wave energy gradients across a maldivian atoll implications for island geomorphology exposure to wave energy has been used to account for a range of ecological geological and geomorphic processes in coral reef systems but few attempts have been made to quantify spatial variations in energy at the atoll scale this study presents results of measurements of wave energy on reef platforms across south maalhosmadulu atoll maldives and their implications for island geomorphology the atoll has a perforated rim 37 effective aperture and experiences predictable shifts in monsoon winds from the west 8 months and northeast 4 months results show that wave energy affecting the atoll is considerably greater during the westerly monsoon atoll structure promotes significant changes in wave energy and wave characteristics across the atoll short period 3 8 s monsoon driven wave energy which is significant on windward reefs is dissipated on the peripheral reef network and the density of lagoonal patch reefs limits development of locally generated wind wave energy across the lagoon however longer period swell 8 20 s propagates through the lagoon to leeward reefs a windward to leeward decay in wave energy is evident in the westerly monsoon but not in the northeast monsoon when long period swell from the southwest remains significant on western reefs net energy calculations that account for seasonal changes in wave energy across the atoll identify a steep west east gradient that has geomorphic significance for island building western reefs are dominated by westerly flowing energy that is 4 5 7 times the total energy input elsewhere in the atoll wave energy on central reefs is balanced whereas net energy on eastern reef platforms is dominated by eastward propagating waves this steep energy gradient provides a physical explanation for the presence and distribution of islands on reef platforms across the atoll and provides quantitative support for the theory of gardiner gardiner j s 1903 the fauna and geography of the maldives and laccadives archipelagoes cambridge university press london to explain the prevalence of islands on the eastern atoll reef rim

a p t t d discontinuity in east central nepal implications for the evolution of the himalayan mid crust abstract rock specimens collected from lower middle and upper portions of the exhumed himalayan mid crust in the upper tama kosi region of east central nepal yield pressure temperature time deformation p t t d paths that demonstrate the presence of a structural metamorphic and geochronologic discontinuity a p t t d path from below the discontinuity defines a loading path with deformation at staurolite grade metamorphic conditions occurring at 10 8 ma p t t d paths from above the discontinuity in contrast record an earlier and protracted metamorphic history that includes decompressional heating monazite ages from specimens collected above the discontinuity constrain prograde garnet growth to be 21 ma with decompression related garnet breakdown initiating at c 19 ma and likely continuing until c 15 ma these contrasting p t t d histories separated by a tectonometamorphic discontinuity are consistent with an evolutionary model for the himalaya in which rocks above the discontinuity were metamorphosed in the deep hinterland of the orogen and deformed during lateral extrusion from beneath tibet while rocks below the discontinuity were deformed and metamorphosed later within the shallower foreland of the orogen these results demonstrate the spatial and temporal relationships and compatibility between lateral midcrustal extrusive flow and wedge taper processes within an evolving orogen

new model of reef island evolution maldives indian ocean a new model of reef island evolution based on detailed morphostratigraphic analysis and radiometric dating of three islands in south maalhosmadulu atoll maldives is presented islands initially formed on a foundation of lagoonal sediments between 5500 and 4500 yr b p when the reef surface was as much as 2 5 m below modern sea level islands accumulated rapidly during the following 1500 yr effectively reaching their current dimensions by 4000 yr b p since then the high circum island peripheral ridge has been subject to seasonal and longer term shoreline changes while the outer reef has grown upward reducing the energy window and confining the islands this new model has far reaching implications for island stability during a period of global warming and raised sea level which will partially reactivate the energy window although it is not expected to inhibit upward reef growth or compromise island stability

from magmatic to hydrothermal sn li nb ta w mineralization the argemela area central portugal abstract the argemela mineralized area ama central portugal exhibits a nearly continuous magmatic to hydrothermal ore forming sequence typical of variscan granite related rare metal deposits disseminated and vein type mineralization are distributed in two systems the argemela mine am and the cabeco da argemela ca disseminated mineralization includes montebrasite cassiterite and columbite tantalite dispersed in rare metal granites vein type mineralization occurs both in granites and country rocks the ca system exposes three generations of intragranitic veins with montebrasite in the two earliest and montebrasite wolframite cassiterite and columbite tantalite in the latest country rock veins include a swarm of cassiterite and montebrasite veins am and rare isolated wolframite veins ca disseminated cassiterites are enriched in ta2o5 and nb2o5 compared to vein cassiterites disseminated columbite tantalites evolve toward mn and ta rich chemistries that contrast with the more fe and nb rich compositions in intragranitic veins in the ca system both intragranitic and country rock veins crystallize early mn rich wolframites followed by late more fe rich compositions associated with nb ta poor cassiterite the later replaced by stannite field relations structural mineralogical and geochemical data suggest that the disseminated and vein type mineralization are expressions of a continuous metallogenic evolution initiated at the magmatic stage pursued during the magmatic hydrothermal transition and ended with hydrothermal circulations in country rock the two mineralized systems share similarities but they also show major differences structural analysis demonstrates that the intragranitic veins in the ca and the country rock veins in the am were emplaced under the same tectonic regime therefore the two systems are variants of the same local metallogenic evolution sn and w show markedly contrasted behaviors both have a magmatic source but only sn reaches concentrations leading to saturation of the melt with cassiterite w is deposited later and preferentially to sn in intragranitic veins at the hydrothermal stage cassiterite and wolframite deposition are disconnected and overall wolframite occurs only in minor amounts the metallogenic model proposed for the ama emphasizes magmatic rare metal concentration processes exsolution of magmatic fluids and selective deposition of metals during the magmatic hydrothermal and later hydrothermal stages the sn li nb ta dominated and w poor signature of the ama makes it similar to lct pegmatites of the central iberian zone but is distinctive from the world class w sn cu panasqueira deposit nearby

metamorphic response to collision in the central himalayan orogen abstract closure of the neotethys ocean and high angle continent continent collision between india and asia after about 55 ma resulted in low angle subduction of the indian plate below the tibetan plateau and by 30 ma established an arcuate 2300 km long shallow north dipping metamorphic fold thrust belt in the foreland this himalayan metamorphic front quickly established an upper plate lower plate paired metamorphic architecture centred on the median high himal thrust that largely controlled subsequent evolution the upper plate is a thick slab of high t moderate p high grade migmatized metamorphic rocks whereas the lower plate is an inverted series of moderate t high p schists in two crustal wedges the broad main central thrust zone and at lowest structural levels the footwall below the basal main central thrust spatial and temporal patterns of metamorphic response in the evolving himalayan metamorphic front has been characterized in a large scale integrated structural metamorphic study based on 8 profiles across eastern nepal metamorphic response at all structural levels is established using a large dataset n 160 of internally consistent quantitative pt determinations petrology of metapelite samples semi quantitative p t paths metamorphic mapping and metamorphic field gradients these results are integrated with previously published metamorphic studies structural profiles and metamorphic chronology from these datasets the architecture and evolution of the himalayan metamorphic front is constrained by rock kinematics metamorphic field gradients showing discontinuities and diachronous metamorphism with contrasting p t evolutions at different structural levels each of the three panels constituting the himalayan metamorphic front upper plate main central thrust zone and footwall experienced distinctly different tectono metamorphic histories crustal processes operating during metamorphism and exhumation differ between the upper and lower plates the upper plate experienced long lived metamorphism starting from at least 28 38 ma and tracking low p t clockwise p t paths that culminated at 19 27 ma in peak high grade condition with 27 31 c km thermal regimes protracted high grade conditions produced significant partial melt which facilitated gravity driven southward extrusion involving internal ductile flow processes southward extrusion of the upper plate was accommodated by coeval reverse movement on the high himal thrust and top down to the north normal reactivation of the south tibet detachment system between 22 10 ma transport of this thick slab to the south resulted in further prograde burial of the lower plate below culminating in peak metamorphism at the highest pressures attained in the lower plate rocks the lower plate consists of at least two deeply buried 7 5 9 4 kb crustal wedges both of which experienced steep p t hairpin clockwise p t paths with isothermal decompression the main central thrust zone experienced 20 26 c km metamorphism at 12 22 ma and was exhumed along the basal main central thrust after 11 ma whereas loading by the main central thrust zone gave rise to further prograde burial of the footwall which experienced 16 21 c km metamorphism at 4 10 ma and was exhumed along the main boundary thrust at 3 9 ma in contrast to the upper plate both crustal wedges were exhumed by a process of out wedging which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls this three stage foreland propagating lateral exhumation history resulted in telescoping of the himalayan metamorphic front in concert with peak metamorphic events at different structural levels during main phase orogenesis and is not the result of superimposed retrograde reactivation of the belt

controls on links between geomorphical and surface sedimentological variability aitutaki and maupiti atolls south pacific ocean abstract isolated carbonate platforms and atolls occur throughout the geologic record from archean to present although the roles of sea level change tectonics and sediment supply on large scale changes in stratigraphical architecture of these systems are relatively well understood the details of the nature and controls on sedimentological variability between and within individual geomorphic elements on platforms and atolls are less well constrained the purposes of this study are 1 to describe compare and contrast geomorphological and sedimentological characteristics of surficial holocene sediments from two south pacific atolls aitutaki and maupiti representing different physical and chemical oceanographic settings and 2 to explore possible causes for sedimentological heterogeneity by contrasting the patterns with those present on other platforms and regions both atolls include annular shelf edge reef systems with a red algal rim and reef flat flanked lagoonward by reef sand aprons up to 1 500 m wide these aprons consist of moderately sorted coarse sand and gravel with an abundance of halimeda coral and red algal fragments broadly sediments become finer and better rounded away from margins water depths increase abruptly inboard of these reef sand aprons into platform interiors with depths up to 25 m maupiti and 9 m aitutaki although patch reefs dot these lagoons sediment is commonly poorly sorted with bimodal and polymodal size distributions and includes a mix of whole and fragmented skeletal grains peloids and ooids mud and fine sand are abundant up to 80 on maupiti 85 on aitutaki the occurrence of peloids fine ooid sand and oolitically laminated skeletal grains on maupiti atoll as previously documented on aitutaki is consistent with interpretations of the impact of elevated regional ocean total alkalinity ta and ph levels in this part of the pacific on these wave dominated atolls open ocean waves impinging on the platform margins generate currents that transport sediment from the reef across the sand apron and towards the platform interior unlike the tide dominated platforms of the bahamas however weak tides preclude strong daily agitation and circulation so ooids do not grow large and mud and fine sand transported into the atoll interiors is sequestered there in the interiors both sediment produced in situ and fine allochthonous sediment are more influenced by biological processes than by physical transport processes so bioturbated muddy sand is most common collectively the comparative analysis provides actualistic process based conceptual models for the nature and controls on variability of shelf margin reef and reef apron systems and platform interiors within and among atolls

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

the importance of large benthic foraminifera to reef island sediment budget and dynamics at raine island northern great barrier reef low lying reef islands are among the most vulnerable environments on earth to anthropogenic induced climate change and sea level rise over the next century because they are low composed of unconsolidated sediment that is able to be mobilised by waves and currents and depend on sediments supplied by reef organisms that are particularly sensitive to environmental changes e g ocean temperatures and chemistry therefore the spatial and temporal links between active carbonate production and island formation and dynamics are fundamental to predicting future island resilience yet remain poorly quantified in this paper we present results of a detailed geomorphological and sedimentological study of a reef and sand cay on the northern great barrier reef we provide an empirical investigation of the temporal linkages between sediment production and reef island development using a large collection of single grain ams 14c dates large benthic foraminifera lbf are the single most important contributor to contemporary island sand mass 47 ranging from 36 to 63 at raine island reflecting rapid rates of sediment production and delivery standing stock data reveal extremely high production rates on the reef 1 8 kg m 2 yr 1 while ams 14c dates of single lbf tests indicate rapid rates of sediment transferral across the reef we also demonstrate that age is statistically related to preservation and taphonomic grade severely abraded tests moderately abraded tests pristine tests we construct a contemporary reef and island sediment budget model for raine island that shows that lbf baculogypsina marginopora and amphistegina contribute 55 of the sediment produced on the reef annually of which a large proportion 54 contribute to the net annual accretion of the island the tight temporal coupling between lbf growth and island sediment supply combined with the sensitivity of lbf to bleaching and ocean acidification suggests that islands dominated by lbf are likely to be very sensitive to short and long term climate change projections potential outcomes of this work relate to improving the understanding of the future change dynamics of reef islands in response to climate change

the greer lake leucogranite manitoba and the origin of lepidolite subtype granitic pegmatites abstract the archean greer lake leucogranite intruded metabasalts of the bird river greenstone belt in the southwestern part of the superior province of southeastern manitoba the considerably evolved multiphase peraluminous b p and s poor leucogranite k rb 132 to 24 was probably generated by fault friction assisted anatexis of dominantly metatonalitic rocks and subsequent differentiation the leucogranite produced interior transitional non crosscutting pods of barren beryl columbite and lepidolite subtype pegmatites that solidified from local segregations of highly fractionated residual melt steep fractionation gradients characterize the granite to pegmatite transition most conspicuously so in the case of the most evolved li rb cs be mn sn nb ta f rich lepidolite subtype pod ac 3 with k rb 16 and cs 330 ppmwt in accessory k feldspar 2 5 and 11 200 ppmwt respectively in lepidolite cs 28 000 ppmwt in beryl and ta ta nb at 0 95 in manganotantalite the greer lake example documents beyond any doubt the igneous derivation of lepidolite subtype pegmatites from a plutonic parent most cases of generally very scarce lepidolite subtype pegmatites obscure this relationship as the volatile rich highly fluid melts stable to relatively low temperatures commonly migrate to great distances from their plutonic sources

age and preservation of amphistegina foraminifera in hawaiian beach sand implication for sand turnover rate and resource renewal radiocarbon dating of tests of amphistegina spp from the surface sand of hawaiian beaches has revealed ages up to 1500 years or more preservation is related to age the residual umbos are older than the intact tests the antiquity of some of the tests suggests that predictions of a sand turnover rate of less than 100 years time based on amphistegina productivity studies are in error and that the majority of tests produced in nearshore environments of hawaii do not accumulate on the beach

age and sedimentary characteristics of beach sediments from yongle atoll south china sea implications for sediments supply in a coral reef system abstract low lying reef islands constructed from unconsolidated sediments are of growing interest due to concerns over the future stability of island landforms in response to climatic change and sea level rise sediment characteristics combined with the constituents and physical processes are fundamental to understand the links between sediment production and their supply to an island s beach reservoir the grain size constituents and 230th age of beach sediments from five islands at yongle atoll in the south china sea were analyzed data reveal that coral grains are the dominant constituents of the beach sediments followed by mollusks coralline algae foraminifera halimeda and bryozoans the mean grain sizes of the beach sediment were within a range of 226 4215 m and the coarsest sands were located near the passages in the atoll rim transportation by tropical cyclone generated waves and winnowing by tides are potentially the main factors that influenced the grain size characteristics calibrated 230th age dates for bulk sand samples date the beach sediment between 424 yr bp and 5953 yr bp dating of coral sand samples from the beach sediment provides ages of 686 5780 yr bp the coral sands from a vertical section 1 2 m depth located on the beach at jinqing island were dated at 1154 3824 yr bp the age reversal on the vertical section with similar ages of beach sediment on any single island and different age ranges on different islands in an atoll indicates that the coral sediment supply processes occurred within a relatively close time period and that different islands had different sediment supply rates the temporal link between the coral dominated sediment production and the beach reservoir provides an important insight into understanding the sediments supply mechanism of atoll islands in the northwestern pacific ocean

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

habitats of larger foraminifera on the upper reef slope of sesoko island okinawa japan larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off sesoko island japan show strong habitat differences this study closely examines the distributions of larger foraminifers and relates these to a number of key environmental factors using rigorous statistical methods since all larger foraminifera house symbiotic algae light attenuation by the water column is the most important limiting factor that must be dealt with wall structures water energy is also countered by test structure the local topography is responsible for different intensities of hydrodynamic forces which are expressed in various substrates mostly coral rubble and coarse grained sand the genus peneroplis very common on the reef flat clearly prefers hardgrounds of the shallowest slope parts down to 30 m while dendritina is restricted to sandy bottoms and avoids the uppermost meters of the slope it can be found down to 50 m at least alveolinella shows a similar depth distribution to dendritina but is common on hard bottom the distribution of parasorites which is restricted to sandy substrates starts at 20 m and extends to 80 m sorites on the other hand was found only on firm substrates between the reef edge and 50 m the same depth distribution was recorded for amphisorus but this genus is not correlated with specific substrates most of the amphistegina species prefer hardgrounds while amphistegina radiata is also common on sand the calcarinids capable of withstanding high water energy are abundant on firm substrates close to the reef edge only baculogypsinoides inhabits deeper parts of the slope on sandy bottom and avoids the shallowest parts sections with hard substrates are settled by heterostegina even down to 80 m although this genus was occasionally found on sandy bottoms nummulites in contrast is restricted to sands between 20 and 70 m operculina starting at 20 m also prefers sandy substrates but rare individuals were detected on coral rubble and macroids

monazite chemical composition some implications for monazite geochronology an investigation of the chemical composition of monazite from a number of localities has been carried out samples used include monazites from metamorphic rocks granitic rocks and a hydrothermal ore deposit the ree distribution pattern of monazite varies greatly in accordance with its geological environment a remarkable feature of the monazites studied is that their chondrite normalised ree distribution patterns are mostly uniform between grains within the same sample but differ significantly from sample to sample this characteristic apparently indicates that there is an important effect on the ree distribution of monazite exerted by the host rock or source material from which monazite crystallised another important feature shown by the monazites studied is that monazites in rocks containing garnet as a major mineral show extreme depletion of hree whereas monazites in rocks without garnet or monazite that formed after the garnet breakdown contain significantly higher amounts of y and hree this suggests that the phase assemblage especially garnet plays an important role in the ree distribution of monazites in these rocks the value of ree distribution in monazite is exemplified with regard to the origin of monazite in the lewisian metamorphic rocks which is a fundamental issue in monazite geochronology

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

fine grained carbonates in nearly closed reef environments mataiva and takapoto atolls central pacific ocean abstract the nature origin and mode of accumulation of fine grained carbonate sediments have been investigated in the nearly enclosed lagoons of two french polynesian atolls mataiva and takapoto the fine sized fraction 20 m is substantially higher in amount 70 of the total fine sediments on average than the mud portion and may increase volumetrically 90 99 in some localities aragonite is the predominant mineral present 90 of the total calcium carbonate the fines appear to be mainly skeletally derived the silt fraction includes coral and molluscan detritus sponge chips juvenile benthic foraminiferans and other biogenic debris the mud is chiefly composed of aggregated nanograins ascidian spicules skeletal nanograins coral generated mainly and coccoliths a minor part of the mud is certainly of non skeletal origin some portion of freely deposited fines fill cavities or are attached upon sand grain surfaces they are associated with scattered inorganic precipitates and contribute to the formation of micrite envelopes and aggradation of host grains such a process is highly significant in the total carbonate budget of the reef the fine carbonate sediments result directly from the biological disintegration of nearby buildups mainly through the boring activity of sponges and lithophagid molluscs we suggest that the authigenic mud sized crystallites are controlled in their precipitation both by carbonate supersaturation and anoxic conditions seasonally affecting the interstitial sediment waters enclosed atoll lagoons are relatively self governing environments of deposition which are influenced by long term quiescent water situations rather than by rare catastrophic events

synchronous granite intrusion and e w extension in the cuonadong dome southern tibet china evidence from field observations and thermochronologic results the tethys himalaya sedimentary sequence ths is characterized by n s trending extensional rifts nstr and the north himalayan gneiss domes nhgd the cuonadong dome as one of the nhgd is located at the n s trending cuona rift in the eastern part of the tethys himalaya the dome had undergone four major deformation events d1 characterized by top to s thrust resulting in n s shortening and vertical thickening d2 characterized by vertical thinning and n s extensional deformation d3 approximately e w extensional deformation associated with intrusion of leucogranites and d4 late collapse structural deformation around the core of the cuonadong dome there are numerous granitic dykes at the contact zone between the granite and surrounding rocks in the middle unit of the cuonadong dome field observations show that granite intrusion occurred in part synchronously with d3 e w extensional deformation u pb zircon dating shows that the granite crystallization took place at ca 17 5 15 6 ma while muscovite ar ar geochronological data from the deformed pegmatite and mylonitic schist in the cuonadong dome show that the onset of the e w extensional deformation is between 16 5 and 14 8 ma and suggesting that granite intrusion was synchronous with the e w ductile extensional deformation in the cuonadong dome southern tibet combined with previously published ages of the south tibetan detachment system stds our study shows that granite intrusion was at least locally contemporaneous with both the e w and n s extensional deformation especially with the e w extension

direct shear fabric dating constrains early oligocene onset of the south tibetan detachment in the western nepal himalaya a newly identified and dated segment of the south tibetan detachment in the karnali klippe western nepal himalaya constrains initiation of mid crustal tectonically driven exhumation to the early oligocene the folded top to the northeast high temperature 600 c shear zone separates amphibolite facies rocks with a ca 36 30 ma prograde metamorphic history in the footwall from weakly to non metamorphosed upper crustal rocks in the hanging wall in situ dating of syn kinematic post metamorphic peak monazite indicates that the base of the shear zone was active from ca 30 29 to 24 ma and a post deformation muscovite cooling age implies that ductile shearing had ceased by ca 19 ma deformation along the south tibetan detachment in western nepal was thus synchronous with thrust sense shearing along the lower boundary of a zone of migmatitic rocks compatible with tectonic models involving mid crustal channelized flow during the oligocene along with other published data from the himalayan range this suggests that the south tibetan detachment actively exhumed the middle crust for almost 20 m y

a comparison of settling and sieve techniques for the analysis of bioclastic sediments this paper examines differences in the use of sieve and settling techniques for the determination of textural parameters of grain size distributions for 30 bulk bioclastic reefal deposits and examines the interpretive use of the results a comparison of results of the key textural parameters shows that sieve size estimates deviate from settled size determinations of mean grain size and dispersion values by up to 2 and up to 1 5 phi units respectively these differences are explained by the different grain properties measured by the two techniques exacerbated by the heterogeneous character of bioclastic deposits changes in sample components which control grain shape and grain bulk sample density also influence the magnitude of size and dispersion differences observed differences are discussed in relation to interpretation of the depositional environment and hydraulic regime leading to the conclusion that sieve results can grossly distort depositional and energy processes operating within bioclastic environments in contrast settled size estimates an index of deposit hydraulic behaviour show that bioclastic sediment transport systems operate within a much narrower energy regime than sieve sizes suggest hydraulic size estimates are considered to provide a better tool with which to interpret sedimentary processes in bioclastic environments

sedimentary facies of bora bora darwin s type barrier reef society islands south pacific the unexpected occurrence of non skeletal grains abstract barrier reefs when encircling small islands have been comparatively little noticed by voyagers but they well deserve attention in their structure they are little less marvelous than atolls and they give a singular and most picturesque character to the scenery of the islands they surround darwin 1842 p 2 sediment sampling revealed six modern sedimentary facies in the barrier reef system around the volcanic island of bora bora including mixed skeletal packstone peloidal packstone halimeda rich packstone to grainstone coralgal grainstone wackestone and mudstone whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals mud rich sediments with mollusks and foraminifera occur in deep lagoons 15 40 m carbonate mud is composed largely of aragonite needles probably derived from codiaceans like halimeda and coccoliths in moderate abundances despite the proximity to a volcanic island the content of siliciclastics in the sediments is low 10 on average which is a consequence of the absence of permanent water courses in addition to skeletal grains non skeletal grains cemented fecal pellets aggregates occur in high abundance 30 50 in shallow lagoons 5 m on the eastern side of bora bora this observation opposes the widely held concept that non skeletal carbonate grains are abundant on platforms from the atlantic ocean but virtually missing in recent indo pacific reefs and carbonate platforms in bora bora non skeletal grains and aggregates apparently form in warm shallow 5 m moderately agitated areas with relatively low sedimentation rates in addition early cementation is probably favored by elevated alkalinity and ph in surface waters in this part of the south pacific in the same area some 900 km to the southwest of the study area ooids and peloids have recently been discovered in the shallow lagoon of aitutaki cook islands more occurrences of abundant non skeletal grains probably exist in the indo pacific region however too few locations have been systematically studied a comparison of the new bora bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk foram halimeda and non skeletal grains and fines still grain abundances may vary significantly among locations and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments

rare metal mineralization related to granites and pegmatites phuket thailand rare metal mineralization on phuket island southern thailand comprises deposits of sn nb ta and w mineralization is related to cretaceous granites of the khao tosae suite and their pegmatite derivatives the khao tosae suite granites and the pegmatites intrude other granite suites and the carboniferous permian metasedimentary rocks of the phuket group the khao tosae suite consists of fine to medium grained porphyritic biotite muscovite or tourmaline granites the pegmatites are grouped into three types according to their main mineral assemblages k feldspar muscovite tourmaline k feldspar albite muscovite and albite k feldspar lepidolite dikes petrogenetic studies indicate that sn and nb ta mineralization is extended from the late magmatic stage to the pegmatite and postmagmatic hydrothermal stages of the khao tosae suite besides its occurrence in the pegmatites cassiterite precipitated during at least three periods in the khao tosae suite granites each of which has distinct petrochemical characteristics nb ta minerals occur in both the khao tosae suite granites and the pegmatites as wolframoixiolite niobian tantalian rutile and columbite tantalite exsolutions in cassiterite in addition discrete grains of columbite tantalite and microlite locally occur in the pegmatites wolframite is represented by huebnerite and is associated with the last stage of cassiterite deposition occurring in late vugs and or quartz veins in the khao tosae suite granites the phuket deposits represent a rather rare example of a granite related sn nb ta w bearing system with substantial evolution of pegmatites as well as postmagmatic greisen and vein mineralization the pegmatites are notable for their largely greenschist facies environment lack of be and p minerals tourmaline sharply decreasing in abundance from early to late generations of pegmatite dikes and a distinct accumulation of sr and ba in the otherwise most fractionated lepidolite rich dikes the pegmatites also provide the first example of fe mn and nb ta fractionation in successive generations of primary granitic to pegmatitic cassiterite as reflected in its exsolved columbite tantalite which perfectly mimics fractionation trends established for primary columbite tantalite in corresponding categories of pegmatites

how does the mid crust accommodate deformation in large hot collisional orogens a review of recent research in the himalayan orogen abstract the presence of hot weak crust is a central component of recent hypotheses that seek to explain the evolution of continent continent collisions and in particular may play an important role in accommodating the 3000 km of convergence within the himalaya tibetan collision over the last 55 myr models that implicate flow of semi viscous midcrustal rocks south toward the front of the himalayan orogen channel flow are able to account for many geologic observations in the himalaya while alternative models of collision particularly thrust wedge taper demonstrate that much of the observed geology could have formed in the absence of a low viscosity mid crustal layer several recent studies synthesized here have prompted a shift from initial assumptions that channel flow and thrust wedge taper processes are by definition mutually exclusive these new studies reveal the presence of several tectonometamorphic discontinuities in the midcrust that appear to reflect a continuum of deformation in which both channel and wedge type processes operate in spatially and temporally distinct domains within the orogen and further that the system may migrate back and forth between these types of behavior this continuum of deformation styles within the collisional system is of crucial importance for explaining the evolution of the himalayan orogen and hence for understanding the evolution of earth s many continent continent collision zones

studies on settling traction and entrainment of larger benthic foraminiferal tests implications for accumulation in shallow marine sediments settling and traction velocities were measured on optimally preserved tests of larger foraminifera using a settling tube and flume tank within larger foraminifera with porcelaneous tests the peneroplids peneroplis antillarum p planatus p pertusus and dendritina cf d zhengae are distinguished by low test densities ca 1 2 that do not change with growth buoyancy is high because of low reynolds numbers and increases in large individuals because of the allometric change of test shape the fusiform alveolinella quoyi with test densities ca 1 6 is characterized by high reynolds numbers inducing the weakest buoyancy within porcelaneous larger foraminifera the highest buoyancy was recorded for the three soritids parasorites orbitolitoides sorites orbiculus and amphisorus hemprichii because of their low test densities ca 1 25 and the extremely flat biconcave plate like shape flat tests however reduce traction and entrainment from smooth surfaces within hyaline larger foraminiferat the amphisteginids show thick lenticular amphistegina lobifera a radiata to thin lenticular tests a bicirculata a papillosa influencing buoyancy here high test densities ca 1 8 decrease with growth in a lobifera a lessonii and a bicirculata and remain constant in a radiata and a papillosa minimum velocities required for entrainment are lower for thick lenticular tests and higher for thin lenticular tests test densities remain constant with growth in the calcarinid baculogypsina sphaerulata 1 78 and decrease slightly in calcarina gaudichaudii and neorotalia calcar starting at 1 85 all living under extreme hydrodynamic conditions density decreases the most in baculogypsinoides spinosus starting at 1 8 resulting in higher buoyancy through low reynolds numbers traction is promoted in spherical tests of baculogypsina and baculogypsinoides within nummulitids the thick lenticular palaeonummulites venosus test density decreasing with size starting at 1 78 is less buoyant expressed in high reynolds numbers but easily entrained thick lenticular juveniles and extremely flat adults distinguish operculinella cumingii heterostegina depressa and the giant cycloclypeus carpenteri test densities increase during growth starting from ca 1 6 and attaining a maximum of 1 8 buoyancy is low in small tests and high in large tests while entrainment velocities are reduced as the tests flatten high buoyancy is also a characteristic of the entirely flat tests in operculina ammonoides from deeper regions and planostegina operculinoides which is expressed in the lowest reynolds numbers within larger foraminifera

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

geochemical and mineralogical characteristics of ion adsorption type ree mineralization in phuket thailand geochemical and mineralogical studies were conducted on the 12 m thick weathering profile of the kata beach granite in phuket thailand in order to reveal the transport and adsorption of rare earth elements ree related to the ion adsorption type mineralization the parent rock is ilmenite series biotite granite with transitional characteristics from i type to s type abundant in ree 592 ppm ree are contained dominantly in fluorocarbonate as well as in allanite titanite apatite and zircon the chondrite normalized ree pattern of the parent granite indicates enrichment of lree relative to hree and no significant ce anomaly the upper part of the weathering profile from the surface to 4 5 m depth is mostly characterized by positive ce anomaly showing lower ree contents ranging from 174 to 548 ppm and lower percentages of adsorbed ree from 34 to 68 compared with the parent granite in contrast the lower part of the profile from 4 5 to 12 m depth is characterized by negative ce anomaly showing higher ree contents ranging from 578 to 1 084 ppm and higher percentages from 53 to 85 the negative ce anomaly and enrichment of ree in the lower part of the profile suggest that acidic soil water in an oxidizing condition in the upper part mostly immobilized ce4 as ceo2 and transported ree3 downward to the lower part of the profile the transported ree3 were adsorbed onto weathering products or distributed to secondary minerals such as rhabdophane the immobilization of ree results from the increase of ph due to the contact with higher ph groundwater since the majority of ree in the weathered granite are present in the ion adsorption fraction with negative ce anomaly the percentages of adsorbed ree are positively correlated with the whole rock negative ce anomaly the result of this study suggests that the ion adsorption type ree mineralization is identified by the occurrence of easily soluble ree fluorocarbonate and whole rock negative ce anomaly of weathered granite although fractionation of ree in weathered granite is controlled by the occurrence of ree bearing minerals and adsorption by weathering products the ion adsorption fraction tends to be enriched in lree relative to weathered granite

monazite geochronology unravels the timing of crustal thickening in nw himalaya abstract greenschist to amphibolite grade haimanta metasediments of the nw himalaya preserve much of the prograde metamorphic history of eohimalayan crustal thickening which has been erased by oligo miocene migmatization elsewhere in the himalaya our zircon and monazite u th pb data unravel a multi stage prograde metamorphic evolution the earliest evidence of prograde barrovian metamorphic monazite growth is 41 ma peak metamorphic conditions 8 8 5 kbar 600 700 c were attained at 37 36 ma and followed by a prolonged evolution at high temperatures with at least three distinct episodes of monazite growth which may be related to the formation of the northern himalayan nappes e g shikar beh nappe nyimaling nappe rapid exhumation of the crystalline started at 26 ma and resulted in cooling through the muscovite 40 ar 39 ar closure temperature by 21 8 ma although a local continuation of the south tibetan detachment is not unambiguously identified in central himachal pradesh extrusion was likely facilitated by a system of several minor late oligocene early miocene top to the n to ne shear zones in contrast to the crystalline of zanskar and eastern himachal pradesh extrusion was not accompanied by widespread decompression melting

recent sedimentary facies of isolated carbonate platforms belize yucatan system central america abstract distribution of recent sedimentary facies is significantly different in four closely spaced isolated carbonate platforms off the coasts of belize and yucatan se mexico these differences are largely controlled by variations in submarine topography which are likely the result of differential subsidence and karstification from platform to platform a variety of depositional styles and patterns is found in platform interiors that developed during the same holocene sea level rise composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms facies maps are based on analysis of 454 sediment samples and high resolution satellite imagery glovers reef is characterized by a circular facies distribution the nearly continuous reef margin is composed of a coral red coralline algae halimeda grainstone mixed nonskeletal peloidal skeletal wackestones and packstones are present in shallow lagoon parts 5 m water depth behind the margin the deep interior from 5 to 18 m water depth is characterized by mollusk foram halimeda wackestones with over 860 patch reefs of coral red algae halimeda mollusk packstones lighthouse reef also has a coral grainstone and coral red algae halimeda grainstone rim but the facies distribution in the interior is strongly asymmetrical the 8 m deep eastern lagoon is floored by mollusk foram halimeda wackestones and packstones the 3 m deep western lagoon has the mixed peloidal skeletal wackestone to grainstone facies a linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons banco chinchorro is similar to lighthouse reef inasmuch as facies distribution patterns of the interior are strongly asymmetrical mollusk foram halimeda wackestones grainstones are present in eastern lagoon areas whereas shallow 5 m western parts of the lagoon are composed of mixed peloidal skeletal grainstones packstones and wackestones most of turneffe islands is protected on the east by lighthouse reef accordingly turneffe has a narrower reef and skeletal grainstone rim than the other two platforms restricted interior lagoons are up to 8 m deep and are enclosed by wide mangrove rims and surface sediments dominated by halimeda rich wackestone rich in organic matter coral patch reefs are absent in contrast the unprotected northernmost part of turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk foram halimeda wackestones packstones with abundant patch reefs

geomorphology and sediment transport on a submerged back reef sand apron one tree reef great barrier reef back reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems the development of these features influences the evolution and defines the maturity of coral reefs however the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport current and wave conditions on a back reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron reef flats and lagoon the current and wave processes that may entrain and transport sediment were assessed using second order small amplitude stokes wave theory and shields equations the morphodynamic interactions between current flow and geomorphology were also examined the results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents a morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel like areas directing current off the sand apron towards the lagoon or the reef crest these results show that the short term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium

a review of definitions of the himalayan main central thrust most workers regard the main central thrust mct as one of the key high strain zones in the himalaya because it accommodated at least 90 km of shortening because that shortening exhumed and buried hanging wall and footwall rocks and due to geometric and kinematic connections between the main central thrust and the structurally overlying south tibet detachment geologists currently employ three unrelated definitions of the mct metamorphic rheological age of motion structural or protolith boundary structural these disparate definitions generate map and cross section mct positions that vary by up to 5 km of structural distance the lack of consensus and consequent shifting locations impede advances in our understanding of the tectonic development of the orogen here i review pros and cons of the three mct definitions in current use none of these definitions is flawless the metamorphic rheological and age of motion structural definitions routinely fail throughout the orogen whereas the protolith boundary structural definition may fail only in rare cases all limited to sectors of the eastern himalaya accordingly a definition based on high strain zone geometry and kinematics combined with identification of a protolith boundary is the best working definition of the mct

pressure temperature deformation time constraints on the south tibetan detachment system in the garhwal himalaya nw india a peculiar feature of the himalaya is the occurrence of a system of low angle normal faults and shear zones the south tibetan detachment system stds at the mountain crests the stds was active during syn convergent tectonics we describe the stds related sheared rocks along the dhauli ganga valley in the garhwal himalaya nw india where the malari granite reported as an undeformed igneous body cross cutting the stds occurs a detailed multidisciplinary study integrating field based microstructural petrographic and geochronological analyses was carried out on rocks along this valley we demonstrate how the non coaxial ductile portion of the stds affected the upper part of the greater himalaya sequence migmatite which experienced peak pressure p temperature t conditions of 0 9 1 1 gpa and 750 c at 24 ma this migmatite has been reworked structurally upwards leading to the formation of high t sillimanite bearing mylonites further upward medium t shearing deformed the malari granite and leucogranite dykes forming medium t mylonites ductile shearing was temporally constrained based on new in situ monazite datings and previously published ar ar geochronology between 20 15 ma we demonstrate that a preserved ductile to brittle spatial and temporal transition of the stds deformation exists with the brittle features overprinting ductile ones our data shed new light on the geological evolution of the stds in the nw himalaya with implications for the relationship and relative timing of partial melting granite emplacement and deformation along low angle normal faults

microprobe monazite geochronology putting absolute time into microstructural analysis abstract high resolution compositional mapping and dating of monazite on the electron microprobe is a powerful addition to microstructural analysis and an increasingly important tool for tectonic analysis microprobe monazite geochronology can be an efficient reconnaissance tool for evaluating metamorphic and deformational age domains but more importantly its in situ nature and high spatial resolution offer an entirely new level of structurally and texturally specific geochronologic data that can be used to put absolute time constraints on p t d paths constrain the rates of metamorphic and deformational processes and provide new links between metamorphism and deformation microprobe geochronology is particularly applicable to three persistent microstructural microtextural problem areas 1 constraining the chronology of metamorphic assemblages 2 constraining the timing of deformational fabrics and 3 interpreting other geochronological results although some monazite generations can be directly tied to metamorphism or deformation at present the most common constraints rely on monazite inclusion relations in porphyroblasts that in turn can be tied to the deformation and or metamorphic history microprobe mapping and dating allow geochronology to be incorporated into the routine microstructural analytical process resulting in a new level of integration of time t into p t d histories

defining the himalayan main central thrust in nepal an inverted metamorphic field gradient associated with a crustal scale south vergent thrust fault the main central thrust has been recognized along the himalaya for over 100 years a major problem in himalayan structural geology is that recent workers have mapped the main central thrust within the greater himalayan sequence high grade metamorphic sequence along several different structural levels some workers map the main central thrust as coinciding with a lithological contact others as coincident with the kyanite isograd up to 1 3 km structurally up section into the tertiary metamorphic sequence without supporting structural data some workers recognize a main central thrust zone of high ductile strain up to 2 3 km thick bounded by an upper thrust mct 2 vaikrita thrust and a lower thrust mct 1 munsiari thrust some workers define an upper lesser himalaya thrust sheet that shows similar p t conditions to the greater himalayan sequence others define the main central thrust either on isotopic nd sr differences differences in detrital zircon ages or as being coincident with a zone of young

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

structural analysis of sheath folds and geochronology in the cuonadong dome southern tibet china new constraints on the timing of the south tibetan detachment system and its relationship to north himalayan gneiss domes

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

modelling holocene relative sea level observations from the caribbean and south america abstract holocene data from the caribbean and the atlantic coast of south america have been critically assessed and a subset of the best quality data are presented these data cover a large north south geographic extent and display a distinct spatial variation we make the first comparisons of this data set to predictions based on a realistic model of glaciation induced sea level change with the main aims of understanding the cause of the observed spatial trend and estimating a eustatic signal for the holocene the spatial variation is dominated by the influence of the ice and ocean mass redistribution on sea level change with the ice induced effect dominating the observed north south trend a best fitting model is applied to estimate a holocene eustatic signal from the observations we find that the model corrected data are consistent with a relatively rapid rise of 7 8 mm yr in the early holocene with a marked reduction in this rate around 7 cal kyr bp from this time until present the model corrected data suggest that the volume of mass transfer between ice sheets and oceans was no more than 1 m eustatic sea level equivalent

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

the durability of bioclastic sediments and implications for coral reef deposit formation the generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of caco3 in conjunction with physical biological and chemical processes which act to break down and disperse skeletal remains using the results of detailed tumbling barrel experiments this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits the durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels results indicate that constituent durability varies considerably amongst common reef sediment constituents calcareous algae halimeda was the least durable constituent tested followed by larger benthic foraminifera baculogypsina sphaerulata and marginopora vertebralis and the pelecypod fragum fragum two species of branching coral acropora sarmentosa and acropora nasuta were found to be the most resistant to physical destruction these findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

extrusion vs duplexing models of himalayan mountain building 2 the south tibet detachment at the dadeldhura klippe abstract himalayan mountain building has been dominantly explained by two types of models extrusion and duplexing to elucidate possible roles of these mechanisms during emplacement of the himalayan crystalline core we investigate an area speculated to contain the southern leading edge of the crystalline core the northeastern margin of the dadeldhura klippe western nepal we found an 700 m thick primarily top to the north shear zone within the klippe we term this as the tila shear zone the shear zone occurs within a right way up metamorphic field gradient and separates footwall gneiss from hanging wall schist similarly deformation temperatures estimated from quartz and feldspar microstructures and quartz c axis fabrics indicate a right way up thermal gradient of 77 189 c km u pb zircon dating of post kinematic leucogranite dikes suggests that ductile shearing along the tila shear zone occurred prior to 17 14 ma we correlate the tila shear zone to the south tibet detachment std on the basis of consistent structural fabrics shear sense lithologies metamorphism and deformation timing this interpretation in combination with regional constraints indicates southwards increasing proximity of the std tila shear zone and the main central thrust mct these two shear zones are separated by 3 km of structural section in the northern portion of our study area and become close to within 1 km of separation in the southern portion interpolation suggests that the std tila shear zone and mct merge 15 10 km southwest of our study area the increasing to south proximity and potential merger of the two shear zones suggest that the std formed as a backthrust from the mct this interpretation contrasts with the long standing normal fault interpretation of the std because the std and mct bound the himalayan crystalline core these findings document crystalline core emplacement at depth via tectonic wedging this kinematic evolution is consistent with duplexing but not extrusion to the surface

controls on platform scale patterns of surface sediments shallow holocene platforms bahamas isolated carbonate platforms occur throughout geological history and commonly exhibit considerable spatial variability to evaluate the controls on the nature of sediment accumulation across the expansive shallow platform tops this study systematically compares and contrasts patterns in surface sediments from several shallow 10 m holocene bahamian examples remote sensing data field observations petrographic characterization and quantitative grain size analyses reveal the spatial patterns of sediment accumulation on crooked acklins platform and the berry islands bank integration of these data with synoptic observations of waves tides and currents along with regional geochemical data provides a means to explore the factors that influence platform scale sedimentary patterns these data illustrate that the platform interiors of both crooked acklins platform and berry islands bank are blanketed with medium to coarse sand size sediment peloids are most common in the interior of crooked acklins platform whereas the berry islands bank includes more abundant composite grains in both areas very little mud is present with surface sediments averaging 2 mud comparison of these results with published data from little bahama bank great bahama bank and caicos platform suggest that contrary to previous interpretations the presence of open margins and or brisk winds are not necessary for the occurrence of a platform top with little mud although the muddy sediment fraction of the interior can be suspended by elevated wave energy wind generated current speeds in protected platform interiors are relatively low instead in parts of the platform interiors transport and winnowing of fines is enhanced greatly by tidal currents which carry suspended sediments off the shallow platforms even if shielded by islands beyond physical influences however regional geochemical compilations suggest that the bahamian tides supply highly supersaturated waters rich in dissolved oxygen to these platform interiors this exchange is interpreted to facilitate favourable conditions for calcium carbonate precipitation in the form of ooids marine cements and hardened peloids across vast expanses of the platform interiors such fundamental controls on holocene platform scale sediment dynamics are likely to have influenced carbonate systems through the geological record

off reef transport of coral fragments at lizard island australia abstract the generation and movement of coral rubble is important to the sedimentary budget of a reef in sediment facies development and in the promotion of reef growth this study examined the rate of down slope transport of live and dead coral fragments from shallow reef fronts at lizard island on the great barrier reef australia ten large 1 m2 collecting trays were deployed and cleared annually for 4 years at each of two sites at the base 8 12 m depth of the steeply sloping fringing reef the rate of export of coral fragments down the reef slope was very high an average of 132 fragments weighing 1 87 kg was recorded each year per meter of reef front a mean of 2 25 of the fragments representing 43 species was alive in the trays at each annual census yielding an average rate of colonization onto the reef slope of 2 7 live fragments per meter of reef front per year reworking of hard calcareous substrates towards the slope promotes reef growth by two mechanisms 1 passive dispersal of live coral fragments to peripheral soft sediment habitats that are unsuitable for larval settlement and 2 subsequent colonization of rubble by coral larvae there were no major storms during the course of the study indicating that significant down slope transport of fragments can occur even in the absence of cyclones

the muscovite granites parental rocks to the nanling range tungsten mineralization in south china abstract muscovite granites mgs in the nanling range south china occur as satellite intrusions within or surrounding batholitic biotite monzogranites bms the mgs are massive and fine grained with a porphyritic texture and contain quartz k feldspar and albite in nearly equal portions the accessory minerals in the mgs include alumina rich minerals e g mn and fe rich garnet andalusite topaz and tourmaline anatase rutile wolframite cassiterite xenotime chalcopyrite molybdenite and volatile rich minerals e g microlite topaz tourmaline fluorite and calcite compared with the bms the mgs are geochemically enriched in major elements of si k and na and incompatible trace elements of rb cs y u nb ta w sn pb bi li and be and depleted in major elements of fe mg ca ti and p and compatible trace elements of ba sr co ni cr cd v as well as zr and hf the chondrite normalized ree patterns of the mgs are flat with large negative eu anomalies the mineralogical and geochemical features of the mgs indicate that they crystallized from highly fractionated granitic magmas zircons separated from the mg samples which were collected from six different tungsten deposits show characters of hydrothermal origin according to their morphologies chemical compositions and inclusions in situ u pb dating of the zircons yields a weighted mean 206pb 238u age of 133 4 1 0 ma this age is similar to the mean age of the zircons from wolframite bearing quartz veins wqvs in the nanling range 133 7 1 3 ma reported from our previous study zircon hf isotopes also reveal that the mgs and the wqvs are homologous these mineralogical geochemical and zirconological features indicate that the mgs are the parental rocks of the tungsten deposits in the nanling range this study provides a new guidance for the exploration of magmatic hydrothermal tungsten deposits

reef island accretion and soil development on makin kiribati central pacific the late holocene accretionary history of reef islands on makin the northernmost table reef of the gilbert atoll chain western kiribati has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples and ams radiocarbon dating of individual grains makin is geomorphologically and sedimentologically simple comprising one main island with only a minor residual lagoon and composed of sand dominated by the reef flat foraminifera calcarina spengleri amphistegina lobifera and baculogypsina sphaerulata deposition commenced in mid platform around 2500 years ago in situ fossil coral heliopora dated at 2400 80 years bp indicates that sea level was 0 4 0 5 m above present at that time progradation occurred progressively to westward at a relatively constant rate of 200 300 m ka 1 however progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago the soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts and do not reflect reef island depositional history remnant stands of pisonia forest with an associated phosphatic soil are not related to any particular geomorphological feature or period of deposition the reef islands are continuing to accrete as a result of production of foraminifera on the reef flat

linking pattern to process in reef sediment dynamics at lady musgrave island southern great barrier reef linking surficial sediment patterns in reef environments to the processes that underlie their depositional dynamics enables predictions to be made of how environmental changes will influence reef associated sedimentary landforms such as islands and beaches geomorphic linkages between sediment deposition patterns and the biophysical processes that drive them are often poorly resolved particularly at broad landscape scales where tangible statements can be made about structural changes to landforms the present study applies geospatial techniques to link patterns in reef sediment dynamics at lady musgrave island to the underlying processes driving them in situ calcification is characterized by developing a high resolution map of the surficial calcium carbonate producing communities inhabiting the reef platform and associated sediments across the reef flat are analysed for grain size kurtosis sorting and threshold bed shear stress to explore transport pathways across the reef flat and lagoon wave energy is modelled across the entire reef platform as a potential driver of sediment dynamics and morphometric linkages are empirically defined between wave energy and grain size findings indicate that carbonate sediments are primarily sourced from calcifying communities colonizing the outer periphery of the reef platform and that sediment grain size can be reliably linked to wave energy by virtue of a linear model

reef to island sediment connections on a maldivian carbonate platform using benthic ecology and biosedimentary depositional facies to examine island building potential reef islands are low lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate producing reef organisms and are therefore perceived as highly vulnerable to environmental change however basic elements of island composition are not well described and given their high inter and intra basinal variability a better understanding of reef and island sedimentary environments and the connections between them are needed to predict future morphological response here we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of vabbinfaru platform maldives field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways carbonate production was dominated by coral framework mean 52 within a narrow zone on the outer reef rim 22 of platform area resulting in coral rich detrital sediments reef 51 island 64 that closely resemble living assemblages the net transfer of sediment occurred lagoonward by wave driven processes leading to a decrease in grain size towards the island r2 0 502 which acts as a major control on depositional facies development within the lagoon island sediments were distinct from reefal deposits comprising a restricted suite of durable sands mean 1 34 throughout long term development our findings suggest that the production breakdown and redistribution of coral derived sediment by platform currents is fundamental to future island stability at vabbinfaru and although alterations away from current ecological states may reduce sediment supply the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island grade sand copyright 2016 john wiley sons ltd

onset of mid crustal extensional flow in southern tibet evidence from u pb zircon ages new ion microprobe u pb dates from zircon in deformed orthogneiss and migmatite and an undeformed granite in mabja dome are the first to constrain the timing of peak metamorphism and onset and duration of mid crustal ductile extension in southern tibet at 35 0 0 8 ma and 12 19 million years the structural metamorphic and intrusive his tories in mid crustal rocks exposed in these north himalayan gneiss domes are similar to those recorded in the greater himalayan sequence suggesting that middle crust was continuous from beneath southern tibet southward to the high himalaya strain compatibility indicates that 35 ma ductile extension in mid crustal rocks of southern tibet was accommodated to the south at shallow crustal levels via normal slip along the southern tibetan detachment system the oldest age estimate for slip along this normal fault zone and extrusion of its footwall if gravitational collapse is an additional important process driving extension then southernmost tibet may have been at or near maximum elevation by late eocene early oligocene time

the effects of callianassa bioturbation on the preservation of carbonate grains in davies reef lagoon great barrier reef australia abstract coring air life excavation and tracer sediment experiments in the lagoon floor sediments of davies reef revealed that callianassid shrimp had produced during their feeding a 5 60 cm thick surface layer of moderately to poorly sorted gravel free sediment above very poorly sorted gravelrich sediment the subsurface gravel is epilithic in origin close to reef framework but consists predominantly of infaunal molluscs through most of the lagoon these infaunal skeletons tend to be buried rapidly in a well preserved state escaping the microboring that attacks all grains on the surface two geologically significant points emerge first the surface layer will not get preserved in its present form and any analyses of surface samples can give a false impression of the accumulating sedimen pile and the prevailing hydraulic regime and second the combination of continuous fine sediment recycling and surface microboring can lead to a bias in the fossil reefal limestone record with epilithic organisms seemingly subordinate to infaunal molluscs

carbonate sediment production transport and supply to a coral cay at raine reef northern great barrier reef australia a facies approach abstract coral cays are low lying typically 2 mm grain size and the relative abundances of foraminifera and coral grains gravelly coral dominated sediment is concentrated at the reef margins whereas facies on and around the leeward cay are dominated by the sand size tests of benthic foraminifera mud is absent in reef sediments and reflects the prevailing high energy wave dominated setting as well as a paucity of mud producers benthic foraminifera tests are the major sediment component constituting an average proportion of 39 range 2 77 sediment derived from the skeletal remains of corals 24 1 65 mollusks 15 3 30 halimeda 14 4 36 and coralline algae 6 0 20 are present in lesser volumes foraminifera content is highest 40 on tidally emergent algal pavement where they live in greatest abundance and on the cay shorelines where their tests are deposited and comprise the bulk of beach sand 36 63 a comparison of the raine island data with other exposed modern reefs and platforms of the central and western pacific shows that occurrence and distribution of facies types is broadly consistent beyond these sedimentological data the taphonomy of foraminifera at raine island indicates that tests are vulnerable to destruction due to abrasion when transport and reworking is prolonged therefore the foraminifera rich facies adjacent to and on the cay disjunct from the source zones as well as taphonomic evidence imply that transport from the outer reef flat to the cay must be relatively quick these short temporal links between ecological source zones and depositional landforms are likely to have important ramifications for the contemporary management of reef associated landforms e g cays in the future

oligocene initiation of the south tibetan detachment system constraints from syn tectonic leucogranites in the kampa dome northern himalaya abstract himalayan leucogranites provide a robust record of the thermal and tectonic processes that occurred during convergence of the eurasian and indian tectonic plates we present structural petrological mineralogical whole rock geochemical sr nd isotope and geochronological results for cenozoic leucogranites from the kampa dome northern himalaya the kampa leucogranites are typical syn tectonic granites and occur as a series of sills dikes and puddings in the kampa shear zone which is considered to be the exhumed portion of the south tibetan detachment system stds in the northern himalaya the kampa syn tectonic leucogranites provide information about the timing and nature of regional kinematics and record thermal conditions and the initiation of the stds whole rock geochemistry and sr nd isotope analyses show that the kampa leucogranites are characterized by the following 1 they are peraluminous and have high sio2 al2o3 and a cnk low tio2 mgo p2o5 and tfe2o3 and variable cao na2o k2o and total alkalis 2 they are enriched in large ion lithophile elements e g k and rb and depleted in high field strength elements e g zr and ti with negative eu anomalies and 3 they display variable initial 87sr 86sr compositions 0 7507580 826065 and their end i values range between 7 6 and 12 2 anatexis of graywackes and metapelites in the great himalayan crystalline series played an important role in the formation of the kampa leucogranites anatexis was controlled by fluid absent partial melting of muscovite mineralogical and petrological analyses show that zircons belong to an early crystallization phase whereas monazites are remnants of the final crystallization phase of the granitic melt zircon u pb dating reveals that anatexis in the deep himalayan crust occurred at ca 32 23 ma during the oligocene monazites yield homogeneous 208pb 232th ages of ca 23 5 ma and record rapid emplacement in the kampa shear zone these results indicate that movement on the stds was initiated during the early oligocene and became well developed during the late oligocene in the kampa region the oligocene was a unique period of counterbalance between continued plate convergence and intense extension in the himalayan orogen

sediment produced from abrasion of the branching stony coral oculina varicosa abstract soft rubber tumbling barrels some with screen windows were used to simulate natural abrasion of coral branches tumbled for equal times sealed barrrels produced more sediment from coral branches than barrels with windows and dead coral produced more sediment than live coral tumbled dead coral produced a gravel mode 2 4 mm of fragmented barnacles and a sand mode 0 2 mm of coral tumbled live coral produced similar results but lacked barnacles time series tests of 1 1000 minutes showed that closed barrels produced increasingly greater percentages of carbonate mud and increasingly finer sand grain size modes tumbling barrels with screen windows yielded particles of unchanging size through the same intervals natural sediment with broken coral branches contained coral sand most abundantly between 0 125 0 250 mm which is the same as produced by tumbling dead coral in barrels with screen windows strong grain size modes at 0 2 mm produced by sonification and tumbling of live and dead coral in sealed and screen window barrels support the sorby principle of skeletal breakdown

kinematics of the dadeldhura klippe shear zones w nepal implications for the foreland evolution of the himalayan metamorphic core mapping combined with structural analyses in the foreland edge of the metamorphic core of the himalayas in sw nepal highlights the existence of two north dipping shear zones with opposite sense of shear here the metamorphic core is mainly affected by non coaxial top to the south sense of shear at temperatures between 450 c and 550 c that switch to a top to the north sense of shear at the top of the metamorphic core we regionally correlate this upper shear zone with the south tibetan detachment system ar dating on white mica indicates that both shear zones operated between 23 ma and 17 ma restoration of the folded south tibetan detachment in far western nepal yields a minimum dip slip distance of 190 km compatible with predictions made by models of extrusion of a weak mid crustal channel our results support an orogenic model in which channel flow in the hinterland coexisted with thrust wedge mechanics in the foreland

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

physical oceanographic influences on sedimentology of reef sand aprons holocene of aranuka atoll kiribati equatorial pacific abstract depositional facies are the net product of a complex set of processes that impact sediment supply and transport in geomorphic systems although the general facies motifs of many isolated platforms throughout the geologic record are well documented the details of geomorphological and sedimentological patterns and the physical oceanographical processes that can impact sedimentological differentiation are less well constrained on these platforms accumulations of reef associated debris in platform top reef sand aprons can form expansive geomorphic elements hosting prolific hydrocarbon reserves in geologic analogs to better understand the nature and scale of reef sand apron accumulations this project integrates remote sensing field petrographical and granulometrical characterization of surficial holocene sediments with physical oceanographical observations and modeling of aranuka atoll republic of kiribati in the western equatorial pacific results illustrate trends in hydrodynamics geomorphology and sedimentology from the platform margin to the platform interior current meter data and modeling illustrate how the tides 2 5 m spring tide amplitude modulate wave energy open ocean annual average swell height of 2 m distal swell can be larger to produce dominant on platform flow speeds up to 90 cm s on the northern reef sand apron the strongest currents there appear to be impacted by southward propagating waves related to fronts that pass thousands of kilometers north of the atoll not local wind generated waves these hydrodynamical influences are interpreted to have led to the development of the expansive northern reef sand apron 2000 m wide the southeastern apron with currents that reverse with the tides includes a distinct narrower sand apron 1500 m wide concomitantly the hydrodynamical patterns and platformward decrease in energy across the reef sand apron coupled with changes in biota are interpreted to control variability in sedimentary structures bottom types and sediment attributes sediment near the margin on the reef sand apron contains coral and red algal rich coarse sand and gravel passing to foraminifera rich medium to coarse sand toward the lagoon the lagoon includes even finer sediment chiefly fine and very fine sand and patch reefs collectively the results of this study illustrate that selective winnowing differentiation of sediment size type and sorting and nature and size of geomorphic elements ultimately are linked to the hydrodynamical patterns across the platform the sedimentological depositional porosity and permeability and geomorphic facies bodies variability and the processes active on this reef sand apron provide a general conceptual model that may be applicable to predict trends in ancient reservoir analogs

constraints of hydrothermal and magmatic zircon on the origin of the yaogangxian tungsten deposit southern china abstract the yaogangxian tungsten deposit located in the central nanling range is a well known vein type tungsten deposit and has been mined for centuries this study focuses on the morphology geochronology and geochemistry of zircon crystals from wolframite bearing quartz veins and coexisting alkali feldspar granite to better understand the source of ore forming materials and the exact timing of tungsten mineralization all zircon grains separated from the muscovite alkali feldspar granite and the wolframite bearing quartz veins show core to rim structure the overgrowth rims of the zircon grains from the muscovite alkali feldspar granite and the wolframite bearing quartz veins have crystallization ages of 133 4 1 3 ma and 133 7 1 3 ma whereas the relict cores have ages of 155 3 1 6 ma and 154 8 1 6 ma respectively the ages of the cores are identical to the crystallization age of the hosting yaogangxian biotite monzogranite thus these cores were derived from the biotite monzogranite whereas the overgrowth rims should have crystallized during the intrusion of muscovite alkali feldspar granite and wolframite bearing quartz veins the geochemical consanguinity and similar ages of the muscovite alkali feldspar granite and the ore veins suggest that they were both formed from the highly fractionated granitic magma in an extensional setting this highly fractionated granitic melt might be extracted from the biotite monzogranitic mush in a long surviving deep seated magma chamber

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

granite related tin metallogenic events and key controlling factors in peninsular malaysia southeast asia new insights from cassiterite u pb dating and zircon geochemistry

leucogranite geochronological constraints on the termination of the south tibetan detachment in eastern himalaya abstract the south tibetan detachment system stds developed between the very low grade tethyan himalayan sequence ths and the high grade metamorphic greater himalayan sequence ghs over an along strike distance exceeding 2000 km within the himalayan orogen motion along the stds has been associated with the exhumation of the ghs and the uplift of the himalayan mountains geological field mapping and u th pb geochronological analyses were performed to trace and date the stds in the yadong region of southern tibet where it is a top to the north shear zone juxtaposing the yadong klippe of the ths with the high grade ghs this shear zone is intruded by multiple generations of leucogranites emplaced mainly at ca 23 ma ca 20 18 ma and ca 17 16 ma the undeformed textures of the leucogranites and their cross cutting relationships with the shear zone indicate that ductile motion along the stds terminated by ca 20 ma this is largely consistent with the deformation history of the stds in central and western himalaya the termination of shearing along the stds during the early miocene occurred well before the rapid cooling of the ghs during the middle miocene suggesting that exhumation and decompression of the ghs was still ongoing after the cessation of motion along the stds

sediment characteristics in reef areas influenced by eutrophication related alterations of benthic communities and bioerosion processes abstract this study investigated sediment deposits and suspended particulate matter in three reef areas of reunion island characterized by varying benthic communities and bioerosion processes as a result of different eutrophication levels the sediments were sampled using two different methods hand collecting directly on the reef bottom and sampling by traps this approach allowed a comparison between the composition of reefal bottom sediments and suspended particles in locations where algal communities prevailed over corals as a result of nutrification a shift from coral to coralline algae dominated sediments could be observed in addition a decrease in sediment production and a prevalence of very fine sand to mud sized grains over medium to fine sands existed in the nutrient enriched areas this grain size difference probably is caused by a decrease in grazing activity in the enriched areas high proportions of coralline algal debris and sponge spicules were specifically found in the sediments within areas receiving high nutrient input these two diagnostic components were abundant in both the suspended particulate matter and in the fine fractions