Investigation of the mechanism of island arc formation and the back-arc spreading of the lithosphere

Category: 15-4
S.V. Gavrilov


UDC 550.311



S.V. Gavrilov


Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia


Abstract. The island arc morphology and the position of the back-arc spreading centre are clarified on the assumption that the manifestations of the thermal instability and the two types of convection in the mantle wedge are spatially separated. At sufficiently small distances from the trench the thermal instability dominates, further from the trench the convection in the form of the variable thickness longitudinal rolls prevails while still further from the trench there is located the upwelling flow of the Karig vortex responsible for the back-arc spreading. The growth rate of the longitudinal rolls convection is maximum at certain distance from the trench where the volcanic chain appears, the leading arc being ahead of it, originated probably owing to the thermal instability. At longer distances from the trench the longitudinal rolls convection does not occur while there arises the upwelling flow of Karig vortex, or the transversal convective roll perpendicular to the subduction velocity, as the downward entrainment of the mantle material, heated due to viscous dissipation is energetically disadvantageous. The mutual location of the leading arc, volcanic chain and the back-arc spreading centre is shown to tightly constrain the mean viscosity of the mantle wedge: £8×1019 Pa×s at the Peru Andes.



Keywords: thermal instability, convection, forearc, volcanic chain, back-arc lithosphere spreading.



Gavrilov S.V. and Abbott D.Kh., Thermomechanical model of heat and mass transfer in the vicinities of the subduction zone, Izv. Phys. Earth, 1999, no. 12, pp. 3–12.

Ueda S., Novyi vzgliad na Zemlyu (New view to the Earth), Moscow: Mir, 1980.

Barazangi M. and Isacks B.L. Spatial Distribution of the Earthquakes and Subduction of the Nazca Plate beneath South America, Geology., 1976, vol. 4, pp. 686–692.

McKenzie D.P., Speculations on the Consequences and Causes of  Plate Motions, Geophys. J. Roy. Astron. Soc., 1969, vol. 18, pp. 1–32.

Rabinowicz M., Lago B., and Froidevaux C., Thermal Transfer between the Continental Asthenosphere and Oceanic Subducting Lithosphere: its Effect on Subcontinental Convection, J. Geophys. Res., 1980, vol. 85. N B4, pp. 1839–1853.

Schubert G., Turcotte D.L., and Olson P., Mantle Convection in the Earth and Planets. New York: Cambridge University Press, 2001. 940 p.

Simpkin T. and Siebert L., Volcanoes of the World. Tucson, Arizona: Geoscience Press. 1994. 349 p.

Turcotte D.L., Schubert G., Geodynamics., Cambridge: Cambridge University Press. 2002. 448 p. 

Vidale J.E. and Mooney W.D. The Earth’s Topography: the Influence of the Lower Lithosphere, Nature, 1997. N 324, pp. 23–24.