Paleosecular variation for understanding young volcanoes of the Holocen

Abstract:

The paleosecular variation of the geomagnetic field had been increasingly recognized as a powerful tool for understating volcanic processes. Based on the assumption that every volcanic unit record instantaneously the local magnetic field while cooling down is implied that the paleomagnetic directions from different and uncorrelated units can be correlated. Moreover, volcanic successions well-constrained in ages represent an invaluable tool for understanding the variations of the geomagnetic field across the time quasi-continuously. When a reference curve describing in detail the paleosecular variations of directions and intensities is available for a given region, the curves can be safely used to constrain the age of uncorrelated volcanic deposits such as lava cooling units, pyroclastic deposits, and ignimbrites. I present here an overview of examples where I used paleomagnetism as a correlating and dating tool: from the Azores Archipelago (Faial and Terceira), to the Trindade Island (Brazil) and Chile. At the Faial island, a Holocene volcanic cone field history was entirely reconstructed by an extensive paleomagnetic investigation, while at Terceira the last historical eruptive event was successfully correlated and reinterpreted. At the remote Trindade Island, paleomagnetic directions helped to propose an age to the more recent Volcano of the island. Finally in the Chilean volcano of LLaima, the directions obtained from one historical flow are compared with expected values from the global models with interesting insights. In the two examples from the Azores Archipelago, the statistical comparison of the mean paleomagnetic full vector values from the studied deposit with the fluctuations of the geomagnetic field described in the reference curve provided a very good tool for age constraints.