Lutetium-Hafnium Ages and the P-T History of High-Pressure Rocks in the Appalachians

我们的研究是针对开发技术，将解决的地质历史套件的岩石，曾经深埋在俯冲洋壳或在随后的大陆碰撞。 这些岩石都是在北美东部阿巴拉契亚山脉的一次古老的造山运动中被埋在40-60公里深的地方。 这一地区经历了复杂的构造历史，有三个造山事件与中生代海洋物质或外来碎屑的增生有关：450 Ma，在ca. 400 Ma，而阿勒格尼期开始于320 Ma。 一些构造切片包含的物质也是古北美的一部分，并在大约1.1 Ga前的格伦维尔时间经历了更古老的高级变质作用。 在任何这种反复变形、埋藏和断层的岩石圈中，通常很难确定任何特定事件的发生时间，需要强大的地质年代学和温压技术来确定矿物的生长，而不是在随后的造山运动中冷却或重置。 我们的工作将Lu-Hf同位素测年技术应用于这些元素（石榴石、单斜辉石、金红石和锆石）具有高阻断温度的矿物，这些元素可以从高压岩石（榴辉岩和石榴石麻粒岩）中分离出来，在某些情况下，这些岩石经历了随后的低级事件（角闪岩相变质作用）。 这项工作将与新的温压技术相结合，旨在尽量减少在大多数榴辉岩中发现的高方差组合中遇到的问题。 这些方法将结合绘图，结构分析和U-Pb地质年代学正在做的我们的合作者，以更好地建立在阿巴拉契亚山脉冲断层片的早期构造历史的时间。

Essene/MukasaEAR-0087448Our research is directed toward developing techniques that will address the geological history of suites of rocks that were once deeply buried during subduction of ocean crust or during subsequent continental collision. The rocks under consideration all were buried to depths of 40-60 km during an ancient mountain-building event, the Taconic Orogeny, in the Appalachian Mountains of eastern North America. This area has undergone a complex tectonic history, with three mountain-building events linked to accretion of oceanic materials or exotic terranes in the Phanerozoic: the Taconic at ca. 450 Ma, the Acadian at ca. 400 Ma, and the Alleghenian beginning at 320 Ma. Some tectonic slices contain materials that were also part of ancient North America and underwent a much older high-grade metamorphism in Grenville time about 1.1 Ga ago. In any such repeatedly deformed, buried and faulted terrane, it is often difficult to identify with certainty the timing of any given event, and robust geochronogical and thermobarometric techniques are needed to identify the growth of minerals rather than their cooling or resetting during some subsequent orogeny. Our work will apply the Lu-Hf isotopic dating technique on minerals with high blocking temperatures for these elements (garnet, clinopyroxene, rutile and zircon) that can be separated from high-pressure rocks (eclogites and garnet granulites) which, in some cases, have undergone subsequent lower grade events (amphibolite facies metamorphism). This effort will be combined with new thermobarometric techniques designed to minimize the problems encountered in high-variance assemblages found in most eclogites. These approaches will be combined with mapping, structural analysis and U-Pb geochronology being done by our collaborators to better establish the timing of the early tectonic history of thrust slices in the Appalachians.