The origin of the serpentinite enclaves in metacarbonates of the Sa Nghia area in the Kon Tum Massif, Central Vietnam

Abstract

Metacarbonate rocks surrounded by schists, amphibolites and quartzites, occur abundantly in the Sa Nghia – Ho Moong area of Kham Duc Complex in the Kon Tum Massif (Central Vietnam). They contain serpentinite enclaves, which form different bodies such as: sharp-edged rock fragments, lenses, thin layers or small nests often transecting the background of host metacarbonates. The enclaves are mainly built of antigorite. Thin veins crosscutting the serpentinites are commonly filled with microcrystalline carbonates. The relics of olivine and clinopyroxene as well as flaky talc, magnetite, ilmenite, pyrite and zircon occur as accessory components. The serpentinites are slightly enriched in Cs, Th and U, and depleted in Ba, K and Ti. Most probably, such geochemistry could be caused by the influence of fluids derived from primitive tholeiitic melt, which could infiltrate the primary ultramafic rocks before they were hosted by metacarbonates. Another alternative is that the impoverishment in Al, Cr, Ni, Cu, V and Co, together with the presence of numerous grains of carbonates, zircon and pyrite might be indicative for significant secondary metasomatic alterations of pristine ultramafic rocks as the protolith of the serpentinite enclaves.