Química mineral dos stocks Fazenda Lagoas e Riacho do Mingu, Sistema Orogênico Sergipano, sul da Província Borborema, Brasil: Uma interpretação sobre a evolução da cristalização e mistura de magmas.

Abstract

The Fazenda Lagoas Stock (FLS; 623 Ma) and the Riacho do Mingu Stock (RMS) are intrusions emplaced into the metasedimentary rocks of the Macururé Domain (MD), located in its northern portion and in contact with the Belo Monte Jeremoabo Shear Zone, within the Sergipano Orogenic System (SOS). The FLS is a monzonitic intrusion with porphyritic texture, characterised by phenocrysts of alkali feldspar in a matrix of quartz, feldspar, and biotite. Dioritic enclaves suggest hybridisation with the host monzonites, containing calcic amphibole (edenite, pargasite, tschermakite, Mg-hornblende) with Mg# ranging from 0.5 to 0.8. The intensive crystallisation conditions of the monzonites ranged from 5.7 to 9.0 kbar and temperatures between 852°C and 926°C, whereas the enclaves experienced pressures of 2.4 to 9.8 kbar and temperatures up to 929°C. The chemical evolution of amphibole indicates two distinct sources for the monzonites: a mantle-derived source (high pressure and temperature) and a mixed crustal/mantle source (low pressure and temperature), with formation depths reaching up to 33 km. The RMS is a syenitic intrusion that also shows evidence of magma mixing. It exhibits a porphyritic texture, with alkali feldspar phenocrysts set in a matrix of biotite, amphibole, plagioclase, and quartz. Mafic enclaves and the compositions of amphibole and plagioclase confirm the involvement between magmas. Chemical studies of amphibole crystals suggest that the syenites crystallised under pressures ranging from 2.5 to 4.8 kbar, while enclaves formed at pressures of up to 9.1 kbar, with crystallisation temperatures of 672°C to 876°C for the syenites and up to 830°C for the enclaves. Biotite crystallised or re-equilibrated at temperatures between 585°C and 646°C, with its compositions further supporting the interpretation that these rocks formed through the mixing of mafic and felsic magmas.