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Paleomagnetism of the Pleistocene Tequila Volcanic Field (Western Mexico)

机译：更新世龙舌兰火山场（西墨西哥）的古磁性

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This paper presents new paleomagnetic results from 24 independent cooling units in Tequila area (western Trans-Mexican Volcanic Belt). These units were recently dated by means of state-of-the-art 40Ar-39Ar method (Lewis-Kenedy et al ., 2005) and span from 1130 to 150 ka. The characteristic paleodirections are successfully isolated for 20 cooling units. The mean paleodirection, discarding intermediate polarity sites, is I = 29.6°, D = 359.2°, k = 26, α95 = 7.1°, n = 17, which corresponds to the mean paleomagnetic pole position P lat = 85.8°, P long = 84.3°, K = 27.5, A 95 = 6.9°. These directions are practically undistinguishable from the expected Plestocene paleodirections, as derived from reference poles for the North American polar wander curve and in agreement with previously reported directions from western Trans-Mexican Volcanic Belt. This suggests that no major tectonic deformation occurred in studied area since early-middle Plestocene to present. The paleosecular variation is estimated trough the study of the scatter of virtual geomagnetic poles giving SF = 15.4 with SU = 19.9 and SL = 12.5 (upper and lower limits respectively). These values are consistent with those predicted by the latitude-dependent variation model of McFadden et al . (1991) for the last 5 Myr. The interesting feature of the paleomagnetic record obtained here is the occurrence of an intermediate polarity at 671± 13 ka which may correspond the worldwide observed Delta excursion at about 680-690 ka. This gives the volcanic evidence of this event. Two independent lava flows dated as 362± 13 and 354± 5 ka respectively, yield transitional paleodirections as well, probably corresponding to the Levantine excursion.
机译：本文介绍了来自龙舌兰酒区（西跨墨西哥火山带）的24个独立冷却装置的新古磁结果。这些单元最近通过最先进的 40 Ar- 39 Ar方法（Lewis-Kenedy等，2005）进行了测量，时间跨度为1130年至150 ka。成功隔离了20个冷却单元的特征古方向。抛弃中间极性位点的平均古方向为I = 29.6°，D = 359.2°，k = 26，α 95 = 7.1°，n = 17，对应于平均古磁极位置P lat = 85.8°，P long = 84.3°，K = 27.5，A 95 = 6.9°。这些方向实际上与预期的上新世古方向没有区别，后者是从北美极地漂移曲线的参考极推导出的，并且与先前报道的西墨西哥跨火山带的方向一致。这表明，自上中更新世以来至今，研究区未发生大的构造变形。通过研究虚拟地磁极的散射（S F = 15.4，S U = 19.9和S L =）来估计古土壤的变化12.5（分别为上限和下限）。这些值与McFadden等人的纬度相关变异模型预测的值一致。 （1991）中的最后5个Myr。此处获得的古磁记录的有趣特征是在671±13 ka处出现中间极性，这可能与全世界在680-690 ka处观测到的Delta偏移相对应。这提供了此事件的火山证据。两个分别为362±13和354±5 ka的独立熔岩流也产生过渡的古方向，可能对应于黎凡特偏移。

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