HR: 09:30h
AN: V51G-07    [Abstracts]
TI: Plate-driven flow constraints on arc and back arc magma mixing: influence of plate boundary geometry in the Lau Basin
AU: * Harmon, N
EM: nharmon@ucsd.edu
AF: University of California, San Diego, 9500 Gilman Dr. MC #0225, La Jolla, CA 92093, United States
AU: Blackman, D K
EM: dblackman@ucsd.edu
AF: University of California, San Diego, 9500 Gilman Dr. MC #0225, La Jolla, CA 92093, United States
AB: The Lau spreading centers, from the slower-rate Valu Fa ridge in the south to the faster-rate Central Lau rift valley axis in the north, show significant variations in geochemical and geophysical observables that may indicate variable interaction between the ridge system and the arc. In the conceptual model of Martinez and Taylor [2003], the Valu Fa ridge, which is nearest the arc, has increased magma flux and a more andesitic geochemistry due to interaction between the spreading center and the arc melt supplies. This interaction is predicted to decrease as the ridge-arc distance increases steadily to the north along the Eastern and Central Lau spreading centers. To test this conceptual model we develop a series of 2D finite element mantle flow models, for each of the Valu Fa, and Eastern Lau and Central Lau spreading centers. These models are designed to discern effects solely due to changes in the trench-perpendicular plate motion and boundary geometry. The numerical experiments simulate flow, temperature, melting, and depletion of the residual mantle. Preliminary models, with a simple rheology and dry melting, predict that Valu Fa would develop a melting region whose low-fraction (<1%) portion is conjoined with the arc melting region. For the Central Lau spreading center, the lower melt fraction regions are not predicted to be conjoined. The maximum melt fraction beneath the spreading center is greater for the Central Lau model than for models of the southern ridges. The Eastern Lau spreading, in between, is predicted to develop a conjoined melt region. The higher northern model melt fractions are distributed over broader regions than for Valu Fa, indicating that a greater volume of melt should be extracted from the Central and Eastern Lau spreading centers. While the dry melting case does not support the hypothesis of higher melt flux beneath the Valu Fa, we expect that the addition of wet melting in the simulation will produce a significant amount of melting above the slab, and this combined with the dry melting beneath the ridge may produce a greater quantity of melt beneath the Valu Fa. Furthermore, we will explore the effects of different mantle rheologies and different melt extraction assumptions on melt production beneath the ridge.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting