Collaborative Research/RUI: The Role of Orogen Parallel Fault Systems in the Late Exhumation History of a Convergent Orogen

合作研究/RUI：造山带平行断层系统在聚合造山带晚期折返历史中的作用

• 批准号: 0308938
• 负责人: Mary Roden-Tice
• 金额: --
• 依托单位: SUNY College at Plattsburgh
• 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=0308938&HistoricalAwards=false
• 关键词: Collaborative; Research; RUI; Role; Orogen

AbstractPatterns of previously published 40 Ar/ 39 Ar mineral ages and new apatite fission track ages determined by the PIs show distinct time-temperature discontinuities across two major orogen-parallel fault systems in the northern Appalachians. These discontinuities, across a portion of the Norumbega fault system in Maine and the Ammonoosuc fault along the Vermont-New Hampshire border, strongly suggest that portions of these fault systems accommodated significant (perhaps up to 2-3 km) vertical movement in Late Cretaceous or younger time. Both of these fault systems flank the highest grade portions of the Acadian orogen and in both instances the patterns of cooling ages suggest that rocks in the core of the orogen moved up relative to down-dropped rocks on the flanks of the orogen. This proposal outlines a collaborative low-temperature thermochronological study (apatite fission-track and (U-Th)/He) across these two fault systems with the goals of: oDetermining the regional extent of the low-temperature thermochronological discontinuities along these orogen-parallel fault systems. Across strike sampling traverses will allow the PI's to test a working hypothesis that proposes these previously established orogen-parallel zones of weakness accommodated significant differential post-orogenic isostatic uplift across the orogen.oDetermining if the low-temperature discontinuities are confined to the margins of the orogen or whether other structures within the core of the orogen may also be accommodating post-orogenic displacements.oDetermining how long these structures have been active. Preliminary apatite fission track dating traverses across both the Norumbega and Ammonoosuc fault systems have yet to establish a time of contemporaneous cooling across the structures. Results to date suggest portions of both these structures have been active into the Late Cretaceous, but no lower age limit has been established. The PI's propose to incorporate the lower closure temperature (U-Th)/He technique (~ 60-70 o C closure temperature) into their study which will provide information on the timing of cooling at later times and reveal whether the rocks currently juxtaposed across these faults cooled contemporaneously during the Late Cretaceous/Early Tertiary.oEstimating the magnitude of post-orogenic displacement along these orogen-parallel fault systems and determining how important they were in the exhumation history of the orogen.The results of this study will not only provide much needed information on the exhumation history of the northern Appalachians, but will have a broader impact on the understanding of mechanisms and processes associated with post-orogenic mountain belt exhumation. Orogen-parallel zones of weakness are associated with nearly all orogenic belts and what role these structures play in the late exhumation history of mountain belts is unclear. The proposed low-temperature thermochronological study of two orogen flanking fault zones will provide much needed information on the role of these structures in post-orogenic exhumation. This proposed research will involve collaboration between two PI's with experience in low-temperature thermochronology, regional tectonics, and studies of northern Appalachian fault systems. Importantly, undergraduate students from both institutions will be fully integrated into the project and will be involved in sampling, sample processing, data analysis and interpretation.

已发表的40Ar/39Ar矿物年龄和PI测定的新的磷灰石裂变径迹年龄模式表明，阿巴拉契亚北部两个主要的造山带平行断裂系统具有明显的时间-温度不连续性。这些横跨缅因州Norumbeega断层系统和沿佛蒙特州-新罕布夏州边界的Ammonosuc断层的不连续性强烈表明，这些断层系统的一部分在白垩纪晚期或更年轻时进行了显著的垂直运动(可能长达2-3公里)。这两个断裂系统都位于阿卡迪亚造山带最高级别部分的侧翼，在这两种情况下，冷却年龄模式都表明，造山带核心的岩石相对于造山带侧翼的下落岩石向上移动。这项建议概述了一项跨越这两个断裂系统的合作低温热年代学研究(磷灰石裂变径迹和(U-Th)/He)，目的是：1确定沿这些造山带平行断裂系统的低温热年代学不连续的区域范围。跨走向采样导线将允许PI检验一个工作假说，该假说认为这些先前建立的造山带-平行软弱带适应了整个造山带明显的造山后均衡抬升。o确定低温不连续是否局限于造山带边缘，或者造山带核心内的其他构造是否也可能容纳造山后的位移。o确定这些构造活动的时间有多长。初步的磷灰石裂变径迹测年横跨Norumbega和Ammonosuc两个断层系统，尚未确定这些结构的同期冷却时间。到目前为止的结果表明，这两个构造的一部分一直活跃到晚白垩世，但没有确定下限年龄。PI建议将较低的闭合温度(U-Th)/He技术(~60-70℃闭合温度)纳入他们的研究中，这将提供关于后来冷却时间的信息，并揭示目前横跨这些断层的岩石是否在白垩纪晚期/第三纪早期同时冷却。估计沿这些造山带平行断层系统的造山后位移的规模，并确定它们在造山运动折返历史中的重要性。这项研究的结果不仅将为阿巴拉契亚北部的折返历史提供必要的信息，但将对理解与后造山带折返相关的机制和过程产生更广泛的影响。造山带-平行软弱带几乎与所有造山带有关，这些构造在山带晚期折返历史中所起的作用尚不清楚。拟议的两个造山带两侧断裂带的低温热年代学研究将提供有关这些构造在造山后折返中所起作用的迫切需要的信息。这项拟议的研究将涉及两个具有低温热年代学、区域构造和阿巴拉契亚北部断裂系统研究经验的PI之间的合作。重要的是，来自两所大学的本科生将完全融入该项目，并将参与采样、样本处理、数据分析和解释。