THE STRUCTURAL STYLE AND TIMING OF UPLIFT OF THE AILAOSHAN-DIANCANG RANGE,WEST YUNNAN,CHINA

doi:10.3969/j.issn.0253-4967.2012.04.013

Abstract

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 3～4Ma 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 3～5Ma BP.

Key words: Ailaoshan-Diancangshan Range, structural geomorphology, ⁴⁰Ar/³⁹Ar geochronology, tilted fault block

摘要：

滇西高原的隆起是新生代晚期青藏高原构造域重要的地质事件。点苍山-哀牢山地区的地层分布、沉积建造等资料表明:该区的区域地层面理产状存在明显的变化,山脉东侧以陡倾角的构造面理发育为主,西侧以缓倾的层状面理发育为主; 变质变形程度从东北向西南逐渐减弱,依次为高角闪岩相变质的花岗质片麻岩、低角闪岩相和绿片岩相的片岩-千枚岩-板岩组合以及弱变形的中生界沉积岩系; 山脉NE侧发育的断层三角面和正断层面上发育的假玄武玻璃,指示山脉东侧边界是一条快速运动的构造边界。通过 ⁴⁰Ar/³⁹Ar和磷灰石裂变径迹测试揭示,点苍山在3～5Ma经历了快速冷却事件。综合研究认为,点苍山-哀牢山的隆升为掀斜式,东部隆升幅度大,西部隆升幅度小; 其隆升最新时限为距今3～5Ma,为上新世以来隆起形成的山脉。

关键词: 点苍山-哀牢山, 构造地貌, ⁴⁰, Ar/³⁹, Ar年代学, 掀斜式构造

CLC Number:

P542

LI Bao-long, JI Jian-qing, LO Ching-hua, GONG Jun-feng, QING Jian-chun. THE STRUCTURAL STYLE AND TIMING OF UPLIFT OF THE AILAOSHAN-DIANCANG RANGE,WEST YUNNAN,CHINA[J]. SEISMOLOGY AND GEOLOGY, 2012, (4): 696-712.

李宝龙, 季建清, 罗清华, 龚俊峰, 庆建春. 滇西点苍山-哀牢山隆升构造样式和隆升时限[J]. 地震地质, 2012, (4): 696-712.

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