Abstract
The Sandur greenstone belt (SGB) is a distinctive greenstone belt as it
is perched within the Closepet granitoid rocks (CG). The emplacement of
the CG is attributed to intrusion in a crustal scale transcurrent shear
zone towards the end of Archaean (Moyen et al., 2003). The Chitradurga
shear zone that forms the eastern margin of the Chitradurga greenstone
belt, located west of the Closepet granite, is considered as the
boundary between WDC and EDC. As per the division of the Dharwar craton,
the domination of volcano-sedimentary sequences in SGB with abundant BIF
and considerable greywacke-argillite lithologies, attest their
similarity to the greenstone belts of WDC. Closer to the SGB, the rocks
of the CG are known to host excellent mafic microgranular enclaves (MME)
which might indicate interaction between the granitic magma with the
older greenstone belt lithologies during intrusion. It is interesting to
note that there is a progressive increase in crustal thickness from
north towards south in the Dharwar craton and the SGB is found
associated with the CG in the shallow zones of the north (Moyen et al.,
2003). The mafic volcanic rocks are predominantly basaltic in
composition and are composed of amphibole, pyroxene, plagioclase and
quartz with titanite and magnetite as accessory minerals. The rocks are
classified as tholeiitic basalts that were metamorphosed to amphibolite
grade. Preliminary geochemical studies on these rocks show significant
differences in their trace element distribution. The
chondrite-normalized REE patterns show moderate to high contents of REE
and have unfractionated pattern. The basalts show a flat to slightly
LREE enriched pattern. Some samples show slight negative Eu anomaly and
some do not show any significant anomaly. Some associated rocks also
have complementary enrichment-depletion of certain elements. All of
these point to multiple petrogenetic processes involved in the
generation of these magmatic precursor rocks.