Banca de DEFESA: Juliana Rezende de Oliveira

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Juliana Rezende de Oliveira
DATE: 02/09/2022
TIME: 14:00
LOCAL: Sala de videconferência do IGD
TITLE:

PRE-MESOZOIC BASEMENT OF AREQUIPA AND ANTOFALLA TERRANES: GEODYNAMIC IMPLICATIONS AND GENERATION OF MAGMATIC ARCS IN THE BOLIVIA-CHILE REGION.

KEY WORDS:

Cerro Uyarani Metamorphic Complex, Belén Metamorphic Complex, U-Pb/Hf in zircon, Sunsas-Grenville Orogeny, Famatinian magmatism

PAGES: 174
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

In the Central Andes region, specifically on the west coast of South America, two exposures of the pre-Andean basement, in the Cerro Uyarani, in Bolivia and another near Belén, in Chile, record the tectono-magmatic and metamorphic history of the Paleoproterozoic, Mesoproterozoic, Neoproterozoic, and Ordovician pre-gondwanic basement. The study of these areas is of paramount importance because these terranes recorded the evolution history of the western part of South America. The Paleoproterozoic basement of the Arequipa terrane (18 to 14 ºS) occurs from the west coast of Peru to the Bolivian Altiplano. This basement crops out in the Cerro Uyarani area in Oruro department, Bolivia. The Cerro Uyarani Metamorphic Complex (CUMC) – this work, consists of felsic and mafic granulite facies metamorphic rocks. This exposure was recognized as a crustal fragment that experienced magmatic and high-grade metamorphic events in the Paleoproterozoic and lower-grade metamorphism in Mesoproterozoic-Neoproterozoic times. Our new zircon U-Pb (LA-ICP-MS) and first Hf isotopic data reveal a distinct geological history. The zircon textures study combined with U-Pb ages indicate two main events, one during the Paleoproterozoic, indicated by magmatic zircon cores of 1.81-1.75 Ga, and rare metamorphic cores of 1.88 Ga, and a second Mesoproterozoic event, during which the old cores were recrystallized. This second event include a first cycle with basement migmatization at 1.19–1.17 Ga. The second cycle at ~1.1–1.0 Ga recorded the transformation of the migmatitic basement into granulite facies. Hafnium and U-Pb isotopic data together suggest that the CUMC was part of the southernmost portion of the Arequipa terrane at least from ~1.74 Ga, and was added to the Paraguá terrane and Amazonian Craton at 1.19–1.17 Ga. The second event is characterized by a accretionary phase – cycle 1 - followed by a colisional phase – cycle 2 - when metamorphic conditions reached granulitic facies. The zircon U-Pb and εHfT data show similarity with the Arequipa terrane, Rio Apa terrane, SW Amazon Craton, and other Grenvillian inliers.

The Belén Metamorphic Complex comprises mainly orthogneisses, and minor schists, ultramafic rocks, and mafic and felsic dykes emplaced along approximately 20 km extent exposure, in an NNW-SSE arrangement. The U-Pb/Hf (LA-ICP-MS) in these lithotypes zircon grains allow to trace the evolutionary history of Famatinian magmatism in this region. The magmatism flare-ups between 470 and 464 Ma with generation of quartz monzodiorite, granodiorite, and tonalite intruded by syn-plutonic mafic dikes. These rocks are intensely deformed and metamorphosed

to upper amphibolite grade. The εHfT values indicate, as in other areas affected by Famatinian magmatism, juvenile magmatism with high crustal assimilation to the Belén region. Several hypotheses have been postulated to explain how a mantle source magmatism can have an intense crustal signature among them: 1) reworking of old crust; 2) reworking of subducted sediments; or 3) installation of the magmatic arc in an accretionary prism, all involving mantle component input. A few inherited zircon grains (1.97-1.95 Ga) from amphibolite and amphibole gneiss of the CMB and the isotopic Hf data suggest reworking of the Arequipa terrane (CUMC being considered as part of this terrane), which was reworked during the Sunsas-Grenville Orogeny. Then, the BMC would represent a Mesoproterozoic reworked terrane intruded by felsic to mafic plutonic rocks during the Ordovician. The new U-Pb data and the few Hf data provided so far in this thesis are very important to the understanding of the tectonic evolution from the Paleoproterozoic to the Ordovician in the western part of the South America, a place with few basement outcrops.

BANKING MEMBERS:
Externo à Instituição - VICTOR ALBERTO RAMOS
Externo à Instituição - CÉSAR CASQUET MARTÍN
Interna - 1555904 - CATARINA LABOURE BEMFICA TOLEDO
Interno - 2370895 - LUIS GUSTAVO FERREIRA VIEGAS
Presidente - 1897668 - NATALIA HAUSER