U-Pb and Sm-Nd Geochronological Constraints on the Crustal Evolution and Basement Architecture of Ceará State, Nw Borborema Province, Ne Brazil: Implications for the Existence of the Paleoproterozoic Supercontinent "Atlantica"

Abstract

Sm-Nd whole-rock and U-Pb zircon geochronological studies of the basement gneisses of Ceará (NW Borborema Province, NE Brazil) have identified two major pulses of Paleoproterozoic crustal growth within the state; the first between ca. 2.35 to 2.30 Ga, and the second from ca. 2.19 to 2.05 Ga. The former was characterized exclusively by juvenile growth and accretion, whereas the latter involved the amalgamation of new juvenile crustal material, reworked or enriched crust, and Archean crustal fragments. It was during this second event, also known as the Transamazonian orogeny (ca. 2.2 to 2.0 Ga), that Ceará's fundamental crustal framework was assembled. Isotopic and geologic data indicate that this assembly involved the fusion of three distinct crustal blocks; the Northwest Ceará (AKA Médio Coreaú) Domain (NCD), the Central Ceará Domain (CCD), and the Rio Grande do Norte Domain (RND). This network of crustal blocks was subsequently affected by an episode of Late Paleoproterozoic intracratonic rifting at around 1.8 Ga. The presence of similar rift sequences of this age in other parts of South America and Africa lend support to the existence of the Paleoproterozoic supercontinental mass Atlantica. Based on the available data, this supercontinent appears to have included the Paleoproterozoic (and older) basement of the Brasiliano/Pan-African provinces in Brazil and West Africa as well as the cratons adjacent to them.Keywords: Borborema Province, Paleoproterozoic crustal growth, U-Pb zircon and Sm-Nd whole-rock geochronology (Almeida et al. 1981). Although the BP formed at the end of the Precambrian during the assembly of West Gondwana, its crustal framework is made up primarily of older Mesoproterozoic to Archean crustal fragments and domains . Understanding the growth and evolution of these constituent basement blocks is important for reconstructing the precollisional history of the BP and that of West Gondwana. As Ceará encompasses a significant portion of the BP, accurate constraints on the growth and evolution its basement complex are key for unraveling the early growth of the BP.Pioneering Rb-Sr and K-Ar geochronological studies in Ceará State and the surrounding region, e.g., Brito ), Brito Neves et al. (1978, Torquato et al. (1986), andPessoa et al. (1986), provided clues to the antiquity of lithologic units in the region, but the data lacked the necessary accuracy and precision to resolve age differences between different rock units and crustal domains. Furthermore, the susceptibility of the Rb-Sr and K-Ar systems to metamorphic resetting left some doubt as to whether the data represented original or reset ages, e.g. Caby and Arthaud (1986). In recent years, however, U-Pb zircon and Sm-Nd whole-rock studies, e.g., Van Schmus et al. (1995, 1997, Dantas et al. (1995, 1998) and Fetter et al. (1995, 1997, have provided precise and accurate constraints on the formation ages and crustal histories of different blocks within the BP.In this paper, we report Sm-Nd whole-rock and U-Pb zircon geochronological da...

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

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Conservation of geosites as a tool to protect geoheritage: the inventory of Ceará Central Domain, Borborema Province - NE/Brazil

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