Geochemistry and petrogenesis of the Puttetti syenite, south India
Nair, N. G. K.; Santosh, M.
Neues Jahrbuch für Mineralogie - Abhandlungen Band 151 Heft 2 (1985), p. 213 - 227
28 references
published: Mar 21, 1985
DOI: 10.1127/njma/151/1985/213
ArtNo. ESP154015102006, Price: 29.00 €
Abstract
The NNW-SSE elongated syenite pluton near Puttetti in south India which shows spatial relationship with the intersection of a NW-SE trending fault-lineament and a NE-SW trending seismically active fault zone belongs to the group of Late Precambrian-Early Paleozoic alkaline intrusives in the region. The rock is dominantly composed of alkali feldspar (Or38.14Ab61.76) with pyroxene of hedenbergite composition (Ca0.906Mg0.193Fe0.901Si2O6) as the principal mafic mineral. The syenite shows association of phlogopite and well-developed zircon crystals. Major and trace element geochemistry of the syenite and associated cumulate pyroxenite are presented and discussed. The association, phlogopite-hedenbergite, is unique and suggests high pressures for melt equilibration under low H2O activity, substantiated by the occurrence of CO2-rich fluid inclusions. Trace element data preclude garnet or amphibole in the source and suggest melting of probable K-rich upper mantle. The syenite underwent strong crystal fractionation as suggested by the Fe-enriched nature. Rare earth element fractionation by accessory phases like zircon, apatite and sphene was also significant. The generation and emplacement of the syenite are correlatable with the pre-rift tectonics of the Indian continent.
Keywords
Syenite • cumulate pyroxenite • mineralogy • major elements • trace elements • petrogenesis • South India