Thermal and petrological structure of the lithosphere beneath Hannuoba, Sino-Korean Craton, China: evidence from xenoliths

被引:234
作者
Chen, SH
O'Reilly, SY [1 ]
Zhou, XH
Griffin, WL
Zhang, GH
Sun, M
Feng, JL
Zhang, M
机构
[1] Macquarie Univ, Dept Earth & Planetary Sci, GEMOC, N Ryde, NSW 2109, Australia
[2] Chinese Acad Sci, Inst Geol & Geophys, Lab Lithosphere Tecton Evolut, Beijing 100029, Peoples R China
[3] CSIRO Explorat & Min, N Ryde, NSW 1670, Australia
[4] Univ Hong Kong, Dept Earth Sci, Hong Kong, Hong Kong, Peoples R China
[5] Hebei Coll Geol, Dept Geol, Shijiazhuang 050031, Peoples R China
关键词
mantle xenoliths; Sino-Korean Craton; Eastern China lithosphere; mantle trace elements; granulite xenoliths; Hannuoba lithosphere structure;
D O I
10.1016/S0024-4937(00)00065-7
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Deep-seated xenoliths entrained in the Hannuoba basalts of the northern Sino-Korean Craton include mafic and felsic granulites, mantle wall-rock from spinel- and garnet-spinel peridotite facies, and basaltic crystallisation products from the spinel-pyroxenite and garnet-pyroxenite stability fields. The mineral compositions of the xenoliths have been used to estimate temperatures and, when possible, pressures of equilibration. and to construct a geothermal framework to interpret the upper mantle and lower crustal rock-type sequences for the region. The xenolith-derived paleogeotherm is constrained in the depth interval of 45-65 km and like others from areas of young basalt magmatism. is elevated and strongly convex toward the temperature axis. Two-pyroxene granulites give the lowest temperatures and garnet pyroxenites the highest. while the spinel lherzolites fall between these two groups. The present-day Moho beneath the Hannuoba area is defined at 42 km by seismic data, and coincides with the deepest occurrence of granulite. Above this boundary, there is a lower crust-upper mantle transition zone about 10-km thick, in which spinel lherzolites and mafic granulites (with variable plagioclase contents) are intermixed. It is inferred that this underplating has resulted in a lowering of the original pre-Cenozoic Moho (then coinciding with the crust-mantle boundary, CMB) from about 30 km to its present-day position and was due to intrusions of basaltic magmas that displaced peridotite mantle wall-rock and equilibrated to mafic granulites. Trace element patterns of the diopsides (analysed by laser ablation-ICPMS) from the Cr-diopside series spinel lherzolites and associated layered xenoliths (spinel lherzolites and pyroxenites) indicate 3 fertile uppermost mantle with moderate depletion by low degrees of partial melting and little evidence of metasomatic activity. The similarity in major and trace element composition?; of the minerals in both rock types suggests that the layered ultramafic xenoliths formed by mantle deformation processes (metamorphic segregation), rather than by melt veining or metasomatism. (C) 2001 Elsevier Science B.V. All rights reserved.
引用
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页码:267 / 301
页数:35
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