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"

ALLEN HUTCHESON FETTER, WILLIAM RANDALL VAN SCHMUS, TICIANO JOSÉ SARAIVA DOS SANTOS, JOSÉ ARAUJO NOGUEIRA NETO, MICHEL HENRI ARTHAUD

Resumo


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.

Palavras-chave


Borborema Province; Paleoproterozoic crustal growth; U-Pb zircon and Sm-Nd whole-rock geochronology.

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