Massive Volcanism in the Altiplano-Puna Volcanic Plateau and Formation of the Huge Atacama Desert Nitrate Deposits: A Case for Thermal and Electric Fixation of Atmospheric Nitrogen

Abstract

The origin of the giant nitrate deposits of the Atacama Desert (Chile) is a controversial issue. At a global scale, the Atacama Desert nitrates constitute a rare singularity because no equivalent deposits are found anywhere else. Previous hypotheses for origin of the Chilean nitrates have failed to recognize the importance of the 70,000 km2 Late Miocene to present Altiplano-Puna volcanic plateau (APVP), only 50-200 km eastward from the nitrate deposits. We argue that the extrusion of a volume of over 104 km3 of pyroclastic rocks at the APVP may have created the conditions to induce thermal and electric fixation of an estimate of 2800 Mt of atmospheric nitrogen in the form of NO3. This figure exceeds the amount of nitrogen required to account for the Atacama Desert nitrate deposits. Thus, the origin of the nitrate deposits may be found in an unusual combination of hyper-arid conditions (vital for the final stabilization and preservation of the NaNO3 mineral phase) and massive volcanism (key to fixation of large amounts of atmospheric nitrogen). Volcanic eruptions have far more environmental implications than usually assumed, decisively contributing to the global cycles of many chemical elements and compounds. For example, nitrogen fixation by volcanic activity could also explain the current excess of NOx compounds in the pristine marine atmosphere of the mid-Pacific, a realm conspicuously surrounded by the world's largest concentration of active volcanoes.