MONA LISA - Deep seismic investigations of the lithosphere in the southeastern North Sea

Research output: Contribution to journalArticlepeer-review

Authors

  • T. Abramovitz
  • A. Berthelsen
  • F. Schjøth
  • H. Thybo
  • N. Balling
  • L. Nielsen
  • E. R. Flueh
  • S. Hübinger
  • L. B. Pedersen
  • J. Schmidt
  • R. W. England
  • R. W. Hobbs
  • P. K H Maguire

Colleges, School and Institutes

External organisations

  • Aarhus Universitet
  • University of Cambridge
  • University of Leicester
  • Geological Institute
  • Copenhagen University
  • Department of Earth, Atmospheric, and Planetary Sciences
  • Aarhus University
  • University Medical Centre Schleswig-Holstein, Campus Kiel
  • Solid Earth Geophysics
  • Uppsala University
  • Box 556
  • St Andrews Geology department
  • GEOMAR - Helmholtz Zentrum für Ozeanforschung Kiel
  • Brit. Institutions' Reflection P.

Abstract

The MONA LISA collaborative project has collected 1112 km of seismic normal-incidence reflection data (recorded to 26 s) and wide-angle data from 26 onshore and 2 offshore locations along 4 profiles in the southeastern North Sea. The seismic data clearly image structures in the crust and uppermost mantle that may be related to Caledonian collision and Late Palaeozoic to Mesozoic rifting and basin formation. For the first time, dipping and subhorizontal reflections from the mantle have been observed to 24 s twt in seismic normal-incidence reflection sections. Strong sub-horizontal reflections are observed on two perpendicular profiles at c. 21 s twt, which is near the base of the lithosphere. These deep reflections are sharper than expected from a thermal-rheological transition suggesting that they are generated at lithological or tectonic interfaces. The Moho is reflective along all four profiles. Particularly strong and sharp normal-incidence and wide-angle reflections were recorded from the Moho south of the Caledonian Deformation Front. The normal-incidence reflection sections show unusually low intra-crustal reflectivity. Lower crustal, subhorizontal reflectivity is only observed west of the Central Graben and in a short profile segment at the base of the interpreted Caledonian Deformation Front. The crustal suture between Avalonia and Baltica is interpreted to be south- to west-dipping. SSW- and N-dipping reflections to 20 s twt are observed from the uppermost mantle. Two models of Tornquist Sea subduction may explain these events: either southward subduction and later extensional reactivation or northward subduction with later extension along a SSW-dipping shear zone. The crust is c. 5 km thinner below the Central Graben than below the surrounding parts of the Mid North Sea-Ringkøbing-Fyn High. The lower crust is reflective on the western flank of the Central Graben. East-dipping reflections from the lower crust and the upper mantle to the east of the graben may indicate a component of simple shear in the evolution of the rift structure.

Details

Original languageEnglish
Pages (from-to)1-19
Number of pages19
JournalTectonophysics
Volume269
Issue number1-2
Publication statusPublished - 30 Jan 1997

Keywords

  • Caledonian Orogeny, Central Graben, North Sea, Deep seismic sounding, Suture zones, Upper mantle

ASJC Scopus subject areas