Paleomagnetic constraints on the age of Lomo Negro volcanic eruption (El Hierro, Canary Islands)

Abstract

A paleomagnetic study has been carried out in 29 cores drilled at 6 different sites from the volcanic products of Lomo Negro eruption (El Hierro, Canary Islands, Spain). Systematic thermal and alternating field demagnetization of the samples’ NRM (Natural Remanent Magnetization) revealed a northward, stable paleomagnetic direction similar in all the samples. Rock magnetic experiments indicate that this paleomagnetic component is carried by a mixture of high-Ti and low-Ti titanomagnetite crystals typical of basaltic lithologies that have experienced a significant degree of oxyexsolution during subaerial cooling. The well constrained paleomagnetic direction of Lomo Negro lavas was used to perform a paleomagnetic dating of the volcanic event, using the SHA.DIF.14k global geomagnetic model restricted for the last three thousand years. It can be unambiguously concluded that Lomo Negro eruption occurred well before the previously proposed date of 1793 AD, with three different age ranges being statistically possible during the last 3 ka: 115 BC-7 AD, 410-626 AD, and 1499-1602 AD. The calibration of a previously published non-calibrated 14C dating suggests a XVI c. date for Lomo Negro eruption. This conclusion leaves open the possibility that the seismic crisis occurred at El Hierro in 1793 AD was related to an intrusive magmatic event that either did not reach the surface or either culminated in an unregistered submarine eruption similar to the one occurred in 2011-2012 at the southern off-shore ridge of the island.