Natasha Wodicka

The Parry Sound domain (PSD) is an allochthon of quite different character to adjacent rocks in the Central Gneiss Belt, southwestern Grenville orogen, Ontario. Three distinct tectonostratigraphic units are recognized in the domain: the Parry Island and Twelve Mile Bay thrust sheets are dominated by upper amphibolite facies supracrustal rocks with subordinate plutonic rocks, whereas the overlying Parry Sound thrust sheet comprised mostly granulite facies plutonic rocks with lesser supracrustal rocks. The pre-Grenvillian history of the Parry Island and Twelve Mile Bay thrust sheets involved deposition of sedimentary detritus after ca. 1385 Ma, anorthositic to granitic magmatism between ca. 1350 and 1290 Ma, and granodiorite-tonalite magmatism in the period ca. 1312-1288 Ma. Sedimentation in the overlying Parry Sound thrust sheet predated intrusion of ca. 1294-1279 Ma tonalitic plutons.

The Grenvillian history of the PSD was primarily marked by several distinct episodes of deformation and metamorphism. The earliest episode involved high-PT granulite facies metamorphism of Parry Sound thrust sheet rocks which shortly predated northwestward thrusting at ca. 1159-1157 Ma. In turn, ca.1163-1151 Ma anorthosite and mafic dyke emplacement, intermediate- PT granulite facies metamorphism, and orogen-parallel extension in the Parry Island thrust sheet occurred penecontemporaneously with early thrusting. Rocks from the bottom part of the Parry Island thrust sheet record a second northwestward thrusting event at ca. 1120 Ma which may have closely coincided with high-Pt metamorphism. Large-scale erosion, as recorded by detrital zircon ages from post-ca. 1120-1140 Ma synorogenic sediments, may have led to thrusting and rapid exhumation of PSD rocks. At ca. 1080-1075 Ma, PSD rocks were reheated, possibly in response to major reactivation of the structurally higher Central Metasedimentary Belt boundary thrust zone. Finally, the in the footwall of a shear zone developed within a ca. 1020-970 Ma episode of late extension.

The pre- and early Grenvillian history (between ca. 1400 and 1120 Ma) of the PSD is strikingly similar to that described from the Central Metasedimentary Belt, suggesting that the latter represents the source region of the Parry Sound allochthon.

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Supervisor: Rebecca A. Jamieson