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Petrological and Os Isotopic Characteristics of Zedong Peridotites in the Eastern Yarlung–Zangbo Suture in Tibet
Author(s) -
LAI Shengmin,
YANG Jingsui,
DILEK Yildirim,
XIONG Fahui,
JIANG Rui,
CHEN Yanhong
Publication year - 2018
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13536
Subject(s) - geology , geochemistry , mantle (geology) , partial melting , ophiolite , peridotite , olivine , massif , ultramafic rock , paleontology , tectonics
The Zedong ophiolites in the eastern Yarlung–Zangbo suture zone of Tibet represent a mantle slice of more than 45 km 2 . 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 (Fo 89.7–91.2 ), orthopyroxene (En 88–92 ), clinopyroxene (En 45–49 Wo 47–51 Fs 2–4 ) 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 187 Os/ 188 Os=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.