Rock-magnetic study on shield basalts from Gran Canaria containing a recorded reversal of the erth’s magnetic field

Rock-magnetic study on shield basalts from Gran Canaria containing a recorded reversal of the erth’s magnetic field

Nap, A.

Molengraaff Fonds

2017

The Earth’s magnetic field is known to exhibit reversals in polarity. Such a reversal seems imminent to occur in the future, but little is known about the processes that govern such a reversal. We created a detailed record of a polarity reversal recorded in (Mid-Miocene) shield building lavas of Gran Canaria. In this part of the research we created a detailed record of the rock-magnetic properties of these lavas to assess their suitability as recorders of information on the ancient geomagnetic field. We used a Kappabridge (KLY-3) to obtain a magnetic susceptibility curve and a VSM (vibrating sample magnetometer) to determine if the samples are single domain (SD), pseudo-single domain (PSD) or MD (multi domain). With these techniques we determine the behaviour of samples when subjected to alternating temperatures (magnetic susceptibility) and strong magnetic fields (VSM). The results show that 80 of the samples are PSD and 17 are close to MD. We found that the samples have a higher abundance in magnetite than titanomagnetite and are in general characterized by high (< 500 ⁰C) Curie temperatures. Correlating the rock-magnetic data to IZZI-Thellier measurements (Marijnissen, 2017) we found that most successful samples originate from the same susceptibility groups and agree with curves presented in de Groot et al. (2015). This implicates that in future measurements a higher success rate can be attained by measuring more flows that show the same magnetic susceptibility behaviour. Researching possible ways to minimize alteration could be to heat and cool the samples within an oxygen deprived environment (Lattard et al., 2012). This would possibly minimize high temperature oxidation making the samples more reliable during IZZI-Thellier measurements.

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Utrecht University

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