Determination and appraisal of pyroclastic flow directions using magnetic anisotropy on ignimbrites from Mount Aragats, Armenia

利用亚美尼亚阿拉加茨山熔结岩的磁各向异性确定和评估火山碎屑流方向

• 批准号: 273101564
• 负责人: Professor Dr. Valerian Bachtadse
• 金额: --
• 依托单位: Sektion Geophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/273101564?language=en
• 关键词: Determination; appraisal; pyroclastic; flow; directions

Mount Aragats, one of the largest stratovolcanoes on the Turkish-Iranian plateau, is located rather close to Yerevan and only about 30 km from the only nuclear power plant in Armenia (ANPP). Besides a series of lava flows, Mt. Aragats is believed to be the locus nascendi of at least one huge pyroclastic eruption resulting in a widespread ignimbrite sheet with a radius of about 50 km. In contrary to well studied ignimbrite deposits in Europe (e.g. Campanian Ignimbrite, Italy) or the USA (e.g. Bishop Tuff, California), the precise eruption evolution and succession is still rather unconstrained and whether all ignimbrites have originated from Mt. Aragats is still debated. The diversity of geochemical composition and color of the ignimbrites add some uncertainty to the problem. We propose a study using paleomagnetic parameters to add important constraints to the py- roclastic eruption. The workflow will start by constraining the temporal relationship between ignimbrites with different lithological properties by applying paleomagnetic methods in order to determine the direction of the natural remanence. Based on the fact that ignimbrites have a rather fast cooling history it is a well known fact that these rocks record secular variation of the geomagnetic field which can be used to differentiate between flows of different age. In a next step we will analyse the magnetic anisotropy of the rocks and attempt to document how the pyroclastic flows (or flow) evolves and whether and how it is changing its flow characteristics (i.e. radially away from the center or topography controlled). This result can be used to investigate if a large eruption in the future is likely to hit the ANPP or maybe even the capital Yerevan. Finally, we will add rock-magnetic measurements to distinguish the carrier of the magnetic signal, which might help to get information about the thermal evolution of the flow during deposition. During a previous field trip twelve ignimbrite outcrops had already been sampled. Preliminary results show that (a) the magnetic signal of the ignimbrites is very strong, (b) characteristic magnetization directions of ten out of twelve outcrops are of normal polarity, (c) whereas the remaining two are of inverse polarity and (d) the magnetic mineral content varies slightly. These results will be enlarged in order to obtain a statistically significant data set. Preliminary results of the anisotropy of magnetic susceptibility at one outcrop to the south of Mt. Aragats (IG3) shows a tight clustering and suggests a southward direction of the flow radially away from Mt. Aragats. A short fieldtrip to Armenia will be used to add additional samples from sites previously unsam- pled to the collection.

阿拉加特火山是土耳其-伊朗高原上最大的层状火山之一，距离埃里温相当近，距离亚美尼亚唯一的核电站(ANPP)仅约30公里。除了一系列的熔岩流外，山上还有。阿拉加茨据信是至少一次巨大火山碎屑喷发的地点，导致了半径约50公里的广泛的点火岩片。与欧洲(如意大利坎帕尼亚纪的Ignimbrite)或美国(如加利福尼亚州的毕晓普凝灰岩)对褐沸石矿床的研究相反，准确的喷发演化和演替仍然相当不受限制，是否所有的褐沸石都起源于Mt.阿拉加茨仍有争议。点火沸石的地球化学成分和颜色的多样性给这个问题增加了一些不确定性。我们建议利用古地磁参数进行研究，以增加对火山碎屑喷发的重要约束。工作流程将首先通过应用古地磁方法来约束具有不同岩性的褐沸石之间的时间关系，以确定自然剩磁的方向。根据点火沸石具有相当快的冷却历史这一事实，众所周知，这些岩石记录了地磁场的长期变化，可以用来区分不同时代的流动。在下一步，我们将分析岩石的磁各向异性，并试图记录火山碎屑流(或流)是如何演化的，以及它是否以及如何改变其流动特征(即径向远离中心或受地形控制)。这一结果可以用来调查未来的一次大喷发是否可能袭击ANPP，甚至首都埃里温。最后，我们将添加岩石磁测量来区分磁信号的载体，这可能有助于获得有关沉积过程中流动的热演化的信息。在之前的一次实地考察中，已经对12个褐煤露头进行了采样。初步结果表明：(A)亮沸石的磁信号很强，(B)12个露头中有10个特征磁化方向为正极性，(C)其余2个为逆极性，(D)磁性矿物含量变化不大。这些结果将被放大，以获得具有统计意义的数据集。南山一个露头磁化率各向异性的初步结果。Aragats(IG3)显示了一个紧密的聚集，表明径向远离山体的流动是向南的。阿拉加特。对亚美尼亚的一次短途实地考察将用于将以前未保存过的遗址的更多样本添加到收集中。