Subduction-related magmatism in the Indochina Terrane: Insights from Triassic volcanic rocks in Central Thailand

Abstract

The volcanic rocks in the Saraburi–Lop Buri area of Central Thailand consist of three main units: a basaltic–andesitic rock unit predominantly composed of plagioclase and hornblende with a typical porphyritic texture, an andesitic rock unit usually composed of plagioclase, hornblende and quartz, and a rhyolitic rock unit dominated by quartz, plagioclase, K-feldspar, and muscovite. Whole-rock compositions suggest that basaltic–andesitic rocks originated from low-K calc-alkaline magma via melting of a subducted slab with a relatively high degree of partial melting. The andesitic and rhyolitic rocks are possibly differentiated from high-K calc-alkaline magmas. All volcanic rocks are probably emplaced in a continental arc tectonic setting. The zircon U–Pb ages of the basaltic–andesitic rock unit and andesitic rock unit are 213.4 ± 0.5 Ma and 203.5 ± 0.3 Ma, respectively, indicating that the arc volcanism resulted from subduction during the Late Triassic.