Collaborative Research: Paleomagnetism and Geochronology of the Mono Lake Event [?] Recorded in the Lava Section at Santa Maria Volcano, Guatemala

密歇根理工大学和威斯康星大学麦迪逊分校发起了一项合作研究项目，以验证圣玛丽亚火山火山口壁暴露的熔岩流记录了被称为莫诺湖事件的地磁偏移的假设，并且该事件的范围是全球性的。莫诺湖是许多被提出的地磁不稳定的短暂时期之一，它使地球的地磁场在更长的时间间隔内处于恒定的正常或反向极性。其中一些短暂的不稳定性影响全球地磁场，而另一些则在程度上更局部。在这两种情况下，这些不稳定时期或地磁场的偏移通常是用古地磁方向在岩石记录中表示的，这些古地磁方向的变化超出了长期变化的正常范围，几乎完全逆转。全球性的、精确测年的断层是重要的地层标志，对理解地球动力学过程至关重要。迄今为止，关于Mono湖漂移是否是一个全球性事件，仍然存在相当大的争论，因为以前的研究要么来自沉积物，测年有问题，定向数据不如火山岩可靠，要么来自火山岩研究缺乏精确的放射性同位素年龄，或者基于不完整的古地磁数据。因此，本研究的目的是利用古地磁技术全面表征圣玛丽亚火山火山口壁暴露的熔岩流记录的地磁变化（从而确定Mono湖事件），并利用40Ar/39Ar增量加热法精确确定地磁事件的年龄。如果40Ar/39Ar年龄证实了圣玛丽亚熔岩流记录了莫诺湖事件的假设，那么就有明确的证据表明这种地磁偏移是全球性的。此外，圣玛丽亚熔岩流的40Ar/39Ar年龄的明确定义，将为圣玛丽亚火山锥生长后期的火山通量提供重要的边界条件。至于这项研究的更广泛方面，密歇根理工大学与危地马拉监测和灾害机构（insvumeh和CONRED）的火山学家密切合作超过35年，发展了一种协同关系，该大学提供了先进的实验室和研究应用程序，这些火山学家为获取相关样品提供了强有力的现场背景。近年来，几位中美洲火山学家获得了密歇根理工大学的学位。这项研究将延续这一传统，将一位危地马拉火山学家带到美国，在密歇根理工大学的古地磁实验室进行研究，并参与威斯康星大学麦迪逊分校圣玛丽亚熔岩流的年代测定。在完成硕士学位后，这位火山学家将回到危地马拉，在那里他有望在几十年的重要火山灾害工作中发挥领导作用。

Michigan Technological University and the University of Wisconsin-Madison have initiated a collaborative research project to test the hypothesis that the lava flows exposed in the crater wall of Santa Maria Volcano record a geomagnetic excursion known as the Mono Lake Event and that this event is global in extent. The Mono Lake is one of many proposed short-lived periods of geomagnetic instability that riddle Earth's geomagnetic field within longer intervals of constant normal or reversed polarity. Some of these short-lived instabilities affect the geomagnetic field globally whereas others are more local in extent. In either case, these periods of instability or excursions of the geomagnetic field are generally expressed in the rock record by paleomagnetic directions whose variation is outside the normal bounds of secular variation to the point of being almost fully reversed. Excursions which are global and have been dated precisely are important stratigraphic markers and are critical to understanding geodynamo processes. To date, there remains considerable debate as to whether the Mono Lake excursion is a global event as previous studies either are from sediments where dating is problematic and directional data not as reliable as from volcanic rocks or are from studies on volcanic rocks which either lack precise radioisotopic ages, or are based on incomplete paleomagnetic data. Therefore, the objective of this research is to fully characterize the geomagnetic variations (and therefore the Mono Lake Event) recorded by the lava flows exposed in the crater wall of Santa Maria Volcano using paleomagnetic techniques and to precisely determine age of the geomagnetic event using the 40Ar/39Ar incremental heating method. If the 40Ar/39Ar ages bear out the hypothesis that the Santa Maria lava flows record the Mono Lake event, then there is unequivocal evidence that this geomagnetic excursion is global in extent. An addition, well-defined 40Ar/39Ar ages for the lava flows at Santa Maria will place important boundary conditions on the volcanic flux for the latter stages of growth of the Santa Maria's cone.As for broader aspects of this research, Michigan Tech has worked closely with Guatemalan volcanologists at monitoring and hazards agencies (INSIVUMEH and CONRED) for more than 35 years, developing a synergistic relationship where the University has provided access to advanced laboratory and research applications and these volcanologists supply strong field context for obtaining relevant samples. In recent years, several Central American volcanologists have obtained degrees at Michigan Tech. This research will continue that tradition bringing a Guatemalan volcanologist to the United States to study both in the paleomagnetism laboratory at Michigan Tech and to participate in the dating of the Santa Maria lava flows at the University of Wisconsin-Madison. After completing his MS degree, this volcanologist will return to Guatemala where he is expected to provide leadership in important volcanic hazards work for decades.