HR: 0830h
AN: V31C-0952    [PDF]
TI: Structural, Geochemical, and Isotopic Studies on Magmatic Dyke Swarms of the South Shetland Islands Volcanic Arc, West Antarctica - Revealing the Geodynamic History
AU: * Kraus, S
EM: stefan.kraus@iaag.geo.uni-muenchen.de
AF: Dept. of Earth and Environmental Sciences, Section of Geology, Luisenstr. 37, Munich, 80333 Germany
AU: Miller, H
EM: hubert.miller@iaag.geo.uni-muenchen.de
AF: Dept. of Earth and Environmental Sciences, Section of Geology, Luisenstr. 37, Munich, 80333 Germany
AB: Between 2000 and 2002 areas of up to 100,000 m$^{2}$ have been mapped at several locations of the South Shetland Islands, mainly on King George and Livingston Islands. A structural analysis of the dykes and the host rocks was undertaken, and about 250 dykes were sampled for geochemical studies.\\ On Livingston Island six different strike directions were identified, yielding a reliable relative time sequence as deduced from field-relationships. Geochemically, these dykes can be separated into five different groups, correlating with the different strike directions, one of those groups comprising two directions. Analysis of the structural data shows, that at least on Livingston Island only minor changes of the tensional situation occurred.\\ Geochemical data reveal that all dykes of the South Shetland Islands belong to a calc-alkaline, arc-related suite, ranging from primitive basalts to highly differentiated rhyolites.\\ Interpretation of Sr isotopic data of the dykes proves difficult, as there are indications for sea-water induced Sr-alteration.\\ Nd isotopic analysis yield better results, revealing a three-stage development from the oldest dykes ($\epsilon$Nd -0.2 to 0.6) on Livingston Island towards a second, younger group ($\epsilon$Nd 2.8 to 4.2, also Livingston), terminating with a third one ($\epsilon$Nd 5.2 to 7.6), which includes the youngest dykes on Livingston and all dykes on King George and also Penguin Island. Either two mantle sources were involved, or the amount of crustal contamination changed considerately with time. It may have been high during initial arc volcanism, because of a still unstretched crust, then decreasing continually with progressing volcanism. In any case, the pattern reflects a chronological sequence corresponding with other authors' hypothesis of a migrating arc volcanism from SW to NE, i.e. from Livingston (older dykes) towards King George Island (younger dykes).\\ Pb isotopic data, plottet together with MORB- and sediment-samples dredged from the Drake Passage, indicate a three-component mixture of the arc magma. Mixing of MORB- and sediment-sources alone cannot explain the observed pattern. An additional source, maybe the crust underlying the South Shetland block, was involved.
DE: 1040 Isotopic composition/chemistry
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 9310 Antarctica
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting