Abstract

The Glen Dessary Syenite crops out in the steep belt of the Northern Highland Moine. It is enclosed within a psammite envelope which was previously assigned to the Glenfinnan Division, but which is here correlated with the psammites of the Loch Eil Division exposed to the E of the Loch Quoich Line. Three episodes of deformation have been identified in the Moine metasediments of the Glen Dessary area, but only the latest (D3) is thought to have deformed the syenite, imposing on it a strong, steeply plunging mineral lineation. The syenite is thought to occupy the core of a large, intensely curvilinear, D3 synform. The D3 structures which deform the syenite can be correlated with upright structures, which reworked previously flat-lying, already crystalline rocks, recognized at Loch Quoich. Upright reworking must be younger than the Glen Dessary Syenite, dated by U-Pb methods at 456 ± 5 Ma.

Two, hitherto unrecorded, small bodies of granitic gneiss, similar to the c. 1020 Ma Ardgour Gneiss, have been identified in psammites of the Loch Eil Division near the W end of Loch Arkaig. Their presence suggests that the Loch Eil Division has a Grenville history, and is part of the 'Old Moine'.

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