Exhumation of subducted oceanic crust: Key issues and discussion

	Exhumation of subducted oceanic crust: Key issues and discussion
	Chen Yi; Ye Kai
刊名	ACTA PETROLOGICA SINICA
	2013-05-01
卷号	29 期号:5 页码:1461-1478
关键词	Exhumation Subducted oceanic crust Density Light hydrous minerals Serpentinized subduction channel Accretionary wedge
ISSN号	1000-0569
文献子类	Article
英文摘要	The exhumation mechanism of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks formed by the subduction of oceanic crust is one of the primary uncertainties associated with the subduction factory. Based on a worldwide compilation of key information for oceanic eclogites including petrologic characteristics, peak P-T conditions, and exhumation P-T paths, this study reappraises the exhumation of oceanic eclogites, which have received much less attention than continental ones during the last two decades. The oceanic eclogites reported in typical oceanic subduction zones worldwide can be subdivided into three groups based on peak mineral assemblages, P-T conditions, and geothermal gradients as follows: (1) Coesite-bearing UHP lawsonite eclogites (2.7 similar to 3. 2GPa, 470 similar to 610 degrees C, 5 similar to 7 degrees C/km); (2) HP lawsonite eclogites (1.7 similar to 2. 6GPa, 360 similar to 620 degrees C, 5 similar to 8 degrees C/km); and (3) HP epidote eclogites (1.5 similar to 2.3GPa, 540 similar to 630 degrees C, 7 similar to 12 degrees C/km). Compared with HP and UHP eclogites in continental subduction-collision zones, oceanic eclogites have lower peak P-T conditions and contain more light hydrous minerals. Kyanite, a common dense mineral in continental eclogites, is extremely rare in natural oceanic eclogites. All the hypotheses for the exhumation of oceanic eclogites are based on the assumption that oceanic eclogites were denser than the surrounding mantle; therefore, their exhumation must be aided by low-density serpentinites or metasedimentary rocks. Thermodynamic modeling for MORB suggests that the mineral assemblages, mineral proportions and density of oceanic crust subducted along a cold P-T path are quite different from those of crust subducted along a warm P-T path and that the density of oceanic eclogites is largely controlled by the stability of low-density hydrous minerals, such as lawsonite, chlorite, glaucophane and talc. Along a cold subduction P-T path with a geotherm of similar to 6 degrees C/km, the density of subducted oceanic crust is always lower than that of the surrounding mantle at depths shallower than 110 similar to 120km (P < 3. 3 similar to 3. 6GPa). However, along a warm subduction P-T path with a geotherm of similar to 10 degrees C /km, the subducted oceanic crust becomes denser than the surrounding mantle at depths greater than 60km (P > 1. 8GPa). On the basis of natural observations and our calculations, we suggest that beyond depths around similar to 120km (1) oceanic eclogites are not light enough, (2) there are no serpentinites to compensate the negative buoyancy of the oceanic crust, and (3) increasing the dip angle of subducted oceanic plate inhibits the exhumation of HP-UHP metasedimentary rocks and eclogites from greater depth. They may be the reasons for explaining the lack of oceanic eclogites returned from ultradeep mantle (> 120km) to the Earth's surface. The formation of kyanite through lawsonite breakdown reactions would hamper the exhumation of oceanic crust, that may be the reason for the fact that lawsonite-free kyanite-bearing eclogite is extremely scarce in the oceanic subduction zones worldwide.
WOS关键词	HIGH-PRESSURE METAMORPHISM ; NE NEW-CALEDONIA ; P-T EVOLUTION ; INTERMEDIATE-DEPTH EARTHQUAKES ; ECLOGITE-FACIES METAMORPHISM ; NORTHERN TIBETAN PLATEAU ; MONVISO META-OPHIOLITE ; ZERMATT-SAAS OPHIOLITE ; LAGO-DI-CIGNANA ; NW-CHINA
WOS研究方向	Geology
语种	英语
出版者	SCIENCE PRESS
WOS记录号	WOS:000321226200001
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/87336]
专题	中国科学院地质与地球物理研究所
通讯作者	Chen Yi
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	Chen Yi,Ye Kai. Exhumation of subducted oceanic crust: Key issues and discussion[J]. ACTA PETROLOGICA SINICA,2013,29(5):1461-1478.
APA	Chen Yi,&Ye Kai.(2013).Exhumation of subducted oceanic crust: Key issues and discussion.ACTA PETROLOGICA SINICA,29(5),1461-1478.
MLA	Chen Yi,et al."Exhumation of subducted oceanic crust: Key issues and discussion".ACTA PETROLOGICA SINICA 29.5(2013):1461-1478.