In Situ d18-O and U-Pb Studies of Single Zircons in the Franciscan

本研究将结合联合收割机原位离子探针氧同位素比值分析和加州方济各杂岩高压变质岩中锆石U-Pb年龄。 本研究的目标包括：建立这些岩石的压力-温度-时间-流体（P-T-t-流体）的历史之前，期间和之后的埋藏和折返;确定高压变质岩的原岩;提高地质年代学的可靠性;和测试竞争的理论，如果折返的榴辉岩。样本将从方济各会的知名地点选择，包括沃德溪、詹纳、帕诺奇山口和圣卡塔利纳岛。分析将集中在锆石和伴生矿物。将特别注意晶内同位素分带和矿物包裹体。锆石单点d18 O和年龄的组合将直接耦合时间流体和热事件。我们的初步研究已经描述和分析了来自榴辉岩、蓝片岩和方济各斜长角闪岩的锆石，以及可能代表高压岩石原岩的年轻海底样品（辉长岩、斜长花岗岩、蛇纹岩）。d18 O的分析将使用威斯康星州大学的新Cameca 1280离子微探针。采用斯坦福大学/美国地质调查局SHRIMP-RG进行U-Pb年龄和稀土元素分析。离子探针分析将使用锆石晶体在薄切片和颗粒安装，已被岩石学研究的包裹体和共存的矿物，并通过光学，BSE，CL和X射线成像。这项研究的更广泛的影响包括研究生培训和新的威斯康星州离子微探针实验室的安装，这也将用于其他研究有关的社会问题，如环境修复，古气候学，二氧化碳封存和营养。

This study will combine in situ ion microprobe analysis of oxygen isotope ratios and U-Pb ages on zircon crystals from high pressure metamorphic rocks of the Franciscan Complex, California. The goals of this study include: establishing the pressure-temperature-time-fluids (P-T-t-fluid) history of these rocks before, during and after burial and exhumation; determining the protoliths of the high pressure metamorphic rocks; improved reliability of geochronology; and testing competing theories if exhumation for eclogites. Samples will be chosen from well-known localities in the Franciscan, including Ward Creek, Jenner, Panoche Pass, and Santa Catalina Island. Analysis will focus on zircons and associated minerals. Special attention will be paid to intracrystalline isotope zonation and mineral inclusions. The combination of d18O and age from single spots in zircon will directly couple timing to fluid and thermal events. Our preliminary studies have already described and analyzed zircons from eclogite, blueschist, and amphibolite of the Franciscan, as well as young ocean floor samples (gabbronorite, plagiogranite, serpentinite) that may represent protoliths to high pressure rocks. Analysis of d18O will employ the new Cameca 1280 ion microprobe at the University of Wisconsin. Analysis of U-Pb age and REEs will employ the Stanford/USGS SHRIMP-RG. Ion microprobe analysis will be made using zircon crystals both in thin section and in grain mounts that have been petrologically studied for inclusions and coexisting minerals; and imaged by optics, BSE, CL, and X-rays. The broader impacts of this research include post-graduate training and installation of the new Wisconsin ion microprobe lab, which will also be employed in other studies related to societal problems such as environmental remediation, paleoclimatology, CO2 sequestration, and nutrition.