Full text
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| Author(s): |
Nádia Borges Gomes
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências |
| Defense date: | 2019-05-24 |
| Examining board members: |
Ticiano José Saraiva dos Santos;
Renato de Moraes;
Vinicius Tieppo Meira
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| Advisor: | Ticiano José Saraiva dos Santos |
| Abstract | |
The formation of Western Gondwana involved ocean closure with subduction of lithosphere, arcs generation, and continental collision. In the Central Ceará Domain, in the Borborema Province, the records of this event are the Santa Quitéria Continental Magmatic Arc (SQCMA), the Lagoa Caiçara unit and the ultra-high pressure retrogressed eclogites identified on the east and west edges (Forquilha Eclogitic Zone) of the arc. Thus, there are evidences of Neoproterozoic suture zones of the Brasiliano/Pan-African event. On the eastern margin, migmatitic orthogneisses with anastomosed foliation outline the arc and, together with a sequence of high grade metasedimentary rocks, form thrust systems with vergence out of the arc. The para-derived rocks represent passive and active margin sequences juxtaposed and submitted to upper amphibolite facies metamorphism and with marked retrogression in greenschist facies. Retrogressed eclogite slice embedded in migmatitic paragneiss contains coesite relic as inclusion in garnet. Its identification was based on Raman spectroscopy. Empirical to semi-empirical thermobarometric data and phase diagram allowed to model and reconstruct the clockwise metamorphic path for the retroeclogitic body, with a peak pressure at 35.8 ± 5.2 kbar, and a peak temperature above 770 ºC. The retrometamorphism undergoes amphibolite facies conditions (pl + amp coronas on granada, well developed amphibole in the matrix and replacement of pyroxene vermiculas by amphibole) and incipient greenschist conditions, defined by the presence of chlorite in the garnet fractures. Hosted in migmatitic paragneisses occurs Mg-Al rich boudin, that comprises corundum, garnet, cordierite, gedrite and biotite, intensely chloritized. The highest metamorphic conditions obtained by Average PT mode (THERMOCALC) for this rock were ca. 13 kbar and ca. 800 ºC. The SQCMA evolution model involves double subduction with convergent polarities to W-NW and E-SE, reinforced by the presence of coesite in the Forquilha Eclogitic Zone and in the east, as presented here. This tectonic setting correlates with that observed in Africa, in the Pharusian belt region, and is part of the reconstruction of Western Gondwana (AU) | |
| 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 |