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Millard F. Coffin, The University of Tokyo & Japan Marine Science and Technology Center, Japan Fred A. Frey, Massachusetts Institute of Technology, USA Paul Wallace, University of Oregon, USA ODP Leg 183 Scientific Party
From Early Cretaceous time (~120 million years We suggest that either multiple plume “drops” ago (Ma)) until separated by seafloor spreading emanated from the source region at the boundary at !40 Ma, the Kerguelen Plateau and Broken between the Earth’s mantle and core, or that vigorous Ridge formed a contiguous plateau with an area mantle circulation caused strong mantle shear during of nearly two million square kilometers, or Early Cretaceous time that may have split the initial roughly one-third the size of Australia. Scientists plume into several “drops” of varying sizes, had long debated whether these huge, buoyancies, and mantle ascent rates. In either predominantly undersea features are formed scenario, different drops could account for the small mainly of continental or oceanic type crust. volumes of dispersed continental basalts on India, Drilling of igneous basement by the ODP and Australia, and Antarctica, and the relatively large subsequent petrological, geochemical, and volumes of basalts of the Southern Kerguelen geochronological analyses of core samples Plateau, Elan Bank, the Central Kerguelen Plateau, demonstrated convincingly that the Kerguelen and Broken Ridge that formed over an interval of 30 Plateau and Broken Ridge comprise a hybrid of million years. Subsequently, the plume conduit oceanic and continental rocks. Gneiss, a became continuous and formed the Ninetyeast Ridge. continental rock, was found as clasts within a conglomerate at one drill site in 1999, and is the Figure (Page 2) first unequivocal evidence of continental crust Plate tectonic reconstructions of the southern Indian from the plateau. Fragments of East Gondwanan Ocean (left), using a hotspot reference frame, and (Indian, Antarctic, and Australian) continental Kerguelen hotspot output (right), from !130 million lithosphere became isolated within the nascent years ago to present. The Kerguelen hotspot has Indian Ocean, perhaps related to surfacing of the produced !25 x 106 km3 of mafic crust since !130 Ma. Kerguelen mantle plume (see Figure), and, in Magma output has varied significantly through time, addition to the gneiss, geochemical traces of beginning with low volumes contemporaneous with these fragments have been found in multiple or postdating continental breakup, extending through locations on the Kerguelen Plateau and Broken at least one and possibly two peaks from !120 to !95 Ridge. Nevertheless, the uppermost crust of both Ma, and then decreasing to relatively steady-state features is dominated by basaltic rock, although output ever since. Output rates between !120 and more silica-rich magmas were erupted !95 Ma exceed those of most other hotspot traces; explosively during the final stages of plateau subsequently, output rates have been at levels typical formation. Subsidence of the Kerguelen Plateau of many hotspots, including Hawaii. Reconstructed since formation resembles that of normal oceanic positions of the Kerguelen hotspot, assuming that lithosphere, and is attributed to contractional either the Kerguelen Isles (K) or Heard Island (H) is cooling, implying that continental components in the current location of the hotspot, are indicated by the lithosphere are not volumetrically significant. red stars. Volcanic rock associated with the Kerguelen hotspot is indicated in black, and lamprophyres (L) as Radiometric (40Ar/39Ar) age determinations of diamonds, as they have appeared through geologic Kerguelen hotspot basalts and crustal volume time. Continental margins appear in dark gray, and estimates have been used to infer temporal continents in light gray. Dashed line indicates a variations in hotspot magma output (see Figure). possible northern boundary for Greater India. IND: Most models for the origin of continental flood India; ANT: Antarctica; AUS: Australia; EB: Elan basalts and oceanic plateaus predict initially Bank; NP: Naturaliste Plateau; BB: Bunbury Basalts; voluminous (“plume head”, or the rising bulbous RAJ: Rajmahal Basalts; SKP: Southern Kerguelen head of a plume) magmatism over a relatively Plateau; CKP: Central Kerguelen Plateau; BR: Broken short period of 1-2 million years, followed by Ridge; WP: Wallaby Plateau; SB: Skiff Bank; NER: steady-state (“plume tail”, or the trailing straw- Ninetyeast Ridge; NKP: Northern Kerguelen Plateau. like appendage below the plume head) magma References output at much lower rates. Furthermore, Coffin, M.F., Frey, F.A., Wallace, P.J., et al., 2000. Proceedings of massive magma output from hotspots is the Ocean Drilling Program, Initial Reports, 183 [CD-ROM]. commonly, but not always associated in space Available from: Ocean Drilling Program, Texas A&M University, and time with continental breakup. Our results College Station, TX 77845-9547, U.S.A. require a more complex scenario to explain the Frey, F. A., et al., 2000. Origin and evolution of a submarine large prolonged duration, the spatial extent, and the igneous province: the Kerguelen Plateau and Broken Ridge, timing of magmatism (see Figure). Initial Southern Indian Ocean, Earth and Planetary Science Letters, 176: magmatism associated with the Kerguelen 73-89. hotspot(s) post-dates continental breakup Frey, F.A., Coffin, M.F., Wallace, P.J., and Quilty, P., eds., 2002. between India and Antarctica, and between India Proceedings of the Ocean Drilling Program, Scientific Results, 183 and Australia, although that magmatism affected [CD-ROM]. Available from: Ocean Drilling Program, Texas A&M both continental and expanding Indian Ocean University, College Station, TX 77845-9547, U.S.A. lithosphere. Wallace, P.J., Frey, F. A., Weis, D., and Coffin, M.F., eds., 2002. Origin and evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago, Journal of Petrology. 43: 1105-1413. Indian Plate Reconstructions and Kerguelen Hotspot Output Magma Flux (km3/yr) 0 0.5 1.0
80˚ 90˚ 0 70˚ 100˚ ˚ 110 60 ˚
˚ -30 -30 ˚
NKP ˚ -40 -40 ˚ K H ˚ -50 -50 ˚
˚ -60 -60 ˚
˚ -70 -70 ˚ 110 ˚ 60 ˚ 23.4 Ma Northern Kerguelen 80˚ 90˚ 20 70˚ 100˚ ˚ 110 60 ˚
˚ -30 -30 ˚
˚ -40 -40 K ˚ H
˚ -50 -50 ˚
˚ -60 -60 ˚
˚ -70 -70 ˚ 110 ˚ 60 ˚ 46.3 Ma
80˚ 90˚ 40 70˚ 100˚ ˚ 110 60 ˚
˚ -30 -30 NER ˚
˚ -40 -40 K ˚ H SB ˚ -50 -50 ˚
˚ -60 -60 ˚
˚ -70 -70 ˚ 110 ˚ 60 ˚ 62.5 Ma
80˚ 90˚ 60 70˚ 100˚ ˚ 110 60 ˚
˚ -30 -30 ˚ Ninetyeast Ridge + Skiff Bank
˚ -40 -40 K ˚ H
˚ -50
˚ Age
-50 (Ma)
˚ -60 -60 ˚
˚ -70 -70 ˚ 110 ˚ 60 ˚ 83 Ma 80 80˚ 90˚ 70˚ 100˚ ˚ 110 60 ˚
˚ -30 -30 ˚
BR WP ˚ -40 -40 ˚ K CKP H ˚ -50 -50 ˚
SKP ˚ -60 -60 ˚ Broken Ridge ˚ -70 -70 110 ˚ ˚ ˚ 95 Ma 60 100 80˚ 90˚ 70˚ 100˚ ˚ 110 Central Kerguelen 60 ˚
˚ -30 -30 ˚ Elan Bank ˚ -40 -40 ˚ RAJ L L ˚ -50 -50 ˚ K H BB -60 Southern Kerguelen + Rajmahal + Lamprophyres ˚ -60 ˚
L ˚ -70 -70 ˚ 110 ˚ 60 ˚ 110 Ma 120 80˚ 90˚ 70˚ 100˚ ˚ 110 Bunbury - Gosselin 60 ˚
˚ -30 -30 ˚
˚ -40 -40 ˚ Bunbury - Casuarina
˚ -50 -50 IND AUS ˚ NP ˚ EB -60 -60 K ˚ ANT H ˚ -70 -70 ˚ 110 ˚ 60 ˚ 130.9 Ma 140