 21 737 16 and 929 67 932 86 m respectively the results show d values of 116 to 64 for garnet and 104 to 82 for omphacite consistent with incorporation of meteoric water into protoliths of uhp metamorphic rocks by high t alteration both equilibrium and disequilibrium h isotope fractionations were observed between garnet and omphacite suggesting fluid assisted h isotope exchange at local scales during amphibolite facies retrogression while bulk water analysis gave total h2o concentrations of 522 1584 ppm for garnet and 1170 20745 ppm for omphacite structural hydroxyl analysis yielded h2o contents of 80 413 ppm for garnet and 228 412 ppm for omphacite it appears that significant amounts of molecular h2o are present in the minerals pointing to enhanced capacity of water storage in the uhp eclogite minerals hydrogen isotope variations in the transition between eclogite and gneiss show correlations with variations in their water contents petrographically the degree of retrograde metamorphism generally increases with decreasing distance from the eclogite gneiss boundary thus retrograde metamorphism results in mineral reactions and h isotope variation because hydroxyl solubility in nominally anhydrous minerals decreases with dropping pressure significant amounts of water are expected to be released from the minerals during decompression exhumation decompression exsolution of structural hydroxyl from 1 m3 volume of eclogite composed of only garnet and omphacite results in release of a quantitative estimate of 3 07 3 44 kg water that can form 140 156 kg amphibole during exhumation therefore it is concluded that fluid for retrogression of the eclogites away from the eclogite gneiss boundary was derived from the decompression exsolution of structural hydroxyl and molecular h2o in nominally anhydrous minerals for the eclogites adjacent to gneiss in contrast the retrograde metamorphism was principally caused by aqueous fluid from the gneiss which is relatively rich in water consequently both the origin and availability of metamorphic fluid during exhumation of deeply subducted continental crust are deciphered by this combined study focusing on the transitions and the retrograde processes between the felsic and mafic uhp rocks

stable and radiogenic isotope systematics in epidote group minerals epidote minerals the epidote group together with the orthorhombic polymorph zoisite occur in a wide range of igneous metamorphic and sedimentary lithologies although often present in only small quantities epidote group minerals can nonetheless be used to generate important quantitative constraints on processes such as regional metamorphism deep seated pluton emplacement and uplift hydrothermal fluid flow and sedimentary provenance e g zen and hammarstrom 1984 brandon et al 1996 cartwright et al 1996 keane and morrison 1997 spiegel et al 2002 petrologic studies on epidote group minerals formed by these and other processes are reviewed in bird and spieler 2004 grapes and hoskin 2004 enami et al 2004 and schmidt and poli 2004 in this chapter stable and radiogenic isotope studies of epidote group minerals will be reviewed although stable and or radiogenic isotope data exist for epidote group minerals from a number of different geologic settings such data have produced particularly important insights into 1 fluid flow associated with variable grades of metamorphism particularly ultra high pressure uhp metamorphism 2 intrusion of deep seated plutonic systems 3 the nature of hydrothermal alteration in geothermal systems 4 age relations in hydrothermal systems and 5 sedimentary provenance based on the chemical composition of naturally occurring epidote minerals oxygen hydrogen and chlorine stable isotopes all have the potential to be important petrogenetic indicators in systems involving epidote minerals oxygen is present in epidote minerals bound in isolated to4 tetrahedra t2o7 groups and in the hydroxyl site as both oh and o 2 hydrogen and chlorine are present in the hydroxyl site as oh and cl respectively although cl is present in only very small quantities frei et al 2004 to date oxygen and hydrogen isotope systematics have been studied both

subduction ultrahigh pressure metamorphism and regurgitation of buoyant crustal slices implications for arcs and continental growth abstract intracontinental collisional belts that retain mineralogic relics of phanerozoic ultrahigh pressure uhp metamorphism are increasingly being recognized adjacent regions generally lack evidence of coeval calcalkaline volcanism plutonism following consumption of intervening oceanic lithosphere each orogen marks the site of a deeply subducted microcontinental promontory fragments of which later returned to midcrustal levels mafic and ultramafic rocks are volumetrically minor pressures in uhp complexes approached or exceeded 2 8 gpa at 600 900 c subduction zones involve low t prograde gradients and constitute the only plate tectonic realm where such conditions exist although internal portions of descending plates may have even lower geothermal gradients crustal upper margins are typified by p t trajectories of 5 10 c km attending underflow clinoamphibole rich metabasaltic rocks dehydrate at pressures 2 2 2 5 gpa this accounts for the kinetically favorable solid state production of mafic eclogites and partial fusion of morbs to form hydrous andesitic melts devolatilization of partly serpentinized mantle lithosphere also introduces h 2 o to the magmagenic zone as large masses of continental crust enter deeper portions of subduction zones mineralogic transformations slow or cease because micas the major oh bearing phases in such rocks retain volatile contents to pressures 4 gpa persistence of hydroxyl bearing layer silicates may explain the metastable preservation of low density assemblages in continental crust subjected to uhp conditions and the dearth of calcalkaline magmatism in most collision belts exhumed uhp terranes are intensely deformed and disaggregated all consist dominantly of quartzofeldspathic compositions mafic eclogites garnet peridotites constitute only a few volume percent eventual decoupling of the relatively low density subducted crust promotes buoyancy propelled transport to shallow depths along the subduction channel with the hanging wall lithosphere acting as a stress guide extensional collapse and erosional unroofing of rising masses result in the continued ascent of deeply subducted but buoyant crustal material although equidimensional massifs must return surfaceward large volume to surface areas render the contained uhp phase assemblages virtually unquenchable surviving uhp terranes thus consist of relatively thin slabs of continental crust allochthons that retain uhp relics apparently lost heat by conduction across both upper normal fault and lower reverse fault contacts based on present exposures estimated thicknesses of uhp sheets are qinling dabie sulu belt 5 km kokchetav complex 1 3 km dora maira massif 1 2 km western gneiss region 1 km slices evidently rose to midcrustal levels at exhumation rates approaching 10 mm per year back reaction attending decompression in all cases was nearly complete where uhp mineral inclusions persisted retrogression apparently was limited by the relative impermeability of the rocks to catalytic aqueous fluids and by declining temperatures the coarse grain size of host phases also disfavored complete retrogression

low 18o scourie dike magmas from the lewisian complex northwestern scotland the scourie dike swarm of the lewisian complex northwestern scotland comprises a dominant suite of quartz tholeiites and lesser volumes of norites olivine gabbros and bronzite picrites that were emplaced at depths of 14km in two episodes at 2 0 and 2 4 ga unaltered quartz tholeiite dikes have low and homogeneous whole rock 18 o values 2 04 0 14 relative to standard mean ocean water and concordant mineral 18 o values plagioclase 3 1 to 4 1 clinopyroxene 1 5 to 1 9 magnetite 0 3 to 0 6 the dikes intrude granulite facies gneisses that have heterogeneous 18 o whole rock values 5 8 to 9 7 and show no evidence of 18 o depletion low 18 o intrusive igneous rocks are generally believed to have exchanged with high temperature meteoric or oceanic fluids after emplacement the heterogeneous high 18 o values of the country rocks suggest that the lewisian complex has not been pervasively infiltrated by such fluids it is also unlikely that fluids were channeled along the dikes because 1 the gneisses immediately adjacent to the dikes have unaltered mineralogies and stable isotope ratios 2 the dikes preserve unaltered igneous textures and mineralogies 3 the dike minerals do not show open system oxygen isotope resetting and 4 surface derived fluids generally do not penetrate to the depths at which the dikes were intruded it is more likely that these dikes were emplaced as primary low 18 o magmas derived from the subcontinental lithosphere the geochemistry of the scourie dikes suggests that they have not assimilated large volumes of continental crust and the best explanation of the data is that the dikes were derived from a low 18 o mantle source that possibly contained the remains of subducted hydrothermally altered oceanic crust