Taconian orogeny and the accretion of the Dashwoods block: A peri-Laurentian microcontinent in the Iapetus Ocean

The stratigraphy of the external Humber zone of the western Newfoundland Ap palachians records protracted Neoproterozoic-Early Cambrian rifting, follow ed by development of a passive margin that persisted until late Early Ordov ician (Arenigian) time (ca. 475 Ma). However, adjacent metamorphic rocks, d erived from the Laurentian margin and preserved in the Dashwoods subzone, w ere deformed, overthrust by ophiolites, and intruded by arc plutons by 488 Ma. The adjacent Notre Dame subzone also records isotopic evidence of inter action with the margin by 488 Ma. We propose that a microcontinent (Dashwoo ds microcontinent) was rifted from Laurentia during the Early Cambrian afte r an earlier, Neoproterozoic opening of the Iapetus Ocean, and was separate d from the margin by a narrow oceanic tract (Humber seaway). Attempted subd uction of the Dashwoods microcontinent prior to 488 Ma was followed by:clos ure of the Humber seaway in the Taconian orogeny.