| dc.description | The Ming's Bight Group (MBG) comprises a sequence of Late Proterozoic to Early Ordovician continental margin siliciclastic rocks of Humber Zone tectonostratigraphic affinity which is surrounded by Early Ordovician volcanic arc and ophiolitic rocks of Dunnage Zone affinity on the eastern side of a major terrane boundary (the Baie Verte-Brompton Line; BVL) on the Baie Verte Peninsula (BVP) in northwest Newfoundland. Dextral transtensional structures were observed in a single shear zone in the thesis area, and are overgrown by titanite porphyroblasts with a U-Pb age of 388 +/- 4 Ma. This shearing is tentatively correlated with a dextral transpressional shear zone exposed further west along the main trace of the BVL. Dextral transtensional structures are symmetrically developed about the MBG. To the southeast, the MBG is bounded by a thick zone of penetrative, southeast-directed, normal-sense, non-coaxial shear which initiated during peak amphibolite facies metamorphism (T ≥ 600°C; P ≥ 6 kbar), and continued to greenschist facies conditions. 40 Ar/39Ar cooling ages of 377--382 +/- 3 Ma from syntectonic hornblende in the footwall of this zone indicate extensional shearing through Middle to Late Devonian time. To the northwest, a series of narrow, high-angle, brittle-ductile, greenschist facies, dextral-normal, oblique-slip shear zones bound the MBG. 40Ar/ 39Ar muscovite cooling ages throughout the MBG cluster between 360 +/- 3 and 368 +/- 4 Ma, indicating that this deformation, and coeval rapid post-metamorphic cooling through the muscovite closure temperature, continued through to Early Carboniferous time. Based on the geometry of these extensional structures and the spatial patterns of cooling ages and cooling rates, the MBG is interpreted to be a symmetrical metamorphic core complex. These relationships indicate that the recently proposed models for Silurian extensional collapse of the Newfoundland Appalachians cannot account for rapid post-metamorphic cooling in either the MBG or FdLS. The regional transition from a deformation regime of sinistral transpression to a regime of dextral transtension is interpreted to result from a regional-scale counterclockwise rotation of the kinematic axes from northwest-southeast in the late-Early to Late Silurian, to east-west in the Late Silurian to late-Early Devonian, to southwest-northeast in the late-Early to Late Devonian, similar to that documented in other portions of the northern Appalachians. This study indicates that transpressional shear zones controlling gold mineralization on the BVP are far more widespread than previously recognized, and provides a new model which may assist future volcanogenic massive sulphide (VMS) exploration in the vicinity of the Rambler VMS deposits. (Abstract shortened by UMI.) | en_US |
