A paleomagnetic study of the Mull lava succession

Abstract

A paleomagnetic study has been made of a succession of 139 nonoverlapping basaltic lavas, representing 91 per cent of the longest remaining succession of flows associated with the Paleogene Mull volcano. All the lavas have experienced considerable hydrothermal alteration, probably at up to several million years after initial magnetization and frequently with alteration to the opaque minerals and the production of new potentially magnetic phases. The question of whether directional remagnetization has taken place while preserving within-unit directional consistency and discreteness of unit mean direction is discussed. Extensive directional remagnetization is excluded as an explanation for the data. If stable directions obtained by alternating field remanence cleaning coincide with original TRM directions then a mean pole position for all temporally independent lava directions from the British Tertiary igneous province is at 71.9"N, 167.2"E, with k: 22 and a95:3.Oo.This pole is significantly different from the geographic pole. If the difference in palaeomaaetic and geographic poles is interpreted in terms of absolute plate motion, then 2010km of northwards motion of the western part of the Eurasian Plate, at 3.7 cm/yr, has taken place over the last 55 Myr. This motion has implications for the geological history of the Arctic and for the complexity of mantle motions.

The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye

“…The overall mean palaeomagnetic pole position (Table 2), not tilt corrected, of this dyke swarm may be taken as 162.2" E, 82.3" N ( c P = 1.9", d M = 2.3"). This pole position is about 10" closer to the present geographic pole than that of other tilt-corrected British Tertiary lava piles, including the Skye lavas (see Dagley 1977 and, but on the other hand the palaeomagnetic poles of the present swarm agree well with those of the Vaternish dyke swarm of Northern Skye . The significance of all these poles can only be discussed in an overall British Tertiary igneous province paper.…”

Magnetostratigraphy of the Tertiary igneous rocks of Arran

“…The composite intrusions provide further evidence, because their margins and centres, though of very different compositions, have the same polarity and generally closely similar directions. Other evidence against Storedvedt's hypothesis is found elsewhere in the BTIP, such as the correlation of Antrim lavas over some kilometres using detailed variation of palaeomagnetic directions (Wilson, 1970), while Hall et al (1977) discuss the evidence from the Mull lavas. Thus we believe that the polarities given in section 3 are primary with a few noted exceptions, though some degree of dispersion of direction by remagnetisation cannot be ruled out, and may account for our inability to correlate bodies using precise directions.…”

The North Atlantic Igneous Province reconstructed and its relation to the Plume Generation Zone: the Antrim Lava Group revisited

“…Recent and very welcome studies have been performed on the extensive lava sequences in Western Greenland by Riisager & Abrahamsen (1999), Riisager et al (2003a) and Riisager et al (2003b) and the Faeroe Islands lavas by Riisager et al (2002). The lava sequences of the BTIP on the other hand, have not received much attention paleomagnetically since the 1970s (Wilson 1970; Løvlie et al 1972; Hall et al 1977; Mussett et al 1980). Following their work in Western Greenland (Riisager et al 2003a; Riisager et al 2003b) and the Faeroes Islands (Riisager et al 2002), Riisager et al (2003b) noted similarity between the paleomagnetic poles from these two subprovinces after correcting for the later opening of the North Atlantic.…”