Physical characteristics of the Tilting Layered Suite, Fogo Island, Newfoundland

Abstract

The Tilting Layered Suite (TLS) is part of a complex Siluro-Devonian pluton exposed on Fogo Island. The TLS exhibits a wide range of rock types, from peridotite to diorite, which occur in four main zones (Zone I-IV). Although the TLS apepars to differ significantly in its scale and magmatic history from most well-known mafic layered intrusions, it displays comparable layers and layering. In general, layers are planar, uniform, and steeply inclined layer contacts are sharp and concordant, and layers vary in thickness from 1-2 cm to 1-20 m. Modal, textural, phase, and grain-size layering are present. The TLS exhibits two main crystallization sequences: the early crystallization of cumulus orthopyroxene occurs in Zones I to III; the late crystallization of cumulus orthopyroxene occurs in Zone IV. From field and petrographic data, it is clear that the evolution of the TLS involved complex interaction of several processes including magma replenishment, in situ crystallization, current deposition and postcumulus/subsolidus modifications. -from Authors