The geomagnetic field intensity in New Zealand: palaeointensities from Holocene lava flows of the Tongariro Volcanic Centre
The geomagnetic field intensity in New Zealand: palaeointensities from Holocene lava flows of the Tongariro Volcanic Centre
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新西兰的地磁场强度：汤加里罗火山中心全新世熔岩流的古强度
DOI：
10.1093/gji/ggx327
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发表时间：
2017
影响因子：
2.8
通讯作者：
Greve A
中科院分区：
文献类型：
--
作者：
Greve A
新西兰全新世岩石的绝对古强度数据很少。在这里，我们展示了一套新的高质量的古强度，得到了详细的岩石磁学研究的支持。对来自新西兰陶波火山带汤加里罗火山中心10个不同喷发单元的23个地点的样品进行了研究。采用传统的双重加热法和微波古强度法。古强度数据的可靠性随样品的岩石磁性而变化，特别是与它们在熔岩流中的位置相对应。最高的成功率来自流顶附近的样品，在那里有相当大比例的剩磁在中温(200-350℃)下不受阻。相比之下，来自血流中心的样本，特别是显示板状骨折的部分，成功率最低。获得了可靠、高质量的古强度结果，范围为32.4±5.1μT至72.1±44.7μT，年龄约为12800年至今。这些虚拟偶极矩对应于虚拟偶极矩，从全新世早期的52°±10.10 ZAM2增加到大约300年前的112°±11.14 ZAM2。这些数据与从新西兰湖泊沉积物中标定的相对古强度很好地吻合。火山和沉积数据一起得出了全新世虚拟轴向偶极矩曲线，该曲线与全新世早期的全球平均变化很好地吻合，但在最近数千年却有很大的不同。这种差异与最近南高纬度核-地幔边界通量叶向新西兰迁移有关，正如在全球场模型中所看到的那样。
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 ZAm2in the early Holocene and peak at 112 ± 14 ZAm2about 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.