Detrital zircon U-Pb geochronology and whole-rock Nd-isotope constraints on sediment provenance in the Neoproterozoic Sergipano orogen, Brazil: From early passive margins to late foreland basins

摘要

SHRIMP U-Pb detrital zircon geochronology and depleted-mantle Nd-model ages of clastic rocks were combined to understand the sediment provenance in the Neoproterozoic Sergipano Belt. The Sergipano is the main orogenic belt between the Borborema province and the Sao Francisco Craton, eastern South America; it is divisible into several lithostratigraphic domains from North to South: Caninde, Pogo Redondo-Maranco, Macurure, Vaza Bards, and Estancia. Nd model ages (TDM) and detrital zircon U-Pb SHRIMP geochronology indicate that the protoliths of clastic metasedimentary rocks from the Maranco and Macurure domains were mostly derived from eroded late Mesoproterozoic to early Neoproterozoic rocks (1000-900 Ma), whereas detritus of similar rocks from the Caninde domain came from a younger source (ca. 700 Ma and 1000 Ma). Samples from the Vaza Bards domain show the greatest scatter of both TDM and zircon ages amongst all domains, but with important contributions from Proterozoic sources (690-1050 Ma and ca. 2100 Ma) and less from Archaean sources. The Estancia domain samples have zircon population peaks at 570 Ma, 600 Ma, and 920-980 Ma, with a few older grains; one diamictite contains only ca. 2150 Ma zircon grains. Our preliminary results support a model in which sediments of the Maranco and Macurure domains were deposited on a continental margin of the ancient Borborema plate before its collision with the Sao Francisco Craton; the Caninde domain is likely to be an aborted Neoproterozoic rift assemblage within the southern part of the Borborema plate (Pernambuco-Alagoas massif). The basal units of the Vaza Bards and Estancia domains have clast sources from the Sao Francisco Craton and are best interpreted as passive margin sediments. However, the uppermost units of the Estancia and Vaza Bards domains come from foreland basins formed during collision of Borborema plate with the Sao Francisco Craton. (C) 2015 Elsevier B.V. All rights reserved.