The Origin of Bimodal Volcanic Suites: A Study of Newberry Volcano, Oregon

双峰式火山作用的成因一直是火成岩岩石学中一个特别长期存在的问题。该项目旨在了解玄武岩-流纹岩双峰火山岩套的岩石学过程。一些岩石成因研究认为，这种火山岩套是由在单一、大型、长寿的岩浆室中运行的机制形成的，在那里需要复杂的AFC过程来解释双峰套岩中的成分变化。据此认为，双峰型岩套是镁铁质岩浆反复注入地壳形成的。这些小体积的天体导致地壳的部分融化。玄武岩-流纹岩岩浆是在一系列不相连的小型储集层中产生的。在短时间内大面积喷发的熔岩可能只与它们共同的深熔起源有关。反复注入镁铁质岩浆，以及随后的地壳部分熔融和熔融结晶，将使长期存在的火山系统之下的地壳性质发生重大变化。最近的地球物理研究和出色的地质约束使这座火山成为测试这一提议模型的理想之选。全新世熔岩将被用来测试这个火山岩套在小而不相连的岩浆室中的生成。然后，将通过比较全新世和更新世火山岩套的差异来检验地壳蒸馏模型的适用性，以确定熔岩特征的时间变化是否与预测相符。这一模型的确认可能会极大地影响岩石学家对岩浆房的认识，以及从时间和空间上相关的熔岩对地球化学数据的定量模拟。

The origin of bimodal volcanism has been a particularly persistent problem in igneous petrology. This project seeks to understand the petrologic processes responsible for bimodal basalt-rhyolite volcanic suites. Some petrogenetic studies have assumed such volcanic suites formed by mechanisms operating in a single, large, long-lived magma chamber, where complex AFC processes are required to explain the compositional variations in bimodal suites. Here it is suggested that bimodal suites are produced by repeated injection of mafic magma into the crust. These small volume bodies cause partial melting of the crust. Basalt-rhyolite magmas are generated in a series of small, unconnected reservoirs. Lavas erupted over a large area within a short time may be related only by their common anatectic origin. Repeated injection of mafic magma, and subsequent crustal partial fusion and melt crystallization will generate significant changes in the character of the crust beneath long-lived volcanic systems. Recent geophysical studies and excellent geologic constraints make this volcano ideal for testing this proposed model. Holocene lavas will be used to test the generation of this volcanic suite in small unconnected magma chambers. Then the applicability of the crustal distillation model will be tested by comparing differences in the Holocene and Pleistocene volcanic suites to determine if temporal changes in lava characteristics agree with predictions. Confirmation of this model could dramatically affect petrologists' perceptions of magma chambers and quantitative modelling of geochemical data from temporally and spatially related lavas.