Petrochemistry and mineral chemistry of Late Permian hornblendite and hornblende gabbro from the Wang Nam Khiao area, Nakhon Ratchasima, Thailand: Indication of Palaeo-Tethyan subduction

• Hornblende + plagioclase + clinopyroxene as the dominant mineral assemblage.
• 257 Ma magmatism related to subduction of Palaeo-Tethys beneath Indochina.
• Crystallization at ∼9.8 kbar/∼1000 °C to ∼8.8 kbar/∼850 °C.
• Volcanic arc-related hydrous magma emplaced in the lower crust.

In the Wang Nam Khiao area, Nakhon Ratchasima, northeastern Thailand, there are various mafic-ultramafic plutons composed of hornblendite, hornblende gabbro and hornblende microgabbro. The rocks are generally dominated by hornblende, plagioclase and clinopyroxene. The mineral chemistry and whole-rock geochemistry of hornblendite, hornblende gabbro and hornblende microgabbro show their similarities, suggesting a close relationship of their magmatic evolution. The flat REE pattern and low HREE concentration indicate fractional crystallization from hydrous magma. The enrichment in LILE (e.g. Ba, K, Sr) and depletion of HFSE (e.g. Nb, Ta, Zr) together with compositions of clinopyroxene and hornblende reflect arc-related subduction. Hornblende-plagioclase geothermometry and Al-in-hornblende geobarometry indicate the PT conditions of crystallization are 5.3–9.8 kbar and 670–1000 °C, 7.6–9.0 kbar and 850–950 °C, and 7.6–8.8 kbar and 750–850 °C for hornblendite, hornblende gabbro and hornblende microgabbro, respectively, at the lower crustal depth (28–31 km). Zircon U-Pb age of hornblende microgabbro dike, that intruded into hornblendite, yields 257 Ma of intrusion age, suggesting the emplacement of the mafic-ultramafic rock in this area is related to Late Permian arc magmatism resulted from subduction of Palaeo-Tethys beneath Indochina Terrane.

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