Petrogenesis of the Flood Basalts Forming the Northern Kerguelen Archipelago: Implications for the Kerguelen Plume

• Published in: Journal of Petrology
• Main Authors: Yang, Huai-Jen, Frey, Frederick A., Weis, Dominique, Giret, Andre, Pyle, Doug, Michon, Gilbert
• Format: Text
• Language: English
• Published: Oxford University Press 1998
• Subjects: Articles; Antarctic; Indian; Kerguelen; Southeast Indian Ridge; The Antarctic; Antarc*
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/39/4/711; https://doi.org/10.1093/petroj/39.4.711

The thick, >20 km, crust of the Kerguelen Archipelago formed as the tectonic setting of the Kerguelen Plume changed from an oceanic ridge-centered location at 43 Ma to its present location beneath the Antarctic plate. The uppermost crust is dominantly flood basalt with a thickness of up to 10 km. Inverse isochron 40Ar/39Ar ages for upper and lower lavas in a 630 m section of basalt flows from Mont Bureau are 30.4 and 29.0 Ma; Re–Os isotopic systematics are consistent with this age. Most of the lavas in two stratigraphic sections (Mont Bureau and Mont Rabouillere) from the northern part of the archipelago have Sr, Nd and Pb isotopic characteristics similar to the youngest (Upper Miocene to Pleistocene) lavas erupted in the southeast part of the archipelago, i.e. initial 87Sr/86Sr <0.7050, 143Nd/144Nd <0.5127 and 206Pb/204Pb <18.3. The dominance of this isotopic signature in archipelago lavas for 30 my and its presence in ∼40 Ma gabbros is consistent with the previous interpretation that these are isotopic characteristics of the Kerguelen Plume. Although this component occurs in high (>10%) MgO alkalic lavas in the Southeast Province of the archipelago, in these northern sections it is confined to transitional lavas with <6% MgO. A low plume flux and extensive crustal processing are inferred. In contrast to the plume–derived lavas, ∼15% of the flood basalts in these sections have lower initial 87Sr/86Sr (to 0.70396), higher 143Nd/144Nd (to 0.51289), and they hae some compositional characteristics of plagioclase-rich cumulates, i.e. high Sr/Nd and Ba/Th and positive Eu anomalies. However, plagioclase phenocrysts are absent in most of these lavas; therefore a plagioclase-rich component is required in their source. A plausible interpretation is that plagioclase-rich cumulates formed in the lower oceanic crust when the Southeast Indian Ridge was coincident with the plume at ∼43 Ma; subsequently these cumulates were melted by the plume and the melts contributed to a small proportion of the flood ...