flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

phytoplankton and nutrient dynamics of six south west indian ocean seamounts abstract a survey of six seamounts and two transects through the subtropical convergence zone scz in the south indian ocean in november and december 2009 showed a strong latitudinal gradient from the subtropics to the sub antarctic front concentrations of oxygen nitrate nitrite soluble reactive phosphorous as well as phytoplankton biomass measured as chlorophyll a increased while salinity and temperature decreased with an increase in latitude these differences resulted in significant differences between seamounts the chlorophyll a maximum became shallower at higher latitudes changing from a depth of 85 m in the subtropics to 35 m over the seamounts and in the scz the mixed layer depth also increased from 50 m in the subtropics to 100 m at higher latitude stations the n p and n si ratio indicated that no 3 was limiting at all the seamounts except one at which sio 4 was the limiting nutrient the phytoplankton community also showed a latitudinal gradient with decreasing diversity and a change in dominance from dinoflagellates in the tropics to diatoms towards the scz the dominant diatom genus of the survey 50 of the cell counts was pseudo nitzschia nutrients exhibited an inverse linear relationship with temperature and salinity the oligotrophic subtropical areas differed from the mesotrophic seamounts in temperature while waters over seamounts north and south of the agulhas return current arc differed in salinity the phytoplankton 148 taxa responded to these differences showing three communities subtropical seamount phytoplankton atlantis seamount walters seamount and off mount samples phytoplankton of the waters north of the arc melville bank sapmer bank middle of what seamount and phytoplankton south of the arc coral seamount scz1 characterised by a bloom of phaeocystis antarctica the environmental drivers most strongly linked to these observed differences were nitrate temperature and oxygen these environmental drivers displayed a clear latitudinal gradient unaffected by mesoscale variability of the arc eddy field and allowing the three phytoplankton communities to persist phytoplankton biomass was enhanced in the shallow

a hybrid origin for lachlan s type granites the murrumbidgee batholith example the murrumbidgee batholith is typical of other composite s type granite batholiths in the lachlan fold belt lfb of southeastern australia consisting of discrete peraluminous cogenetic granite suites however it contains a unique suite murrumbucka at its southern extremity that has chemical and petrological features transitional with metaluminous i type granites previous detailed structural and metamorphic studies have shown that the batholith is tilted northward exposing subvolcanic plutons in the north and root zones in the south originally located at depths of not vert similar10 km a transition from mafic foliated sheet like granites in the south to felsic generally less foliated homogeneous granites in the north is consistent with magma ascent via subvertical structurally controlled sheets to emplacement in an overlying magma chamber in the inferred root zones the murrumbucka suite hosts migmatitic metasedimentary and gabbroic rocks both of which have transitional contacts and show evidence for mafic felsic interaction with the murrumbucka suite the migmatites extend southward to become part of the high t low p cooma metamorphic complex which contains a core of heterogeneous remobilised diatexitic granite cooma suite lenses of which also occur throughout the southern deeper parts of the murrumbidgee batholith the composition of the most mafic rocks from the batholith lies on a chemical tie line between cooma suite granites and the gabbros for almost all elements this chemical coincidence is interpreted to reflect derivation of parental murrumbidgee s type granite magmas by bulk mixing between a felsic crustal and mafic mantle derived component consistent with sr and nd isotopic results and field observations based on the tie lines and simple numerical modelling the murrumbucka suite is estimated to be a 50 50 mix of mantle and crustal derived magmas whereas the more peraluminous and widespread clear range suite which is very typical of lachlan s type granites is modelled as a 40 60 mix chemical variation trends diverge from the mixing lines and suggest that much of the fractionation process operated after mixing mixing occurred within sheets during the ascent of the magmas whereas fractionation was the dominant process generating chemical diversity during emplacement in the magma chamber generation of the s type granites probably occurred in an extensional tectonic environment

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

circulation stratification and seamounts in the southwest indian ocean abstract circulation in the vicinity of six seamounts along the southwest indian ridge was studied as part of a multidisciplinary survey in november 2009 examination of altimetric data shows that several of the seamounts lie in the area of slow mean westward flow between the southern tip of madagascar 25 s and the agulhas return current arc flowing eastward between 37 s and 40 s the mean westward drift of mesoscale features was 4 1 0 9 cm s 1 integrated between madagascar and 37 s this westward drift can account for 50 sv 1 sv 106 m3 s 1 which added to 25 sv of southward flow past madagascar is sufficient to account for the total agulhas current transport of 70 21 sv the transport of the arc was also measured at two longitudes down to 2000 m combined with earlier crossings of the arc in 1986 and 1995 the full depth transport of the arc is estimated at 71 85 sv at longitudes 40 50 e indicating that the agulhas current then arc transport continues unreduced as far as 50 e before beginning to recirculate in the southwest indian ocean subtropical gyre the primary control on the circulation near each seamount was its position relative to any mesoscale eddy at the time of the survey melville lay on the flank of a cyclonic eddy that had broken off the arc and was propagating west before remerging with the next meander of the arc nearby sapmer on the other hand was in the centre of an anticyclonic eddy resulting in very weak stratification over the seamount at the time of the survey middle of what lies most often on the northern flank of the arc in strong currents but was at the time of the survey near the edge of the same eddy as sapmer coral in the subtropical front south of the arc was in waters much colder fresher denser and more oxygenated than all the other seamounts walter was close to the path of eddies propagating southwest from east of madagascar while atlantis the furthest east and north seamount experienced the weakest eddy currents

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

the effects of accretion erosion and radiogenic heat on the metamorphic evolution of collisional orogens petrological and thermochronological data provide our best record of the thermal structure of deeply eroded orogens and in principle might be used to relate the metamorphic structure of an orogen to its deformational history in this paper we present a two dimensional thermal model of collisional orogens that includes the processes of accretion and erosion to examine the p t evolution of rocks advected through the orogen calculated metamorphic patterns are similar to those observed in the field metamor phic temperatures depths and ages generally increase with distance from the toe of the orogen p t paths are anti clockwise with rocks heating during burial and early stages of unroofing followed by cooling during late stage unroofing the results indicate that peak metamorphic temperatures within the core of a collisional orogen and the distance from the toe of an orogen to the metamorphic core can be related to the relative rates of accretion erosion and plate convergence model orogens displaying high metamorphic temperatures 600 c are associated with low ratios of accretion rate to plate convergence velocity and with high heat flow through the foreland model orogens with metamorphic cores far from the toe of the orogen are associated with high ratios of accretion rate to erosion rate calculated metamor phic gradients mimic steady state geotherms and inverted thermal gradients can be preserved in the metamorphic record suggesting reconsideration of the concept that the metamorphic record does not closely reflect geothermal gradients within an orogen

pelagic communities of the south west indian ocean seamounts r v dr fridtjof nansen cruise 2009 410 the seamounts of the southern indian ocean remain some of the most poorly studied globally and yet have been subject to deep sea fishing for decades and may face new exploitation through mining of seabed massive sulphides in the future as an attempt to redress the knowledge deficit on deep sea benthic and pelagic communities associated mainly with the seamounts of the south west indian ridge two cruises were undertaken to explore the pelagic and benthic ecology in 2009 and 2011 respectively in this volume are presented studies on pelagic ecosystems around six seamounts five on the south west indian ridge including atlantis bank sapmer seamount middle of what seamount melville bank and coral seamount and one un named seamount on the madagascar ridge in this paper existing knowledge on the seamounts of the southwestern indian ocean is presented to provide context for the studies presented in this volume an account of the overall aims approaches and methods used primarily on the 2009 cruise are presented including metadata associated with sampling and some of the limitations of the study sampling during this cruise included physical oceanographic measurements multibeam bathymetry biological acoustics and net sampling of phytoplankton macrozooplankton and micronekton nekton the studies that follow reveal new data on the physical oceanography of this dynamic region of the oceans and the important influence of water masses on the pelagic ecology associated with the seamounts of the south west indian ridge new information on the pelagic fauna of the region fills an important biogeographic gap for the mid to high latitudes of the oceans of the southern hemisphere

an introduction to the physical oceanography of six seamounts in the southwest indian ocean exploratory surveys of six seamounts in the southwest indian ocean provide a description of physical processes induced by seamounts along the southwest indian ridge mean currents 15 25 cm s 1 in the vicinity of each seamount were dominated by mesoscale eddies the dominant seamount driven process was the generation of internal tides by the barotropic tide interacting with the seamount crests this led to enhanced shear in the vicinity of the crests resulting in mixing where stratification was weak for example in the core of an anticyclonic mesoscale eddy or where there had been a winter mixed layer tidally driven up and downwelling was observed at the seabed with associated variability in bottom temperature of up to 3 c over a tidal cycle vertical displacement of isopycnals by internal tidal waves reached 200 m peak to trough fluorescence in the surface eutrophic layer could thus extend down to the seamount crest on each tidal cycle apparently spatial variations in short conductivity temperature depth sections across each seamount were probably aliased temporal variations from the strong tidal signal evidence for taylor caps or other potential trapped circulations at the seamount crest was weak most likely because currents associated with mesoscale eddies were too strong to allow their formation

the distribution of pelagic sound scattering layers across the southwest indian ocean abstract shallow and deep scattering layers sls were surveyed with split beam echosounders across the southwest indian ocean swio to investigate their vertical and geographical distribution cluster analysis was employed to objectively classify vertical backscatter profiles correlations between backscatter and environmental covariates were modelled using generalized additive mixed models gamms with spatial error structures structurally distinct sl regimes were found across the subantarctic front gamms indicated a close relationship between sea surface temperature and mean volume backscatter with significantly elevated backscatter in the subtropical convergence zone the heterogeneous distribution of scattering layer biota reflects the biogeographic zonation of the survey area and is likely to have implications for predator foraging and carbon cycling in the indian ocean

offshore postseismic deformation of the 2011 tohoku earthquake revisited application of an improved gps acoustic positioning method considering horizontal gradient of sound speed structure

first active hydrothermal vents on an ultraslow spreading center southwest indian ridge the ultraslow spreading southwest indian ridge is a major tectonic province representing one of the important end member mid ocean ridge types for its very slow and oblique spreading and providing the only known route for migration of chemosynthetic deep sea vent fauna between the atlantic and indian oceans we report the investigation of the first active high temperature hydrothermal field found on any ultraslow mid ocean ridge worldwide located on southwest indian ridge at 37 47 s 49 39 e it consists of three zones extending 1000 m laterally and it is one of four recently discovered active and inactive vent sites within a 250 km long magmatically robust section our results provide the first direct evidence for potentially widespread distribution of hydrothermal activity along ultraslow spreading ridges at least along magmatically robust segments this implies that the segment sections with excess heat from enhanced magmatism and suitable crustal permeability along slow and ultraslow ridges might be the most promising areas for searching for hydrothermal activities it is surprising that the special vent fauna appear to indicate some complex affinity to those on the central indian ridge southern mid atlantic ridge and the southwest pacific ocean

the spatial distribution of particulate organic carbon and microorganisms on seamounts of the south west indian ridge abstract 1 the ecology and biogeochemistry of oceanic seamounts is not very well understood and explored pelagic ecosystems above the summits and flanks of seamounts have been observed to show different biological or biogeochemical properties to off seamount areas such as enhanced chlorophyll concentrations a phenomenon referred to as the seamount effect in addition seamount biogeography has been hypothesised to be similar to islands where community structure differences in multiple organisms have been shown to change between seamounts and across frontal systems we used elemental analysis to measure particulate organic carbon poc and flow cytometry to estimate abundance of microorganisms from above four seamounts coral melville middle of what and atlantis along the southwest indian ridge swir from latitude 32 6 s to 41 3 s longitude 57 1 e to 42 7 e samples were collected from the surface to the bottom using a ctd fitted with optical sensors poc was predicted from models created from in situ transmission optical data cp the high resolution predicted poc in the euphotic zone showed a heterogeneous distribution both above individual and between seamounts the shallow penetration of two of the seamounts displayed an effect on the poc concentration in the euphotic zone depleting the layer around the summit the transmission data showed higher concentrations of particles towards the surface caused by primary production and near to the seabed probably resulting from re suspension of sediments the poc concentrations and microbial abundance were positively correlated to cp and fluctuated with particle abundance with microorganisms accounting for 50 of the observed poc based on non metric multidimensional scaling it is clear that the microbial clusters strongly indicate three separate biological regimes associated with northeastern central and southwestern zones of the section of the swir that was sampled this biological zonation is associated with physical oceanographic boundaries represented by the subtropical and subantarctic fronts forming three distinct biogeographical regions

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

relict proterozoic basement in the nanling mountains se china and its tectonothermal overprinting 1 the basement beneath the caledonian belt in se china has been overprinted by indosinian and yanshanian events and is poorly known in situ u pb and hf isotope analysis of zircons from granites and surrounding rocks in the nanling mountains area of the fold belt reveal that the lanhe felsic gneiss is an outcrop of mesoproterozoic basement probably with a partly late archean protolith this is consistent with nd model ages of granites in this region and exposures of cathaysia basement in the coastal area of se china in the nanling mountains this basement was reactivated to generate granitoid rocks during the caledonian indosinian and yanshanian tectonothermal events the caledonian overprint is documented in extensive exposures of the zhuguang migmatites 425 470 ma and by previous u pb zircon dating of adjacent granites the jiangnan granite may be of similar age but strongly reworked the indosinian overprint resulted in the formation of granites such as the luxi and xiazhuang bodies 233 246 ma in the guidong complex the yanshanian overprint produced the most widely distributed granites circa 160 ma such as the jiufeng and fogang bodies and parts of the guidong complex hf isotope data show that all of the phanerozoic magmatic rocks were derived from the mesoproterozoic basement and minor archean components without obvious contributions from juvenile sources the presence of zircons with archean age 2 5 2 7 ga in both the lanhe gneiss and devonian sediments indicates that the badu and mayuan groups may not be the oldest basement of the cathaysia block some archean basement circa 2 5 2 7 ga may still be exposed but unrecognized in this region and cathaysia may include archean microcontinental fragments

observations of fauna attending wood and bone deployments from two seamounts on the southwest indian ridge the southwest indian ridge is an ultraslow spreading mid ocean ridge with numerous poorly explored seamounts the benthic fauna of seamounts are thought to be highly heterogeneous within even small geographic areas here we report observations from a two year opportunistic experiment which was comprised of two deployments of mango wood and whale bones one was deployed at 732 m on coral seamount 32 s and the other at 750 m on atlantis bank 41 s two areas with little background faunal knowledge and a significant distance from the continental shelf the packages mimic natural organic falls large parcels of food on the deep sea floor that are important in fulfilling the nutritional needs and providing shelter and substratum for many deep sea animals a large number of species colonised the deployments 69 species at coral seamount and 42 species at atlantis bank the two colonising assemblages were different however with only 11 species in common this is suggestive of both differing environmental conditions and potentially barriers to dispersal between these seamounts apart from xylophaga and idas bivalves few organic fall specialists were present several putative new species have been observed and three new species have been described from the experiments thus far it is not clear however whether this is indicative of high degrees of endemism or simply a result of under sampling at the regional level

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

softening the lower crust modes of syn transport transposition around and adjacent to a deep crustal granulite nappe parry sound domain grenville province ontario canada 1 the parry sound domain is a granulite nappe stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the mesoproterozoic grenville orogeny field observations suggest the following with respect to the ductile sheath 1 formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the parry sound domain and separating it from high strain gneiss of adjacent allochthons this ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones 2 transposition initiated by hydration amphibolization of granulite facies gneiss by introduction of fluid along cracks accompanying pegmatite emplacement shear zones nucleated along pegmatite margins and subsequently linked and rotated the source of the pegmatites was most likely subjacent migmatitic and pegmatite rich units or units over which parry sound domain was transported comparison of gneisses of the ductile sheath with high strain layered gneiss of adjacent allochthons show the mode of transposition of penetratively layered gneiss depended on whether or not the gneiss protoliths were amphibolite or granulite facies tectonites before initiation of transposition resulting in e g folding before shearing no folding before shearing respectively meter scale truncation along high strain gradients at the margins of both types of transposition related shear zones observed within and marginal to parry sound domain mimic features at kilometer scales implying that apparent truncation by transposition originating in a manner similar to the ductile sheath may be a common feature of deep crustal ductile reworking

observation of a mesoscale eddy dipole on the northern madagascar ridge consequences for the circulation and hydrography in the vicinity of a seamount abstract based on satellite and in situ data the dynamic characteristics and vertical structure of a surface intensified mesoscale eddy dipole recently expelled from the south east madagascar current semc is described for the first time the dipole was surveyed 250 nautical miles south of madagascar between 14 and 23 november 2016 during west east and south north transects carried out over the northern madagascar ridge the dipole consisted of two counter rotating vortices of similar size 100 km and intensity 0 7 f and an intense southwestward jet 150 cm s 1 in the frontal region between the two eddies the cyclonic eddy was lying on the western side of the anticyclonic eddy with azimuthal velocities reaching 100 cm s 1 at the surface and decreasing slowly with depth 40 cm s 1 at 600 m this dipole was defined as a highly non linear ro 0 7 isolated eddy type structure c 11 cm s 1 and u c 0 7 capable of trapping and advecting water masses over large distances the enhanced concentration of chlorophyll a found in the cyclone relative to the anticyclone could be tracked back to the spin up phase of the two eddies and attributed to eddy pumping the eddy cores were located above the pycnocline 1026 4 kg m 3 within the upper 600 m and consisted of varieties of subtropical underwater stuw found within the semc the stuw found in the anticyclone was more saline and oxygenated than in the cyclone highlighting mixing with the inshore shelf waters from the southeastern coastal upwelling cell off madagascar observations suggest that the dipole interacted strongly with the chaotic bathymetry of the region characterized by a group of five seamounts lying between 240 m and 1200 m the bathymetry blocked its westward advection trapping it in the vicinity of one shallow seamount for more than 4 weeks so enhancing the role of the eddy induced velocities in stirring the surrounding water masses squeezed between the southern madagascan shelf and the northern flank of the anticyclone two filament like dynamic features with very different water mass properties could be observed on the south north transect i one filament highly concentrated in chlorophyll a demonstrating the capacity of the eddy to export shelf water offshore ii intrusions of southern type stuw generally found south of the south indian counter current sicc recirculating on the external flanks of the anticyclone although the observed circulation and hydrography were largely constrained by the presence of the mesoscale eddy dipole unmistakable fine scale dynamics were also observed in the vicinity of the mad ridge seamount superimposed onto the mesoscale eddy flow

thermal control on post orogenic extension in collision belts abstract intracontinental extension develops in two different ways in the rhine graben the baikal or the east african rifts it is localized in a long and narrow zone along a few normal faults which often delineate a single graben in contrast in the basin and range province or the tibetan plateau it is distributed over a much broader area up to more than 1000 km across this difference arises from differences in rheology and applied forces widespread extension probably reflects the thinning of a previously thickened crust geological observations indicate that only wide orogenic belts undergo late or post orogenic thinning a related fact is that anatectic granites seem to be most abundant in wide orogenic belts the general correlation between belt width and occurrence of both extension and anatectic granites suggest that it reflects in part the characteristics of horizontal heat transfer between thickened crust and surroundings in wide orogenic plateaux the large amount of heat produced in the crust by radioactive decay and lack of erosion leads to high temperatures in narrow mountain belts horizontal heat transfer and high erosion rates concur to prevent temperatures from rising to values at which the crust may yield in extension we have tested this hypothesis using transient two dimensional numerical models of orogenic belts focussing on the effects of the shortening rate the final width of the belt and the rate of crustal radiogenic heat production in the range of geological values the shortening rate has little influence on the results crustal temperatures increase as a function of belt width we find that the sensitivity of crustal temperatures to belt width is most pronounced in the 100 300 km width range and for large values of crustal heat generation the pressure temperature paths followed by geological formations depend on the belt width which is consistent with available data the integrated shear strength of the lithosphere decreases with time as the belt is being built and then eroded this evolution is sensitive to belt width if extension occurs when the integrated shear strength drops below a critical value our results yield a framework for comparing different orogenic belts we predict that extension starts late in the history of wide belts and never occurs in narrow belts a final implication of this study is that the average rate of crustal heat production is probably close to 1 1 10 6 w m 3 which is in the upper range of possible values we present a simple and convenient diagram summarizing the thermal characteristics of orogenic belts as a function of width and shortening rate

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block