The structural style and timing of uplift of the Ailaoshan-Diancang Range, West Yunnan, China
Journal
Dizhen Dizhi
Journal Volume
34
Journal Issue
4
Pages
696-712
Date Issued
2012
Author(s)
Abstract
The uplift of West Yunnan plateau is one of the late Cenozoic great geological events in the Qinghai-Tibet Plateau tectonic domain, and the Ailaoshan-Diancangshan Range uplift is the key to understanding this tectonic process. In the former researches, many researchers mainly emphasized on the strike-slip movements and times of the Ailaoshan-Red River shear zone. The formation of Ailaoshan-Diancang Range has been widely considered to be the result of the strike-slip movements of the Ailaoshan-red River shear zone. Usually, the formation of geomorphic unit is the result of latest tectonic activity, for the time scale of topography-shaping process is much smaller than that of tectonic movement in the study of tectonic geomorphology. Based on the collection of detailed evidences, the structural style and timing of the uplift of Ailaoshan-Diancangshan Ranges are studied. Detailed evidences are as follows: First of all, the primary structural foliations in the study region have obvious distinctness. On the east side of the Ailaoshan-Diancang Ranges, steep-dipping structural foliation is developed, but on the west, bedding foliation is developed. In Ailaoshan, the dip direction transforms from northeast to southwest, and the dip decreases steadily. Second, the degree of deformation and metamorphism reduces gradually from northeast to southwest, producing different belts. From northeast to southwest, the metamorphic belts are, in turn, the high-amphibolite facies metamorphic granitic gneiss, the low-amphibolite facies and greenschist facies composite of schist, phyllite and slate, and the weakly deformed sedimentary rocks. Third, the fault facets developed on the northeast side of the Ailaoshan and the pseudotachylite discovered on the normal fault planes indicate that the eastern boundary of the ranges is a fast-moving tectonic boundary. 40Ar/39Ar step-heating experiments were performed on biotite and K-feldspar extracted from granitic mylonite collected from the east side of Diancangshan near Xiaguan. The 40Ar/39Ar geochronological data suggest that Diancangshan experienced a fast cooling event at 3~4 Ma BP. Therefore, we draw the conclusions that: The formation of the Ailaoshan-Diancang Range shows a tilted uplift structural style, with larger amplitude of uplift in the east and smaller in the west. The latest uplift of the Ailaoshan-Diancang Range is constrained to be in Pliocene, about 3~5 Ma BP.
Type
journal article