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High - K Calc-Alkaline granitoids of ca. 1 ga. tdm along the limit peal Massif/Sergipano fold Belt, Ne Brazil and their geotectonic significance.

Zeppelini Editorial
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  • Chemistry
  • Earth Science
  • Geography


The Pernambuco - Alagoas Massif is located in the Southern Domain of the Borborema Province. Sm/Nd isotopic data show the existence of 15 Brasiliano granitic intrusions (ca. 0.6 Ga) with Sm/Nd TDM ages ranging from 0.9 Ga to 1.2 Ga. They can be divided into two groups: Group 1 includes metaluminous diorites, monzogranites, and granodiorites showing SiO. contents between 60 and 68 wt.%, NajO + K2O ~8 wt.%, high LILE/HFSE ratios, and spiderdiagrams characterized by troughs at Nb, Sr and n. Group 2 comprises peraluminous leucosyenogranites and leuco-monzogranites. They have high SiO2 (70 - 75 wt.%), and spidergrams and LILE contents similar to those of Group 1. Both groups show volcanic arc signatures and åNd(t) at 0.6 Ga from +3.0 to -1.7. Granitoids from both groups were generated from sources with similar Sm/Nd signatures. Brasiliano granitoids showing such young Nd isotopic signatures have not been recorded in other domains of the BP. Geochemical and isotopic data suggest mafic underplating during the late Mesoproterozoic or early Neoproterozoic in the Southern Domain of the Borborema Province. The volcanic arc and Nd signatures suggest that the mafic magma may have been a mixture from a subducting oceanic slab (-1.0 Ga?) and older lithospheric mantle. The mafic magmas differentiated to yield a zoned lower crust, explaining the geochemical differences among the granitoid magmas subsequently derived from it. TDM values < 1.0 Ga require later addition of younger juvenile material to the 1.0 Ga lower crust.

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