碩士 / 國立臺灣師範大學 / 地球科學系 / 105 / Orogeny refers to the event of making mountain belt. During orogeny, a mountain belt experienced different orogenic stages, including syn-orogeny, post-orogeny, and an-orogeny, with various conditions of temperature, pressure, geochemical signature, stress and fluid pressure. Researchers usually expect to observe different stress regimes corresponding to different orogenic stages. So far, no document had reported the phenomena of stress evolution from reverse faulting via strike-slip faulting to normal faulting stress regimes in stages of syn-orogenic, post-orogenic and an-orogenic, respectively.
However, Study of dikes from Kinmen Island can shed light to show the stress evolution of orogeny. The Kinmen Island, located in the southeastern continental margin of Mainland China, cropped out the middle-lower continental crust, which was experienced different deformation and metamorphism during Late Yenshanian Orogeny. Based on previous studies of geochemistry, geochronology, and P-T condition, different types of dikes are identified. They are syn-orogenic dikes of amphibolite (138-132Ma), post-orogenic dikes of pegmatite and aplite (110-100Ma), and an-orogenic dike of gabbro (94-76Ma).
The mechanism of dike development is when magma pressure overcomes the minimum stress, magma can create the intrusive dike perpendicular with the minimum stress. By investigating the distribution and attitude of dikes with different lithologies, stress orientation corresponding to the different orogenic stage can be estimated. With the constraint of rock strength, mean stress from geobarometer and vertical stress in each stage, the magnitude of stress field and magma pressure for each stage can be further calculated.
This research restructured crustal dynamics evolution during Late Yanshanian Orogeny by measuring the attitude of dike around Kinman and Leiyu island.
(1) Compared with orogenic stage and crustal stress regime: syn-orogeny was reverse faulting stress regime, post-orogeny and an-orogeny were normal faulting stress regime. But, the value of post-orogenic stage stress field was strike-slip faulting stress regime.
(2) As the syn-orogenic stage, amphibolite and tonalite dike intrusion appeared as low dip angle, which reflected that reverse faulting regime and horizontal maximum stress direction in E-W orientation. This orientation was oblique the orientation of mountain belt, NW-SE. The stress ratio was 0.54±0.18. The fluid ratio was 0.59. The intrusive depth was 24.9km. These result reflected ellipsoid reverse faulting stress regime. The geothermal gradient was 30.1℃/km. Dikes formed in the environment, which fluid pressure were higher than lithostatic pressure. Integrate with outcrop result, the stress regime would change to strike-slip faulting stress regime or normal faulting stress regime.
(3)As the post-orogenic stage, this study uses the attitude of pegmatite and aplite dike. Geobarometer uses Al-amp geobarometer inland, SE China. The str ess ratio was 0.69±0.14. The fluid ratio was 1.02. The intrusive depth was 5.5km. These result reflected plate normal faulting stress regime and horizontal maximum stress direction in NW-SE. The geothermal gradient was 93.5℃/km. Dikes formed in the environment, which fluid pressure was higher than lithostatic pressure.
(4)Finally, an-orogenic dike intrusion struck NE-SW with steep dip angle direction, which reflected that normal faulting regime and NE-SW horizontal maximum stress direction. The stress ratio was 0.68±0.08. The fluid ratio was 0.72 or 0.17. The intrusive depth was 4.5km. The geothermal gradient was 77.7℃/km. These result reflected plate normal faulting stress regime. Dikes formed in the environment, which fluid pressure were lower than lithostatic pressure.
(5)The vertical stress variation, a.k.a. erosion velocity ,in Kinmen area during Late Yanshanian Orogeny, syn-orogenic stage to post-orogenic stage erosion velocity was 0.82-0.49mm/yr, and post-orogenic stage to an-orogenic stage was 0.35-0.04mm/yr.
| Identifer | oai:union.ndltd.org:TW/105NTNU5135008 |
| Date | January 2017 |
| Creators | Chen, Ping-Chuan, 陳炳權 |
| Contributors | Yeh, En-Chao, 葉恩肇 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 103 |
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