Structure of remanent magnetization and magnetic mineralogy of the Cheviot lavas (lower Devonian), northeast England

Abstract

Demagnetization data and magnetomineralogical results from the Lower Devonian Cheviot lavas have revealed a complex remanence structure associated with extensive low-temperature alteration of the primary magnetic oxides. The original cooling magnetization has apparently been replaced by chemical remanences acquired in one or more dual polarity fields. Superposition of normal and reverse field components appears to have created fairly stable, but what may be palaeomagnetically irrelevant, directions which, if not recognized or experimentally resolved, may easily lead to incorrect conclusions. Evaluation of the total data base suggests that the characteristic palaeomagnetic axis is sub-horizontal with an approximately N–S declination. The age range of this magnetization may vary from Lower Devonian to Lower Carboniferous. The new experimental results throw into question some previous palaeomagnetic conclusions regarding the British Lower Old Red Sandstone lavas. Further critical study of the fossil magnetization of Lower Devonian rocks from Britain should be on intrusive masses, as such rocks are likely to have escaped at least the extensive surface oxidation, and associated remagnetization complexities, that have apparently developed in the extrusive suites.