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新疆阿尔泰地区矿产存在着明显的东西差异,究共原因是阿尔泰处于三大板块的会聚部位.不同的基底性质有所不同。该地区前寒武系基底主要由元古代克木齐群和富蕴群岩石组成,克木齐群属中下元古代,主要分布于阿尔泰西部和南部.富蕴群属中上元古代.主要分布于阿尔泰东部、东北部。岩石学和岩石化学特征表明,克木齐群更多具有上地幔和下地壳的成分.富蕴群则具有上地壳的成分;稀土元素分配特征和铅同位素特征表明东西部矿床和各自的基底关系密切,后者的差异导致了新疆阿尔泰地区矿产特征的差异。 相似文献
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The Aravalli mountain range (AMR) in the northwestern part of the Indian Peninsula consists of two main Proterozoic metasedimentary and metaigneous sequences, the Aravalli and Delhi Supergroups, respectively, which rest over the Archaean gneissic basement. A synthesis and reinterpretation of the available geological, geochronological and geophysical data, including results of own field work and geophysical interpretations pertaining to the AMR, indicate its origin as an inverted basin: rifting into granitoid basement began ca. 2.5; Ga ago with Aravalli passive rifting (ca. 2.5–2.0 Ga) and Delhi active rifting (ca. 1.9–1.6 Ga). Associated mafic igneous rocks show both continental and oceanic tholeiitic geochemistry and are comparable with Phanerozoic, rift-related magmatic products. Available data showed no conclusive evidence for oceanic lithoshere and island-arc/active margin magmatic activity in the AMR. Subsequent inversion and orogeny (Delhi orogeny, ca. 1.5-1.4 Ga) lead to complex deformation and metamorphism. Only in the western and central zones has the basement been involved in this mid-Proterozoic (Delhi) deformation, whereas it is unaffected in the eastern part, except for local shear zones mainly along the basement/cover interface. The grade of metamorphism increases from the greenschist facies in the east to the amphibolite facies in the west with local HP assemblages. These latter are explained by rapid burial and exhumation of thin and cool continental lithosphere. Subsequently, during a final, mild phase of inversion, the Vindhyan basins consisting mainly of sandstones, limestones and shales, flanking the AMR formed which are comparable to foreland basins. The tectonic evolution of the AMR is therefore interpreted as an example of a major inverted continental rift and of a Proterozoic intra-continental orogen. 相似文献
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本文就扬子板块东南缘湖南段上元古代三套同期异相沉积层—泥市群、板溪群及高涧群的构造变形特征分别作了简要概述。指出它们的主体构造变形是显生宙以来构造叠加变形的综合反映,其中,板溪群与高涧群的构造变形型式迥然有别,“雪峰隆起”的南北两侧不仅在组成上而且结构上均具显著的不对称性。 相似文献
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根据近两年对华南元古宙地壳演变过程的研究,提出了华南基底构造格架的划分方案;同时发现了华南陆下存在相对稳定高速高阻冷的古地幔柱的残留部分一“残烃柱”;指出华南古大洋基底蛇绿岩层序中存在斜长花岗岩等酸性组分;探讨了陆下地幔新矿物相;初步建立了华南及西太平洋壳一幔分层柱体模型;讨论了华南部分地区下地壳及上地幔的岩石流变学特征。对元古宙Cu、Au等成矿作用也作了初步的总结并提出了有希望的成矿远景区。 相似文献
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通过对目前全世界元古宙———寒武纪地层中的浮游植物 (疑源类 )的统计 ,发现在新元古代晚期和早、中寒武世相对较短的时间间隔内发生了一系列的微体植物 (疑源类 )辐射和绝灭事件。而这些辐射和绝灭事件又与早期后生生物的辐射、绝灭都有密切的镜像关系。通过对古海洋的δ13 C、87Sr/ 86Sr研究 ,发现元古宙—寒武纪浮游植物 (疑源类 )的辐射演化、绝灭作用与古海洋环境变化有着密切的关系 ,即生物辐射时期 ,δ13 C、 87Sr/ 86Sr呈现高异常 ;生物绝灭时期 ,δ13 C、87Sr/ 86Sr呈现低异常 ;冰期δ13 C呈现明显的负异常。 相似文献