Petrology and age of the Fazenda Lagoas stock, Macururé Domain, Sergipano Orogenic System, NE-Brazil

The Fazenda Lagoas Stock (SFL), has 20 km² area and age of crystallization of 623 ± 4 Ma and is intrusive into the metasedimentary rocks of the Macururé Domain. The northern boundary of the SFL is affected by the Belo Monte-Je-remoabo Shear Zone (BMJSZ), which prints gneiss structure to the rocks in this stock. The SFL consists essentially of quartz monzonites, having subordinate monzogranites and granodiorites. The microgranular enclaves are abundant and correspond to diorite and gabbro. The rocks present predominantly porphyritic texture and the mineralogy pre-sents solid state deformation, which was associated with regional shear (plagioclase and biotite kinks, feldspar and biotite rotation, quartz ribbon). Plagioclase crystals exhibit normal and inverse cyclic zonations and alkaline feldspar reverse zonation. Plagioclase composition varies from oligoclase to andesine in monzonites and enclaves varies from oligoclase to labradorite. The composition of brown biotite indicates origin from orogenic magma. Igneous amphiboles correspond to pargasite and edenite, total aluminum barometry indicated pressures ranging from 6.7 to 7.8 kbar (15-25 km) for monzonites and between 7.2 to 9.8 kbar (20-30 km) to the enclaves. The geochemistry showed high K shoshonitic and calcium alkaline affinities for the SFL forming magmas. The trace elements in multi-elemental diagrams show negative anomalies for Ta, Nb, Ti and P indicate that the SFL was formed in a collisional environment. Textures and geochemical evolution indicate fractional crystallization and mixing between felsic (monzonite) and mafic (gabbroic) magmas were important in the formation of the SFL rocks. (author)