NEW 40AR/39AR MUSCOVITE COOLING DATES FROM LIVERPOOL LAND, EAST GREENLAND AND THEIR CONSTRAINTS TO MODELS OF THE COLLISION BETWEEN BALTICA AND LAURENTIA

A recently discovered high-pressure (HP) Caledonian eclogite province in Liverpool Land, east Greenland provides constraints to the regional exhumation history of the Caledonian orogen. 40Ar/39Ar analysis had not previously been reported in Liverpool Land thereby limiting our understanding of the cooling history. We collected a series of samples from various lithologies and structural levels for 40Ar/39Ar dating of muscovite to constrain the metamorphic and cooling history in this region. 40Ar/39Ar ages were determined by single grain fusion and incremental heating in the Auburn Noble Isotope Mass Analysis Laboratory (ANIMAL). Muscovite from an undeformed pegmatite in the hanging wall of a major extensional shear zone (the Gubbedalen shear zone) yields an age of 387±1.5 Ma, and records Middle Devonian regional cooling prior to the shear zone formation. The initial 40Ar/39Ar ages from Liverpool Land are comparable to Middle Devonian ages from the Western Gneiss Region (WGR; Hacker, 2007) and Lofoten (Hames & Andresen, 1996; Steltenpohl et al., 2004), whereas ages from the North-East Greenland Eclogite Province (NEGEP) tend to be older (Late Silurian; Gilotti et al., 2004). The Middle Devonian and younger history of intrusion and cooling in Liverpool Land are consistent with the evolution of this Laurentian terrane in an overriding slab along a subduction boundary juxtaposed with and above the Baltic Lofoten terrane.