Isotopic evidence for the magmatic and tectonic histories of the Carolina terrane: Implications for stratigraphy and terrane affiliation.

Ingle, S., Mueller, P., Heatherington, A. and Kozuch, M., 2003, Tectonophysics, v. 371, p. 187-211.

Abstract

Establishing the age and crustal nature of exotic terranes and their underlying basements helps to determine their paleogeographic origin and tectonic histories. We present U-Pb ages of zircons and Sm-Nd whole rock isotopic data for volcanic and plutonic rocks of the Carolina terrane, one of several peri-Gondwanan terranes that were accreted to the margins of the circum-Atlantic continents during the Paleozoic. Volcanism in this subduction-related arc culminated in the eruption of the Morrow Mountain rhyolite, at ca. 540 Ma; thus magmatism in the Carolina terrane ceased at the beginning of the Cambrian. The presence of inherited zircons and non-juvenile depleted mantle model ages of Carolina slate belt rocks favor a basement that is, at least in part, composed of evolved continental crust. Ages of inherited xenocrystic zircons cluster at ca. 1000 Ma, 2100 Ma and 2500 Ma. These ages, in addition to volcanism at ca. 618 - 540 Ma, correlate best with well-known tectonic events in present-day northern South America. Specifically, the Orinoquian – Sunsas, the Trans-Amazonian and the Central Amazonian orogenic zones are likely candidates for potential basement correlatives to the Carolina terrane. Sm-Nd isotopic signatures vary significantly, but permit assimilation of Orinoquian-age (~1000 Ma) crust by magmas derived from the depleted mantle in a subduction (arc-related) setting. Our findings are also consistent with proposed correlations between the Carolina terrane and Avalonia, which is likewise believed to have formed along the northern margin of present day South America.

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