Summary: American Mineralogist, Volume 92, pages 1535­1538, 2007
0003-004X/07/0809­1535$05.00/DOI: 10.2138/am.2007.2640 1535
INTRODUCTION
Short-lived radioactive isotopes provide unique information
about time scales of melting and magma transport processes
that operate in the Earth's crust and mantle. Any differentiation
process that chemically fractionates parent and daughter elements
from a decay chain will produce secular disequilibrium in which
the activity ratio of the parent and daughter isotopes differs from
unity.After approximately ve half-lives of the daughter isotope,
secular disequilibrium can no longer be measured and the decay
rates of the parent and daughter are again equal. Because the
half-life of 226
Ra is ~1600 years, (226
Ra)/(230
Th) disequilibria
produced within the past 8000 years may be preserved, making
it an important chronometer of recent magmatic activity.
Successful interpretation of 226
Ra-230

Source: Asimow, Paul D. - Division of Geological and Planetary Sciences, California Institute of Technology,

Collections: Geosciences