Geochemical evolution within a Devonian intra-oceanic island arc: The Gamilaroi terrane, southern New England orogen, Australia |
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| Authors: | James M C Stratford Jonathan C Aitchison |
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| Institution: | Department of Geology and Geophysics, University of Sydney, New South Wales 2006, Australia;Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong |
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| Abstract: | Abstract Geochemical analyses of volcanic rocks in the Gamilaroi terrane reveal several phases of arc activity within an intra-oceanic island-arc terrane. Felsic volcanic rocks at the base of the section have rare earth element (REE) and trace element compositions which indicate that they were derived from an island-arc source. Basalts immediately overlying the felsic volcanic rocks have a distinctive geochemical signature with low levels of Ti and Y and high levels of Ni, Cr and Mg. Low concentrations of REE and trace elements relative to mid-ocean-ridge basalts (MORB) indicate that they were also derived from an intra-oceanic island-arc source. Extensive basalts and basaltic andesites among the youngest rocks of the terrane have typically flat to enriched REE and trace element compositions, indicating a transitional arc-back-arc source. The change in basalt compositions indicates that rifting had occurred by this stage in the evolution of the arc. Confirmation of an intra-oceanic setting for this terrane enables a more detailed comparison with similar intra-oceanic rocks in the northern New England orogen. This study of the Gamilaroi terrane is an example of the potential use of geochemical data to identify other ancient intra-oceanic island-arc-rift suites. |
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| Keywords: | Devonian Gamilaroi terrane geochemistry island arc New England orogen |
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