| Petrological and Os Isotopic Characteristics of Zedong Peridotites
in the Eastern Yarlung–Zangbo Suture in Tibet |
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| 作者姓名： | LAI Shengmin YANG Jingsui Yildirim DILEK XIONG Fahui JIANG Rui CHEN Yanhong |
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| 作者单位： | 1 School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China
2 CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,1 School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China
2 CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,3 Department of Geology, Shideler Hall, Miami University, Oxford, OH 45056, USA,2 CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,4 PetroChina Southwest Oil ＆ Gasfield Company Engineering Technology Research Department, Chengdu 618300, China and 2 CARMA, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| 基金项目： | Thanks to Dengzhu Ba for assistance in the field work. We are also grateful to He Rong, Hongling Yan and Jie Li for their help during the laboratory work. This study was supported by the Project IGCP–649 and the China Geological Survey (No. DD20160023–01). |
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| 摘 要： | 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(Fo89.7–91.2), 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.
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| 关 键 词： | Os isotopes Zedong peridotites Yarlung-Zangbo suture zone mid–ocean ridge (MOR) supra-subduction zone (SSZ) |
| 收稿时间： | 2016/5/17 0:00:00 |
| 修稿时间： | 2017/11/8 0:00:00 |
Petrological and Os Isotopic Characteristics of Zedong Peridotites in the Eastern Yarlung–Zangbo Suture in Tibet |
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| Authors: | LAI Shengmin YANG Jingsui Yildirim DILEK XIONG Fahui JIANG Rui and CHEN Yanhong |
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| Institution: | 1. School of Earth Science and Mineral Resources, China University of Geosciences, China;2. CARMA, Institute of Geology, Chinese Academy of Geological Sciences, China;3. Department of Geology, Shideler Hall, Miami University, Oxford, USA;4. PetroChina Southwest Oil & Gasfield Company Engineering Technology Research Department, China |
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| 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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| Keywords: | Os isotopes Zedong peridotites Yarlung‐Zangbo suture zone mid– ocean ridge (MOR) supra‐subduction zone (SSZ) |
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