Geology of the 1.33--1.32 Ga Barth Island Ring Complex, near Nain, Labrador.

摘要

The ca. 40 km2 Barth Island Ring Complex comprises spatially associated, concentric sheets of leucotroctolite, leuconorite, ferrogabbroid, and monzonite. The ring complex is a part of the ca. 1.36 - 1.29 Ga Nain Batholith, a typical Proterozoic massif-type anorthosite complex located in northern Labrador, Canada. Unlike most anorthosites in the Grenville Province to the south, the Nain Batholith (NB) was not involved in regional ductile deformation and therefore offers an excellent opportunity to probe the problem of the formation of Proterozoic massif-type anorthosites. The Barth Island Ring Complex contains, in close proximity, some of the distinctive rock types of massif-type anorthosite complexes. The ring complex therefore provides an ideal opportunity for study of the 'anorthosite problem'.; Previous workers had considered the ring complex to be the result of closed-system differentiation of a single pulse of magma in a single chamber. However, mapping at a scale of 1:20 000 has resulted in a reappraisal of the mechanisms of formation and magmatic history of the Barth Island Ring Complex. (Abstract shortened by UMI.)