Abstract
Shear zones in the Flin Flon area record five episodes of development. These have been studied using structural analysis and 40Ar/39Ar thermochronology. Deformation occurred as a result of collision between the Archean Rae‐Hearne and Archean Superior plates during the Trans‐Hudson Orogeny (1900 to 1700 Ma). The geodynamic evolution encompasses a transition from island arc supracrustal development (∼1900 Ma) to tectonic mountain building under brittleductile conditions (>1860 Ma), two episodes of ductile lineation‐schistosity (L‐S) shear zones on the prograde metamorphic path (1860–1810 Ma), and two episodes of retrograde displacement between 1790 and 1690 Ma, during final suturing of the Archean cratons with Paleoproterozoic assemblages. Metamorphism evolved in three stages. Contact aureoles to granitoid bodies formed at 1860–1840 Ma. Hornblende homfels facies 40Ar/39Ar ages indicate cooling through 500°C at ∼1840 Ma. This was followed by regional heating (burial), which produced regional peak thermal recrystallization at ∼1820–1790 Ma, under lower greenschist to lower amphibolite conditions. Lastly, retrograde metamorphism took place during unroofing between 1790 and 1690 Ma, with a regional cooling rate of 2 °C/m.y.
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