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

在大型熔结凝灰岩喷发过程中，缺乏关于破火山口塌陷与喷发进程之间关系的详细现场数据。 我们将研究浮岩和偶然的岩石碎片组成的变化与地层高度和地理位置在化学分区Otowi成员的Bandelier凝灰岩，爆发在1.61 Ma的形成过程中的瓦勒斯破火山口，新墨西哥州。 浮石成分的变化提供了有关熔结凝灰岩侵位叶采样的岩浆体的一部分（S）的信息。 将把岩石碎片岩性与破火山口前地质联系起来，以确定喷口位置，并研究喷口几何形状和位置如何随时间变化。 我们将使用这些数据来限制火山口崩溃的进展，因为岩浆体在喷发过程中排出。 在这个过程中，我们将测试我们的新模型的破火山口的形成，通过横向块滑动后，通过建立堤坝饲料内的发展破火山口的初始通风口。 新的喷口然后打开周围的破火山口边缘作为无支撑块移动，以填补中央空隙，使快速喷发从更深层次的系统。 这个模型可能具有普遍适用性的所有大型大陆火山口及其喷发产物。

Self9910148There 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.