Photogrammetric survey of the structural geology of the Sudbury-McGregor Bay District,Ontario, Canada

New information is presented regarding the structural geology of the Huronian rocks (Middle Precambrian) of the Sudbury-McGregor Bay district of Ontario, Canada. Using standard photogrammetric techniques a base map of the area was prepared from photographs taken at a height of about 11,000 m. Extrapolation from the work ofYoung &Church (1966) together with the evidence deduced from the aerial photographs facilitated the construction of a lithological map at the scale of 1∶187,500 (Fig. 2). From this map large scale type 2 interference pattern is recognised (seeRamsay, 1967) and a tentative structural history is suggested for the area.     

The variscan geology of the Pyrenees

The main outlines of the geology of the Variscan part of the Pyrenees are discussed. Rocks involved in this cycle are high-grade basement gneisses, Palaeozoic sediments and their metamorphic equivalents, late intrusive granodiorites and early, pre-Variscan granites. The main features of the stratigraphy of the Palaeozoic are given.Structures fall into two domains: a low-grade suprastructure, essentially with steep folds and cleavages, and a high-grade infrastructure with dominantly low-dipping foliations. An important phase of early, pre-cleavage folding occurs in low-grade rocks mainly along the southern border of the Axial zone. In high-grade rocks most structures and the metamorphism postdate the main cleavage phase in low-grade rocks. The influence of the Alpine orogeny on the Variscan structures consists mainly of faults, steep, reverse faults in the northern, and south-directed thrusts in the southern part of the Pyrenees. Metamorphism took place under high geothermal gradients and low pressures, as indicated by the abundant occurrence of andalusite and cordierite