A detailed palaeomagnetic study of the oldest (≈15 Myr) lava sequences in Northwest Iceland

Abstract

S U M M A R YWe have determined the directions of primary remanence in over 400 lava flows in the northwestern peninsula of Iceland (near 66.1 • N, 23.3 • W). These lavas were sampled in 16 profiles spread across 75 km, at the stratigraphic level of the oldest (approximately 15 Myr in age) of several distinctive lignite-bearing sediments in the peninsula. We find that the pattern of polarity reversals in the lava pile is broadly similar in these profiles but it is generally not possible to trace short polarity zones and excursions over more than a few kilometres laterally. Our results, which also include measurements on the lignite sediments at three sites, are consistent with previous suggestions that these sediment beds represent a time gap of the order of 0.2 Myr between the lavas above and below. The mean virtual geomagnetic pole of this collection is 'far-sided' by approximately 7 • , and the scatter of individual poles is greater than that in palaeomagnetic surveys on younger lava series in Iceland.

Stratigraphy and paleomagnetism of a 2.9-km composite lava section in Eyjafj�rdur, Northern Iceland: a reconnaissance study

“…4 Extended alternating field demagnetization of seven lava specimens from the present collection. The numbers shown between some data points indicate direction changes, whenever these exceed 1.5 rotational remanence (RRM) could be seen in our samples, but RRM has been noted occasionally at 30 mT AF treatment or beyond in material collected elsewhere in Iceland (e.g., Kristjansson et al 2003).…”

“…A number of composite sections, each containing hundreds of lava flows, have been mapped since 1964. The methods introduced by Walker have been applied in combination with mapping of paleomagnetic polarity zones, and sometimes K-Ar radiometric dating (Watkins and Walker 1977;McDougall et al 1977;Kristjansson et al 1980;Saemundsson et al 1980;McDougall et al 1984;Kristjansson et al 1995Kristjansson et al , 2003Johannesson 1996, 1999;Hardarson et al 1997). Although these sections have provided new insights into the generation of the lava pile and its subsequent tectonics, they should be considered as being only preliminary reconnaissance surveys.…”

“…However, later surveys (e.g. Kristjansson et al 2003) furnished evidence for considerable temporal and spatial variations in the rate of buildup. Processes such as the lateral movement of the major volcanic zones in Iceland have left hiatuses that may reach hundreds of ka; they are not always evident in the field or detectable at the present resolution level of radiometric dates.…”

The growth, collapse and quiescence of Teno volcano, Tenerife: new constraints from paleomagnetic data

“…Numerous radiometric ages were published for Teno. Magnetostratigraphic investigations provide important additional constraints regarding the temporal evolution of volcanic regions, as has been demonstrated in Iceland (Kristjansson et al 2003), and also on several Canary Islands (Guillou et al 1996(Guillou et al , 2001). Here, we analyze the past geomagnetic field as recorded in volcanic rocks and provide new clues to better understand the evolution of Teno.…”

“…The two major sector collapse events are denoted Masca collapse (MC) and Carrizales collapse (CC). Regarding the age constraints as given in the text, the obtained magnetic polarity data (P) are correlated to the GPTS (Cande and Kent 1995) Kristjansson et al 2003) and might be related to persistent multipole components of the geomagnetic field. The explicit reason for this often observed effect remains unclear.…”