Geochronology and Geochemistry of Mesoproterozoic Mafic Rocks in the Kontum Complex and Its Implication for the Columbia Reconstruction

The assembly–breakup of the Columbia/Nuna supercontinent is one of the most important issues in the Precambrian geology. The reconstruction of the Indochina Block in the Columbia supercontinent is poorly constrained by far, due to the deficiency of available geochronological and geochemical data for the exposed Precambrian rocks. The Mesoproterozoic plagioclase amphibolites in the Kontum Complex have significant implication for the reconstruction of the Indochina Block within the Columbia supercontinent. This study presents detailed petrological, zircon U–Pb geochronological and Lu–Hf isotopic, and whole-rock geochemical analyses for the plagioclase amphibolites. The plagioclase amphibolite protoliths were formed at ~1432–1403 Ma and experienced metamorphism at 486–457 Ma, suggesting the preservation of a Mesoproterozoic basement in the Kontum Complex. The samples are strongly enriched in LREEs and LILEs but depleted in Nb, Ta, and Ti. They have relatively low (87Sr/86Sr)i ratios (from 0.705055 to 0.708728), positive εNd (t) values (from +2.6 to +2.8), and positive zircon εHf (t) values (from +9.9 to +17.1). Such signatures suggest that they were derived from a mantle wedge that has been metasomatized by sediment-derived melts in an arc setting and caused the breakup of the Columbia supercontinent. The Kontum Complex from the Indochina Block, along with Laurentia and East Antarctica, was distributed at the Columbian periphery.

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