Abstract
New systematic Nd isotope and U-Pb geochronology data were applied to Precambrian rocks of northeastern Brazil to produce a crustal-age distribution map for a small basement inlier (1,500 km2). The results support episodic crustal growth with five short periods of crustal formation at ca. 2.9 Ga, 2.65 Ga, 2.25 Ga, 2.0 Ga, and 0.6 Ga. Based on the frequency histogram of U-Pb zircon ages and Nd isotopic data, we suggest that about 60% of the continental crust was formed during the Archean between 2.9 Ga and 2.65 Ga. The remaining 40% of crust was generated during the Rhyacian to Neoproterozoic (~2.0–0.6 Ga). This overall continental growth is manifested by accretionary processes that involved successive accretions surrounding an older core, becoming younger toward the margin. Strikingly, this repetitive history of terrane accretion show a change from lithospheric peeling dominated accretionary setting during the late Archean to a more, modern-day akin style of arc-accretion during the Proterozoic. Similar tectonic processes are observed only in large continental areas (>1,000,000 km2) as in the North American continent basement and in the Amazonian Craton.
Highlights
Understanding the evolution of the continental crust is a challenge due to the diversity of geological environments where it forms and to the variety of reworking processes it may have undergone throughout the geological time
We show evidence of continental growth via terrane accretion within the Campo Grande Block of the Borborema Province, NE Brazil
Nd isotope data and U-Pb geochronology within the distinct terrains provide constraints for the succession of magmatic and metamorphic phases that resulted in continental accretion of heterogeneous rocks from 2.9 Ga to ca. 566 Ma ago in northeast Brazil
Summary
Understanding the evolution of the continental crust is a challenge due to the diversity of geological environments where it forms and to the variety of reworking processes it may have undergone throughout the geological time. The preservation of Meso- to Neoarchean felsic continents may represent the initiation of plate tectonics in some form[15,16] In this debate, the application of a geodynamic unifying model or the reconciliation of different models for the ancient continents generation is still in dispute[15,16,17]. Compositional diversity and complex evolution of the accretionary orogens are related to the plate boundary parallel migration, and orthogonal accretion of juvenile and reworked crustal segments[9] In this context, Sm-Nd isotopes may provide a mean for determining (1) the crustal residence time[24,25], (2) crustal reworking processes[26], and (3) mantle mixing[27]. Ages and Sm-Nd isotopic data, we show that repetitive accretion of crustal terranes occurred within this area from the late Archean to the Neoproterozoic
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