新生代中部地殼流動與丹巴背斜隆起之數值模擬:以鋯石和磷灰石核飛跡年代制約

Numerical Simulation of Middle Crustal Flow And Formation of The Danba Anticline: Constrained by Apatite And Zircon Fission Track Ages

黃承加(CHENG-JIA HUANG)

指導教授 ： 王維豪

國立中正大學/理學院/地球與環境科學系地震研究所/碩士(2016年)

摘要

本研究應用有限差分方法，模擬丹巴複背斜的熱演化史並探討其成因。丹巴複背斜位於四川盆地西北方，松潘甘孜造山帶內。由於其背斜軸與地表壓縮方向呈小角度相交，因此該背斜並非由單純的拱彎作用所隆起。我們懷疑丹巴背斜的隆起與中部地殼流動有關。由於GPS的速度場在四川盆地與西藏的交界處產生急遽的變化，因此我們認為較韌性的中部地殼是沿著較剛性的四川盆地邊界向東北及西南方向分流，與上部地殼運動方向並不一致。本研究以角隅流的流動模型估計出丹巴背斜附近的中部地殼流動方向與速度，並發現中部地殼流動方向與丹巴背斜軸幾乎正交，因此我們認為該背斜是由中部地殼注入拱起所隆起。我們利用理論滑脫褶皺的速度場以及熱擴散方程計算出丹巴複背斜熱運動史，並且計算出磷灰石及鋯石的理論核飛跡年代，並與實際的核飛跡資料比對。根據研究結果顯示，在新生代時期(<25 Ma)的中部地殼流動速度是逐漸增加的，且中部地殼渠道厚度約為14公里，褶皺兩翼的寬度為140公里，背斜軸的理論剝蝕量約為19公里，與利用在中生代滑脫面上地質壓力計所估算出的剝蝕量17~26公里，大致相符合。

關鍵字

四川丹巴 ； 核飛跡 ； 數值模擬

並列摘要

We applied a finite difference method to simulate the thermal evolution of the Danba Anticline, Sichuan, China. The anticline is located to the northwest of the Sichuan Basin within the Songpan-Ganzi orogen. Because the fold axis of the anticline is subparallel to the direction of the surface compression, buckling is unlikely the mechanism responsible for the growth of the Danba Anticline. We suspect that the formation of the Danba Anticline in Cenozonic period may be related to the middle crustal flow. The sharp change in GPS velocity field near the Sichuan Basin implies that the ductile middle crust materials flow around the relatively rigid Sichuan Basin. As a result, the velocity fields between the upper crust and middle crust are different. In this study, we employed the corner flow model to estimate the velocity and direction of middle crust flow in Danba area. We found that the direction of the middle crust flow is nearly perpendicular to the fold axis of the Danba Anticline. This finding confirms that the growth of the Danba Anticline may result from injection of the middle crust materials, which are driven by the uprising Tibet, beneath the Danba Anticline. We used the apatite and zircon fission track ages across the Danba Anticline as our model constraints. With that we can simulate the thermal history of the Danba Anticline by solving thermo-kinematic equations for detachment folding and calculated the corresponding fission track ages. According to our results, the velocity of middle crust increased with time in Cenozoic (<25Ma), and the thickness of the middle crust channel is about 14 km, the width of the anticline is about 140 km, and the amount of exhumation in the hinge of the Danba Anticline is about 19 km, which agrees with the amount of exhumation (17~26 km) estimated by geobarometry upon a Mesozoic decollement.

並列關鍵字

Danba ； Fission track ； Numerical simulation

參考文獻

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