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

Rheic Ocean在从冈瓦那北缘裂开形成最突出的古生代全球地貌之一的地壳块体之后打开；它的关闭是产生盘古大陆的主要碰撞之一的原因之一。尽管它在古生代的全球演化中很重要，但人们对它的古地理学知之甚少。已知的大部分情况都是基于在欧洲发现的有限风险敞口。关于瑞克海的这些基本问题，包括其开放的时机和方式，以及相对于古生代大陆元素的几何形状，都存在一些关键问题。在北美，沿着阿巴拉契亚造山带东侧的一条3000公里长的冈德瓦南周地壳块体带界定了Rheic在开放时的前缘，但这些岩石中记录的Rheic的历史被忽略了。这项研究集中在阿巴拉契亚环冈湾地区最大的两个与Rheic相关的元素，卡罗莱纳和阿瓦隆地带。这项研究的主要目标是1)确定风化洋的打开时间，2)确定风化打开的方式，3)在演化过程中限制风化的几何形状。这些目标是通过综合几个研究方向来实现的，包括重点地质野外填图、地球化学、高精度U-Pb和碎屑锆石来源分析。通过对卡罗莱纳带晚期镁铁质深成岩的高精度U-Pb年代学研究，探讨了Rheic Ocean的特征和打开的时间。与冈瓦那阿瓦隆裂谷的确定时间相比，这些数据将更好地约束Rheic的开放模式。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这样一种假设，即卡罗莱纳和阿瓦隆曾构成从冈瓦那裂开的单一“带状大陆”。来自每个带的时间相当的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，这些变化可能是由于裂谷、碰撞或漂移经过其他侵蚀的地壳块体而引起的。碎屑锆石年龄谱的趋势和变化，结合其他可用的数据，对这两个带的相对古地理构成了新的制约。碎屑锆石数据也被用于其他现存的数据集，试图确定卡罗莱纳和阿瓦隆的源区(S)；这些地壳块体的原始位置是描绘Rheic诞生时的几何图形的先决条件。高精度的锆石U-Pb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场关系的信心。目前正在结合所有采样进行重点实地地质测绘。

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.