Renato de Assis Barros , Renato Moraes , Marco Aurélio Piacentini Pinheiro , Ciro Duarte de Carvalho , Cristiano de Carvalho Lana
{"title":"Boa Vista de Minas群的年代学和地层学:以角闪岩-麻粒岩相中新太古代绿岩带为例","authors":"Renato de Assis Barros , Renato Moraes , Marco Aurélio Piacentini Pinheiro , Ciro Duarte de Carvalho , Cristiano de Carvalho Lana","doi":"10.1016/j.jsames.2025.105459","DOIUrl":null,"url":null,"abstract":"<div><div>The Boa Vista de Minas Group is a suite of metamorphic rocks ranging from amphibolite to granulite facies. It appears as disrupted, folded, and keel-shaped bands amidst the metagranite-migmatite domes of the Divinópolis Complex. It is challenging to define its lithostratigraphic architecture and thickness due to intense weathering and tectonic overprints. The internal organization of the complex is characterized by three main Formations. The basal level, known as the Nova Serrana Formation, primarily consists of amphibolites and mafic granulites (metabasites), meta-ultramafic rocks, cummingtonite schists, and cordierite-anthophyllite schists (immature volcanogenic metagraywackes). Zircon U-Pb analysis (LA-ICP-MS) from a sample of cordierite-anthophyllite schists from the Nova Serrana Formation yielded a maximum deposition age of <em>ca.</em> 2.82 Ga. Orthopyroxene-bearing iron formations and ferruginous meta-cherts define interbedded layers within the basal sections, collectively referred to as the Córrego do Cedro Formation. Above these units lies the Igaratinga Formation, which consists of calc-silicate rocks interspersed with lenses of amphibolites and granulites, sillimanite gneisses, and meta-ultramafic rocks, including common lenses of biotite-orthopyroxene granulite (immature volcanogenic metagraywackes). A sample of biotite- orthopyroxene granulite from this Formation provided a maximum deposition age of <em>ca.</em> 2.72 Ga (U-Pb, LA-ICP-MS). Additionally, zircon rims showing light luminescence and newly formed zircon yielded a Concordia age of approximately 2.0 Ga, interpreted as reflecting a high-grade metamorphic overprint. The patterns of LREE enrichment, Nb-Ta-Ti depletions, and variable Th/Nb ratios observed in the metabasic rocks of both the Nova Serrana and Igaratinga Formations are similar to those formed under interactions between LREE-enriched plumes and arcs. The similarities in lithology, lithogeochemistry, and depositional ages of the rocks in the Boa Vista de Minas Group suggest that it represents a high-grade counterpart to the Pitangui Greenstone Belt. This implies that the tectonic-thermal metamorphic event associated with the final stages of the Minas-Bahia Orogeny extended to the northern limit of the Divinópolis Complex and is more extensive than previously anticipated.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"157 ","pages":"Article 105459"},"PeriodicalIF":1.7000,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Geochronology and stratigraphy of the Boa Vista de Minas Group: An example of a Meso-to Neoarchean greenstone-belt in amphibolite-to granulite-facies\",\"authors\":\"Renato de Assis Barros , Renato Moraes , Marco Aurélio Piacentini Pinheiro , Ciro Duarte de Carvalho , Cristiano de Carvalho Lana\",\"doi\":\"10.1016/j.jsames.2025.105459\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>The Boa Vista de Minas Group is a suite of metamorphic rocks ranging from amphibolite to granulite facies. It appears as disrupted, folded, and keel-shaped bands amidst the metagranite-migmatite domes of the Divinópolis Complex. It is challenging to define its lithostratigraphic architecture and thickness due to intense weathering and tectonic overprints. The internal organization of the complex is characterized by three main Formations. The basal level, known as the Nova Serrana Formation, primarily consists of amphibolites and mafic granulites (metabasites), meta-ultramafic rocks, cummingtonite schists, and cordierite-anthophyllite schists (immature volcanogenic metagraywackes). Zircon U-Pb analysis (LA-ICP-MS) from a sample of cordierite-anthophyllite schists from the Nova Serrana Formation yielded a maximum deposition age of <em>ca.</em> 2.82 Ga. Orthopyroxene-bearing iron formations and ferruginous meta-cherts define interbedded layers within the basal sections, collectively referred to as the Córrego do Cedro Formation. Above these units lies the Igaratinga Formation, which consists of calc-silicate rocks interspersed with lenses of amphibolites and granulites, sillimanite gneisses, and meta-ultramafic rocks, including common lenses of biotite-orthopyroxene granulite (immature volcanogenic metagraywackes). A sample of biotite- orthopyroxene granulite from this Formation provided a maximum deposition age of <em>ca.</em> 2.72 Ga (U-Pb, LA-ICP-MS). Additionally, zircon rims showing light luminescence and newly formed zircon yielded a Concordia age of approximately 2.0 Ga, interpreted as reflecting a high-grade metamorphic overprint. The patterns of LREE enrichment, Nb-Ta-Ti depletions, and variable Th/Nb ratios observed in the metabasic rocks of both the Nova Serrana and Igaratinga Formations are similar to those formed under interactions between LREE-enriched plumes and arcs. 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引用次数: 0
摘要
Boa Vista de Minas群是一套从角闪岩到麻粒岩相的变质岩。它在Divinópolis杂岩的变花岗岩-杂岩圆顶中表现为断裂、折叠和龙骨状带。由于强烈的风化作用和构造叠加作用,确定其岩石地层结构和厚度具有挑战性。该建筑群的内部组织以三个主要地层为特征。基底层,被称为Nova Serrana组,主要由角闪岩和基性麻粒岩(变质岩)、变质超基性岩、明辉岩片岩和堇青石-花青岩片岩(未成熟的火山成因变质岩)组成。对Nova Serrana组堇青石-花青石片岩样品进行锆石U-Pb分析(LA-ICP-MS),发现其最大沉积年龄约为2.82 Ga。含铁正辉石岩组和含铁变质燧石岩定义了基底剖面内的互层,统称为Córrego do Cedro组。在这些单元之上是Igaratinga组,由钙硅酸盐岩石组成,间杂有角闪岩和麻粒岩透镜体、硅麻质片麻岩透镜体和变质超镁铁质岩石透镜体,包括常见的黑云母-正辉石麻粒岩透镜体(未成熟的火山成因元辉岩)。该组黑云母-正辉石麻粒岩样品的最大沉积年龄约为2.72 Ga (U-Pb, LA-ICP-MS)。此外,显示发光的锆石边缘和新形成的锆石显示出约2.0 Ga的Concordia年龄,解释为反映了高级变质叠印。Nova Serrana组和Igaratinga组变质岩中LREE富集、Nb- ta - ti耗尽和Th/Nb比值变化的模式与LREE富集羽流和弧相互作用下形成的模式相似。Boa Vista de Minas群岩石在岩性、岩石地球化学和沉积时代上的相似性表明,它与Pitangui绿岩带具有高等级对应关系。这表明,与米纳斯-巴伊亚造山运动末期相关的构造-热变质事件延伸到Divinópolis杂岩的北部边界,并且比先前预期的更为广泛。
Geochronology and stratigraphy of the Boa Vista de Minas Group: An example of a Meso-to Neoarchean greenstone-belt in amphibolite-to granulite-facies
The Boa Vista de Minas Group is a suite of metamorphic rocks ranging from amphibolite to granulite facies. It appears as disrupted, folded, and keel-shaped bands amidst the metagranite-migmatite domes of the Divinópolis Complex. It is challenging to define its lithostratigraphic architecture and thickness due to intense weathering and tectonic overprints. The internal organization of the complex is characterized by three main Formations. The basal level, known as the Nova Serrana Formation, primarily consists of amphibolites and mafic granulites (metabasites), meta-ultramafic rocks, cummingtonite schists, and cordierite-anthophyllite schists (immature volcanogenic metagraywackes). Zircon U-Pb analysis (LA-ICP-MS) from a sample of cordierite-anthophyllite schists from the Nova Serrana Formation yielded a maximum deposition age of ca. 2.82 Ga. Orthopyroxene-bearing iron formations and ferruginous meta-cherts define interbedded layers within the basal sections, collectively referred to as the Córrego do Cedro Formation. Above these units lies the Igaratinga Formation, which consists of calc-silicate rocks interspersed with lenses of amphibolites and granulites, sillimanite gneisses, and meta-ultramafic rocks, including common lenses of biotite-orthopyroxene granulite (immature volcanogenic metagraywackes). A sample of biotite- orthopyroxene granulite from this Formation provided a maximum deposition age of ca. 2.72 Ga (U-Pb, LA-ICP-MS). Additionally, zircon rims showing light luminescence and newly formed zircon yielded a Concordia age of approximately 2.0 Ga, interpreted as reflecting a high-grade metamorphic overprint. The patterns of LREE enrichment, Nb-Ta-Ti depletions, and variable Th/Nb ratios observed in the metabasic rocks of both the Nova Serrana and Igaratinga Formations are similar to those formed under interactions between LREE-enriched plumes and arcs. The similarities in lithology, lithogeochemistry, and depositional ages of the rocks in the Boa Vista de Minas Group suggest that it represents a high-grade counterpart to the Pitangui Greenstone Belt. This implies that the tectonic-thermal metamorphic event associated with the final stages of the Minas-Bahia Orogeny extended to the northern limit of the Divinópolis Complex and is more extensive than previously anticipated.
期刊介绍:
Papers must have a regional appeal and should present work of more than local significance. Research papers dealing with the regional geology of South American cratons and mobile belts, within the following research fields:
-Economic geology, metallogenesis and hydrocarbon genesis and reservoirs.
-Geophysics, geochemistry, volcanology, igneous and metamorphic petrology.
-Tectonics, neo- and seismotectonics and geodynamic modeling.
-Geomorphology, geological hazards, environmental geology, climate change in America and Antarctica, and soil research.
-Stratigraphy, sedimentology, structure and basin evolution.
-Paleontology, paleoecology, paleoclimatology and Quaternary geology.
New developments in already established regional projects and new initiatives dealing with the geology of the continent will be summarized and presented on a regular basis. Short notes, discussions, book reviews and conference and workshop reports will also be included when relevant.