青藏高原东缘龙门山前陆逆冲带复合结构与生长

位于青藏高原东缘的北东向龙门山逆冲带，研究已经证明是中生代与新生代前陆复合扩展和生长的结果。然而，2008年5·12汶川地震地表破裂、余震和滑坡等的单向和分段迁移现象，对龙门山复合逆冲带的结构认识提出了挑战。文章在已有研究成果基础上，针对龙门山复合生长下构建的特殊结构进行了野外调查和构造解析。结果表明，以中生代与新生代两期前陆逆冲带复合生长为基础，龙门山复合逆冲带具有特殊的、主要由前陆逆冲楔叠加后形成的复合结构，而且这种复合逆冲楔具有分级和时序特征；中生代前陆逆冲楔是以逆冲断层-褶皱为特征，并分别组合形成碧口厚皮逆冲推覆体、唐王寨薄皮逆冲推覆体和龙王庙逆冲推覆体，总体从晚三叠世以前开始，至~160 Ma向南递进扩展生长；新生代前陆逆冲楔由逆冲断层和逆冲岩片组成，分为约35~10 Ma和10 Ma以来两个阶段，向南东向递进扩展生长，并可能与川西盆地东侧龙泉山构造相连通。因此，龙门山逆冲带具有前陆逆冲带和生长过程的双重复合结构。 

Composite structure and growth of the Longmenshan foreland thrust belt in the eastern margin of the Qinghai-Tibet Plateau

It has been proved that the NE-trending Longmenshan thrust belt in the eastern margin of the Qinghai-Tibet Plateau was a composite of the expansion and growth of the Mesozoic and Cenozoic foreland thrust belts. However, puzzle is remained for the unidirectional and segmented migration of earth surface failures, aftershocks, and landslides of the Wenchuan earthquake on May 12, 2008. This puzzle challenges the understanding for the texture of the Longmenshan composite thrust belt. Based on the previous studies, this paper applied geological investigation and structural analysis focusing on a possible special texture produced by the composite growth of the Longmenshan thrust belt. The results reveal a composite texture produced by the growth of the Cenozoic foreland thrust belt superimposed over the Mesozoic foreland thrust belt with foundation of the composite thrust wedge. The composite thrust wedge could be graded with formational sequence. The Mesozoic foreland thrust wedges are characterized by thrust fault-related anticlines. Thrust complexes of Bikou, Tangwangzhai and Longwangmiao, which are combined by foreland thrust wedges, were initiated before the late Triassic (237 Ma) and terminated at ~160 Ma. The Cenozoic foreland thrust wedge is composed of thrust fault and sheet, and was staged produced by SE-ward progressive propagation at about 35~10 Ma and 10 Ma, respectively. This thrust wedge propagation might result in the Longquanshan uplift in the east of the western Sichuan basin. Therefore, the Longmenshan foreland thrust belt has characteristics of composite texture and composite growth.