PETROLOGY AND GEOCHEMISTRY OF THE ALLS AW ANORTHOSITE: A SCAPOLITIZED META-ANORTHOSITE IN GRENVILLE PROVINCE, ONTARIO

摘要

INTRODUCTION The Grenville Orogen is an enormous belt of rocks stretching from southern Texas to northern Newfoundland. It represents a long-lived convergent margin of North America until formation of the super-continent Rodinia ca. 1.1 Ga. This paper focuses on a specific section of the orogen in southern Ontario, the Central Metasedimentary belt (CMB). The CMB represents an accreted arc, sandwiched on both sides by the autochthonous Central Gneiss Belt to the Northwest and the Adirondack Granulite Terrane to the southeast (Carr et al., 2000). The Central Metasedimentary Belt boundary thrust zone (CMBbtz) demarcates the boundary between the CMB and the Central Gneiss Belt (CGB). The CMBbtz is about 200 km long and between 10 and 35 km across. It is internally heterogeneous, made up of anastomosing marble breccia shear zones and gneissic intrusive thrust sheets (Hanmer and McEachern, 1992). Between two of these gneissic thrust sheets, the Glamorgan and Dysart thrust sheets (Fig 1.), are smaller anorthosite bodies thought to have perhaps been a single intrusion torn apart by shearing in the Denna Lake Structural Complex (DLSC). The Allsaw anorthosite is mapped as two separate bodies, a main body located near Allsaw, ON and a satellite body located just east of the main body. Smaller sub-bodies exist but are not significant enough to map (Easton, 1990).