深反射地震数据揭示的拉萨地体北部到羌塘地体南部地壳厚度的变化

Crustal thickness variation from Northern Lhasa terrane to Southern Qiangtang terrane revealed by deep seismic reflection data

摘要: 由多个地体拼接而成的青藏高原，有着世界上最厚的地壳。在高原中部，从拉萨地体到羌塘地体，穿过班公湖-怒江缝合带（BNS）的地壳厚度变化长期存在争议。本文主要论述从拉萨地体北端横跨BNS到达羌塘地体的深地震反射剖面探测的结果。探测发现了清晰的Moho反射，揭示了拉萨地体-羌塘地体Moho深度和地壳厚度的变化。探测结果表明，在BNS下方Moho深度由南至北出现了6.2 km的急剧减小，并且与BNS向北28 km处的羌塘地体南部比较，地壳厚度变浅了12.5 km。否定了前人对BNS下方Moho存在20 km显著变化的认识。

Abstract: The Tibetan Plateau, which is made up of a number of terranes, has the world's most thick crust. There is a long-term dispute concerning crustal thickness across the Bangong-Nujiang suture (BNS) from the Lhasa terrane to the Qiangtang terrane. This paper mainly reports the result of the study of deep seismic reflection profile in this area. A clear reflection of Moho was detected, which reveals the change of crustal thickness from the Lhasa terrane to the Qiangtang terrane. Moho exhibits a sharp decrease of 6.2 km across the BNS and becomes 12.5 km shallower from the northernmost Lhasa terrane to the south Qiangtang terrane at 28 km north of the BNS. The viewpoint based on deep seismic reflection data denies previous understanding of a 20 km offset.