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研究生:吳詩敏
論文名稱:非洲中部剪切帶岩石學分析與構造史之研究
論文名稱(外文):Petrographic Analysis and Structural History of Central African Shear Zone
指導教授:李通藝李通藝引用關係葉孟宛
學位類別:碩士
校院名稱:國立臺灣師範大學
系所名稱:地球科學系
學門:自然科學學門
學類:地球科學學類
論文種類:學術論文
論文出版年:2011
畢業學年度:100
語文別:中文
論文頁數:66
中文關鍵詞:非洲中部剪切帶泛非洲顯微構造應變分析岩石學Rf/φ分析法應變橢球福林氏圖
外文關鍵詞:Central African Shear ZonePan-Africanmicrostructurestrain analysispetrographyRf/φ methodstrain ellipsoidFlinn diagram
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非洲中部剪切帶 (Central African Shear Zone,CASZ) 為一東北-西南走向從喀麥隆至查德向東北延伸至蘇丹之剪切帶,於喀麥隆地區分為北偏東70 度之中喀麥隆剪切帶 (Central Cameroon Shear Zone,CCSZ) 與北偏東50 度之 Tcholliré-Banyo 剪切帶(Tcholliré-Banyo Shear Zone,TBSZ),且在大陸漂移前延伸至巴西東北部。而板塊構造背景可追溯至泛非洲時期,剛果地塊、西非地塊及東撒哈拉地塊之拼合。部分學者提出CASZ 有同構造之花岡岩侵入,並以鈾-鉛鋯石定年640 至557 Ma 之結果為花崗岩與剪切帶形成之時間;另一部分研究則以沿CASZ 有裂谷盆地分布與其打開的時間為大西洋張裂之時,進而探討130 Ma 至84Ma 之板塊構造演化,認為CASZ 之形成與大西洋張裂相關,而同剪切花崗岩中常含有高溫變質岩,因此本研究於TBSZ 系統以顯微岩石學之分析來了解其礦物相,並以指標礦物
推測其變質事件發生之溫度條件;並根據野外觀察、顯微構造及應變分析釐清整個構造演化歷史及應力分布情況,歸納此地區的變形史可分為至少三期:早期的為Dn-1,形成一東北-西南走向,低角度向東南傾之偃臥褶皺,葉理Sn-1 組成礦物為角閃石+黑雲母+石榴子石+鈉長石,此礦物相為角閃岩相之變質條件,而Dn-1 應為泛非洲時期東撒哈拉地塊由北向南碰撞變形造成之逆衝nappe;Dn 形成東北-西南走向,近垂直傾向西北走向平行剪切帶之直立褶皺,顯微影像與電子影像分析顯示Sn 葉理礦物相為黑雲母+綠泥石+鉀長石+榍石,此礦物成分指出溫壓條件為綠色片岩相,而此變形期為CASZ 左移剪切的時期,由重建應變橢球顯示主應力方向在北北西-南南東至西北-東南向,應
變模式為左移伸張;Dn+1 為脆性變形事件,發生於接近地表的低溫條件。
The N70˚E trending Central Cameroon shear zone (CCSZ) and the N50˚E trending Tcholliré-Banyo Shear zone (TBSZ) are the southwest extension of the Central African Shear Zone (CASZ). The evolution of CASZ is interpreted in two different models. The activation of the CASZ was considered to relate to the evolution of the Western Gondwana. Many researchers proposed the emplacement of these plutons are syn-kinematic, with U-Pb zircon ages of 640-580 Ma for various shear zone parallel batholith. The activation of the CASZ is due to amalgamation of the Congo craton to the West Africa craton and the Eastern Saharan Block. However, there are many rift basins along CASZ. The formations of these rift systems are associated with the opening of Atlantic Ocean. CASZ can also be activated or reactivated due to the opening of the southern Atlantic Ocean during 130-84 Ma. There are existences of high-temperature metamorphic rocks due to shearing heating in syn-shearing granite. In order to understand the metamorphic conditions, micropetrography helps to indicate the mineral assemblage and, which helps to delineate the temperature comdition of metamorphism. With new field observation, microstructural data and strain analysis, the tectonic history of TBSZ can be devided into at least three events. The earlier event Dn-1 formed recumbent folds with NE-SW striking, SE dipping fold axial planes. The mineral assemblage of Sn-1 is hornblend ± garnet ± biotite ± Albite suggested that P-T conditions in under middle Amphibolite facies. Dn-1 is result from the amalgamation of the Congo craton and the Eastern Saharan Block in N-S direction by the analysis of structure and strain. Dn event formed tight upright folds with NE-SW striking subvertical axial planes and parallel to CASZ. Sn with mineral assemblage Biotite ± Chlorite ± Sphene ± K-feldspar form under greenschist facies and left-lateral shearing. By reconstruction of strain ellipsoids, the main stress direction is NNW-SSE to NW-SE during Dn with transtension strain pattern . Dn+1 is brittle deformation close to surface by low temperature.
摘要 i
Abstract iv
目錄 vi
圖目錄 ix
表目錄 xiv
第1章 緒論 1
1.1 中非剪切帶簡介 1
1.2 喀麥隆構造單位 4
1.2.1 泛非洲褶皺帶 4
1.2.2 裂谷盆地 7
1.3 喀麥隆的構造發展 8
1.3.1 地殼增厚 8
1.3.2 左移剪切運動 9
1.3.3 右移剪切事件 9
1.4 中非剪切帶之發展 10
1.4.1 泛非洲 (Pan-African) 運動時期 11
1.4.2 大西洋張裂模式 13
1.5 研究動機與目的 17
第2章 研究材料與方法 19
2.1 研究材料 19
2.2 研究方法 21
2.2.1 構造分析流程 21
2.2.2 應變分析法 23
2.2.2.1 應變分析法- Rf/φ分析法 23
2.2.2.2 福林氏分析法 (Flinn method) 27
2.2.2.3 應變橢球分析法 28
2.2.3 顯微岩石學分析法 30
2.2.3.1 掃描式電子顯微鏡 (Scanning Electron Microscope;SEM) 31
2.2.3.2 能量分散式光譜分析(Energy Dispersive System;EDS) 32
第3章 結果與分析 34
3.1 重建構造史 34
3.1.1 TBSZ 34
3.1.2 糜稜岩帶 39
3.2 應變分析 40
3.2.1 TBSZ 40
3.2.1 糜稜岩帶 46
3.3 岩石學分析 47
3.3.1 TBSZ 51
3.3.2 糜稜岩帶 53
第4章 討論 56
4.1 構造發展 56
4.2 應變分析 57
4.3 主應力方向與板塊構造之意義 59
第5章 結論 61
參考文獻 62
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