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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Magnetic fabric and palaeomagnetic analyses of the Plio-Quaternary calc-alkaline series of Aegina Island, South Aegean volcanic arc, Greece
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Magnetic fabric and palaeomagnetic analyses of the Plio-Quaternary calc-alkaline series of Aegina Island, South Aegean volcanic arc, Greece

机译：希腊南爱琴海火山弧埃伊纳岛的Plio-第四纪钙碱性系列的磁性织物和古地磁分析

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摘要

The South Aegean volcanic arc represents the magmatic expression of active subduction of the African plate beneath Eurasia in the region of Greece. Plio-Quaternary calc-alkaline (dacite and andesite) lava flows exposed on the island of Aegina have been sampled for palaeomagnetic analyses to determine whether the western arc area has experienced vertical axis rotations. In addition, these units allow an assessment of the use of magnetic fabric (anisotropy of magnetic susceptibility; AMS) data as indicators of lava flow directions in silicic extrusive rocks, providing a complement to the existing literature on AMS of basaltic flows. The magnetic mineralogy of both dacites and andesites is dominated by fine-grained magnetite/Ti-poor titanomagnetite. Sampled flows are characterised by oblate magnetic fabrics at site level which are co-axial to flow surfaces, although most sites also contain specimens with prolate AMS ellipsoids. Where magnetic lineations are developed, they are systematically aligned either parallel or orthogonal to average (exposurscale) lava flow directions. Magnetic lineations in these rocks, therefore, may be interpreted in terms of flow directions only when the latter are known a priori. Observed variability in the directions of remanent magnetisation recorded by the Aegina lava flows may be explained wholly in terms of geomagnetic variations. Several sites record spot readings of the geomagnetic field during polarity transitions. Scatter of directions at the remaining sites is consistent with that expected from secular variation. Post-eruption tilting of magnetisation vectors is shown to be limited. The in situ mean direction of magnetisation of the non-transitional sites is indistinguishable from the geocentric dipolar field used as a reference direction for these young (＜5 Ma) rocks. This indicates that the island has not experienced significant Plio-Quaternary tectonic rotations, in contrast to other parts of the Aegean volcanic arc. The magnetic data also further constrain the timing of volcanic activity in the western part of the South Aegean arc, when used in conjunction with existing radiometric and stratigraphic ages. The most recent volcanic products are shown to correlate with the Pleistocene part of the Matuyama polarity epoch. The Aegina volcanic centre has, therefore, been inactive for at least the last 720 000 yr, in contrast to the historical activity further to the east on Santorini.
机译：南爱琴海火山弧代表了希腊地区欧亚大陆下非洲板块活跃俯冲的岩浆表现。已对暴露于埃伊纳岛上的第四纪第四纪钙碱性（达克石和安山岩）熔岩流进行了古地磁分析，以确定西弧区是否经历了垂直轴旋转。此外，这些单元可以评估磁性织物（硅磁化率各向异性; AMS）数据作为硅质挤压岩中熔岩流向指标的用途，为现有有关玄武岩流AMS的文献提供了补充。天然铁矿和安山岩的磁性矿物学均以细粒磁铁矿/贫钛钛磁铁矿为主。采样流的特征是在站点级别上与流动表面同轴的扁圆形磁性织物，尽管大多数站点还包含带有扁平AMS椭球的样本。在磁力线发育的地方，它们被系统地排列成平行或正交于平均（火山灰）熔岩流的方向。因此，只有先验地知道这些岩石中的磁线，才能根据流动方向进行解释。由埃伊纳火山熔岩流记录的在剩余磁化方向上观察到的变化可以完全用地磁变化来解释。几个站点记录了极性转换过程中地磁场的点读数。其余部位的方向散射与预期的长期变化一致。喷发后磁化矢量的倾斜被证明是有限的。非过渡部位的原位平均磁化方向与作为这些年轻（＜5 Ma）岩石参考方向的地心偶极场没有区别。这表明与爱琴海火山弧的其他部分相比，该岛没有经历过明显的第四纪-第四纪构造旋转。当与现有的辐射时代和地层时代结合使用时，磁数据还进一步限制了南爱琴弧线西部火山活动的时间。已显示最新的火山产物与Matuyama极性时代的更新世部分相关。因此，埃伊纳岛火山中心至少在过去72万年中一直处于非活动状态，这与圣托里尼岛以东更远的历史活动形成了鲜明的对比。

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