Petrography and geochemistry of the Ben Giang and Van Canh granitoid in Sa Thay area, Kontum province

Abstract

The Ben Giang and Van Canh complexes in Sa Thay area, Kon Tum province, are exposed as small blocks. Their petrographical composition includes hornblende biotite diorite, biotite granodiorite (the Ben Giang complex), fine-grained to medium-grained biotite granite and fine-grained biotite granite (the Van Canh complex). The SiO₂ content varies from 59.84 to 77.29 wt.% coupled with an enriched alumina content (12.53–17.26 wt.%). All samples show a relatively high total alkali content (4.71–8.36 wt.%). The K₂O/Na₂O ratio is greater than 1, and a narrow variation of the ASI index (1.41–1.68) indicates that the rocks belong to the calc-alkaline series. The rocks’ negative anomalies of Ta, Nb, and Ti are typical for a magma melt generated at the edge of an active subduction zone. The low content of Sr (76–549 ppm, 347 ppm on average), Zr (111–296 ppm, 167 ppm on average), and Nb (9–15 ppm, 11 ppm on average) together with noticeably high Rb content (171–309 ppm), etc. imply that the Ben Giang and the Van Canh magmatic rocks derived from a mantle source, contaminated with crustal materials.