SM-ND AGES OF ARCHEAN METAVOLCANICS OF THE DHARWAR CRATON, SOUTH-INDIA

Well constrained Sm-Nd arrays of whole rocks are reported for the firs t time from three important stratigraphic units of the Dharwar volcano -sedimentary sequence of south India. If interpreted as isochrons, the se 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 Kalasa pura mafic basal metavolcanics of the Bababudan greenstone belt; 2.848 +/- 0.070 Ga and -0.88 +/- 0.82 for the Santaveri Formation comprisin g mafic to felsic metavolcanics overlying the Kalasapura rocks; and 2. 747 +/- 0.015 Ga and +1.72 +/- 0.10 for the Ingaldhal mafic-felsic met avolcanic suite of the Chitradurga greenstone belt. The possibility th at these Sm-Nd arrays are mixing lines between unrelated components de pleted and enriched, respectively, in light rare earth elements has be en discussed, leading to the conclusion that the ages closely correspo nd 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 Chitraduga belt from one with a prior history of LREE depletion.