Volume 92, Issue 2 pp. 442-461
Original Article
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Petrological and Os Isotopic Characteristics of Zedong Peridotites in the Eastern Yarlung–Zangbo Suture in Tibet

Shengmin LAI

Shengmin LAI

School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083 China

CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037 China

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Jingsui YANG

Corresponding Author

Jingsui YANG

School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083 China

CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037 China

Corresponding author. E-mail: [email protected]Search for more papers by this author
Yildirim DILEK

Yildirim DILEK

Department of Geology, Shideler Hall, Miami University, Oxford, OH 45056 USA

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Fahui XIONG

Fahui XIONG

CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037 China

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Rui JIANG

Rui JIANG

PetroChina Southwest Oil & Gasfield Company Engineering Technology Research Department, Chengdu 618300 China

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Yanhong CHEN

Yanhong CHEN

CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037 China

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First published: 27 April 2018
Citations: 8

About the first author:

LAI Shengmin, Male; born in 1991; A Ph. D Candidate from China University of Geosciences, Beijing; Major in mineralogy, petrology and economic geology. E–mail: [email protected].

Abstract

The Zedong ophiolites in the eastern Yarlung–Zangbo suture zone of Tibet represent a mantle slice of more than 45 km2. This massif consists mainly of mantle peridotites, with lesser gabbros, diabases and volcanic rocks. The mantle peridotites are mostly harzburgite, lherzolite; a few dike-like bodies of dunite are also present. Mineral structures show that the peridotites experienced plastic deformation and partial melting. Olivine (Fo89.7–91.2), orthopyroxene (En88–92), clinopyroxene (En45–49Wo47–51Fs2–4) and spinel [Mg#=100×Mg/(Mg+Fe)]=49.1–70.7; Cr#=(100×Cr/(Cr+Al)=18.8–76.5] are the major minerals. The degree of partial melting of mantle peridotites is 10%–40%, indicating that the Zedong mantle peridotites may experience a multi–stage process. The peridotites are characterized by depleted major element compositions and low REE content (0.08–0.62 ppm). Their “spoon–shaped” primitive–mantle normalized REE patterns with (La/Sm)N being 0.50–6.00 indicate that the Zedong ultramafic rocks belong to depleted residual mantle rocks. The PGE content of Zedong peridotites (18.19–50.74 ppb) is similar with primary mantle with Pd/Ir being 0.54–0.60 and Pt/Pd being 1.09–1.66. The Zedong peridotites have variable, unradiogenic Os isotopic compositions with 187Os/188Os=0.1228 to 0.1282. A corollary to this interpretation is that the convecting upper mantle is heterogeneous in Os isotopes. All data of the Zedong peridotites suggest that they formed originally at a mid-ocean ridge (MOR) and were later modified in supra–subduction zone (SSZ) environment.

 

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