Depositional Patterns and Tectonic Setting of Early Tertiary Basins in the NE Margin of the Tibetan Plateau: A Case Study of the Nangqian and Xialaxiu Basins
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摘要: 一系列中小型早第三纪红色盆地出露于青藏高原的东北缘,它们是在印度—欧亚板块碰撞过程中因陆壳变形和高原隆升产生的。典型早第三纪盆地的地质填图和详细的沉积学研究,及构造、沉积和岩浆热事件的综合分析表明,这些盆地具有两阶段构造—沉积特征,即早期受控于逆冲挤压背景,盆地接受底部冲积扇体系的粗碎屑岩段沉积,局部伴有岩浆活动;晚期受控于走滑—拉分背景,盆地充填湖泊—三角洲体系的含膏砂泥岩段夹薄层灰岩,并伴有广泛的岩浆作用。青藏东北缘早第三纪盆地在盆地构造格架、沉积层序结构、沉积物组成和岩浆活动等方面均存在明显的阶段性演化。盆地古水流统计和岩浆岩4 0 Ar/ 3 9Ar定年结果表明,青藏东北缘早第三纪盆地沉积物主要形成于始新世晚期—渐新世早期 (38～ 2 9Ma)。盆地沉积型式和岩浆活动受印度—欧亚板块碰撞早期逆冲挤压和走滑—拉分构造格局的控制。Abstract: Many red Early Tertiary basins are exposed in the northeastern margin of the Tibetan Plateau due to intracontinental deformation and uplift induced by the Indo-Asian collision. Based on detailed mapping and sedimentologic investigations of two Early Tertiary basins, Nangqian and Xialaxiu, and combining with the comprehensive analysis of tectonism, sedimentation and magmatism, two stages for the tectonic and depositional evolution of the basins are revealed, i.e. the early stage is controlled by thrusting and characterized by coarse-grained alluvial-fan clastic sediments at the bottom and local magmatic activities; and the late stage is controlled by strik-slip and pull-apart and characteristic of fine-grained lacustrine-delta gypsum- sandstones and mudstones interbedded with thin-bedded limestones and widespread igneous activities. There is a clear episodic evolution resulting from the basin tectonic framework, the thickness and structure of sedimentary sequences, sediment constituents and magmatism. The data of the basin paleocurrent and 40 Ar/ 39 Ar dating for igneous rocks in the basins suggest that the sediments in the early Tertiary basins were formed in the period of Late Eocene-Early Oligocene (38～29 Ma). Depositional patterns and magmatic activities in the Early Tertiary basins in the NE margin of the Tibetan Plateau were controlled by thrusting and strike-slipping in the early period of the Indo-Asian collision.
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Key words:
- depositional patterns /
- basin-filling sequences /
- thrust /
- strike-slip /
- Early Tertiary basins /
- Tibetan Plateau /
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