Geochemistry of charnockites from Sa~o Paulo State, Brazil

Details Geochemistry of charnockites from Sa~o Paulo State, Brazil Geochemistry of charnockites from Sa~o Paulo State, Brazil

Feb 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979e%26psl..42..311g&link_type=abstract

Earth and Planetary Science Letters, Volume 42, Issue 2, p. 311-320.

Physics

3

Scientific paper

REE and Ba, Th, U, Au, Hf, Sb, Sc and Cs were determined by neutron activation techniques on samples belonging to an acidic high-K charnockitic formation outcropping along the coast of Sa~o Paulo State, Brazil. This formation was dated by the Rb-Sr method and gave whole-rock isochron ages of 546-558 m.y. and initial 87Sr/86Sr ratios of 0.7098-0.7117. A mineral isochron gave an age of 479 m.y. Isotopic and geochemical data support the hypothesis that these rocks derive from the intrusion of a granitic magma produced by crustal anatexis. The source rocks were probably differentiated from the mantle 300-700 m.y. before the solidification of the charnockite. Th/U, K/Cs and Rb/Cs ratios and Au concentrations indicate that the source rock probably was of high metamorphic grade.

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