Abstract

Transcurrent terrane boundaries commonly evolve into long-lived faults that preserve little evidence for early docking events. A remarkable exception is exposed at Clarke Head along the Appalachian Meguma terrane boundary in Nova Scotia, Canada, where a Late Carboniferous fault megabreccia contains Devonian (369 Ma: U-Pb zircon) granulite-grade mylonite fractured by veins filled with Visean amphibole (ca. 335 Ma: Ar-Ar). This fractured mylonite was later mixed with Early Carboniferous sedimentary rocks during megabrecciation (ca. 315–310 Ma). These three fault events are reflected in the tectonostratigraphic record. Devonian (ca. 370–360 Ma) transpressional terrane docking ramped Meguma up against Avalonia and shed clastic detritus across the fault system. The Visean brittle deformation recorded by the amphibole veins was coeval with marine regression at surface. The late Namurian megabrecciation event similarly produced unconformity followed by renewed nonmarine clastic sedimentation. The Clarke Head megabreccia therefore preserves an episodic late Paleozoic fault history spanning some 55 m.y. during convergence between Laurentia and Gondwana and the assembly of the Pangean supercontinent.

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