Characteristics and origin of the Ediacaran peperites in the northwestern Tarim Basin, and their geological implications
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摘要: 熔积岩是一类由炽热的岩浆物质与湿冷的未固结沉积物发生同生混合而形成过渡型岩石,具有重要的古环境指示意义。通过野外露头地质调查和微观岩石学分析研究,在塔里木盆地西北缘埃迪卡拉系基性火山岩中识别出典型的熔积岩,主要包括块状熔积岩和流态熔积岩两种类型,其宿主为紫红色砂质沉积物。熔积岩主要通过岩浆顺层侵入富水未固结砂质沉积物或者在其表面流动形成,其中较薄层岩浆侵入和地表溢流玄武岩底部主要形成流态熔积岩,而较厚层岩浆侵入则发育块状熔积岩。综合分析认为塔里木克拉通北缘早埃迪卡拉世总体仍处于与罗迪尼亚超大陆裂解相关的板内裂谷背景,熔积岩的发育指示该地区玄武岩喷发时主要为滨岸水下沉积环境;伴随着火山喷发的结束,晚埃迪卡拉世向构造相对稳定的被动陆缘盆地或克拉通盆地转换。Abstract: Peperite is a kind of transitional rock formed by the syngenetic mixing of hot magmatic materials and wet and cold unconsolidated sediments, which has important paleoenvironmental implications. Based on outcrop geological survey and microscopic petrological analysis, typical peperites are recognized in Ediacaran basic volcanic rocks in northwestern Tarim Basin, which mainly include blocky peperites and fluidal peperites, and their host is purplish red sandy sediments. The peperites were mainly formed by the intrusion of magma into the water-rich unconsolidated sandy sediments or by the flow of magma on the surface of the water-rich unconsolidated sandy sediments. Among them, the thinner magmatic intrusion and the bottom of the surface flood basalt mainly formed the fluidal peperites, while the thicker magmatic intrusion developed the blocky peperites. It is concluded that the northern margin of the Tarim craton was still in an intraplate rift setting related to the breakup of the Rodinia supercontinent during the early Ediacaran, and the development of peperite indicates that the basalt eruption in this area was mainly in a littoral subaqueous sedimentary environment; with the end of volcanic eruption, the northern Tarim Craton transformed into a relatively stable passive continental margin basin or a cratonic basin during the late Ediacaran.
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