新生代紅河-哀牢山剪切帶變形歷史之探討

Cenozoic Deformation History of the Ailao Shan-Red River Shear Zone

蔡宜伶(Yi-Ling Tsai)

指導教授 ： 李通藝

國立臺灣師範大學/理學院/地球科學系/碩士(2007年)

摘要

紅河-哀牢山剪切帶為南中國陸塊與中南半島上之一條地質和地形學上的不連續帶，為新生代印度板塊碰撞歐亞板塊所造成的主要走向滑移斷層之一。為了釐清紅河-哀牢山剪切帶自中生代以來的構造史，本研究藉由在哀牢山變質帶利用定向標本進行顯微構造分析，測量各期葉理交軸(FIA)之位態，進而了解此區的應力狀態。並在象背山變質帶利用氬-氬雷射探針定年分析法求得剪切帶橫向年代變化。顯微構造觀察分析結果顯示此區經歷三期的塑性變形作用。第一期變形(D1) 可能發生於印支期時，形成新葉理面S1 並右旋剪切更早期的葉理S0/1；所測量出之第一組葉理交軸為西北-東南向(126-306)，傾角介於11~55°之間，顯示σ1 為東北-西南向水平擠壓力。第二期變形(D2) 可能發生於中新世早期紅河剪切帶左移運動，形成新葉理面S2並左旋剪切更早期的葉理S1；所測量出之第二組葉理交軸為西北-東南向(106-286)，傾角介於16~65°之間，顯示σ1 為東北-西南向水平擠壓力。第三期變形(D3) 可能與紅河剪切帶右移運動有關，形成新葉理面S3 並右旋剪切更早期的葉理S2；所測量出之第三組葉理交軸為西北-東南向(139-319)，傾角介於6~68°之間，顯示σ1 為東北-西南向水平擠壓力。總結上述之結果，所觀測到此三期塑性變形的葉理交軸之方位一直保持西北-東南向，顯示其水平擠壓力一直保持東北-西南向，並無歷時或因地而改變方向。氬-氬定年實驗結果所得年代約集中於晚期漸新世至早期中新世(27- 21 Ma)，其中角閃石所得的年代在26.9 - 24.7 Ma，黑雲母所得的年代在24.7 - 21.5 Ma。同礦物中的年代變化量不大，顯示象背山變質帶在研究區域中南-北兩側應為同時抬升。總結上述之結果傾向於支持中部地殼流動模式(Middle Crustal Flow Model)的看法。

關鍵字

葉理交軸 ； 氬-氬定年 ； 紅河-哀牢山剪切帶 ； 哀牢山 ； 象背山

並列摘要

The Ailao Shan-Red River Shear Zone (ASRRSZ) is a geologic discontinuity in Southeast Asia, and is one of the major strike-slip features caused by India convergence with Asia during the Cenozoic. In order to dewpher the structural evolution of the highly deformed ASRRSZ, matrix Foliation Intersection/Inflection Axes (FIAs) measurements from oriented samples are utilized to delineate to the structural evolution, which samples collected from the Ailao Shan metamorphic massif. We also used 40Ar/39Ar Laser Probe Analysis to look for the variation of age crossed to the Day Nui Con Voi (DNCV) metamorphic massifs. Microstructural observation recorded three ductile deformation events in this region. D1 possibly occurred during the Indosinian orogeny, showed the S1 and dextral shearing the S0/1. The orientations of FIA set 1 is sub-horizontal NW-SE trending (126-306), indicating NE-SW compressional σ1. D2 possibly resulted from the left-lateral strike-slip movement of the Ailao Shan-Red River shear zone during early Miocene, and showed the S2 and sinistral shearing the S1. The orientation of FIA set 2 is sub-horizontal NW-SE trending (106-286), indicating NE-SW compressional σ1. D3 possibly resulted from the right-lateral strike-slip movement of the Ailao Shan-Red River shear zone, and showed the S3 and dextral shearing the S2. The orientations of FIA set 3 is sub-horizontal NW-SE trending (139-319), indicating NE-SW compressional σ1. Integrating previous results of structural analyses, the FIA data show the orientations of FIA is sub-horizontal NW-SE trending and NE-SW compressional σ1, which the stress patterns didn’t change with time. The 40Ar/39Ar dating results centered on the late Oligocene - Early Miocene (27- 21 Ma), in which the ages of amphiboles centered on the 26.9 - 24.7 Ma, and the ages of biotites centered on the 24.7 - 21.5 Ma. The variation of ages is rather smail in the same mineral, indicating that the north and south of DNCV metamorphic massifs both side should be uplift at the same period of time. These analysical results supported those predicted by the Middle Crustal Flow Model.

並列關鍵字

FIAs ； Ar-Ar dating ； Ailao Shan-Red River Shear Zone ； Ailao Shan ； Day Nui Con Voi

參考文獻

inclusion trails during multiple metamorphism and folding: Journal

of Metamorphic Geology, v. 20, p. 397-412.

deformed region using the axes of spiral, staircase and sigmoidal

along an orogen and its effects on porphyroblast growth during

of magnetic anomalies and seafloor spreading stages in the South