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

里海在冈瓦纳大陆北缘的地壳块体破裂后打开，形成了古生代最突出的全球特征之一；它的关闭导致了一次主要的碰撞，产生了盘古大陆。尽管它在全球古生代演化中具有重要意义，但人们对它的古地理知之甚少。大多数已知的情况都是基于在欧洲发现的有限暴露。关于里海的这些基本方面存在着关键的问题，包括它的开放时间和模式，以及它与古生代大陆元素的几何形状。在北美，沿着阿巴拉契亚造山带东侧的一条3000公里长的冈瓦南周边地壳块带确定了Rheic的前缘，但这些岩石中记录的Rheic历史却被忽视了。本研究的重点是阿巴拉契亚周边冈瓦南地区两个最大的rheic相关元素，卡罗莱纳和阿瓦隆地区。本研究的主要目标是：(1)确定Rheic洋的开放时间；(2)确定Rheic洋的开放模式；(3)限制Rheic洋演化过程中的几何形状。这些目标正在通过整合几条研究线来实现，包括集中的地质野外测绘、地球化学、高精度U-Pb和碎屑锆石物源分析。通过对卡罗莱纳地区晚期基性深成岩的地球化学-高精度U-Pb年代学联合研究，探讨了大洋开闭的特征和时间。通过与阿瓦隆从冈瓦纳裂谷的确定时间进行比较，这些数据将更好地约束Rheic的打开方式。碎屑锆石研究阐明了卡罗莱纳与阿瓦隆之间的原始古地理关系。这些数据被用来验证卡罗莱纳和阿瓦隆曾经构成一个从冈瓦纳分裂出来的单一“带状大陆”的假设。每个带中时间等效岩屑组合的碎屑锆石年龄谱阐明了源区的长期趋势和变化，这些变化可能是由裂谷、碰撞或经过其他侵蚀地壳块体的漂移引起的。结合其他资料，碎屑锆石年龄谱的趋势和变化为两个带的相对古地理提供了新的约束条件。碎屑锆石数据也正在与其他现有数据集一起使用，试图确定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Rheic诞生时几何形状的先决条件。高精度U-Pb锆石定年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野外关系的信心。在所有取样的同时，正在进行重点外地地质测绘。

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.