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The geomagnetic field intensity in New Zealand : Palaeointensities from Holocene lava flows of the Tongariro Volcanic Centre

Greve, Annika ; Hill, Mimi J. ; Turner, Gillian M. and Nilsson, Andreas LU (2017) In Geophysical Journal International 211(2). p.814-830
Abstract

Very few absolute palaeointensity data exist from Holocene-aged rocks in New Zealand. Here we present a new suite of high-quality palaeointensities, supported by detailed rock magnetic investigations. Samples from 23 sites representing 10 distinct eruptive units of the Tongariro Volcanic Centre, Taupo Volcanic Zone, New Zealand, were studied. Both traditional double heating and microwave palaeointensity methods were employed. The reliability of the palaeointensity data varies with rock magnetic properties of the samples, corresponding, in particular, to their positions within the lava flows. The highest success rates are from samples obtained from near the flow tops where a significant proportion of the remanence unblocked at... (More)

Very few absolute palaeointensity data exist from Holocene-aged rocks in New Zealand. Here we present a new suite of high-quality palaeointensities, supported by detailed rock magnetic investigations. Samples from 23 sites representing 10 distinct eruptive units of the Tongariro Volcanic Centre, Taupo Volcanic Zone, New Zealand, were studied. Both traditional double heating and microwave palaeointensity methods were employed. The reliability of the palaeointensity data varies with rock magnetic properties of the samples, corresponding, in particular, to their positions within the lava flows. The highest success rates are from samples obtained from near the flow tops where a significant proportion of the remanence unblocked at intermediate temperatures (200-350 °C). By contrast, samples from flow centres, particularly the parts showing platey fracturing, have the lowest success rates. Reliable, high-quality palaeointensity results ranging from 32.4 ± 5.1 μT to 72.1 ± 4.7 μT were obtained from six flows with ages between c. 12 800 yr BP and the present. These correspond to virtual dipole moments that increase from 52 ± 10 ZAm2 in the early Holocene and peak at 112 ± 14 ZAm2 about 300 yr ago. The data agree well with calibrated relative palaeointensities from New Zealand lake sediments. The volcanic and sedimentary data together yield a Holocene virtual axial dipole moment curve that fits the global average variation well in the early Holocene, but which differs significantly in recent millennia. This difference is associated with recent migration of the southern high latitude core-mantle boundary flux lobe towards New Zealand, as is seen in global field models.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Magnetic mineralogy and petrology, New Zealand, Palaeointensity, Palaeomagnetic secular variation
in
Geophysical Journal International
volume
211
issue
2
pages
17 pages
publisher
Wiley-Blackwell
external identifiers
  • scopus:85052509059
ISSN
0956-540X
DOI
10.1093/GJI/GGX327
language
English
LU publication?
yes
id
72d975de-e537-4765-b2bd-5a7852c5f3cf
date added to LUP
2018-09-27 08:57:48
date last changed
2020-01-13 00:57:47
@article{72d975de-e537-4765-b2bd-5a7852c5f3cf,
  abstract     = {<p>Very few absolute palaeointensity data exist from Holocene-aged rocks in New Zealand. Here we present a new suite of high-quality palaeointensities, supported by detailed rock magnetic investigations. Samples from 23 sites representing 10 distinct eruptive units of the Tongariro Volcanic Centre, Taupo Volcanic Zone, New Zealand, were studied. Both traditional double heating and microwave palaeointensity methods were employed. The reliability of the palaeointensity data varies with rock magnetic properties of the samples, corresponding, in particular, to their positions within the lava flows. The highest success rates are from samples obtained from near the flow tops where a significant proportion of the remanence unblocked at intermediate temperatures (200-350 °C). By contrast, samples from flow centres, particularly the parts showing platey fracturing, have the lowest success rates. Reliable, high-quality palaeointensity results ranging from 32.4 ± 5.1 μT to 72.1 ± 4.7 μT were obtained from six flows with ages between c. 12 800 yr BP and the present. These correspond to virtual dipole moments that increase from 52 ± 10 ZAm<sup>2</sup> in the early Holocene and peak at 112 ± 14 ZAm<sup>2</sup> about 300 yr ago. The data agree well with calibrated relative palaeointensities from New Zealand lake sediments. The volcanic and sedimentary data together yield a Holocene virtual axial dipole moment curve that fits the global average variation well in the early Holocene, but which differs significantly in recent millennia. This difference is associated with recent migration of the southern high latitude core-mantle boundary flux lobe towards New Zealand, as is seen in global field models.</p>},
  author       = {Greve, Annika and Hill, Mimi J. and Turner, Gillian M. and Nilsson, Andreas},
  issn         = {0956-540X},
  language     = {eng},
  month        = {08},
  number       = {2},
  pages        = {814--830},
  publisher    = {Wiley-Blackwell},
  series       = {Geophysical Journal International},
  title        = {The geomagnetic field intensity in New Zealand : Palaeointensities from Holocene lava flows of the Tongariro Volcanic Centre},
  url          = {http://dx.doi.org/10.1093/GJI/GGX327},
  doi          = {10.1093/GJI/GGX327},
  volume       = {211},
  year         = {2017},
}