Discovery of the William's Ridge and Rig Seismic Seamount microcontinents, Kerguelen Plateau: signatures of a fragmented rifted margin

The Kerguelen large igneous province (LIP), situated dominantly in the southern Indian Ocean, has several exceptional characteristics. These include an episodic and protracted formation over a ∼130 Myr period, sustaining the longest, continuous high-magma-flux emplacement interval of any LIP (>38 Myr), and the preservation of multiple Gondwanan continental fragments within the Kerguelen Plateau. Here, we document two new microcontinents—William's Ridge and Rig Seismic Seamount—in the eastern Kerguelen Plateau based on dredge samples acquired by RV Investigator voyage IN2020_V01. Dredge haul characteristics coupled with petrographic, geochemical (whole rock X-ray fluorescence, inductively coupled plasma mass spectrometry) and in situ geochronological (zircon U-Pb, apatite U-Pb, apatite Lu-Hf and garnet Lu-Hf) characterization of the recovered continental rocks suggest these samples are talus deposits from exposed escarpments. At William's Ridge, Mesoproterozoic amphibolitic–granitic orthogneiss (1,490–1,430, 1,100 Ma) and metavolcanic basement (1,600 Ma) correlate with the Shillong Plateau in northeastern India. Rig Seismic Seamount contains Archean granitic–granodioritic orthogneisses (∼3,500, 2,500 Ma), Mesoproterozoic metasedimentary rocks, charnockite (1,170 Ma), and Ordovician granite (480 Ma), potentially linked to the Vestfold Craton in East Antarctica. These newly identified microcontinents expand the inventory of known microcontinents in this region and suggest an extensive continental ribbon was rifted from the eastern margin of Greater India. Thermal weakening of the eastern Indian margin by the Kerguelen plume, a Cretaceous plate tectonic reorganization event, and the rapid motion of India relative to Australo-Antarctica during breakup contributed to significant fragmentation of this rifted margin.