EarthRef.org Reference Database (ERR) -- Koppers et al. 1998

The Magellan Seamount Trail (MST) delineates a northwest trending chain of four Cretaceous guyots in the West Pacific Seamount Province (WPSP). Seamount morphology, Ar-40/Ar-39 geochronology and Sr-Nd-Pb geochemistry of the MST provides evidence for a hotspot origin between the Samoa, Rarotonga and Society hotspots of the South Pacific Isotopic and Thermal Anomaly (SOPITA). The MST yields an excellent linear age progression of 47.6 +/- 1.6 mm/yr (r(2) = 1.000; MSWD = 0.23; 1 sigma SE) including Vlinder guyot (95.1 +/- 0.5 Ma, n = 5; 2 sigma SD), Pako guyot (91.3 +/- 0.3 Ma, it = 3) and Ioah guyot (87.1 +/- 0.3 Ma, it = 2). The MST also exhibits a small range in Sr-Nd-Pb isotopic compositions indicating enriched mantle sources with an affinity of EMI. Nevertheless, three volcanic events are found out of sequence with linear MST hotspot volcanism: (1) an independent volcanic pedestal was formed 4-7 Myr before shield-volcanism started at Vlinder guyot, (2) a post-erosional volcanic cone was formed at least 20-30 Myr after drowning of Vlinder guyot, and (3) Ita Mai Tai guyot (118.1 +/- 0.5 Ma, it = 3) was formed 34-36 Myr before the MST hotspot arrived at the predicted location of this guyot. By identifying and ruling out discordant volcanic events, we can use the age progression in MST to test the fixity of its hotspot. When presuming the fixed hotspot hypothesis, the local age progressions of the MST (47.6 +/- 1.6 mm/yr) and the copolar Musicians seamount trail (55.8 +/- 6.4 mm/yr) are not compatible with their 100-80 Ma Euler pole. We investigate two options: (1) acceptance of a 'forced' Euler pole obeying the hotspot hypothesis by using both the age progressions and the azimuths of the studied seamount trails, or (2) acceptance of a 'best-fit' Euler pole by using the azimuths of the studied seamount trail exclusively. In the first option, the angular speed of the Pacific plate during the 100-80 Ma stage pole is calculated at 0.502 +/- 0.017 degrees/Myr. In the second option, the 'best-fit' Euler pole is found approximately 35 degrees different from the 'forced' Euler pole. We argue that the observed age progressions can only be reconciled with the 'best-fit' pole when allowing for the relative movement of the MST and Musicians mantle plumes with respect to one another. The calculated maximum velocity component parallel to the line of age progression could then be as much as 23 mm/yr for the mantle plumes - when assuming one tired hotspot in this alternate model. (C) 1998 Elsevier Science B.V. All rights reserved.