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991.
B.J. Keely J.S. Sinninghe Damst S.E. Betts Ling Yue J.W. de Leeuw J.R. Maxwell 《Organic Geochemistry》1993,20(8)
Principal components analysis (PCA) has been used to investigate changes in concentrations of the components of the hydrocarbon fractions extracted from 71 marl samples, selected to cover two total organic carbon (TOC) maxima in the lower part of the Salt IV formation, a Lower Oligocene evaporitic sequence from the Mulhouse Basin, France. The analysis indicates that the fractions can be ascribed as lying between two end member distributions. The changes in these distributions are gradual, suggesting that they resulted from fairly gradual changes in the depositional palaeoenvironment. These changes are related to increased algal productivity associated with the evolution of a restricted lacustrine environment through to one with a greater marine influence. Systematic variations in the concentrations of selected components relative to the TOC profile point to a repeated sequential evolution in the biological assemblage during deposition of the sequence. 相似文献
992.
Abstract This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2-3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian-Cambrian boundary strata with those of the adjacent areas. 相似文献
993.
对于羌塘盆地是否存在横贯东西的中央隆起带,目前学术界仍有分歧.本文提供的最新高精度航空重、磁资料证实存在呈东西向贯通羌塘盆地的中央隆起带,并对该带的构造特征进行了精细刻画.隆起带受南北两侧深大断裂控制,其空间跨度(宽度)由西向东逐渐收敛,并被一组近南北向的隐伏断裂系切割、左滑错动.重、磁场资料还显示中央隆起带在双湖东、西两侧存在明显差异:西段基底大规模隆起,基岩深度一般在3~5 km以内,明显浅于南北羌塘坳陷7~15 km的基底埋深;东段基底隆起幅度明显降低,主要表现为潜伏的低隆起,其中双湖—雅曲段基底埋深5~7 km,雅曲—岗尼段基底埋深7~9 km;即中央隆起带基底自西向东"台阶状"降低,隆起的幅度和分布范围受到近南北向断裂控制.构造分层表明,与南羌塘地块相比,北羌塘地块的基底隆起幅度小、稳定性更好.南北羌塘基底地球物理属性的显著差异说明羌塘盆地并不存在统一的前寒武系变质基底,中央隆起带的形成应该与古特提斯洋关闭时形成的混杂岩带有关. 相似文献
994.
柴北缘乌兰地区中生代岩浆岩分布广泛,主要出露辉长岩、闪长岩、花岗闪长岩和花岗岩。乌兰北部两件辉长岩样品的LA-ICP-MS锆石U-Pb测年显示其加权平均年龄分别为(241.9±0.9) Ma和(245.4±1.9) Ma,说明其形成于中三叠世早期。辉长岩的w(SiO2)为47.94%和52.01%,全碱质量分数较低(ALK为1.25%和1.47%),里特曼指数为0.33和0.26,属钙碱性系列岩石;w(Cr)(1 661.00×10-6和1 418.00×10-6)、w(Ni)(394.00×10-6和280.00×10-6)和Mg#值(81和79)极高,具幔源原生玄武岩浆特征。轻、重稀土元素分馏较弱,LREE/HREE为3.92和3.44,无明显负Eu异常,表明未发生明显的岩浆分异作用;富集K、Rb等大离子亲石元素,不同程度地亏损Nb、Ta、Ti等高场强元素,表现为与俯冲作用相关的弧岩浆岩特征。辉长岩的εHf(t)值(-3.0~9.3)变化较大,暗示来自地幔的基性岩浆中有地壳组分的加入。结合区域地质演化特征研究成果,认为辉长岩形成于古特提斯洋向北俯冲背景下的大陆边缘弧环境,俯冲的洋壳板片脱水产生的流体导致上覆地幔楔部分熔融,形成玄武质岩浆,岩浆上升侵位过程中遭受地壳物质混染或与壳源岩浆发生混合作用。 相似文献
996.
997.
Geology of the Grove Mountains in East Antarctica 总被引:2,自引:0,他引:2
Grove Mountains consists mainly of a series of high-grade (upper amphibolite to granulite facies) metamorphic rocks, including
felsic granulite, granitic gneiss, mafic granulite lenses and charnockite, intruded by late tectonic gneissic granite and
post-tectonic granodioritic veins. Geochemical analysis demonstrates that the charnockite, granitic gneiss and granite belonged
to aluminous A type plutonic rocks, whereas the felsic and mafic granulite were from supracrustal materials as island-arc,
oceanic island and middle oceanic ridge basalt. A few high-strained shear zones disperse in regional stable sub-horizontal
foliated metamorphic rocks. Three generations of ductile deformation were identified, in which D1 is related to the event before Pan-African age, D2 corresponds to the regional granulite peak metamorphism, whereas D3 reflects ductile extension in late Pan-African orogenic period. The metamorphic reactions from granitic gneiss indicate a
single granulite facies event, but 3 steps from mafic granulite, with P-T condition of M1 800°C, 9.3×105 Pa; M2 800–810°C, 6.4 × 105 Pa; and M3 650°C have been recognized. The U-Pb age data from representative granitic gneiss indicate (529±14) Ma of peak metamorphism,
(534±5) Ma of granite emplacement, and (501±7) Ma of post-tectonic granodioritic veins. All these evidences suggest that a
huge Pan-African aged mobile belt exists in the East Antarctic Shield extending from Prydz Bay via Grove Mountains to the
southern Prince Charles Mountains. This orogenic belt could be the final suture during the Gondwana Land assemblage. 相似文献
998.
999.
1000.
1. Introduction In our previous paper, MSPAS (Modi?ed Soil-Plant-Atmosphere Scheme) was fully introduced andthe e?ectiveness of the model was also well proved (Liuet al., 2004). In this paper, some sensitivity experi-ments are performed to test the sta… 相似文献