Tectonic Implication of the Permo-Triassic Khao Yai Mafic Volcanic Rocks in Nakhon Nayok Province, Thailand: Evidence from Geochemistry and Rare Earth Elements (REEs)

Abstract

The Permo-Triassic Khao Yai Volcanics in Nakhon Nayok Province, Thailand, is a part of the Loei-Phetchabun-Nakhon Nayok Volcanic Belt. The purpose of this study is to clarify the geochemistry and REEs characteristic of Khao Yai Volcanics that is useful for identifying the paleo-environment or tectonic setting eruption in this area. The least-altered, mafic volcanic rocks from the Permo-Triassic Khao Yai volcanics, are seriate-textured to porphyritic, with variable amounts of phenocrysts/microphenocrysts. The mineral compositions include plagioclase, clinopyroxene, orthopyroxene, olivine, minor Fe-Ti oxide mineral, amphibole, apatite, biotite/phlogopite, monazite/zircon, glassy, and quartz. The geochemical characteristic of the Khao Yai Volcanics informed that the rocks had the same parental magma with different degrees of crystal fractionation. Most of the mafic volcanic rocks are subalkalic andesite on the basis of their Zr/TiO2 and Nb/Y ratios and calc-alkalic on diagrams Ti-Zr, Ti-Zr-Y, Hf-Th-Ta and Y-La-Nb. The least-altered mafic volcanic rocks have (La/Sm)cn and (Sm/Yb)cn ranging from 2.41 to 2.71 and 1.86 to 2.22, respectively. The studied calc-alkalic andesite are analogous to the Quaternary calc-alkalic dacite and andesite from Maca Volcano, Patagonian Andes and the Middle Eocene andesite from Shimokoh cauldron, SW Japan in terms of chondrite-normalized REEs and N-MORB normalized patterns. Accordingly, the studied Khao Yai volcanics have been developed in an active continental margin, formed by eastward underthrusting Paleo-Tethys, the leading edge of Shan-Thai, beneath Indochina in the Late Permian to Early Triassic. HIGHLIGHTS New tectonic model of the Permo-Triassic Khao Yai mafic volcanic rocks in Nakhon Nayok Province, Thailand The geochemistry and rare earth elements (REEs) analysis by XRF and ICP-MS The REEs analog to modern volcanic rock The classification of pre-Jurassic volcanic belt in Thailand GRAPHICAL ABSTRACT

Geology and petrochemistry of volcanic rocks in the Lam Sonthi area, Lop Buri province

“…The Pre-Cenozoic volcanic rocks can be sub-divided into 4 belts including Chiang Rai-Chiang Mai volcanic belt, Chiang Khong-Lampang-Tak volcanic belt, Nan-Uttaradit suture and Sa Kaeo suture zone, and Loei-Phetchabun-Nakhon Nayok volcanic belt (Fig. 2.2) (Barr and Charusiri, 2011;Jundee et al, 2017;Jungyusuk and Khositanont, 1992;Panjasawatwong et al, 2006).…”