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利用中国数字台网（CDSN）记录的85个远震事件的宽频带P波波形数据和分离接收函数的最大或然性反褶方法,获得了CDSN台网10个台站不同方位的岩石层接收函数.利用这些台站不同方位的平均接收函数和非线性接收函数反演方法,获得了上述各台站下方100km深度范围内的岩石层S波速度结构.结果表明CDSN台网各台站下方的地壳厚度和岩石层速度结构存在明显的差别.其中,拉萨台下方的地壳厚度为66kin,壳幔界面较模糊,而余山台下方的地壳厚度为34km,壳慢界面两侧速度反差明显.刮用本文方法估计的地壳厚度与已有的结果基本一致,由于CDSN台网覆盖了中国大陆的各主要构造单元,本文的结果为研究中国大陆的岩石层S波速度结构及其横向变化提供了新的证据. 相似文献
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Metamorphic Petrology of Xenoliths from Kenya and Northern Tanzania and Implications for Geotherms and Lithospheric Structures 总被引：5，自引：4，他引：1
Pyroxenitic and peridotitic xenoliths from the Quaternary volcanicfield of Marsabit (northern Kenya) bear strong evidence of decompressionand cooling. Pyroxenites are mostly garnet (grt) websteritesand grt clinopyroxcnites with some olivine (ol) and amphibole(amph). Grt is mostly rimmed by kelyphitic reaction zones butotherwise appears to have been in stable association with thepyroxenes. Along contacts between grt and rare ol, medium-grainedsymplectites consisting of orthopyroxene (opx), clinopyroxene(cpx), and spinel (spl) occur. Garnets do show significant compositionalvariations from core to rim. Primary pyroxenes are strained,have exsolution lamellae, and are chemically zoned. Integratedcore compositions of pyroxenes and grt compositions yield temperaturesof 1065–950 C and pressures of 28–23 kb (stage1). Pyroxene rims in contact with grt or kelyphite show Ca concentrationssimilar to, but Al concentrations higher than pyroxene rimsremote from garnet. Grt-opx contacts yield pressures of 11.5–9.0kb, and temperatures of 860–770C are obtained from pyroxenerims (stage 2). Peridotites from Marsabit show various stages of transformationfrom the garnet peridotite to the spinel peridotite stabilityfield. On the basis of differences in textures and mineral compositionsthey can be grouped into four types. Type I has a granular textureand contains fine-grained opx-cpx-spl symplectites frequentlysurrounding kelyphite which, in turn, may enclose relict grt.Rare matrix spl has higher Cr/(Cr + Al) ratios (0.25–0.32)than symplectitic spl (0.09). As in grt pyroxenites, matrixpyroxenes are strained, show exsolution lamellae, and have rimcompositions which are dependent on their positions relativeto former garnet. Integrated core compositions of matrix pyroxenessuggest former equilibration temperatures between 1050 and 880Cand pressures between 25 and 19 kb (opx—grt barometryusing composition of relict grt; stage 1). Pyroxene rims yieldsignificantly lower temperatures of 920–785 C (stage2). These P—T estimates and the occurrence of one compositexenolith consisting of type I peridotite and grt pyroxenitepoint to a common P—Tevolution of both grt pyroxenitesand type I peridotites. Granular type II peridotites are characterizedby medium-grained clusters of opx + cpx + spl amph and containmatrix spl, too. Pyroxenes are never strained and are free ofexsolution lamellae. All minerals are homogeneous and thereare no compositional differences between pyroxenes and spinelsof the matrix and those of the spl—opx—cpx clusters.Cr/(Cr+Al) ratios of spl are between 0–07 and 0.11. Two-pyroxenetemperatures are relatively uniform (970–925 C at anassumed pressure of 12 kb; stage 2). Type III peridotites arecoarse-grained granular spl peridotites without any indicationof the former presence of grt. Cr/(Cr + Al) ratios of spl aresimilar to those of peridotite type II. Pyroxenes show minorchemical zoning with Ca increasing in opx but decreasing incpx from core to rim indicating temperatures of 960–900C for pyroxene cores and of up to 1000C 相似文献
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MARSCHALL HORST R.; LUDWIG THOMAS; ALTHERR RAINER; KALT ANGELIKA; TONARINI SONIA 《Journal of Petrology》2006,47(10):1915-1942
High-pressure (HP) metamorphic blocks enclosed in a mafic toultramafic matrix from a mélange on the island of Syrosare rimmed by tourmaline-bearing reaction zones (blackwalls).The B isotopic composition of dravitic tourmaline within theseblackwalls was investigated in situ by secondary ion mass spectrometry.Boron in these tourmalines is unusually heavy, with 11B valuesexceeding +18 in all investigated samples and reaching an extremevalue of +28·4 in one sample. Blackwalls formed duringexhumation of the HP mélange at a depth of 20–25km at temperatures of 400–430°C, by influx of externalhydrous fluids. The compositions of the fluids are estimatedto be in the range of 100–300 µg/g B with 11B valuesof +18 to +28. The high 11B values cannot be explained by tourmalineformation from unmodified slab-derived fluids. However, suchfluids could interact with the material in the exhumation channelon their way from the dehydrating slab to the site of tourmalineformation in the blackwalls. This could produce exceptionallyhigh 11B values in the fluids, a case that is modelled in thisstudy. The model demonstrates that subduction fluids may beeffectively modified in both trace element and isotopic compositionduring their migration through the material overlying the subductingslab. Blackwall tourmaline from Syros has a large grain size(several centimetres), high abundance, and an exceptionallyhigh 11B value. The formation of tourmaline at the contact betweenmafic or felsic HP blocks and their ultramafic matrix involvedfluids released during dehydration reactions in the subductingslab. It forms a heavy-boron reservoir in hybrid rocks overlyingthe subducting slab, and may, thus, have a significant impacton the geochemical cycle of B and its isotopes in subductionzones. KEY WORDS: boron isotopes; tourmaline; subduction zone; fluid, high pressure 相似文献
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SHAHRAM ASHRAFI ASHIM DAS GUPTA MUKAND SINGH BABEL NORIHIRO IZUMI RAINER LOOF 《水文科学杂志》2013,58(2):253-268
Abstract Advances in the traditional method of subsurface porous clay pipe irrigation rely on knowledge of the distribution of water in the soil. Knowing the relationships among the hydraulic and physical parameters in the system is important for both the design and management of the system. To simulate the infiltration from the porous clay pipe and predict the wetted zone geometry in the soil, a computer model is developed herein. Laboratory experiments were conducted on soil samples representing two different soil textures in a specially designed bin to understand the flow phenomenon and to validate the developed model. In a given soil texture, the installation depth of the pipe and the volume of water applied in the soil are the major factors affecting the wetted zone. The relationships among various parameters, namely lateral spacing, installation depth, irrigation run time, hydraulic conductivity of the body of the pipe, and hydraulic head in the system, were established using the developed model. 相似文献
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New Constraints on the P-T Evolution of the Alpe Arami Garnet Peridotite Body (Central Alps, Switzerland) 总被引：1，自引：0，他引：1
The metamorphic evolution of the garnet peridotite body of AlpeArami, Central Alps, is a matter of current controversy. Inthis paper, the inter- and intragrain distribution of majorand trace elements obtained by electron and ion probe microanalysesis used to better constrain the P–T evolution of thisperidotite. Using the compositions of homogeneous porphyroclastcores, peak metamorphic conditions of 1180 ± 40°Cand 5·9 ± 0·3 GPa are estimated, basedon consistent results from the application of several independentthermometers (Fe–Mg exchange between garnet, pyroxenesand olivine, Ni exchange between garnet and olivine, Co andNi exchange between orthopyroxene and clinopyroxene), the Al-in-orthopyroxenebarometer and the Ca–Cr systematics of garnet. Orthopyroxeneand clinopyroxene porphyroclasts are, however, not in equilibriumwith respect to some elements with low diffusivities, such asCa, Ti, Cr, V and Sc. This disequilibrium appears to be themain cause for the lower P–T values suggested by someof the previous workers. On the other hand, there is no evidencefor an ultradeep (>200 km) origin of the Alpe Arami bodyas postulated recently. Chemical zonation profiles across mineralgrains suggest that during retrograde evolution a near-isothermaldecompression was followed by accelerated cooling. KEY WORDS: Alpe Arami; Central Alps; garnet peridotite; ultrahigh-pressure metamorphism; geothermobarometry; secondary ion mass spectrometry (SIMS) 相似文献
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The aftermath of the Carnian carbonate platform demise: a basinal perspective (Dolomites, Southern Alps) 总被引：1，自引：0，他引：1
In the Dolomites of northernmost Italy the carbonate‐platform growth came to a standstill late in the Early Carnian (Late Triassic). The response to this shutdown of shallow‐water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments, giving rise to today's scenic landscape of the Dolomites. Mapping in the central part of the Dolomites and newly available core material has recently revealed a well‐preserved succession of basinal rocks within the Heiligkreuz Hospiz Basin (ital. Ospizio di Santa Croce Basin). In this paper, the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin. The uppermost St. Cassian Formation, the time‐equivalent basinal rocks to the prograding carbonate platforms, is overlain by the Heiligkreuz Formation, whose basal succession was deposited in a restricted and oxygen‐depleted environment immediately post‐dating the platform demise. The succession consists mainly of mudrocks, marlstones, and peloidal packstones, with abundant low‐diversity ostracod and pelecypod fauna and early diagenetic dolomite. C and O isotope values of the basal Heiligkreuz Formation, post‐dating platform demise, average + 2·4 and ? 2·4‰, respectively, and largely overlap the isotopic composition of St. Cassian carbonates. A shift toward slightly lower δ13C values in the Heiligkreuz Formation may reflect incorporation of isotopically depleted C released during bacterial sulphate reduction in the Heiligkreuz sediments. Sedimentological, palaeobiological and geochemical indices suggest that near‐normal marine conditions persisted long after the shutdown of shallow water carbonate‐platform growth, although there are clear indications of severely reduced oxygen levels in the restricted Heiligkreuz Hospiz interplatform basin. The Early Carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow‐water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters. It is inferred that anoxia extended at least temporarily to the top of the carbonate slope, as indicated by the onlap of normal‐marine mounds by dark marlstones of the basal Heiligkreuz Formation. 相似文献
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GURENKO ANDREY A.; TRUMBULL ROBERT B.; THOMAS RAINER; LINDSAY JAN M. 《Journal of Petrology》2005,46(12):2495-2526
Glass inclusions in plagioclase and orthopyroxene from daciticpumice of the Cabrits Dome, Plat Pays Volcanic Complex in southernDominica reveal a complexity of element behavior and Li–Bisotope variations in a single volcanic center that would gounnoticed in a whole-rock study. Inclusions and matrix glassesare high-silica rhyolite with compositions consistent with about50% fractional crystallization of the observed phenocrysts.Estimated crystallization conditions are 760–880°C,200 MPa and oxygen fugacity of FMQ + 1 to +2 log units (whereFMQ is the fayalite–magnetite–quartz buffer). Manyinclusion glasses are volatile-rich (up to 6 wt % H2O and 2900ppm Cl), but contents range down to 1 wt % H2O and 2000 ppmCl as a result of shallow-level degassing. Sulfur contents arelow throughout, with <350 ppm S. The trace element compositionof inclusion glasses shows enrichment in light rare earth elements(LREE; (La/Sm)n = 2·5–6·6) and elevatedBa, Th and K contents compared with whole rocks and similaror lower Nb and heavy REE (HREE; (Gd/Yb)n = 0·5–1·0).Lithium and boron concentrations and isotope ratios in meltinclusions are highly variable (20–60 ppm Li with 7Li= +4 to +15 ± 2; 60–100 ppm B with 11B = +6 to+13 ± 2) and imply trapping of isotopically heterogeneous,hybrid melts. Multiple sources and processes are required toexplain these features. The mid-ocean ridge basalt (MORB)-likeHREE, Nb and Y signature reflects the parental magma(s) derivedfrom the mantle wedge. Positive Ba/Nb, B/Nb and Th/Nb correlationsin inclusion glasses indicate coupled enrichment in stronglyfluid-mobile (Ba, B) and less-mobile (Th, Nb) trace elements,which can be explained by fractional crystallization of plagioclase,orthopyroxene and Fe–Ti oxides. The 7Li and 11B valuesare at the high end of known ranges for other island arc magmas.We attribute the high values to a 11B and 7Li-enriched slabcomponent derived from sea-floor-altered oceanic crust and possiblyfurther enriched in heavy isotopes by dehydration fractionation.The heterogeneity of isotope ratios in the evolved, trappedmelts is attributed to shallow-level assimilation of older volcanicrocks of the Plat Pays Volcanic Complex. KEY WORDS: subduction; volcanic arcs; igneous processes; melt inclusions; SIMS; trace elements; lithium and boron isotopes; diffusion 相似文献
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KERSTIN KOLDITZ OLAF DELLWIG JAN BARKOWSKI RAINER BAHLO THOMAS LEIPE HOLGER FREUND HANS‐JÜRGEN BRUMSACK 《Sedimentology》2012,59(2):337-355
The barrier islands of the southern North Sea were formed during the Holocene sea‐level rise. These islands form part of a highly dynamic environment whose evolution continues today. Subjected to sea‐level changes, tides and storm events, the sedimentary record reflects processes occurring under varying energy conditions. This article presents geochemical, mineralogical and diatom investigations carried out in the salt marsh of the East Frisian barrier island of Langeoog, which is re‐exposed to a rising sea‐level due to de‐embankment. The major aim of this study is to improve the knowledge of the sedimentological and geochemical development of these deposits under the influence of sea‐level rise, with a special focus on the geochemistry and distribution of heavy mineral‐associated elements. Correlation diagrams between FeO, TiO2 and MnO, as well as ternary plots (Al2O3–SiO2–Zr or TiO2), clearly indicate the variable appearance of heavy minerals in different lithological facies, comprising marsh soil, mixed and sand flat, and relocated beach sands. A dominating abundance of ilmenite followed by zircon, garnets and some other heavy minerals is evidenced by Scanning Electron Microscope‐Energy Dispersive X‐ray measurements. The data presented here suggests that these geochemical proxies are useful tools for characterizing depositional energy conditions. Increasing depositional energy is evident for the lithological units in the following order: marsh soil, mixed flat, sand flat and relocated beach sand. The energetic conditions during sediment deposition, as well as the sedimentary history, are confirmed by diatom analyses as an additional independent indicator. Depending on source rock composition, the geochemical parameters used in this study may also help to investigate depositional energy regimes of other siliciclastic sedimentary systems. 相似文献
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利用Ｓｈａｍｗａｙ和Ｄｅｒ的多道最大或然性反褶积原理，讨论了从单台三分量远震Ｐ波波形中分离接收函数径向与垂向分量复谱比的方法．根据Ｔａｒａｎｔｏｌａ的波形反演理论发展了接收函数复谱比的非线性反演方法．本文的反演方法除了拟合接收函数的复谱比之外，还需拟合时间域中接收函数垂向与径向分量的初至振幅比．合成波形数据反演的结果表明本文方法的反演结果不依赖初始模型．利用该方法和ＣＤＳＮ台网兰州台记录的宽频带远震Ｐ波波形数据，研究了该台站的接收函数及其随方位角的变化．接收函数复谱比非线性反演给出了该台站下方１４０ｋｍ深度岩石层的Ｓ波速度结构，得到兰州台下方地壳厚度为５４ｋｓ，岩石层厚度为９４ｋｍ． 相似文献