The metasedimentary Macururé Complex (Sergipano Belt, Borborema Province, Brazil) in southern Alagoas state: geology and geochronology
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Abstract
The Sergipano Belt is part of the Southern Subprovince of the Borborema Province (NE Brazil) and separates the Pernambuco-Alagoas Domain from the São Francisco Craton. The Macururé Domain is the largest unit of the Sergipano Belt and comprises a basement of Paleoproterozoic age (Jirau do Ponciano Dome) and a supracrustal succession (Macururé Complex). Here we present the results of field, petrographic and structural work and of geochronological dating conducted in an area in the southern part of Alagoas state, northeast of the city of São Brás. The lithological associations of the Macururé Complex include quartzite, schist and banded metasedimentary rocks (metarhythmites). The main foliation shows a gentle dip to the southwest and is associated with a SW-plunging mineral lineation. The mineral assemblage muscovite+biotite+garnet±kyanite±staurolite in schist and metarhythmite indicates medium pressure and temperature conditions (amphibolite facies) typical of Barrovian metamorphism. U-Pb dating of detrital zircon grains from a quartzite sample yielded dominantly Tonian ages, showing a large age peak at c. 985 Ma. These zircon grains are thus derived from sources related to the Cariris Velhos event. The youngest grain has a 206Pb/238U age of 939±36 Ma (2s), which is considered as the maximum age of deposition. Two smaller age populations of c. 2.0 Ga and 1.1 Ga are also present. The most probable provenance of c. 2.0 Ga zircon grains is the nearby Jirau do Ponciano Dome. The other age group is more enigmatic and could be related to erosion of A-type rocks formed during local extensional events preceding the Cariris Velhos event.
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