Geochemical and Nd isotopic constraints for the origin of eclogite protoliths, northern Cordillera: implications for the Paleozoic tectonic evolution of the Yukon-Tanana terrane

摘要

On the basis of trace-element data, basalticprotoliths for Paleozoic eclogites from the Yukon-Tanana terrane(YTT) have diverse origins. Eclogites from Stewart Lake andthe Simpson Range have characteristics of basaltic protolithsgenerated by subduction-zone magmatism, are hosted byserpentinitic-gabbroic rocks, and record Mississippian high-pressure metamorphism and cooling. In contrast, eclogites fromFaro, Ross River, and Last Peak show either within-plategeochemistry or mid-ocean ridge protolith geochemistry with asmall subduction component, are hosted by continentalmetasedimentary rocks of the Nisutlin assemblage, and recordPermian high-pressure metamorphism and cooling. We interpretthese results to derive from the following tectonic events in thePaleozoic history of the YTT: (1) activity at a Devonian-Mississippian convergent plate margin at the distal edge ofNorth America, with near-contemporaneous subduction-zonemagmatism and high-pressure metamorphism; (2) Mississippianrifting of that margin to form the outboard YTT, the SlideMountain marginal basin, and the Faro, Ross River, and LastPeak eclogite protoliths; and (3) west-dipping subduction of theSlide Mountain Ocean under the outboard YTT in Permian time,to produce the Faro, Ross River, and Last Peak eclogites andPermian arc magmatism throughout the YTT. The basalticprotoliths of the Paleozoic YTT eclogites bear close similarity tothose produced in rifted convergent margins, such as theMiocene Japanese arc - back-arc system.