HR: 08:50h
AN: V21B-04    [PDF]
TI: Secondary Hotspots in the South Pacific as a Result of Mantle Plumelets and Lithospheric Extension?
AU: * Koppers, A
EM: akoppers@ucsd.edu
AF: Scripps Institution of Oceanography, IGPP, La Jolla, CA 92093-0225 United States
AU: Staudigel, H
EM: hstaudigel@ucsd.edu
AF: Scripps Institution of Oceanography, IGPP, La Jolla, CA 92093-0225 United States
AU: Wijbrans, J
EM: wijj@geo.vu.nl
AF: Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Pringle, M
EM: M.Pringle@surrc.gla.ac.uk
AF: SURCC, Rankine Avenue, East Kilbride, G75 0QF United Kingdom
AB: By far the largest number of secondary hotspots (cf. Courtillet et al., 2003) can be found in the "South Pacific Thermal and Isotopic Anomaly" (SOPITA) or "Superswell" region. Its Cretaceous counterpart is preserved in a large range of seamounts and guyots found in the "West Pacific Seamount Province" (WPSP). The seamounts in these regions display very distinct and long-lived isotopic signatures (Staudigel et al., 1991; Koppers et al., 2003) that can be used to combine source region chemistry and seamount geochronology to map out mantle melting anomalies over geological time. These mappings may resolve many important questions regarding the stationary character, continuity and longevity of the melting anomalies in the South Pacific mantle - and its secondary hotspots. Of all secondary hotspots that are currently active in the SOPITA we could identify only two hotspots that appear to be long-lived and that have Cretaceous counterparts in the WPSP. Plate reconstructions show that the "HIMU-type" Southern Wake seamounts may have originated from the Mangaia-Rurutu "hotline" in the Cook-Austral Islands, whereas the "EMI-type" Magellan seamounts may have originated from the Rarotonga hotspot. All other hotspots in the SOPITA and WPSP are short-lived (or intermittently active) as evidenced by the presence of numerous seamount trail "segments" representing no more than 10-40 Myr of volcanism. Our observations violate one or more assumptions of the classical Wilson-Morgan hotspot hypothesis: (1) none of the South Pacific hotspots are continuously active, (2) most are short-lived, (3) some show evidence of hotspot motion, and (4) most of them have poor linear age progressions, if any at all. On top of this we have evidence for volcanism along "hotlines" and the "superposition" of hotspots. The simple and elegant "hotspot" model, therefore, seems insufficient to explain the age distribution and source region characteristics of intra-plate volcanoes in the South Pacific. This has lead to new models that retain the concept of mantle plumes, but these lack both simplicity and predictive power. New models that call on "extension" are indeed simple and they may explain most characteristics of Earth's intra-plate volcanism, but they also have limited predictive power, making it more difficult to test for their validity. We argue that we require a combination of processes: one that forces regional magmatism from a large-scale source of buoyancy from below (like the rise of plumelets shooting off the top of a superplume) and one process that acts from above, as intra-plate extension opens up pathways that allow the lithosphere to be penetrated by magma.
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8155 Plate motions--general
DE: 8157 Plate motions--past (3040)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting