Hainan mantle plume produced late Cenozoic basaltic rocks in Thailand, Southeast Asia

Quanshu Yan,Ian Metcalfe,Thanyapat Sirichaiseth,Ying Zhang,Long Yuan,Narumol Kornkanitnan,Xuefa Shi,Shengfa Liu,Hui Zhang,Taoyu Xu

doi:10.1038/s41598-018-20712-7

Abstract

Intraplate volcanism initiated shortly after the cessation of Cenozoic seafloor spreading in the South China Sea (SCS) region, but the full extent of its influence on the Indochina block has not been well constrained. Here we present major and trace element data and Sr-Nd-Pb-Hf isotope ratios of late Cenozoic basaltic lavas from the Khorat plateau and some volcanic centers in the Paleozoic Sukhothai arc terrane in Thailand. These volcanic rocks are mainly trachybasalts and basaltic trachyandesites. Trace element patterns and Sr-Nd-Pb-Hf isotopic compositions show that these alkaline volcanic lavas exhibit oceanic island basalt (OIB)-like characteristics with enrichments in both large-ion lithophile elements (LILE) and high field strength elements (HFSEs). Their mantle source is a mixture between a depleted Indian MORB-type mantle and an enriched mantle type 2 (EMII). We suggest that the post-spreading intraplate volcanism in the SCS region was induced by a Hainan mantle plume which spread westwards to the Paleozoic Sukhothai arc terrane.

Highlights

The geodynamic setting of the intraplate volcanism in the South China Sea (SCS) region is still debated
Loss on ignition (LOI) values of the samples range from 0.16 to 2.71 wt. %, which are due to variable amounts of secondary hydrous/altered minerals
After major oxides analyses recalculated to 100% on an H2O and CO2− free basis, all samples were plotted on a plot of total alkalis (Na2O + K2O) versus silica (SiO2)[50] (Fig. 3)

Summary

Introduction

The geodynamic setting of the intraplate volcanism in the SCS region is still debated. Thailand and the surrounding region can be divided into three tectonostratigraphic units: a western Sibumasu block (Sino- Burma- Malaya- Sumatra), a middle Sukhothai arc terrane and an eastern Indochina block hosting the Khorat Plateau. These three terranes are separated by two Paleo-Tethys sutures. The other suture is the back-arc Nan-Uttaradit Sra Kaeo suture which is composed of disaggregated Paleozoic ophiolites and melanges[17,39,40] (Fig. 2) Both the Sibumasu block and the Indochina block have Precambrian basements, and were part of the India–Australian margin of eastern Gondwanaland in the Early Paleozoic. Two major Cenozoic strike-slip faults (Mae Ping fault and Three Pagodas fault) cut through the western part of Thailand (Fig. 2)

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Conclusion