Isotopic character of Cambro-Ordovician plutonism, southern Victoria Land, Antarctica

• Published in: New Zealand Journal of Geology and Geophysics
• Main Authors: Cox, Simon C., Parkinson, David L., Allibone, Andrew H., Cooper, Alan F.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Taylor & Francis 2000
• Subjects: Antarctic; Bonney; Dromedary; Valhalla; Vanda; Victoria Land; Antarc*; Antarctica
• Online Access: https://researchonline.jcu.edu.au/12972/1/12972_Cox_2000.pdf

Previous mapping of granitoid rocks in the Dry Valleys area of southern Victoria Land, Antarctica, identified the calc‐alkaline (DV1a), adakitic (DV1b), and monzonitic (DV2) suites. A fourth older suite comprising alkaline gabbro, syenite, and A‐type granite occurs in the Mt Dromedary area c. 80 km to the south. U‐Pb zircon dating of Bonney Pluton, the largest calc‐alkaline DV1a intrusion, indicates emplacement of this regional‐scale body at 505 ± 2 Ma. Pb‐loss and inherited zircon were common to Bonney Pluton analyses of this study. U‐Pb dating of monazite from Valhalla Pluton, a principal DV1b suite adakitic intrusion, indicates emplacement at 488 ± 2 Ma. The Bonney Pluton age constrains the peak of calc‐alkaline plutonism at 505 Ma and the Valhalla Pluton age records the major pulse of adakitic plutonism that is inferred to mark the final stages of subduction c. 490 Ma along this section of the East Antarctic margin. Nd and Sr isotope data for the calc‐alkaline DV1a suite and adakitic DV1b suite define distinct ranges for each suite, supporting their subdivision on the basis of field relationships, petrography, and whole‐rock geochemistry. Calc‐alkaline DV1a suite granite magmas have ϵNd(T) = ‐4–2 to ‐6.1 and Srᵢ = 0.7071–0.7079, whereas the adakitic DV1b suite rocks have a wider range of ϵNd(T) = ‐1.9 to ‐7.2 and Srᵢ = 0.7065–0.7097. The isotopic data suggest a significant mantle component and subordinate crustal component in the source region of both suites. Time‐dependent variations in the isotopic ratios of DV1a and DV1b suites imply a progressive increase in the proportion of more radiogenic material in the source region of the granitoid rocks, either mantle‐ or crust‐derived material. Larger adakitic DV1b plutons are more “evolved” than equivalent, smaller plutons of the same DV1b suite. Vanda Dikes and monzonitic DV2 suite intrusions are characterised by particularly low Srᵢ = 0.7044–0.7067 and near‐constant ϵNd(T) = ‐4.8 to ‐5.3, which indicate a petrogenesis for these younger intrusions distinct from ...