An evaluation of paleomagnetic techniques to determine emplacement temperatures of pyroclastic density currents at Mount St. Helens

uring a volcanic eruption, pyroclastic density currents (PDCs) deposit new pumice and ash and rip out and transport lithic fragments from past eruptions. Magnetic minerals in the lithic fragments, such as titanomagnetite, may be partially or completely remagnetized, depending on their emplacement temperature with respect to their Curie and blocking temperatures. By finding the temperature at which this remagnetized overprint is removed, the emplacement temperature of the pyroclastic flow is estimated. This method assumes that the rock magnetic properties that govern magnetic unblocking are constant given a specific magnetic mineral composition, but recent studies demonstrate that Curie temperatures (Tc) in many natural titanomagnetites are a strong function of thermal history. Such variations in Curie temperature may bias estimates of PDC emplacement temperature. The purpose of this study is to evaluate the extent to which this is true.;In 2014, ash, pumice, and lithic clasts from pyroclastic debris containing titanomagnetite were collected from the pumice fields north of Mount St. Helens in order to satisfy the three goals of this study. The goals of this study were to (1) examine how the temperature at which magnetization is removed varies with thermal history; (2) determine to what extent this might bias emplacement temperature estimates; and (3) to examine how stratigraphic variations in magnetic properties might be used to estimate emplacement temperature.;In reference to goal ;For goal ;To satisfy goal...