Collaborative Research: Record of Mafic Inputs to an Arc Magma System: Analysis of Enclaves and Their Host Lavas Cored During Phase I, Unzen Scientific Drilling Program

Eichelbergerstrom-0106834本提案寻求支持，以使PI参与对日本云仙科学钻探项目（USDP）第一阶段期间获得的样品进行的国际合作地球化学调查。USDP是国际大陆钻探计划（ICDP）的一个发展中项目，旨在利用钻探作为一种工具来促进对大陆地壳基本过程的理解。美国通过国家科学基金会，是综合社区发展项目的主要伙伴和资金来源。USDP的目标是了解云仙火山作为一类重要的安山质弧火山的代表的喷发行为。这将通过钻探、钻孔观察和岩心分析计划来完成，并与正在进行的地表地质和地球物理研究以及最近火山爆发期间进行的一系列卓越的地球物理和地球化学观察相补充。这一毁灭性事件发生在1991年至1994年期间，夺去了44人的生命，造成了大约20亿美元的损失，在项目的第一阶段-通过本提案要求得到支持-正在向建筑物底部钻750米和1 500米的侧孔，以便获得火山活动的完整的物理和化学记录。与此同时，也将根据这一请求得到支持，将对第二阶段进行规划，在该阶段将获得通过管道的多个岩心部分，以解决岩浆运输和脱气问题。这些观察将有助于理解富水岩浆喷涌喷发的悖论。这一工作的总体科学原理和计划已在ICDP的提案中提出，并将在此以简要形式重复，以提供背景。ICDP本身只支持钻探，而不支持相关科学，因此需要提出这一要求。最近云岑、皮纳图博和苏弗里埃山火山的喷发生动地证明了这样一个概念，即镁铁质岩浆注入地壳淤泥是一个重要的岩石学过程和火山触发因素。这些事件的高可见度有助于加强火山岩和深成岩工作者之间的对话，并重振了对镁铁质包体和不平衡斑晶组合的调查。一个基本的问题变成了：我们如何将这些由镁铁质充注或补充所产生的岩浆系统的开放系统行为的产物与更广泛的地壳深成岩作用和火山作用相适应？这个问题的一个子集，这一建议试图回答，是：什么是长期的岩石学后果的重复镁铁质输入地壳岩浆系统？迄今为止的研究已经阐明了单个事件的喷发产物或查看了许多这类事件的最终产物的镁铁质和层状侵入体（MASLI）的形式采样。我们希望研究50万年云仙火山喷发提供的时间序列，以描述该系统的输入，并了解它们对其化学演化的影响。这项工作将与日本在确定火山序列的年代和记录火山地质和化学演变方面的补充努力相协调。

EichelbergerEAR-0106834This proposal seeks support for the PIs to participate in internationally collaborative geochemical investigations of samples now being obtained during the first phase of the Unzen Scientific Drilling Project (USDP), Japan. USDP is a developing project of the International Continental Drilling Program (ICDP), which seeks to use drilling as a tool to advance understanding of fundamental processes of continental crust. The United States is a major partner and funding source for ICDP, through the National Science Foundation. The goal of USDP is to understand the eruptive behavior of Unzen as representative of an important class of andesitic arc volcanoes. This is to be done through a program of drilling, borehole observation, and core analysis in complement with ongoing surface geological and geophysical studies as well as the remarkable suite of geophysical and geochemical observations made during the recent eruption. That devastating episode occurred during 1991 to 1994, claimed 44 lives, and did some $2 billion in damage.In the first phase of the project, for which support is requested through this proposal, flank holes of 750 m and 1500 m are being drilled to the base of the edifice in order to obtain a complete physical and chemical record of the volcano's activity. Simultaneously, and also to be supported under this request, planning will be undertaken for the second phase in which multiple core sections through the conduit will be obtained in order to address problems of magma transport and degassing. These observations will aid in understanding the paradox of effusive eruption of water-rich magma. The overall scientific rationale and plan for this undertaking are presented in the proposals to ICDP and will be repeated in condensed form here to provide context. ICDP itself supports drilling only, not the associated science, hence the need for this request.Recent eruptions of Unzen, Pinatubo, and Soufriere Hills volcanoes have graphically demonstrated the concept that injection of mafic magma into a crustal slush is an important petrologic process and a volcanic trigger. The high visibility of these events has served to strengthen a dialog between workers on volcanic and plutonic rocks, and reinvigorated the investigation of mafic enclaves and disequilibrium phenocryst assemblages. A basic question has become: how do we fit these products of open system behavior of magma systems, produced by mafic recharge or replenishment, into the broader picture of crustal plutonism and volcanism? A subset of that question, which this proposal seeks to answer, is: What are the long term-petrologic consequences of repeated mafic inputs to the crustal magma system? Studies to date have elucidated single events as sampled by eruption products or viewed the end product of many such events in the form of mafic and silicic layered intrusions (MASLI). We wish to look at the time series provided by 500,000 years of Unzen eruptions, to characterize the inputs to the system and understand their influence on its chemical evolution. The work will be coordinated with complementary efforts in Japan on dating the sequence and documenting the geologic and chemical evolution of the volcano.