title: The petrology and geochemistry of a metabasite belt along the southern margin of Alaska.
abstract: A 600 km long metabasite belt is exposed at the southern border of the Chugach terrane in southern Alaska, south of the Eocene Chugach Metamorphic Complex (CMC). In this contribution, we present petrologic and geochemical results for parts of this metabasite belt. The metabasites studied are amphibolite grade and theirPTconditions are evaluated with hornblende-plagioclase thermometry and the averagePTmethod. From west to east the peak metamorphic conditions calculated are: about 730-793 °C for pressures between 5 and 15 kbar in the westernmost part, about 740-760 °C and 5 kbar in the middle locality and about 640-675 °C and 8 kbar in the easternmost locality. These results are comparable with the metamorphic conditions obtained on metapelite of the CMC for the westernmost and easternmost localities. In contrast, in the central part of the CMC, the metabasites experienced probably lower pressures than the metapelites to the north. Rare earth and trace element patterns of the metabasite belt are comparable with typical altered basalt patterns and reveal MORB and arc-tholeiitic geochemical characteristics. The presence of Ba and U anomalies are interpreted as a result of alteration prior to subduction, the Pb anomaly as a result of an intra-oceanic island arc signature and the Sr anomaly as a result of the interaction of sediments with the metabasites during subduction. We suggest that the association of MORB and arc tholeiitic rocks in the metabasite belt is likely derived from an intra-oceanic island arc which accreted to the Alaskan margin.
authors.affiliation: Department of Earth Sciences, Karl-Franzens Universität, Universitätsplatz 2, 8010 Graz, Austria ; School of Earth and Environmental Sciences, Portsmouth University, Burnaby building, Burnaby Road, Portsmouth PO1 3QL, United Kingdom.
authors.forename: E
authors.initials: E
authors.lastname: Bruand
authors.affiliation: Department of Earth Sciences, Karl-Franzens Universität, Universitätsplatz 2, 8010 Graz, Austria ; Department of Geosciences, University of Oslo, PO Box 1047, 0316 Oslo, Norway.
authors.forename: D
authors.initials: D
authors.lastname: Gasser
authors.affiliation: Department of Earth and Environmental Sciences, The Open University, Milton Keynes, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: Bonnand
authors.affiliation: Department of Earth Sciences, Karl-Franzens Universität, Universitätsplatz 2, 8010 Graz, Austria.
authors.forename: K
authors.initials: K
authors.lastname: Stuewe
keywords: Accretionary prism; Amphibolite; Chugach Metamorphic Complex; Intra-oceanic island arc; Subduction