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ALBUQUERQUE, Carlos Alberto Ribeiro de. Origin of the plutonic mafic rocks of sourthern Nova Scotia. Geological Society of America Bulletin., v. 90, parte 1, p. 719-731. Ago.1979.

RESUMO

Mafic rocks of the Appalachian orogenic belt of sourthern Nova Scotia were analyzed for major elements, Ba, Sr, Rb, Zr, Nb, Y, and rare-earth elements. These plutonic rocks comprise plagioclase peridotite, norite, high-K diorite, and tonalite. Comparisons with volcanic rocks and other plutonic calc-alkalic rocks indicate that mafic rocks of orogenic belts are very similar in composition to continental tholeiitic besalts, whereas the plagio clase peridotite is chemically comparable to picrites. The high-K diorites have distictive geochemical characteristics and show only a few analogies with volcanic rocks. It is suggested, on the basis of the modeling of the data, that the noritic magma could have been originated by partial melting of upper-mantle material with light rare-earth element abundances five to ten times those of chondrites and heavy rare-earth element abundances two to five times the chondritic abundances. The plagioclase peridotite can be derived from a contaminated magma, although the contamination appears to be of mantle (or lower crust) origin. An origin by hybridization of mafic magma with a granitic liquid for the high-K diorites is consistent with the data available.

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