Small(< 1 metre) phacoids of high-pressure, low-temperature (HP-LT) metamorphic rocks located in the Peel-Manning Fault system of the southern New England Orogen provide a record of Cambrian subduction and Ordovician exhumation that is difficult to reconcile with tectonic models of the New England Orogen. In this talk, I present new thermodynamically constrained pressure-temperature data from these eclogite and blueschist facies metamorphic rocks. Combined with new thermochronological data and existing geochronological constraints, it can be shown that the high-pressure rocks share a common metamorphic history, and can therefore, be used to reconstruct a pressure-temperature-time path for the Cambrian-Ordovician convergent margin. These data indicate that there was a significant time lag between eclogite (∼ 536 Ma) and blueschist facies metamorphism ( 470 Ma), which took place at crustal depths of 85 km and 20km, respectively. This ∼ 65 .million year window indicates that approximately 65 km of exhumation occurred either very slowly ( ∼ 1 mm/yr) or, was discontinuous. This is in stark contrast with rapid, single-stage exhumation models currently proposed for some high-pressure rock localities. Interestingly, the high-pressure rocks are also considerably older than the orogen that contains them; which provide an intriguing link between early Palaeozoic subduction and the Permian evolution of the New England Orogen. Finally, the terminal exhumation and exposure of the high-pressure rocks during the Permian was facilitated by localised extrusion along the sepentinite-rich Peel-Manning Fault system.
New England Orogen 2010 (NEO 2010). NEO 2010: Conference Proceedings (Armidale, N.S.W. 16-19 November, 2010) p. 266-269