ROCK MAGNETISM, PALEOMAGNETISM AND PALEOINTENSITY OF IMBABURA VOLCANO (ECUADOR) - IMPLICATIONS FOR THE SPATIOTEMPORAL GROWTH MODEL

Abstract:

The Imbabura volcanic complex is one of the most prominent features in the Ecuadorian Inter-Andean valley and a potentially active stratovolcano, posing a hazard to the ~400,000 people living on its flanks. Previous works suggest three volcanic edifices likely being fed by the same magmatic chamber: 1) Taita Imbabura, the main edifice, subdivided into Imbabura I, II-1, and II-2; 2) Cubilche, a contemporaneous volcanic edifice to the southeast subdivided into old and young Cubilche; and 3) Huarmi, the youngest single unit located to the southwest of Taita Imbabura. Despite the existing studies, a complete picture of the evolution of this volcanic complex in space and time is still lacking. Additionally, there is an absence of paleomagnetic and paleointensity data which can help constrain the spatiotemporal evolution of the volcanic growth by refining the timing, zonality, and life cycle of the volcanic complex. Here we present a detailed analysis of rock- and paleomagnetic properties of all the units of the Imbabura volcano. A total of 238 independently oriented in situ samples from 33 sites distributed across the different volcanic edifices were collected for this purpose. Cubilche, Huarmi and Taita Imbabura lavas differ from each other based on their thermo-magnetic behavior and rock magnetic properties. Lavas from both old and young Cubilche have very similar rock magnetic properties, indicating a long-lived feeding system. Moreover, our results improve the geographic division of Taita units. In contrast, the Huarmi edifice can be divided into two sub-units. In all samples, the main magnetization carrier is low-Ti titanomagnetite with pseudo single domain structure except for samples from Huarmi II which exhibit multi-domain characteristics. The paleo-directions and intensity of these units will be used for refining the model based on the rock-magnetic properties. Combining our new results with existing geochronological and geochemical data will allow us to create an improved spatiotemporal model of the Imbabura volcano and, in turn, help us better understand the risks this volcanic complex poses to the surrounding populations.