No abstract

ISBN 90 5809 545 2;xv + 294 pp.; US $109.

No abstract

Rubidium‐strontium and potassium‐argon dating of whole rocks and separated biotites from charnockites and granites of the Eastern Ghats delineate two episodes after the culmination of the Eastern Ghats orogeny 1600 m.y. ago: (1) emplacement of charnockites and granites 1300 to 1520 m.y. ago and (2) their subsequent metamorphism and uplift 500 m.y. ago (postdating the deposition of the Cuddapahs). The 500‐m.y. cycle is represented in the southwest coast of India (Travancore) and Ceylon, and the age data are consistent with structural and other geological evidence. Whole‐rock K‐Ar ages of five dolerites emplaced in the Lower Cuddapahs in the western part of the Cuddapah Basin, and of two slates of the Cumbum stage of the Nallamalai series, permit the dating of the following events in the history of the Cuddapah Basin: (1) the initiation of the Cuddapah sedimentation sometime after the completion of the Eastern Ghats orogeny (1600 m.y. ago), but before 1160 m.y. ago (minimum age limit for dolerites), and (2) metamorphism of the Cuddapahs about 500 m.y. ago (as indicated by the slate ages).

SummaryTrace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6·4; U/K (× 104), 0·7; K/Cs (× 10−4), 3·6; Th/K (× 104), 5·3; Fe2O3/(FeO+Fe2O3), 0·27) as well as 87Sr/86Sr initial ratio (0·705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis: Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history—palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.