Collaborative Research: A Record of the Timing, Nature and Geometry of the Rheic Ocean in the Appalachian Carolina and Avalon Zones

冈瓦纳北方边缘的地壳块体断裂后，形成了最突出的古生代全球特征之一，而莱茵洋的闭合则是形成泛古陆超大陆的主要碰撞之一。 尽管它在全球古生代演化中的重要性，但对其古地理的认识却很少。大多数已知的情况都是基于在欧洲发现的有限暴露。关键问题存在于这些基本方面的莱茵洋，包括其时间和模式的开放和其几何形状与古生代大陆元素。 在北美，沿阿巴拉契亚造山带东翼沿着的3000 km长的冈瓦纳地壳块体带确定了Rheic开启期间的前缘，但这些岩石中记录的Rheic历史一直被忽视。 本研究的重点是阿巴拉契亚冈瓦纳周边地区的两个最大的流变学相关元素，卡罗莱纳和阿瓦隆带。 本项研究的主要目的是1）确定Rheic洋开启的时间，2）识别Rheic开启的模式，3）限制Rheic在其演化过程中的几何形状。这些目标是通过几条研究线的整合来实现的，包括重点地质野外填图，地球化学，高精度U-Pb和碎屑锆石物源分析。 通过对卡罗莱纳带晚基性深成岩的地球化学-高精度U-Pb年代学研究，探讨了Rheic洋的特征和开启时间。 通过与冈瓦纳阿瓦隆裂谷形成时间的对比，这些资料将更好地制约莱茵河的开启方式。 碎屑锆石研究正在阐明卡罗莱纳和阿瓦隆之间的原始古地理关系。 这些数据被用来检验一个假设，即卡罗莱纳和阿瓦隆曾经构成一个单一的“带状大陆”从冈瓦纳分裂。碎屑锆石年龄谱的时间等效的岩屑组合在每个区域阐明长期的趋势和变化，可能会产生裂谷，碰撞，或漂移过去的其他侵蚀地壳块源区。碎屑锆石年龄谱的趋势和变化，与其他可用的数据相结合，代表了新的约束相对古地理的两个区域。 碎屑锆石数据还与其他现存数据集一起使用，试图识别卡罗莱纳和阿瓦隆的源区;这些地壳块体的原始位置是描绘莱茵河诞生时几何形状的先决条件。 高精度的锆石U-Pb定年法为具有特殊意义的岩石提供了严格的年龄限制。 最后，任何地质年代学/地球化学研究最重要的方面是对取样岩石的现场关系的信心。 在进行所有取样的同时，正在进行有重点的实地地质测绘。

The Rheic Ocean opened in the wake of crustal blocks rifted from the northern margin of Gondwana to form one of the most prominent Paleozoic global features; its closure is responsible for one of the major collisions that produced the supercontinent of Pangea. Despite its importance in the global evolution of the Paleozoic, there is little knowledge of it paleogeogaphy. Most of what is known is based on limited exposures found in Europe. Critical questions exist regarding such fundamental aspects of the Rheic Ocean, including its timing and mode of opening and its geometry with respect to Paleozoic continental elements. In North America, a 3000 km long belt of peri-Gondwanan crustal blocks along the eastern flank of the Appalachian orogen defined the leading edge of the Rheic during its opening, yet the history of the Rheic recorded in these rocks has been neglected. This study focuses on the two largest Rheic-related elements of the Appalachian peri-Gondwanan realm, the Carolina and Avalon zones. The primary objectives of this study are to 1) determine the time of opening of the Rheic Ocean, 2) identify the mode of Rheic opening, and 3) constrain the geometry of the Rheic during its evolution.These objectives are being addressed through the integration of several lines of study, including focused geologic field mapping, geochemistry, high precision U-Pb and detrital zircon provenance analysis. The character and timing of opening of the Rheic Ocean are being addressed by combined geochemical- high precision U-Pb geochronological studies on late stage mafic plutonic rocks in the Carolina zone. By comparison with the established time of rifting of Avalon from Gondwana, these data will better constrain the mode of opening of the Rheic. The detrital zircon study is elucidating the original paleogeographic relationship between Carolina and Avalon. These data are being used to test the hypothesis that Carolina and Avalon once constituted a single 'ribbon continent' rifted from Gondwana. Detrital zircon age spectra from time equivalent lithic assemblages throughout each zone are elucidating long term trends and changes in source areas that might arise from rifting, collision, or drift past other eroding crustal blocks. Trends and changes in detrital zircon age spectra, considered in conjunction with other available data, represent new constraints on the relative paleogeography of the two zones. Detrital zircon data are also being utilized with other extant data sets in an attempt to identify the source region(s) of Carolina and Avalon; the original location of these crustal blocks is a prerequisite to delineating the geometry of the Rheic at its birth. High precision U-Pb zircon dating is providing tight age constraints on rocks of particular significance. Finally, the most important aspect of any geochronological/geochemical study is confidence in the field relations of the sampled rocks. Focused field geologic mapping is being conducted in conjunction with all sampling.