東久－米林剪切帶為東喜馬拉雅構造結之西界斷層，東喜馬拉雅構造結自早新生代印歐板塊碰撞事件以來，一直處於一個地體碰撞樞紐地帶，而地表斷裂與強烈變形作用也深受其影響。前人曾探討此構造結之形成過程與機制，但也都未能全然的了解此地區複雜的地體架構模式。為釐清東喜馬拉雅構造結形成之過程，本研究選定其西界之東久－米林剪切帶，藉由野外調查、顯微構造之葉理分析以及葉理交軸分析，並配合 40Ar/39Ar 定年法來探討此剪切帶構造演化與熱事件過程，以期能更進一步瞭解東喜馬拉雅構造結的形成機制。
初步分析結果顯示此區域構造作用可分為三期塑性變形事件 (D1、D2、D3) 與最後一期的脆性變形事件 (D4)：第一期變形作用 (D1) 為早新生代印歐板塊聚合作用而造成平行於剪切帶之同斜褶皺 (Isoclinal fold)，褶皺軸面 (S1) 走向北偏東30~50°向西北傾約60~70°，並呈現西北－東南向 bulk shortening，shear sense 顯示出左剪壓縮作用，是為剪切帶主要形成之作用期。第二期變形作用 (D2) 介於早新生代印歐板塊碰撞與 20.1±0.2Ma 之間，主要產生趨水平向偃臥褶皺 (Recumbent fold)，褶皺軸面 (S2) 走向為北偏東 20~70°向西北傾約 5~40°，shear sense 顯示出近水平向東南逆衝作用，可能於此時期岩圈在 D1 後因西藏高原增厚並造成重力垮塌之循環作用。第三期變形作用 (D3) 主要產生平行於剪切帶東北－西南走向的葉理 (S3；N23~45°E；NW65~85°)，呈高角度向西北傾，shear sense 呈現右剪壓縮之剪動方向，並造成剪切帶在 20.1±0.2~11.4±0.1Ma 由南往北不同時剪動抬升，並認為東南亞早在 20Ma 則開始以東喜馬拉雅構造結順時針旋動。

The Eastern Himalaya syntaxis is the center of current clockwise rotation of surrounding Asia blocks. Previous studies had considered the formation of the Eastern Himalaya syntaxis as an Indian continental wedge jabbing into the Asia plate during the early-Cenozoic India-Eurasia collision. However, other researchers argued that the Eastern Himalaya syntaxis represents a huge antiform complex with rigid high grade metamorphic core. In order to understand the forming mechanism and evolution history of the Eastern Himalaya syntaxis, this thesis reconstructs the structural evolution and thermal history of the Tungchiu-Milin shear zone by field work, micro-structural foliation analysis, matrix Foliation Intersection/Inflection Axes (FIAs) measurement and 40Ar/39Ar dating. The Tungchiu-Milin shear zone is the western boundary of the syntaxes. The structural reconstruction revealed D1 left-lateral transpression and formed the Isoclinal fold (attitude of fold axis plane, NE30~50°；N60~70°), D2 sub-horizontal thrusting from northwestern to southeastern and formed the Recumbent fold (attitude of fold axis plane, NE20~70°；N5~40°), D3 right-lateral transtension and formed the upright fold (attitude of fold axis plane, NE23~45°；N65~85°), the last one D4 due to the last brittle deformation of structure deformation event and showed last left-lateral strike-slip fault and right-lateral strike-slip fault. The geochronology correlation revealed the right-lateral shearing event to be between 20.1±0.2~11.4±0.1 Ma, which is older than that suggested by previous studies. The biotite plateau ages distributed from south to north range from 20.1±0.2Ma to 11.2±0.0Ma with a distinct pattern of younging northward along the shear zone.

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