Origin and implication of corona structures within diabase dykes intruding the Archean orthogneisses of the central Grenville Province, east of Chibougamau, Quebec.

Abstract

Geological mapping has defined a distinct group of NNE trending diabase dykes east of the Grenville Front in the Chibougamau area. These dykes are found intruding Archean orthogneisses within a narrow zone, the Parautochthonous terrane, bounded to the northwest by the Grenville Front and to the southeast by the Allochthon Front. The best preserved dykes, exhibiting primary igneous minerals and textures, are located along the Grenville Front, whereas the most metamorphosed dykes (i.e. amphibolites) are located along the Allochthon Front. The dykes are tholeiizic to weakly alkaline and can be divided into four main groups, based on texture and certain major and trace elements: (1) low-TiO$\sb2$; (2) high-TiO$\sb2$; (3) high-TiO$\sb2$ segregations; and (4) high-Al$\sb2$O$\sb3$. Igneous minerals include olivine, augite, plagioclase, magnetite, biotite, and pargasite. The principal metamorphic minerals are enstatite, hornblende, spinel, corundum, garnet, albite, and quartz. (Abstract shortened by UMI.)