DID THE WILMINGTON COMPLEX ORIGINATE AS A PERI-GONDWANAN ARC?

The Wilmington Complex has historically been interpreted as a peri-Laurentian arc that was accreted to North America during the Ordovician Taconic Orogeny. Though this model remains consistent with recent zircon (Aleinikoff et al., 2001) and monazite data (Bosbyshell et al., 2001), a peri-Laurentian origin for the Wilmington Complex has never been supported by available paleomagnetic data (Rao and Van der Voo, 1980). The recent geochronological data provide greater precision on the timing of magmatism in the Arden pluton (434 +/- 5 Ma) and granulite facies metamorphism in the Wilmington Complex (~430 Ma) and hence the magnetization of these rocks. Assuming that rigid block tilting of the Arden pluton has not occurred since magnetization, Rao and Van der Voo's (1980) pole is a good match to Silurian pole positions for Avalonian rocks. Silurian mafic igneous rocks in the Wilmington Complex are geochemically similar to some mafic members of the Cranberry Island volcanics, Maine, which have been interpreted as Avalonian, and may have formed in a similar extensional setting.

The Wilmington Complex formed above a subduction zone during the Early Ordovician (ca. 480 - 475 Ma). Detrital zircon data from volcanic and clastic members indicate Grenvillian provenance and provide an additional constraint on the location of the Wilmington Complex at that time. Early Ordovician plate reconstructions indicate that Avalonia was rifting from northern Gondwana and that subduction was occurring on both sides of Iapetus, along the Gondwanan/Avalonian and Laurentian margins. A model which places the Wilmington Complex above the peri-Gondwanan subduction zone on crust that eventually rifted to become part of Avalonia is most compatible with all currently available data. In this model, final accretion of the Wilmington Complex to North American occurred in the Devonian.