Geochemical Evolution and Environmental Changes of Qinghai—Xizang Plateau Since Late Cenozoic     

余素华  文启忠等 《中国地球化学学报》1998,17(3):258-264

Long-and short-term climatic curves were preliminarily established based on the comprehensive analysis of geochemical information since the Late Cenozoic in the Qinghai Xizang(Qinghai-Tibet)Plateau.The curves show that the climate in the plateau was alternatively dry-warm and cold-wet during the period of 30-3.4 Ma when the plateau was not uplifted to an enough altitude and the monsoon was not completely formed either,In the period of 3.4-0.73 Ma.the climate fluctuated between dry-cold and wet-warm when the plateau was rapidly uplifted and the Asian monsoon was consequently formed.Since 0.73 Ma.the climate became even drier when the plateau continuously rose.In the Holocene period.the climate alternatively changed with a complex model of being cool-dry,warm-wet and cold-wet.  相似文献   

Constraints on the age of basement and crustal growth in Tianshan Orogen by Nd isotopic composition   总被引：3，自引：0，他引：3  

Aiqin Hu  Guoxin Zhang  Qianfeng Zhang  Yibing Chen 《中国科学D辑(英文版)》1998,41(6):648-657

Based on study of Nd isotopic composition for 101 rocks of various types from Tianshan Orogen, the age and character of basement and continental crustal evolution of the Tianshan Orogen were proposed. It is deduced that the continental crustal basement of the Tianshan Orogen was formed 1. 8 Ga ago. The protolith of its metamorphic rocks was derived from long-term depleted mantle source in the ancient are tectonic setting probably. The Tianshan Orogen is obviously different from the North Tarim Block in age of basement and post-evolution history. It was also shown that Paleozoic continental crustal growth happened extensively in the Tianshan Orogen, which is distinguished from Yangtse Block and Cathaysia Block in eastern China. Project supported by the National Natural Science Foundation of China (Grant No. 49633250). It belongs to the National “305” Project in Xinjiang, which is one of the National Key Projects in the Ninth Five-Year Plan (96-915-07-05A).  相似文献   

Ca, Al-rich inclusions in Yamato 791717 (CO3) carbonaceous chondrite: Formation and alteration     

Yangting Lin  Daode Wang  Makoto Kimura 《中国科学D辑(英文版)》1998,41(5):513-521

In three polished thin sections of Yamato 791717 (CO3). fifty-five Ca, Al-rich inclusions were found, which include two hibonite-bearing, eight melilite-rich and forty-five spinel-pyroxene inclusions. Based on the petrography and mineral chemistry of the inclusions, it is proposed that the melilite-rich inclusions and spinel-pyroxene inclusions condensed in the solar nebula, and the hibonite-bearing inclusions crystallized from melts. The heavy alteration of the inclusions in Yamato 791717, which probably took place under a very oxidizing condition in the solar nebular, is also confirmed. Project supported by the National Natural Science Foundation of China (Grant No. 49673200). and by the Japanese Society for Promotion of Sciences (JSPS).  相似文献   

遥感技术在南盘江地区油气烃类检测中的应用     

马跃良  何在成 《海相油气地质》1998,3(2):47-54

应用陆地卫星 TM 资料对南盘江地区进行了烃类微渗漏蚀变信息检测研究。岩石土壤地球化学特征分析表明,该区不同程度地存在着“褪红”、“粘土矿化”、“碳酸盐矿化”等烃类蚀变异常现象。选择 FeO/Fe_2O_3作为褪红的成分因子;(K_2O+Na_2O+Al_2O_3)、(K_2O+Na_2O)/Al_2O_3、(K_2O+Na_2O+Al_2O_3)/S∶O_2和 K_2O/Na_2O 等作为粘土矿化的成分因子;CaO+MgO 和 CaO/MgO 作为碳酸盐矿化的成分因子。利用 TM1/TM3、TM1/TM4识别褪红蚀变信息,TM5/TM7、TM5/TM4用干识别粘土矿化和碳酸盐矿化蚀变信息。建立了地球化学—光谱—遥感图像三位一体的遥感找油气模式,根据油气遥感色调异常对南盘江地区进行了评价和分类。  相似文献   

华南晋宁期造山运动──地质年代学和地球化学制约   总被引：9，自引：0，他引：9       下载免费PDF全文

李献华 《地球物理学报》1998,41(Z1):184-194

综合了前人和作者最新的地质年代学和地球化学研究成果,对华南晚元古代晋宁期造山运动的演化提供了化学地球动力学制约晚元古代早期（0．97－1．0Ga）的皖南、赣东北和桂北蛇绿岩在元素地球化学上具有相似的岛弧特征,但它们的Nd同位素组成明显不同新获得的高精度结石U－Ph年龄资料表明,桂北地区的本洞、三防和元宝山等三个主要花岗岩岩体均形成于820-825Ma,排除了本区有中元古代晚期花岗岩的存在．扬子南缘中元古代到三叠纪各个时代地层中的泥质沉积岩的TDM在晚元古代早期从约1．8Ga急剧降低至约1．3Ga,反映了这个时期的沉积物源区有大量新生馒源物质的加入．根据研究资料,提出了华南和扬子块体晋宁期陆-弧-陆碰撞模式  相似文献   

Detrital zircon geochronology and provenance of sediments within the Mesozoic basins:New insights into tectonic evolution of the Qinling Orogen     

《地学前缘(英文版)》2021,12(3)

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Extinction of deep-sea foraminifera as a result of Pliocene–Pleistocene deep-sea circulation changes in the South China Sea (ODP Sites 1143 and 1146)     

《Quaternary Science Reviews》2007,26(5-6):808-827

During the Late Pliocene–Middle Pleistocene, 56 species and 15 genera of elongate, cylindrical benthic foraminifera disappeared from the deep sea in the South China Sea (ODP Sites 1143 and 1146) as part of the last global extinction in the deep sea. This extinction group (Ext. Gp) exhibited a pulsed decline in abundance and species richness mostly during glacials, and often associated with periods of expansion of polar ice that resulted from increased cooling of the Earth's climate since ∼2.5 Ma, particularly during the Mid-Pleistocene Climate Transition (MPT, 1.2–0.6 Ma). We infer that the Ext. Gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep-sea water masses. The detailed record of withdrawal of the Ext. Gp differs between the two sites, with far more disappearances occurring prior to the MPT in the deeper Site 1143 (2772 m) than in the shallower Site 1146 (2092 m). The Late Pliocene and Early Pleistocene declines in deeper parts of the South China Sea (Site 1143) may have resulted from enhanced glacial production of deep, southern-sourced water passing over the sill into the basin from the North-west Pacific. During the MPT however, the Ext. Gp declines and disappearances were of similar timing and magnitude in both sites, implying that both were influenced by the same deep-water mass during glacials at this time. This could have been North Pacific Deep Water, which many workers infer was formed in the northern Pacific during the last glacial, and may have begun forming during MPT glacials, in association with the progressively enhanced cooling of the Northern Hemisphere.  相似文献   

CURRENT LITERATURE SURVEY     

《Journal of African Earth Sciences》2011,59(5):857-859

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GEOCHEMISTRY ARTICLES – July 2012     

《Organic Geochemistry》2012

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Numerical simulations of depressurization-induced gas production from gas hydrate reservoirs at the Walker Ridge 313 site,northern Gulf of Mexico     

《Marine and Petroleum Geology》2012,35(1):169-185

In 2009, the Gulf of Mexico (GOM) Gas Hydrates Joint-Industry-Project (JIP) Leg II drilling program confirmed that gas hydrate occurs at high saturations within reservoir-quality sands in the GOM. A comprehensive logging-while-drilling dataset was collected from seven wells at three sites, including two wells at the Walker Ridge 313 site. By constraining the saturations and thicknesses of hydrate-bearing sands using logging-while-drilling data, two-dimensional (2D), cylindrical, r-z and three-dimensional (3D) reservoir models were simulated. The gas hydrate occurrences inferred from seismic analysis are used to delineate the areal extent of the 3D reservoir models. Numerical simulations of gas production from the Walker Ridge reservoirs were conducted using the depressurization method at a constant bottomhole pressure. Results of these simulations indicate that these hydrate deposits are readily produced, owing to high intrinsic reservoir-quality and their proximity to the base of hydrate stability. The elevated in situ reservoir temperatures contribute to high (5–40 MMscf/day) predicted production rates. The production rates obtained from the 2D and 3D models are in close agreement. To evaluate the effect of spatial dimensions, the 2D reservoir domains were simulated at two outer radii. The results showed increased potential for formation of secondary hydrate and appearance of lag time for production rates as reservoir size increases. Similar phenomena were observed in the 3D reservoir models. The results also suggest that interbedded gas hydrate accumulations might be preferable targets for gas production in comparison with massive deposits. Hydrate in such accumulations can be readily dissociated due to heat supply from surrounding hydrate-free zones. Special cases were considered to evaluate the effect of overburden and underburden permeability on production. The obtained data show that production can be significantly degraded in comparison with a case using impermeable boundaries. The main reason for the reduced productivity is water influx from the surrounding strata; a secondary cause is gas escape into the overburden. The results dictate that in order to reliably estimate production potential, permeability of the surroundings has to be included in a model.  相似文献