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姓名 張簡婉晴(Wan-Ching Chang-Chien) 查詢紙本館藏 畢業系所 地球科學學系 論文名稱 青藏高原東緣區域之熱變質紀錄與構造演化探討
(Preliminary thermal metamorphic constraints on tectonic evolution in the eastern margin of Tibetan Plateau)相關論文 檔案 [Endnote RIS 格式] [Bibtex 格式] [相關文章] [文章引用] [完整記錄] [館藏目錄] 至系統瀏覽論文 ( 永不開放) 摘要(中) 青藏高原為世界上海拔最高的區域,由歐亞板塊及印度板塊碰撞所產生,其東緣—龍門山—為高原最陡峭的邊界,在2008年及2013年發生的汶川地震和廬山地震,揭示出此邊界仍為一構造活動區域,使龍門山成為研究青藏高原演化歷史的關鍵區域。青藏高原的演化歷史較複雜,經歷了兩期的造山運動,分別為三疊紀的印支期造山及新生代的喜山期造山。雖然其構造演化始於三疊紀的印支期造山運動,但主要的增厚是發生在喜山期造山時期,而前人對此階段的演化模型具有非常大的爭議。因此,對該區域第三紀前構造演化的定量限制對於描述喜馬拉雅地球動力學至關重要,只有在明確了解印支期的演化歷史,並將其去除後,才能更進一步解析青藏高原在喜山期的演化歷史。
本研究在青藏高原東緣,沿多條西北—東南方向 (垂直龍門山構造帶) 路線及在彭灌雜岩南方,以間隔3公里採集50個樣本,並利用碳質物拉曼光譜 (Raman spectroscopy of carbonaceous material, RSCM) 地質溫度計來測量岩石在深埋及抬升變形過程中所經歷過的最高溫度 (RSCM-T)。經過實驗分析後發現,RSCM-T的分布與火成侵入岩體和地層年代之間皆無相關性,排除RSCM-T受到接觸變質或盆地深埋加熱機制影響的可能性,在進一步和現有RSCM-T數據整合後確認其分布是受到構造活動所控制。並透過熱定年數據的約束了解到此最大變質是發生在印支期造山運動,其分布受到深埋機制差異的影響,喜山期的區域性掘升速率差異仍不足以改變此狀況。
綜合實驗結果及推論,本研究嘗試提出青藏高原東緣之演化歷史:在三疊紀初期,松潘—甘孜盆地有三疊紀複理石的堆積,並由於羌塘地塊的北移導致海洋開始關閉,造成其隱沒、增積;至三疊紀中期,部分物質受到底部加積作用被帶入造山楔下方深部 (13~19 km),並在此過程中受到褶皺變形、達到最高溫度;接著由於雙軌構造的發育而掘升進入增積岩體之中,在早侏儸紀時期被掘升至地下10~14公里深處;最終在新生代喜山期造山運動時,由於青藏高原大幅度的縮短、抬升,使得地層受到變形並掘升至地表,形成如今的樣貌。
在松潘—甘孜與龍門山的邊界部分,為解釋汶川斷層以西之高變質度 (RSCM-T > 400°C) 被動大陸邊緣沉積物的存在,本研究提出以下模型:在古特提斯洋隱沒的過程中,由於海洋由西向東關閉,造成增積楔由西向東增厚、輸送,在海陸邊界形成向東逆衝的底脫面,而底脫面的向東遷移 (migrate),導致原先被構造深埋的被動大陸邊緣沉積物受底部加積作用沿底脫面掘升、出露至地表。此底脫面最終被汶川斷層所繼承,因此在汶川斷層以西之志留紀至二疊紀被動大陸邊緣地層擁有較高度的變質 (RSCM-T > 400°C),與受到底部加積作用之三疊紀複理石有連續性的分布。摘要(英) The Tibetan Plateau, resulting from the active Eurasian-India collision, presents a major scientific challenge in understanding its growth and propagation. One key region is the Longmen Shan mountain belt in western Sichuan, which forms the steepest margin of the plateau and has been active as demonstrated by the Mw 7.9 Wenchuan (2008) and Mw 6.6 Lushan (2013) earthquakes. Tectonic history of the Longmen Shan belt and the neighboring Songpan-Garze terrane, however, began in the Triassic Indosinian orogenesis, which complicates the geologic records. But the major thickening of Tibet was formed in Himalayan orogenesis. Therefore, quantitative constraints on the pre-Tertiary tectonic evolution of the region are crucial in delineating Himalayan geodynamics.
In this study, 50 samples were collected in eastern margin of Tibetan Plateau along several transects in NW-SE direction, perpendicular to the structural grain of the Longmen Shan and its border with the neighboring Songpan-Garze terrane. The raman spectroscopy of carbonaceous material (RSCM) geothermometer is applied to the samples to obtain their peak metamorphic states. The distribution of the peak temperatures from RSCM analyses (RSCM-T) is not correlated to later igneous intrusions, ruling out significant contact metamorphism overprint. And there is no apparent geothermal gradient between RSCM-T and stratigraphy, showing that the strata were affected by peak thermal event after basin diagenesis. Together with existing data, it is confirmed that its distribution is controlled by tectonic activities. Furthermore, through the constraints from thermochronometers data, it can be certain that peak thermal metamorphism documented as RSCM-T occurred during the Indosinian orogeny, and its distribution was affected by the different mechanism of wedge growth (frontal/basal accretion). The difference of regional exhumation rate in the Himalayan orogeny is still not enough to change this situation.
The evolution history of eastern Tibet Plateau inferred from the result shows that the Triassic flysch was been accreted due to the closure of Paleotethys. Some of the flysch rocks were underplated under the rear part of the orogenic wedge at around 13-19 km depth, at the same time acquired their peak thermal metamorphic state in lower-middle Triassic. The stacking of the basal accreted duplex system led the thrust slices been exhumed within the wedge at depth of 10-14 km during early Jurassic. Finally, during the Cenozoic Himalayan orogeny, due to the substantial shortening and uplift of the Tibet Plateau, the metamorphosed flysch rocks were exhumed to the surface.
At the boundary between Songpan-Garze and Longmen Shan: the oblique subduction of the Paleotethys, causing the accretionary wedge to thicken and transport to east, forming an eastward thrust decollement at the boundary. And the eastern migration of the decollement, caused the passive margin sediments which has been tectonic buried to be exhumed by basal accretion and exposed to the surface along the decollement. This decollement was eventually inherited by the Wenchuan Fault. Therefore, the Silurian to Permian passive margin sediment west of the Wenchuan fault has high degree of metamorphism (RSCM-T> 400°C), having continuous RSCM-T with Triassic flysch.關鍵字(中) ★ 青藏高原
★ 龍門山
★ 碳質物拉曼光譜關鍵字(英) ★ Tibetan Plateau
★ Longmen Shan
★ RSCM geothermometer論文目次 摘要 i
Abstract iii
致謝 v
目錄 vi
圖目錄 viii
表目錄 xi
一、 前言 1
1-1 研究動機與目的 1
1-2 論文架構 2
二、 地質背景 3
2-1 青藏高原大地構造分區 3
2-2 本研究區域之地層與構造 4
2-3 青藏高原之地體構造演化 10
2-3-1 印支期演化模型 13
2-3-2 喜山期演化模型 14
2-4 變質度與熱定年之前人研究 23
2-4-1 熱變質度研究 23
2-4-2 熱定年研究 26
三、 方法 32
3-1 野外觀察與測量 32
3-1-1 中視尺度構造 32
3-2 碳質物拉曼光譜 34
3-2-1 碳質物拉曼光譜的組成及特徵 35
3-2-2 碳質物拉曼光譜的應用 37
3-2-3 樣本製備 39
3-2-4 碳質物拉曼光譜的測量 41
3-3 薄片觀察分析 43
3-3-1 礦物組成分析 43
3-3-2 岩石組構分析 44
四、 結果 46
4-1 採樣點位置 46
4-2 野外中視尺度構造觀察 48
4-3 拉曼光譜分析結果 52
4-4 薄片觀察分析結果 61
五、 討論 64
5-1 影響RSCM-T分布之因素探討 64
5-1-1 RSCM-T分布與火成侵入岩體之關聯性 65
5-1-2 RSCM-T分布與地層之關聯性 67
5-1-3 RSCM-T分布與大地構造之關聯性 69
5-2 RSCM-T形成之年代 73
5-3 RSCM-T分布與地體構造演化之關聯性 75
5-3-1 深埋程度的差異 77
5-3-2 掘升速率的不同 79
5-4 地體構造演化模型 80
六、 結論 85
參考文獻 87
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吳俁(2018)從台灣中部板岩帶之熱變質紀錄探討台灣活動造山帶構造演化,國立臺灣大學地質科學研究所碩士論文,共103頁。指導教授 陳致同(Chih-Tung Chen) 審核日期 2020-8-11 推文 facebook plurk twitter funp google live udn HD myshare reddit netvibes friend youpush delicious baidu 網路書籤 Google bookmarks del.icio.us hemidemi myshare