Sm-Nd Thermochronology of Garnets in Metamorphic Rocks: A New Method and Tectonic Applications

我们将使用一种新的热年代学方法定量研究造山环境中地壳深部岩石的冷却和折返速率。该应用程序的基本科学目标是评估正断层、韧性减薄和侵蚀对岩石折返的相对贡献。这种理解是一个基本概念，以增加我们的知识大陆构造。这种方法允许通过单一的放射性衰变系统从年龄剖面或矿物的岩心年龄和体年龄之间的差异来确定冷却速率。本文用同位素稀释法和热电离质谱法测定了石榴石晶体中心段和边缘段的Sm-Nd年龄。年龄将根据从规定尺寸的岩心中钻取的少量样品确定。这些数据将与基于离子交换和矿物反应的传统温压法相结合，以限制岩石在500 ℃以上的折返历史。将新的和传统的热年代学的数据与岩石学观测相结合，将使我们能够对高级变质岩的剥露历史作出比目前更全面的描述。样品的套房是从碰撞造山带，喜马拉雅山脉（尼泊尔），弧根组合从塞拉内华达州（加州），和俯冲复合体，卡塔利纳岛（加州）。

Ducea/GangulyEAR-0087424We will quantitatively investigate cooling and exhumation rates of deep crustal rocks from orogenic environments using a new thermochronological method. The basic scientific goal of the application is to asses the relative contribution of normal faulting, ductile thinning and erosion to rock exhumation. This understanding is a fundamental concept to add to our knowledge of continental tectonics. This method permits determination of cooling rates from the age profile or the difference between the core and bulk ages of a mineral by a single radiogenic decay system. We will determine the Sm-Nd ages of central and rim segments of garnet crystals by isotope dilution and thermal ionization mass spectrometry. The ages will be determined from small quantities of samples drilled from the cores of defined dimensions. These data will be combined with conventional thermobarometry based on ion exchange and mineral reactions to constrain the exhumation history of the rocks above 500 oC. Integration of the data derived from the new and conventional thermochronology with petrological observations would permit construction of a more comprehensive picture of the exhumation history of high-grade metamorphic rocks than has been possible so far. The suites of samples are from a collisional orogen, the Himalaya Mountains (Nepal), arc root assemblages from the Sierra Nevada (California), and a subduction complex, the Catalina Island (California).