2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 49
Presentation Time: 8:00 AM-12:00 PM


BUCHANAN II, John Wesley1, AUGLAND, Lars Eivind2, STELTENPOHL, Mark G.3 and ANDRESEN, Arild2, (1)Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, (2)Department of Geology, University of Oslo, PO Box 1047 Blindern, Oslo, 0316, Norway, (3)Department of Geology and Geography, Auburn University, 210 Petrie Hall, Auburn University, Auburn, AL 36849, jbuchana@mines.edu

The southern portion of Liverpool Land, East Greenland is characterized by the Caledonian HP metamorphism of a 1.6 Ga old migmatitic orthogneiss complex. Variable pristine and retrogaded eclogites occur as boudins and pods wrapped with crystal-plastic mylonites that retrograde the surrounding migmatite foliation. Along with the eclogites, garnet-pyroxenite, amphibolite, and ultramafic bodies occur as pods and layers within the migmatite complex. This terrane comprises the footwall block of the Gubbedalen Shear Zone (GSZ), a ~400 m thick, N-dipping high-strain zone with a complex tectonometamorphic history, including tops-south (contraction) as well as tops-north (extension) displacement. The hanging wall of the GSZ is dominated by the Silurian Hurry Inlet Granite (445-430 Ma) and its migmatized country rocks, interpreted to be correlative with the Krummedal Sequence. The hanging wall block also includes an undeformed monzodiorite and a swarm of N-S striking lamprophyre dikes.

U-Pb ages on zircon and rutile grains separated from the eclogites yield an age of eclogitization of c. 400 Ma with subsequent cooling and growth of rutile at c. 391 Ma. The pristine eclogite mineralogy has in most cases been retrogressed by the breakdown of omphacite into variably fine- and coarse-grained symplectites composed of low-Na clinopyroxne and plagioclase. Microprobe analyses on Na-bearing clinopyroxenes, garnet, plagioclase, and different generations of amphibole were carried out in an attempt to estimate PT conditions during the HP metamorphism. The temperature of formation based on mineral chemical data from the most pristine sample is ~850C. Pressure could not be calculated due to the high Ca-content in the garnets.