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

这项研究将结合原位离子微探针分析氧同位素比值和对加利福尼亚州方济各坎杂岩高压变质岩中锆石晶体的U-Pb年龄。这项研究的目标包括：建立这些岩石在埋藏和折返之前、期间和之后的压力-温度-时间-流体(P-T-t-流体)历史；确定高压变质岩的原岩；提高年代学的可靠性；以及检验榴辉岩折返的相互竞争的理论。样本将从方济各会著名的地方挑选，包括沃德克里克、詹纳、帕诺什山口和圣卡塔利纳岛。分析将集中在锆石和伴生矿物上。将特别注意晶体内的同位素分带和矿物包裹体。来自锆石中单个斑点的d18O和年龄的组合将直接将计时与流体和热事件耦合在一起。我们的初步研究已经描述和分析了方济各会榴辉岩、蓝片岩和角闪岩中的锆石，以及可能代表原岩到高压岩石的年轻海底样品(辉长岩、斜长花岗岩、蛇纹岩)。对d18O的分析将使用威斯康星大学的新Cameca 1280离子微探测器。U-Pb年龄和REES的分析将采用Stanford/USGS SHRIMP-RG。离子微探针分析将使用薄片和颗粒中的锆石晶体进行，这些晶体已经进行了岩石学研究，以寻找包裹体和共存矿物；并通过光学、BSE、CL和X射线成像。这项研究的更广泛影响包括研究生培训和安装新的威斯康星州离子微探针实验室，该实验室还将用于其他与社会问题有关的研究，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.