RESUMO. Este trabalho apresenta um estudo paleomagnético realizado em rochasácidas da Suíte Colíder e rochas máficas associadas, situadas no Norte do Mato Grosso, parte sudoeste do Cráton Amazônico. Foram coletados 5 cilindros e 42 blocos orientados de rochasácidas e intermediárias (12 sítios) da Suíte Colíder e 75 cilindros e 3 blocos orientados de rochas máficas (11 sítios) pertencentesà Intrusiva Guadalupe eà Suíte Intrusiva Flor da Serra localizados nas proximidades de Alta Floresta, Colider, Terra Nova e Matupá. A Suíte Colíder foi datada pelo método UPb em zircões e apresenta idades entre 1,80 e 1,78 Ga. Para a Intrusiva Guadalupe ainda não existem determinações radiométricas que estabeleçam a sua idade. A investigação da mineralogia magnética feita através de curvas termomagnéticas, de indução magnética e de histerese, além do tratamento térmico e por campos magnéticos alternados, indica a hematita como sendo o principal portador magnético da maioria das rochasácidas. Por outro lado, as rochas máficas apresentam grãos de titanomagnetita pobre em Ti, a maioria com estrutura de pseudo-domínio simples (PSD). Espécimes destas rochas após as desmagnetizações térmicas e por campos magnéticos alternados apresentaram duas direções de magnetização característica. Uma delas (componente B)é representada por direções norte (sul) com inclinações negativas ( ABSTRACT. This work presents a paleomagnetic study performed on felsic volcanic rocks of the Colider Suite (5 oriented cores and 42 oriented hand samples, 12 sites), Flor da Serra and Guadalupe mafic rocks (75 oriented cores and 3 oriented hand samples, 11 sites). These units are situated in the northern Mato Grosso State (southwestern Amazon Craton), close to the Alta Floresta, Colider, Terra Nova, and Matupá cities. The Colider Suite rocks have been dated by the U-Pb (zircon) method, and ages vary between 1.80 and 1.78 Ga. Radiometric determinations are not yet available for the Guadalupe Intrusive. Two very stable magnetization components were isolated after AF and thermal demagnetization: northern (southern) directions with moderate to steep downward (upward) inclinations (component B -Dm = 187.4 • , Im = 50.9 • , N = 16, α 95 = 11.3 • , K = 11.7) were isolated for most Colider Suite rocks and associated mafic rocks. Northern upward direction with moderate inclination (component ADm = 356.5 • , Im = 47.6 • , N = 3, α 95 = 15.8 • , K = 61.9) was found for the Guadalupe gabbro and other two mafic dikes. Rock magnetism experiments show that the magnetization is carried by hematite, which is probably primary in origin, in the felsic rocks. In the mafic rocks the main magnetic carrier is Ti-poor titanomagnetite in the PSD magnetic structure. Two paleomagnetic poles were determined for these components, which are located at 289.4 • E, -65.4 • N (α 95 = 12.9 • ) (SC pole, Colider Suite) and 298.8 • E, 50.4 • N (α 95 = 15.1 • ) (IG pole, Guadalupe Intrusive). An age of 1.780 ± 7 Ma is attributed to pole SC (quality factor Q = 5), which is considered a key pole for the ...
_______________________________________________________ This work presents a paleomagnetic study perfomed on felsic volcanic rocks of the Colider Suite (5 oriented cores and 42 oriented hand samples, 12 sites), Flor da Serra and Guadalupe mafic rocks (75 oriented cores and 3 oriented hand samples, 11 sites). These units are situated in the northern Mato Grosso State (southwestern Amazonian Craton), close to the Alta Floresta, Colider, Terra Nova, and Matupá cities. The Colider Suite rocks have been dated by the U-Pb (zircon) method, and ages vary between 1.80 and 1.78 Ga. Radiometric determinations are not yet available for the Guadalupe Intrusive. Two very stable magnetization components were isolated after AF and thermal demagnetization: northern (southern) directions with moderate to steep downward (upward) inclinations (component B-Dm=187.4°, Im=50.9°, N=16 α95=11.3°, K=11.7) were isolated for most Colider Suite rocks and associated mafic rocks. Northern upward direction with moderate inclination (component A-Dm=356.5°, Im=47.6°, N=3, α95=15.8°, K=61.9) was found for the Guadalupe gabbro and other two mafic dikes. Rock magnetism experiments show that the magnetization is carried by hematite, which is probably primary in origin, in the felsic rocks. In the mafic rocks the main magnetic carrier is Ti-poor titanomagnetite in the PSD magnetic structure. Two paleomagnetic poles were determined for these components, which are located at 289.4°E,-65.4°N (α95=12.9°) (SC pole, Colider Suite) and 298.8°E, 50.4°N (α95=15.1°) (IG pole, Guadalupe Intrusive). An age of 1.780 ± 7 Ma is attributted to pole SC (quality factor Q=5), which is considered a key pole for the Amazon Craton. Paleogeographic reconstructions using Paleoproterozoic key poles suggest 65 xviii Sumário _______________________________________________________ Agradecimentos iii Resumo vi Abstract viii Lista de Figuras x Lista de Tabelas xvii Capitulo 1: Introdução Capitulo 2: Contexto Geológico 2.1. O conceito de Cráton 2.2. Aspecto Geológico do Cráton Amazônico 2.3. Contexto Geológico Regional 2.4. Geologia Local 2.4.1. Suíte Colíder 2.4.2. Intrusivas Máficas Guadalupe 2.4.3. Suíte Intrusiva Flor da Serra 2.4.4. Dados Geocronológicos 2.5. Localização da Área de Estudo 2.6. Análise Petrográfica
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.