Devonian Extension in Northwestern Newfoundland: 40Ar/39Ar and U‐Pb Data from the Ming’s Bight Area, Baie Verte Peninsula

Abstract

Abstract The Ming’s Bight Group of northwestern Newfoundland, an outlier of Humber Zone continental margin rocks, is entirely surrounded by ophiolitic rocks of the Dunnage Zone. Structures in the Ming’s Bight Group and adjacent units record three main phases of deformation. The earliest structures relate to Silurian sinistral transpression previously documented in the region. Two later phases of extensional deformation produced a series of dextral oblique‐normal shear zones and faults that now separate the Ming’s Bight Group in the footwall from ophiolitic and granitoid rocks in the hangingwall. 40Ar/39Ar and U‐Pb data constrain the times of oblique‐normal shear and cooling. Metagabbro in the Point Rousse Ophiolite Complex, which lies in the hangingwall, preserves disturbed Ordovician hornblende 40Ar/39Ar ages, whereas adjacent shear zones record Devonian ages. Hornblendes in Pacquet Harbour Group amphibolites within extensional shear zones mainly record 40Ar/39Ar ages of 390–380 Ma. Synkinematic titanite...