Palaeomagnetism of the Late Cretaceous–Tertiary volcanics from Disko

• Main Authors: E. R. Deutsch, L. G. Kristjansson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1974
• Subjects: Arctic; Curie Point; Greenland; East Greenland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1027.4900; http://gji.oxfordjournals.org/content/39/2/343.full.pdf

Various magnetic properties of three lava profiles (45 flows), basalt breccia and intrusives from the southernmost part of the west Greenland basalt area have been measured. All samples contain a stable remanence com-ponent of reverse (R) polarity, in accord with most other rocks of the Brito-Arctic Lower Tertiary province. Three magnetic groupings were found: Class r. In the majority of lava samples, the NRM is dominated by the stable R component, which remains stable in direction under AF cleaning and has a characteristic single, high Curie point (T, = 550-570 "C). Class n. One-quarter of the lava samples had a soft, normal NRM whose polarity switched to R under AF treatment at 50-100 Oe and became stable in higher fields. Class n samples often show both a low T, (G300 "C) and a high T,, and their mean Koenigsberger ratio (0.43) is low compared to class r (2-9). Class r ' behaviour, combining r and n features, occurs especially in the breccia, intrusives and remaining lavas. Laboratory viscous build-up tests indicate that the soft component prominent in n and r ' rock is a VRM acquired during the present (Brunhes) geomagnetic epoch. Rock of different classes frequently co-exists even in single flows; this is attributed simultaneously to (1) spatial dif-ferences in oxygen fugacity during initial cooling, and (2) variations in titanomagnetite domain-size distribution near the singledomain-super-paramagnetic threshold. Spatial variations in the rate of lava extrusion and of cooling can explain both effects. One flow has a K-Ar age of 70+4 My. From the magnetic results on 37 flows, it is concluded that the stable remanence is of primary origin and that its between-flow dispersion (19") is due largely to secular variation. The average palaeo-field direction calculated from these flows corresponds to a reverse pole at 62 " N, 169 " W, with dp = 8", dm = 9". This pole agrees with a published Lower Tertiary pole for east Greenland but is displaced from poles of similar age for north-western Europe. This is compatible ...