reported two deformation stages in both the Shawanaga Domain and the Parry Sound Domain (Figure 5.4). The first deformation phase is represented by nappes and the second deformation phase is characterized by NNW-SSE-trending upright folds with fold axes plunging toward SSE. Culshaw et al. (1994) reported a thrusting and an extension characterized by normal shear zones and transverse folds in the Shawanaga Domain on the shore of Georgian Bay. The thrusting occurred in granulite to upper amphibolite facies metamorphism, and the extension occurred in amphibolite facies metamorphism (Tuccillo et al., 1992; Culshaw et al., 1994, 1997). Ketchum et al. (1998) shows that the thrusting occurred at > 1070-1030 Ma and the extension occurred at 1028-1018 Ma. Corrigan et al. (1994) discovered three deformation phases in the region of Key Harbour in south Britt Domain. The first two deformation stages are pre-Grenvillian (one >1694Ma and the other > 1450 Ma), and the last one is Grenvillian (> 1035~990 Ma). Post-extension deformation has not been reported in the Shawanaga Domain and the Parry Sound Domain. However, titanite growth during 1008-1000Ma and isotopic resetting during 967-956 Ma cooling through titanite closure temperature have been reported (Corrigan et al., 1994; Ketchum et al., 1998).
5.3.1
Regional correlation of structures and kinematics
D1 deformation fabrics in the study area are consistent with the thrusting and nappe associated fabrics in the Shawanaga Domain and the Parry Sound Domain based on fabric styles, orientations, and metamorphic facies (Gower, 1992; Culshaw et al., 1994). The thrust shear zones and nappes in the Shawanaga and the Parry Sound Domains are consistent with the High Grade Nappe Association (HGNA) of Williams and Jiang (2005). The Shawanaga and the Parry Sound Domains have the same kinematics as my study area, and are reflected by the transposition ST1 foliation and isoclinal folds in the D1 deformation phase. Moreover, D1 deformation fabrics in the study area developed in upper amphibolite-facies metamorphism which is comparable to the granulite-to-upper- amphibolite-facies metamorphism of thrusting in the Shwanaga and the Parry Sound
Figure 5.4 Fold structures in the Shawanaga Domain and the Parry Sound Domain. Modified from Gower (1992). This area is also the study area of Culshaw et al. (1994, 1997).
Domains. Therefore, it is reasonable to conclude that the thrusting in the Shawanaga Domain and Parry Sound Domain belongs to our D1 deformation phase. The first two deformation phases (one >1694 Ma and the other > 1450 Ma) of Corrigan et al. (1994) predate D1, and fabrics produced in them were modified in their third deformation phase (D1 of this study). Assuming that the same deformation structures occurred approximately at the same time in a not very large area, the D1 deformation phase in the GFTZ and north Britt Domain occurred >1070-1030 Ma.
D2 deformation in the area of this study represents NNW-SSE extension, which can be correlated to the extension in the Shawanaga and the Parry Sound Domains during 1028- 1018 Ma. The D2 fabrics in my study area are folds whose style and orientation are the same as those of transverse folds in the Shawanaga and the Parry Sound Domains. Moreover, these folds in both my study area and those south of it overprinted on the same D1 deformation fabrics. Therefore, D2 deformation in my area can be correlated to the extension in the Shawanaga and the Parry Sound Domains, and it occurred during 1028- 1018 Ma.
The late stage of D3 deformation represented by mylonite zones in the GFTZ indicates top-to-the-NW thrusting, and it is responsible for cooling of the titanites through their closure temperature in the Shawanaga Domain and the Parry Sound Domain. Therefore the 967-956 Ma can be assigned to the late stage of D3 deformation.
5.3.2 Previous geochronological evidence for the timing of each
deformation phase
The correlation of the deformation structures in the study area and those in the Shawanaga and the Parry Sound Domains leads to the conclusion that in the area of this study D1 deformation is > 1070-1030 Ma, D2 deformation, between 1028-1018 Ma, and D3 deformation between 967-956 Ma. This is supported by existing geochronological data in my study area. Corfu and Easton (2001) reported a concordant U-Pb age of 1050 Ma from a zircon in the GFTZ. Dadus et al. (1994) reported ages of 1032-1024 Ma for the relative coarse anhedral zircons in Sudbury dikes in the GFTZ. These zircons crystallized during the metamorphism which is associated with D1 deformation. Chen et
al. (1995) reported lower intercept ages of concordia diagrams of zircons in the range of 996-975 Ma from orthogneiss in northern Britt Domain. Haggart et al. (1993) reported lower intercept ages of 978Ma from a concordia plot of U-Pb data of 11 titanite fractions and 1 zircon fraction in gneisses in the GFTZ. This age has been confirmed and supplemented by Krogh (1994). Dadus et al. (1994) reported metamorphic ages around 1000 Ma based on small zircons from Sudbury dikes. Corfu and Easton (2001) concluded that 995-980 Ma lower intercept age of concordia plot (mainly titanites, some zircons and monazites) is the age for deformation and metamorphism during the Grenvillian compression in the GFTZ. The lower intercept age in the range of 1000-975 Ma represents the isotopic resetting during D3 deformation in our study area.
The proposed timing of deformation is also consistent with the observed overprinting relationship and our current knowledge of tectonic evolution of the Parry Sound Domain. D1 deformation fabrics (F1/2 folds) have been observed in Cosby granitic gneisses with primary age of 1430 Ma in the Britt Domain (Figure 5.2; Lumbers, 1975). Therefore the emplacement of the 1430 Ma granite predated the end of D1 deformation. The Parry Sound Domain was attached to the Shawanaga Domain around 1180 Ma (Culshaw et al., 1997), and the D1 structures are consistently present in both the Shawanaga Domain and the Parry Sound Domain, suggesting that D1 deformation occurred no earlier than 1180 Ma.