Provenance Analysis and Drainage Evolution in Late Cenozoic Chengdu Basin on Eastern Margin of Tibetan Plateau
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摘要: 成都盆地位于青藏高原东缘，夹于龙门山与龙泉山之间，盆地中充填了3.6Ma以来的大邑砾岩、雅安砾石层和晚更新世—全新世砾石层，其物源均来源于盆地西侧的龙门山，具横向水系和单向充填的特征。本次以物源区分析作为切入点，以岷江和青衣江水系为重点，采用砾岩成分分析、砂岩岩屑成分分析、重矿物分析和砾石的地球化学分析等基本方法，开展青藏高原东缘晚新生代以来的古水系重建工作，研究结果表明，成都盆地主要有两个物源区，其中成都盆地北部的都江堰街子场、崇州白塔山、大邑白岩沟、大邑氮肥厂、彭州丁家湾、彭州葛仙山等剖面中的砾石层在碎屑成分、重矿物和花岗岩砾石的地球化学成分等方面相似，应为古岷江的产物，而其与现代岷江在砾岩成分和重矿物特征等方面的差异性则表明古岷江可能存在改道的现象；成都盆地南部的庙坡剖面和熊坡东剖面中的砾石层在碎屑成分、重矿物和花岗岩砾石的地球化学成分等方面相似，应为古青衣江的产物，但其流向却与现代青衣江的流向不同，表明熊坡背斜是在大邑砾岩沉积之后隆起的，它的隆起迫使古青衣江改道。Abstract: Chengdu basin developed ahead of Longmen Shan along eastern margin of Tibetan Plateau, lying between the Longmen Shan and Longquan Shan. The filling in the basin include Dayi conglomerate, Yaan gravel layer and Late Pleistocene and Holocene gravel layer since 3.6Ma，and the sediments in the basin were derived from Longmen Shan with transverse drainage patterns. Based on results by the component analysis of gravel, heavy mineral and geochemistry of major elements in the sediments of Chengdu basin, we draw conclusion that there were two provenances and two paleorivers, one of them was paleoMinjiang, which developed in the northern part of the basin, another was paleoQingyijiang ,which developed in the southern part of the basin. According to the difference between Dayi conglomerate and modern fluvial deposit, we can infer Minjiang and Qinyijiang have changed their course after period of Dayi conglomerate deposition.
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Key words:
- provenance analysis /
- drainage evolution /
- Late Cenozoic /
- Chengdu basin /
- Eastern margin /
- Tibetan plateau
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