New Zealand Journal of Geology and Geophysics abstracts

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The Fontaine Pluton: an early Ross Orogeny calc-alkaline gabbro from southern Victoria Land, Antarctica

John M. Cottle^*
Alan F. Cooper^†

Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
alan.cooper@stonebow.otago.ac.nz

^*Present address: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom.

^†Author for correspondence.

Abstract  The Fontaine Pluton is a previously undescribed mafic intrusion outcropping at Fontaine Bluff on the south side of the Carlyon Glacier in southern Victoria Land, Antarctica. It is the southern-most member of a laterally extensive mafic suite emplaced at mid-crustal depths during the initial stages of the Ross Orogeny. The pluton comprises recrystallised hornblende-biotite gabbro, which in places shows well-defined centimetre to metre scale primary igneous layering. Recrystallised ultramafic enclaves composed of amphibole-chlorite-talc are inferred to be remnants of a chemically and mineralogically distinct cumulate fraction. The intrusion has a ⁸⁷Sr/⁸⁶Sr_(i) ratio of 0.70679 and a ¹⁴³Nd/¹⁴⁴Nd_(i) ratio of 0.51187 (εNd_(i) = –1.2). This, coupled with other geochemical data, implies that the Fontaine Pluton was formed by c. 15% partial melting of a depleted mantle source that was subsequently contaminated by continental crust. Preliminary U-Pb geochronology on zircon suggests an emplacement age for the pluton of 546 ± 10 Ma. These new data indicate that Ross Orogeny magmatism in this area of southern Victoria Land was initiated in the late Neoproterozoic along a subducting plate margin.

Keywords  Fontaine Pluton; Ross Orogeny; calc-alkaline; gabbro; Antarctica

G04039; Received 13 October 2004; accepted 19 January 2006; Online publication date 12 May 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49: 177–189
0028–8306/06/4902–0177  © The Royal Society of New Zealand 2006

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