How does the formation of the Hawaiian Island chain differ from island chains along the Ring of Fire?

Question

How does the formation of the Hawaiian Island chain differ from island chains along the Ring of Fire?

Answer 1

Whereas plume theory successfully predicts many observations at some volcano chains [Courtillot et al., 2003], it is insufficient to explain the whole spectrum of oceanic intraplate volcanism on Earth. Many ridges, though aligned by plate motion, lack inear age-distance relationships and an association with an oceanic plateau as predicted by plume theory. A mantle plume is assumed to be the geodynamic explanation for a fixed hotspot. But any alternative explanation for a relatively fixed hotspot also needs to account for the linear age-distance relationship of the associated volcanism. On the Pacific plate, prominent chains with voluminous volcanism violate this prediction, such as the Cook-Austral, Marshall, and Line Islands. Thus, these chains cannot have been formed by the Pacific plate overriding stationary hotspots [Koppers et al., 2003; Koppers et al., 2007; Davis et al., 2002; Bonneville et al., 2006].

A mechanism that has often been invoked to account for non-hotspot volcanic ridges is lithospheric cracking. Cracks may be induced by tensile stresses [Sandwell et al., 1995], by loading with volcanic edifices [Hieronymus & Bercovici, 2000], or by thermal contraction [Sandwell & Fialko, 2004; Gans et al., 2003]. Cracks are supposed to control where and when volcanism occurs [Natland, 1980]. However, they do not provide an explanation for the magma generation itself. The cracking hypothesis rather presumes a broad reservoir of pre-existing partial melt that may be tapped. Such a layer of partial melt in the asthenosphere was originally proposed to account for anomalously low seismic-wave velocities [Anderson and Sammis, 1970]. However, recent studies show that partial melt is not required to explain seismic observations [Faul & Jackson, 2005; Stixrude & Lithgow-Bertelloni, 2005; Priestley & McKenzie, 2006]. Moreover, partial melting in the asthenosphere would tend to increase seismic wave velocities due to dehydration of the residue [Karato & Jung, 1998]. Since a reservoir of partial melt in the asthenosphere is at odds with geophysical observations, we neglect the lithospheric cracking hypothesis.

Another possible mechanism for intraplate oceanic volcanism without linear age-distance relationships is small-scale sublithospheric convection [SSC; Bonatti & Harrison, 1976; Haxby & Weissel, 1986; Buck & Parmentier, 1986; Marquart et al., 1999; Ballmer et al., 2007]. SSC spontaneously develops at the base of mature oceanic lithosphere, whenever the cold thermal boundary layer below the lithosphere exceeds a threshold thickness. Thereafter, convection is a more efficient heat transport mechanism than conduction. It organizes itself in rolls aligned with plate-motion [Richter & Parsons, 1975], with parallel upwellings spaced at 200-300 km apart (Figure 1).



Figure 1: SSC develops in rolls aligned with plate motion, as soon as the thermal boundary layer exceeds a critical thickness. Its onset is earlier adjacent to lateral density heterogeneities and later for larger Tm or ηeff. (from Ballmer et al., 2007).



Whether and how much melting occurs due to SSC depends on the onset age of the SSC. The onset age is most sensitive to:

   1. the effective viscosity in the asthenosphere ηeff, and

   2. the amount of pre-existing lateral density heterogeneity [Huang et al., 2005; Korenaga & Jordan, 2002; Dumoulin et al., 2005].

Low ηeff and lateral heterogeneity both tend to trigger SSC beneath younger seafloor. If SSC onsets beneath relatively old and thick lithosphere, the rather small thermal anomalies resulting (e.g., compared with a plume) are unable to generate significant melting. Higher mantle temperatures Tm also enable SSC melting beneath thicker lithosphere, for later onset ages (Figure 2).

Answer 2

Hawaii is on a hotspot - in the middle of the pacific plate. Others, are formed at plate boundaries.

More info on Hotspots at: http://en.wikipedia.org/wiki/Hotspot_%28...