The Teslin suture zone (TSZ) is a Late Triassic to mid-Jurassic subduction complex and forms the fundamental boundary between rocks deposited along the ancient western margin of North America, and allochthonous terranes to the west. The north-northwest-trending TSZ in the Big Salmon Range includes sedimentary and volcanic strata, basalt, peridotite, and granodiorite metamorphosed to middle greenschist to epidote-amphibolite facies and variably mylonitized. Petrochemical study of co-existing phases now being initiated should allow the assignment of P-T limits attending the recrystallization.
Geologic mapping and structural analysis along three 10-15 km transects normal to the trend of the TSZ delineates two populations of stretching lineations, Lm1 and Lm2, in north-northwest-trending, steeply-dipping mylonitic foliation. Lm1, best developed in the western portion of the TSZ, plunges moderately to steeply west. Tight to isoclinal fold axes parallel Lm1. Lm2, best developed to the east, plunges gently north-northwest and south-southeast. Open to isoclinal fold axes parallel to Lm2, and fractures are locally present normal to Lm2. Folds initiated during mylonitization as open structures with axes parallel to Lm, and do not record unrelated pre- to post-mylonitic fold events. Crenulation and intersection lineations vary in orientation between schistosity planes in the shear zone. The stretching lineations, Lm1 and Lm2, formed parallel to their bulk movement directions. Kinematic indicators consistently record right-lateral movement parallel to Lm2. Preliminary interpretation of Lm1 kinematics indicate dominantly normal movement parallel to Lm1, or west-side-down.