Magnetic state of 10-40 Ma old ocean basalts and its implications for natural remanent magnetization

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doi: 10.1016/S0012-821X(02)01094-4
Author(s): Matzka, Jürgen; Krása, David; Kunzmann, Thomas; Schult, Axel; Petersen, Nikolai
Author Affiliation(s): Primary:
Ludwig-Maximilians-Universität München, Department for Earth and Environmental Sciences, Munich, Federal Republic of Germany
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 206(3-4), p.541-553. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 42 refs.; illus., incl. 2 tables
Summary: The natural remanent magnetization (NRM) of ocean basalts, giving rise to the pattern of marine magnetic anomalies, is known to be of comparatively low intensity for about 20 Ma old oceanic crust. The aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age, and to establish a link between magnetomineralogy, rock magnetic parameters, and the low NRM intensity. Ocean basalts covering ages from 0.7 to 135 Ma were selected for rock magnetic experiments and their room temperature hysteresis parameters, Curie temperature and temperature dependence of saturation magnetization MS(T) was determined and complemented by reflected light microscopy. The majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age. For these, a strong dependence of hysteresis parameters on the age of the samples is found. The samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 Ma, coinciding with the age interval of low NRM intensity. The observed change in saturation magnetization is in the same order as that for the NRM intensity. A further peculiarity of the titanomaghemites from this age interval is the shape of their MS(T) curves, which display a maximum above room temperature (Neel P-type) and, sometimes, a self-reversal of magnetization below room temperature (Neel N-type). These special rock magnetic properties can be explained by titanomagnetite low-temperature oxidation and highly oxidized titanomaghemites in the age interval 10-40 Ma. A corresponding measurement of the NRM at elevated temperature allows to identify a maximum in NRM intensity above room temperature for the samples in that age interval. This provides evidence that the NRM is equally carried by titanomaghemites and that the low NRM intensities for about 20 Ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites. Abstract Copyright (2003) Elsevier, B.V.
Year of Publication: 2003
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Basalts; Cenozoic; Cretaceous; Crust; Curie point; Deep Sea Drilling Project; Experimental studies; Igneous rocks; Laboratory studies; Maghemite; Magnetic hysteresis; Magnetic minerals; Magnetic properties; Magnetization; Mesozoic; Natural remanent magnetization; Ocean Drilling Program; Oceanic crust; Oxidation; Oxides; Paleomagnetism; Remanent magnetization; Saturation magnetization; Temperature; Tertiary; Thermoremanent magnetization; Titanomaghemite; Volcanic rocks
Record ID: 2003027468
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands

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