The petrological evolution of the Late Paleozoic A-type granites of the Wentworth plutonic complex of the Cobequid shear zone

Abstract

The Wentworth Pluton is a bimodal intrusion which consists principally of a 362 Ma, A-type granite, part of which was remelted by a major gabbro intrusion, resulting in the formation of late granites. REE- rare metal mineralization is widespread in and around the Wentworth Pluton. The Wentworth granites were examined geochemically and petrographically in order to determine the geological processes responsible for their distinct geochemistry. The granites were derived from partial melting of subduction-related trondhjemites, in the lower Avalonian crust, triggered by asthenospheric upwelling in the Late Paleozoic. The parent, REE-enriched magma formed early granites with REE-magmatic minerals. Anatexis of these granites resulted in the release of volatiles and rare metals in hydrothermal fluids, reflected by a variety of hydrothermal REE-rich minerals. This study has introduced new evidence on the petrogenesis of A-type granites and demonstrated the genetic relationship between the REE mineralization and the granites of the Wentworth Pluton.