Relic Oceanic Crust at Sub-Arc Depth: An Example from UHP Eclogites   Enclosed in Serpentinites from the Southwestern Tianshan, China

doi:10.1111/1755-6724.13169

CORC > 北京大学 > 地球与空间科学学院

	Relic Oceanic Crust at Sub-Arc Depth: An Example from UHP Eclogites Enclosed in Serpentinites from the Southwestern Tianshan, China
	Shen, Tingting ; Zhang, Lifei ; Hermann, Joerg ; Liu, Fenglin
刊名	ACTA GEOLOGICA SINICA-ENGLISH EDITION
	2017
关键词	EXHUMATION
DOI	10.1111/1755-6724.13169
英文摘要	Ultra-high pressure (UHP) eclogites that derive from subducted oceanic crust are rarely found at the Earth's surface because they need to be enclosed in a buoyant host rock such as serpentinites that facilitate exhumation (Hermann et al., 2000; Guillot et al., 2001). Under normal subduction geotherms, serpentinites break down just before UHP conditions are reached and therefore most of the exhumed eclogites representing subducted oceanic crust formed under fore-arc conditions. We investigated eclogite blocks enclosed into serpentinites that occur in the southwestern Tianshan oceanic subduction, China. A previous study proved that the serpentinites derive from altered oceanic crust and experienced UHP metamorphism at low temperatures of 510-530 degrees C (Shen et al., 2015). Three relatively fresh eclogite samples were studied in detail. Sample 129-7 shows the retrograde mineral assemblage of amphibole + biotite + albite + chlorite + minor titanite and peak metamorphic relics of omphacite + garnet +/- chlorite. Sample C107-23 is mainly composed of amphibole + albite + chlorite + zoisite + muscovite + minor titanite as a retrograde assemblage and garnet + phengite as the peak metamorphic relics with omphacite only found as inclusions in garnet. Similar to sample C107-23, sample C11066 preserves large-grained euhedral to subhedral garnet relics with omphacite inclusions, and epidote, diopside, amphibole, muscovite, chlorite, albite and biotite are in the matrix belong to the retrograde assemblage. These three retrograde eclogite samples were modelled using thermodynamic calculations in the MnNCKFMSHO (MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Fe2O3) system. Based on the peak assemblage of omphacite+garnet and the crossing of the grossular and pyrope isopleths in garnet, peak P-T conditions of approximate to 460-470 degrees C, 28-29 kbar (129-7), 450-500 degrees C, 28-35 kbar (C107-23), approximate to 475-505 degrees C, 26-29 kbar (C11066) were calculated. The retrograde assemblages indicate near isothermal decompression resulting in a clockwise P-T evolution of these eclogites. The peak metamorphic pressures at 500 degrees C are well within UHP conditions (coesite stability field) and are within error the same as peak conditions of the host serpentinites (Shen et al., 2015). This provides evidence that eclogites and serpentinites shared the same evolution. We infer that the subducted low-density serpentinites were assembled with the high-density eclogites during subdution and helped the latter to exhume back to the surface. The studied eclogites thus represent rare examples of relics of oceanic crust that was subducted to sub-arc depth.; SCI(E); ARTICLE; 35-35; 91
语种	英语
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/473595]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	Shen, Tingting,Zhang, Lifei,Hermann, Joerg,et al. Relic Oceanic Crust at Sub-Arc Depth: An Example from UHP Eclogites Enclosed in Serpentinites from the Southwestern Tianshan, China[J]. ACTA GEOLOGICA SINICA-ENGLISH EDITION,2017.
APA	Shen, Tingting,Zhang, Lifei,Hermann, Joerg,&Liu, Fenglin.(2017).Relic Oceanic Crust at Sub-Arc Depth: An Example from UHP Eclogites Enclosed in Serpentinites from the Southwestern Tianshan, China.ACTA GEOLOGICA SINICA-ENGLISH EDITION.
MLA	Shen, Tingting,et al."Relic Oceanic Crust at Sub-Arc Depth: An Example from UHP Eclogites Enclosed in Serpentinites from the Southwestern Tianshan, China".ACTA GEOLOGICA SINICA-ENGLISH EDITION (2017).