Alteration halos around radioactive minerals in plutonic and metamorphic rocks of the northern Moldanubian area, Bohemian massif
Abstract
Effects of strongly radioactive primary minerals (mainly monazite) on the surroundings are compared in various rocks of the Moldanubian area. Aureoles of secondary phases formed which extend up to 20 µm from the monazite surface.
They mainly consist of low temperature clay minerals usually mixed with Fe-hydroxides; in some samples pyrite is common too. The halos of secondary phases most commonly occur around monazite in cordierite, but also in plagioclase and in quartz.
It seems that the radioactivity promotes reactions of the primary minerals with fluid (fluid inclusions and H2O in channels of the cordierite structure) even at "static" conditions. The frequent association of monazite with hydrated secondary phases may contribute significantly to resetting monazite ages during metamorphism and partial melting.
In addition, the neglecting of the chemical transformation of the nuclear energy for the calculations of radioactive heat production and heat budgets of rocks is questioned.