Thermal Modeling of Cooling Time of Submarine Dacite Lapilli Tuff: Brothers Volcano, Kermadec Arc

Little is known about submarine volcanoes' eruptive histories and styles, even though they are essential to developing island arc systems and represent the second largest volcanic systems on Earth. Scientific drilling allows for the opportunity to study these systems. This study focused on two drill sites on Brothers volcano from IODP Expedition 376: Site U1528, located on the resurgent cone, and Site U1530, located on the caldera rim. Expedition researchers analyzed samples for clast radius, density, thermal conductivity, and specific heat. This data was then entered into the heat transfer equation of a sphere to create a cooling curve model of a lapilli dacite clast from its initial eruption temperature to the Curie temperature of magnetite to compare to the acquisition of the paleomagnetic remanent vector to test modes of eruption style. The model was created using three initial temperatures: 800℃, 900℃, and 1000°C, and a clast radius between 2 and 32 mm. The model shows that below 2 mm, the clast cools instantly, and starting at 6 mm, the clast cools below the Curie temperature at a rate of approximately 10 seconds for every increase of 100°C in eruption temperature. While physical observations of whole rock samples indicate brecciation, earlier paleomagnetic work proves coherent primary magnetization with the same inclination of the Geocentric Axial Dipole, suggesting deposition during a single eruption. The combined observations can be explained as a two-step process through a phreatomagmatic eruption approximately 200m below the ocean’s surface and deposition through a boil-over pyroclastic current.