Evolution of the SW Laurentian Margin: Implications for Proterozoic Crustal Growth and Geodynamics

这项研究旨在提高我们的理解的形成和分散的劳伦（北美祖先）超大陆和这些事件之间的关系和幕式生成和保存大陆地壳沿着其西南边缘。 劳伦大陆的西南边缘是全球独一无二的，因为它包含了前太古代微大陆（怀俄明州省）的残留物，以及两个不同的古元古代造山事件，分别发生在16 - 19亿年前和22 - 25亿年前，产生了新的大陆地壳。 劳伦提斯在古元古代的形成与古元古代晚期（16 - 20亿年前）全球幼年地壳异常快速生长和现有微大陆和弧聚集的时期相吻合。 然而，在这一快速增长时期之前，有一个全球性的时期（20亿至25亿年前），保存的地壳明显缺乏。 在全球岩石记录中，这一时期生成的地壳比之前和之后时期的地壳保存得更少。 此外，这种地壳在现代大陆之间的分布也不均匀。 它更常见于现代南半球大陆，使其存在沿着西南劳伦特边缘独特。 为了完成这项研究，来自佛罗里达大学的科学家们正在对沿着劳伦大陆西南边缘保存的早、晚古元古代岩石进行详细的、综合的地球化学和结构/构造调查。 这是通过在两个关键地区进行地质测绘来完成的，这两个地区是蒙大拿州的高地山脉和犹他州的瓦萨奇山脉，它们构成了对地壳进行化学、同位素和岩石学研究的基础。 这项工作将导致更完整的了解古元古代期间产生的地壳和岩石圈的年龄和起源，并将提供关键和独特的洞察力，以全球范围内的问题，即古元古代早期地壳生产率低，而晚元古代和晚太古代的高得多的速率特征。 这些数据也提供了新的限制之间的关系超大陆的周期和地壳生长速度的变化和一个特定的测试元古代地球动力学模型的基础上的假设，某些功能，如迪亚曼蒂纳线性构造的澳大利亚或Aekit的西伯利亚有一个共同的地质历史与大福尔斯构造带，因此，代表了一个组合功能，横切新元古代边缘的劳伦。除了核心科学目标外，项目资金还支持本科生，研究生和博士后学生，为他们提供参与研究各个方面的机会，提高他们的绘图，样品制备，分析和解释技能，这对他们的专业发展和就业能力至关重要。 这项研究受益于一项既定的合作协议，以帮助支持由凯克基金会和国家科学基金会支持的新的本科生实地研究计划。这项研究还与正在进行的美国地质调查局矿产资源项目（爱达荷州和蒙大拿州中元古代沉积岩的成矿演化）协调进行，该项目依赖于对预先存在的大陆地壳的年龄和分布的准确评估，例如本项目所针对的。 在较长的时间范围内，这项研究将为NSF赞助的EarthScope研究项目的决策提供有价值的投入。 完成后，研究结果将被纳入一个在线地图，使技术导向的个人以及公众都可以看到这项研究的结果如何与该区域和其他地方的现有数据相关联。 这项研究的结果也通过同行评审的科学期刊，在线全球数据库和专业协会会议上的演讲提供。

This research is directed at improving our understanding of the formation and dispersal of the Laurentian (ancestral North America) supercontinent and the relationship between these events and the episodic generation and preservation of continental crust along its southwestern margin. The southwestern margin of Laurentia is globally unique because it contains remnants of a former Archean microcontinent (Wyoming province) and two distinct Paleoproterozoic orogenic events at 1.6-1.9 billion years ago and 2.2-2.5 billion years ago, which produced new continental crust. Formation of Laurentia in the Paleoproterozoic coincides with a global period of exceptionally rapid growth of juvenile crust and aggregation of existing micrcontinents and arcs during the late Paleoproterozoic (1.6-2.0 billion years ago). This period of rapid growth was preceded, however, by a global period (2.0-2.5 billion years ago) with a pronounced paucity of preserved crust. Crust generated during this interval is less commonly preserved than crust from periods preceding and succeeding it in the global rock record. In addition, such crust is unevenly distributed among the modern continents. It is more commonly preserved in modern southern hemisphere continents, making its presence along the southwest Laurentian margin unique. To complete this research scientists from the University of Florida are conducting a detailed and integrated geochemical and structural/tectonic investigation of both the early and late Paleoproterozoic rocks preserved along a part of the southwestern margin of Laurentia. This is being accomplished by geologic mapping in two critical areas, the Highland Mountains of Montana and the Wasatch Mountains of Utah, which form the basis for sampling this crust for chemical, isotopic, and petrologic studies. This work is leading to more complete understanding of the ages and origins of crust and lithosphere generated during the Paleoproterozoic and will provide critical and unique insight into the global scale problem of low crustal production rates in the early Paleoproterozoic vs. much higher rates characteristic of the late Proterozoic and late Archean. These data are also providing new constraints on the relationship between supercontinent cycles and changes in crustal growth rates and a specific test of Proterozoic geodynamic models based on assumptions that certain features such as the Diamantina lineament of Australia or Aekit terrane in Siberia share a common geologic history with the Great Falls tectonic zone and, therefore, represent a combined feature that transects the Neoproterozoic margin of Laurentia. In addition to the core science objectives, project funds are supporting undergraduate, graduate, and post-doctoral students by providing opportunities for their participation in various aspects of the research that is enhancing their mapping, sample preparation, analytical, and interpretive skills important to their professional development and employability. The research is benefiting from an established cooperative agreement to aid in supporting new undergraduate field research program supported by both the Keck Foundation and the National Science Foundation. The research is also being coordinated with an ongoing a U.S. Geological Survey mineral resources project (Metallogenic Evolution of Mesoproterozoic Sedimentary Rocks in Idaho and Montana) that is dependent on an accurate assessment of the age and distribution on pre-existing continental crust, such as that targeted in this project. On a longer time frame, this research will provide valuable input to decisions made for the NSF-sponsored EarthScope research project. When complete, the results of the research will be integrated into an on-line map that will allow both technically oriented individuals as well as the general public to see how the results from this research related to existing data from this region and elsewhere. Results of this research also are being made available through peer-reviewed scientific journals, on-line global databases, and presentations at professional society meetings.