High temperature gas–solid reactions in calc–silicate Cu–Au skarn formation; Ertsberg,Papua Province,Indonesia     

Richard?W.?HenleyEmail authorView author&#;s OrcID profile  Frank?J.?Brink  Penelope?L.?King  Clyde?Leys  Jibamitra?Ganguly  Terrance?Mernagh  Jill?Middleton  Christian?J.?Renggli  Melanie?Sieber  Ulrike?Troitzsch  Michael?Turner 《Contributions to Mineralogy and Petrology》2017,172(11-12):106

The 2.7–3 Ma Ertsberg East Skarn System (Indonesia), adjacent to the giant Grasberg Porphyry Copper deposit, is part of the world’s largest system of Cu–Au skarn deposits. Published fluid inclusion and stable isotope data show that it formed through the flux of magma-derived fluid through contact metamorphosed carbonate rock sequences at temperatures well above 600° C and pressures of less than 50 MPa. Under these conditions, the fluid has very low density and the properties of a gas. Combining a range of micro-analytical techniques, high-resolution QEMSCAN mineral mapping and computer-assisted X-ray micro-tomography, an array of coupled gas–solid reactions may be identified that controlled reactive mass transfer through the ~ 1 km³ hydrothermal skarn system. Vacancy-driven mineral chemisorption reactions are identified as a new type of reactive transport process for high-temperature skarn alteration. These gas–solid reactions are maintained by the interaction of unsatisfied bonds on mineral surfaces and dipolar gas-phase reactants such as SO₂ and HCl that are continuously supplied through open fractures and intergranular diffusion. Principal reactions are (a) incongruent dissolution of almandine-grossular to andradite and anorthite (an alteration mineral not previously recognized at Ertsberg), and (b) sulfation of anorthite to anhydrite. These sulfation reactions also generate reduced sulfur with consequent co-deposition of metal sulfides. Diopside undergoes similar reactions with deposition of Fe-enriched pyroxene in crypto-veins and vein selvedges. The loss of calcium from contact metamorphic garnet to form vein anhydrite necessarily results in Fe-enrichment of wallrock, and does not require Fe-addition from a vein fluid as is commonly assumed.  相似文献   

Black–White and Hispanic–White Segregation in U.S. Counties     

James P. Allen  Eugene Turner 《The Professional geographer》2013,65(4):503-520

Residential segregation in metropolitan areas has been the subject of much research, but this article analyzes patterns of white–black and white–Hispanic segregation in counties across the United States. Our purpose was to understand county variations in this one dimension of inequality. Conceiving of segregation as relative inequality of access to neighborhood resources, we measured segregation in 2000 by the index of dissimilarity (D) calculated by blocks, mapped the index values, and correlated them with census variables. Three filters enabled us to eliminate counties with characteristics that could have corrupted the analyses, leaving us with more than 1,000 counties in each analysis. Both minority groups were less segregated from whites in the West and South and in metropolitan counties. Lower segregation was strongly associated with higher minority socioeconomic status and higher percentages of minorities living in housing built in the 1990s, and Hispanic–white segregation was lower where more Hispanics were U.S.-born or English proficient. The racial threat hypothesis was supported only weakly and inconsistently. Mapping made it possible to identify regional and local patterns of high and low segregation as well as the lower segregation of suburban counties in some large metropolitan areas.  相似文献   

Rapid magmatic processes accompany arc–continent collision: the Western Bismarck arc, Papua New Guinea     

Heather Cunningham  Jim Gill  Simon Turner  John Caulfield  Louise Edwards  Simon Day 《Contributions to Mineralogy and Petrology》2012,164(5):789-804

New U–Th–Ra, major and trace element, and Sr–Nd–Pb isotope data are presented for young lavas from the New Britain and Western Bismarck arcs in Papua New Guinea. New Britain is an oceanic arc, whereas the latter is the site of an arc–continent collision. Building on a recent study of the Manus Basin, contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc–continent collision and possible slab detachment. All three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle. However, the Western Bismarck arc lavas diverge from the Pb isotope mixing array formed by the New Britain and the Manus Basin lavas toward elevated ²⁰⁸Pb/²⁰⁴Pb. We interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision. ²³⁸U and ²²⁶Ra excesses are preserved in all of the lavas and are greatest in the Western Bismarck arc. High-Mg andesites with high Sr/Y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge. Data for two historical rhyolites are also presented. Although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions, both formed from mafic parents within millennia.  相似文献   

Using idealized snow forcing to test teleconnections with the Indian summer monsoon in the Hadley Centre GCM   总被引：2，自引：1，他引：1  

A. G. Turner  J. M. Slingo 《Climate Dynamics》2011,36(9-10):1717-1735

Anomalous heavy snow during winter or spring has long been regarded as a possible precursor of deficient Indian monsoon rainfall during the subsequent summer. However previous work in this field is inconclusive, in terms of the mechanism that communicates snow anomalies to the monsoon summer, and even the region from which snow has the most impact. In this study we explore these issues in coupled and atmosphere-only versions of the Hadley Centre model. A 1050-year control integration of the HadCM3 coupled model, which well represents the seasonal cycle of snow cover over the Eurasian continent, is analysed and shows evidence for weakened monsoons being preceded by strong snow forcing (in the absence of ENSO) over either the Himalaya/Tibetan Plateau or north/west Eurasia regions. However, empirical orthogonal function (EOF) analysis of springtime interannual variability in snow depth shows the leading mode to have opposite signs between these two regions, suggesting that competing mechanisms may be possible. To determine the dominant region, ensemble integrations are carried out using HadAM3, the atmospheric component of HadCM3, and a variety of anomalous snow forcing initial conditions obtained from the control integration of the coupled model. Forcings are applied during spring in separate experiments over the Himalaya/Tibetan Plateau and north/west Eurasia regions, in conjunction with climatological SSTs in order to avoid the direct effects of ENSO. With the aid of idealized forcing conditions in sensitivity tests, we demonstrate that forcing from the Himalaya region is dominant in this model via a Blanford-type mechanism involving reduced surface sensible heat and longwave fluxes, reduced heating of the troposphere over the Tibetan Plateau and consequently a reduced meridional tropospheric temperature gradient which weakens the monsoon during early summer. Snow albedo is shown to be key to the mechanism, explaining around 50% of the perturbation in sensible heating over the Tibetan Plateau, and accounting for the majority of cooling through the troposphere.  相似文献   

The ECORS-Truc Vert’08 nearshore field experiment: presentation of a three-dimensional morphologic system in a macro-tidal environment during consecutive extreme storm conditions     

Nadia Senechal  Stéphane Abadie  Edith Gallagher  Jamie MacMahan  Gerd Masselink  Hervé Michallet  Ad Reniers  Gerben Ruessink  Paul Russell  Damien Sous  Ian Turner  Fabrice Ardhuin  Philippe Bonneton  Stéphane Bujan  Sylvain Capo  Raphael Certain  Rodrigo Pedreros  Thierry Garlan 《Ocean Dynamics》2011,61(12):2073-2098

A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results.  相似文献   

The Caspian Sea: a microcosm for environmental science and international cooperation     

de Mora SJ  Turner T 《Marine pollution bulletin》2004,48(1-2):26-29

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Comprehensive Utilization of Vanadium–Titanium Magnetite Deposits in China Has Come to a New Level     

HAO Ziguo  FEI Hongcai  LIU Lian  Susan TURNER 《《地质学报》英文版》2013,87(1):286-287

There are two production areas for vanadium-titanium magnetite deposits in China:the Panzhihua area in Sichuan Province and the Chengde area in Hebei Province. The Panzhihua vanadium titanomagnetite iron ore deposits are hosted by a mafic-ultramafic intrusive complex,and belong to late magmatic differentiation condensation of crystalline iron deposits.The rock mass is characterized by good differentiation,clear and differentiated facies zones and rhythm.The rock assemblage can be divided into the following rock facies combination:gabbro,gabbro-norite,gabbro troctolite,gabbro-plagioclase,gabbro-eclogite-olivine pyroxenite,and diabase types.The orebodies occur mostly as close-bedded,distributed in the dark facies zone in the bottom layers of the middle or lower part of the stratiform rock mass.The main ore minerals are granular ilmenite,magnetite,ilmenite spar,and magnesium aluminum spinel,with small amounts of pyrrhotite,pyrite and cobalt,nickel and copper sulfide.The ores have siderite and mosaic textures and occur as compact massive,banded and disseminated structures;they consist of TFeO 20％-45％,TiO2 3％-16％,V2O50.15％-0.5％,Cr2O30.1％-0.38％,associated with trace amounts of Cu,Co,Ni,Ga,Mn,P,Se,Te,Sc and Pt group elements.  相似文献   

Aftershock of the Wenchuan Earthquake in Sichuan Triggers Large Earthquake in Minxian County, Gansu     

Hao Ziguo  Fei Hongcai  Liu Lian  and Susan Turner 《《地质学报》英文版》2013,87(4):1182-1184

Because of the confining compression of the Pacific,Eurasian and Indian plates,the Chinese mainland is frequently stricken with earthquakes,especially in the Qinghai-Tibet Plateau and surrounding areas and along the NS-trending tectonic zone from Yinchuan to Lanzhou,Chengdu,and finally to the Kunming tectonic belt (Fig.1).Historical records show that there are 14 earthquakes of＞Ms 8 occurring in the two regions,eight of which occurred along the latter tectonic belt.The 2008 Wenchuan earthquake located on both the NS tectonic zone and the Longmenshan fault zone along the eastern margin of the Qinghai-Tibet Plateau.  相似文献   

Thermal history of the Rio Muni (West Africa)–NE Brazil margins during continental breakup     

Jonathan P. Turner  Paul F. Green  Simon P. Holford  Stephen R. Lawrence 《Earth and Planetary Science Letters》2008,270(3-4):354-367

We document the thermal record of breakup of the conjugate Rio Muni (West Africa) and NE Brazil margins using apatite fission track analysis, vitrinite reflectance data and stratigraphic observations from both margins. These results permit determination of the timing of four cooling episodes, and the temperature of samples at the onset of each episode. All samples are interpreted to have experienced higher temperatures in the geological past due to i) elevated basal heatflow (palaeogeothermal gradient in Rio Muni-1 well decaying from 58 °C/km during the Mid Cretaceous to 21.5 °C/km in the Late Cenozoic) and ii) progressive exhumation from formerly greater burial depth. A well constrained history of changing palaeogeothermal gradient allows for much more precise quantification of the thickness of eroded section (exhumation) than if a constant heatflow is assumed. Cooling episodes identified from the palaeotemperature data at 110–95 Ma (both margins) and 85–70 Ma (Rio Muni only) coincide with major unconformities signifying, respectively, the cessation of rifting (breakup) and compressional shortening that affected the African continent following the establishment of post-rift sedimentation (drift). The interval between these separate unconformities is occupied by allochthonous rafts of shallow-water carbonates recording gravitational collapse of a marginal platform. The rift shoulder uplift that triggered this collapse was enhanced by local transpression associated with the obliquely divergent Ascension Fracture Zone, and thermal doming due to the coeval St Helena and Ascension Plumes. The data also reveal a c.45–35 Ma cooling episode, attributed to deep sea erosion at the onset of Eo-Oligocene ice growth, and a c.15–10 Ma episode interpreted as the record of Miocene exhumation of the West African continental margin related to continent-wide plume development. Integration of thermal history methods with traditional seismic- and stratigraphy-based observations yields a dynamic picture of kilometre-scale fluctuations in base level through the breakup and early drift phases of development of these margins. Major unconformities at ocean margins are likely to represent composite surfaces recording not only eustasy, but also regional plate margin-generated deformation, local ‘intra-basinal’ reorganization, and the amplifying effect of negative feedbacks between these processes.  相似文献   

Source depletion and extent of melting in the Tongan sub-arc mantle   总被引：3，自引：0，他引：3  

J.T. Caulfield  S.P. Turner  A. Dosseto  N.J. Pearson  C. Beier 《Earth and Planetary Science Letters》2008,273(3-4):279-288

The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab.  相似文献