Serra da Garganta Pluton as record of calc-alkaline magmatism in Rio Piranhas – Seridó Domain, Northeastern of Borborema Province

Abstract

There is an intense Ediacaran plutonism, related to the Brasilian/Pan African cycle in Borborema Province, denoted by numerous bodies of different chemical nature. The Serra da Garganta Pluton, located within the central portion of the Rio Piranhas–Seridó Domain, was the subject of cartographic, petrographic, chemical (whole rock and mineral) and geochronologic (zircon U-Pb) studies, in order to characterize its magmatic affiliation and crystallization age. The rocks that build up the SGP are grouped into two petrographic facies: (i) equigranular, fine- to medium-grained, gray-colored biotite tonalites to granodiorites with K-feldspar (microcline), oligoclase (An23-25), quartz, and biotite as the main mafic mineral; accessory minerals are amphibole, titanite, epidote, and allanite, as well as minute and rare crystals of opaque minerals, zircon, and apatite; and, (ii) equigranular, fine-grained, dark-gray-colored amphibole biotite quartz diorites with plagioclase, quartz, K-feldspar, and biotite as the chief minerals, with minor contents of amphibole and titanite; accessory phases are epidote, opaque minerals, allanite, and traces of zircon and apatite. It is common to observe field features indicating coexistence of magmas. The obtained results reveal rocks from both facies are metaluminous to peraluminous, with affinity of calc-alkaline rocks, which is not common for plutonic bodies in the extreme NE of Borborema Province. The U-Pb dating, for the main facies, of the 598±5 Ma (MSWD = 0.37) obtained in zircons (Shrimp) confirms Ediacaran age for its crystallization.