5:15 PM - 6:30 PM
[SMP14-P06] Igneous activity of Paleoarchean TTGs around Chitradurga, western Dharwar craton, India
Keywords:TTG, Dharwar Craton, India
Although the TTGs are generally composed of granitic to tonalitic gneisses, we can group them into two types in correspondence with their petrographic features; K-feldspar (Kfs)-poor meta-trondhjemite and Kfs-rich meta-granite. The Kfs-poor meta-trondhjemite has suitable petrographic feature of slab-derived TTGs. On the other hand, the Kfs-rich meta-granite contains abundant K-feldspar, a mineral phase that is not common in the TTGs.
The Kfs-poor meta-trondhjemite (SiO2: 65-75 wt%) have typical TTGs in composition, with high Al2O3 (14.7-19.1 wt%) and Na2O contents (3.6-5.2 wt%), and correlated low K2O/Na2O (0.27-0.74) as well as moderately high Sr (195-527 ppm) and Sr/Y (21-109), although the REE patterns have fairly variable from flat to fractionated ((La/Yb)n=1.2-26), with no Eu anomaly. However, the Kfs-rich meta-granite (SiO2: 69-78 wt%) shows different geochemical characteristics than that of TTGs. In particular, their Al2O3 (13.4-15.7 wt%) and Sr (68-310 ppm) contents are not enriched, and their K2O/Na2O (0.5-1.9) ratios are higher. The REE patterns are largely sub-divided into two types, one is fractionated ((La/Yb)n=10-64) with no Eu anomaly, the other is moderately fractionated ((La/Yb)n=1.8-21) associated with significant negative Eu anomaly. Probably, the Kfs-rich meta-granite had been formed by several different types of magmatic activities. In Paleoarchean, the western Dharwar craton was intruded by many slab-derived TTGs. In addition, it is probable that the various granitic activities were derived from strong magma differentiation and/or crustal reworking operated simultaneously to form a stable continental crust.
References: Chadwick et al., 1981, Precambrian Research 16, 31-54, Chadwick et al., 2000, Precambrian Research 99, 91-101, Jayananda et al., 2006, Precambrian Research 150, 1-26, Jayananda et al., 2013, Precambrian Research 227, 55-76, Hokada et al., 2013, Precambrian Research 227, 99-119