Subduction-related metasomatism in the thinning lithosphere: Evidence from a composite dunite-orthopyroxenite xenolith entrained in Mesozoic Laiwu high-Mg diorite, North China Craton

doi:10.1029/2005GC000938

	Subduction-related metasomatism in the thinning lithosphere: Evidence from a composite dunite-orthopyroxenite xenolith entrained in Mesozoic Laiwu high-Mg diorite, North China Craton
	Chen, LH; Zhou, XH
刊名	GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
	2005-06-21
卷号	6
关键词	Mantle Xenolith Mantle Metasomatism Lithosphere Thinning Subduction North China Craton Geochemistry : Composition Of The Mantle Mineralogy And Petrology : Mantle Processes Mineralogy And Petrology : Subduction Zone Processes
ISSN号	1525-2027
DOI	10.1029/2005GC000938
文献子类	Article
英文摘要	The North China Craton (NCC) lost its Archean keels in the Phanerozoic. Prevalent and intensive magmatism, mineralization, and development of extensional basins in the late Mesozoic NCC imply that the late Mesozoic could be the key stage for this transformation. Ultramafic xenoliths in the Early Cretaceous high-Mg diorites of Shandong province might provide key information about the transformation of subcontinental lithospheric mantle (SCLM) beneath the NCC. Here we present a unique composite dunite-orthopyroxenite xenolith from Tietonggou, one of the high-Mg diorite-dominated plutons in Laiwu, Shandong province. The petrography and mineral chemistry of the xenolith suggest complicated metasomatic processes, which occurred before its entrainment in the host magma. Early stage metasomatism includes the growth of intergranular phlogopite and clinopyroxene and the development of a phlogopite- and amphibole-bearing clinopyroxenite veinlet. Late-stage metasomatism (termed Si (Na) metasomatism) is characterized by the growth of secondary orthopyroxene, Na-rich plagioclase and amphibole with resorption of olivine and clinopyroxene, and the decomposition of phlogopite. The xenolith has exceptionally high concentrations of Na2O and Al2O3 and shows enrichments in Cs, Rb, Th, U, K, and the light rare earth elements. It also shows positive Pb and Sr anomalies and negative Nb, Ta, P, and Ti anomalies in a primitive mantle normalized spider gram. The geochemistry, as well as the elevated delta(18)O, suggests that this Si (Na) metasomatism is associated with subduction. The secondary orthopyroxene in the orthopyroxenite portion of the xenolith has exceptionally low Mg# values, which may be the result of reaction between silica-rich melts and olivine with high melt: rock ratios. Mg-Fe disequilibrium of the minerals in the orthopyroxenite indicates that Si (Na) metasomatism may have been introduced shortly before entrainment of the xenolith in the host magma. Correlation of the Sr-Nd-Pb isotopic compositions of ultramafic xenoliths, high-Mg diorites, and adakitic granites of the Tietonggou indicates there may be a genetic relationship between these rocks. Thus we propose that the SCLM beneath Shandong may have been metasomatized by a slab-derived melt. Since Si (Na) metasomatism occurred at the key stage of lithospheric thinning, oceanic subduction might have been involved in the thinning process.
WOS关键词	SUB-ARC MANTLE ; PAPUA-NEW-GUINEA ; WESTERN SHANDONG PROVINCE ; SINO-KOREAN CRATON ; SPINEL PERIDOTITE XENOLITHS ; LOWER CONTINENTAL-CRUST ; PB ISOTOPE SYSTEMATICS ; EASTERN CHINA ; TRACE-ELEMENT ; ULTRAMAFIC XENOLITHS
WOS研究方向	Geochemistry & Geophysics
语种	英语
出版者	AMER GEOPHYSICAL UNION
WOS记录号	WOS:000230168900003
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/65148]
专题	中国科学院地质与地球物理研究所
通讯作者	Chen, LH
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, LH,Zhou, XH. Subduction-related metasomatism in the thinning lithosphere: Evidence from a composite dunite-orthopyroxenite xenolith entrained in Mesozoic Laiwu high-Mg diorite, North China Craton[J]. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS,2005,6.
APA	Chen, LH,&Zhou, XH.(2005).Subduction-related metasomatism in the thinning lithosphere: Evidence from a composite dunite-orthopyroxenite xenolith entrained in Mesozoic Laiwu high-Mg diorite, North China Craton.GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS,6.
MLA	Chen, LH,et al."Subduction-related metasomatism in the thinning lithosphere: Evidence from a composite dunite-orthopyroxenite xenolith entrained in Mesozoic Laiwu high-Mg diorite, North China Craton".GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 6(2005).