CAREER: Investigating Controls on Arc Flare-ups and the Growth of Lower Continental Crust

拟议的研究计划侧重于研究新西兰菲奥德兰白垩纪岩浆弧的岩浆和热演化，主要目标是确定下弧壳的岩浆构造速度和机制。将利用地质年代学和地球化学数据检验三个假说：1)进入下中地壳的岩浆通量是阶段性的，在空间上是瞬变的，并在大约300万年的短暂高通量事件中达到顶峰；2)深部地壳岩浆来自地幔楔形和先前存在的地壳源，并产生了大量的高压榴辉岩堆积；以及3)弧根经历了不均匀的加热和冷却，这不是简单的单调冷却模型容易解释的，而可能与岩石圈弧根下的软流圈上涌驱动的镁铁质底侵作用相一致。解决这些假设将被用来评估弧根的构建和改造过程，并创建白垩纪Fiordland弧的4维岩石学模型。岩浆弧是地球上的俯冲工厂，在那里产生了大量的中间或安山岩大陆地壳。地球科学中的一个基本问题是，在弧形环境中，地幔部分熔融产生的主要岩浆是贫硅玄武岩，而不是中间安山岩。长期以来，人们一直推测，从玄武岩到安山岩的地幔岩浆演化可能发生在弧根最深处(25-60公里深)，在那里发生了致密矿物的分离结晶、岩浆混合和对原有地壳的同化等基本过程。最近，弧岩的高精度同位素测年导致了这样一种想法，即在以强烈的弧形活动为特征的爆发事件期间，可能会产生大量的岩浆。这些观点表明，岩浆弧中的大陆地壳结构可能是高度间歇性的，我们在现代弧中看到的大部分岩浆地球化学多样化可能发生在岩浆弧根部的短暂时期内。该项目的重点是新西兰菲奥德兰一个独特的陆弧深地壳段，那里的深地壳暴露在25-65公里的古深度。初步数据显示，超过70%的弧根是在一次短暂的高通量事件中就位的，该项目将允许评估这一岩浆弧深部大陆地壳构造的时间和地球化学过程。除了该项目的科学目标外，它还强调将研究与旨在传播从K-12到研究生教育的所有学术水平的知识的动态教学和指导计划相结合。加州州立大学北岭分校(CSUN)的本科生将参加美国和新西兰的实地和实验室研究。拉丁裔少数族裔和女性学生(在地球科学和STEM中的代表性不足的群体)将通过“ROCS”推广计划(CSUN学生的研究机会)招募和指导。“ROCS”计划旨在让CSUN中代表性不足的本科生及早参与和指导研究项目，并通过研讨会和每周会议就毕业生和地球科学的职业道路提供指导。PI和CSUN的学生还将与菲奥德兰国家公园(联合国教科文组织世界遗产)的深湾户外教育信托基金合作，为新西兰南岛各地的K-12学生创建动手的地球科学活动。突出菲奥德兰地质学独特方面的活动和短片将在CSUN主办的网站、YouTube和Vimeo上提供，向公众广泛传播。

The proposed research program focuses on investigating the magmatic and thermal evolution of an exhumed, Cretaceous magmatic arc in Fiordland, New Zealand with the primary goal of determining the tempo and mechanisms of magmatic construction of lower arc crust. Geochronologic and geochemical data will be used to test three hypotheses: 1) magmatic fluxes into the lower and middle crust were episodic, spatially transient, and culminated in a brief, approximately 3 million year high flux event; 2) deep-crustal magmas were derived from both mantle wedge and pre-existing crustal sources and generated voluminous high-pressure eclogitic cumulates; and 3) the arc root experienced heterogeneous heating and cooling that is not easily explained by simple monotonic cooling models, but instead may be compatible with mafic underplating driven by asthenospheric upwelling beneath the lithospheric arc root. Addressing these hypotheses will be used to evaluate processes of arc root construction and modification, and to create a 4-dimensional petrologic model for the Cretaceous Fiordland arc. Magmatic arcs are the subduction factories on earth where large volumes of intermediate, or andesitic, continental crust are created. A fundamental problem in Earth sciences is that the dominant magmas generated from partial melting of the mantle in arc environments are silica poor basalts, rather than intermediate andesites. It has long been speculated that the evolution of mantle-derived magmas from basalt to andesite likely occurs in the deepest roots (25-60 kilometers depth) of arcs where fundamental processes such as fractional crystallization of dense minerals, magma mixing and assimilation of preexisting crust occur. Recently, high-precision isotopic dating of arc rocks has led to the idea that large volumes of magmas may be generated during flare-up events, characterized by intense periods of arc activity. These ideas suggest that continental crustal construction in magmatic arcs may be highly episodic and that much of the geochemical diversification of magmas that we see in modern arcs may occur during brief time periods within the roots of the magmatic arc. This project focuses on a unique, exhumed deep-crustal section of a continental arc in Fiordland, New Zealand where the deep crust is well exposed to 25-65 kilometers paleodepth. Preliminary data suggests that over 70% of the arc root was emplaced during a brief, high-flux event, and this project will allow the evaluation of the temporal and geochemical processes of continental crust construction in the deep roots of this magmatic arc.In addition to the scientific goals of the project, it also emphasizes the integration of research with a dynamic teaching and mentoring program that aims to disseminate knowledge at all academic levels from K-12 to graduate education. California State University Northridge (CSUN) undergraduate students will participate in field and laboratory research in the United States and New Zealand. Latino minority and female students (both underrepresented groups in the geosciences and STEM) will be recruited and mentored through the 'ROCs' outreach program (Research Opportunities for CSUN students). The 'ROCs' program is aimed at early involvement and mentoring of underrepresented undergraduate CSUN students in research projects and providing guidance on graduate and geosciences career paths through workshops and weekly meetings. The PI and CSUN students will also work with the Deep Cove Outdoor Educational Trust in Fiordland National Park (a UNESCO World Heritage site) to create hands-on, geoscience activities for K-12 students from across the South Island of New Zealand. Activities and short videos highlighting unique aspects of Fiordland geology will be available on a CSUN-hosted website, YouTube and Vimeo for broad dissemination to the public.