雲南哀牢山變質岩帶構造史分析與鋯石定年

Structural Evolution Analsis and Zircon U-Pb Dating of the Ailao Shan Metamorphic Belt, Yunnan, SW China

黃寧祥(Ning-Hsiang Huang)

指導教授 ： 李通藝 ； 葉孟宛

國立臺灣師範大學/理學院/地球科學系/碩士(2011年)

摘要

哀牢山變質岩體位於雲南南部，屬於紅河-哀牢山剪切帶的一部分。自新生代以來，印度和歐亞大陸互相聚合碰撞，而導致地體構造運動，控制了東南亞地體構造的演化，造成喜馬拉雅山與西藏高原的抬升和產生一系列明顯的構造線。西北-東南走向紅河-哀牢山剪切帶中，從元江到紅河之間轉彎為近東-西走向。為了釐清紅河-哀牢山剪切帶右移剪切是沿著西北-東南走向，還是受到南-北走向之鮮水河-小江斷裂帶左移，而使哀牢山彎曲且右移旋動，因此利用野外、微構造和鋯石鈾-鉛定年等方法來分析哀牢山南段構造演化史。根據野外資料此區至少經歷三期的塑性變形事件：最早的變形事件為低角度的偃臥褶皺 （Dn-1），形成次水平的褶皺軸面（Sn-1）；由副片岩之碎屑鋯石鈾鉛定年得到185 Ma，故得知沉積作用必然晚於185 Ma，因此推論Dn-1發生年代亦晚於185 Ma。Dn塑性變形事件是此區經歷最主要的變形事件，形成大規模高角度的直立褶皺，形成西北-東南走向次垂直的褶皺軸面（Sn）；由於Sn平行左移剪切面且在大構造與微構造中皆顯示左旋的葉理與黑雲母變形排列，因此推測Dn變形事件可能是因紅河-哀牢山剪切帶左移而產生，且由花崗岩脈鋯石鈾-鉛定年得到約發生於27~22 Ma。Dn+1塑性變形事件為高角度的直立褶皺，形成南-北走向次垂直的褶皺軸面（Sn+1）；由順時針右旋的葉理與石英變形斷裂推論為右移變形造成，並且利用Rf-φ 應變分析法得知此地區為右移伸張。由於Sn+1葉理平行鮮水河-小江斷層帶，因此我們認為此變形可能是下部地殼流體，由藏東以東喜馬拉雅構造結為中心延著鮮水河-小江斷層帶發生順時針旋轉，所發生時間可能晚於中新世中期。

關鍵字

東喜馬拉雅構造結 ； 哀牢山-紅河剪切帶 ； 鋯石鈾-鉛定年

並列摘要

The Ailao Shan (ALS) metamorphic complex is part of the NW-SE trending Ailao Shan- Red River Shear Zone (ASRR) in SE China. The E-W bending of the ASRR between Yuanjiang and Honghe along the southern section of the ALS was considered due to the clockwise block rotation around the Eastern Himalaya Syntaxes along the Xianshuihe Xiaojiang fault zone. In order to decipher the interaction structural pattern and kinematic relationship between these two fault systems in this region, field, micro-structural and U-Pb zircon geochronology analysis were conducted. Three deformation events of: an oldest isoclinal recumbent fold forming event (Dn-1) with sub-horizontal fold axial planes occurred younger than 185Ma. Dn deformation event is the strongest deformation event forming large-scale upright folds with NW-SE striking sub-vertical fold axial planes (Sn) for gneiss outcrops and S/C shear fabrics along mylonite zones. Since the Sn is parallel to the dominant shear plane with left-lateral sense of shear demonstrating biotite fish, we interpreted the Dn is the left-lateral shear event of the ASRR which occurred between 27~22Ma. Dn+1 deformation event formed upright folds with N-S striking sub-vertical fold axial plane (Sn+1) with right-lateral sense of shear indicators such as: clockwise sigmoid foliations and quartz ribbons. As the Sn+1 fabrics are parallel to the Xianshuihe-Xiaojiang fault zone, we suggest this deformation might be due to the clockwise rotation of crustal fragments around the Eastern Himalaya syntaxis possibly around mid Miocene.

並列關鍵字

Eastern Himalaya syntaxis ； Ailao Shan- Red River Shear Zone (ASRR) ； Ziron Dating

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