CONSIDERATIION OF HOTSPOT/MANTLE PLUME ORIGIN AS RELATED TO THE KERGUELEN PLATEAU, SE INDIAN OCEAN, A NEXUS OF INTERSECTING SPREADING RIDGES

The genesis of hotspots/mantle plumes is shown to be related to intersections of propagating belts of extensional lithospheric weakness. Such intersections offer points of maximum crustal tension prompting translithospheric penetration of the already near-surface asthenosphere characteristic of spreading ridges and rift systems. Crossings allow the outpourings, from vertical and lateral sources, of the voluminous basalts associated with mantle plumes and hotspots. On the finite planetary surface such crossings are inevitable and allow for a globally common mode of mantle plume/hotspot origin.

As a complex example the Kerguelen Plateau, a nucleus of continental dispersion, is divisible into three major divisions: the southern Kerguelen (SKP), the Central Kerguelen (CKP) and the Northern Archipelago (NKA). These divisions are part of separated and displaced igneous provinces which marked the site of spreading ridge intersections. Today, two of the provinces can be traced along hotspot wakes to their originating mantle plumes. Hotspot wakes link the SKP and CKP to two crossings and the NKA to a hotspot wake - spreading ridge merger.

The original location of the Crozet and Heard hotspots can be traced to the Rajmahal–SKP basalts, (~120+ Ma) and to the slightly younger Sylhet-CKP basalts (~110 Ma), respectively. The offshore western Australia spreading system (OWASS) intersected by the northern Greater-India-margin spreading formed the Crozet Basin mantle plume-Rajmahal–SKP basalts. The Australia/Antarctica separation, and its presumed continuation into the India and Greater India opening, crossing with the OWASS formed the Sylhet-CKP basalts. The SKP and CKP were left behind by the rapid northern migration of the Indian Plate.

The continuation of the Ninetyeast hotspot wake on the south side of the South East India Ridge (SEIR) links directly to the Heard Mantle Plume. The 300+ igneous outpourings of the NKA can be traced to the mixing ~40 Ma ago of the Ninetyeast-Heard hotspot wake with the merging of the propagating SEIR with the now fossil Wharton Ridge.

Studies of hotspots/mantle plumes in other oceans admit to an “intersection” hypothesis. This makes hotspots/mantle plumes an integral part of the global plate tectonic process rather than a random, stand-alone and totally ad hoc phenomenon