Collaborative Research: Collapse of the Valles Caldera: An Integrated Lithic and Pumice Compositional Study of the Bandelier Tuff

在大的火成岩喷发过程中，火山口崩塌与喷发过程之间的关系缺乏详细的现场数据。我们将研究Bandelier凝灰岩的Otowi成员的浮石和偶然岩石碎片组成随地层高度和地理位置的变化，该成员于1.61 Ma喷发，形成于新墨西哥州的Valles火山口。浮石成分的变化提供了岩浆体的哪一部分是由点烟煤位瓣取样的信息。岩石碎片岩性将与前火山口地质联系起来，以确定喷口位置，并研究喷口的几何形状和位置如何随时间变化。我们将利用这些数据来限制火山喷发期间岩浆体喷发时火山口崩塌的进程。在这个过程中，我们将测试我们的新破火山口形成模型，通过侧向块体滑动，然后通过在发育中的破火山口内建立岩脉来提供初始喷口。随着未支撑的板块移动，填满中央的空隙，新的喷口会在火山口边缘打开，从而允许从系统的更深层次快速喷发。该模型可能普遍适用于所有大型大陆火山口及其喷发产物。

Wolff9909700There is a lack of field data bearing on the details of how caldera collapse relates to eruption progress during large ignimbrite eruptions. We shall study the variation of both pumice and accidental rock fragment composition with stratigraphic height and geographic position in the chemically zoned Otowi Member of the Bandelier Tuff, erupted at 1.61 Ma during formation of the Valles caldera, New Mexico. Pumice compositional variations supply information about which part(s) of the magma body were sampled by an ignimbrite emplacement lobe. Rock fragment lithologies will be tied to pre-caldera geology to identify vent locations, and to study how vent geometries and positions change with time. We shall use these data to constrain the progress of caldera collapse as the magma body vented during the eruption. In the process, we shall test our new model of caldera formation through lateral block sliding following unbuttressing by establishment of dikes feeding an initial vent inside the developing caldera. New vents then open around the caldera margin as unbuttressed blocks move to fill the central void, allowing rapid eruption from deeper levels in the system. This model potentially has general applicability to all large continental calderas and their eruptive products.