OCCURRENCES OF PSEUDOTACHYLYTE AT THE EAST BULL LAKE AND SHAKESPEARE-DUNLOP INTRUSIONS, ONTARIO, CANADA

Pseudotachylyte bodies were recently identified within and adjacent to the Early Proterozoic East Bull Lake and Shakespeare-Dunlop intrusion s, located approximately 25-40 km west-southwest of the western margin of the Sudbury Igneous Complex. These breccia-like bodies locally for m extensive vein networks and are preferentially developed along the c ontact between the intrusions and older Archean granitoid rocks. The p seudotachylyte veins comprise variable proportions of locally derived rock fragments and an aphanitic to fine-grained crystalline matrix tha t commonly displays flow textures. The veins appear to have formed by intense cataclasis and (or) frictional melting. These occurrences are very similar in appearance to Sudbury Breccia dykes that are observed at a radial distance of up to 80 km from the Sudbury Igneous Complex. Sudbury Breccia is widely believed to have formed as a result of the S udbury event-a cataclysmic explosion that occurred at 1.85 Ga. The loc ation of the pseudotachylyte veins described herein may coincide with one of the concentric bands of relatively intense Sudbury Breccia deve lopment observed to the north of the Sudbury Igneous Complex.