Heterogeneous mantle source and magma differentiation of quaternary arc-like volcanic rocks from Tengchong,SE margin of the Tibetan Plateau |
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| Authors: | Email author" target="_blank">Mei-Fu?ZhouEmail author Paul?T?Robinson Christina?Yan?Wang Jun-Hong?Zhao Dan-Ping?Yan Jian-Feng?Gao John?Malpas |
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| Institution: | (1) Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China;(2) Department of Earth Sciences, The University of Hong Kong, Hong Kong, China;(3) Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;(4) State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, 430074, People’s Republic of China;(5) State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, 430074, People’s Republic of China |
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| Abstract: | The Tengchong volcanic field north of the Burma arc comprises numerous Quaternary volcanoes in the southeastern margin of
the Tibetan Plateau. The volcanic rocks are grouped into four units (1–4) from the oldest to youngest. Units 1, 3 and 4 are
composed of olivine trachybasalt, basaltic trachyandesite and trachyandesite, and Unit 2 consists of hornblende dacite. The
rocks of Units 1, 3, and 4 form a generally alkaline suite in which the rocks plot along generally linear trends on Harker
diagrams with only slight offset from unit to unit. They contain olivine phenocrysts with Fo values ranging from 65 to 85 mol%
and have Cr-spinel with Cr# ranging from 23 to 35. All the rocks have chondrite-normalized REE patterns enriched in LREE and
primitive mantle-normalized trace element patterns depleted in Ti, Nb and Ta, but they are rich in Th, Ti and P relative to
typical arc volcanics. Despite minor crustal contamination, 87Sr/86Sr ratios (0.706–0.709), εNd values (−3.2 to −8.7), and εHf values (+4.8 to −6.4) indicate a highly heterogeneous mantle source.
The Pb isotopic ratios of the lavas (206Pb/204Pb = 18.02–18.30) clearly show an EMI-type mantle source. The underlying mantle source was previously modified by subduction
of the Neo-Tethyan oceanic and Indian continental lithosphere. The present heterogeneous mantle source is interpreted to have
formed by variable additions of fluids and sediments derived from the subducted Indian Oceanic lithosphere, probably the Ninety
East Ridge. Magma generation and emplacement was facilitated by transtensional NS-trending strike-slip faulting. |
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