| Popis: |
The focus of the present work is the rebound of the magmatism at the late stages of orogenic collapse in the Aracual Belt, in Brazil. At the end of the orogen bimodal inversely zoned plutons were emplaced along a tectonic corridor following the Atlantic coast of Brazil. This event culminates around 500 Ma. We review geology, petrography, geochemistry and geochronology of these plutonic structures in the region of Espirito Santo. New geochemical modeling of trace element data together with new whole rock Sm-Nd and Rb-Sr isotopic data depict a gradual process of mantle contamination during different stages of the orogen. In the post-orogenic stage contamination reaches extreme values. Basic rocks reach epsilon Nd-(0.5Ga) values below -10. Gabbros to peridotites are more enriched in Ba, Zr, LREE and Sr than the surrounding metasediments. Four new U-Pb data sets from determinations in zircon and monazite crystals, (central northern part of the belt) confirm peak magma production around 500 +/- 15 Ma, ranging up to 525 +/- 3 Ma in one of the structures. Based on the pictured data, we discuss the significance of this magmatism and present a possible model: a process of gradational delamination of the subcontinental lithospheric mantle and adjacent deep continental crust through underplating. As a consequence, an already enriched mantle was dramatically further contaminated. At the end of this event the intrusion of alkaline melts, with less negative epsilon Nd (-5) and further enrichment in incompatible elements, point towards a new input of deeper juvenile mantle magma. Our data suggest the possible onset of a hotspot due to the destabilization of the asthenospheric mantle after orogenic collapse. (C) 2016 Elsevier Ltd. All rights reserved. |
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