Shear zone cooling and fabrics of synkinematic plutons evidence timing and rates of orogenic exhumation in the northwest Borborema Province (NE Brazil)

Author(s)

Avila, Carlos F. ^[1] ; Archanjo, Carlos J. ^[1] ; Hollanda, Maria Helena B. M. ^[1] ; de Macedo Filho, Antomat A. ^[1] ; Lemos-Santos, V, Daniel do

Affiliation

^[1] V, Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: Precambrian Research; v. 350, NOV 2020.
• Web of Science Citations: 0

Abstract

Ediacaran convergence and collision resulting from amalgamation of West Gondwana are documented in the Borborema Province by high-pressure rock units, contractional tectonics and anatexis. Thermochronological (zircon U-Pb and amphibole-biotite Ar-Ar) and structural (Anisotropy of Magnetic Susceptibility) constraints from shear zone-bounding synkinematic plutons in the Ceara Central Domain provide timing and rates of their subsequent post-collisional evolution. Our results show that: (i) U-Pb ages of zircons of 585-571 Ma record magma crystallisation and a protracted history of assembly for the Taua batholith, synchronous with deformation in the bounding transcurrent shear zone junction; (ii) AMS fabrics document chamber construction processes and the effect of long-lived strongly localized shear zone deformation; and (iii) Ar-40/Ar-39 plateau ages of amphibole and biotite from the synkinematic plutons at 577-562 and 559-554 Ma, respectively, yield cooling rates of 20-40 degrees C/Myr characterising differential cooling paths. Integration of various thermochronometers available for the strike-slip shear zones and the internal high-pressure domain reveals a fast isothermal decompression (long-term unroofing rate of 1.9-5.8 mm/yr), which exhumed high-pressure rock units. Subsequently, fast nearly isobaric cooling (20-40 degrees C/Myr) occurred in the whole terrane until 590 Ma, with temperatures falling below 320 degrees C. Due to enhanced magmatic activity during the deformation, the shear zones experienced much higher temperatures at that same depth at 584 Ma followed by fast cooling (20-40 degrees C/Myr) to temperatures below 320 degrees C at 560 Ma. These final cooling episodes were accompanied by slow unroofing at an estimated rate of 0.3-0.9 mm/yr, sufficient to bring these rocks close to the surface at 540 Ma, when molassic, pull-apart basins were formed. (AU)

• FAPESP's process: 19/10167-6 - Electron Backscatter Diffraction (EBSD) analysis of deformation microstructures - Constraining rheology and deformation conditions of northern Borborema Province (NE Brazil)
• Grantee: Carlos Fernando Ávila Rodrigues
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• FAPESP's process: 17/21440-0 - Cooling ages and tectonics of the Ceará Central (Borborema Province, NE Brazil)
• Grantee: Carlos José Archanjo
• Support Opportunities: Regular Research Grants
• FAPESP's process: 16/22226-9 - Deformation and chronology of the granitic magmatism associated with the Tauá and Senador Pompeu shear zones (Borborema Province, NE, Brazil)
• Grantee: Carlos Fernando Ávila Rodrigues
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)