Origin and evolution of a submarine large igneous province: the Kerguelen Plateau and Broken Ridge, southern Indian Ocean

Abstract

Oceanic plateaus form by mantle processes distinct from those forming oceanic crust at divergent plate boundaries. Eleven drillsites into igneous basement of Kerguelen Plateau and Broken Ridge, including seven from the recent Ocean Drilling Program Leg 183 (1998^99) and four from Legs 119 and 120 (1987^88), show that the dominant rocks are basalts with geochemical characteristics distinct from those of mid-ocean ridge basalts. Moreover, the physical characteristics of the lava flows and the presence of wood fragments, charcoal, pollen, spores and seeds in the shallow water sediments overlying the igneous basement show that the growth rate of the plateau was sufficient to form subaerial landmasses. Most of the southern Kerguelen Plateau formed at V110 Ma, but the uppermost submarine lavas in the northern Kerguelen Plateau erupted during Cenozoic time. These results are consistent with derivation of the plateau by partial melting of the Kerguelen plume. Leg 183 provided two new major observations about the final growth stages of the Kerguelen Plateau. 1: At several locations, volcanism ended with explosive eruptions of volatilerich, felsic magmas; although the total volume of felsic volcanic rocks is poorly constrained, the explosive nature of the eruptions may have resulted in globally significant effects on climate and atmospheric chemistry during the late-stage, subaerial growth of the Kerguelen Plateau. 2: At one drillsite, clasts of garnet^biotite gneiss, a continental rock, occur in a fluvial conglomerate intercalated within basaltic flows. Previously, geochemical and geophysical evidence has been used to infer continental lithospheric components within this large igneous province. A continental geochemical signature in an oceanic setting may represent deeply recycled crust incorporated into the Kerguelen plume or continental fragments dispersed during initial formation of the Indian Ocean during breakup of Gondwana. The clasts of garnet^biotite gneiss are the first unequivocal evidence of continental crust in this oceanic plateau. We propose that during initial breakup between India and Antarctica, the spreading center jumped northwards transferring slivers of the continental Indian plate to oceanic portions of the Antarctic plate. ß

Origin, Distribution and Evolution of Plume Magmatism in East Antarctica

“…Origin of the latter is directly connected with the melting of continental lithospheric mantle (Andronikov & Egorov, 1993;). (Frey et al, 2000). Figure 9a demonstrates the closeness of characteristic ratios (Th/Nb)n vs (La/Nb)n for magmatic rocks in two provinces of eastern Antarctica.…”

“…Numerous investigations and reconstructions of the influence of the Kerguelen plume on the lithosphere of Antarctica and India suggest that the plume head spreads in the northeastern direction (Coffin et al, 2002;Frey et al, 1996Frey et al, , 2000Kent, 1991;Mahoney et al, 1995). The possible early occurrence of the plume at 130 Ma is reconstructed from the magmatism of continental margins (Fig.…”

“…7. Primitive mantle-normalized (Sun & McDonough, 1989) distribution of lithophile element patterns in the Schirmacher Oasis dolerites (a), Jetty Oasis alkaline picrites (b), Kerguelen Plateau tholeiites (Frey et al, 2000) (c) and the Afanasy Nikitin Rise tholeiites (Borisova et al, 2001) …”

“…8) reveals close relations between U and Th, Pb and Th, La and Th, and Yb and Th and poor correlations between other lithophile elements. These relations are less obvious for sample 47133-1, which has relatively low contents of Ta, Nb, Hf, Zr, and Sr. For the sake of comparison, Figure 8 shows the fields of enriched tholeiites from the Kerguelen Plateau recovered at ODP site 749 (Frey et al, 2000). It should be noted that the Schirmacher basites are distinguished by lower contents of Yb and Hf, and, probably, Sr, but the similar ratios of the majority of incompatible elements (especially, Ta/Th, U/Th, and Pb/Th) suggest similar geochemical nature of the enriched sources of both of the magma types.…”

“…10c) Riley et al, 2003) connected with distribution of Karoo-Maud plume to the south along Transantartic mountains are even more enriched in radiogenic lead which reflects the specific character of lithospheric mantle in this region. (Table 1, 2;Antonini et al, 1999;Belyatsky et al, 2002;Borisova et al, 2001;Frey et al, 2000;Heinonen et al, 2010;Sushchevskaya et al, 1996;Sushchevskaya et al, 2003). Chemical types of DML basalts (low-Nb, D-FP, E-FP, CT) refer to (Heinonen et al, 2010).…”