Tectonics of the Grenville orogen and micropetrology in metamorphic rocks

变质岩石学中的一个长期存在的问题是，无法明确地将变质岩的P-T估计值(由地热压力计确定)与变质作用的时间(由地质年代学确定)联系起来。出现这个问题的原因是，通常用于地质热压测量的矿物(如石榴石、辉石、斜长石等主要硅酸盐相)与通常用于地质年代学的矿物(如锆石、独居石、钛铁矿、金红石)不同，而且在传统的测年方法中，岩石被压碎，从而破坏矿物物种与其内部任何分区之间的空间关系。在过去的几年里，新的分析方法在解决这一问题方面取得了重大进展。这些方法包括：(1)对地质年代学中使用的各种矿物相对于变质组构的各种成分和地热气压测量中使用的矿物的位置进行成像，(2)对地热气压测量和地质年代学中使用的矿物的分带模式进行成像和对比，从而显示同期的生长或溶解，以及(3)EPMA、LA ICPMS或离子探针的原位微探针年代学方法，这些方法减少或消除了粉碎岩石的需要，从而保留了重要的空间信息。我们建议使用和发展这些方法来应用于前寒武纪(格伦维尔，奴隶)和古生代(阿巴拉契亚)造山带。将从这类研究中获得的数据与区域构造信息结合起来，可以深入了解变质过程，并能够有力地重建造山带地壳的构造演化。

A long-standing problem in metamorphic petrology has been the inability to unequivocally link the P-T estimates of metamorphic rocks (determined by geothermobarometry) to the timing of the metamorphism (determined by geochronology). The problem arises because the minerals generally used for geothermobarometry (e.g., major silicate phases such as garnet, pyroxene, plagioclase) are not the same as those typically used for geochronology (e.g., zircon, monazite, titanite, rutile), and because in conventional dating methods the rock is crushed, thereby destroying the spatial relationships between mineral species and any zoning within them. In the last few years, new analytical approaches have yielded significant advances towards the resolution of this problem. These include: (i) imaging the locations of individual minerals used in geochronology with respect to the various components of the metamorphic fabric and the minerals used in geothermobarometry, (ii) imaging and correlation of zoning patterns of minerals used in geothermobarometry and geochronology, thereby demonstrating contemporaneous growth or dissolution, and (iii) in situ microprobe methods of geochronology by EPMA, LA ICPMS, or ion microprobe that reduce or eliminate the need to crush the rock, thereby retaining important spatial information. We propose to use and develop these methods for application to Precambrian (Grenville, Slave) and Paleozoic (Appalachian) orogens. Coupling the data obtained from studies of this kind with regional structural information provides insight into metamorphic processes, as well as permitting robust reconstructions of the tectonic evolution of the orogenic crust.