https://scholars.lib.ntu.edu.tw/handle/123456789/45100
標題: | 斜向碰撞板塊前緣之下部岩圈動力流場側向變化 | 作者: | 喬凌雲 | 關鍵字: | 對流擾動;板塊聚合;台灣造山運動;convective instability;oblique plate convergence;Taiwan orogeny | 公開日期: | 2002 | 出版社: | 臺北市:國立臺灣大學海洋研究所 | 摘要: | 台灣造山運動的研究一向主要依賴地表淺部 地質以及反射震測。「薄層刮積模型」則是據以解 釋觀測資料以及嘗試瞭解造山之理論架構。近年 來,根據若干較能反應深部構造之地球物理觀測則 顯示深達岩圈範圍之機制似乎亦積極參與。但是發 展已趨完整的「薄層刮積模型」至少可以提供半定 量的描述與預測,而岩圈模型則尚處於揣度,屹未 建立物理模型。其中尤以岩圈下段之地幔中可能啟 動之動力流場之角色不易評估。事實上,板塊碰撞 前緣之可能地幔動力過程已成為甚受國際地體動 力學界矚目之研究課題。對於許多著名之板塊碰撞 區,已有重要的研究工作嘗試建構簡化之二維理論 模型以據以解釋不易以傳統地質模型概括之若干 地物觀測。這些模型在基本觀念上則主要考慮可能 發生在地幔岩圈(mantle lithosphere)中簡化之雷力 ▁泰勒不穩定(Rayleigh-Taylor instability), 或比較完整考慮溫度結構之對流不穩定 (convective instability)。根據這些模型,發生 於碰撞板塊前緣之下部岩圈不穩定將導致明顯的 地球物理信號,包括剪波的非均向性以及岩圈深處 之波速異常構造。對於台灣造山而言,類似的觀察 已有文獻報導。因此對於本構造區岩圈深度角色之 理論架構有必要探索。我們發展三維非牛頓對流系 統數值模型來探討歐亞岩圈深處由對流不穩定所 帶動的可能變形,並討論據以解釋地球物理觀測的 可能。我們發現,本構造區內從北而南,在數百公 里波長尺度範圍內板塊碰撞強度以致於地幔岩圈 內之對流不穩定強度有明顯的變化,理論上,在相 對而言甚短的空間及時間尺度內這種顯著側向變 化極可能是銜接南北不同極性之隱沒在上地幔之 轉圜。本研究的主要最終目的是希望對於台灣造山 運動研究,以及其他類似斜向架構之造山活動提供 新的視野。 Taiwan orogeny has been interpreted in terms of the “thin-skinned tectonics” model based on observations of surface geology and shallow seismic reflection profiles. It has been challenged that deep process in the lithospheric depth might be actively involved based on deep geophysical observations. The potential involvement of dynamic flow of the mantle lithosphere further complicates the construction of a feasible theoretical model. In fact, dynamic processes during plate collision have been a research topic of great interest in recent years. Conceptual models constructed to account for a suit of geophysical observations that are otherwise un-comprehensible based on geological models in several noted collision zones have been devised. The physics behind these models concern mainly the Rayleigh-Taylor instability, or the more general convective instability, if the thermal effect is incorporated into the analysis of the instability, occurring within the mantle lithosphere. It has been shown that these types of lithospheric instability result in various geophysical manifestations, including seismogenic structure, S-wave anisotropy and seismic velocity anomaly in the deep lithosphere. For the Taiwan orogeny, there have already been documented signatures of this type that demands the exploration of how such lithosphere-wise process might be adopted in the Taiwan tectonic region. We build the three-dimensional, thermal-mechanical, numerical modeling tool to explore the theoretical aspects of the potential convective instability within the deep Eurasia lithosphere, and the capability of consistently interpreting geophysical observations. It is found that due to the significant lateral variation of the rigors of the plate collision within a wavelength of only a few hundred kilometers form north to south, convective instability within the relatively short wavelength and timescale is not only very likely to occur but also may serve as the critical transition in between the two subduction systems to the north and south that has flipping polarity. Our ultimate goal in this study is to shed insights on the theoretical framework of the Taiwan Orogeny and other orogeny with similar oblique configurations. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/14798 | 其他識別: | 902611M002002 | Rights: | 國立臺灣大學海洋研究所 |
顯示於: | 海洋研究所 |
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