Heavy radioactive and trans-lanthanide elements in the geothermal microecology of the Los Azufres volcanic complex

Abstract

The distribution of the heavy metals 80Hg, 82Pb, 90Th and 92U in the biogeochemical microcosm of three geo and hydro thermal sites of the Los Azufres volcanic complex have been determined by the nuclear analytical techniques of Polarised Energy Dispersive X-Ray Fluorescence spectrometry and Instrumental Neutron Activation Analysis. We have shown that the sites chosen can be considered to be ‘real-time’ natural laboratories to simulate the Ordovician-Devonian periods. We observe that (1) the primitive, extremophilic plants of the fumaroles – the mosses and ferns – are efficient agents of pedogenesis; (2) that their rhizospheric soil retains more heavy metal than the hydrothermal sediments. The former implies that large-scale photosynthesis and the consequent burial of soil organic carbon could have substantially contributed to the late-Ordovician climate cooling by CO2 draw-down, and the latter, that dissolved heavy metals in the hydrothermal seas could have been one of the reasons for the marine extinction of that period. This ‘holistic’ approach at simulating the Paleozoic environment differs from extant purely laboratory-based studies. However, it corroborates the findings of some earlier works.