Laboratory Measurements of Trace Element Partition Coefficients Between Zircon, Aqueous Fluid and Silicate Melt at High and Ultrahigh Pressures

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。在高压和超高压下对锆石、水溶液和硅酸盐熔体之间的微量元素分配系数进行实验室测量。尽管锆石被广泛用于确定地质事件的年代和确定地壳岩石的来源(地幔与再循环地壳)，但它还没有发展成为表征流体-岩石相互作用的工具。锆石可能被用来测定流体渗透事件的时间，并估计流体的微量元素组成。这对于评估流体在形成高压和超高压(HP和UHP)岩石中的作用特别有用，这些岩石通常形成于俯冲带。建议进行实验室实验，以表征锆石在水溶液和硅酸盐熔体存在下的行为。将在1.5-3.5 Gpa范围内测量P、Na、Ca、Mg、Sc、Sr、Y、Nb、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Tb、Dy、Er、Tm、Yb、Lu、Hf、Pb、Th和U的D(锆石/流体)分配系数。在800-1100°C的亚固相合成(正向)实验中，锆石+石英和锆石+斜纹石组合将在fO2=nno时与不同的流体成分(H2O、1MNaOH、1MHCl)平衡，以测量锆石的水溶解度和D(锆石/流体)值。在类似条件下的再结晶(反转)实验中测得的D(锆石/流体)值将用于测试平衡。将测量的D(锆石/流体)值与最近在相同条件下测量的D(锆石/熔体)值进行比较，以识别热液和岩浆锆石的微量元素模式的显著特征。在1000-1200°C的超固相线实验中，锆石、熔体和水相流体达到平衡，可以同时测量所有25种微量元素的D(熔体/流体)、D(锆石/熔体)和D(锆石/流体)。这些值将与在相同条件下使用其他方法测量的D(锆石/熔体)和D(锆石/流体)值进行比较，以检查内部一致性。晶格应变理论对矿物/流体系统的适用性也将得到测试。对岩浆和热液锆石的微量元素特征进行表征，将有助于更准确地识别热液锆石，并解释现场测量的锆石U-Pb年龄。测量的D(锆石/流体)和D(锆石/熔体)值可以用来估计在俯冲板块或其他HP-UHP环境中与锆石平衡的流体和熔体的组成。锆石分配系数将能够更准确地对断章取义的锆石进行分类，包括Hadean碎屑和捕虏晶锆石，其中一些已被证明含有钻石包裹体，并可用于计算源岩的组成(例如，稀土元素模式)，并通过类比识别源岩的类型(地壳与地幔、花岗岩与英云闪长岩)。该项目将资助一名博士后研究员，一名范德比尔特大学博士生，1-2名未来的硕士或博士生，以及1-2名本科生。它还将通过P.I.参与的一个研究实习项目为1-2名高中生的研究提供资金。结果将由P.I.和学生在国内和国际会议上以及在期刊出版物上公布。私家侦探将继续开展外展活动，比如在小学做报告，出版有关他的研究的通俗描述。在过去的两年里，他撰写或撰写了三篇关于他的研究的流行文章。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Laboratory Measurements of Trace Element Partition Coefficients Between Zircon, Aqueous Fluid and Silicate Melt at High and Ultrahigh PressuresIntellectual Merit. Although zircon is widely used for dating geologic events and identifying the source (mantle versus recycled crust) of crustal rocks, it has not been developed as a tool for characterizing fluid-rock interaction. Zircon could potentially be used to date fluid infiltration events and estimate the trace element composition of fluids. This would be particularly useful for evaluating the role of fluids in the formation of High- and Ultrahigh-Pressure (HP and UHP) rocks that typically form in subduction zones. Laboratory experiments are proposed to characterize the behavior of zircon in the presence of aqueous fluids and silicate melts. D(zircon/fluid) partition coefficients will be measured for P, Na, Ca, Mg, Sc, Sr, Y, Nb, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu, Hf, Pb, Th and U at 1.5-3.5 GPa. In subsolidus synthesis (forward) experiments at 800-1100°C the assemblages zircon + quartz and zircon + baddeleyite will be equilibrated with various fluid compositions (H2O, 1m NaOH, 1m HCl) at fO2 = NNO to allow measurement of zircon aqueous solubility and D(zircon/fluid) values. D(zircon/fluid) values measured in recrystallization (reversal) experiments at similar conditions will be used to test for equilibrium. Measured D(zircon/fluid) values will be compared with D(zircon/melt) values recently measured at the same conditions to identify the distinctive features of the trace element patterns of hydrothermal and magmatic zircons. Supersolidus experiments at 1000-1200°C in which zircon, melt and aqueous fluid are equilibrated will allow simultaneous measurement of D(melt/fluid), D(zircon/melt), and D(zircon/fluid) for all 25 trace elements. These values will be compared with D(zircon/melt) and D(zircon/fluid) values measured at the same conditions using other methods to check for internal consistency. The applicability of lattice strain theory to mineral/fluid systems will also be tested. Characterizing the trace element signatures of magmatic and hydrothermal zircons will allow for more accurate identification of hydrothermal zircons and interpretation of zircon U-Pb ages measured in-situ. Measured D(zircon/fluid) and D(zircon/melt) values can be used to estimate compositions of fluids and melts that equilibrated with zircons in subducting slabs or other HP-UHP settings. Zircon partition coefficients will enable more accurate classification of 'out of context' zircons, including Hadean detrital and xenocrystic zircons, some of which have been shown to contain diamond inclusions, and can be used to calculate the composition of the source rock (e.g., REE pattern) and to identify by analogy the type of source (crust vs. mantle, granite vs. tonalite).Broader Impacts. This project will fund one post-doctoral researcher, one current Vanderbilt Ph.D. student, 1-2 future M.S. or Ph.D. students, and 1-2 undergraduate students. It will also fund the research of 1-2 high school students through a research internship program that the P.I. is involved in. Results will be presented by the P.I. and students at national and international meetings and in journal publications. The P.I. will continue outreach activities such as primary school presentations and publication of popular accounts of his research. He has written or contributed to three popular articles about his research in the last two years.