Abstract Voluminous early to middle Pleistocene pyroclastic flow deposits were generated from Mount Aragats (Aragats Volcanic Province, AVP), one of the largest volcanoes in the Arabia-Eurasia continental collision zone. Here we report paleomagnetic results, in combination with anisotropy of magnetic susceptibility (AMS) analysis, from 31 outcrops belonging to six ignimbrite units of the western part of the AVP (covering an area of more than 5000 km2). Paleomagnetic directions analysis of samples from 26 outcrops of the three younger ignimbrite units yields a well-defined normal polarity direction of D = 339.2°, I = 55.7°, k = 278.4 and α95 = 1.7°. The virtual coincidence of the paleomagnetic directions seems to point to an emplacement of the units within a restricted time of similar geomagnetic secular variation (i.e., few hundred years). However, new isotope 40Ar/39Ar ages of the three units suggest two separated events at ~0.65 and ~ 0.75 Ma. We cannot fully exclude the possibility of similar paleomagnetic directions at 0.65 and 0.75 Ma or the occurrence of a widespread remagnetization event at 0.65 Ma, but both scenarios are highly unlikely. In contrast to that, five sites from the three older units all show reversed magnetic polarity, which implies an age of emplacement older than the last magnetic polarity reversal at ~780 ka. This agrees with recent 40Ar/39Ar ages of the three older units at ~0.93 Ma. The paleomagnetic scatter of the older units is high compared to the younger ones. Even if paleomagnetic directions and radiometric age are similar, available data cannot unequivocally indicate if the three older units were generated from the same or three different eruptions. The high quality AMS data result in three different types of fabric (lineated, foliated and undetermined) that are all commonly observed in the studied pyroclastic deposits. Accordingly, we use lineation, tilt of foliation, or both for the determination of paleoflow direction. Results reveal a radial flow pattern surrounding Mt. Aragats, which is, however, highly influenced by topographic features, such as valleys, even in proximity of the eruption center.

中文翻译：

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亚美尼亚西部更新世熔凝灰岩 - 古地磁和磁各向异性对流动方向和地层的限制

摘要 大量早至中更新世火山碎屑流沉积物产生于阿拉加特山（阿拉加特火山省，AVP），该火山是阿拉伯-欧亚大陆碰撞带中最大的火山之一。在这里，我们报告了古地磁结果，并结合磁化率各向异性 (AMS) 分析，来自属于 AVP 西部（覆盖面积超过 5000 平方公里）的六个熔凝岩单元的 31 个露头。对来自三个较年轻的火山熔岩单元的 26 个露头的样品进行古地磁方向分析，得出明确定义的法向极性方向为 D = 339.2°、I = 55.7°、k = 278.4 和 α95 = 1.7°。古地磁方向的虚拟重合似乎表明这些单位在类似地磁长期变化的有限时间内（即几百年）就位。然而，三个单元的新同位素 40Ar/39Ar 年龄表明在 ~0.65 和 ~0.75 Ma 处有两个分离的事件。我们不能完全排除在 0.65 和 0.75 Ma 处古地磁方向相似或在 0.65 Ma 处发生大范围再磁化事件的可能性，但这两种情况都极不可能。与此相反，来自三个较旧单元的五个站点都显示出反转的磁极，这意味着就位年龄比上一次磁极反转时的~780 ka 还要早。这与三个较旧单元最近的 40Ar/39Ar 年龄一致，约为 0.93 Ma。与较年轻的单元相比，较旧的单元的古地磁散射率较高。即使古地磁方向和辐射年龄相似，可用数据也不能明确表明三个较旧的单元是由相同的还是三个不同的喷发产生的。高质量的 AMS 数据产生了三种不同类型的织物（线状、叶状和未确定），它们在所研究的火山碎屑沉积物中都很常见。因此，我们使用线状、叶理倾斜或两者来确定古流向。结果揭示了围绕 Mt. 的径向流动模式。然而，即使在喷发中心附近，阿拉加特也受到地形特征的高度影响，例如山谷。