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High paleointensities of the geomagnetic field from thermomagnetic studies on rift valley pillow basalts from the Mid- Atlantic Ridge.

Journal of Geophysical Research

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Abstract

Nineteen pillow basalts dredged within the rift valley of the Mid-Atlantic Ridge at 36.8oN were studied by the Thellier stepwise heating method in order to determine the paleointensity of the geomagnetic field when they erupted on to the sea floor. Previously reported fission track ages are 2000-6000 yr for the youngest rocks (mainly olivine basalts) and 10 000-100 000 yr for the others (mainly plagioclase basalts and pyroxene basalts). All but three pillow basalts meet the conditions commonly considered as indicative of quite reliable paleointensity estimates; stability of the direction of NRM during its thermal demagnetization, constant ratio of NRM/TRM (natural remanent magnetization to thermoremanent magnetization) over 50% or more of the original NRM intensity (80 to 94% for 11 specimens), and reproducibility of low-temperature partial TRM(PTRM). However, strong field thermomagnetic measurements indicate that 11 of these 16 samples display a significant increase in Curie temperature (15 to 80oC) during the paleointensity experiments below 250oC, notwithstanding the linearity of the NRM-TRM plot in this temperature interval. This alteration, probably due to low-temperature oxidation of the specimens, seems typical of young pillow basalts and may result in paleointensity estimates which are too high.-from Authors

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
High paleointensities of the geomagnetic field from thermomagnetic studies on rift valley pillow basalts from the Mid- Atlantic Ridge.
Series title:
Journal of Geophysical Research
Volume
88
Issue:
B3
Year Published:
1983
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
2316
Last page:
2326
Number of Pages:
11