Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Williams, Q. Articles by Revenaugh, J. Search for Related Content GeoRef GeoRef Citation

Ancient subduction, mantle eclogite, and the 300 km seismic discontinuity

¹ Department of Earth Sciences, University of California, Santa Cruz, California 95064, USA
² Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA

A seismic discontinuity is frequently observed near 300 km depth beneath continents and island arcs. Here we show that this discontinuity is generated by SiO₂-stishovite formation in eclogitic assemblages. Such free silica is petrologically anticipated within materials of mid-oceanic-ridge basalt chemistry at these depths, and the 300 km discontinuity is likely associated with either the coesite to stishovite transition or exsolution of stishovite from clinopyroxenes containing excess silica. The presence and amplitude of this seismic feature provide a means for determining how much subducted, or delaminated, formerly basaltic material is present at deep upper-mantle depths. Thus, the distribution of the 300 km discontinuity yields a measure of mantle geochemical heterogeneity and provides a means for locating the residue of ancient subduction within the upper mantle.

Key Words: eclogite • discontinuities • mantle • subduction • coesite • stishovite

This article has been cited by other articles:

				J. van Wijk, J. van Hunen, and S. Goes Small-scale convection during continental rifting: Evidence from the Rio Grande rift Geology, July 1, 2008; 36(7): 575 - 578. [Abstract] [Full Text] [PDF]

				Y. Zheng, T. Lay, M. P. Flanagan, and Q. Williams Pervasive Seismic Wave Reflectivity and Metasomatism of the Tonga Mantle Wedge Science, May 11, 2007; 316(5826): 855 - 859. [Abstract] [Full Text] [PDF]