Paleosecular variation of the earth magnetic field at the Canary Islands over the last 15 ka.
Abstract:To improve the knowledge of secular variation of the geomagnetic field in southwestern Europe, 38 lava flows were investigated in Tenerife and Gran Canaria (Canary Islands, Spain). One flow is an historical one (1706 AD) and 28 flows are dated by radiocarbon between 1550 AD and about 13200 BC. Nine other flows are not dated but they have stratigraphic links with the other flows. Thermomagnetic curves, unblocking temperatures and coercivities suggest that the main carrier of the remanent magnetization is titanomagnetite with various Titanium contents and in the pseudo-single domain range as an average grain size. Paleomagnetic directions were obtained by thermal demagnetization on more than 400 specimens and alternating field demagnetization on about 150 twin specimens. The original Thellier and Thellier method was applied for each of the 400 cores and, with PICRIT-03, allowed to determine absolute paleointensity values. Combined with the data previously published for the last 500 years, this new dataset is the first long PSV record available for the Canary Islands.
Comparison with model predictions indicates that, on the long-term, models account for most of the data but during short time intervals, more variable paleomagnetic directions and intensities suggest a faster variability of the earth magnetic field than predicted by the models. In particular, around 600 BC and 1200 BC, very high paleointensity values (~ 150 ZAm^2) are consistent with data obtained previously in Portugal, Azores, Hawaii and Israel. Also, around 4650 BC, variability in paleomagnetic directions could reflect short-term changes of the geomagnetic field.
These paleomagnetic results are consistent with the field derived stratigraphic position of the undated sites and confirm that the eruption rate of the Gran Canaria volcanic system was high around 600 BC, 1000 BC and 4650 BC.