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Buoyant melting instabilities beneath extending lithosphere: 1. Numerical models

Hernlund, John W. and Tackley, Paul J. and Stevenson, David J. (2008) Buoyant melting instabilities beneath extending lithosphere: 1. Numerical models. Journal of Geophysical Research. Solid Earth, 113 (B4). Art. No. B04405. ISSN 2169-9313. doi:10.1029/2006JB004862.

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Buoyant decompression melting instabilities in regions of partially molten upper mantle have been proposed to be an important process that might account for some characteristics of intraplate volcanism on Earth and other terrestrial planets. The instability is driven by variations in the melting rate within a partially molten layer whenever a relative decrease in density accompanies decompression melting of ascending mantle. Here, the development of buoyant decompression melting instabilities in a plane layer of passively upwelling and partially melting mantle beneath diffusely extending lithosphere is studied using numerical convection models covering a wide range of physical parameters. We find that the occurrence and nature of these instabilities in such a scenario is strongly affected by the rate of extension and melt percolation, as well as depth distribution of solid density variations arising from melt depletion. In some cases, instabilities do not occur during extension, but only develop after extension has slowed or stopped completely. This behavior creates two pulses of magma generation due to passive upwelling accompanying extension followed by the subsequent instability and is favored by a faster rate of extension, higher mantle viscosity, higher rate of melt percolation, and smaller amount of solid residuum depletion‐derived buoyancy. Larger degrees of solid density changes accompanying melt depletion can enhance the instability of partially molten mantle during extension but decrease the cumulative volume of generated melt. This kind of behavior modifies the conventional expectation of spatially and temporally correlated volcanism and extension and may lend insight into the observed increase in localized volcanic activity following Miocene Basin and Range extension in the western United States.

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Stevenson, David J.0000-0001-9432-7159
Additional Information:© 2008 American Geophysical Union. Received 18 November 2006; revised 18 October 2007; accepted 14 December 2007; published 8 April 2008. Reviews of preliminary versions of this material by Abby Kavner, Paul Roberts, and Gerald Schubert greatly improved the quality and flow of the presentation. Reviews by Harro Schmeling, Yanick Ricard, and Justin Revenaugh helped to improve the clarity and substance of this work. We are also grateful for discussions with Ken Deuker, Eugene Humphreys, Mark Jellinek, James Kellogg, Stéphane Labrosse, William Moore, and Derek Schutt. This work was supported in part by the NSF CDYEL project and a grant from IGPP Los Alamos.
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Institute of Geophysics and Planetary PhysicsUNSPECIFIED
Subject Keywords:extension; melting instabilities; mantle convection
Issue or Number:B4
Record Number:CaltechAUTHORS:20181127-090406138
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Official Citation:Hernlund, J. W., P. J. Tackley, and D. J. Stevenson (2008), Buoyant melting instabilities beneath extending lithosphere: 1. Numerical models, J. Geophys. Res., 113, B04405, doi: 10.1029/2006JB004862
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91211
Deposited By: Tony Diaz
Deposited On:27 Nov 2018 18:13
Last Modified:16 Nov 2021 03:39

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