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

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 mantlenormalized 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, 87 Sr/ 86 Sr ratios (0.706-0.709), eNd values (-3.2 to -8.7), and eHf values (?4.8 to -6.4) indicate a highly heterogeneous mantle source. The Pb isotopic ratios of the lavas ( 206 Pb/ 204 Pb = 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.

Geochemical and geochronological constraints on Late Jurassic volcanic rocks at Tuen Mun, Hong Kong, with implications for the Palaeo-Pacific subduction

“…The original magma would have had higher concentrations of Ti, Al, Fe, Mn, Mg, and P, among which the concentrations of Ti, Al, and P are similar to those of andesite from the upper unit of Tuen Mun Formation . Such geochemical characteristics are also similar to calc-alkaline basaltic andesites to andesites, although the content of Ca is generally lower and those of K and Na higher (Eichelberger 1975;Anderson 1976;Sakuyama 1979;Cole 1982;Tatsumi and Ishizaka 1982;Ewart and Hawkesworth 1987;Woodhead 1989;Yogodzinski et al 1995;Shimoda et al 1998;Kelemen et al 2003;Wang et al 2006;Zhou et al 2012). The general trend of depletion in Mg, Ca, and Ni but enrichment in incompatible elements compared with primitive andesites (Yogodzinski et al 1995;Kelemen et al 2003) suggests that the andesitic lava have undergone fractionation of olivine, pyroxene, and plagioclase.…”

Magma-derived CO 2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone

“…8 Ma) and continued to historical period (i.e., AD 1609), giving rise to widespread lava flows and pyroclastic rocks (e.g., Huangfu and Jiang, 2000;Zhou et al, 2012;Gao et al, 2015;Guo et al, 2015a). Holocene volcanic eruptions occurred at three active volcanoes (i.e., the Maanshan, Dayingshan and Heikongshan volcanoes; Fig.…”

Tracing the Transhimalayan magmatic belt and the Lhasa block southward using zircon U–Pb, Lu–Hf isotopic and geochemical data: Cretaceous – Cenozoic granitoids in the Tengchong block, Yunnan, China

“…(3) Late Miocene to recent predominantly basaltic-andesitic volcanism (5.5-0.01 Ma) within NE-to NNE-trending rift basins in the central parts of the Tengchong block (Zhu et al, 1983;Wang et al, 2007;Zhou et al, 2012 …”