George A. O'Reilly

The granitic Brenton pluton intrudes the Cambrian to early Silurian sequences of the Meguma Group and White Rock Formation of the south-western Nova Scotia mainland. It is a lense-shaped body 7.5 sq.mi. (13 Sq.Km) in area and exhibits a well developed planar foliation which parallels the regional structural trends of the Meguma massif. The foliation is a result of strong deformation of a pluton which must have been intruded with or before the first events of the Acadian orogenic cycle which affected the area in early Devonian time.

The Brenton pluton is chemically distinct from the South Mountain batholith and related intrusives which comprise the rest of the granitic material found on the mainland. It is chemically and petrographically homogeneous and represents a highly silicic and potassic melt of eutectic composition.

Theories of granite magma generation are discussed and lead to a model for the origin of the Brenton pluton in the early stages of crustal melting.

Six new age dates on co-existing muscovite and biotite from the pluton by the ³⁹Ar - ⁴⁰Ar method have yielded an age of 325 +/- 9 m.y. This date is sho\ro to represent a cooling stage in the history of the granite and not the date of intrusion. From the age dates an erosion rate of 0.08 - .4 mm/yr for the Meguma massif was calculated, which agrees well with values from other orogenic belts.

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Pages: 108
Supervisor: Gunter Muecke