Interpretation of aeromagnetic data along the Jan Mayen fracture zone, JAS-05

Abstract

Aeromagnetic data from the Jan Mayen Fracture Zone (JAS-05) were acquired and processed during the autumn of 2005 and compiled with neighbouring data-sets. Data processing comprised spike removal and data editing, IGRF correction, statistical levelling of tie lines and profiles. The new JAS-05 survey has been merged with more than 40 other surveys including the mainland of Norway, Svalbard and East-Greenland. A compilation of the existing gravity data in the area has also been carried out. Potential field modelling has been constrained by available data on density, magnetic properties and reflection and refraction (OBS) seismics. New features have been revealed by the interpretation of the Jan Mayen Aeromagnetic Survey 2005 (JAS-05). The Aegir Marginal High (AMH) represents an inverted structure, uplifted during late Oligocene-early Miocene time. The thickening of the oceanic crust is syn-accretion and is not necessarily related to a Late Miocene underplaying (post-accretion), as previously assumed. The magnetic anomaly map shows also evidences of earlier deformation and block rotation linked with a propagator system along the Aegir through. A late Eocene displacement of the magnetic chrons suggests a progressive plate reorganisation leading to a major pulse in Oligocene. The major pulse coincides with two main unconformities seismically observed along the Jan Mayen Corridor (PM and MU) and could explain the main uplift phase of the AMH as well. We propose also a new challenging model for the Mid-Norwegian breakup system. Our tectonic analysis suggests that a triple junction Ridge-Ridge-Fracture Zone was initiated during the Late Paleocene-Early Eocene breakup between Greenland-Jan Mayen and Norway. Our interpretation infers also that the north Atlantic breakup probably started earlier at C24R or C25 time south of the EJMFZ. Spreading rates between the Aegir and Mohns ridges appear on the new magnetic compilation to differ by ~2 mm\/yr for much of the period ranging from continental break up to extinction of the Aegir Ridge. The contrasting spreading rates of either side of the Jan Mayen Fracture Zone (JMFZ) resulted in dextral strike-slip along the JMFZ. Preliminary modelling suggests that such a minor difference in spreading rates could have led to significant shortening in the Vøring Basin. This model can explain why most of the mid-Norwegian domes are located to the north of the Jan Mayen Lineament.