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启动了一个合作研究项目，以检验以下假设：暴露在圣玛丽亚火山火山口墙上的熔岩流记录了被称为莫诺湖事件的地磁漂移，并且这一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，这些不稳定时期在较长的恒定、正常或反转的磁极间隔内困扰着地球的地磁场。其中一些短暂的不稳定性影响全球地磁场，而另一些则更多地影响局部范围。在任何一种情况下，这些不稳定或地磁场漂移的周期通常在岩石记录中用古地磁方向来表示，其变化超出了长期变化的正常范围，几乎完全反转。全球性的、测年准确的偏移量是重要的地层标志，对了解地球发电机过程至关重要。迄今为止，关于莫诺湖漂移是否是全球性事件，仍然存在相当大的争议，因为以前的研究要么来自沉积物，在那里测年有问题，方向数据不如火山岩可靠，要么来自火山岩研究，要么缺乏准确的放射性同位素年龄，要么基于不完整的古地磁数据。因此，这项研究的目的是利用古地磁技术全面刻画圣玛丽亚火山火山口壁上暴露的熔岩流记录的地磁变化(从而确定Mono Lake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，这种地磁漂移是全球性的。此外，圣玛丽亚熔岩流的明确40Ar/39Ar年龄将为圣玛丽亚锥体生长的后期阶段的火山流量设定重要的边界条件。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(INSIVUMEH和CONRED)的火山学家密切合作超过35年，发展了一种协同关系，该大学提供了访问高级实验室和研究应用程序的途径，这些火山学家为获取相关样本提供了强有力的现场背景。近年来，几位中美洲火山学家在密歇根理工大学获得了学位。这项研究将延续这一传统，将一名危地马拉火山学家带到美国，在密歇根理工大学的古地磁学实验室学习，并在威斯康星大学麦迪逊分校参与圣玛丽亚熔岩流的测年。在完成硕士学位后，这位火山学家将返回危地马拉，在那里他有望在那里领导数十年的重要火山灾害工作。

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.