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

摘要以前发表的40 Ar/ 39 Ar矿物年龄和新的磷灰石裂变径迹年龄的PI确定的模式显示，在北方阿巴拉契亚山脉两个主要的造山带平行断层系统的时间-温度不连续性。这些不连续性横跨缅因州的诺伦贝加断层系统的一部分和沿着佛蒙特州-新罕布什尔州边界的阿蒙诺奥蒂断层，强烈表明这些断层系统的一部分在晚白垩世或更早的时候容纳了显著的（可能高达2-3公里）垂直运动。这两个断层系统侧翼的最高等级的部分，在这两种情况下，冷却年龄的模式表明，岩石在造山带的核心移动相对于下降的岩石在造山带的侧翼。该建议概述了一个合作的低温热年代学研究（磷灰石裂变径迹和（U-Th）/He）在这两个故障系统的目标：o确定区域范围的低温热年代学不连续沿着这些造山带平行的故障系统。跨走向取样导线将允许PI检验一个工作假设，该假设提出这些先前建立的造山带平行弱化带适应了造山带上的显著差异造山后均衡隆起。确定这些构造活动的时间。初步的磷灰石裂变径迹测年横跨Norumbega和Ammonoooiti断层系统，尚未确定整个结构的同期冷却时间。迄今为止的结果表明，这两个结构的部分已经活动到晚白垩世，但没有下限的年龄已经建立。PI建议采用较低闭合温度（U-Th）/He技术（~ 60-70 o C闭合温度）的影响，这将提供有关后期冷却时间的信息，并揭示目前横跨这些断层的岩石是否在晚白垩世/早第三纪期间同时冷却。平行断层系统，并确定如何重要，他们是在造山带折返的历史。这项研究的结果将不仅提供急需的信息，对北方阿巴拉契亚山脉折返的历史，但将有更广泛的影响，与造山后山带折返的机制和过程的理解。平行造山带软弱带几乎与所有造山带都有联系，这些构造在造山带晚期折返历史中所起的作用尚不清楚。对两个造山带侧翼断裂带的低温热年代学研究将为这些构造在造山后折返作用中的作用提供急需的信息。这项拟议的研究将涉及在低温热年代学，区域构造学和北方阿巴拉契亚断层系统的研究经验的两个PI之间的合作。重要的是，来自这两个机构的本科生将完全融入该项目，并将参与采样，样品处理，数据分析和解释。

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.