Crustal structure and composition of the Oslo Graben, Norway

TY - JOUR

T1 - Crustal structure and composition of the Oslo Graben, Norway

AU - Stratford, Wanda Rose

AU - Thybo, Hans

PY - 2011/4/15

Y1 - 2011/4/15

N2 - Although more than 250. my old, the Oslo Graben has retained a distinctive distribution of P-wave velocities associated with rifting, intrusion and underplating of the thinned crustal section. We calculate Poisson's ratio values from crustal P and S-wave velocities along an ~. 400. km long profile across the southern Scandinavian Peninsula, with a focus on the Oslo Graben. Plutonic rocks are now exposed at the surface in the graben due to post rifting erosion and the corresponding low (5.5. km/s) P-wave velocities extend to depths of ~. 3. km. The P-wave velocity and Poisson's ratio between depths of 6 and 34. km are 5% higher inside than outside the rift boundaries which, together with thickening of the >7. km/s lower crust beneath the rift, indicate magmatic intrusions. Poisson's ratio of 0.27 and high 7.1-7.4. km/s velocities indicate a heterogeneous composition lower crust. The thickened high velocity lower crust is 1.5 times wider than the surface expression of the rift and extends to both the east and west of the main rift axis. Depth dependant extension may have occurred within the rift and may account for the significant volumes of volcanic output despite the small surface extension observed. The added volume of intrusive material may explain why the Moho up warp is small (as little as 2. km) at the rift. Based on the new P-wave velocities, Poisson's ratio measurements and the thickness of the magmatic underplate, apparent β values for the rift are estimated to be 1.5 but, when intrusion within the crust is included, could be as high at 2.3.

AB - Although more than 250. my old, the Oslo Graben has retained a distinctive distribution of P-wave velocities associated with rifting, intrusion and underplating of the thinned crustal section. We calculate Poisson's ratio values from crustal P and S-wave velocities along an ~. 400. km long profile across the southern Scandinavian Peninsula, with a focus on the Oslo Graben. Plutonic rocks are now exposed at the surface in the graben due to post rifting erosion and the corresponding low (5.5. km/s) P-wave velocities extend to depths of ~. 3. km. The P-wave velocity and Poisson's ratio between depths of 6 and 34. km are 5% higher inside than outside the rift boundaries which, together with thickening of the >7. km/s lower crust beneath the rift, indicate magmatic intrusions. Poisson's ratio of 0.27 and high 7.1-7.4. km/s velocities indicate a heterogeneous composition lower crust. The thickened high velocity lower crust is 1.5 times wider than the surface expression of the rift and extends to both the east and west of the main rift axis. Depth dependant extension may have occurred within the rift and may account for the significant volumes of volcanic output despite the small surface extension observed. The added volume of intrusive material may explain why the Moho up warp is small (as little as 2. km) at the rift. Based on the new P-wave velocities, Poisson's ratio measurements and the thickness of the magmatic underplate, apparent β values for the rift are estimated to be 1.5 but, when intrusion within the crust is included, could be as high at 2.3.

U2 - 10.1016/j.epsl.2011.02.021

DO - 10.1016/j.epsl.2011.02.021

M3 - Journal article

SN - 0012-821X

VL - 304

SP - 431

EP - 442

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

ER -