A review of the Brasiliano magmatism in southern Espírito Santo, Brazil, with emphasis on post-collisional magmatism

Cristina P. De Campos, Júlio Cezar Mendes, Isabel P. Ludka, Silvia R. de Medeiros, Jorge C. de Moura, and Carin Wallfass

Located at the Atlantic continental margin of Brazil, the Espírito Santo State links two Brasiliano-age fold belts: the northern Ribeira Belt and the southern Araçuaí Belt. In the central part of this region a deeply eroded crust is exposed, disclosing the roots of the Araçuaí-Ribeira Belt and the core of a continent-continent collision, which took place during Precambrian times. During the main collisional event (from W to E: 590 Ma to 575 Ma), considerable crustal thickening was generated from large to small scale isoclinal folding, refolding and the piling up of crustal segments and flakes along thrust faults. In this work we describe the major igneous events of the orogen, focusing particularly on the early and late post-collisional plutonism.

Metamorphism in the central zone of the orogeny reached high amphibolite to granulite facies at ~ 590 Ma and produced a high-grade metamorphic complex made up mostly of sillimanite + garnet ± cordierite ± biotite kinzigitic gneisses grading into hypesrthene granulites, sillimanite quartzite and marbles. These rocks were intruded by syn-collisional tonalitic magmas at ~580 Ma associated with widespread crustal anatexis (anatexis I) and the coeval intrusion of minor amounts of basic to intermediate magmas.

This early high-grade metamorphism was followed by cooling and then reheating of the gneisses and granulites, which caused retrograde metamorphism, new partial melting (anatexis II) and the early post-collisional phase of enderbitic magmatism at around 560 Ma. The youngest magmatic phase, known as the late post-collisional magmatism, is characterized by sills, dykes and mostly bimodal complexly zoned plutons with extensive mingling between, and varying in composition from orthopyroxene-gabbro to granite. They intruded between 530 to 480 Ma with a peak at 500 Ma, and were associated with the third phase of anatexis (anatexis III). Metaluminous to peraluminous, high-K calc-alkaline, I-type granitoids of this late post-collisional phase progressively evolve into more markedly alkaline suites. While the early post-collisional sequences were probably generated by dehydration melting of a metasedimentary crust with small contributions from other sources, the late post-collisional association originated from contrasting sources: a) partial remelting from a mainly metaluminous continental crust, b) new dehydration melting from slightly peraluminous crustal portions, and c) important mafic contributions from an enriched mantle.