Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit

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	Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit
	Chen, SY (Chen Songyong); Yang, JS (Yang Jingsui); Li, Y (Li Yuan); Xu, XZ (Xu Xiangzhen)
刊名	JOURNAL OF EARTH SCIENCE
	2009
卷号	20 期号:2 页码:332-347
关键词	ultramafic rock ophiolite eclogite Sumdo Lhasa block
ISSN号	1674-487X
英文摘要	Recently, an over 100 km long MORB-type eclogite belt of Permian was discovered in the Sumdo ((sic)) region of the Lhasa block, Tibet. A critical question thus is what is the tectonic setting of the eclogite belt and is it related to an unrecognized suture in the region? Further investigations show that there are some mafic and ultramafic rocks spacially associated with the eclogite belt in the region. Three ultramafic massifs were recognized in the Sumdo region, and called the Luomaling ((sic)) Gongbupala ((sic)) and Qiazhasumdo ((sic)) massifs. All the massifs are fault-contacted with greenschist (Chasagang ((sic)) Formation) or muscovite-quartz schist (Mabuku ((sic)) Formation), and individuals are about 100 mx50 m in size extending in EW as the regional structure. All the ultramafic rocks have been entirely serpentinized, and the Gongbupala massif has been selected for study in geochemistry. Eleven chemical analyses of the rocks from the Gongbupala massif show a narrow range in contents SiO(2) (35.97-40.63) wt.%, MgO (37.02-38.60) wt.%, TiO(2) (0.01-0.08) wt.%, Al(2)O(3) (0.80-1.64) wt.%, (Na(2)O+K(2)O) less than 0.1 wt.%, with high volatile contents (H(2)O+CO(2)) (11.24-14.91) wt.%. After recalculation without H(2)O+CO(2), the mean values are SiO(2) 45.24 wt.%, MgO 43.54 wt.%, FeO(T) (7.45-9.97) wt.% (8.55 wt.% in average), (MgO+FeO(T),) 52.09 wt.%, Mg(#) (100xMg/(Mg+Fe), where Fe represents total Fe)=89.42-90.08, (m+f)/Si ((atomicity Mg+atomicity Fe) /atomicity Si)=1.53-1.75 (1.59 in average), respectively. The mean M/F (atomicity Mg/atomicity Fe) ratio of the rocks is 9.05, which is classified as magnesium enriched-type of ultramafic rocks. The compositional features, depleted in K, Na, Ca, Al and Ti and enriched in Mg(#), indicate the characteristics of peridotite originated from a depleted mantle. The rocks have low Sigma REE with (1.60-2.68)x10(-6) similar to those of the primitive mantle. The chondrite-normalized REE patterns of all samples show slightly enrichment in LREE, with (Ce/Yb)(N) 1.03-2.46, but a little depleted in HREE. Most samples show a slight negative anomaly in Eu, a feature in REE from a relic mantle and common features in highly serpentinized ultramafic rocks in the Yarlung-Zangbo ((sic)) ophiolite and the Bangong ((sic))-Nujiang ((sic)) ophiolite in Tibet. The primitive mantle-normalized spiderdiagram of trace elements for Gongbupala ultramafic rocks yields uniform distributed pattern. They are relatively enriched in Rb, Ba, La, P element (LHSE) and depleted in Sm, Ti, Y, Yb element (HFSE), a feature of metasomatic mantle peridotite. The geochemical features of the rocks suggest that the protolith of Gongbupala serpentinite in Sumdo region is harzburgite, a typical depleted mantle rock, and may represent a dismembered ophiolite unit in the region.
学科主题	火成岩岩石学
WOS关键词	GEOCHEMICAL CHARACTERISTICS ; GEOLOGICAL SIGNIFICANCE ; ISOTOPIC COMPOSITIONS ; U-PB ; ECLOGITE ; BELT ; PERIDOTITE ; EVOLUTION ; EARTH ; ZONE
WOS研究方向	Geology
语种	英语
出版者	CHINA UNIV GEOSCIENCES
WOS记录号	WOS:000265653900009
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/39026]
专题	中国地质调查局
作者单位	Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China
推荐引用方式 GB/T 7714	Chen, SY ,Yang, JS ,Li, Y ,et al. Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit[J]. JOURNAL OF EARTH SCIENCE,2009,20(2):332-347.
APA	Chen, SY ,Yang, JS ,Li, Y ,&Xu, XZ .(2009).Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit.JOURNAL OF EARTH SCIENCE,20(2),332-347.
MLA	Chen, SY ,et al."Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit".JOURNAL OF EARTH SCIENCE 20.2(2009):332-347.