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

合作研究：墨西哥南部阿卡特兰杂岩的构造热历史：瑞克洋闭合的记录？

• 批准号: 0308105
• 负责人: R. Damian Nance
• 金额: --
• 依托单位: Ohio University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0308105&HistoricalAwards=false
• 关键词: Collaborative; Research; Tectonothermal; History; Acatl

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.

摘要墨西哥南部暴露的阿卡特兰杂岩记录了一个主要古生代海洋的闭合。该杂岩体暴露了墨西哥最大的古生代地质区域（27,500平方公里），由反复变形的碎屑变沉积层序、局部榴辉岩相镁铁质-超镁铁质岩组以及与弧相关的花岗岩体组成，共同记录了古生代造山作用的漫长历史。与中元古代晚期具有亚马逊亲和力的麻粒岩相片麻岩（瓦哈坎杂岩）相比，阿卡特兰杂岩的构造地层记录的性质不仅是墨西哥增生历史的核心，而且还与古生代大陆重建的更广泛问题有关。然而，尽管它很重要，但尚未对需要解开其构造历史的复杂类型进行有针对性的构造地质年代学研究。因此，其地质演化的重要方面是不确定的，并且现有的构造发展模型是相互冲突的。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未知，其初始变形与阿巴拉契亚山脉的塔科尼、盐碱和阿卡迪亚事件存在不同的相关性，其演化归因于土卫八和瑞克洋的闭合。为了帮助解决这些争议并澄清该复合体的构造历史，PI 建议进行一项研究，将详细的野外测绘、结构运动学分析和地球化学与精确的激光探针 40 Ar/ 39 Ar、传统的 U-Pb 和离子探针年龄测年相结合。该调查将采用有针对性的方法，旨在确定（1）该杂岩体花岗岩体的精确年龄、遗传和运动学意义，（2）其变沉积序列的沉积年龄、来源和构造热历史，以及（3）其镁铁质-超镁铁质单元的精确年龄和构造热演化。这些数据对于了解该复合体的构造历史至关重要，并将用于确定其在墨西哥增生历史中的作用，并评估其与阿巴拉契亚山脉的联系。 智力优点：构造运动学分析与地球化学指纹和精确地质年代学相结合，为揭示复杂地质区域的构造历史提供了强大的工具。拟议的项目将极大地阐明这个重要的古生代地体的演化，从而为墨西哥古生代增生历史的关键方面、其与阿巴拉契亚山脉发展的关系，以及其在新元古代和古生代劳伦西亚-亚马逊地区连接中的作用提供新的见解。更广泛的影响：对阿卡特兰杂岩体的构造地层记录的初步分析，加上它与中元古代晚期瓦哈坎杂岩体（其古生代覆盖层含有冈瓦纳亲缘性化石）的密切联系，表明该杂岩体记录了瑞克洋的闭合。如果是这样，它的构造热演化将为人们对这个重要但知之甚少的海洋的历史提供新的见解，在盘古大陆组装期间，该海洋的闭合导致冈瓦纳大陆和劳俄罗斯之间发生了瓦希托-阿勒格尼-瓦里西亚碰撞的顶峰。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。