P-T-t reconstruction of a coesite-bearing retroeclogite reveals a new UHP occurrence in the Western Gondwana margin (NE-Brazil)

Author(s)

Gomes, Nadia Borges ; dos Santos, Ticiano Jose Saraiva ; Tedeschi, Mahyra ; Galante, Douglas ; Luvizotto, George Luiz

• Document type: Journal article
• Source: LITHOS; v. 446, p. 23-pg., 2023-04-03.

Abstract

The ultra-high pressure metamorphic rocks of the West Gondwana Orogen are the earliest evidence of deep subduction on Earth. The West Gondwana Orogen resulted from the closure of the Pharusian-Goianides Ocean in the Late Neoproterozoic, leading to the formation of the Santa Quite ' ria Continental Magmatic Arc (SQCMA) in NE Brazil and the Forquilha Eclogitic Zone, located on the western margin of the SQCMA, suggesting subduction from W to E. This research investigated and reports the occurrence of a coesite-bearing eclogite on the eastern margin of SQCMA, bringing new insights into the regional tectonic evolution of the West Gondwana Orogen. Although extensively retrogressed during exhumation, the coesite-bearing eclogite still records UHP conditions. The multiple stages of the pressure-temperature path were reconstructed by combining textural relationships, integrating symplectite domains in compositional maps, phase equilibrium modeling and Zr-in-rutile thermometry. The pressure peak is estimated at 35.8 +/- 5.2 kbar, reached at a temperature from 700 +/- 15 degrees C to 804 +/- 15 degrees C. Retrogression formed symplectite and corona textures at ca. 18 kbar and 760-860 degrees C. Our results indicate a clockwise P-T path that is characterized by a nearly isothermal decompression associated with a slight temperature increase after the baric peak, followed by decompression and cooling. Geochronological data indicate that the UHP rocks were metamorphosed in the Brasiliano/Panafrican orogenic event during the Western Gondwana amalgamation in the Neoproterozoic. Remnants of intra-oceanic arcs were described at the SQCMA eastern margin. We propose two main tectonic models for the evolution of these rocks: i) double subduction with convergent polarities to E-SE and W-NW, which can be correlated to the scenario proposed to the Hoggar belt in NW Africa and is also supported by geophysical data, and ii) exhumation of the eclogite as a diapir in the mantle wedge. (AU)

• FAPESP's process: 16/08289-8 - EAST BORDER OF THE SANTA QUITÉRIA MAGMATIC ARC: A NEW ULTRA-HIGH PRESSURE BELT IN THE CEARÁ CENTRAL DOMAIN?
• Grantee: Ticiano José Saraiva dos Santos
• Support Opportunities: Regular Research Grants
• FAPESP's process: 17/09206-1 - Thermobarometric evolution (P-T) of the volcano sedimentary rocks of the eastern edge of the Magmatic Arc of Santa Quitéria, Ceará
• Grantee: Nádia Borges Gomes
• Support Opportunities: Scholarships in Brazil - Master