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Geometry and strain partitioning within lower-crustal intraplate strike-slip shear zones can be extremely complex, compared with analogous structural levels of interplate strike-slip shear zones sited at plate margins. Striding-Athabasca mylonite zone, Canadian Shield, is a spectacular ca. 500 km long granulite facies continental intraplate shear zone. The shear zone is composed of Middle Archean granulite facies annealed mylonites (ca. 3.13 Ga) and Late Archean (ca. 2.62-2.60 Ga) granulite facies ribbon mylonite belts, which thread a sinuous course along a chain of crustal-scale ‘lozenges’ cored by relatively stiff rocks of mafic to intermediate composition. To the northeast, the mylonites form a N-S-trending, 5–10 km thick, dextral strike-slip belt. To the southwest, this bifurcates into a pair of conjugate strike-slip shear zones, overlain by a contemporaneous dip-slip shear zone. Striding-Athabasca mylonite zone was kinematically inefficient as a strike-slip fault and cannot have accommodated large wallrock displacements. Nevertheless, spectacular granulite facies ribbon mylonites were formed throughout the shear zone, reflecting the very high temperatures (ca. 850–1000 °C), high recrystallization rate/strain rate ratios, and the transpressive nature of the deformation (Wk < 1), possibly accommodated by significant volume loss by magma migration. |
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