Paleomagnetism of Keweenawan Intrusive Rocks, Minnesota
Paleomagnetism of Keweenawan Intrusive Rocks, Minnesota
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明尼苏达州 Keweenawan 侵入岩的古地磁学
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发表时间：
1970
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通讯作者：
M. Beck
中科院分区：
文献类型：
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作者：
M. Beck
对明尼苏达州Keweenawan侵入岩131个正常磁化点的古地磁极位置进行了计算，结果表明：Keweenawan侵入岩的古地磁极位置为34.5°N，168.5°W。逆（R）极性的辉长岩和双辉岩也是已知的，但仅限于靠近加拿大边境的北方库克县的有限区域。R-极性站点产生的极点位置为42.5°N，156.5°W，可能比N-极性站点更古老。这些岩石中的磁场强度变化了4个数量级，与其他强烈的岩性差异保持一致，共同反映了活跃的岩浆分异作用。侵入岩中的磁方向分散表明，自Keweenawan时代以来，非偶极与偶极场强之比没有明显变化。据认为，根据目前的证据，明显的极地漂移相对于北美是最好的描述，而模糊定义的西南走向的路径几十度的宽度。在有利的情况下，极移路径内的位置可用于地质对比。北美前寒武纪玄武岩火山活动的几个事件被用来说明古地磁技术的长距离相关。
A paleomagnetic pole position calculated for 131 sites in normally (N) magnetized Keweenawan intrusive rock from Minnesota lies at 34.5°N, 168.5°W. Gabbro and diabase of reverse (R) polarity also are known but only from a limited area in northern Cook County, near the Canadian border. R-polarity sites yield a pole position of 42.5°N, 156.5°W and probably are older than the N-polarity sites. Magnetic intensities in these rocks vary by 4 orders of magnitude, in keeping with other strong differences in lithology, which together reflect active igneous differentiation, Dispersion of magnetic directions in the intrusive rocks indicates that the ratio of nondipole to dipole field-intensity has not changed markedly since Keweenawan time. It is suggested that, on the basis of current evidence, apparent polar wandering relative to North America is best described by a rather vaguely defined southwestwardly trending path several tens of degrees in width. Under favorable circumstances positions within the path of polar wandering can be used for geological correlation. Several episodes of Precambrian basaltic volcanism in North America are used to illustrate long-distance correlation by paleomagnetic techniques.