gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.1.227 Magma Chamber Evolution as Revealed by ²²⁶Ra-²³⁰Th Disequilibrium at Longonot Volcano, Kenya Evans P. Rogers N. W. Hawkesworth C. J. Dept. of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, UK Scott S. C. Dept. of Geology, University of Plymouth, Drakes Circus, Plymouth, PL4 6AA, UK 1998 62A 1 428 429 Copyright © 1998, The Mineralogical Society 1998