Collaborative Research: Use and Abuse of Zircon Thermometry - Integrating Modeling, Trace Element Chemistry and Isotopes to Maximize the Use, Limit the Abuse

锆石（ZrSiO 4）可以说是解释大陆地壳演化的最有力的矿物。该提案将利用锆石记录地壳中产生的岩浆的温度历史的能力。我们将特别针对大约10.5亿年前地球历史时期（格伦维尔造山事件）产生的花岗岩。 我们先前的研究表明，这是一个独特的插曲，产生大量的异常热（900-1100摄氏度）的花岗岩岩浆。 这些热花岗岩的指纹包括高锆含量和明显高的锆石模态丰度，其不包含先前锆石的捕虏晶（即，锆石不是从其他地壳岩石中回收的，而是花岗岩的主要化学/矿物学特征）。 对热花岗岩中锆石的初步化学分析表明，锆石还具有高钛含量，这证明了高的锆石结晶温度。对高锆花岗岩结晶历史的计算机模拟也表明，锆石在~1000 oC开始结晶。这些初步结果对地球演化的重要启示是什么？地壳的一个重要特征是，必须有独特的岩石圈条件才能产生如此热的花岗岩。拟议的研究将针对北美东部（弗吉尼亚州谢南多厄市）蓝岭省（格伦维尔）的一套更大的花岗岩进行研究，我们已在该地区发现了一个广泛分布的高锆花岗岩。研究的目的是更彻底地阐明温度历史的格伦维尔花岗岩套件和详细检查的化学和结构的关系，锆石的散装岩石化学和模态矿物学，以更精确地确定的条件下，锆石结晶。我们将进行全岩地球化学分析，使用程序流纹岩MELTS结晶建模，单个锆石颗粒的阴极射线成像以探索潜在的捕虏晶，以及锆石中微量元素和同位素的离子探针分析。这项研究将由来自合作机构的研究生和本科生进行，为未来的地球科学家提供关键培训。

Zircon (ZrSiO4) is arguably the single most powerful mineral for elucidating the evolution of the continental crust. The proposal will take advantage of the ability of zircon to record the temperature history of magma generated in the crust. We will specifically target granites produced in the period of earth history at approximately 1.05 billion years ago (the Grenville orogenic event). Our prior research demonstrated that this is a unique episode for generation of large volumes of exceptionally hot (900-1100 oC) granitic magma. The fingerprint of these hot granites includes high zirconium contents and conspicuously high modal abundance of zircon that does not contain xenocrysts of prior zircon (i.e., the zircon is not recycled from other crustal rocks and represents a primary chemical/mineralogic feature of the granites). Preliminary chemical analysis of the zircon in the hot granites demonstrates that the zircon also has high titanium contents, which prove high zircon crystallization temperatures. Computer modeling of the crystallization history of the high zirconium granites also demonstrates that zircon begins crystallization at ~1000 oC. The important insight from these preliminary results regarding the evolution of the Earth?s crust is that there must be unique lithospheric conditions in order to generate such hot granites. The proposed research will target for study a much larger suite of granites from the Grenville Blue Ridge Province in eastern North America (Shenandoah massif, Virginia) where we have identified a terrane-wide occurrence of high zirconium granites. The purpose of the research is to more thoroughly elucidate the temperature history of the Grenville granite suite and examine in detail the chemical and textural relationship of zircon to the bulk rock chemistry and modal mineralogy, in order to more precisely ascertain the conditions at which the zircon crystallized. We will conduct whole rock geochemical analysis, crystallization modeling using the program rhyoliteMELTS, cathodolomuninescence imaging of individual zircon grains to explore for potential xenocrysts, and ion microprobe analysis of trace elements and isotopes in zircon. The research will be conducted by graduate and undergraduate students from the collaborating institutions, providing critical training for future geoscientists.