Sedimentology and provenance of newly identified Upper Cretaceous trench basin strata, Dênggar, southern Tibet: Implications for development of the Eurasian margin prior to India–Asia collision
Sedimentology and provenance of newly identified Upper Cretaceous trench basin strata, Dênggar, southern Tibet: Implications for development of the Eurasian margin prior to India–Asia collision
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DOI：
10.1111/bre.12521
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发表时间：
2020-10
期刊：
影响因子：
3.2
通讯作者：
D. Orme;A. Laskowski;Misia F. Zilinsky;Wang Chao;Xudong Guo;Fulong Cai;D. Lin
中科院分区：
文献类型：
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作者：
D. Orme;A. Laskowski;Misia F. Zilinsky;Wang Chao;Xudong Guo;Fulong Cai;D. Lin
西藏拉萨地体南缘保存的海沟盆地是新生代印度-亚洲碰撞前汇聚边缘过程的沉积学记录。我们提供了西藏丹加尔附近荣玛瓦组及其周围地层的新的沉积学、岩石学和地质年代学资料，以确定沉积环境、物源和时代。沉积年龄约为92~87 Ma，岩相与低密度和高密度浊流的沉积以及深海海沟盆地中远洋碎屑的悬浮沉积相一致。砂岩模式分析和U-Pb年代学研究表明，本区海沟盆地碎屑岩来源于拉萨地体。我们解释说，白垩纪俯冲海沟接受了轴向泥沙扩散系统的碎屑，该系统将拉萨中南部靠近拉萨市的地体源头的沉积物直接输送到海沟，然后平行于海沟向西流动。晚白垩世沉积的海沟盆地地层的保存与92 Ma之前和80 Ma之后的海沟沉积的缺失相比较，表明在这一时期边缘经历了一段显著的增积期。此外，海沟盆地地层的沉积发生在晚白垩世埃达克岩浆作用和高温变质作用期间，推测这是由拉萨地体南缘洋脊或俯冲带撤退和相关的上板块伸展作用解释的。洋脊的俯冲可能提供了一种潜在地侵蚀弧前盆地地层的机制，并促进了直接向海沟输送更多的沉积物。
Trench basins preserved along the southern margin of the Lhasa Terrane, Tibet, are sedimentologic records of convergent margin processes preceding Cenozoic India–Asia collision. We present new sedimentologic, petrographic and geochronologic data from the Rongmawa Formation and surrounding strata near Dênggar, Tibet, to determine depositional environment, provenance and age. Depositional ages range from ca. 92 to 87 Ma and lithofacies are consistent with deposition by low‐ and high‐density turbidity currents and suspension settling of pelagic detritus in a deep‐marine, trench basin setting. Sandstone modal analyses and U–Pb geochronology indicate that trench basin detritus in this region was derived from the Lhasa Terrane. We interpret that the Cretaceous subduction trench received detritus from an axial sediment dispersal system that transported sediment from headwaters in the central‐southern Lhasa terrane near Lhasa City directly to the trench and then flowed westwards parallel to the trench. The preservation of trench basin strata deposited during Late Cretaceous time compared with the lack of trench deposits prior to ca. 92 Ma and after ca. 80 Ma suggests the margin experienced a period of significant accretion during this interval. In addition, deposition of trench basin strata occurred during Late Cretaceous adakitic magmatism and high‐temperature metamorphism, which are hypothesized to be explained by subduction of an oceanic ridge or subduction zone retreat and related upper plate extension along the southern margin of the Lhasa terrane. Subduction of an oceanic ridge may provide a mechanism to potentially erode forearc basin strata and promote increased sediment delivery directly to the trench.