Research Articles

Short-Lived Radioactivity and Magma Genesis

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Science  04 Sep 1992:
Vol. 257, Issue 5075, pp. 1368-1376
DOI: 10.1126/science.257.5075.1368

Abstract

Short-lived decay products of uranium and thorium have half-lives and chemistries sensitive to the processes and time scales of magma genesis, including partial melting in the mantle and magmatic differentiation in the crust. Radioactive disequilibrium between 238U, 230Th, and 226Ra is widespread in volcanic rocks. These disequilibria and the isotopic composition of thorium depend especially on the extent and rate of melting as well as the presence and composition of vapor during melting. The duration of mantle melting may be several hundred millennia, whereas ascent times are a few decades to thousands of years. Differentiation of most magmas commonly occurs within a few millennia, but felsic ones can be tens of millennia old upon eruption.

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