TY - JOUR
T1 - Variations of shear-wave splitting in Greenland: Mantle anisotropy and possible impact of the Iceland plume
AU - Ucisik, Nur
AU - Gudmundsson, Ólafur
AU - Hanka, Winfried
AU - Dahl-Jensen, Trine
AU - Mosegaard, Klaus
AU - Priestley, Keith
N1 - Funding Information:
The GFZ instrument pool (GIPP) provided mobile stations for GLATIS and data were retrieved from the GIPP and data archive facilities at GFZ-Potsdam, SEIS-UK, GEUS and IRIS. We thank P. Voss and S. Pilidou for assistance of retrieving GEUS and SEIS-UK data. We are grateful to A. Higgins to check over the Greenland Geology section of the manuscript and his improvements. We thank R. Kind for his constructive comments. We also thank the editor J. Plomerová and three anonymous reviewers for their careful and constructive reviews. We acknowledge SAC2000 ( Goldstein et al., 2003 ). This research was started at the Danish Lithosphere Center and supported by the National Research Foundation of Denmark (Dansk Grundforskningsfond). Figs. 2 and 8 were created with the Generic Mapping Tools (GMT) software ( Wessel and Smith, 1991 ).
PY - 2008/12/15
Y1 - 2008/12/15
N2 - Seismic anisotropy was investigated by measuring shear-wave splitting at 19 broadband stations in Greenland. We examined mostly SKS and SKKS phases, but also some PKS and depth phases of SKS (e.g. pSKS, sSKS) for deep events. Splitting parameters (fast polarization and time delay) were determined for these phases. The fast polarizations at nine sites in southern Greenland are quite uniformly oriented about N-NE. Two sites in central northern Greenland show a similar geometry to southern Greenland. Similar fast polarizations in southern and central northern Greenland suggest continuity of structural fabric beneath large parts of Greenland. This coherent pattern extends across a number of geological provinces of varying age and suggests a common cause of anisotropy not related to the bitwise formation of the Greenland continental block. Four sites in an east-west oriented belt crossing central Greenland show varying fast polarizations and suggest a separate process causing the anisotropy there, which may indicate that these processes are not currently active. The overall pattern of anisotropy in our results, with the exception of variations across central Greenland, is similar to results obtained from Rayleigh waves. The irregular geometry of splitting across central Greenland may be related to the impact of the Iceland plume at ∼ 60 Ma. Reported splitting time delays range from 0.4 to 1.4 s with an average of 0.8 s, which can generally not be explained by crustal anisotropy alone. If confined to a lithosphere of thickness on the order of 100 km, time delays of up to 1.4 s indicate anisotropy of up to about 6%, assuming that the a crystallographic axis of olivine is preferentially contained in the horizontal plane. We suggest that the anisotropy beneath Greenland is located mainly in the upper mantle but some contributions from the crust and lower mantle may be present.
AB - Seismic anisotropy was investigated by measuring shear-wave splitting at 19 broadband stations in Greenland. We examined mostly SKS and SKKS phases, but also some PKS and depth phases of SKS (e.g. pSKS, sSKS) for deep events. Splitting parameters (fast polarization and time delay) were determined for these phases. The fast polarizations at nine sites in southern Greenland are quite uniformly oriented about N-NE. Two sites in central northern Greenland show a similar geometry to southern Greenland. Similar fast polarizations in southern and central northern Greenland suggest continuity of structural fabric beneath large parts of Greenland. This coherent pattern extends across a number of geological provinces of varying age and suggests a common cause of anisotropy not related to the bitwise formation of the Greenland continental block. Four sites in an east-west oriented belt crossing central Greenland show varying fast polarizations and suggest a separate process causing the anisotropy there, which may indicate that these processes are not currently active. The overall pattern of anisotropy in our results, with the exception of variations across central Greenland, is similar to results obtained from Rayleigh waves. The irregular geometry of splitting across central Greenland may be related to the impact of the Iceland plume at ∼ 60 Ma. Reported splitting time delays range from 0.4 to 1.4 s with an average of 0.8 s, which can generally not be explained by crustal anisotropy alone. If confined to a lithosphere of thickness on the order of 100 km, time delays of up to 1.4 s indicate anisotropy of up to about 6%, assuming that the a crystallographic axis of olivine is preferentially contained in the horizontal plane. We suggest that the anisotropy beneath Greenland is located mainly in the upper mantle but some contributions from the crust and lower mantle may be present.
KW - Greenland lithosphere
KW - Iceland plume
KW - Mantle anisotropy
KW - Shear-wave splitting
UR - http://www.scopus.com/inward/record.url?scp=56549128079&partnerID=8YFLogxK
U2 - 10.1016/j.tecto.2007.11.074
DO - 10.1016/j.tecto.2007.11.074
M3 - Article
SN - 0040-1951
VL - 462
SP - 137
EP - 148
JO - Tectonophysics
JF - Tectonophysics
IS - 1-4
ER -