Other
Scientific paper
Mar 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977e%26psl..34..247p&link_type=abstract
Earth and Planetary Science Letters, Volume 34, Issue 2, p. 247-263.
Other
8
Scientific paper
The Gardar lavas (<1600 m.y., >1310 m.y.) within the Eriksfjord Formation of South Greenland were a prelude to major hypabyssal magmatism within the Gardar alkaline igneous province. This paper reports a palaeomagnetic study of the lower two-thirds of the lava stratigraphy comprising three groups of flows separated by sediments. The lower group (palaeomagnetic pole at 239°E, 7°N, 7 sites, dΨ = 7.6°, dχ = 14.1°) includes one reversal of magnetisation and two intermediate directions, and the upper group (pole at 222°E, 16°N, 24 sites, dΨ = 4.8°, dχ = 9.0°) includes four reversals and two intermediate directions. The middle group of 13 lavas yields anomalous directions with respect to the other groups and appears to have been erupted during a polarity excursion of uncertain significance. Opaque petrographic analysis reveals all stages of deuteric oxidation (800-500°C) plus lower-temperature hydrothermal alteration to epidote grade. In addition to high reversal frequency, the succession illustrates asymmetry of the dipole source, and there is a suggestion that lavas with easterly directed magnetisations have higher deuteric oxidation states than those with westerly directed magnetisations. Collective palaeomagnetic results from the Gardar Province are linked to a number of Rb-Sr isochrons, and comparison with contemporaneous North American data confirms the 500-fathom continental reconstruction for Proterozoic times. The poles define a movement of the Laurentian craton from low palaeolatitudes (1400-1220 m.y.) to high palaeolatitudes (1168-1070 m.y.) with a quasi-static interval at 1280-1220 m.y. coinciding with the Mackenzie igneous episode. The youngest Gardar data correlate with the oldest Keweenawan palaeomagnetic poles and restrict deposition of this group to the interval ca. 1160-1040 m.y.
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