Collaborative Research: Formation and Exhumation of UHP and HP Terranes in the Greenland Caledonides - Understanding Processes at the Base of Continental Collisions Grant uri icon

Overview

abstract

  • Both the Greenland and Scandinavian Caledonides expose huge slabs of continental crust that have experienced high-pressure (HP) metamorphism during the collision between Laurentia and Baltica. An ultrahigh-pressure (UHP) terrane has been recognized in western Norway for the past fifteen years, while the first evidence for UHP metamorphism has just been found in Greenland a few months ago. Taken together, these two coherent continental eclogite terranes comprise the most extensive exposure of a deep, ancient mountain root on the planet - giving us a view of mountain belt anatomy that is generally hidden at the base of active orogens like the Himalayas. The ultimate goal of this project is to understand how this thick or deep orogenic root formed, and how it was brought back up to the earth's surface. Extensional collapse of overthickened crust, whereby HP and UHP rocks are unroofed along listric normal faults, is an oft-cited mechanism of exhumation; however, major extensional structures are not exposed in the Geenland eclogite province. Gilotti's earlier NSF supported research found that the peak pessure was attained approximately 410 to 370 Ma ago; whereas, workers in the Fjord Region, to the south of the eclogite province, are finding widespread evidence of synchronous melting, leucogranite generation and extensional faulting that is 10-70 Ma older. Either the observed extensional detachments in the south have nothing to do with eclogite exhumation, or the PI's previous ages are recording cooling at the end of the exhumation path instead of peak pressure conditions. The main objectives of the proposed research are: 1) to identify the extent and timing of UHP metamorphism; 2) to test the robustness of our previous ages for HP metamorphism by comparing zircon populations from the retrograde margins of eclogite pods to zircon populations from the well-preserved centers; 3) to establish the pressure-temperature-time history of this slab of eclogite-bearing crust as it returns to the earth's surface; and 4) to determine the geometry and timing of contractional and strike-slip fabrics that might be possible exhumation structures. The PI's data set is essential for formulating an orogen-wide model of eclogite formation and exhumation in this important continent-continent collision. Although the necessary studies are underway in Norway, their results cannot be put into context without the corresponding knowledge of HP and UHP metamorphism in Greenland. The preliminary results also have the potential to provide new insight on the behavior of U-Pb isotope systems during HP/UHP metamorphism and subsequent decompression.

date/time interval

  • August 15, 2002 - July 31, 2006

total award amount

  • 162,310

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