Abstract

Unusually closely spaced Barrovian series isograds have been described along the flanks of the Kigluaik Mountains, Seward Peninsula, Alaska, where they separate a high-grade gneiss complex intruded by granites of Cretaceous age from surrounding, regionally developed, blueschist to greenschist facies rocks. Structural mapping of the transition zone between the two metamorphic types indicates that their juxtaposition was aided by significant syn- to late- metamorphic solid-state flow that served to attenuate the overlying rock column and thus collapse the field metamorphic gradient. On the basis of field relations, structural data, petrography, and geochronologic data, strain appears to have accompanied the rapid (adiabatic) rise of high-temperature rocks from several tens of kilometres to less than 10 km depth during the Cretaceous, in an event younger than and unrelated to high-P metamorphism. Granite-cored gneiss domes on the Seward Peninsula may have formed during extension of previously thickened continental crust, resulting in the ∼35-km-thick crust and near-sea-level elevations of the region today.

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