CRIOGENIAN AND EDIACARAN MAGMATISMS (643 TO 603 Ma) IN THE MACURURÉ DOMAIN, SOUTH OF THE BORBOREMA PROVINCE

Abstract

The Macururé Domain is part of the Sergipano Orogenic System. It comprises two units: a metasedimentary succession called the Macururé Complex and Cryogenian-Ediacaran magmatism, where around fifty-four stocks and two batholith are found. Geochronological studies, especially U-Pb determinations in zircon by SHRIMP and LA-ICP-MS, have allowed us to identify four intervals of emplacement of different magmatic suites: [1] Macururé Mafic Suite (643-628 Ma); [4] Shoshonitic Suite (631-603 Ma); [2] High-K Calc-Alkaline Granitic Suite (630-626 Ma); and [4] High-K Calc-Alkaline Granodioritic Suite (625-618 Ma).

Keywords: GRANITES; U-Pb GEOCHRONOLOGY; SERGIPE

Introduction

The Brasiliano/Pan-African Orogeny in the Borborema Province, northeastern Brazil, is characterized by extensive magmatism, development of continental-scale shear zones, and metamorphism. The Sergipano Orogenic System (SOS) is in the southernmost segment of the Borborema Province and exposes large volumes of intrusive rocks. The SOS terranes in Sergipe have been compartmentalized into six domains (Davison and Santos 1989), whose boundaries are defined by shear zones. From north to south, four domains host intrusive rocks: Canindé, Poço Redondo, Marancó, and Macururé.

The Macururé Domain comprises two units (Figure 1): (i) the metasedimentary succession of the Macururé Complex and (ii) the Cryogenian-Ediacaran magmatism. The Macururé Complex comprises metaturbidite rocks metamorphised under greenschist and amphibolite facies, such as biotite schists and phyllites with garnet, metarenites, metagraywackes, and quartzites.

Until the last decade, the SOS magmatism has been grouped into 630-618 Ma and 590-570 Ma (Bueno et al. 2009; Oliveira et al. 2010, 2015). However, recent data show a continuum of crystallization ages marking changes in the composition of igneous rocks from (1) high-K calc-alkaline and shoshonitic gabbros and diorites (Pereira et al. 2020, 2023, 2024) to (2) leucogranites containing muscovite and biotite (Conceição 2017), and (3) high-K calc-alkaline to shoshonitic granodiorite-monzonitic intrusions. These data suggest that the magmatic episodes in the MD need to be refined in light of new data to unravel the geodynamic evolution of the southern Borborema Province.

Experimental

Zircon concentrates were obtained using conventional crushing, grinding, and panning methods, followed by magnetic and gravimetric separation. The zircon crystals were handpicked and mounted in epoxy discs 25 mm in diameter, then polished until the longitudinal section of the crystals was exposed. The mount surface was gold-coated, and the zircon internal domains were investigated by cathodoluminescence images using a scanning electron microscope.

U‒Pb isotopic ratios were measured using (i) the Sensitive High-Resolution Ion Microprobe (SHRIMP IIe) installed at the Centro de Pesquisas Geocronológicas, Universidade de São Paulo (CPGeo-USP); (ii) a sector field inductively coupled plasma mass spectrometer (LA-SF-ICP-MS) Element 2 Thermo Finnigan coupled with a Photon Machines 193 nm ArF Excimer laser ablation system, at the Departamento de Geologia, Universidade Federal de Ouro Preto (DEGEO/UFOP); and (iii) a Thermo Scientific iCAP-Q quadrupole ICP-MS coupled with a Nd:YAG LSX-213 G2 CETAC laser ablation system, at the Laboratório de Geologia Isotópica, Universidade Federal do Pará. Age calculations employed the uranium decay constants recommended by Steiger and Jäger (1977) and were performed using the Isoplot 4.15 Excel add-in Ludwig (2009). All reported ages include analytical uncertainties at the 2σ confidence level.

Figure 1. Geological outline of the Macururé Domain. Yellow stars, U-Pb SHRIMP ages in zircon obtained by our research group. Blue stars, U-Pb ages in zircon and titanite (Bueno et al. 2009; Oliveira et al. 2010, 2015). The values in brackets correspond to the εHf(t) obtained by Pereira et al. (2023). BMJSZ = Belo Monte-Jeremoabo shear zone, SMASZ = São Miguel do Aleixo shear zone, PFSZ = Porto da Folha shear zone, 1- Camará, 2- Aquidabã, 3- Capela, 4- Campo Grande, 5- Dores, 6-Itabi, 7 – Fazenda Alvorada, 8- Altos Verdes, 9- Fazenda Lagoas, 10- Rio do Cachorro, 11- Glória Norte, 12- Propriá, 13- Mocambo, 14- Amparo do Sõo Francisco, 15- Graccho Cardoso, 16- Pedra Furada, 17- Glória Sul, 18- Coronel João Sá, 19- Santa Helena e 20- Lagoa do Roçado.

Results and Discussion

Our team has studied the magmatism of the Macururé Domain over the last ten years, and around fifteen intrusions have been dated. Its geological characteristics and petrographic, geochemical, and isotopic data allow it to be grouped into four magmatic suites (Figure 1).

Macururé Mafic Suite (643-628 Ma): formed by diorites, gabbros, monzonites with subordinate granites, which are high-K calc-alkaline, shoshonitic, and intrusive pre- to syn-tectonic to regional deformation; and the U-Pb ages of the main intrusions are Camará (643 Ma), Aquidabã (636 Ma), Capela (631 Ma), Campo Grande (629 Ma), and Dores (628 Ma).

Shoshonitic Suite (631-603 Ma): essentially composed of monzonites, with subordinate granites and syenites. This suite stands out for its abundance of microgranular and lamprophyric shoshonitic and ultrapotassic mafic enclaves. The Itabi (631 Ma), Fazenda Alvorada (630 Ma), Altos Verdes (625 Ma), Fazenda Lagoas (623 Ma), Rio do Cachoro, (621 Ma), Glória Norte (621 Ma), Propriá (615 Ma), Mocambo (613 Ma), Amparo do São Francisco (608 Ma), and Graccho Cardoso (603 Ma) stocks have been dated.

High-K Calc-Alkaline Granitic Suite (630-626 Ma): corresponds to metaluminous and peraluminous leucocratic granites of the magnetite series, showing I-type geochemical signature of Cordilleran granites. The Pedra Furada (630 Ma) and Glória Sul (626 Ma) stocks have been dated.

High-K Calc-Alkaline Granodioritic Suite (625-618 Ma): these are intrusions where granodiorites with diopside dominate, granites are subordinate, and have the geochemical signature of a volcanic arc; the U-Pb ages of the main bodies are Coronel João Sá (625 Ma), Santa Helena (619 Ma), and Lagoa do Roçado (618 Ma).

The main features of magmatism in DM are: the predominance of potassic magmas (high-K calc-alkaline and shoshonitic); intermediate rocks dominate in the intrusions; the presence of microgranular and ultramafic shoshonitic and ultrapotassic mafic enclaves in the different magmatic suites; the occurrence of calcium amphibole as a liquidus mineral in the shoshonitic magmas (latitic, trachytic and basaltic), which indicates the hydrated nature of these magmas; and the temporal overlap of the intrusions of the different suites. The predominance of potassic magmas and the absence of typical calc-alkaline magmas in the DM reflect the geodynamic conditions in their genesis, with low partial melting rates and high depths.

Pereira et al. (2023) present the first Lu-Hf data for granites from the Macururé Domain (Figure 1). This research highlights the significant role of subduction associated with the Rhyacian Orogeny in the enrichment of the lithospheric mantle beneath the southern Borborema Province. This enrichment led to more radiogenic Hf values, producing Paleoproterozoic Hf model ages.

Conclusions

Based on the geochronological data, it can be concluded that the different potassic magmatisms in the Macururé Domain were emplaced synchronously. The most abundant rocks are shoshonitic and are distributed in two main zones of the DM: in the central part, aligned in a NE-SW direction, and in the eastern portion, following an almost east-west trend.

Acknowledgements

The work received support from Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (Herbet Conceição – grant 310740/2021-5 and Maria de Lourdes da Silva Rosa – grant 311023/2021-5), Fundação de Apoio à Pesquisa e à Inovação Tecnológica do Estado de Sergipe – FAPITEC, and Secretaria de Estado de Políticas para as Mulheres – SPM. The authors thank the Condomínio de Laboratórios Multiusuários das Geociências of the Universidade Federal de Sergipe (CLGeo-UFS) for the geochemical analyses.