CORRELATION OF TACONIC ARC ACCRETIONS FROM NEWFOUNDLAND TO NEW ENGLAND: CONTINUOUS OR DISCONTINUOUS?

The polyphase Taconic orogenic cycle in the Newfoundland Appalachians, the tectonically most complex segment of the Taconic Appalachians, initiated with obduction of the Cambrian Lush’s Bight oceanic tract SSZ ophiolites at 500 to 495 Ma onto a peri-Laurentian microcontinent, followed by development of 490-485 Ma Baie Verte oceanic tract (BVOT) ophiolites and 489-476 Ma Notre Dame arc (ND arc), followed by their collision with Laurentia between 479 and 470 Ma. This was in turn followed by development of east-facing peri-Laurentian arcs and SSZ ophiolites, and their accretion at ca. 467 Ma. The Taconic cycle was terminated by arrival of the Ganderian Victoria arc at ca. 455 Ma.

The Taconic orogeny however shows considerable along-orogen differences in the timing and complexity of terrane accretion to the Laurentian margin. Quebec and NW Maine may preserve fragments of the ND arc based on seismic and isotopic evidence. However, equivalents of the BVOT ophiolites formed 5-15 My later than in Newfoundland and were obducted onto the Laurentian margin between 470 and 460 Ma. These age differences suggest that the geometry of the Quebec re-entrant was a major factor controlling formation of the BVOT ophiolites, and that BVOT and ND arc formed in close proximity to the Laurentian margin. BVOT and ND arc equivalents have not been recognized further south in western New England. New England ophiolites preserve evidence of subduction and hence were derived from the subducting plate, a setting similar to the Birchy Complex in Newfoundland. In contrast to Newfoundland, Quebec and NW Maine, the first recognized accretion in New England is represented by the ca. 476 Ma docking of the Ganderian? Moretown terrane, which may be a part of the Penobscot arc.

Available data indicate that BVOT and ND arc died out immediately south of Newfoundland or in southern Quebec, suggesting that they were bound to the south by a transform fault (similar to the northern termination of Tonga-Kermadec arc). The arrival of the leading peri-Gondwanan terranes shows ~ 20 My diachroneity with Iapetus closure becoming younger to the northeast, indicating the leading edge of Ganderia came in at a markedly oblique angle. It also implies that the Iapetus suture makes a jog from immediately east of the Laurentian Chain Lakes Massif to the westernmost extent of the Moretown in northern Vermont.