Structural style of basin inversion at mid-crustal levels: two transects in the internal zone of the Brasiliano Araçuai Belt, Minas Gerais, Brazil

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• 作者：Cunningham ; W. Dickson ; Marshak ; Stephen ; Alkmim ; Fernando F.
• 刊名：Precambrian Research
• 出版年：1996
• 出版时间：March, 1996
• 年：1996
• 卷：77
• 期：1-2
• 页码：1-15
• 全文大小：1.30 M

文摘

The Araçuai belt is the orogenic belt that directly borders the eastern margin of the São Francisco Craton in eastern Brazil. Detailed structural investigations in the Governador Valadares region of Minas Gerais indicate that the amphibolite-to granulite-grade internal zones of the Araçuai belt contain several major, west-vergent, crystalline overthrust sheets. These thrust sheets contain approximately homoclinal east-dipping gneissic banding and are separated from one another by zones of isoclinally and sheath-folded, ductiley sheared, metasedimentary units that behaved as mechanically weak glide horizons during deformation. We interpret this regionally imbricated sequence of basement and cover to be the mid-crustal level manifestation of closure of a mid-Neoproterozoic rift basin that existed to the east of the São Francisco Craton. The major thrusts, which are all craton-vergent, are of Brasiliano/Pan-African age (650-450 Ma) because they cut the Neoproterozoic Galiléia batholith. Older fabrics are locally preserved in the basement slices, and these fabrics may be relicts of the Transamazonian orogeny (2.0 Ga). Discrete zones of ductile-brittle extension that were identified in several localities in the study area suggest the occurrence of post-orogenic collapse following Brasiliano overthrusting. Alternations of rigid crystalline thrust sheets and highly deformed metasedimentary sequences, such as those of the Governador Valadares region, may be a common structural geometry at a depth of 15-20 km in modern regions of collision and basin closure.