T344 Exhumation of Continental Ultrahigh-Pressure Terranes

Thursday, 9 October 2008
8:00 AM - 12:00 PM

The Timing of Exhumation and Basin Development In the North-East Greenland Caledonides

Paper number: T344-4
Program: Technical Sessions
Time: 8:40 AM – 8:55 AM

Authors

Abstract

Exhumation of ultrahigh-pressure (UHP) rocks is commonly ascribed to a two-stage history: travel from UHP conditions to the lower or middle crust, followed by final exhumation to the upper crust. Laurentian continental basement in NE Greenland records high-pressure (HP) and UHP metamorphism in the upper plate of the Caledonian collision. On the basis of U-Pb ages, three eclogite-bearing structural blocks experienced exhumation from peak conditions over a span of ca 90 my. HP metamorphism in the western and central blocks occurred at 400 Ma. Western block exhumation started by 390 Ma and continued through 350 Ma. Central block pegmatites indicate exhumation between 370 and 340 Ma and record multiple zircon growth events at 360, 340, 333, and 320 Ma related to deformation-induced fluid flow. Coesite-bearing zircons in the eastern block give ages from 364 ± 8 to 350 ± 4 Ma. UHP rocks give a Sm-Nd mineral isochron age of 342 ± 6 Ma. Titanite ages of 310 Ma record final exhumation of the UHP rocks. Correlation of ages with metamorphic-deformation history indicates exhumation of UHP rocks in NE Greenland is consistent with a two-stage model, with exhumation to the lower crust by 345 Ma at 4–11 mm/year, followed by a slower phase to approximately 20 km at 329 Ma at rates of approximately 1 mm/year.

U-Pb ages from the HP/UHP Laurentian basement allow correlation of exhumation with Carboniferous basin development. Middle Devonian basins in central East Greenland formed during initial exhumation of HP rocks in the western block at 390 Ma. Widespread subsidence is coincident with central block pegmatite emplacement and UHP exhumation at 345 Ma. Final UHP exhumation at 310 Ma was coincident with onset of marine sedimentation in the Wandel Sea Basin and a shift towards regional subsidence and carbonate deposition north of 75°N.