of Marilyn Monster
High-resolution records of geomagnetic field behaviour: the next generation of joined 40Ar/39Ar dating and paleointensity determination for the last 150 kyr
Earth's magnetic field is generated in the liquid outer core of the
planet. At the Earth's surface, the magnetic field is essentially a
dipole field, but regionally variations in direction and intensity that
cannot be described by a dipole can occur. Analyses of geomagnetic
field variations have resulted in a series of geomagnetic field models
such as CALS10k (Korte and Constable, 2011) for the past 10 kyr. The
intensity information feeding into these models, however, is much less
well-constrained than the directional data. Furthermore, for ages >
10 kyr, the database is considerably more fragmentary and is dominated
by records from Hawaii.
first component of this research project is to obtain reliably absolute
palaeointensities (PIs) from lavas from two regions: the Mediterranean
(Sicily, Nisyros) and the Canary Islands (El Hierro). PI determination
is a notoriously difficult and laborious process with a rather low
success rate. Many specimens fail selection criteria and the ones that
pass may yield erroneous PI estimates. To increase the success rate a
multi-method approach is used. Comparing results from three different
PI determination methods (the classic Thellier-Thellier method
(Thellier and Thellier, 1959), the microwave method (e.g. Hill and
Shaw, 1999) and the multispecimen protocol (Dekkers and Boehnel, 2006;
Fabian and Leonhardt, 2010)) provides an extra check on the reliability
of the obtained PIs. When two or all three methods yield the same PI,
the obtained PI is close to the correct value. (Marilyn's MSc project;
results to be published in 2014.)
in lava flows on El Hierro
second component of this project consists of (re)dating sites that
yield good PI results using the new Thermo Fisher HELIX MC
multi-collector mass spectrometer. It was installed at VU University
Amsterdam in 2013 and will start measuring samples in the first months
of February. Its peak valley resolution and peak resolving power are
very high, allowing to fully resolve isobaric interferences of
hydrocarbon fragments and partially resolve hydrochloric interferences.
Measuring a resolved Ar-36 beam should result in a dramatically more
accurate determination of the argon isotope ratios and thus more
precise Ar/Ar ages.
El Hierro - view over El Golfo valley
of Marilyn Monster
- Monster, M.W., de Groot, L.V. and Dekkers, M.J.
MSP-Tool: a VBA-based software tool for the analysis of multispecimen paleointensity data.
Front. Earth Sci.
- Monster, M.W.L., de Groot, L.V., Biggin, A.J. and Dekkers,
M.J. (2015). The performance of various palaeointensity techniques as a
function of rock-magnetic behaviour - a case study for La
Palma, Physics of the Earth and Planetary Interiors, 242, 36-49.
- Monster, M.W.L. (2014). Aadmagnetisch veld van de afgelopen 500.000 jaar gereconstrueerd, Geo.brief, 39(4), 10 - 11.
- S. Semraua,
M.W.L. Monster, M. van der Knaap, B.I. Florea, T. Schmidt and M.
(2010). Membrane lysis by gramicidin S visualized in red blood cells
giant vesicles, Biochim. Biophys. Acta, 1798,