On the recovery of effective elastic thickness using spectral methods: Examples from synthetic data and from the Fennoscandian Shield
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On the recovery of effective elastic thickness using spectral methods: Examples from synthetic data and from the Fennoscandian Shield

  • Author(s): Perez-Gussinye, Marta
  • Lowry, Anthony R
  • Watts, Anthony B
  • Velicogna, Isabella
  • et al.
Abstract

 There is considerable controversy regarding the long-term strength of continents (T e ). While some authors obtain both low and high T e estimates from the Bouguer coherence and suggest that both crust and mantle contribute to lithospheric strength, others obtain estimates of only <25 km using the free-air admittance and suggest that the mantle is weak. At the root of this controversy is how accurately T e  can be recovered from coherence and admittance. We investigate this question by using synthetic topography and gravity anomaly data for which T e  is known. We show that the discrepancies stem from comparison of theoretical curves to multitaper power spectral estimates of free-air admittance. We reformulate the admittance method and show that it can recover synthetic T e  estimates similar to those recovered using coherence. In light of these results, we estimate T e  in Fennoscandia and obtain similar results using both techniques. T e  is 20–40 km in the Caledonides, 40–60 km in the Swedish Svecofennides, 40–60 km in the Kola peninsula, and 70–100 km in southern Karelia and Svecofennian central Finland. Independent rheological modeling, using a xenolith-controlled geotherm, predicts similar high T e  in central Finland. Because T e  exceeds crustal thickness in this area, the mantle must contribute significantly to the total strength. T e  in Fennoscandia increases with tectonic age, seismic lithosphere thickness, and decreasing heat flow, and low T e  correlates with frequent seismicity. However, in Proterozoic and Archean lithosphere the relationship of T e  to age is ambiguous, suggesting that compositional variations may influence the strength of continents.

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