Collaborative Research: Tectonothermal History of the Acatlán Complex, Southern Mexico: A Record of the Closure of the Rheic Ocean?

摘要墨西哥南部暴露良好的阿卡特兰杂岩记录了一个主要古生代海洋的关闭。该杂岩暴露出墨西哥最大的古生代地质区域(27,500平方公里)，由一系列反复变形的碎屑变沉积序列、局部榴辉岩相镁铁质-超镁铁质岩套和与弧形有关的花岗岩类岩体组成，共同记录了古生代造山的漫长历史。与具有亚马逊亲缘关系的中元古代晚期麻粒岩相片麻岩(瓦哈卡坎杂岩)并列，Acatlan杂岩的构造地层记录的性质不仅对墨西哥的增殖史至关重要，而且与更广泛的古生代大陆重建问题有关。然而，尽管它很重要，但对揭示其构造历史所需的那种类型的杂岩进行有针对性的结构-地质年代学研究尚未进行。因此，其地质演化的重要方面是不确定的，现有的构造发展模式也相互矛盾。因此，复杂记录的构造热事件的年龄和数量是不确定的，其运动学历史的关键方面也是未知的，其初始变形与阿巴拉契亚的Taconic、Salinic和Acadian事件有不同的关联，其演化被归因于Iaptus和Rheic海洋的关闭。为了帮助解决这些争议并阐明该杂岩的构造史，国际地球物理研究所建议进行一项调查，将详细的野外测绘、构造运动学分析和地球化学与精密激光探针40Ar/39Ar、常规U-Pb和离子微探针测年相结合。调查将采用有针对性的方法，以确定(1)杂岩类花岗岩类岩体的准确年龄、继承性和运动学意义，(2)其变质沉积序列的沉积年龄、物源和构造热史，以及(3)其镁铁质-超镁铁质单元的准确年龄和构造热演化。这些数据对了解该杂岩的构造史至关重要，并将用于确定其在墨西哥增殖史中的作用，并评估其与阿巴拉契亚山脉的联系。智力优势：构造运动学分析与地球化学指纹和精确的地质年代学相结合，为解开复杂地质区域的构造史提供了强有力的工具。拟议的项目将极大地阐明这一重要古生代地体的演化，从而为墨西哥古生代增生史的关键方面提供新的见解，它与阿巴拉契亚山脉的发展的关系，以及它在新元古代和古生代劳伦西亚-亚马逊连接中的作用。更广泛的影响：对Acatlan杂岩的构造地层记录的初步分析，以及它与中元古代晚期瓦哈坎杂岩的密切联系，表明该杂岩记录了瑞克大洋的关闭。如果是这样的话，它的构造热演化有望为这片重要但鲜为人知的海洋的历史提供新的洞察力，它的关闭在盘古大陆组装期间产生了冈瓦那和劳鲁西亚之间的高潮瓦奇塔-阿勒格尼安-瓦里斯坎碰撞。该项目还代表了美国和墨西哥之间的国际合作，将促进联合研究和教育伙伴关系，并为本科生和研究生提供独特的研究和国际交流机会。

AbstractThe well-exposed Acatlan Complex of southern Mexico records the closure of a major Paleozoic ocean. Exposing Mexico's largest area of Paleozoic geology (27,500 km2 ), the complex comprises an assemblage of repeatedly deformed clastic metasedimentary sequences, locally eclogite-facies mafic-ultramafic suites, and arc-related granitoid bodies that together record a protracted history of Paleozoic orogenesis. Juxtaposed against granulite facies gneisses of late Mesoproterozoic age with an Amazonian affinity (the Oaxacan Complex), the nature of the tectonostratigraphic record of the Acatlan Complex is not only central to the accretionary history of Mexico, but also bears upon wider issues of Paleozoic continental reconstructions. Despite its importance, however, a targeted structural-geochronological study of the complex of the type needed to unravel its tectonic history has yet to be undertaken. As a result, significant aspects of its geologic evolution are uncertain and existing models for its tectonic development are in conflict. Thus, the age and number of tectonothermal events the complex records are uncertain, key aspects of its kinematic history are unknown, its initial deformation has been variably correlated with the Taconic, Salinic and Acadian events of the Appalachians, and its evolution has been attributed to closure of both the Iapetus and Rheic oceans. To help resolve these controversies and clarify the complex's tectonic history, The PI's propose to conduct an investigation that combines detailed field mapping, structural-kinematic analysis and geochemistry with precise laserprobe 40 Ar/ 39 Ar, conventional U-Pb and ion-microprobe age dating. The investigation will use a targeted approach aimed at determining (1) the precise age, inheritance and kinematic significance of the complex's granitoid bodies, (2) the depositional age, provenance and tectonothermal history of its metasedimentary sequences, and (3) the precise age and tectonothermal evolution of its mafic-ultramafic units. These data are essential to understanding the tectonic history of the complex and will be used to establish its role in Mexico's accretionary history and to evaluate its linkages to the Appalachians.Intellectual Merit: Structural-kinematic analysis in combination with geochemical fingerprinting and precise geochronology provides a powerful tool for unraveling the tectonic history of regions of complex geology. The proposed project will greatly clarify the evolution of this important Paleozoic terrane and, in so doing, provide new insight into key aspects of the Paleozoic accretionary history of Mexico, its relationship to the development of the Appalachians, and its role in Laurentia-Amazonia connections for the Neoproterozoic and Paleozoic. Broader Impact: Preliminary analysis of the tectonostratigraphic record of the Acatlan Complex coupled with its close association with the late Mesoproterozoic Oaxacan Complex, the Paleozoic cover of which contains fossils of Gondwanan affinity, suggests that the complex records the closure of the Rheic Ocean. If so, its tectonothermal evolution promises new insight into the history of this important but poorly understood ocean, the closure of which produced the climactic Ouachita-Alleghenian-Variscan collision between Gondwana and Laurussia during the assembly of Pangea. The project also represents an international collaboration between the United States and Mexico that will promote joint research and educational partnerships and provide both undergraduate and graduate students with unique opportunities for research and international exchange.