Estrutura Petrologia e Geocronologia do Batolito Brejo da Madre de Deus (Estado de Pernambuco), relaÃÃes com a zona de cilhamento Leste , Nordeste do Brasil / Structure Petrologia and Geocronologia of the Batolito Heath of the Madre de Deus (Been of Pernambuco), relations with the cilhamento zone East, Northeast of Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The Brejo da Madre de Deus batholith (BBMD), located in the central eastern part of Pernambuco state, constitutes the central portion of the Caruaru-Arcoverde bathoith, the largest body of the high-K calc-alkalic association in northeastern Brazil. It intrudes dominantly orthogneisses with dioritic to graitic composition and consists of three main facies: coarse-grained to porphyritic amphibole biotite monzongranite to syenogranite; medium-grained equigranular amphibole biotite syenogranite; and quartz diorite. The porphyritic facies is dominant, being intruded by the equigranular facies and displayng evidence of contemporaneity with the mafic facies. The porphyritic facies is early-tectonic with respect to the dextral East Pernambuco shear zone (EPSZ), which bounds the batholith to the south, whereas the equigranular facies is not tectonically deformed in the solid state. Field and anisotropy of magnetic susceptibility studies show that the magmatic and magnetic fabrics are similar, with dominance of low- to moderately dipping, E- to NE-striking foliations. The magmatic/magnetic foliation is superimposed, in the southern part of the BBMD, by a milonitc fabric related to the EPSZ and it is reoriented, in the central portion, to the direction of a intrabatholithic sinistral, NNE-trending shear zone. The BBMD is metaluminous and has SiO2 contents around 70 wt% in the equigranular facies, varying from 65 to 72 wt% in the porphyritic facies and from 51 to 59 wt% in the mafic facies. In the three facies, K2O/Na2O ratios are greater than 1; the rare earth elements (REE) patterns are characterized by light REE enrichment and small to negligible negative Eu anomalies; and spiderdiagrams of trace elements show depressions in Ba, Nb, Sr and Ti. The trace element characteristics are similar to those of subduction zone magmas, but in view of lack evidence for subduction events in the area, they must have been inherited from the source rocks. Pb-Pb zircon dating of the porphyritic and equigranular facies yielded ages of 591􀁲5 Ma and 583􀁲5 Ma, respectively. Although within error, these data confirm the younger age of the equigranular granite. Orthogneisses in the northen and southern parts of the BBMD yielded similar ages ranging between of 2070 Ma a 2090 Ma, suggesting that the batholith did not intrude a terrain boundary.

ASSUNTO(S)

geocronologia, geotectÃnica, asm, petrologia e geoquÃmica geocronologia, geotectonic, asm, petrology and geochemistry geociencias

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