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31.
西藏雅鲁藏布蛇绿岩形成构造环境的地球化学鉴别 总被引：9，自引：7，他引：2
本文对西藏雅鲁藏布蛇绿岩带中部日喀则地区夏鲁蛇绿岩中的基性岩石进行了元素地球化学研究。岩石为低钾亚碱性玄武质岩石,具有低TiO2(0.64%～1.5%)、低K2O(<0.69%)、富Na2O(2.5%～6.0%)、烧失量普遍较高(2.0%～7.5%)的特征,表明样品普遍遭受蚀变。岩石具有与N-MORB类似的稀土元素和总体一致的微量元素特征,但是岩石明显富集大离子亲石元素和亏损高场强元素,显示了洋脊玄武岩向着岛弧岩浆作用的过渡趋势。日喀则蛇绿岩不是典型的洋中脊成因,应为SSZ型蛇绿岩,可能形成于与洋内俯冲有关的SSZ型的弧后或者弧前盆地中。对东西延伸超过1500km的雅鲁藏布蛇绿岩246套基性岩石形成的构造环境进行的地球化学判别,表明至少存在大陆岛弧型、地幔柱-洋内热点型、洋中脊-大洋岛弧型和典型大洋岛弧型等四种类型洋壳,揭示了特提斯洋存在多种构造环境的特征,有利于恢复和还原一个长期演化的、丰富的特提斯洋。 相似文献
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Using simulation results from three different regional ocean models (HOPS, ROMS and FVCOM) we show that only a few spatio-temporal POD (proper orthogonal decomposition) modes are sufficient to describe the most energetic ocean dynamics. In particular, we demonstrate that the simulated ocean dynamics in New Jersey coast, Massachusetts Bay and Gulf of Maine is energetically equivalent to the wake dynamics behind a cylinder at low Reynolds number. Moreover, the extrema of the POD spatial modes are very good locations for sensor placement and accurate field reconstruction. We employ a modified POD theory to incorporate a limited number of measurements in reconstructing the velocity and temperature fields, and we study systematically the corresponding reconstruction errors as a function of the sensor location, number of sensors, and number of POD modes. This new approach is quite accurate in short-term simulation, and hence it has the potential of accelerating the use of real-time adaptive sampling in data assimilation for ocean forecasting. 相似文献
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正The second IGCP-649 Workshop,held in Agros-Cyprus during 14-20 May 2016,brought together nearly fifty international scientists from around the world,and included a 5-day field excursion on the classic Troodos ophiolite.Organized by the IGCP-649 Project Leadership and the Geological Survey Department of Cyprus,the 相似文献
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Neotethyan suprasubduction zone ophiolites represent anomalous oceanic crust developed in older host basins during trench rollback cycles and later entrapped in orogenic belts as a result first of trench-passive margin and then continent–continent collisions. The Middle Jurassic Mirdita zone ophiolites in northern Albania constitute a critical transition between the dominantly mid-ocean ridge basalt (MORB)-related Early Jurassic Alpine–Apennine ophiolites in the west and supra-subduction zone (SSZ)-generated Cretaceous Eastern Mediterranean ophiolites in the east. The previously recognized Western- and Eastern-type ophiolites in the Mirdita zone display significant differences in their internal structure and pseudostratigraphy, but their geochemical affinities are more gradational in contrast to the earlier claims that these ophiolites may have formed in different tectonic settings at different times. Crosscutting relations of dike intrusions in the Eastern-type ophiolites indicate changes in the chemistry of magmatic plumbing systems from basaltic to andesitic, dacitic, rhyodacitic, and boninitic compositions through time and from west to east. The chemostratigraphy of the extrusive sequence in the Western-type ophiolites shows that the MORB-like tholeiitic rocks display a significant decrease in their TiO2 contents and Zr concentrations stratigraphically upward, although their εNd(T) values (+ 7.3 to + 6.9) show minor variation. The basaltic andesites in the upper 100 m of the Western extrusive sequence have island arc tholeiite (IAT)-like chemical characteristics (low-Ti, lower HFSE and HREE distribution, significant LREE depletion and higher Co, Ni, and Cr contents) that signify increased subduction influence in magma/melt evolution. The Eastern-type extrusive rocks range in composition from basaltic andesite to andesite, dacite and rhyodacite stratigraphically upward mimicking the temporal changes in the sheeted dikes, and they display constant Zr ( 50 ppm) but significantly varying Cr contents. The TiO2 contents of their pyroxenes are < 0.3 wt.%, and their εNd(T) values decrease from + 6.5 in the lower parts to + 3.1 in the uppermost section of the sequence. Farther east in the extrusive sequence the youngest boninitic lavas and dikes have εNd(T) values between − 1.4 and − 4.0. These chemical variations through time point to a mantle source increasingly contaminated by subduction-derived aqueous fluids and sediments, which were incorporated into the melt column beneath an extending protoarc–forearc region. Slab retreat and sinking played a major role in establishing asthenospheric upwelling and corner flow beneath the forearc mantle that in turn facilitated shallow partial melting of highly depleted harzburgitic peridotites, producing boninitic magmas. This chemical progression in the Mirdita zone ophiolite volcanism is similar to the temporal variations in magma chemistry documented from very young intraoceanic arcs built on recently generated backarc crust (i.e., South Sandwich arc). The Western and Eastern-type ophiolites in the Mirdita zone are therefore all subduction-related with the subduction zone influence in the lavas increasing stratigraphically upward as well as eastwards, suggesting a west-dipping slab geometry. The Mirdita zone and the Western Hellenic ophiolites in the Balkans were produced within a marginal basin that had evolved between the Apulian and Pelagonian microcontinents, and were subsequently emplaced onto their passive margins diachronously through different collisional processes. 相似文献
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Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the MORB to SSZ evolution of a marginal basin oceanic crust 总被引：7，自引：0，他引：7
The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian and Pelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changes in thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone (SSZ) environment. The 3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro, and gabbro. These peridotites and gabbroic rocks are overlain directly by a 600-m-thick extrusive sequence containing basaltic pillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The 12-km-thick Eastern Mirdita Ophiolite (EMO) includes tectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivine clinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. The plutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites and feeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartz diorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The 1.1-km-thick extrusive sequence comprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flows in the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic and basaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection (TiO2 = 3.5–0.5%, Zr = 300–50 ppm), while Nd(T) (+ 8 to + 6.5) varies little. These magmas were derived from partial melting of fertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREE abundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in the evolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO2 ( 0.5%) and Zr ( 50 ppm) contents but Nd(T) values (+ 7 to + 6.5) are similar to those of the WMO lavas. These rocks show variable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacites and boninites within the upper 400 meters of EMO lavas show low TiO2 ( 0.8–0.3%) and Nd(T) (+ 6.5 to + 3.0). The mantle source of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations in Ba, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative Nd (T) values (− 1.4 and − 4.0, respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. The MORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the Nd(T) values from + 8.0 to − 4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slab rollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in the evolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin, which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision. 相似文献
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Abstract We review the carbon‐isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow‐ and intermediate‐spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The δ13C values of the bioaltered glassy samples from the CAO show a large range, between ?17 and +3‰ (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ?17‰ and ?7‰. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low δ13C values (less than ?7‰) are attributed to carbonate precipitated from microbially produced CO2 during oxidation of organic matter. Positive δ13C values >0‰ likely result from lithotrophic utilization of CO2 by methanogenic Archaea that produce CH4 from H2 and CO2. High production of H2 at the slow‐spreading CAO crust may be a consequence of fault‐bounded, high‐level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer‐cake pseudostratigraphy with much less faulting and supposedly less H2 production. A comparison of the δ13C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow‐spreading CAO crust, with a similar range in δ13C values of biogenic carbonates. The Late Ordvician Solund–Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate‐spreading mid‐ocean ridge and displays δ13C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate‐dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the δ13C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas. 相似文献
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This study aims to remove of Cu2+, Cd2+, and Pb2+ ions from solution and to investigate the adsorption isotherms, adsorption kinetics, and ion‐exchange affinities of these metals using waste activated sludge (AS) biomass. The adsorptions of the metals on biomass were optimal at an acidic pH value of 6.0 based on its monolayer capacities. Maximum monolayer capacities of AS biomass (qmax) were calculated as 0.478, 0.358, and 0.280 mmol g?1 for Cu2+, Cd2+, and Pb2+, respectively, and the adsorption equilibrium time was found as 60 min for each metal. The adsorbed amount of metal rose with increasing of initial metal ion concentration. The equilibrium adsorption capacity of AS for initial 0.25 mmol L?1 metal concentration was determined as 0.200, 0.167, and 0.155 mmol g?1 for Cu2+, Cd2+, and Pb2+ ions, respectively. These relevant values were determined as 0.420, 0.305, and 0.282 mmol g?1 for Cu2+, Cd2+, and Pb2+ ions, respectively, when initial metal concentration was 0.50 mmol L?1. In the multi‐metal sorption system, the adsorption capacity of AS biomass was observed in the order of Cu2+ > Cd2+ > Pb2+. In the presence of 100 mmol L?1 H+ ion, the order of ion‐exchange affinity with H+ was found as Cu2+ > Cd2+ > Pb2+. The adsorption kinetics were also found to be well described by the pseudo‐second‐order and intraparticle diffusion models. Two different rate constants were obtained as ki1 and ki2 and ki1 (first stage) was found to be higher than ki2 (second stage). 相似文献
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NIU Xiaolu LIU Fei YANG Jingsui Yildirim DILEK XU Zhiqin FENG Guangying XIONG Fahui Kyaing SEIN 《《地质学报》英文版》2017,91(Z1):24-25
Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar,and represent the remnants of the Neotethyan oceanic lithosphere(Sengupta et al.,1990;Mitchell,1993).These ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone(YZSZ)in southern Tibet farther northwest(Mitchell,1993;Fareeduddin and Dilek,2015),as indicated by their coeval crystallization ages and geochemical compositions(Yang et al.,2012;Liu et al.,2016).The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges(Fig.1).composition of these ophiolites from the central Tibetan Plateau(CTP)is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs,which is inconsistent with most ophiolites worldwide(Robinson and Zhou,2008;Zhang et al.,2008).But the generation and tectonic nature of these ophiolites are still controversial.*The Kalaymyo peridotites consist mainly of harzburgites,which show typical porphyroclastic or coarse-grained equigranular textures.They are composed ofolivine(Fo=89.8–90.5),orthopyroxene(En86-91Wo1-4Fs8-10;Mg#=89.6–91.9),clinopyroxene(En46-49Wo47-50Fs3-5;Mg#=90.9–93.6)and spinel(Mg#=67.1–78.9;Cr#=13.5–31.5),and have relatively homogeneous whole-rock compositions with Mg#s of90.1–90.8 and Si O2(41.5–43.65 wt.%),Al2O3(1.66–2.66wt.%)and Ca O(1.45–2.67 wt.%)contents.TheydisplayLightRareEarthElement(LREE)-depleted chondrite-normalized REE patterns with(La/Yb)CN=0.04–0.21 and(Gd/Yb)CN=0.40–0.84,and show a slight enrichment from Pr to La with(La/Pr)CN in the range of 0.98–2.36.The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic(Pd/Ir)CN ratios(1.15–2.36).Their calculated oxygen fugacities range between QFM–0.57 and QFM+0.90.These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees(5–15%)of partial melting at a mid-ocean-ridge(MOR)environment.The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts,percolating through these already depleted,residual peridotites.The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges hence represent mid-ocean ridge(MOR)–type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction–accretion system along the eastern margin of India. 相似文献
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