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

• Published in: Precambrian research Vol. 350; p. 105940
• Main Authors: Ávila, Carlos F., Archanjo, Carlos J., Hollanda, Maria Helena B.M., Macêdo Filho, Antomat A. de, Lemos-Santos, Daniel do V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2020
• Subjects: Ar/Ar thermochronology; Borborema Province; Magnetic fabrics; Multi-stage exhumation; Shear zone cooling; Magnetic fabrics; Multi-stage exhumation; Ar/Ar thermochronology; Borborema Province; Shear zone cooling
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2020.105940

•Uncoupled AMS fabrics and protracted 15 Myr assembly characterise the Tauá batholith.•Ar-Ar thermochronology shows relatively fast shear zone cooling at 20–40 °C/Myr.•Isothermal decompression and isobaric cooling characterise the NW Borborema Province. 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 Ceará 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 Tauá 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) 40Ar/39Ar plateau ages of amphibole and biotite from the synkinematic plutons at 577–562 and 559–554 Ma, respectively, yield cooling rates of 20–40 °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 °C/Myr) occurred in the whole terrane until 590 Ma, with temperatures falling below 320 °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 °C/Myr) to temperatures below 320 °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.