青藏高原中东部古近纪盆地封闭的构造-沉积-岩浆活动和古气候响应

The Closure of Paleogene Basins of East-Central Tibet in Response to Tectonic,Sedimentation,Magmatism and Paleoclimate

青藏高原中东部分布着一系列中小型古近纪盆地,详细的野外地质调查、盆地构造-沉积学和生物地层学、地球化学和岩浆岩的40Ar/39Ar年代学结果表明,盆内充填了紫红色的陆源碎屑岩夹火山碎屑岩、碳酸盐岩和石膏层,并被晚期岩浆岩所切割,盆缘地层发生大规模掀斜而形成高陡地层和挤压向斜,盆内地层发生褶皱变形。地层内部细碎屑岩孢粉和古植物、火山碎屑岩和侵入岩的40Ar/39Ar年代学揭示盆地充填沉积物形成于38～28Ma(晚始新世—早渐新世)。古近纪紫红色沉积物、碳酸盐岩和石膏层的出现代表干旱-炎热的古气候环境。印度-欧亚板块碰撞过程中因陆壳变形和高原早期构造隆升产生的走滑拉分和逆冲挤压是导致高原中东部古近纪盆地裂解和封闭的主要原因。

In east-central Tibet,Many Paleogene elongate basins with medium-mini-type are distributed along the large-scale arc-shaped strike-slip and thrust belt of the Nangqian-Yushu and Batang-Lijiang.Detailed mapping,structural-sedimentologic,biostratigraphic,geochemical,and ^40Ar/^39Ar chronologic data from five Pleogene basins（Dongba,Shanglaxiu,Nangqian,Gongjue,and Mangkang）in the Nangqian-Yushu and Batang region of east-central Tibet indicate that the strata in basin margin developed a large-scale of tilting to form high-steep dip and extrusing syncline,fold and deformation,filled amaranth clastics interbeded with volcanoclastic rock,carbonite and gypsum in basins,and incised by late magmatite.Pollen and paleoflora in fine-clastic rock,^40Ar/^39Ar dating of volcanoclastic rock and magmatite show that the basin-filling sediments formed at 38-28 Ma（Late Eocene—Early Oligocene）.Paleogene amaranth sediments,carbonate and gypsum present a dry-fervent,evaporated paleoclimate environment.At the late Eocene to early Oligocene in Tibetan plateau（38～28 Ma）,the break and closure of Paleogene basins of east-central Tibet may foreshow the start of wide early tectonic uplift and crust deformation due to the Indo-Asia collision.