Ediacaran to Cambrian magmatic suites in the Rio Grande do Norte domain, extreme Northeastern Borborema Province (NE of Brazil): Current knowledge

Abstract

The Ediacaran–Cambrian plutonic activity is one of the most important geological features of the Rio Grande do Norte Domain (Borborema Province, NE Brazil). It is represented by several batholiths, stocks and dykes. Based on the petrographic, geochemical and geochronological characteristic of different rocks, this plutonic activity can be grouped in six separate suites: shoshonitic (Shos), porphyritic high-K calc-alkaline (PHKCalcAlk), equigranular high K calc-alkaline (EHKCalcAlk), calc-alkaline (CalcAlk), alkaline (Alk) and charnockitic alkaline (ChAlk). Geochemically, the Shos, CalcAlk and Alk suites are differentiated from the others, while ChAlc can be distinguished from the others in some diagrams. The greatest difficulty lies in distinguishing between the chemically similar PHKCalcAlk and EHKCalcAlk. To this end, existing geochronological data as well as related petrographic and textural field aspects may be used to distinguish the two mentioned suites (PHKCalcAlk and EHKCalcAlk).Petrographically, the Shos suite has composition between gabbro/diorite and quartz monzonite. Monzogranites (with subordinate granodiorites and quartz monzonites) predominate in both PHKCalcAlk and EHKCalcAlk. Calc is composed of granodiorites to tonalites. Alc is formed by alkali feldspar granites (with subordinate alkali feldspar quartz syenites and syenogranites), whereas ChAlc has quartz mangerites and charnockites.The suites were emplaced between the Ediacaran (635–541 Ma) and Cambrian (541–485 Ma), predominantly in the Ediacaran, based on 34 U–Pb datings (zircon, titanite, monazite and columbite–tantalite), 17 Rb–Sr (whole rock) and 1 Sm–Nd (total rock and mineral) internal isochrons. The Shos suite has U–Pb ages varying from 599 ± 16 (Poço Verde pluton) to 579 ± 7 (Acari and São João do Sabugi plutons), slightly older than those of the PHKCalcAlk suite, which ranges between 591 ± 4 Ma (Totoró pluton) and 544 ± 7 Ma (São José de Espinharas pluton). The CalcAlk Suite has only one dated body, aged 598 ± 3 Ma (Serra da Garganta pluton). The EHKCalcAlk suite U–Pb dating is younger than the aforementioned suites, ranging from 582 ± 5 Ma (dykes in Dona Inês pluton) and 527 ± 8 (Cerro Corá pluton). The Alk suite was dated at 578 ± 14 Ma (Caxexa pluton, Sm–Nd internal isochron) and at 597 ± 4 Ma (Japi pluton, U–Pb zircon), while ChAlc U–Pb zircon ages of 601 ± 10 Ma and 593 ± 5 Ma (Umarizal pluton). The magmatism of Cambrian age in the Rio Grande do Norte Domain is represented by pegmatite dykes with U–Pb dating between 515 and 510 Ma.