Original Paper

Contributions to Mineralogy and Petrology

, Volume 163, Issue 5, pp 841-860

Open Access This content is freely available online to anyone, anywhere at any time.

Heterogeneous mantle source and magma differentiation of quaternary arc-like volcanic rocks from Tengchong, SE margin of the Tibetan Plateau

  • Mei-Fu ZhouAffiliated withKey Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of SciencesDepartment of Earth Sciences, The University of Hong Kong Email author 
  • , Paul T. RobinsonAffiliated withDepartment of Earth Sciences, The University of Hong Kong
  • , Christina Yan WangAffiliated withKey Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
  • , Jun-Hong ZhaoAffiliated withState Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences
  • , Dan-Ping YanAffiliated withState Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences
  • , Jian-Feng GaoAffiliated withDepartment of Earth Sciences, The University of Hong Kong
  • , John MalpasAffiliated withDepartment of Earth Sciences, The University of Hong Kong

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.

Keywords

Arc-like volcanic rocks Heterogeneous mantle source Sr–Nd–Pb–Hf isotopes Magma chamber processes Tengchong SE margin of the Tibetan Plateau