Collaborative Research: Tectonic Significance of ca. 1.6 Ga Deformation in SW Laurentia and New Insights on a Protracted Mazatzal Orogeny

合作研究：约的构造意义。

• 批准号: 0948501
• 负责人: Michael Williams
• 金额: $ 9.01万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948501&HistoricalAwards=false
• 关键词: Collaborative; Research; Tectonic; Significance; ca.

The period between 1.78 and 1.63 billion years ago (Ga) was a time of important southward growth of the North American continent. The rate of growth within this 150-million-year period far exceeds Phanerozoic (542 million years ago to the present) crustal growth rates. As a result of recent work in southern Wyoming and northern Colorado, in a region known as SW Laurentia, the PIs have identified a deformational, magmatic, and thermal event at 1.62-1.58 Ga, which is surprising because the region was thought to be tectonically quiescent. The researchers will combine detailed kinematic histories of shear zones in northern and central Colorado, with precise, texturally-linked dates on deformation, and well-dated metamorphic pressure-temperature paths to evaluate two end-member hypotheses where the enigmatic tectonic 1.6 Ga event may represent either (1) intracratonic deformation of the newly accreted continental crust with stresses transmitted far inboard of the active plate margin or (2) deformation associated with delayed subduction of a long-lived remnant ocean basin. The 1.6 Ga tectonism may reflect the closing of this basin and the final accretion at the southern edge of the North American continent. The recognition of 1.62 to 1.58 Ga deformation, magmatism, and metamorphism as much as 1200 km away from the continent-ocean plate boundary has important implications on several levels. First, the event may have Phanerozoic analogues in the Laramide (80 million years ago) orogeny or the modern Tibetan Plateau. If correct, this hypothesis would suggest rapid stabilization of, and efficient stress transfer within, newly accreted crust of this age. The present midcrustal level of exposure of rocks affected by the 1.6 Ga event affords an opportunity to investigate the crustal stress transfer in the strongest part of the crust. There are also implications for modern earthquake hazards well away from active plate boundaries. Alternatively, if the event reflects closure of a small ocean basin, then the crustal growth process was not a simple north to south progression and indeed was not completed in some of the northernmost regions until after 1.6 Ga. This might also explain some of the anomalous features on recent deep seismic surveys of the region. In either case, results from this study are likely to result in substantial revision of tectonic models for Paleoproterozoic crustal growth, assembly, and stabilization in SW Laurentia.

17.8亿年前至16.3亿年前（Ga）是北美大陆向南生长的重要时期。 在这1.5亿年期间的增长率远远超过了中生代（5.42亿年前到现在）的地壳增长率。由于最近在怀俄明州南部和北方科罗拉多的一个被称为西南劳伦蒂亚的地区的工作，PI已经确定了1.62-1.58 Ga的变形，岩浆和热事件，这是令人惊讶的，因为该地区被认为是构造静止的。 研究人员将联合收割机结合北方和科罗拉多中部剪切带的详细运动学历史，以及精确的、与纹理相关的变形日期，和年代确定的变质压力-温度路径来评估两种端元假说，其中神秘的构造1.6 Ga事件可能代表（1）新增生的大陆地壳的克拉通内变形，应力传递到活动板块边缘的内侧，或者（2）与长期残留洋盆延迟俯冲有关的变形。1.6Ga的构造活动可能反映了该盆地的闭合和北美大陆南缘的最终增生。 1.62至1.58 Ga的变形，岩浆作用，变质作用的识别距离大陆-海洋板块边界多达1200公里，具有重要的意义在几个层面上。首先，该事件可能在Laramide（8000万年前）或现代青藏高原的中生代类似物。如果正确的话，这一假设将表明快速稳定，有效的应力转移，新增生地壳的这个年龄。目前中地壳水平的岩石暴露的影响，1.6 Ga事件提供了一个机会，调查地壳应力转移的最强部分的地壳。这也意味着现代地震灾害远离活动板块边界。另一方面，如果该事件反映了一个小洋盆的闭合，那么地壳生长过程就不是一个简单的从北到南的过程，而且直到1.6 Ga之后才在最北部的一些地区完成。这也可以解释最近对该地区进行的深层地震调查中出现的一些异常特征。在任何一种情况下，从这项研究的结果很可能会导致在西南劳伦特古元古代地壳生长，组装和稳定的构造模型的大幅修订。