https://scholars.lib.ntu.edu.tw/handle/123456789/37506
標題: | CREATE III: 東亞地函動力及板塊互動研究─藏東與鄰近地區斷層帶剪切作用研究(1/3) | 作者: | 羅清華 | 關鍵字: | 40Ar/39Ar;Dien Bien Phu Fault;Vietnam;印度-歐亞板塊碰撞運動;氬同位素定年學 | 公開日期: | 2004 | 出版社: | 臺北市:國立臺灣大學地質科學系暨研究所 | 摘要: | 本年度計畫利用氬氬定年法分析越南奠邊府斷層內之變形花崗岩,探討斷層之活 動歷史,及其在印度-歐亞板塊碰撞過程中地殼變形所扮演之角色。研究成果已於2003 年Fall meeting of the American Geophysical Union、中國地質學會年會等學術會議發表, 目前正撰寫期刊論文,其重要內容分別摘錄於下。 位於北越,將華南與中南半島間馬河縫合帶錯移數十公里的奠邊府斷層帶,長久 以來被視為受印歐碰撞產生之新生代板塊脫逸作用影響所形成的第三紀剪切帶。然而, 在缺乏良好定年材料的情況下,奠邊府斷層真正的活動歷史始終處於一個暧昧不明的情 況。本研究利用於奠邊府地區採得的片岩與糜稜狀花岡岩,及於華南地塊邊緣花岡岩帶 採得之未變形的花岡岩樣本,進行氬氬定年分析,以求能一窺奠邊府斷層帶活動時間的 相關資訊。 目前初步的研究結果顯示,利用階段加溫擷取未變形的花岡岩樣本內的鉀長石、 角閃石及黑雲母內含的氬氣,得到的坦原年代範圍約落於201-272Ma 之間,反應了印 支期中南半島向北隱沒產生的弧後火成活動;而利用單礦物燒熔法進行片岩及變形花岡 岩內黑、白雲母的定年,則得到205-184Ma 的區間,指出奠邊府斷層活動可能早在早 中生代隱沒作用結束後即已發生,而非是脫逸作用的產物。 The Song Ma belt, a suture zone located in between the South China and Indochina blocks, was offset by the Dien Bien Phu Fault (DBF) in northern Vietnam. Previous studies 2 suggested that the Dien Bien Phu Fault is one of the Tertiary shear zones, resulted from the Cenozoic extrusion tectonics due to the India-Eurasia collision. However, the timing of the movement along DBF is remained unknown due to lacking of age constraints. In order to reveal the movement age of DBF, schist samples from DBF and granites from the granite belt along the northern margin of the Indochina block, were dated by 40Ar-39Ar method in the present study. K-feldspar, hornblende, and biotite samples form granite plutons yield very different age ranges between the opposite sides of DBF. Hornblende separates from an undeformed granite, on the west side, exhibit plateau dates at around 277Ma. This age appears to be older than the early Triassic collision age (~245Ma) registered in the Song Ma suture zone (Lepvrier et al., 1997), indicating that arc magmatism may have actively occurred on the northern margin of the Indochina block, before the early Triassic collision. On the other hand, deformed granitic samples from the east side of DBF exhibit plateau ages of 218-230 Ma which are younger than the collision age, which are close to the age range previously reported for the Truong Son belt (a shear belt formed during or after the early Triassic Indochina-South China collision event). Surprisingly, biotites and muscovites extracted from the schists collected from DBF, also show similar 40Ar/39Ar ages ranging form 192Ma to 211Ma, which are close to the deformation age of the Truong Son belt. This indicates that the Dien Bien Phu Fault and the Truong Son Fault may have formed a conjugate fault system, activated by the early Triassic collision event during the Indosinian Orogeny. Whether the Dien Bien Phu Fault has once been reactivated by the Tertiary India-Eurasia collision, or not? This question is still waiting for answer. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/11839 | 其他識別: | 922116M002006 | Rights: | 國立臺灣大學地質科學系暨研究所 |
顯示於: | 地質科學系 |
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922116M002006.pdf | 90.03 kB | Adobe PDF | 檢視/開啟 |
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