Collaborative Research: Timescales of Continental Magmatism and Development of Large Silicic Systems: Insights from Accessory Phases

这个奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。该项目将解决安第斯山脉阿尔蒂普诺-普纳火山杂岩中基岩规模的硅质岩浆系统组装和组织的时间尺度问题。拟议的工作建立在最近的努力基础上，这些努力探索将大型硅质火山田(LSVF)视为通往地壳上部岩层顶部的窗口，这些岩层是大陆地壳的基础。火山活动的时空体积记录表明，LSVF在岩浆爆发期间发展，并以平行超级喷发脉冲的形式间歇性喷发，随着时间的推移变得更加强烈。这一记录通常被认为反映了与之相关的上地壳岩基的积累记录。然而，如果这一观点要得到证实，关于火山和深成领域之间联系的关键问题仍有待解决。其中包括：(1)火山活动的表面模式意味着什么与深部深成系统的发展有关？这些喷发代表着从喷发前形成的一批不同的岩浆中撤离，还是代表了一个长寿的区域岩浆体的周期性敲击？(2)大型破火山口系统的旋回性和喷发的区域一致性意味着什么，关于下面的岩浆系统的发展？静止期代表的是下一批岩浆发育的时间尺度，还是喷发的岩浆发育时间比静止期短得多？3)单个石器时代规模的岩浆系统的自组织，例如一个分区系统的发展，告诉我们这些系统分化和演化的动力学和时间尺度是什么？在APVC日益成熟的时空体积记录的基础上，将特别侧重于三个假设来审查这些问题：(1)APVC中的超级喷发疏散了在喷发前数十万年内积累的不同岩浆批次；(2)旋回超级火山系统的休息期远远长于形成下一批喷发岩浆的时间尺度；以及(3)岩基规模-硅质岩浆室可以在数十万年的时间尺度上形成显著的分带。这些想法将在地质年代学、微量元素地球化学和辅助物相温度测定的基础上进行评估，最明显的是锆石(初步数据表明这一提议成功的可能性很大)。拟议的工作是及时的，将引起广泛的兴趣，因为大型硅质岩浆系统的建造和演化的时间尺度、火山-深成岩浆的联系以及超级火山的发展近年来一直是相当大的讨论主题。此外，该项目还得到了该区域其他研究的补充。皮？S正在合作调查阿根廷的塞罗加兰火山口建筑群，俄勒冈州立大学的同事安妮塔·格兰德正在智利的奥坎奎尔查火山群中研究类似的问题。这些数据集的组合将促进不同规模的系统之间的比较，并提供中央安第斯山脉的广阔前景。国际合作将使首席PI能够继续合作和指导一个新兴的玻利维亚火山学小组，该小组的重点是APVC。出版和传播科学成果，培训一名研究生和一名本科生，并将内容纳入未来的课程，所有这些都扩大了更广泛的影响。此外，通过俄勒冈州的SILE计划和备受瞩目的火山世界网站的在职和职前教师讲习班传播成果，将向更多的非正式科学受众和K-U支持者传播研究结果。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit. This project will address the time scales of assembly and the organization of batholith-scale silicic magma systems in the Altiplano Puna Volcanic Complex (APVC) of the Central Andes. The proposed work builds on recent efforts that explore the recognition of large silicic volcanic fields (LSVFs) as windows into the tops of upper crustal batholiths that are the foundations of the continental crust. The space-time-volume record of volcanism indicates that LSVFs develop during magmatic flare-ups and erupt episodically as pulses of parallel supereruptions that become more intense with time. This record is often assumed to mirror the accumulation record of the associated upper crustal batholith. However, key questions about the link between the volcanic and plutonic realms remain to be addressed if this view is to be substantiated. Among these are: (1) What does the surface pattern of volcanism imply concerning the development of plutonic systems at depth? Do these eruptions represent evacuation from a distinct batch of magma that formed just prior to eruption or do they represent the periodic tapping of a long lived regional magma body? (2) What does the cyclicity of large caldera systems and the regional concordance of eruptions imply concerning the development of the magmatic systems beneath? Does the repose period represent the time scale of development of the next magma batch or does the erupted magma develop in a timescale much shorter than the repose period. 3) What does the self-organization of single batholithic scale magmatic systems, for instance the development of a zoned system, tell us about the dynamics and time scales over which these systems differentiate and evolve? Building on the maturing space-time-volume record of the APVC, these issues will be examined by specifically focusing on three hypotheses: (1) Supereruptions in the APVC evacuated distinct magma batches that accumulated within a few hundred thousand years prior to eruption; (2) The repose period of cyclic supervolcanic systems is considerably longer than the time scale to develop the next eruptible magma batch; and (3) Batholith scale-silicic magma chambers can develop significant zonations on time scales of a few hundred thousand years. These ideas will be evaluated on the basis of geochronology, trace element geochemistry, and thermometry of accessory phases most notably zircon (for which preliminary data suggest strong likelihood of success of this proposal.Broader Impacts. The proposed work is timely and will be of broad interest because time scales of construction and evolution of large silicic magmatic systems, the volcano-plutonic connection and the development of supervolcanoes have been the subject of considerable discussion in recent years. Moreover, this project is complemented by other studies in the region. The PI?s are collaborating on an investigation of the Cerro Galan resurgent caldera complex in Argentina, and Oregon State University colleague Anita Grunder is working on similar problems at the Aucanquilcha Volcanic Cluster, Chile. Combination of these datasets will facilitate comparison across different scales of systems and provide a Central Andean wide perspective. International collaboration will allow the lead PI to continue his collaboration and mentoring of a burgeoning Bolivian volcanological group focused on the APVC. Publication and dissemination of the scientific results, the training of a graduate and an undergraduate student, and incorporation of content into future coursework all amplify the broader impacts. Moreover, dissemination of results through in-service and pre-service teacher-workshops with the SMILE program in Oregon and the high profile VolcanoWorld website will transmit findings to the larger informal scientific audience and K-U constituency.