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- Kind, R., et al.
(författare)
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Scandinavia : A former Tibet?
- 2013
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Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 14:10, s. 4479-4487
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Tidskriftsartikel (refereegranskat)abstract
- The Himalaya and the Tibetan Plateau are uplifted by the ongoing northward underthrusting of the Indian continental lithosphere below Tibet resulting in lithospheric stacking. The layered structure of the Tibetan upper mantle is imaged by seismic methods, most detailed with the receiver function method. Tibet is considered as a place where the development of a future craton is currently under way. Here we study the upper mantle from Germany to northern Sweden with seismic S receiver functions and compare the structure below Scandinavia with that below Tibet. Below Proterozoic Scandinavia, we found two low-velocity zones on top of each other, separated by a high-velocity zone. The top of the upper low-velocity zone at about 100 km depth extends from Germany to Archaean northern Sweden. It agrees with the lithosphere-asthenosphere boundary (LAB) below Germany and Denmark. Below Sweden it is known as the 8 degrees discontinuity, or as a mid-lithospheric discontinuity (MLD), similar to observations in North America. Seismic tomography places the LAB near 200 km in Scandinavia, which is close to the top of our deeper low-velocity zone. We also observed the bottom of the asthenosphere (the Lehmann discontinuity) deepening from 180 km in Germany to 260 km below Sweden. Remnants of old subduction in the upper about 100 km below Scandinavia and Finland are known from controlled source seismic experiments and local earthquake studies. Recent tomographic studies indicate delamination of the lithosphere below southern Scandinavia and northern Germany. We are suggesting that the large-scale layered structure in the Scandinavian upper mantle may be caused by processes similar to the ongoing lithospheric stacking in Tibet.
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- Gregersen, S., et al.
(författare)
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Uniqueness of modeling results from teleseismic P-Wave tomography in Project Tor
- 2010
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 481:1-4, s. 99-107
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Tidskriftsartikel (refereegranskat)abstract
- Within Project Tor. which is about Teleseismic Tomography across the Tomquist Zone in Germany-Denmark-Sweden, we have confirmed very significant deep lithosphere differences And modeling is substantiated via completely independent methods. In 1996-1997 our 130 seismographs constituted the largest seismic antenna ever in Europe. The Tor area was chosen along a well studied crustal profile of an earlier project, and the modeling efforts were concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km The Tor data have been subjected to P-wave travel time tomography. surface wave and receiver function analysis as well as anisotropy and scattering measurements An important goal of the project was to make several independent inversions of the tomography data. and compare the results in an attempt to evaluate uniqueness, resolution and accuracy of these inversions. The comparisons of this paper involve more diversity in methods than any previous comparison. The geological outcome is a substantiation of earlier statements that, "The transition is interpreted to be sharp and steep in two places It goes all through the lithosphere at the northern rim of the Tornquist Zone near the border between Sweden and Denmark, and here the lithosphere difference is large to depths more than 200 km. The other lithosphere difference. of smaller scale, is found near the southern edge of the Ringkobing-Fyn High near the border between Denmark and Germany Also this transition is sharp and steep. and goes all through the lithosphere to depths around 120 km. These two sharp transitions divide the Tor region into 3 different lithosphere structures distinguishable in P-wave travel time tomography. surface wave dispersion. P- and S-wave anisotropy and partly in P-wave scattering" The mentioned broad-scale features are judged to be unambiguously determined, with well-described resolution and accuracy Unfortunately a detail like the slope of the subcrustal lithosphere transition right under the Tronquist Zone cannot be constrained even if this is where the resolution is best. and the curiosity largest.
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