Paleointensity variation across the Matuyama-Brunhes polarity transition: Observations from lavas at Punaruu Valley, Tahiti
Paleointensity variation across the Matuyama-Brunhes polarity transition: Observations from lavas at Punaruu Valley, Tahiti
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DOI：
10.1029/2010jb008093
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发表时间：
2011-06
影响因子：
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通讯作者：
N. Mochizuki;H. Oda;O. Ishizuka;T. Yamazaki;H. Tsunakawa
中科院分区：
文献类型：
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作者：
N. Mochizuki;H. Oda;O. Ishizuka;T. Yamazaki;H. Tsunakawa
[1]我们对塔希提岛普纳鲁山谷34个连续熔岩流中记录的松山 - 布容（M - B）极性转换进行了古强度研究。记录的下部呈现反向极性，主要方向变化来自记录的中部，上部则记录为正向极性。这些古地磁方向以及五个\(^{40}Ar/^{39}Ar\)年龄（加权平均值为\(771±8\)（\(1\sigma\)）千年）表明，30个熔岩流记录了跨越M - B转换的地磁场。来自32个熔岩流的215个标本采用了肖氏方法的双加热技术并结合低温退磁（LTD - DHT肖氏方法），从18个熔岩流中获得了73个成功结果。在主要方向变化之前的反向极性时期，古强度在3到38微特斯拉之间呈现类似振荡的变化，对应虚拟偶极矩（VDMs）在\(0.9×10^{22}\)到\(9.6×10^{22}\)安平方米之间。在主要方向变化期间，获得了5微特斯拉的弱古强度，其虚拟偶极矩为\(1.0×10^{22}\)安平方米。在正向极性时期，古强度为14 - 21微特斯拉，虚拟偶极矩为\(3.5 - 5.2×10^{22}\)安平方米。在主要方向变化之前的反向极性时期，在虚拟偶极矩与虚地磁极纬度的关系图上可识别出相关系数为0.96的线性关系。这种线性关系可能是M - B转换开始时地球发电机的一种前兆特征。
[1] We have conducted a paleointensity study of the Matuyama-Brunhes (M-B) polarity transition recorded in 34 successive lava flows of Punaruu Valley on Tahiti. A reversed polarity is obtained from the lower part of the record, major directional changes are derived from the middle part of the record, and a normal polarity is recorded in the upper part of the record. These paleomagnetic directions and five 40Ar/39Ar ages yielding a weighted mean of 771 ± 8 (1σ) ka indicate that 30 lava flows recorded the geomagnetic field across the M-B transition. The 215 specimens from 32 flows were subjected to the double-heating technique of the Shaw method combined with low-temperature demagnetization (LTD-DHT Shaw method), yielding 73 successful results from 18 flows. For the reversed polarity period just prior to the major directional changes, paleointensity shows an oscillation-like variation between 3 and 38 μT corresponding to virtual dipole moments (VDMs) between 0.9 × 1022 and 9.6 × 1022 Am2. For the major directional changes, a weak paleointensity of 5 μT is obtained, which gives a VDM of 1.0 × 1022 Am2. For the normal polarity period, paleointensities are 14–21 μT, giving VDMs of 3.5–5.2 × 1022 Am2. For the reversed polarity period just prior to the major directional changes, a linear relationship with a correlation coefficient of 0.96 is recognized on the diagram of VDM versus virtual geomagnetic pole latitude. This linear relationship may be a precursory feature of the geodynamo at the onset of the M-B transition.