Publication Abstract [View Article (PDF)]

Marton, F. C., C. R. Bina, S. Stein, and D. C. Rubie, Effects of slab mineralogy on subduction rates, Geophysical Research Letters, 26, 119-122, doi:10.1029/1998GL900230, 1999.

Abstract. Although velocities of cold subducting slabs should be primarily controlled by their negative thermal buoyancies, their mineralogy can also have significant effects. We explore this by using thermo-kinetic modeling to predict mineralogy and compare the resultant buoyant (driving) force to the opposing viscous drag. Phase transformations of (Mg,Fe)2SiO4 in subducting slabs depend on thermal structure in two ways. First, equilibrium phase boundaries should be deflected upwards, causing negative local buoyancy anomalies, or downwards causing positive ones, depending on the sign of the Clapeyron slope. As slabs first enter the transition zone, negative anomalies should accelerate them, whereas positive anomalies that form when the slabs' ends exit the transition zone should decelerate them. These effects may induce geologically abrupt changes in plate motions. Second, metastable olivine in slabs below the alpha -> gamma equilibrium boundary would create regions of low density and positive buoyancy which would reduce the slabs' velocities. This effect would be strongest for the coldest and fastest slabs, slowing them more and narrowing the range of feasible subduction rates. Decreased descent rates, however, allow slabs to warm up, causing thermal erosion of the metastable wedges. Such negative feedback mechanisms may serve to regulate subduction rates.

Copyright © 1999 American Geophysical Union
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Copyright © 1998 Craig R. Bina.