Geological setting of the Whistle-Parkin Offset Dyke, Sudbury Impact Structure, Ontario.

摘要

The 1.85 Ga Sudbury Structure of Ontario is now widely accepted to be a 200--250 km diameter multi-ring impact basin. The structure consists of the 27 by 60 km Sudbury Igneous Complex (SIC) (a differentiated impact melt sheet), the Whitewater Group, (composed of fallback and overlying sedimentary rocks), as well as various impact breccias in the footwall.; The so-called offset dykes consist of melt-breccia dykes that emanate from the SIC. This work has revealed that the offset dykes comprise a variety of different rock types. These include Quartz Diorite (QD), containing little or no inclusions, Inclusion-rich Quartz Diorite (IQD), Radial Breccia, Mafic Sulfide-Bearing Breccia (MSBB), Sudbury Breccia and Sublayer.; The Whistle-Parkin Offset Dyke is a 12 km long radial offset dyke located in the NE sector of the impact structure. The Whistle-Parkin Offset Dyke is connected to the SIC via a 0.5 km long, 250 m wide embayment. The Whistle segment of the dyke narrows to a width of approximately 30 m and extends for about 1.5 km from the SIC, where it is cut by the Post Creek Fault Zone. This fault displaces the dyke 2 km to the NW, beyond which it continues as the Parkin segment of the dyke. The Parkin segment extends a further 10 km NNE. The Whistle-Parkin Offset Dyke and genetically associated embayment comprise numerous rock types. These include the Sublayer, Radial Breccia, MSBB, IQD and QD. Economic Ni-Cu-PGE mineralization is found in association with the Sublayer, MSBB and IQD phases in the dyke. Rare earth element (REE) data reveal that the dyke lithologies are representative of bulk SIC melt.; A multistage emplacement mechanism is proposed for radial and concentric offset dykes. The inclusion-bearing phases (Radial Breccia, MSBB and IQD) in the radial offset dykes were the first lithologies to be emplaced, by means of preferential forceful injection into radial cracks generated in the trail of the shock wave. Subsequent modification stage processes allowed for the injection of QD into these melt-breccia filled radial dykes. Concurrently, large-scale modification-related faults (superfaults), which generated large volumes of pseudotachylyte, offset the radial offset dykes and allowed for the intrusion of QD into the concentric offset dykes. Following these events, the impact-generated ∼3 km thick Sudbury Igneous Complex differentiated, allowing for the Sublayer to be emplaced within the trough and embayment structures in the footwall of the structure. (Abstract shortened by UMI.)