Paleomagnetism, rock magnetism and age determination of effusive and explosive Holocene volcanism in the Momotombo-Managua-Masaya region, Nicaragua

Abstract

The Central America Volcanic Arc shows an intense and continuous volcanic activity spanning the last 10 ky because of the subduction processes parallel to the Middle America Trench. Several volcanic events have occurred during the Plio-Holocene, along the coastal Nicaraguan region, characterized either by explosive or effusive activity. Volcanic deposits were emplaced at high temperatures and have similar basaltic-andesitic composition suggesting a long-lived magma chamber but emplaced and cooled by different mechanisms. We present paleodirectional and paleointensity results of four lava flows, and the paleointensity recorded on different pyroclastic deposits in the Managua-Masaya region, western Nicaragua. For each, we characterize the rock magnetic properties as a function of temperature and magnetic field. Absolute paleointensity experiments estimated a mean range from 38.6 to 52.9 μT; and a mean virtual axial dipole moment from 9.4 × 1022 Am2 to 12.8 × 1022 Am2. Two paleomagnetic ages were determined for two cooling units: (1) the Masaya Caldera Walls with an age range of 8580–8535 BP, and (2) a dating for a lava flow from Momotombo Volcanic Complex estimated of 1500–1600 CE. These results are consistent with the expected values according to the actual paleosecular variation global models, and with the regional stratigraphy and historical ages. The high reliability of paleointensity determination from these pyroclastic deposits and lava flows suggest that both are suitable for paleomagnetic dating. Finally, an accurate chronology of the volcanic events, will improve the understanding of the evolution of the volcanism and their implications for volcanic risk on the region. This knowledge will help to decrease the considerable hazard for the population on the surrounding areas.