HR: 13:45h
AN: U12A-01    [PDF]
TI: Tales of Two LIPs: Kerguelen/Broken Ridge (Indian Ocean) and Ontong Java (Pacific Ocean)
AU: * Coffin, M F
EM: mcoffin@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8649 Japan
AB: The Kerguelen Plateau/Broken Ridge (KP/BR) and Ontong Java Plateau (OJP) are among Earth's largest igneous provinces (LIPs), with crustal volumes of 2.5 and 5.7 x 10$^{7}$ km$^{3}$, respectively. Recent investigations, culminating in ODP Leg 183 to KP/BR, and Leg 192 to OJP, have revealed significant differences between the two. The Kerguelen hotspot has been active since at least 120 Ma. KP/BR contain microcontinental fragments. Upper crust of KP/BR is structurally complex, and although dominantly tholeiitic basalt, it includes basalts to rhyolites. Nearly all of the drilled upper crust formed subaerially, and subsequently subsided beneath sea level at rates comparable to those of typical oceanic crust. In contrast to KP/BR, OJP is entirely oceanic, includes no continental material, and cannot be linked to any hotspot track or currently active hotspot. It formed instantaneously, in a geological sense, at $\sim$120 Ma, together with flood basalts in older neighboring oceanic basins. OJP's upper crust is structurally relatively simple, and is homogeneously tholeiitic. To date, all rocks drilled on the plateau and sampled from obducted OJP sections in the Solomon Islands formed underwater, and subsequent lithospheric subsidence was either minimal or erratic. OJP is characterized by a low velocity mantle root extending several hundred kilometers into the asthenosphere that is interpreted as chemically, not thermally, anomalous. This root appears to deflect normal Pacific Ocean asthenosphere around it, and thus seems to be rigidly coupled to OJP crust. Extant plume theory explains neither KP/BR nor OJP. Plume models predict massive flood volcanism roughly coeval with continental breakup, yet the onset of voluminous KP/BR magmatism post-dated separation of India and Antarctica by at least 10 million years. Plume theory also predicts short-lived (approximately 1 Myr) plume head volcanism followed by long-lived (10-100 Myr) plume tail volcanism, yet peak magma output of the Kerguelen hotspot lasted approximately 25 Myr. Plume models predict major lithospheric uplift approximately coeval with voluminous magmatism, and subsequent plateau subsidence at rates similar to normal oceanic lithosphere, but the main OJP was never above sea level and has experienced only slight or erratic ensuing subsidence.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 9340 Indian Ocean
DE: 9355 Pacific Ocean
DE: 9609 Mesozoic
SC: U
MN: 2003 Fall Meeting