The deep crustal magnetic structure of Britain

Abstract

The deep crustal magnetic structure of Britain has not previously been described in a uniform manner. We provide a new assessment of the deep crustal magnetic bodies responsible for the long wavelength magnetic features. The study area contains deep crustal relics of the destruction of early Palaeozoic oceanic lithosphere along the Thor-Tornquist Suture and primarily the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Spectral decomposition is applied to a merged onshore and offshore magnetic anomaly data set. Thirty idealised basement bodies are compared with a representation of the subsurface obtained by a coarse 3D inversion of the data. The central area separating Laurentia and Avalonia, is largely characterised by an absence of high susceptibilities throughout the whole crustal volume. We find that the idealised basement bodies are largely consistent with relatively high susceptibility zones at depths in excess of 10 km. The zones of higher relative susceptibility are referenced to the tectonic-terrane framework of the area and possible geological explanations for the contrasts are reviewed. In the north, the Laurentian terranes are diverse, comprising crust first created in the Archaean (Hebridean Terrane), Palaeoproterozoic (Rhinns Terrane), Mesoproterozoic? (Midland Valley Terrane), Neoproterozoic (sub-Southern Upland rocks) and Ordovician. Magnetic anomalies further record the assembly of the Gondwanan (Eastern Avalonian) part of the country through Neoproterozoic and Ordovician (Tornquist) arc magmatism and accretion. The convergence zones between Laurentia, Avalonia and Baltica have all left a magnetic imprint, as has Variscan convergence to the south.

Plio‐Pleistocene fault reactivation within the Crag Basin, eastern UK: implications for structural controls of landscape development within an intraplate setting

“…In this study, a long‐term tectonic inheritance is demonstrated between: (i) Caledonian and Acadian orogenic structure (Beamish et al . 2016; Pharaoh 2018); (ii) structural configuration of the Anglo‐Brabant Massif and controls on Mesozoic sedimentation (Woods & Chacksfield 2012; Woods 2015); (iii) Oligocene structure and the development of the ‘Crag Basin Shear Zone’ (this study); and (iv) localized Plio‐Pleistocene dip‐slip reactivation of some trough‐bounding faults (this study) within the Crag Basin. The cause of this tectonic inheritance can only be speculated.…”

“…1995; Beamish et al . 2016). The origins and evolution of the Caledonides of Southern Britain, specifically the crust beneath East Anglia, are complex (Pharaoh 2018; : fig.…”

Magnetic Structure of the Earth’s Crust in the White Sea Region

“…The TDR derivative is positive above the magnetic source, is close to zero near its boundaries and is negative where no source exists [8]. Similarly [8],…”

“…The role of a spatial filter was played by a vertical to horizontal field derivative ratio expressed as the arc tangent of an angle denoted as a TDR derivative or a TDR an-gle [42]. The TDR derivative is positive above the magnetic source, is close to zero near its boundaries and is negative where no source exists [8]. Similarly [8],…”

“…Linking geomagnetic field states to time helps reconstruct the past states of the geomagnetic field, lithosphere and climate [5]. Such models are usually constructed for geodynamically active regions [6] [7] [8].…”