Mafic dykes at the southwestern margin of Eastern Ghats belt: Evidence of rifting and collision |
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| Authors: | S Bhattacharya A K Chaudhary W Teixeira |
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| Institution: | (1) Department of Geology, J. K. College, Purulia, 723 101, West Bengal, India |
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| Abstract: | The southwestern margin of the Eastern Ghats Belt characteristically exposes mafic dykes intruding massif-type charnockites.
Dykes of olivine basalt of alkaline composition have characteristic trace element signatures comparable with Ocean Island
Basalt (OIB). Most importantly strong positive Nb anomaly and low values of Zr/Nb ratio are consistent with OIB source of
the mafic dykes. K-Ar isotopic data indicate two cooling ages at 740 and 530 Ma. The Pan-African thermal event could be related
to reactivation of major shear zones and represented by leuco-granite vein along minor shear bands. And 740 Ma cooling age
may indicate the low grade metamorphic imprints, noted in some of the dykes. Although no intrusion age could be determined
from the present dataset, it could be constrained by some age data of the host charnockite gneiss and Alkaline rocks of the
adjacent Prakasam Province. Assuming an intrusion age of ∼1.3Ga, Sr-Nd isotopic composition of the dykes indicate that they
preserved time-integrated LREE enrichment. In view of the chemical signatures of OIB source, the mafic dykes could as well
be related to continental rifting, around 1.3Ga, which may have been initiated by intra-plate volcanism. |
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