Thrusting of the North Lhasa Block in the Tibetan Plateau

A huge thrust system, the North Lhasa Thrust (NLT), was discovered in the northern Lhasa block of the Tibetan Plateau based on geological mapping of the Damxung region and its vicinity, the Deqen-Lunpola traverse and the Amdo-Bam Co profile. The NLT consists of the Dongqiao-Lunpola thrust (DLT), the west Namco thrust (WNT) and the south Damxung thrust (SDT) and ductile shear zones, ophiolite slices and folds extending in a WNW direction. Major thrust faults of the NLT seem to merge into a single deep-seated detachment of the upper-crust and totally displaced southward as far as 100-120 km. Chronological analyses with 39Ar-40Ar of plagioclase and hornblende, Rb-Sr isochron of minerals and fission-tracks of apatite from mylonite within the WNT yield ages of 174-173 Ma, 109 Ma and 44 Ma, showing 3 periods of thrusting in the north Lhasa block caused by subduction of the Tethys oceanic plate and the India-Eurasia continental collision respectively.

拉萨地块北部逆冲推覆构造系统

拉萨地块北部发育大型逆冲推覆构造系统(NLT),由前锋纳木错构造带、根部安多—伦坡拉构造带和底部滑脱构造带所构成。前锋纳木错构造带总体呈WNW向展布,由20多条向北倾斜的逆掩断层、宽阔的韧性剪切带、4条蛇绿岩片带与大量不同类型的构造岩片所组成。根部安多—伦坡拉构造带位于班公—怒江缝合带中段,由3条WNW向一近EW向逆冲断裂带、宽阔的蛇绿混杂岩岩片与已发生褶皱的古近纪盆地所组成。底部为中上地壳滑脱带,对应于15～30km深处的高导层,主要由蛇绿岩和构造岩组成。NLT推覆距离达120～150km,主要形成时代为古近纪晚期—新近纪早期。