IAPETAN ARC TERRANES OF THE NEWFOUNDLAND APPALACHIANS

The Newfoundland Dunnage Zone is made up of a collage of terranes comprising oceanic volcano-sedimentary arc sequences and, in some cases, plutonic suites interpreted to represent the magmatic roots of volcanic arcs. A major divide, the Red Indian Line, originally based on differences of faunal provinciality and isotopic signatures of Ordovician arc-related rocks, separates the Dunnage Zone into Notre Dame and Exploits subzones. These subzones host sequences interpreted to have North American and Gondwanan affinities respectively.

Arc-related volcanic rocks range in age from 505 to 470 Ma in the Notre Dame, and 513 to 464 Ma in the Exploits subzone. However, many important volcanic units are undated, limiting our ability to link different sequences through geochemistry/magmatic process and age to paleotectonic setting within Iapetus. In only a few well studied examples can we reasonably link separate volcanic groups and intrusive complexes - eg. Wild Bight and Exploits Groups and South Lake Igneous Complex.

In tectonic models it is oft assumed that Notre Dame arc rocks accreted to the margin during the Ordovician, driving Taconic orogenesis. However, many arc sequences are bounded by long lived fault zones and there is not solid evidence for an Ordovician age of accretion. In many cases the first clear overlap sequence or cross cutting pluton is of Silurian age.

As all Dunnage Zone sequences are allochthonous, age, lithologic and geochemical correlations of volcanic units need not imply proximity of those sequences in the Iapetus Ocean. We have no knowledge at all of the extent of potential strike slip movements in the oceanic realm and very little knowledge of the extent of such movements later in the orogen.