HR: 0800h
AN: V51B-0570    [Abstracts]
TI: Widespread Synchronous Volcanism Reveals a Broad Galapagos Hotspot Melting Anomaly
AU: * O'Connor, J M
EM: John.O.Connor@falw.vu.nl
AF: Department of Isotope Geochemistry, Vrije University, Amsterdam, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Stoffers, P
EM: pst@gpi.uni-kiel.de
AF: Institute for Geosciences, Christian-Albrechts-University, Ludewig-Meyn-Str. 10, Kiel, D-24118 Germany
AU: Wijbrans, J R
EM: Jan.Wijbrans@falw.vu.nl
AF: Department of Isotope Geochemistry, Vrije University, Amsterdam, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Worthington, T J
EM: tw@gpi.uni-kiel.de
AF: Institute for Geosciences, Christian-Albrechts-University, Ludewig-Meyn-Str. 10, Kiel, D-24118 Germany
AB: The massive aseismic ridges and associated seamounts dominating the morphology of the Panama Basin, eastern Central Pacific, have long been attributed to a Galapagos hotspot melting anomaly linked to a deep-seated mantle plume. Although these structures can provide information about the origin of hotspots and existence, or otherwise, of mantle plumes very little is known about their volcanic histories due to a lack of direct age and geochemical information. We report here 74 whole rock and 2 plagioclase $^{40}$Ar/$^{39}$Ar ages for rocks dredged from 53 locations during the first systematic sampling of the Cocos, Carnegie, Coiba and Malpelo aseismic ridges and associated seamounts (F.S. SONNE PAGANINI expedition). In addition we also report ages for DSDP drill sites on Cocos, Carnegie and Coiba ridges and 7 Cocos Island subaerial samples. The distribution of new, and published ages for the Galapagos Archipelago-platform and NE end of the Cocos Ridge, show a general trend of increasing age with distance from the Galapagos Archipelago. A more dominant trend however is one of aseismic ridge-seamount formation in a progression of broad zones of synchronous, often overlapping volcanism created at discrete intervals. Broad zones of coeval Cocos and Carnegie volcanism once formed much larger regions of synchronous volcanism that have been split apart by the complex history of seafloor spreading associated with the Cocos-Nazca spreading center. We link these broad regions of synchronous volcanism to a correspondingly large hotspot melting anomaly. The present day, as yet unfragmented, zone of synchronous volcanism associated with this proposed broad hotspot is marked by the extensive region of recent volcanism extending across the Nazca and Cocos plates encompassing the Galapagos Archipelago-Platform and the Cocos Ridge as far north as Cocos Island. The complex tectonic history of the Cocos-Nazca spreading-center has controlled how the broad zones of synchronous, often overlapping volcanism created by the broad Galapagos melting anomaly have been fragmented between the Cocos and Nazca plates. However, interplay between the broad Galapagos melting anomaly and the Cocos-Nazca spreading center is a second-order process compared to a fundamental underlying mantle process responsible for a broad Galapagos hotspot melting anomaly exhibiting long-lived characteristics (size, time-progression, episodicity) which, on a first-order, are independent of local tectonics and lithospheric architecture. Evidence for a broad Galapagos hotspot melting anomaly and the possibility of detecting long-lived underlying mantle processes has implications for how oceanic hotspot volcanism is sampled for purposes of rigorously testing the mantle plume paradigm. A major question posed by our results is whether individual Pacific seamount chains are in fact the product of tectonic plate drift over narrow hotspots? If not, then inferring the existence and behavior of a mantle plume on the basis of age progression of volcanism produced by a narrow seamount chain could well prove to be misleading. Thus, although great leaps are being made in the theory and numerical modeling - often on a global scale - of hypothesized deep plumes, significantly more high-quality age and geochemical data are needed for oceanic hotspot volcanism that gave birth to the mantle plume hypothesis in the first place.
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8157 Plate motions--past (3040)
DE: 5480 Volcanism (8450)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting