Tectonic inversion of compressional structures in the Southern portion of the Paramirim Corridor, Bahia, Brazil

Abstract

ABSTRACT:The Paramirim Corridor represents the maximum inversion zone of the Paramirim Aulacogen. Reverse-to-reverse dextral shear zones and various types of folds dominate such corridor. These structures reflect a stress field that is WSW-ENE oriented, developed in units of Aulacogen basement, as well as in the Lagoa Real Intrusive Suite, of Statherian age, in Espinhaço and São Francisco supergroups, of Statherian-Tonian and Cryogenian ages, respectively, and in the Macaúbas-Santo Onofre Group, of Tonian age at the most. A rich collection of extensional structures truncate compressional structures of the Paramirim Corridor, characterized by normal shear zones and foliation, which is sometimes mylonitic, down-dip stretching lineation, drag folds, traction fractures and S/C structures. In these shear zones, quartz occurs truncated by the foliation, while feldspars are fractured and altered to white mica. Distribution of the quartz c-axes is at a maximum of 14° from the Z-axis. Thus, it suggests that the deformation activated mainly the basal glide planes in the <a> direction. The paleostress study using the Win-Tensor software demonstrated that the regimen ranged between radial and pure distention. The S 1 direction oscillated around a vertical trend, while s 3 was sub-horizontal, with a predominant N230-050° direction. Ar-Ar ages in biotite obtained from the extensional shear zones ranged from 480 and 490 Ma. Together, data obtained for the structures associated with the late extensional regimen described in the present study suggest that its nucleation is associated with distal and brittle-ductile sectors of the gravitational collapse zone of Araçuaí-West Congo Orogen.KEYWORDS: Shear Zone; Paramirim Corridor; Gravitational Collapse. RESUMO: O Corredor do Paramirim representa a zona de máxima inversão do Aulacógeno do Paramirim, no qual predominam zonas de cisalhamento reversas-reversas destrais e vários tipos de dobras. Essas estruturas refletem um campo de tensão segundo WSW-ENE, os quais se desenvolvem nas unidades de embasamento do Aulacógeno, assim como na Suíte Intrusiva Lagoa Real, de idade estateriana, nos supergrupos Espinhaço e São Francisco, de idades estateriana-toniana e criogeniana, respectivamente, bem como no grupo Macaúbas-Santo

Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

“…The external fold‐and‐thrust belt and its structural grain trends N‐S in both Brazil and Congo (from Vitoria/Luanda and northward; Figure ), curving east‐southeastward around latitude 15°S toward the present Brazilian coastline, but with a northward extension into and across the craton along the reactivated Paramirim aulacogen (Figure ) (Cruz & Alkmim, ). This modified aulacogen represents a long‐lived pre‐Brasiliano extensional rift basin that was inverted (shortened) during the Brasiliano orogenic evolution, but also with evidence of extensional and transcurrent kinematics interpreted as late or postorogenic (Cruz et al, ). The amount of late Proterozoic shortening across this aulacogen decreases northward, but the structure clearly crosscuts the entire São Francisco craton.…”

Magnetic modelling and physical properties of magnesite deposits and regional sequences of Serra das Éguas, Brumado, Brazil

“…This region has a complex geological evolution, overlapped by orogenic events and riftings inserted in a tectonic context of the northern portion of the Araçuaí intracontinental orogen (Figure 1) (Borges et al., 2015; Cruz & Alkmim, 2017; Cruz et al., 2015). The granitoids and orthogneiss vary from paleoarchean to neoarchean which were generically inserted in the so‐called Gavião and Caraguataí Complex (Figure 2) (Barbosa et al., 2020; Medeiros et al., 2017).…”

IDADES U-Pb EM XENOTÍMIO-(Y) DE UM VEIO DE QUARTZO COM ALMEIDAÍTA E PARISITA-(La), NOVOS MINERAIS ENCONTRADOS NA SERRA DO ESPINHAÇO (NOVO HORIZONTE, BAHIA)

“…Os dois domínios presentes são intracratônicos (Figura 2), e as deformações relacionadas à tectônica regional são nitidamente influenciadas pelos designados "Aulacógeno do Paramirim" (Costa & Inda, 1982), ou "Corredor do Paramirim", que representam a zona de máxima inversão do citado aulacógeno (Cruz & Alkmim, 2006;Cruz et al, 2015). Neste contexto, a tectônica deformadora é dominada por zonas de cisalhamento reversas ou reversas destrais além de vários tipos de dobras, incluindo a geração dos veios de quartzo em sítios de máxima deformação.…”