Late Cenozoic tectonic deformation history and uplift process of the Panxi region, western Sichuan

Abstract： Based on TM image interpretation and field observations, this paper describes the geomorphological features of the deeply incised Daduhe and Anninghe River valleys in the Panxi region and analyses the late Cenozoic tectonic deformation features of the Anninghe fault zone. The late Cenozoic tectonic evolution of the Anninghe fault zone may be divided into 5 stages： late Miocene to early Pliocene, late Pliocene to early Pleistocene, early to middle Pleistocene, middle to late Pleistocene, and late Pleistocene to Holocene. The first stage mainly witnessed transpressional strike-slip faulting； in the second stage obliquely tensional strike-slip motion was dominant； the Yuanmou movement occurring in the third stage caused lacustrine strata of the Xigeda Formation to be folded； in the fourth stage normal faulting took place, forming the Anninghe graben-horst structure； in the fifth stage left-lateral strike-slip motion again predominated. Based on a morphostructural analysis of the deep incised valleys of the Daduhe and Anninghe Rivers, late Cenozoic stratigraphic records and deformation features, the authors propose a 4-stage uplift model for the late Cenozoic uplift history of the Panxi plateau： a stage of gentle uplift and regional peneplanation during the early to middle Miocene (before 12 Ma), a stage of fast uplift and deep valley incision during the late Miocene to early Pliocene (from 12 to 3.4 Ma), a stage of development of the Xigeda lake basin along the deeply incised river valleys during the late Pliocene to early Pleistocene (from 3.4 to 1.1 Ma), and finally a stage of fast uplift and development of river terraces during the mid to late Pleistocene. The Panxi plateau may have attained an elevation of more than 3 000 m above sea level by the late Pliocene (before 3.4 Ma).