Colin B. McKenzie

Approximately one-third of western Nova Scotia is covered by the Middle to Upper Devonian granitic rocks of the South Mountain batholith. The pluton consists largely of a sea of granodiorite enclosing four large adamellitic bodies as well as numerous smaller intrusives and alaskitic dykes. The batholith has invaded regionally metamorphosed Cambrian to Lower Devonian sequences late in the Acadian orogenic cycles. On a large scale the batholith parallels the regional structural trends, however locally it cuts across the Acadian fold structures.

Chemical analyses show that the various rock types of the batholith can all be representatives of a single comagmatic suite, most likely related to one another by fractional crystallization. Comparison of the bulk compositions of the granitic rocks with experimentally determined phase relations in the residual system, in conjunction with such considerations as stratigraphy and structure, all point to lower epizone-upper mesozone emplacement of the batholith. In addition, the occurrence of primary andalusite in late-stage rocks suggests that the final P, T conditions of crystallization were 3.3-3.9 kb and 650-680^oC.

In plate tectonic terms, the Devonian granites of Nova Scotia are at least spatially and perhaps temporally related to a subduction zone which gave rise to the New Canaan volcanics in Silurian times. The rater silicic average composition of the batholith and intermediate Sr87/86 ratios suggest that the parent magma was created from a combination of mantle and crustal rocks.

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Pages:208
Supervisor: D. B. Clarke