STRIKE-SLIP ALLOCHTHONEITY OF TACONIC SUTURES IN THE NEWFOUNDLAND APPALACHIANS

The Northern Appalachians preserve a record of more than 90 my of terrane accretion and hence contain many sutures, most of which are well exposed in Newfoundland. Two sutures of interest are kinematically linked. The Lloyd’s River-Lobster Cove fault zone bounds the Taconic Notre Dame arc and its Dashwood infrastructure in the east, separating it from the adjacent Annieopsquotch accretionary tract. The Baie Verte Line separates the Taconic arc from the Laurentian Humber margin in the west. Both fault zones were active during the Middle-Late Ordovician, but accommodated opposite senses of transcurrent movements, dextral in the west and sinistral in the east, implying that the Notre Dame arc was escaping and hence moving towards the southwest in present coordinates. The Taconic arc-continent collision recorded in the Newfoundland Humber zone was generally soft with little or no metamorphism and moderate deformation, whereas the adjacent Notre Dame arc was intensely deformed and metamorphosed (hard collision), evidenced by widespread Ordovician exhumation of (garnet) amphibolite and granulite facies rocks. However, metamorphic and deep-seated igneous detritus is rare or absent in the Taconic foredeep fill in western Newfoundland. The contrast in style of collision and nature of foredeep fill suggest that the Notre Dame arc didn’t collide with the Humber margin in Newfoundland, but with a part of the Laurentian margin further to the northeast that was also subjected to a hard collision. The Notre Dame arc and its Dashwoods infrastructure may be analogous to the Grampian Connemara terrane in the west of Ireland, both being allochthonous strike-slip arc terranes juxtaposed with unrelated segments of the Laurentian margin late during the Taconic-Grampian arc-continent collision.