Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil

Abstract

At the end of the geotectonic cycle that shaped the northern segment of the Ribeira Mobile Belt (Upper Proterozoic to Paleozoic age), a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. The Várzea Alegre Intrusive Complex is a post-collisional complex. The younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. The combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. The first originated from the partial melting of the mantle. This was previously enriched in incompatible elements, low and intermediate REE and some HFS-elements. A second enrichment in LREE and incompatible elements in this series was due to the mingling with a crustal granitic magma. This mingling process changed the composition of the original tholeiitic magma towards a medium-K calc-alkalic magma to produce a suite of basic to intermediate rock types. The granitic magma from the second high-K, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.

Late Neoproterozoic-Cambrian granitic magmatism in the Araçuaí orogen (Brazil), the Eastern Brazilian Pegmatite Province and related mineral resources

“…The most outstanding features revealed are the roots of diapirs and their inverse zoning, displaying interfingering of mafic to intermediate rocks in the core and syeno-monzonitic to granitic borders, together with widespread evidence of magma mixing (e.g. Bayer et al 1987;SchmidtThomé & Weber-Diefenbach 1987;Wiedemann 1993;Mendes et al 1999Mendes et al , 2005Medeiros et al 2000Medeiros et al , 2001Medeiros et al , 2003Wiedemann et al 2002;De Campos et al 2004;Pedrosa-Soares et al 2006a, b). Metaluminous to peraluminous, high-K calcalkaline, I-type granitoids (e.g.…”

Cambro-Ordovician post-collisional granites of the Ribeira belt, SE-Brazil: A case of terminal magmatism of a hot orogen

“…The same holds for their correlatives in the Araçuaí belt, which include relatively more bimodal examples (e.g. Wiedemann et al, 1995;Medeiros et al, 2001;Mendes et al, 2005). Two consecutive collisions, at ~580 Ma and at 530 Ma, both having produced abundant granitic magmatism, must have generated a thick and hot, therefore gravitationally unstable continental crust.…”

A Origem Das Bordas De Mirmequita Nos Xenocristais De Feldspato Potássico Em Rochas Máficas E Híbridas Do Maciço Santa Angélica – Es

“…Na região sul do Espírito Santo, esta suíte é representada por vários plutons com composição granítica e núcleos gabróicos que caracterizam o estágio de relaxamento termal do orógeno e a origem híbrida resultante da mistura de magmas mantélicos e crustais (Wiedemann, 1993;Pinto et al, 1997Pedrosa-Soares & WiedemannLeonardos, 2000;Wiedemann-Leonardos et al, 2000;Noce et al, 2000;Medeiros et al, 2001;Pedrosa-Soares et al, 2001, 2006Wiedemann et al, 2002;Campos et al, 2004;Martins et al, 2004;Mendes et al, 2005;Silva et al, 2005). Comumente apresentam feições de mistura mecânica (mingling) e química (mixing) de magmas, além de enclaves máficos e xenólitos das rochas encaixantes.…”