Coseismic high-pressure metamorphism: Observations and implications
文献类型：期刊论文
| 作者 | Yang Jianjun |
| 刊名 | ACTA PETROLOGICA SINICA
 |
| 出版日期 | 2015-09-01 |
| 卷号 | 31期号:9页码:2465-2476 |
| 关键词 | High-pressure metamorphism Quenching Earthquake Mechanical model Transformation mechanism |
| 英文摘要 | The last six decades witnessed a continued debate between the hypotheses of subduction-exhumation and tectonic overpressure for the formation of high-pressure metamorphic rocks in orogenic belts. The currently widely held viewpoint is that crustal rocks were subducted to mantle depths, where they were subjected to high-pressure metamorphism and were then exhumed back in the crust. Although blueschist facies metamorphism has been recognized to be related to thrust faults and the metamorphic pressure increases towards the fault planes, and eclogite pseudotachylyte indicating fossil earthquake was found 20 years ago, it is generally considered that the role of faults or shear zones is to introduce fluid that enhances metamorphic reactions at depths. Recently Su et al. (2006) have demonstrated that quartz can transform rapidly to coesite at a pressure in the stability of coesite after being amorphized. They suggest that quartz may transform to coesite during a large earthquake in the crust and deep subduction may not be needed for high-pressure metamorphism to take place. The present review introduces the recent work by the writer and co-workers on some eclogite facies breccia and cataclasite dykes at Yangkou in the Chinese Su-Lu ultrahigh-pressure metamorphic belt, providing geological evidence for this argument. It is pointed out that intergranular coesite occurs only in the fragments but not in the matrix of the eclogite breccia; it can only be preserved by rapid decompression and cooling at the timescale of a seismic event. The eclogite facies cataclasite dykes also record transient higher pressure and temperature relative to the host metagabbro. The micropoikilitic garnet containing numerous high-pressure mineral inclusions, the kyanite needles, and the 'microgranites' in both types of rock are interpreted to be the results of quenching of seismogenic melts or amorphous phases. They indicate no further growth of the high-pressure minerals occurred after the seismic events. This is in contrast to the general idea that high-pressure crystallization occurs only in subducted dry rocks when fluid becomes available, in which continuous crystallization afterwards will erase the quenching textures. Sparse chromite particles in the cataclasite dykes indicate mechanical mixing between the metabasic rocks and the nearby ultramafic rocks during seismic faulting. The Cr-rich eclogite minerals around the chromite grains are unequivocal evidence for transient high-pressure crystallization. The fact that the cataclasite dykes are less hydrated than their host rocks implies the key role of stress rather than fluid during high-pressure phase transformation. The timescale of formation of these high-pressure rocks are too short for the rocks to complete the subduction-exhumation processes. They are more likely the results of eclogitization of a gabbro under high-pressures given rise to by seismic waves in the crust. It is noted that the necessary high pressure cannot be derived from the currently used mechanical models for earthquakes. This is simply because high-pressure phase transformation has not been taken into account in developing the models. It is emphasized that hypotheses and theories are to be tested by observations but not vice versa. The available data show that flash melting and amorphization are the probable mechanisms for transient high-pressure metamorphism. |
| 语种 | 英语 |
| WOS记录号 | WOS:000362800400001 |
| 源URL | [http://ir.iggcas.ac.cn/handle/132A11/62212]  |
| 专题 | 地质与地球物理研究所_岩石圈演化国家重点实验室 |
| 作者单位 | Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, Beijing 100029, Peoples R China |
| 推荐引用方式 GB/T 7714 | Yang Jianjun. Coseismic high-pressure metamorphism: Observations and implications[J]. ACTA PETROLOGICA SINICA,2015,31(9):2465-2476. |
| APA | Yang Jianjun.(2015).Coseismic high-pressure metamorphism: Observations and implications.ACTA PETROLOGICA SINICA,31(9),2465-2476. |
| MLA | Yang Jianjun."Coseismic high-pressure metamorphism: Observations and implications".ACTA PETROLOGICA SINICA 31.9(2015):2465-2476. |
入库方式： OAI收割
来源：地质与地球物理研究所
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