zircon u pb ages and hf isotope compositions of migmatite from the north dabie terrane in china constraints on partial melting migmatite gneisses are widespread in the dabie orogen but their formation ages are poorly constrained eight samples of migmatite including leucosome melanosome and banded gneiss were selected for u pb dating and hf isotope analysis most metamorphic zircon occurs as overgrowths around inherited igneous cores or as newly grown grains morphological and internal structure features suggest that their growth is associated with partial melting according to the hf isotope ratio relationships between metamorphic zircon and inherited cores three formation mechanisms for metamorphic zircon can be determined which are dissolution reprecipitation of pre existing zircon breakdown of zr bearing phase other than zircon in a closed system and crystallization from externally derived zr bearing melt four samples contain magmatic zircon cores yielding upper intercept u pb ages of 807 35 768 12 ma suggesting that the protoliths of the migmatites are neoproterozoic in age the migmatite zircon yields weighted mean two stage hf model ages of 2513 97 894 54 ma indicating reworking of both juvenile and ancient crustal materials at the time of their protolith formation the metamorphic zircons give u pb ages of 145 2 120 2 ma the oldest age indicates that partial melting commenced prior to 145 ma which also constrains the onset of extensional tectonism in this region to pre 145 ma the youngest age of 120 ma was obtained from an undeformed granitic vein indicating that deformation in this area was complete at this time two major episodes of partial melting were dated at 139 1 and 123 1ma the first episode of partial melting is obviously older than the timing of post collision magmatism corresponding to regional extension the second episode of partial melting is coeval with the widespread post collision magmatism indicating the gravitational collapse and delamination of the orogenic lithospheric keel of the dabie orogen which were possibly triggered by the uprising of the cretaceous mid pacific superplume

experimental zircon melt and zircon garnet trace element partitioning and implications for the geochronology of crustal rocks garnet is the most commonly used mineral in thermobarometry whereas zircon is the most robust chronometer to date high grade metamorphic rocks to provide a basis for correlation of zircon and garnet growth we determined experimentally the trace element partitioningbetweenzircon ahydrousgraniticmeltandgarnetat20kbarand800 1000 cforp y rareearthelements ree zr hf th andu inrespecttomelt zirconpreferentiallyincorporatesallinvestigatedelementsapartfromreewithatomicnumberlowerthansm at this pressure and in the chosen composition the distribution coefficient between zircon and melt d zrn melt for ree increases with increasingatomicnumberofthereeandwithdecreasingtemperature dyb is 20at1000 c butmorethananorderofmagnitude higher at800 c the solubilityofzrinhydrousgraniticmelts buffered by zirconisabouta factoroftwo lower at20kbar than what has been previously established for mid crustal pressures large garnet produced in the experiments allowed determination of garnet melt trace element partitioning d grt melt at temperatures of 800 1000 c conditions relevant for partial melting of crustal rocks there is a systematic increase indree with decreasing temperature zircon contains significantly more heavy ree than garnet at temperatures of 800 850 c zircon garnetpartitioncoefficientsofheavy reedecreasewithincreasingtemperaturefromdlu of12at800 cto 1 4at1000 c middle reepartitioningisclosetounityforthewholeinvestigatedtemperaturerange differentempiricallydetermined zircon garnet partition coefficients from granulites and ultra high temperature granulites can potentially be explained by the experimentallydeterminedchangeofpartitioningasafunctionoftemperature thesedatacanassistinestablishingequilibriumbetween garnetandzirconzonesinnaturalrocks andintheconstructionofdetailedpressure temperature timepathsinhigh grademetamorphic rocks

shear at the base of the oceanic mixed layer generated by wind shear alignment observations are used to evaluate a simple theoretical model for the generation of near inertial shear spikes at the base of the open ocean mixed layer when the upper ocean displays a two layer structure the model predicts that large changes in shear squared can be produced by the alignment of the wind and shear vectors a climatology of stratification and shear variance in drake passage is presented which shows that these assumptions are most applicable to summer fall and spring but are not highly applicable to winter temperature salinity and velocity data from a high spatial resolution cruise in drake passage show that the model does not predict all large changes in shear variance the model is most effective at predicting changes in shear squared when it arises owing to near inertial wind driven currents without requiring a rotating resonant wind stress the model is also more effective where there is a uniform mixed layer above a strongly stratified transition layer rotary spectral and statistical analysis of an additional 242 drake passage transects from 1999 to 2011 confirmed the presence of this shear spiking mechanism particularly in summer spring and fall when stratification is stronger

episodic growth of zircon in uhp orthogneisses from the north dabie terrane of east central china implications for crustal architecture of a collisional orogen zircon u pb dating of three orthogneiss samples from the north dabie terrane ndt is undertaken in order to reconstruct their formation and evolutionary histories and also the crustal architecture of the dabie orogen after triassic subduction and exhumation shrimp zircon u pb dating in combination with back scattered electron bse imaging and laser raman spectrometry provides accurate identification of the core mantle and rim structure for zircon growth during protolith formation and overgrowth during subduction exhumation and post collisional metamorphism concordant u pb ages of 760 730 ma and high th u ratios of 0 4 are obtained for relict oscillatory zoning fields of inherited cores that were not metamictized these features suggest that these ages represent the time of magmatic protolith formation during the breakup of rodinia the overgrown mantle domains around the metamictized cores are clean with few mineral inclusions e g quartz garnet and apatite mantle domains have low th u ratios of 0 719 similar to the values obtained from uhp orthogneisses in the cdt it is concluded that as with the cdt the orthogneisses with episodic zircon growths from the ndt should also be a part of the exhumed slice following the continental deep subduction however the orthogneisses in this study were buried at a lower level in the orogenic crust compared with those of the cdt prior to the cretaceous magmatism therefore the orthogneisses from the ndt were affected by the cretaceous magmatism whereas the cdt orthogneisses were not affected

ultrahigh pressure minerals and metamorphic terranes the view from china abstract ultrahigh pressure uhp metamorphism refers to mineralogical modifications of continental and oceanic crustal protoliths associated mafic ultramafic rocks initially formed or emplaced in shallow levels of the lithosphere but which subsequently have experienced p t conditions within or above the coesite stability field 2 7 gpa 700 c typical products include eclogite garnet peridotite and uhp varieties of metapelite quartzite marble paragneiss and orthogneiss uhp metamorphic assemblages require relatively cold lithospheric subduction to mantle depths some recrystallization even occurs under forbidden p t conditions characterized by a geotherm of the current explosion of research on continental uhp terranes reflects their significance for mantle dynamics and the tectonics of continental subduction collision exhumation mantle slab interactions and geochemical recycling a further characterization of uhp phases and positive identification of uhp minerals requires new experimental studies coupled with state of the art analyses for example the very rare occurrence of microdiamond inclusions in zircons from dabie sulu uhp rocks may reflect high f o 2 attending recrystallization inasmuch as epidote is rather common rutile needles within garnets from sulu uhp eclogitic rocks may not be the result of exsolution so in such cases the apparent uhp pressure may have been over estimated hadean igneous microdiamond inclusions in jack hills detrital zircons could have originated from mantle xenoliths whereas abundant detrital phanerozoic diamonds containing inclusions of coesite and other eclogitic minerals from new south wales might have been derived from unexposed uhp metamorphic terranes micro mineral intergrowth and nano size minerals may hold important key to deciphering the actual p t paths of subduction and mantle return flow although most exhumed terranes have returned surfaceward relatively rapidly after short time of uhp condition the long duration of storage at great depth and slow exhumation for the largest uhp terranes remain as major problems

zircon u pb ages ree concentrations and hf isotope compositions of granitic leucosome and pegmatite from the north sulu uhp terrane in china constraints on the timing and nature of partial melting granitic leucosome and pegmatite are widely distributed within biotite bearing orthogneiss in the northern part of the sulu ultrahigh pressure uhp metamorphic terrane eastern china a combined study of mineral inclusions cathodoluminescence cl images u pb shrimp dates and in situ trace element and lu hf isotope analyses of zircons provided insight into the nature and timing of partial melting in these rocks zircon grains separated from biotite bearing orthogneiss typically have three distinct domains 1 pre metamorphic magmatic cores with qtz kfs pl ap inclusions which record a neoproterozoic protolith age of 790 ma 2 mantles with coe phe ap inclusions that record triassic uhp age at 227 3 ma and 3 narrow rims with quartz inclusions that record hp granulite facies retrograde metamorphism at 210 3 ma in contrast zircons separated from granitic leucosome have only two distinct domains 1 the central uhp areas with coe phe ap inclusions record triassic uhp age of 227 3 ma and 2 outer magmatic areas with qtz kfs ab ap inclusions that record partial melting time of 212 2 ma zircons separated from pegmatite contain mineral inclusions of qtz kfs ap and show regular magmatic zoning from centre to edge the centres record partial melting time of 212 2 ma in line with the outer domains of granitic leucosome whereas the edges give a younger age of 201 2 ma related to pb loss and partial recrystallization during late triassic regional amphibolite facies retrogression these data indicate that partial melting in the north sulu uhp gneissic rocks took place during post uhp retrograde hp granulite facies metamorphism pre metamorphic magmatic zircon cores from biotite bearing orthogneiss give uniform 176hf 177hf of 0 28187 0 00003 2 sd standard deviation corresponding to ehf 790 and hf model ages tdm2 of about 16 3 and 2 41 ga respectively this is consistent with the generation of its protolith by reworking of paleoproterozoic to late archean crust in contrast uhp zircon domains from biotite bearing orthogneiss and granitic leucosome are characterized by distinct trace element composition with low lu hf 0 006 low th u 0 1 and considerably higher 176hf 177hf 0 28233 0 00002 2 sd than the pre metamorphic cores the uniform but significantly different hf isotope composition between the uhp ehf 227 14 6 0 8 2 sd and pre metamorphic ehf 227 27 7 domains indicates equilibration of the lu hf isotope system only within the uhp metamorphic mineral assemblage the disequilibrium between whole rock and uhp zircon suggests that about two thirds of the whole rock hf retained in the pre metamorphic zircon domains zircon domains crystallized during partial melting at 212 ma in granitic leucosome and pegmatites have a hf isotope composition indistinguishable from that of the uhp zircon domains this suggests that only hf and zr equilibrated during uhp metamorphism was remobilized during partial melting while pre metamorphic zircon remained stable or was not accessible in contrast the magmatic zircon edges from pegmatite have somewhat lower 176hf 177hf 0 28216 and ehf t 17 6 1 2 2 sd indicating some release of less radiogenic hf for instance by dissolution of pre metamorphic zircon during late regional amphibolite facies retrogression

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

fluid flow during exhumation of deeply subducted continental crust zircon u pb age and o isotope studies of a quartz vein within ultrahigh pressure eclogite quartz veins in high pressure to ultrahigh pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis this flow can occur in the direction of changing temperature pressure during subduction or exhumation shrimp u pb dating of zircon from a kyanite quartz vein within ultrahigh pressure eclogite in the dabie continental collision orogen yields two age groups at 212 7 and 181 13 ma which are similar to two groups of la icpms age at 210 4 and 180 5 ma for the same sample these ages are significantly younger than zircon u pb ages of 224 2 ma from the host eclogite thus the two age groups from the vein date two episodes of fluid flow involving zircon growth the first due to decompression dehydration during exhumation and the second due to heating dehydration in response to a cryptic thermal event after continental collision laser fluorination o isotope analyses gave similar 18o values for minerals from both vein and eclogite indicating that the vein forming fluid was internally derived synchronous cooling between the vein and eclogite is suggested by almost the same quartz mineral fractionation values with regularly decreasing temperatures that are in concordance with rates of o diffusion in the minerals while the quartz veining was caused by decompression dehydration at 700 650 c in a transition from ultrahigh pressure to high pressure eclogite facies retrogression the postcollisional fluid flow was retriggered by heating dehydration at 500 c without corresponding metamorphism in either case the kyanite quartz vein formed later than the peak ultrahigh pressure metamorphic event at the middle triassic pointing to focused fluid flow during exhumation rather than subduction the growth of metamorphic zircon in the eclogite appears to have depended on fluid availability so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

quantifying high frequency wind energy flux into near inertial motions in the southeast pacific abstractwind forced internal waves close to the inertial frequency are ubiquitous throughout the world s oceans but observational constraints on their global energetics and impact on subsurface mixing remain scarce this study reports on velocity measurements from three electromagnetic autonomous profiling explorers em apex deployed in february 2009 these floats observed downward propagating near inertial internal waves near the subantarctic and polar fronts of the antarctic circumpolar current these waves were episodic and enhanced at middepth between 500 and 1000 m depth integrated kinetic energy varied between 1 and 7 kj m 2 and averaged 1 6 kj m 2 with typical group velocities of 40 m day 1 implying an average energy flux of 3 mw m 2 at the mixed layer base decreasing to approximately 25 of that value at 1500 m modeled currents forced by reanalysis winds along each float track agree with observed surface currents from em apex provided that mixed layer depth is restricted to the layer of weak

characterization of wind shear effects on entrainment in a convective boundary layer direct numerical simulations are used to characterize wind shear effects on entrainment in a barotropic convective boundary layer cbl that grows into a linearly stratified atmosphere we consider weakly to strongly unstable conditions z enc l ob gtrsim 4 where z enc is the encroachment cbl depth and l ob is the obukhov length dimensional analysis allows us to characterize such a sheared cbl by a normalized cbl depth a froude number and a reynolds number the first two non dimensional quantities embed the dependence of the system on time on the surface buoyancy flux and on the buoyancy stratification and wind velocity in the free atmosphere we show that the dependence of entrainment zone properties on these two non dimensional quantities can be expressed in terms of just one independent variable the ratio between a shear scale unicode stix x0394 z i s equiv sqrt 1 3 unicode stix x0394 u n 0 and a convective scale unicode stix x0394 z i c equiv 0 25z enc where unicode stix x0394 u is the velocity increment across the entrainment zone and n 0 is the buoyancy frequency of the free atmosphere here unicode stix x0394 z i s and unicode stix x0394 z i c represent the entrainment zone thickness in the limits of weak convective instability strong wind and strong convective instability weak wind respectively we derive scaling laws for the cbl depth the entrainment zone thickness the mean entrainment velocity and the entrainment flux ratio as functions of unicode stix x0394 z i s unicode stix x0394 z i c these scaling laws can also be expressed as functions of only a richardson number n 0 z enc unicode stix x0394 u 2 but not in terms of only the stability parameter z enc l ob

observations and simulations of upper ocean response to wind events during the ocean storms experiment abstract the ocean storms dataset is used to compile observations of the oceanic response to midlatitude storms of particular interest are episodic mixed layer temperature cooling events whose characteristics are reviewed the data include subsurface temperatures from drifting thermistor chains mixed layer temperature and velocity from mixed layer drifters conductivity temperature depth profiles and radiation measurements from ships and the surface meteorological parameters produced by the european centre for medium range weather forecasts a method for processing irregular drifting buoy position fixes to yield estimates of the geostrophic ageostrophic and inertial mixed layer currents is developed and shown to yield residuals that can mostly be attributed to errors in the positioning from these currents the ocean s dynamic responses namely the change in mixed layer inertial kinetic energy and the ageostrophic particle displacement are computed the process of removing horizontal and vertical a

the energy flux from the wind to near inertial motions in the surface mixed layer abstract time series of wind stress computed from long term meteorological buoy data off north america are used to examine the forcing of surface inertial currents by the wind a simple damped slab model of the mixed layer is used to compute h the average flux of energy from the wind to mixed layer inertial currents in a mixed layer of fixed depth h the forcing of mixed layer inertial motions is highly intermittent most of the forcing occurs during the winter months with a few dozen events accounting for typically over half the total energy flux major forcing events are usually associated with translating cold fronts or small lows with scales of about 100 km the larger synoptic scale features have little energy at the inertial frequency and thus result in only weak forcing of inertial currents a strong seasonal signal exists in the inertial forcing at ows p 50 n 145 w 50 m is largest from october to february and is a factor of 12 above the june and july values if seasonally varying

multiple zircon growth during fast exhumation of diamondiferous deeply subducted continental crust kokchetav massif kazakhstan diamondiferous rocks from the kokchetav massif kazakhstan represent deeply subducted continental crust in order to constrain the age of ultra high pressure uhp metamorphism and subsequent retrogression during exhumation zircons from diamondiferous gneisses and metacarbonates have been investigated by a combined petrological and isotopic study four different zircon domains were distinguished on the basis of transmitted light microscopy cathodoluminescence trace element contents and mineral inclusions mineral inclusions and trace element characteristics of the zircon domains permit us to relate zircon growth to metamorphic conditions domain 1 consists of rounded cores and lacks evidence of uhp metamorphism domain 2 contains diamond coesite omphacite and titanian phengite inclusions providing evidence that it formed at uhp metamorphic conditions p 43 kbar t 950 c domain 3 is characterised by low pressure mineral inclusions such as garnet biotite and plagioclase which are common minerals in the granulite facies overprint of the gneisses p 10 kbar t 800 c this multi stage zircon growth during cooling and exhumation of the diamondiferous rocks can be best explained by zircon growth from zr saturated partial melts present in the gneisses domain 4 forms idiomorphic overgrowths and the rare earth element pattern indicates that it formed without coexisting garnet most probably at amphibolite facies conditions p 5 kbar t 600 c the metamorphic zircon domains were dated by shrimp ion microprobe and yielded ages of 527 5 528 8 and 526 5 ma for domains 2 3 and 4 respectively these indistinguishable ages provide evidence for a fast exhumation beyond the resolution of shrimp dating the mean age of all zircons formed between uhp metamorphic conditions and granulite facies metamorphism is 528 3 ma indicating that decompression took place in less than 6 ma hence the deeply subducted continental crust was exhumed from mantle depth to the base of the crust at rates higher than 1 8 cm year we propose a two stage exhumation model to explain the obtained p t t path fast exhumation on top of the subducted slab from depth 140 to 35 km was driven by buoyancy and facilitated by the presence of partial melts a period of near isobaric cooling was followed by a second decompression event probably related to extension in a late stage of continental collision

surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea inertial oscillations are a ubiquitous feature of the surface ocean here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea observations of temperature and current structure from a mooring in the western irish sea reveal episodes of strong currents 0 3 m s 1 lasting several days resulting in enhanced shear across the thermocline while the episodes of strong currents are coincident with windy periods the variance in the shear is not directly related to the wind stress the shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14 85 h these shear maxima coincide with the orientation of the surface current being at an angle of approximately 90 to the right of the wind direction observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear during the periods of enhanced shear gradient richardson number estimates indicate ri 1 4 at the base of the surface mixed layer implying the deepening as a result of shear instability a one dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step like deepening the observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow seasonally stratified sea

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

oxygen isotope equilibrium between eclogite minerals and its constraints on mineral sm nd chronometer abstract sm nd and oxygen isotope analyses were carried out for mineral separates of ultrahigh pressure eclogites from the sulu terrane in eastern china the results show a direct correspondence in equilibrium or disequilibrium state between the oxygen and sm nd isotope systems of eclogite minerals the omphacite garnet pairs of oxygen isotope equilibrium at eclogite facies conditions yield meaningful triassic sm nd isochron ages whereas those of oxygen isotope disequilibrium give non triassic ages of geological meaninglessness this can be reasonably interpreted by the fact that the rates of oxygen diffusion in garnet and pyroxene are lower than or close to those of nd diffusion and thus attainment of isotopic equilibrium in the omphacite garnet o system suggests achievement of nd isotope equilibrium in the same mineral pairs the presence or absence of fluid in the eclogite protoliths is a major rate controlling factor for isotopic equilibration during high grade metamorphism it appears that the state of oxygen isotope equilibrium between cogenetic minerals can provide a critical test for the validity of the sm nd mineral chronometer in addition the exact timing of the ultrahigh pressure metamorphism in the dabie sulu terranes is constrained at early triassic rather than late triassic

migration of neogene marine environments southwestern dominican republic the azua basin contains a 4000 m thick regressive neogene sedimentary sequence that records the effects of neotectonic activity along the northern bounary of the caribbean plate shifts of benthic foraminiferal depth zone boundaries between stratigraphic sections demonstrate a southeastward migration of paleoenvironments in the miocene and early pliocene which suggest that the hispaniola restraining bend was activated near the beginning of the late miocene in the morthwestern part of the azua basin the boundary between the middle and upper bathyal biofacies is in the uppermost miocene globorotalia humerosa zone the bathyal neritic boundary is near the top of the same zone in contrast toward the southeastern i e seaward end of the basin the middle bathyal upper bathyal boundary is just above the base of the lower pliocene globorotalia margaritae margaritae subzone and the bathyal neritic transition falls within the upper part of the same zone or in the overlying globorotalia margaritae evoluta subzone the diachroneity of biofacies boundaries spans a time interval of ca 1 m y the foraminiferal trends are corroborated by the disposition of time transgressive lithofacies

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

significant earthquakes on the enriquillo fault system hispaniola 1500 2010 implications for seismic hazard abstract historical records indicate frequent seismic activity along the north east caribbean plate boundary over the past 500 years particularly on the island of hispaniola we use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 haiti earthquakes to derive an intensity attenuation relation for hispaniola the intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments here we describe a sequence of devastating earthquakes on the enriquillo fault system in the eighteenth century an intensity magnitude m i 6 6 earthquake in 1701 occurred near the location of the 2010 haiti earthquake and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake a series of large earthquakes migrating from east to west started with the 18 october 1751 m i 7 4 7 5 earthquake probably located near the eastern end of the fault in the dominican republic followed by the 21 november 1751 m i 6 6 earthquake near port au prince haiti and the 3 june 1770 m i 7 5 earthquake west of the 2010 earthquake rupture the 2010 haiti earthquake may mark the beginning of a new cycle of large earthquakes on the enriquillo fault system after 240 years of seismic quiescence the entire enriquillo fault system appears to be seismically active haiti and the dominican republic should prepare for future devastating earthquakes online material table listing small earthquakes and figures of intensity assignments and intensity magnitude estimates

the rare earth elements and uranium in garnets from the beinn an dubhaich aureole skye scotland uk constraints on processes in a dynamic hydrothermal system garnets from skarns in the beinn an dubhaich granite aureole isle of skye scotland have a large range of concentrations of uranium 0 2 358 ppm and the rare earth elements ree 23 4724 ppm variations in these concentrations correlate with major element zonation within the garnets and with changes in the shape of ree patterns typical patterns in most garnets display light ree lree enrichment flat heavy ree hree distribution and a negative eu anomaly these patterns are interpreted to represent equilibrium trace element exchange between pre existing pyroxene hydrothermal fluid and calcic garnets iron rich zones are characterized by positive eu anomalies and an increase in the abundance of the lree relative to the hree these patterns are interpreted as resulting from changes in ree speciation related to the introduction of externally buffered fluid to the skarn system relatively fe poor zones show strongly hree enriched patterns with negative eu anomalies and in some instances depletions in y relative to ho and dy which are interpreted as resulting from surface sorption of the ree during rapid disequilibrium garnet growth strong correlations between u abundance and the ree patterns indicate that the same processes have affected u distribution both types of pattern can be modified by the effects of closed system crystallization on ree abundance in the fluid and changes in fluid major element chemistry

evolution of oceanic near surface stratification in response to an autumn storm abstractunderstanding the processes that control the evolution of the ocean surface boundary layer osbl is a prerequisite for obtaining accurate simulations of air sea fluxes of heat and trace ga

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

nonbreaking wave induced mixing in upper ocean during tropical cyclones using coupled hurricane ocean wave modeling the effects of turbulence generated by nonbreaking waves have been investigated by testing and evaluating a new nonbreaking wave parameterization in a coupled hurricane ocean wave model the mpi version of the princeton ocean model pom with hurricane forcing is coupled with the wavewatch iii ww3 surface wave model hurricane ivan is chosen as the test case due to its extreme intensity and availability of field data during its passage the model results are validated against field observations of wave heights and sea surface temperatures ssts from the national data buoy centre ndbc during hurricane ivan and against limited in situ current and bottom temperature data a series of numerical experiments is set up to examine the influence of the nonbreaking wave parameterization on the mixing of upper ocean the sst response from the modeling experiments indicates that the nonbreaking wave induced mixing leads to significant cooling of the sst and deepening of the mixed layer it was found that the nondimensional constant b1 in the nonbreaking wave parameterization has different impacts on the weak and the strong sides of the storm track a constant value of b1 leads to improved predictions on the strong side of the storm while a steepness dependent b1 provides a better agreement with in situ observations on the weak side a separate simulation of the intense tropical cyclone olwyn in north west australia revealed the same trend for b1 on the strong side of the tropical cyclone

rare earth element distributions among coexisting granulite facies minerals scourian complex nw scotland the major rock forming mineral phases pyroxenes plagioclase garnet hornblende of a suite of granulite facies gneisses from the scourian complex nw scotland have been analyzed for their rare earth element ree content although host rock compositions range from felsic to ultramafic ree abundances and patterns for each mineral group show only limited variation the rees exhibit regular and consistent distribution patterns for each mineral which suggest together with major element and textural considerations that the observed distribution coefficients approach equilibrium total ree content follows the sequence hornblende clinopyroxene garnet plagioclase orthopyroxene and mass balance calculations show that even in the felsic gneisses 60 of the rees reside in the major rock forming minerals comparisons of both relative ree abundances and distribution coefficients with those in other rock types reveal a striking resemblance with patterns observed in mineral liquid pairs of dacitic rocks these similarities may have arisen during a partial melting episode in which granite granodiorite melts were generated and removed from the scourian complex leaving a residuum which is severely depleted in the incompatible elements including the rees

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

shrimp u pb dating trace elements and the lu hf isotope system of coesite bearing zircon from amphibolite in the sw sulu uhp terrane eastern china abstract in this study we link mineral inclusion data trace element analyses u pb age and hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi stage metamorphic evolution of amphibolites from the sulu ultrahigh pressure uhp terrane eastern china zircon grains separated from amphibolites from the ccsd mh drill hole g12 and niushan outcrop g13 were subdivided into two main types based on cathodoluminescence cl and laser raman spectroscopy big dusty zircons with inherited cores and uhp metamorphic rims and small clear zircons weakly zoned grey white luminescent inherited cores preserve mineral inclusions of cpx pl ap qtz indicative of a mafic igneous protolith dark grey luminescent overgrowth rims contain the coesite eclogite facies mineral inclusion assemblage coe grt omp phe ap and formed at t 732 839 c and p 3 0 4 0 gpa in contrast white luminescent small clear zircons preserve mineral inclusions formed during retrograde hp quartz eclogite to lp amphibolite facies metamorphism t 612 698 c and p 0 70 1 05 gpa inherited zircons from both samples yield shrimp 206 pb 238 u ages of 695 520 ma with an upper intercept age of 800 31 ma the uhp rims yield consistent triassic ages around 236 225 and 239 225 ma for g12 and g13 with weighted means of 229 3 and 231 3 ma respectively small clear zircons from both samples give 206 pb 238 u ages around 219 210 ma with a weighted mean of 214 3 ma interpreted as the age of retrograde quartz eclogite facies metamorphism matrix amphibole from both samples indicate ar ar ages of 209 0 7 and 207 0 7 ma respectively probably dating late amphibolite facies retrogression the data suggest subduction of neoproterozoic mafic igneous rocks to uhp conditions in middle triassic 230 ma times and subsequent exhumation to an early hp 214 ma and a late lp stage 208 ma over a period of 16 and 6 myr respectively thus early exhumation from a mantle depth of 120 100 km to about 60 km occurred at an average rate of 0 3 cm y while subsequent exhumation to a middle crustal level took place at approximately 0 54 cm y these exhumation rates are considerably slower than those obtained for uhp rocks in the dora maira and kokchetav massifs 2 3 cm y based on similar p t estimates and trace element and hf isotope compositions sulu amphibolites can be identified as retrograde uhp eclogites the ehf 800 of 8 implies a significant input from the depleted mantle to the sulu dabie terrane during the middle neoproterozoic overgrown rims are characterized by a distinct trace element composition with low lu hf and th u and significantly higher 176 hf 177 hf ratios than inherited cores consistent with formation during after garnet re crystallization and fractionation of the lu hf system during uhp metamorphism the combined dataset suggests homogenization of the 176 hf 177 hf ratio within the metamorphic mineral assemblage and during protolith formation observed variations are explained by mixing of material from both domains during laser ablation e g due to partial recrystallization of inherited cores

diverse p t paths of the northern dabie complex in central china and its reworking in the early cretaceous abstract the northern dabie complex ndc in the dabie orogen central china is a high temperature migmatite terrane it is composed mainly of banded gneiss migmatite and minor amphibolite granulite retro eclogite marble and spinel peridotite and intruded by the early cretaceous massive granitoid plutons and subordinate mafic ultramafic rocks whether or not the ndc experienced a high pressure or ultrahigh pressure hp uhp metamorphic history has been a long standing issue however in the last 10 years an increasing number of retrograde uhp eclogite relics and marbles and hp granulites have been identified throughout the ndc this together with the discovery of microdiamond preserved as inclusions in zircons within eclogite relics and gneisses and numerous age dates of 220 240 ma and 130 ma from the ndc supports the notion that at least part of the ndc was subjected to triassic continental subduction and hp uhp metamorphism the youngest ages being related to an intense overprinting of ultrahigh temperature uht granulite facies metamorphism in the early cretaceous distinct peak uhp conditions 2 5 gpa and 800 c 3 5 gpa and 750 800 c 4 gpa and 900 c or 750 c have been inferred from oriented qtz or ab kfs qtz needles in ca na clinopyroxene of retrograde eclogite ti chu bearing assemblage preserved in marble rod like cpx rt ap inclusion in garnet of retrograde eclogite and microdiamond inclusions in zircon of tonalitic gneiss and retrograde eclogite from the ndc the overprinted uht 900 c or 1000 c metamorphism is indicated by osm growth in garnet pgt exsolution in clinopyroxene of retrograde eclogite and spl crd qtz symplectite in felsic granulites diverse p t paths of an overall clockwise evolution are suggested with post peak decompression or heating followed by decompression cooling and consist of two distinct paths opx pl inclusions in garnet and zircon in retrograde eclogite relics indicate that the lower continental crust in the ndc underwent triassic subduction the ndc shows overprinted uht granulite facies metamorphism thus consists of two metamorphic events in contrast to the single event of the central dabie uhp eclogite belt cdb distinct peak p t conditions may be attributed to the lack of suitable mineral assemblages for geobarometry the overall clockwise p t paths consist of a peak hp uhp event with overprinted uht event suggesting that the ndc experienced triassic subduction and intense intracontinental reworking in the early cretaceous the latter stage may be associated with a heat pulse due to asthenospheric upwelling and lithospheric thinning as a result of cretaceous mantle superwelling and the westward subduction of the pacific plate

generation of bulk shear spikes in shallow stratified tidal seas abstract recent finescale observations of shear and stratification in temperate shelf sea thermoclines show that they are of marginal stability suggesting that episodes of enhanced shear could potentially lead to shear instability and diapcynal mixing the bulk shear between the upper and lower boundary layers in seasonally stratified shelf seas shows remarkable variability on tidal inertial and synoptic time scales that has yet to be explained in this paper observations from the seasonally stratified northern north sea are presented for a time when the water column has a distinct two layer structure bulk shear estimates based on adcp measurements show a bulk shear vector that rotates in a clockwise direction at the local inertial period with episodes of bulk shear spikes that have an approximately twice daily period and occur in bursts that last for several days to explain this observation a simple two layer model based on layer averaging of the one dimensional momentum equation is developed

ultrahigh pressure metamorphism and multistage exhumation of eclogite of the luotian dome north dabie complex zone central china evidence from mineral inclusions and decompression textures abstract the studied eclogite is located in the luotian dome in the southwestern part of the north dabie complex zone ndz central china and is a portion of deeply subducted mafic lower continental crust of the south china block petrologic analysis suggests that the eclogite underwent ultrahigh pressure uhp and high pressure eclogite facies metamorphism and subsequent hp granulite facies overprinting and amphibolite facies retrogression during continental subduction and exhumation as a result multiple decompression textures were produced suggesting a multistage exhumation history from eclogite to granulite to amphibolite facies conditions a striking feature of this eclogite is the widespread exsolution of different phases oriented needles of rutile clinopyroxene amphibole apatite in garnet quartz amphibole hypersthene sodic plagioclase in clinopyroxene and pyrrhotite in apatite most importantly we provide for the first time conclusive evidence of quartz pseudomorphs after coesite in garnet and relic coesite confirmed by in situ raman spectroscopy in zircon in addition there are two groups of apatite one is fluor f apatite that occurs as inclusions in garnet or in matrix which is rich in f 3 wt lakes exsolution features and formed at uhp metamorphic conditions the second is associated with the oriented pyrrhotite exsolution and formed during decompression microtextural and petrologic analysis suggests that the eclogites from the southwestern segment of the ndz are similar to eclogites from the northern segment of the ndz e g huangweihe and baizhangyan and underwent uhp metamorphism with a peak pressure 5 7 gpa these results combined with published geochronological data imply that the ndz experienced triassic uhp metamorphism as a coherent unit

metamorphic growth and recrystallization of zircon distinction by simultaneous in situ analyses of trace elements u th pb and lu hf isotopes in zircons from eclogite facies rocks in the sulu orogen simultaneous in situ analyses of trace elements u th pb and lu hf isotopes were carried out on distinct domains of zircons in ultrahigh pressure uhp eclogite facies metamorphic rocks from the main hole of the chinese continental scientific drilling ccsd in the sulu orogen for the first time trace elements are directly linked to lu hf isotopes in metamorphic zircons with reference to their u pb dates this enables methodological integration to distinguish four types of metamorphic zircon solid state replacement and dissolution recrystallizations of protolith zircons and new growth from the aqueous fluid metamorphically grown zircons are characterized by concordant u pb ages for the metamorphism flat hree patterns typical of the garnet effect low contents of ree especially hree y nb ta and th u high contents of hf low lu gd n lu hf and th u 0 1 ratios and elevated 176hf 177hf ratios relative to solid state recrystallized zircons this suggests the effects of both garnet and fluid on the growth of metamorphic zircons in contrast metamorphic recrystallization has reset the u th pb isotope system of protolith zircons to different extents depending on the extents of fluid action during metamorphism solid state recrystallized zircons exhibit the lowest degrees of resetting and thus almost inherit all geochemical features from the protolith zircons which are characterized by discordant u pb ages close to or below the protolith age steep mree hree patterns typical of magmatic origin high contents of trace elements and their ratios and low 176hf 177hf ratios on the other hand dissolution recrystallized zircons show the highest degrees of reworking and thus have concordant or nearly concordant u pb ages for the metamorphism steep mree hree patterns lowered contents of trace elements such as ree th u y nb ta and ti relative to the protolith zircons and almost unchanged hf isotope ratios replacement recrystallized zircons display intermediate degrees of reworking and thus have their many features of elements and isotopes in between while the metamorphic growth in the presence of both garnet and fluid is characterized by both depletion of hree with flat pattern and the low contents of trace elements the metamorphic recrystallization in the presence of aqueous fluid is indicated by gradual decreases of mree to hree without the flat hree pattern therefore the simultaneous in situ analyses of metamorphic zircons have the advantage over single term analyses in making distinction between the new growth and the different types of recrystallization

a granulite record of multistage metamorphism and ree behavior in the dabie orogen constraints from zircon and rock forming minerals abstract a combined study of mineral inclusions u pb ages and trace elements was carried for zircon and coexisting minerals from granulite in the north dabie terrane ndt of the dabie sulu ultrahigh pressure metamorphic uhp zone east central china the results provide insights into the exhumation history of ndt and into rare earth element ree behavior during retrogression besides inherited cores and one magmatic rim zircons separated from the granulite record three episodes of metamorphism under different p t conditions 1 223 8 2 3 ma for domains that contain grt cpx rt f ap aln inclusions without plagioclase and show flat hree patterns without negative eu anomalies representing peak eclogite facies event 2 213 3 2 1 ma for domains that contain pl cpx grt qtz ap inclusions and show rather flat hree patterns with negative eu anomalies corresponding to granulite facies retrogression 3 199 9 3 3 ma for domains that contain amp pl qtz ap inclusions and show high ree contents with steep hree patterns and remarkable negative eu anomalies representing amphibolite facies overprinting therefore the uhp eclogite in ndt experienced decompression heating during the initial exhumation with local hydration in the late stage of the triassic continental collision garnet in the granulite is composed of a corroded core with embayed outline and spongy texture and an overgrowth rim there is equilibrium distribution of hree between garnet rim and granulite facies zircon domain confirming the geological interpretation of 213 3 2 1 ma for the granulite facies metamorphism there is the prograde hree depletion in porphyroblastic garnet from core to rim and the continuous decrease of hree from the eclogitic to granulitic zircons suggesting that the metamorphic transformation from eclogite facies to granulite facies took place in a closed system on the other hand the amphibolitic zircons show steep hree patterns and significantly elevated ree contents suggesting that the amphibolite facies metamorphism took place in an open system with introduction of external fluids containing more ree to the granulite facies rocks residual clinopyroxene partially replaced by amphibole has remarkably elevated ree contents relative to euhedral primary clinopyroxene there is equilibrium distribution of ree between the residual clinopyroxene and the amphibole marking fluid action during the amphibolite facies overprinting

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

excess argon in phengite from eclogite evidence from dating of eclogite minerals by smnd rbsr and 40ar39ar methods the existence of excess ar in phengites from coesite bearing ultrahigh pressure eclogites of the dabie mountains and su lu terrain china has been confirmed by dating of minerals using sm nd rb sr and 40ar39ar methods 40ar39ar ages of phengites for two samples studied are much older than the sm nd and rb sr mineral isochron ages sample ql 1 has rb sr age of 219 5 0 5 ma sm nd age of 226 3 4 5 ma and phengite 40ar39ar age of 877 5 15 9 ma the corresponding ages for sample zb 4 are 223 9 0 9 ma rb sr 228 4 6 0 ma sm nd and 943 3 12 4 ma 40ar39ar phengite an age of 225 ma based on the sm nd and rb sr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the north china and yangtse blocks and formation of these eclogites we call for greater caution in 40ar39ar dating of phengites from other occurrences of ultrahigh pressure environments

open ocean submesoscale motions a full seasonal cycle of mixed layer instabilities from gliders abstractthe importance of submesoscale instabilities particularly mixed layer baroclinic instability and symmetric instability on upper ocean mixing and energetics is well documented in regions of strong persistent fronts such as the kuroshio and the gulf stream less attention has been devoted to studying submesoscale flows in the open ocean far from long term mean geostrophic fronts characteristic of a large proportion of the global ocean this study presents a year long submesoscale resolving time series of near surface buoyancy gradients potential vorticity and instability characteristics collected by ocean gliders that provides insight into open ocean submesoscale dynamics over a full annual cycle the gliders continuously sampled a 225 km2 region in the subtropical northeast atlantic measuring temperature salinity and pressure along 292 short 20 km hydrographic sections glider observations show a seasonal cycle in near surface stratification throughout the fall september november

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

petrogenesis of a high temperature metamorphic terrane a new tectonic interpretation for the north dabieshan central china the northern dabie terrane consists of a variety of metamorphic rocks with minor mafic ultramafic blocks and abundant jurassic cretaceous granitic plutons the metamorphic rocks include orthogneisses amphibolite migmatitic gneiss with minor granulite and metasediments no eclogite or other high pressure metamorphic rocks have been found granulites of various compositions occur either as lenses blocks or layers within clinopyroxene bearing amphibolite or gneiss the palaeosomes of most migmatitic gneisses contain clinopyroxene melanosomes and leucosomes are intimately intermingled tightly folded and may have formed in situ the granulites formed at about 800 830 c and 10 14 kbar and display near isothermal decompression p t paths that may have resulted from crust thickened by collision plagioclase amphibole coronae around garnets and matrix pi hbl assemblages from mafic and ultramafic granulites formed at about 750 800 c partial replacement of clinopyroxene by amphibole in gneiss marks amphibolite facies retrograde metamorphism amphibolite facies orthogneisses and interlayered amphibolites formed at 680 750 c and c 6 kbar formation of oligoclase orthoclase antiperthite after plagioclase took place in migmatitic gneisses at t 490 c in response to a final stage of retrograde recrystallization these p t estimates indicate that the northern dabie metamorphic granulite amphibolite facies terrane formed in a metamorphic field gradient of 20 35 c km 1 at intermediate to low pressures and may represent the sino korean hangingwall during triassic subduction for formation of the ultrahigh and high p units to the south post collisional intrusion of a mafic ultramafic cumulate complex occurred due to breakoff of the subducting slab

polyphase tectonic history of the southern peninsula haiti from folding and thrusting to transpressive strike slip abstract the southern peninsula of haiti is a seismically active east west trending transpressive mountain range with elevations over 2 km present day deformation is mainly partitioned along the left lateral enriquillo plantain garden fault zone epgfz and associated oblique reverse faults and or folds the configuration of these faults their respective timing and the role of structural heritage on their development is poorly understood to address these questions we present the results of extensive field campaigns combined with satellite imagery interpretation and published data which allows us to constrain the cenozoic evolution of the southern peninsula our results show a polyphase tectonic history consisting of three major tectonic events 1 maastrichtian to early paleocene crustal scale folding that developed coevally with predominantly north to northeast dipping thrusts resulting in uplift and erosion of the cretaceous sedimentary cover in large parts of the southern peninsula 2 early miocene uplift and erosion which was strongest in the southwestern part of the peninsula and decreased eastwards did not affect the massif de la selle uplift is most likely unrelated to strike slip activity but resulted from folding in response to ne sw shortening that possibly reactivated older predominantly n to ne dipping thrusts 3 late miocene to present day deformation and uplift spatially distributed strike slip started during the late miocene and became progressively focused along the epgfz in the latest miocene oblique and thrust faults locally post date strike slip activity from the pliocene onward increase in compressional deformation from west to east is reflected by a change in structural style with predominantly strike slip faults in the west and transpressional faults in the east the latter possibly rooted on the epgfz at depth paleo stresses associated with a strike slip regime are at a significantly high angle to the trace of the epgfz indicating that the epgfz is a mechanically weak fault

intermittent intense turbulent mixing under ice in the laptev sea continental shelf vertical mixing in the bottom boundary layer and pycnocline of the laptev sea is evaluated from a rapidly sampled 12 h time series of microstructure temperature conductivity and shear observations collected under 100 sea ice during october 2008 the bottom boundary turbulent kinetic energy dissipation was observed to be enhanced 10 4 w m 3 beyond background levels 10 6 w m 3 extending up to 10 m above the seabed when simulated tidal currents were directed on slope upward heat fluxes into the halocline class waters along the laptev sea seabed peaked at 4 8 w m 2 averaging out to 2 w m 2 over the 12 h sampling period in the laptev sea pycnocline an isolated 2 h episode of intense dissipation 10 3 w m 3 and vertical diffusivities was observed that was not due to a localized wind event observations from an acoustic doppler current meter moored in the central laptev sea near the m2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under ice stress vector upward cross pycnocline heat fluxes from the arctic halocline peaked at 54 w m 2 resulting in a 12 h average of 12 w m 2 these results highlight the intermittent nature of arctic shelf sea mixing processes and how these processes can impact the transformation of arctic ocean water masses the observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near inertial kinetic energy to drive vertical mixing on the arctic shelves

the impact of zircon garnet ree distribution data on the interpretation of zircon u pb ages in complex high grade terrains an example from the rauer islands east antarctica abstract the responsiveness of zircon to granulite metamorphism and post peak fluid infiltration in polymetamorphic terranes has been investigated utilising a case study from the rauer islands of east antarctica imaging bse cl textural analysis in situ ion microprobe trace element analysis of zircon garnet orthopyroxene plagioclase and apatite and ion microprobe oxygen isotope analysis of zircon have been integrated to establish the event significance of c 510 ma zircon age domains that occur within and on c 2840 ma protolith magmatic zircons initial magmatic zircon is characterised by moderate th u 0 4 0 6 and elevated steep hree yb n gd n 20 c 510 ma zircon domains feature lobate cuspate and planar bse and cl zones that have lower th u to 0 05 and either decreased mree or decreased mree and hree metamorphic garnet initially characterised by flat hree shows extensive replacement by orthopyroxene and plagioclase accompanied by near rim increases in hree to values that are consistent with equilibrium between garnet rims and product orthopyroxene zircon garnet mree hree distribution coefficients d ree calculated using compositions of modified zircon domains coupled with both initial metamorphic garnet cores and rims are far removed from presently accepted equilibrium values with the zircon mree being strongly depleted relative to garnet these d ree indicate that the observed modification of zircon did not occur in response to the major high grade metamorphic events recorded in the studied rock mineralogy but instead occurred after the high grade metamorphism the zircon was blind to these metamorphic events but instead was responsive to a later post peak fluid infiltration episode that shifted zircon 18 o values downwards by some 3 the likelihood of blind or unresponsive behaviour of zircon to high grade metamorphism must be considered when reconstructing crustal histories and terrane scenarios based on u pb age data and tested for using an integrated approach that includes in situ ree and other trace element analysis of zircon and its potentially coexisting minerals

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

multistage growth of garnet in ultrahigh pressure eclogite during continental collision in the dabie orogen constrained by trace elements and u pb ages abstract major and trace elements for garnet and other minerals and u pb ages and trace elements for zircon as inclusions in garnet or as matrix were determined on thin sections of uhp eclogite from the western part of the dabie orogen the results provide temporal constraints on growth of garnet during continental subduction zone metamorphism major elements show homogeneous distribution across garnet grains with weak or no zonation of ca and almost flat distribution patterns of mg and fe however their ree compositions display two groups of patterns relative to chondrite group i garnet is characterized by steep patterns from lree to hree whereas group ii garnet shows enrichment of mree relative to lree and hree these two groups of garnet also have different parageneses of mineral inclusions group i garnet always contains abundant inclusions of amphibole epidote allanite rutile plagioclase quartz zircon whereas group ii garnet occasionally contains inclusions of omphacite rutile apatite zircon la icpms u pb dating and trace element analysis of the zircon provide direct constraints on the growth time of the two groups of garnet four types of zircon were identified based on their cl images ree distributions and u pb ages types i and ii zircons are metamorphosed after protolith magmatic zircon with type i being modified by solid state recrystallization and type ii by dissolution recrystallization types iii and iv zircons are metamorphic and grew in the stability field of garnet they gave consistent 206pb 238u ages of 239 6 ma and 222 4 ma respectively in association with groups i and ii garnets this provides a temporal constraint on the two stage growth of garnet respectively predating and postdating the peak uhp metamorphic event therefore we conclude that there are two stages of zircon and garnet growth during continental collision which occurred during the final subduction from hp to uhp phase and the early exhumation from uhp to hp eclogite facies respectively

a global perspective on langmuir turbulence in the ocean surface boundary layer the turbulent mixing in thin ocean surface boundary layers osbl which occupy the upper 100 m or so of the ocean control the exchange of heat and trace gases between the atmosphere and ocean here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the osbl in global climate models which then leads to biases in sea surface temperature one reason we argue is that current parameterizations are missing key surface wave processes that force langmuir turbulence that deepens the osbl more rapidly than steady wind forcing scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing and against buoyancy forcing a global perspective on the occurrence of wave forced turbulence is developed using re analysis data to compute these parameters globally the diagnostic study developed here suggests that turbulent energy available for mixing the osbl is under estimated without forcing by surface waves wave forcing and hence langmuir turbulence could be important over wide areas of the ocean and in all seasons in the southern ocean we conclude that surface wave forced langmuir turbulence is an important process in the osbl that requires parameterization citation belcher s e et al 2012 a global perspective on langmuir turbulence in the ocean surface boundary layer geophys res lett 39 l18605 doi 10 1029 2012gl052932

mixing in the transition layer during two storm events abstract upper ocean dynamics analyzed from mooring array observations are contrasted between two storms of comparable magnitude particular emphasis is put on the role of the transition layer the strongly stratified layer between the well mixed upper layer and the deeper more weakly stratified region the midlatitude autumn storms occurred within 20 days of each other and were measured at five moorings in the first storm the mixed layer follows a classical slab layer response with a steady deepening during the course of the storm and little mixing of the thermocline beneath in the second storm rather than deepening the mixed layer shoals while intense near inertial waves are resonantly excited within the mixed layer these create a large shear throughout the transition layer generating turbulence that broadens the transition layer details of the space time structure of the frequencies in both short waves and near inertial waves are presented small scale waves are excited within the transition

resonant wind driven mixing in the ocean boundary layer abstract the role of resonant wind forcing in the ocean boundary layer was examined using an ocean large eddy simulation les model the model simulates turbulent flow in a box measuring 100 300 m on a side whose top coincides with the ocean surface horizontal boundary conditions are periodic and time dependent wind forcing is applied at the surface two wind forcing scenarios were studied one with resonant winds that is winds that rotated at exactly the inertial frequency at 45 n and a second with off resonance winds from a constant direction the evolution of momentum and temperature for both cases showed that resonant wind forcing produces much stronger surface currents and vertical mixing in comparison to the off resonance case surface wave effects were also examined and found to be of secondary importance relative to the wind forcing the main goal was to quantify the main processes via which kinetic energy input by the wind is converted to potential energy in the form of changes in the

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

trace element partitioning in the granulite facies analyses of trace elements in the mineral phases of granulites provide important information about the trace element distribution in the lower crust since granulites are often considered residues of partial melting processes trace element characteristics of their mineral phases may record mineral melt equilibria thus giving an opportunity to understand the nature and composition of melts in the lower continental crust this study provides an extensive set of mineral trace element data obtained by la icp ms analyses of mafic and intermediate granulites from central finland mass balance calculations using the analytical data indicate a pronounced contribution of the accessory minerals apatite for the ree and ilmenite for the hfse coherent mineral mineral ratios between samples point to a close approach to equilibrium except for minerals intergrown with garnet porphyroblasts mineral trace element data were used for the formulation of a set of d mineral melt partition coefficients that is applicable for trace element modelling under lower crustal conditions d mineral melt were derived by the application of predictive models and using observed constant mineral mineral ratios the comparison of the calculated d mineral melt with experimental data as well as the relationship between mineral trace element contents and a leucosome with a composition close to an equilibrium melt provides additional constraints on mineral melt partitioning the d values derived in this study are broadly similar to magmatic partition coefficients for intermediate melt compositions they provide a first coherent set of d values for sc v cr and ni between clinopyroxene amphibole garnet orthopyroxene ilmenite and melt in addition they emphasize the strong impact that ilmenite exerts on the distribution of nb and ta

trace element signature and u pb geochronology of eclogite facies zircon bergen arcs caledonides of w norway secondary ion mass spectrometry sims u pb and trace element data are reported for zircon to address the controversial geochronology of eclogite facies metamorphism in the lindas nappe bergen arcs caledonides of w norway caledonian eclogite facies overprint in the nappe was controlled by fracturing and introduction of fluid in the proterozoic sveconorwegian granulite facies meta anorthosite norite protolith zircon grains in one massive eclogite display a core rim structure sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith i e 0 31 th u 0 89 heavy rare earth element hree enrichment and negative eu anomaly weakly zoned to euhedral oscillatory zoned caledonian rims are characterized by th u 0 13 low lree content minimum normalized abundance for pr or nd variable enrichment in hree and no eu anomaly a decrease of ree towards the outermost rim especially hree is documented this signature reflects co precipitation of zircon with garnet and clinozoisite in a feldspar absent assemblage and consequently links zircon to the eclogite facies overprint the rims provide a mean 206pb 238u crystallization age of 423 4 ma this age reflects eclogite forming reactions and fluid rock interaction this age indicates that eclogite facies overprint in the lindas nappe took place at the onset of the scandian silurian collision between laurentia and baltica

ocean nutrient pathways associated with the passage of a storm storms that affect ocean surface layer dynamics and primary production are a frequent occurrence in the open north atlantic ocean in this study we use an interdisciplinary dataset collected in the region to quantify nutrient supply by two pathways associated with a storm event entrainment of nutrients during a period of high wind forcing and subsequent shear spiking at the pycnocline due to interactions of storm generated inertial currents with wind the post storm increase in surface layer nitrate by 20 mmol m 2 was predominantly driven by the first pathway nutrient intrusion during the storm alignment of post storm inertial currents and surface wind stress caused shear instabilities at the ocean pycnocline forming the second pathway for nutrient transport into the euphotic zone during the alignment period pulses of high turbulent nitrate flux through the pycnocline up to 1 mmol m 2 day 1 approximately 25 times higher than the background flux were detected however the impact of the post storm supply was an order of magnitude lower than during the storm due to the short duration of the pulses cumulatively the storm passage was equivalent to 2 5 5 of the nitrate supplied by winter convection and had a significant effect compared to previously reported sub mesoscale dynamics in the region as storms occur frequently they can form an important component in local nutrient budgets

continental subduction and exhumation of uhp rocks structural and geochronological insights from the dabieshan east china in the dabieshan the available models for exhumation of ultrahigh pressure uhp rocks are poorly constrained by structural data a comprehensive structural and kinematic map and a general cross section of the dabieshan including its foreland fold belt and the northern dabieshan domain foziling and luzenguang groups are presented here south dabieshan consists from bottom to top of stacked allochtons 1 an amphibolite facies gneissic unit devoid of uhp rocks interpreted here as the relative autochton 2 an uhp allochton 3 a hp rock unit susong group mostly retrogressed into greenschist facies micaschists 4 a weakly metamorphosed proterozoic slate and sandstone unit and 5 an unmetamorphosed cambrian to early triassic sedimentary sequence unconformably covered by jurassic sandstone all these units exhibit a polyphase ductile deformation characterized by i a nw se lineation with a top to the nw shearing and ii a southward refolding of early ductile fabrics the central dabieshan is a 100 km scale migmatitic dome newly discovered eclogite xenoliths in a cretaceous granitoid dated at 102 ma by the u pb method on titanite demonstrate that migmatization post dates hp uhp metamorphism ductile faults formed in the subsolidus state coeval to migmatization allow us to characterize the structural pattern of doming along the dome margins migmatite is gneissified under post solidus conditions and mylonitic ultramylonitic fabrics commonly develop the north and west boundaries of the central dabieshan metamorphics i e the xiaotian mozitan and macheng faults are ductile normal faults formed before late jurassic early cretaceous a cretaceous reworking is recorded by synkinematic plutons north of the xiaotian mozitan fault the north dabieshan domain consists of metasediments and orthogneiss foziling and luzenguang groups metamorphosed under greenschist to amphibolite facies which never experienced uhp metamorphism a rare n s trending lineation with top to the south shearing is dated at 260 ma by the 40ar 39ar method on muscovite this early structure related to compressional tectonics is reworked by top to the north extensional shear bands the main deformation of the dabieshan consists of a nw se stretching lineation which wraps around the migmatitic dome but exhibits a consistently top to the nw sense of shear the central dabieshan is interpreted as an extensional migmatitic dome bounded by an arched top to the nw detachment fault this structure may account for a part of the uhp rock exhumation however the abundance of amphibolite restites in the central dabieshan migmatites and the scarcity of eclogites found only in a few places argue for an early stage of exhumation and retrogression of uhp rocks before migmatization this event is coeval to the n s extensional structures described in the north dabieshan domain recent radiometric dates suggest that early exhumation and subsequent migmatization occurred in triassic liassic times the main foliation is deformed by north verging recumbent folds coeval to the south verging folds of the south dabieshan domain an intense cretaceous magmatism accounts for thermal resetting of most of the 40ar 39ar dates a lithosphere scale exhumation model involving continental subduction synconvergence extension with inversion of southward thrusts into nw ward normal faults and crustal melting is presented

plate boundary readjustment in oblique convergence example of the neogene of hispaniola greater antilles the haitian fold and thrust belt is the major mountain belt of haiti western part of hispaniola greater antilles and resembles a compressive restraining bend between the two major faults which have driven the opening of the cayman basin since the eocene during the rifting stage from the middle to the late eocene this area underwent an extensional evolution with fissural volcanic activity along ne sw tilted blocks the haitian fold and thrust belt was constructed from the early miocene until the present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks which was propagating to the southwest during the construction of the wedge piggyback basins were formed and progressively uplifted during the late neogene convergence is localized in the cul de sac enriquillo trough where the active front proceeds southward onto the beata ridge in this area miocene to quaternary wrench structures of the lower plate like the southern peninsula and the enriquillo plantain garden faults are reactivated as normal faults owing to the loading of the fold and thrust belt

investigation of magnesium isotope fractionation during granite differentiation implication for mg isotopic composition of the continental crust abstract high precision mg isotopic analysis was performed on a suite of well characterized i type granitoids and associated hornblende and biotite minerals from the dabie orogen in central china to address the behavior of mg isotopes during granite differentiation although these granitoids formed through different degrees of partial melting and fractional crystallization with large variations in elemental and mineral compositions their 26 mg values vary from 0 26 to 0 14 and are indistinguishable within our analytical precision 0 07 2 sd coexisting hornblendes and biotites in these granitoids display similar mg isotopic composition with 26 mg ranging from 0 31 to 0 14 in hornblendes and 0 23 to 0 12 in biotites the inter mineral fractionation factors 26 mg hbl bt 26 mg hbl 26 mg bt vary from 0 10 to 0 02 with an average 0 06 0 08 2 sd the limited inter mineral fractionation agrees with the theoretic prediction that mg cations in both hornblende and biotite are octahedrally coordinated with oxygen which restricts the magnitude of equilibrium isotope fractionation overall data from both bulk granitoids and associated mineral separates suggest that mg isotope fractionation during i type granite differentiation is limited collectively granitoids studied here have mg isotopic composition similar to that of terrestrial basalts and peridotites 26 mg 0 21 0 07 vs 0 25 0 07 2 sd confirming that magmatic processes do not significantly fractionate mg isotopes the continental crust in the dabie orogen as sampled by these i type granitoids has a mantle like mg isotopic composition given that significant mg isotope fractionation occurs during chemical weathering processes mg isotopes may potentially be used for tracing granite genesis in particular if sedimentary materials are involved in granite sources

thermocline mixing in summer stratified continental shelf seas 1 a key process in the shelf sea pumping of co2 to the open ocean is vertical mixing in the summer stratified zones of continental shelf seas here we present measurements of profiles of the rate of dissipation of turbulent kinetic energy from which vertical mixing is inferred for several locations in the summer stratified zones of the nw european shelf seas at both sites we find significant thermocline mixing with 20 of the observed turbulent dissipation taking place within the thermocline we then present evidence to demonstrate that the thermocline mixing is a result of shear instability within the thermocline this is contrary to the conventional view that vertical mixing in shelf seas is largely driven by boundary shear stresses

well preserved garnet growth zoning in granulite from the dabie mountains central china ultra high pressure eclogites and granulites both occur in the dabie mountains central china a garnet porphyroblast from felsic granulite in the dabie mountains has been analysed for compositional zoning by electron microprobe two segments of the porphyroblast have opposite compositional variations segment i from centre outward 9 mm to analytical point 18 has decreasing xsps and increasing xpyr while segment ii from analytical point 18 1 mm outward to the rim has increasing xsps and xalm and decreasing xpyr and xgrs the compositional zoning in segment i is considered as growth zoning and that in segment ii as diffusive retrograde zoning garnet growth zoning records a p t path prior to the peak granulite metamorphism the minimum p t conditions are estimated to be 1 35 gpa and 850 c for peak metamorphism based on the highest mg fe mg composition in the garnet analytical point 18 and matrix hypersthene biotite and plagioclase a symplectitic corona surrounds the porphyroblast and appears to have formed at 0 6 gpa and 700 c the well preserved growth zoning in garnet suggests a short residence time for the granulite at peak metamorphism and thus rapid tectonic uplift history the p t path is consistent with that of ultra high pressure eclogite in the area tectonic movements during a collisional event could have brought both the granulite and the eclogite to their present positions

observations of the transition layer abstract the transition layer is the poorly understood interface between the stratified weakly turbulent interior and the strongly turbulent surface mixed layer the transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear vertical stratification and potential vorticity a database of 91 916 km or 25 426 vertical profiles of temperature and salinity from seasoar a towed vehicle is used to define the transition layer thickness acoustic doppler current measurements are also used when available statistics of the transition layer thickness are compared for 232 straight seasoar sections which range in length from 65 to 1129 km with typical horizontal resolution of 4 km and vertical resolution of 8 m transition layer thicknesses are calculated in three groups from 1 vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer 2 the depths below the mixed layer depth of peaks in shear stratification and potenti