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Stress Fields and the Distribution of Intraplate Volcanism in the Pacific Basin

Abstract

Reconstruction of the Pacific basin for the Early Cretaceous through Recent shows that oceanic plateaus formed along ocean ridge systems in the wake of retreating ridge triple junctions, and that ocean island volcanism either followed pre-existing fracture zones/lineaments or was localised along lines of incipient plate tearing induced by variations in plate margin geometry. The distribution of volcanism is more regular than would be expected from deep mantle plumes, but is consistent with suggestions made over a quarter century ago of control by stresses transmitted from the boundaries of the plates.

Before the concept of hotspots/plumes was widely invoked, Jackson & Shaw [1975] proposed the distribution of intraplate volcanism in the Pacific basin was controlled by plate interactions inducing changes in the stress field of the plate (see also Cracks & Stress page). At the time such concepts could not be proven as the bathymetry of the ocean floor and the tectonic history of the basin margins were poorly known. With the increasing popularity of the mantle plume concept, interpretations switched to depicting a random distribution of volcanism generated from deep-seated thermal anomalies. However, few examples of intraplate volcanism in the basin have been shown to conform to the predictions of the plume model.

Figure: Reconstruction of the Pacific basin from Early Cretaceous through Recent based on the paleomagnetic frame [from Smith, 2003]. Oceanic plateau volcanism occurred at triple junctions along ocean ridge systems. Ocean island volcanism is divided into those chains (mostly Late Cretaceous to Eocene) which followed pre-existing fractures, and those which followed propagating fractures induced by plate margin geometry. The fracture system was created by the geometry of the ocean ridge systems as the Pacific plate grew in size. North-northwest/south-southeast lineaments include the Kashima-Eltanin and Emperor-Easter megatrends of Smoot [1999] and are traced back in the reconstruction to transform faulting on the Pacific-Izanagi and Pacific-Phoenix ridges. West-southwest/east-northeast lineaments include the Mendocino and Murray fracture zones and others created by transform faulting on the Pacific-Farallon ridge. Island chains following the fracture systems show the greatest non-linearity in age progression.

Potentially only three examples (Easter-eastern Mid Pacific Mountains, Louisville-Ontong Java, Marquesas-Hess/Shatsky) possess the plateau-island chain sequence expected from the plume head-tail model [Clouard & Bonneville, 2001]. Non-linear age progressions are found in many island chains, including the Cook-Austral-Marquesas, Marshall-Gilberts, and Line Islands. Even the Hawaiian-Emperor chain, generally considered the archetypical example of plume volcanism, does not have the features expected in the plume model. The volcanism lacks an associated plateau, eruption rates have increased rather than decreased over time, and paleomagnetic evidence [Sager, 2002] indicates any hotspot could only have been stationary for half its history. Consideration of other models is therefore long overdue.

Correlations between volcanic output along the ocean island chains can now be correlated with basin-wide plate re-organisations such as at 25 and 5 Ma [Kamp, 1991; Smith, 2003] suggesting the model of Jackson & Shaw [1975] was essentially correct. Reconstruction of the evolution of the Pacific basin demonstrates that oceanic plateaus were generated in zones of tension in the wake of retreating triple junctions, and that ocean island chains may be divided on the basis of propagating- or leaky-fracture origin [Smith, 2003]. The latter, including the Louisville, Marshall-Gilbert, Line Island, and Cook-Austral-Marquesas chains are those characterised by non-linear age progressions. Such volcanism followed pre-existing north-northwest/south-southeast trending fracture zones such as the Kashima-Eltanin and Emperor-Easter megatrends [Smoot, 1999]. The fracture zones form part of a pattern of orthogonally intersecting lineaments which are suggested to have been initiated by transform faulting along ridge systems during the early history of the Pacific plate.

Volcanism attributed to propagating fractures includes the Sala y Gomez, Juan Fernandez, and Caroline chains which extrapolate to breaks in nearby subducting slabs suggesting stressing of the plate by convergent margin geometry [Favela & Anderson, 1999; Smith, 2003].

The Emperor chain is unique in the stress field model in representing volcanism along a propagating fracture induced at a divergent margin. The location and orientation of this chain is attributed to the geometry of the Kula-Pacific ridge following plate re-organisations at 82 Ma which prematurely halted triple-junction volcanism on Meiji seamount. Subsequent volcanism along the Hawaiian chain can be explained by re-orientation of the stress field to control by convergent margin geometry following abandonment of the Pacific-Kula ridge, and does not require a change in Pacific plate motion at the time of the Hawaiian-Emperor bend (43 Ma).

The distribution of Pacific intraplate volcanism is therefore more regular than would be expected than in the plume model. It can be explained as a result of shallow volatile-bearing sources tapped under developing hotcell conditions. The change from oceanic plateau to island chain volcanism reflects changes in the stress field as the Pacific plate changed from having an intra-oceanic setting bordered by ocean ridge systems, to subducting beneath the basin margins [Smith, 2003].

References

  • Clouard, V., and A. Bonneville, How many Pacific hotspots are fed by deep-mantle plumes?, Geology, 29, 695-698, 2001.
  • Jackson, E.D., and H.R. Shaw, Stress fields in central portions of the Pacific plate: delineated in time by linear volcanic chains, J. geophys. Res., 80, 1861-1874, 1975.
  • Kamp, P.J.J., Late Oligocene Pacific-wide tectonic event, Terra Nova, 3, 65-69, 1991.
  • Sager, W.W., Basalt core paleomagnetic data from Ocean Drilling Program Site 883 on Detroit Seamount, northern Emperor seamount chain, and implications for the paleolatitude of the Hawaiian hotspot, Earth planet. Sci. Lett., 199, 347-358, 2002.
  • Smith, A.D., A re-appraisal of stress field and convective roll models for the origin and distribution of Cretaceous to Recent intraplate volcanism in the Pacific basin, Int. Geol. Rev., 45, 287-302, 2003.
  • Smoot, N.C., Orthogonal intersections of megatrends in the Western Pacific ocean basin: A case study of the Mid Pacific mountains, Geomorphology, 30, 323-356, 1999.
last updated 7th June, 2004
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