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Título

THE LAST HIGH MAGMATIC RATE EVENTI IN WEST-GONDWANA, AND THE BUILDING OF THE CARUARU-ARCOVERDE BATHOLITH, NORTHEASTERN BRAZIL

Texto do resumo

The Caruaru-Arcoverde Batholith (BCA; ~3000 km²) is one of the main Neoproterozoic intrusions in the eastern Borborema Province, northeastern Brazil. The use of the geophysical and satellite images associated with field investigation, allowed individualizarion of eight plutons composing the batholith. The rocks of the batholith vary between syenites, granites, monzonites and quartz-diorites, which crystallized under pressure conditions at 4 to 6 kbar. Quartz-diorites are the most mafic rock of the batholith, occurring as mappable bodies, syn-plutonic dikes and microgranular mafic enclaves, showing different levels of mixing/mingling with the more felsic units. Mafic mineralogy constitutes an important point in the individualization of BCA, there are plutons that show only biotite, others show amphibole+biotite, and others pyroxene+amphibole+biotite. The batholith rocks are intermediate to acidic, show affinity with the high-K calc-alkaline and shoshonitic series. Whole rock εNd(0,6 Ga) are variably negative, varying from -10.34 to -20.61, and the TDMNd ages vary from 1.72 to 2.28 Ga and initial ratios 87Sr/86Sr(0.6 Ga) are also variable, ranging from 0.7069 to 0.7114. The U-Pb crystallization ages, recognized in the literature, for some plutonsh are restricted, from 582 to 596 Ma, with the youngest ages observed in the more silica-richer rocks, which show simple mafic mineralogy. The data obtained for the BCA plutons suggest they are genetically related, and their magmas suffered strong crustal contribution from a mainly Paleoproterozoic source, with a progressive larger contribution in the youngest magmas. Presence of pulses of mafic magma, as suggested by co-magmatic quartz-dioritic rocks, as well as the presence of pyroxene-bearing rocks rich, suggest mantle contribution for the formation of the BCA magma. Possibly, the continuous injection of mafic magmas contributed to the widespread melting of the crust. Finally, the large volume of magma generated in a short period of time (~14 Ma) configures magmatism with a high addition rate, 0.002 km³/y (flare-up), in this western portion of Gondwana at the end of the Neoproterozoic.

Palavras Chave

High Magmatic Rate; Caruaru-Arcoverde Batholith; Borborema Province.