Tóm tắt

The Hiep Duc serpentinized peridotites are parts of the ophiolitic complexes that have long been considered as remnants of Paleo-Tethyan oceanic lithosphere between the Kon Tum massif and Truong Son belt. Our analytical data using electron microprobe anlysing system showed that the serpentinized peridotites contain some relicts of mantle-derived Cr-spinel, and a later metamorphic mineral assemblage composed by talc, serpentine-group minerals, and magnetite. The primary compositions of the Cr-spinels from the serpentinized peridotites are used to deduce their petrogenesis and tectonic environments. These spinels are characterized by medium Cr₂O₃content (31.53–37.01 wt.%), high contents of Al₂O₃ (20.01–33.94 wt.%),), FeO (18.13–28.76 wt.%) and MgO (9.71– 13.47 wt.%), and very low TiO₂ content (0.17–0.32 wt.%) with medium Cr# (0.44–0.47) and Mg# (0.62–0.71). They also show low Fe³⁺ and Fe²⁺ of (0.03 – 0.09) and (0.40 – 0.60), respectively. Evaluating all characteristics of the Cr-spinel in the serpentinized peridotites indicate that the rocks are of supra-subduction peridotites. The Cr-spinel compositions combined with Al₂O₃ and TiO₂ contents of parental melts as well as available data within the TPSZ suggest that the rocks probably of back-arc tectonic setting that was triggered by a Paleo-Tethys underneath the Kon Tum Massif during the early Paleozoic.