Microanalysis of Oxygen Isotope Ratios in Zircon

9902973谷这项研究将采用氧同位素比值（d18-O）在火成岩作为监测，否则无法观察到的过程中，在深地壳和上地幔。由于氧是地壳和地幔中的主要元素，其同位素稳定，只有在近地表的低温过程中才形成与平均地幔d18-O值的较大差异。当这种高度分馏的岩石被深埋或俯冲时，如果它们参与岩浆的成因或混染，则它们独特的d18-O很容易被识别。在过去，这类研究一直受到岩浆期后蚀变的阻碍，但最近发展的技术允许对耐蚀变的耐火矿物锆石进行分析。用激光和原位离子微探针对已测得年龄的锆石（U-Pb）进行了高精度的分析。锆石样品将包括已知最古老的地球样品，金伯利岩中的地幔巨晶，以及来自美国西部的构造良好的岩石。主要目标包括：d18-O与年龄的相关性，该年龄监测地壳随时间的成熟，以及埋藏在上地幔和地壳深部的地表衍生岩石的异常区域的映射。本研究的其他方面将进一步发展锆石氧同位素比值作为岩石学和构造学研究的一种强有力的新工具。

9902973ValleyThis study will employ oxygen isotope ratios (d18-O) in igneousrocks as a monitor of otherwise unobservable processes in the deep crustand upper mantle. Because oxygen is the dominant element in the crust andmantle, and its isotopes are stable, large differences from the averagemantle d18-O value are only formed during low temperature processes nearthe surface of the Earth. When such highly fractionated rocks are deeplyburied or subducted, their distinctive d18-O is readily recognized if theybecome involved in the genesis or contamination of magmas. In the past,such studies have been hindered by post-magmatic alteration, but recentlydeveloped technology permits analysis of the refractory mineral zirconwhich is resistant to alteration. Analysis of previously age-dated (U-Pb)zircons will be made at high analytical precision by laser and in situ byion microprobe. Zircon samples will include the oldest known samples of theEarth, mantle megacrysts from kimberlite, and tectonically well constrainedrocks from the western U.S. Major goals include: correlation of d18-O withage which monitors the maturation of the crust through time, and mapping ofanomalous regions of surface-derived rocks buried in the upper mantle anddeep crust. Other aspects of this study will further develop the use ofoxygen isotope ratios in zircon as a powerful new tool for petrologic andtectonic studies.