Geochemistry, zircon U – Pb geochronology, and Hf isotope of the late Permian Sa Thay granite from Kontum massif: Petrogenesis and tectonic implications

Abstract

Sa Thay high - K granites, situated in the western region of Kontum massif, are predominantly composed of biotite granite and biotite - hornblende granite. The major mineral composition comprises plagioclase (26 – 60%), K - feldspar (8 – 22%), quartz (15 – 33%), biotite (3 – 7%), and hornblende (7 – 10%). Accessory minerals include titanite, apatite, zircon, and magnetite. Their SiO 2 concentration varies from 66.81 to 78.14 wt.%, total alkali content ranges from 6.30 to 6.46 wt.%, and A/CNK ratio goes from 0.99 to 1.09. The granites indicate the relative enrichment of large - ion lithophile elements (Sc, Rb, and K), and the negative anomalies for Nb, Ta, and Ti in mantle - normal ized diagrams. The P 2 O 5 content decreases with the increase of SiO 2 content, whilst there is a coupled increase in Th and Tb contents typical of I - type granites. The U - Pb zircon age was determined by the LA - ICP - MS method as 256.7 Ma, corresponding to the Late Permian stage. The ε Hf (t) values, together with the zircon Hf model ages (T DM2 ) of 1440 – 1861 Ma, suggest that parental magma for the Sa Thay granite is derived from the partial melting of Paleoproterozoic mantle rocks and the input of crustal component, following the subduction - collision processes that resulted in the amalgamation of the South China and Indochina blocks (Indosinian Orogeny). Th is geological activity led to the closure of a branch of the Paleo - Tethys Ocean along the Song Ma suture zone during the Late Permian to Early Triassic period.