Xenoliths reveal East Gondwanan basement to Heard Island, Central Kerguelen Plateau

Abstract

Increasingly it is recognised that the breakup of East Gondwana and formation of the Indian Ocean has led to the creation of many microcontinents, including Elan Bank, Gulden Draak Rise, and Batavia Rise. Whether the central and southern sections of the Kerguelen Plateau contain additional Gondwanan microcontinents remains controversial. Continental crust residing in these regions is mainly inferred from geochemical and geophysical datasets but little to no direct sampling evidence corroborates this. Here, we characterise continental rocks trawled from banks and plateaus on the Central Kerguelen Plateau, using petrographic techniques and U-Pb zircon and apatite dating. Recovered granitoids and felsic gneisses have Paleoarchean (∼3.3 Ga) and Mesoproterozoic (∼1.44 Ga, ∼1.19 Ga) zircon U-Pb crystallisation ages, as well as Mesoproterozoic (∼1.6 Ga, 1.15 Ga) and Cambrian (∼0.5 Ga) apatite U-Pb cooling ages. We interpret a microcontinent resides in the Central Kerguelen Plateau and must underly Heard Island, based on: (1) correlation of the U-Pb age groups of the recovered granitoid/gneissic rocks with conjugate Indian crust within East Gondwana, (2) regional geochemical and geophysical evidence for widely distributed microcontinental crust in the Kerguelen Plateau and (3) strong evidence supporting a local origin for the recovered rocks versus an ice-rafted Antarctic origin. Based on a volcanic rim preserved on a gneissic sample, we interpret portions of the Central Kerguelen Plateau microcontinent were entrained as xenoliths during the recent volcanic eruptions associated with Heard Island. A ridge jump of the Southeast Indian Ridge between 115–102 Ma likely formed the Central Kerguelen Plateau microcontinent and we speculate that related ridge jumps formed a near continuous ribbon of microcontinents along the Indian margin during the breakup of East Gondwana.