CONSTRAINTS ON CONDITIONS AND TIMING OF SILURO-DEVONIAN EXTENSION: EVIDENCE FROM THE WESTERN CONNECTICUT VALLEY-GASPÉ TROUGH MARGIN
The NIC dike swarm and associated small plutons are only 2.5 km west of the faulted western border of the Siluro-Devonian Connecticut Valley-Gaspé Trough (CVGT). Immediately east of the eastern faulted border of the CVGT is another dike swarm, the Ludlow Comerford Intrusive Suite, consisting of tholeiitic basalts derived by partial melting of asthenosphere and intruded at 419±1 Ma (Rankin et al., 2007). Both dike swarms are thought to represent melt products tapped from depth during early extension of the CVGT. The presence of significant populations of inherited zircons in the NIC intrusives having both Laurentian and Pan-African affinities requires a pre-emplacement tectonic scenario in which some materials beneath the region were derived from the east. A working model of partial melting of a foundered slab following the end of the Taconian orogeny is compatible with the trondhjemitic compositions of the NIC and the presence of their Pan-African zircon population.