Paper No. 8
Presentation Time: 10:10 AM
A CARIBBEAN-STYLE PLATE IN THE IAPETUS OCEAN
WALDRON, John W.F., Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G2E3, Canada, MURPHY, J. Brendan, Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada and SCHOFIELD, D.I., British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom, john.waldron@ualberta.ca
Compared with the Atlantic, subduction of the Paleozoic Iapetus Ocean began relatively soon after its opening. Vestiges of the Iapetan oceanic lithosphere are preserved as supra-subduction zone ophiolites and related mafic complexes in the Appalachian-Caledonian orogen. The earliest indications of subduction in are recorded in arc rocks preserved in ophiolites only 20 - 40 m. yr. younger than the end of Iapetan rifting. The earliest collisional events occurred almost simultaneously on both margins of the Iapetus ocean.
Available Sm-Nd isotopic data indicate that the mantle source of Iapetan ophiolitic complexes was highly depleted as a result of a history of magmatism that occurred before the Iapetus Ocean existed. We propose that this oceanic lithosphere was captured from the adjacent Paleopacific lithosphere, in a manner analogous to the Mesozoic-Cenozoic “capture” in the Atlantic realm of the Caribbean plate. The early phase of magmatism rendered it more buoyant than surrounding asthenosphere, which facilitated its preservation, implying that highly depleted mantle may be preferentially preserved in the geologic record. This hypothesis may explain the premature closing of the Iapetus Ocean, the timing of the earliest collisional events, and the distribution of peri-Gondwanan terranes in the Appalachian-Caledonian orogen.
