Observations on order-disorder relations of natural plagioclase. Ill. Highly Ordered Plagioclases from the Sudbury Intrusive, Ontario, Canada

Forelesninger holdt ved Advanced Study Institute of Feldspar - Oslo 1962
Lectures held at Advanced Study Institute of Feldspar - Oslo 1962

This study investigates the major rock-types in four traverses across three main layers of the Sudbury lopolith in Ontario, Canada (Figure 1). Two traverses, one on either side of the lopolith, sample all three zones; the other two traverses, both on the south side of the intrusion, sample the lower and middle members.

The principal purpose of this study was to determine whether or not in a deep-seated lopolith there is a variation in composition or orderdisorder of the plagioclases, either vertically or laterally. This PreCambrian intrusion is nearly 7,000 feet thick and intrudes a series of older granites and medium to high rank metamorphosed sediments and volcanic rocks. The three zones include the lower norite and quartz diorite zone, the middle hybrid zone, and the upper micropegmatite zone. The extensive development of such hydrous minerals as actinolite, sericite and chlorite suggest that crystallization of the upper parts was in a water-rich environment.