Palaeomagnetic study of the Derbyshire lavas and intrusions, central England: definition of Carboniferous apparent polar wander

Details Palaeomagnetic study of the Derbyshire lavas and intrusions, central England: definition of Carboniferous apparent polar wander Palaeomagnetic study of the Derbyshire lavas and intrusions, central England: definition of Carboniferous apparent polar wander

Nov 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991pepi...69...37p&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 69, Issue 1-2, p. 37-55.

Physics

5

Scientific paper

The remanence in extrusive volcanic rocks of Lower Carboniferous (Visean) age in the Pennines of central England has been reinvestigated, employing detailed thermal demagnetisation and incorporating new geological knowledge of field relationships. Indications of primary remanence identified by early studies are supported and four successive reversals in the Asbian-Brigantian succession (about 335 Ma) recognised. A mean (reversed) direction of D/I = 203/36° (10 sites, R = 9.75) yields a pole position at 336°E 14°S (dp/dm = 6/10°). Grouping improves slightly when correction is made for mild intra-Carboniferous folding and widespread uniformity of polarity is recognised within individual units. Sporadic Variscan overprinting increases in importance to the southeast. Intrusive dolerite bodies yield two contrasting directions of magnetisation: in the central part of the Derbyshire pericline mixed polarity directions (mean D/I = 211/37° (4 sites, R = 3.92)) comparable to the lavas imply a Lower Carboniferous age of emplacement; in the SE Upper Permian (?) directions of reversed polarity (mean D/I = 221/-23°) define a later intrusive event or comprehensive overprinting.
The primary Lower Carboniferous pole positions accord with contemporaneous poles from the Midland Valley of Scotland and demonstrate that Carboniferous and younger tectonic movements are palaeomagnetically undetectable, at least between these two areas. Apparent polar wander (APW) movement is confirmed between Lower and Upper Carboniferous times at about 335-320 Ma. The Lower Carboniferous limestones have a remanence entirely younger than depositional ages and are therefore unreliable indicators of Carboniferous magnetostratigraphy and tectonics. Silicified limestones prove to have remanences closer to the primary Lower Carboniferous field and appear to have been shielded from the effects of later overprinting. The APW swathe identified from North American Carboniferous rocks coincides in polarity and position with the latter part of the British Carboniferous path on the Pangaean reconstruction.

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