Sm-Nd ages of Archaean metavolcanics of the Dharwar craton, South India

Abstract

Well constrained Sm---Nd arrays of whole rocks are reported for the first time from three important stratigraphic units of the Dharwar volcano-sedimentary sequence of south India. If interpreted as isochrons, these arrays will correspond to the following ages and initial Nd ratios relative to CHUR: 2.911±0.049 Ga and -0.20±0.40 for the Kalasapura mafic basal metavolcanics of the Bababudan greenstone belt; 2.848±0.070 Ga and -0.88 ± 0.82 for the Santaveri Formation comprising mafic to felsic metavolcanics overlying the Kalasapura rocks; and 2.747±0.015 Ga and +1.72 ± 0.10 for the Ingaldhal mafic-felsic metavolcanic suite of the Chitradurga greenstone belt. The possibility that these Sm---Nd arrays are mixing lines between unrelated components depleted and enriched, respectively, in light rare earth elements has been discussed, leading to the conclusion that the ages closely correspond to their time of eruption: the older suites from the Bababudan belt from a mantle source of CHUR-like composition, the younger suite from the Chitradurga belt from one with a prior history of LREE depletion.