Banca de DEFESA: Fernando Santos Diener

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Fernando Santos Diener
DATE: 16/05/2023
TIME: 14:00
LOCAL: Sala de videoconferência do IG e Teams
TITLE:

"Geology of Córrego das Campinas Gabbro-Anorthosite Suite and metamorphic rocks of the southern portion of the Araguaia Belt: relationship with the Goiás Magmatic Arc and implication for the geodynamic evolution of the Tocantins Province"

KEY WORDS:

Tocantins Province, Goiás Magmatic Arc, Rodínia, Gondwana, Heat Traps,  Anorthosite, Araguaia Belt, Monte do Carmo Formation, high thermal gradients.

PAGES: 170
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Tocantins Province, located in Central Brazil, comprises rock types that are related  to important Neoproterozoic geotectonic events. The evolution history of the province is  complex, marked by accretionary and rifting events that led to the Western Gondwana  amalgamation. In order to contribute to the understanding of the evolution processes,  in the present work, rocks of two distinct geological contexts located in the central part  of the Tocantins Province were studied. New possibilities for the geodynamic  processes that resulted in the formation of the Tocantins Province are raised from the  results of this study. In the first area, the Córrego das Campinas Gabbro-Anorthosite  Suite was investigated. It is inserted in the Goiás Magmatic Arc framework, Brasília  Belt. The Córrego das Campinas Gabbro-Anortosite Suite is constituted of a  Proterozoic massive-type anorthosite body associated to a gabbroic body of similar  dimensions and minor intrusions and lenses of tonalite, quartz monzogranite, quartz  syenite, albite granite, Fe-diorite dykes, and ilmenite-enriched layers. The interpretation  of petrographic, lithogeochemistry and mineral chemistry data indicate that the Córrego  das Campinas Gabbro-Anorthosite Suite genesis is in accordance with the traditional  petrological model of the massive-type anorthosites related to calc-alkaline basaltic  magma segregation, plagioclase accumulation in magmatic chambers and its  subsequent diapiric ascent, generating anorthosites, gabbros, and quartz syenites.  Crystallization of residual liquids formed the other rock types. Zircon U-Pb dating of  different rocks of the suite shows crystallization ages of ca. 661 and 648 Ma. The age  of the suite and its positioning indicates a correlation with an important mafic magmatic  event in the Brasília Belt at 670–600 Ma. Interpretation of the Brasília Belt geological  data, associated with the present study, indicates that the rocks of the suite developed  in an active continental margin back-arc environment. The presence of massive type anorthosite in the Brasília Belt context reinforces the thesis that the evolution of  this belt is characterized by thermal gradient raising. It is suggested  that mantle isolation that resulted from a “heat trap”, heat coming from the Rodinia  break-off mantle plume, crustal thickening, and elongated shape of the tectonic plate  were the main factors responsible for the thermal gradients in the context of the  Brasília Belt formation. The other study area is located to the west, in the southern  Araguaia Belt. In this area, NE-SW-oriented layers of mainly immature  metasedimentary rocks associated with metamafic and orthogneiss lenses are  exposed. This framework was affected by compressive forces forming folds and  thrusts, and by the Transbrasiliano Lineament dextral shear zone system. The immature metasedimentary rocks show compositions similar to those of tonalite to  granite, suggesting graywacke and lithoarenite as likely protoliths. Detrital zircon  provenance study indicates Neoproterozoic sedimentation, with maximum depositional  ages at around 600 Ma, and contribution of older Archean to Mesoproterozoic sources.  The metamafic rocks are represented mainly by narrow amphibolite lenses interpreted  as probable dykes and sills. Lithogeochemical data of the amphibolites show basaltic to  andesitic compositions, with OIB and E-MORB signatures developed in a magmatic arc  setting. Zircon U-Pb dating of a fine-grained amphibolite yielded a crystallization age of  ca. 664 Ma. The association between immature metasedimentary rocks and metamafic  lenses indicates an early stage opening or reactivation of basin, in which dyke swarms  and high-energy proximal sedimentation are common. The magmatic arc signature of  metamafic and paraderived rocks, associated with Neoproterozoic ages, indicates a  probable retro-arc basin environment related to the evolution of the Goiás Magmatic  Arc, between approximately 660 and 600 Ma. The metasedimentary and mafic rocks  can be correlated to the Monte do Carmo Formation rocks, indicating the possible  extension of this unit to the southern portion of the Araguaia Belt. Zircon U-Pb dating of  orthogneisses associated with the metasedimentary rocks provided crystallization ages  of 596±18 Ma and 1985±12 Ma. The youngest rock can be correlated to the Aliança  Suite, while the oldest can be associated with the Rio dos Mangues Complex,  interpreted as the Araguaia Belt basement. Geochronological data also revealed two  metamorphic ages (ca. 580 and 540 Ma), indicative of two collisional events in the  context of the Araguaia Belt. From the obtained data, it is discussed the possibility that  the Goiás Magmatic Arc had developed also in the Faixa Araguaia context. The new  evolutional model would explain some peculiar features of the Araguaia Belt, such as  the common presence of textural and mineralogical immature metasedimentary rocks,  two metamorphic peaks, and magmatic arc-related rocks.  The study area represents two distinct geological contexts of the Tocantins Province  evolution, separated by the Porangatu Suture, but displays rocks of similar tectonic  settings and ages. This fact indicates that the province evolution is complex and was  likely marked by many accretionary fronts of the Goiás Magmatic Arc during similar age  periods.  Integration of obtained data from this study and the extensive available data of the  Tocantins Province allows the establishment of the compartments and geotectonic  events of the province and the elaboration of an evolution model. These interpretations  indicate that the geotectonic events that formed the Tocantins Province are correlated  to the processes that induced the Rodinia fragmentation. In this sense, it is suggested that the continuous raising of thermal gradients inside the Tocantins Province is related  to the Rodinia break-off. This condition of elevated temperatures resulted in many  lithological constituents and geodynamic processes generating, for example, adakites,  charnockites, ultrahigh-temperature metamorphism, extensive mafic magmatism with  many layered complexes, and Proterozoic massive-type anorthosites. Corroborating  this correlation between the events, many studies show OIB-type magmatism in the  evolution context of the province, suggesting the likely presence of a mantle plume on  various occasions of its evolution. Further, the rifting processes that took place in the  Province are also time-correlated to the divergent settings of Rodinia fragmentation.  Thus, it appears that the Rodinia break-off had a significant role in the Western  Gondwana generation.  

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