Journal
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
Volume 160, Issue 2, Pages 169-179Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.pepi.2006.11.004
Keywords
rock magnetism; MORB; titanomagnetite; titanomaghemite; natural remanent magnetisation; ODP; DSDP
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We studied the change of magnetic behaviour upon laboratory heating of altered mid-ocean ridge basalt (MORB) samples in the age range of 16-35 Ma to determine the influence of titanomaghemite inversion on the thermal demagnetisation of natural remanent magnetisation (NRM) of these basalts. MORB samples were heated to successively higher temperatures and at the same time the temperature dependence of either saturation magnetisation or NRM was monitored continuously. After each heating step, hysteresis loops and remanent magnetisation curves between 10 K and room temperature were measured. With this procedure, it is shown that the dominant magnetic remanence carrier in our MORB samples is cation deficient titanomaghemite. Moreover, it is demonstrated that the fitanomaghemite is gradually changing to a Ti-poor titanomagnetite as the final inversion product. During inversion, both the Curie temperature as well as the maximum unblocking temperature of the NRM are gradually increasing. We show that the paradox of unblocking temperatures above the Curie temperatures often observed for altered MORBs is an artefact of this gradual, heating induced inversion process. (c) 2006 Elsevier B.V. All rights reserved.
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