HR: 0800h
AN: V41F-1529    [Abstracts]
TI: The Very-low Velocity Province at the Core-mantle Boundary, Surface Hotspot Motion and the DUPAL Anomaly
AU: * Wen, L
EM: Lianxing.Wen@sunysb.edu
AF: State University of New York at Stony Brook, Dept. of Geosciences, Stony Brook, NY 11794 United States
AB: I discuss possible relationship between seismic heterogeneities near the core-mantle boundary, hotspot motion and isotope geochemistry observed on the ocean floor, focusing on the region in the Indian and south-Atlantic oceans as an example. Recent seismic results revealed a rapidly-varying very low-velocity province (VLVP) at the base of the mantle extending from the south Atlantic ocean to the Indian ocean. It has been suggested that the VLVP represents an 'ancient' compositional anomaly produced early in the Earth's history [Wen et al., 2001, Wen, 2001]. At the Earth's surface, the south Atlantic and the Indian oceans have a large number of hotspots and many impressive island chains and aseismic ridges, that are thought to be the tracks left by the passage of surface plates over major hotspots. The orientations, age progressions and plaeomagentic data along these hotspot tracks can be used to study the relative and absolute motions of the hotspots. I show that three major long-lived surface hotspots (Tristan, Marion and Kerguelen) geographically within the VLVP exhibit small relative motions (<9 mm/yr) in the past 80 Ma, while other hotspots appear to drift away from the Tristan-Marion-Kerguelen hotspot group. The ocean floor in the south Atlantic and Indian oceans also exhibits the largest isotopic domain delineated on the Earth's ocean floor, the 'Dupal anomaly', which has been suggested to have formed early in the Earth's history. I show that the 'Dupal anomaly' maximum observed on the Indian-Atlantic ocean floor geographically coincides with the VLVP when the past plate motions are taken into account. These observations can be explained and related by invoking a mechanism that the Tristan-Marion-Kerguelen hotspots manifest long-lived thermo-chemical plumes, and the VLVP serves as an anchor for their relative slow motion and source for the unique Dupal geochemical signature. It is also interesting to note that most of other hotspots, such as Reunion, Comoros, Bouvet and Shona, are geographically adjacent to the VLVP. One possible explanation is that they manifest thermal plumes generated in the adjacent areas of the VLVP. The adjacent areas of the VLVP may experience a large horizontal stress. A large horizontal stress may produce local thickening of the basal thermal boundary layer, and thus create a favorable condition for the development of thermal plumes. Wen, L. et al., EPSL, 189, 141-153, 2001; Wen, L., EPSL, 194, 83-95, 2001.
UR: http://geophysics.geo.sunysb.edu/wen/
DE: 1000 GEOCHEMISTRY
DE: 1040 Radiogenic isotope geochemistry
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8125 Evolution of the Earth (0325)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005