The geology and structural history of the Cape Ray Fault Zone in southwestern Newfoundland

Abstract

Structural studies within the Cape Ray Fault Zone, southwestern Newfoundland indicate that three tectonic events (D1 to D3) have deformed all regional lithologic units. These lithologies are distributed as a tonalitic terrain (intrusive into ophiolitic remnants) to the northwest, a central volcanic–sedimentary terrain, and a staurolite–kyanite gneiss terrain to the southeast. D1 produced the dominant northeasterly striking planar fabrics in the host rocks that are axial planar to isoclinal folds. The fold axes parallel a synkinematic mineral elongation lineation. D2 formed open asymmetrical folds with curvilinear fold axes and local crenulation cleavage. The D3 event produced local conjugate kink folds. Radiometric dates on deformed plutons indicate these deformational events were post-369 ± 12 Ma (post-Middle Devonian) and pre-352 ± 6 Ma (pre-Late Carboniferous).The fault was previously interpreted as a "cryptic suture" along which opposed margins of the Iapetus Ocean were juxtaposed. Supposedly this suture was subsequently partially covered by volcanic and sedimentary rocks. The present work indicates that the deformational events that produced the fault zone overprinted all regional lithologies in a similar manner and that the delineating mylonites were the products of ductile simple shear due to intense localized deformation. The fault itself is a large-scale shear zone and is not the end result of intercontinental collision.