Shear-wave splitting around the Eifel hotspot: evidence for a mantle upwelling

• Published in: Geophysical journal international 2005-12, Vol.163 (3), p.962-980
• Main Authors: Walker, K. T., Bokelmann, G. H. R., Klemperer, S. L., Bock, G.
• Format: Article
• Language: English
• Subjects: Anisotropy; Broadband; Eifel; Electrical raceways; hotspots; Mantle; Mathematical models; plumes; shear-wave splitting; Splitting; Stations; Upwelling; upwellings
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1111/j.1365-246X.2005.02636.x

We present the results of a shear-wave splitting analysis across the Eifel hotspot in west-central Europe. Our data set includes 18 permanent European broadband stations and 102 temporary Eifel broadband and short-period stations. We observe variations in splitting at most permanent stations, but are not able to model them reliably with unique dipping-axis or two-layer anisotropy models. We prefer instead a single-layer model with a horizontal fast axis to approximate the first-order anisotropy, which varies smoothly between stations. We observe a first-order parabolic pattern in fast polarization azimuth around the hotspot, which suggests that a lattice preferred orientation (LPO) of olivine fast axes exists in the asthenosphere as a result of the interaction between the slowly WSW-moving Eurasian plate and a mantle upwelling beneath the Eifel volcanic fields. The minority of the variation not explained by this model correlates with rapid lateral changes in splitting, and is interpreted as a result of additional anisotropy and/or the effects of dynamic recrystallization associated with LPO development in the region of corner flow near the conduit. Our parabolic asthenospheric flow (PAF) interpretation is consistent with Eifel geological, tomographic, receiver function, global absolute plate motion, electrical conductivity anisotropy, and geochemical studies, as well as with splitting studies in the Great Basin and around Hawaii.We suggest that the Eifel upwelling is sporadic, and a result of a low excess upwelling temperature and/or varying crustal stresses that periodically shift and facilitate eruption. The PAF pattern we observe neither suggests nor rules out anisotropy in the conduit associated with a wet Eifel upwelling.We use our optimum PAF model parameters to calculate a Eurasian plate speed of 12 km Ma−1, which is consistent with the recent HS3-NUVEL1A speed of 19 ± 14 km Ma−1.