Vertical axis rotation of the upper portions of the north-east rift of Tenerife Island inferred from paleomagnetic data

Abstract

Paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north-east rift-zone (NERZ) of Tenerife, Canary Islands, Spain. Of the 70 interpretable sites, 16 are of normal polarity and 54 of reversed polarity. Four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons. After inverting the reverse polarity sites through the origin, the in-situ grand mean yields a declination (D) = 023.8°, an inclination (I) = 42.3°, α95 = 3.2°, ĸ = 39.0, N = 51 that is discordant to the expected late Miocene to Pleistocene field direction (D = 357.6°, I = 38.8°, α95 = 4.7°). This discordance can be explained as either a 26° clockwise vertical axis rotation or a 28° WNW-side-down-tilt about an average 009° horizontal tilt axis. The sampled section is composed of numerous semi-vertical dykes cutting mainly lava flow units that are sub-horizontal and cross-cut by steeply dipping faults (70°–90°). Field evidence is therefore more compatible with a vertical-axis rotation rather than a horizontal axis tilt of the drilled units. We argue that this clockwise vertical-axis rotation is likely related to strike-slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes. Six new 40Ar/39Ar age determinations constrain the main interval of dyke emplacement within the NERZ between 0.99 Ma and 0.56 Ma. The intrusive activity in the sampled section of the rift appears to have been almost continuous, with several intrusion pulses that are probably related to flank destabilisation event(s) during the mid Pleistocene. Our study thus demonstrates a long-lived, multi-faceted history that shaped the NERZ.