The Mono Lake excursion recorded in phonolitic lavas from Tenerife (Canary Islands): Paleomagnetic analyses and coupled K/Ar and Ar/Ar dating

摘要

We present a coupled paleomagnetic/dating investigation conducted on three different lava flows from the island of Tenerife (Canary Islands; Spain) erupted during the Mono Lake excursion (MLE). Paleomagnetic analyses consist in zero field demagnetizations (AF and/or thermal) and of Thellier and Thellier experiments using the PICRIT-03 set of criteria to select reliable intensity determinations. One of the flows is characterized by a direction largely deviated from the one expected from an axial geocentric dipole (GAD) field. Its paleointensity value is very low (7.8μT). The two other sites are characterized by inclinations slightly shallower than the GAD value and by low intensity values (about 12 and 21μT; present value: 38μT). The three K/Ar ages combined with two ~(40)Ar/~(39)Ar ages range from 32.0 to 33.2ka and they are not statistically distinguishable from one another. It therefore appears that these lavas have recorded the MLE (the only excursion in this time interval) confirming its brief duration (shorter than the minimum age uncertainties available). The mean age is younger but, within the uncertainties, consistent with the age of the ~(10)Be peak and of the marine intensity low when reported in the most recent ice age model. These new results are the first ones with radiometric dating produced from the northern hemisphere. Combined with existing cosmogenic, marine and volcanic paleomagnetic data, these results are discussed in terms of dating, and geometry of the earth magnetic field during the excursion.