Strain Partitioning along Terrane Bounding and Intraterrane Shear Zones: Constraints from a Long-Lived Transpressional System in West Gondwana (Ribeira Belt, Brazil)

Author(s):Show less -

Faleiros, F. M. ; Ribeiro, B. V. ; Campanha, G. A. C. ; Cawood, P. A. ; Cabrita, D. I. G. ; Yogi, M. T. A. G. ; Milani, L. A. ; Lemos-Santos, D. V. ; Almeida, V. V. ; Rodrigues, S. W. O. ; Malta, I. S. ; Forero-Ortega, A. J.

• Document type: Journal article
• Source: LITHOSPHERE; v. 2022, p. 29-pg., 2022-02-01.

Abstract

Shear zones are zones of localized high strain accommodating differential motion in the lithosphere and impacting the crustal rheology and deformational history of orogenic belts. Although terrane bounding shear zones are widely studied, intraterrane shear zones and their tectonic significance, especially in association with supercontinent assembly, is a largely unexplored topic. The Ribeira Belt (SE Brazil), a Neoproterozoic-Cambrian orogenic belt from West Gondwana, is dissected by a crustal -scale NE-trending transcurrent shear zone system that juxtaposes composite terranes. Despite its extensive coverage and complexity, this shear zone system remains poorly investigated. In this paper, we explore the thermal and deformational regimes, and timing of ductile shearing using a multiscale approach combining structural analysis derived from remote sensing and field-based structural data, microstructures, quantitative structural analysis, and multimineral U-Pb geochronology (zircon, titanite, monazite, and xenotime). Our data, combined with previously published data, indicate a transitional northeastward increase in metamorphic conditions from lower greenschist to granulite facies conditions (from 250-300 to 750-800 & DEG;C), reflecting the different crustal levels that are exposed. Vorticity and finite strain data indicate a complex strain regime with varied contributions of pure and simple shear and oblate-shape ellipsoids in strike-slip shear zones and prolate -shaped ellipsoids in dip-slip reverse shear zones. The strain set suggests that all shear zones were developed under subsimple shear deformational regimes involving thrusting and folding followed by wrench tectonics. The pure shear component of deformation was accommodated in folded domains between shear zones. Geochronological data suggest intermittent ductile shear zone activations from ca. 900-830 to 530 Ma, partially coeval with at least two major episodes of terrane accretion at 850-760 Ma and 610-585 Ma. The spatial and temporal record of shear zones within the Ribeira Belt indicates that some relate to assembly of the belt and represent either terrane bounding structures (e.g., Itapirapua shear zone) or intraterrane structures (e.g., Ribeira, Figueira, and Agudos Grandes shear zones), whereas others are terrane bounding, postcollisional shear zones (e.g., Taxaquara shear zone) reactivated in an intracontinental setting (560-535 Ma). (AU)

• FAPESP's process: 19/10457-4 - Isotope dating coupled to trace element characteristics in igneous and metamorphic minerals from the Embu Terrane, and their implications for the reconstruction of the Ribeira Belt tectonic evolution
• Grantee: Dina Isabel Guerreiro Cabrita
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 18/10012-0 - Fluid flow, deformation and tectonic significance of regional shear zones from the southern Ribeira Belt
• Grantee: Frederico Meira Faleiros
• Support Opportunities: Regular Research Grants
• FAPESP's process: 15/26645-3 - Tectonometamorphic evolution of the Embu Terrane and relationships with adjacent terranes in the Southern Ribeira Belt (São Paulo, Brazil)
• Grantee: Dina Isabel Guerreiro Cabrita
• Support Opportunities: Scholarships in Brazil - Doctorate