綜合前人構造背景與本研究之結果 (表 4.1)，變形期 Dn-1形成東 北-西南走向傾向南之偃臥褶皺，此構造所對應的構造背景為泛非洲 時期剛果地塊、西非地塊與東薩哈拉地塊之拼合，變質發生於角閃岩 相，且從偃臥褶皺區域樣本之應變量 Rs與顯微薄片比較所得其變質 度均大於其他區域可獲得證實；Dn形成東北-西南走向平行剪切帶之 直立褶皺，此構造型態與大西洋張裂模式相符，也為剪切帶活動的時
期，從 Sn-1葉理組成礦物推論溫壓條件為綠色片岩相，糜稜岩帶中只 觀察到此 Dn變形期，因強烈的變形作用使早期之構造皆被 Sn變形而 難以判斷；Dn+1為接近地表之脆性變形事件。本研究光礦薄片觀察與 光譜分析之指標礦物顯示變質條件在角閃岩相至綠色片岩相，非同剪 切受加熱形成的高溫變質岩。
表 4.1 變形期之構造、構造事件與溫壓條件統整表
4.2 應變分析應變分析應變分析應變分析
Rf/φ 分析顯示石榴石角閃片麻岩之應變大，因其位於偃臥褶 皺區域，經歷過早期較高度之變質；而糜稜岩之 XZ 面 Rs 亦明顯 較角閃片麻岩與壓碎岩大，因糜稜岩均受過強烈之變形作用；分
析結果中角閃片麻岩之 XZ 面與 YZ 面差異小，而其 XZ 面 Rs值 樣本為初糜稜岩(protomylonite)，雖然其 Rf/φ 計算結果於合理解 釋範圍內且應變率大，但應變軸位態之重建則不如超糜稜岩 (ultramylonite) 10CC03B 理想，因初糜稜岩中雖然礦物呈明顯之 橢圓顆粒，其顆粒間互相鑲嵌方向不如超糜稜岩中礦物顆粒皆被 變形至葉理方向排列，因此應變三軸重建法於初糜稜岩中之誤差 較大。
圖 4.1 應變分析結果重建之 XY 面赤平投影圖。
4.3 主應力方向主應力方向主應力方向主應力方向與板塊構造之意義與板塊構造之意義與板塊構造之意義與板塊構造之意義
本研究中 Dn-1重建之應變橢球主應力方向為北北西-南南東，與 泛非洲時期東撒哈拉地塊向南碰撞形成逆衝構造之背景符合，此最大 應變軸顯示在東北-西南向之伸張。TBSZ 與糜稜岩帶皆為東北-西南 走向傾向北 (圖 4.2)，由應變橢球所得之壓縮方向為北北西-南南東 至西北-東南向，而最大應變軸於東北-西南向並傾向南，其應力綜合 之結果導致 TBSZ 運動方向為平移伸張，此與大西洋張裂模式所得之 應變形式相符 (Binks and Fairhead, 1992; Fairhead, 1988)，因南大西洋 與赤道大西洋非同時張裂，導致 TBSZ 之左移走滑運動。
圖 4.2 應變橢球位置圖。
第 第
第 第5章 章 章 章 結論 結論 結論 結論
本研究以構造重建、應變分析、岩石學與顯微構造分析釐清 CASZ 地區的構造發展史至少經歷三期事件：Dn-1形成東北-西南走向 傾向南之偃臥褶皺，其為泛非洲時期地塊於西北喀麥隆地區之拼合所 形成，而此變質事件發生於角閃岩相，與同剪切花崗岩形成之高溫變 質岩不相符，因此鈾-鉛鋯石定年顯示的年代也非剪切帶的活動時間，
而是早於剪切發生的年代；Dn 為此區域最顯著的變形期，形成東北-西南走向傾向北的直立褶皺，為剪切帶發生的事件，剪切帶與大西洋 張裂模式中之構造形式相符，而重建之應變橢圓顯示主應力方向在北 北西-南南東至西北-東南向，剪切帶與應力之分布指出在 TBSZ 的應 變模式為左移伸張，其溫壓條件為綠色片岩相；最後一期為 Dn+1脆性 變形事件發生於近地表處。
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