caa a22 4500 477064418 CHVBK 20180405111408.0 cr unu---uuuuu 170330e19961201xx s 000 0 eng 10.1007/BF02440113 doi (NATIONALLICENCE)springer-10.1007/BF02440113 Early Cambrian oceanic plagiogranite in the Silvretta Nappe, eastern Alps: geochemical, zircon U-Pb and Rb-Sr data from garnet-hornblende-plagioclase gneisses [Elektronische Daten] [Bernhard Müller, Urs Schaltegger, Urs Klötzli, Markus Flisch] Garnet-hornblende-plagioclase gneisses rich in incompatible elements occur in the crystalline basement of the Austro-Alpine Silvretta nappe and are associated with clinopyroxene norites and harzburgite cumulates. It is proposed here that the gneisses were formerly oceanic plagiogranites. An εNd(530) value of +5.6 for the gneisses as well as initial87Sr/86Sr values of 0.7036-0.7037 for the gabbroic rocks and 0.7026-0.7027 for the ultramafic rocks suggest a mantle source for this rock association. The geochemical characteristics of the garnet-hornblende-plagioclase gneisses indicate that their precursors were derived by fractional crystallization from a basaltic parent magma, by the same process which produced the adjacent clinopyroxene norites and ultramafic cumulates as well. The combined U-Pb upper intercept ages of zircons from two gneiss samples yield an igneous crystallization age of 532 ± 30 Ma, similar to previously dated (mostly calcalkaline) orthogneisses in the same area. High-quality transparent zircons showed the least degree of discordance, but contain extremely low U and Pb levels. The rock suite, including this plagiogranite, was emplaced within oceanic crust which formed in the latest Precambrian-early Palaeozoic off the northern continental margin of Gondwana. Springer-Verlag, 1996 Austro-Alpine nationallicence Eastern Alps nationallicence Oceanic rocks nationallicence Rb-Sr nationallicence Zircon nationallicence U-Pb nationallicence Magmatism nationallicence Müller Bernhard Department of Earth Sciences, Institute of Isotope Geology and Mineral Resources, ETH Zentrum, CH-8092, Zurich, Switzerland aut Schaltegger Urs Department of Earth Sciences, Institute of Isotope Geology and Mineral Resources, ETH Zentrum, CH-8092, Zurich, Switzerland aut Klötzli Urs Department of Geology, Laboratory for Geochronology and Isotope Geology, University of Vienna, Franz Grill Str. 9, A-1030, Vienna, Austria aut Flisch Markus Brückfeldstr. 23, CH-3012, Bern, Switzerland aut Geologische Rundschau Springer-Verlag 85/4(1996-12-01), 822-831 0016-7835 85:4<822 1996 85 531 https://doi.org/10.1007/BF02440113 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF02440113 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Müller Bernhard Department of Earth Sciences, Institute of Isotope Geology and Mineral Resources, ETH Zentrum, CH-8092, Zurich, Switzerland aut NATIONALLICENCE 700 1- Schaltegger Urs Department of Earth Sciences, Institute of Isotope Geology and Mineral Resources, ETH Zentrum, CH-8092, Zurich, Switzerland aut NATIONALLICENCE 700 1- Klötzli Urs Department of Geology, Laboratory for Geochronology and Isotope Geology, University of Vienna, Franz Grill Str. 9, A-1030, Vienna, Austria aut NATIONALLICENCE 700 1- Flisch Markus Brückfeldstr. 23, CH-3012, Bern, Switzerland aut NATIONALLICENCE 773 0- Geologische Rundschau Springer-Verlag 85/4(1996-12-01), 822-831 0016-7835 85:4<822 1996 85 531 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer