Is there a Pangean suture zone in southeastern New England?

自从图佐·威尔逊（Tuzo Wilson）在1966年发表在《自然》杂志上的一篇著名论文中提出大西洋是否关闭然后重新开放以来，这个想法已经被普遍接受和探索。已经确定的是，大约1.8亿年前，大西洋沿着沿着大致相同的路线打开，大约2.5亿年前，前大西洋周围的大陆闭合并形成超大陆盘古大陆。这个超大陆包括盘古大陆缝合带以西的美洲和欧亚大陆（欧洲和亚洲）以及以东的非洲。然而，如果大西洋在沿着一条不沿着缝合带的线的任何地方打开，那么一些大陆碎片可能从欧亚大陆/非洲转移到美洲，或者反之亦然。迄今为止，这一点尚未得到证实。东部的新英格兰阿巴拉契亚山脉由一组微大陆组成，这些微大陆在大约4.7亿到3.6亿年前，在泛大陆形成之前，与北美碰撞并成为北美的一部分。最后到达的微大陆之一，阿瓦隆大陆，被解释为构成马萨诸塞州东南部，罗得岛和康涅狄格州东南部。最近，2017年发表在《地质学》杂志上的一篇论文的主要研究者和合著者在马萨诸塞州近海发现了一块西非（摩洛哥）地壳碎片，该碎片在盘古大陆解体时搁浅。仔细审查现有的数据，已经被解释为阿瓦隆东南部的新英格兰表明，它的一部分可能实际上是这个西非片段的一部分。拟议工作的目的是检验这一假设。如果这是真的，新英格兰东南部将是第一个已知的盘古大陆缝合带暴露在陆地上的地方。它可能成为第一个在阿巴拉契亚山脉，西非和其他地区工作的地质学家和地质学家可以聚集在一起研究形成最近超大陆的主要缝合带的地方。基岩地质图和我们对马萨诸塞州、罗得岛、康涅狄格州和北方阿巴拉契亚山脉地质的理解可能会发生重大变化。普遍认为的东南部新英格兰阿瓦隆地区的一部分实际上可能是泛大陆分裂后遗留下来的西非碎片，这一想法以前没有被探索过，因为阿瓦隆和西非岩石具有相似的特征和年龄。然而，沉积岩和花岗质岩石中的锆石年龄将它们区分开来。例如，阿瓦隆岩石与大约10亿年的地壳有很强的亲和力，西非岩石与大约20亿年的地壳有很强的亲和力。因此，10亿年前的锆石在阿瓦隆沉积岩中很常见，在那里它们作为沉积物颗粒沉积，在阿瓦隆花岗岩中，它们在花岗岩熔体渗透地壳时被并入。西非岩石中20亿年前的锆石也是如此。在波士顿和以北的纬度，现有的数据表明阿瓦隆的温度。在南部，现有的数据很少，可以用任何一种方式解释。这项工作的目的是分析波士顿纬度以南地区沉积岩和花岗岩中锆石颗粒的年龄，以了解它们的起源和亲缘关系。在没有基岩暴露的地方，将使用现有岩芯样本。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ever since Tuzo Wilson asked whether the Atlantic Ocean closed and then reopened in a famous 1966 paper in the journal Nature, this idea has been generally accepted and explored. It is well established that ~180 million years ago the Atlantic Ocean opened along approximately the same line as where the continents around the pre-Atlantic Ocean had closed and formed supercontinent Pangea by ~250 million years ago. This supercontinent included the Americas to the west and Eurasia (Europe and Asia) and Africa to the east of the Pangean suture zone. It is possible, however, that some continental fragments were transferred from Eurasia/Africa to the Americas and/or vice versa, if the Atlantic Ocean opened anywhere along a line that did not follow the suture zone. To date, this has not been demonstrated. The eastern New England Appalachians consist of a collage of microcontinents that collided with and became part of North America between ~470 and ~360 million years ago, before the formation of Pangea. One of the last of these arriving microcontinents, the Avalon terrane, is interpreted to constitute southeastern Massachusetts, Rhode Island, and southeastern Connecticut. Recently, the principal investigator and coauthors of a 2017 paper published in the journal Geology discovered a fragment of West African (Moroccan) crust in offshore Massachusetts that was stranded during the breakup of Pangea. Careful review of existing data for what has been interpreted as the Avalon terrane of southeastern New England suggests that part of it may in fact be part of this West African fragment. The purpose of the proposed work is to test this hypothesis. If true, southeastern New England will be the first known location where the major Pangean suture zone is exposed on land. It may become the first location where geologists and geophysicists who work in the Appalachians, West Africa and beyond can come together and study the main suture zone that formed the most recent supercontinent. Bedrock geologic maps and our understanding of the geology of Massachusetts, Rhode Island, Connecticut and the northern Appalachians may change significantly.The idea that part of what is generally accepted to be the southeastern New England Avalon terrane may actually be a west African fragment that remained after the breakup of Pangea has not previously been explored, because Avalonian and west African rocks have similar characteristics and ages. However, the ages of zircon in sedimentary and granitic rocks distinguishes them. For example, Avalonian rocks have a strong affinity with approximately one billion year old crust, and West African rocks with approximately two billion year old crust. Therefore, one billion year old zircon is common in Avalonian sedimentary rocks, where they were deposited as grains of sediment, and in Avalonian granitic rocks, where they were incorporated in the granitic melt as it penetrated the crust. The same is true for two billion year old zircon in West African rocks. At the latitude of Boston and to the north, existing data are indicative of the Avalon terrane. To the south, existing data are sparse and can be interpreted either way. The purpose of the proposed work is to analyze the ages of zircon grains in sedimentary and granitic rocks from the area south of the latitude of Boston to understand their origins and affinities. Where no bedrock is exposed, samples from existing drill core will be used.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.