Collaborative Research: RUI: Testing Models of Passive Margin Rejuvenation in the Eastern U.S.

北美东部大陆边缘是在侏罗纪时期（大约1.45亿到2亿年前）大西洋开放期间形成的，从那时起，人们认为它的构造一直保持稳定。然而，最近的证据表明，构造驱动的隆起和侵蚀事件发生在100万到130万年前以及1500万到200万年前，远在裂谷期之后。在与大西洋接壤的其他大陆的边缘也发现了类似的事件。该项目的目的是确定这些事件在北美东部的时间和空间分布，目的是建立与其他大陆事件的关系，并最终提供可能的构造机制来解释同步事件。该项目将通过与当地学校合作开发9-12年级的地球科学模块，并对米德尔伯里大学进行课堂访问和访问，并让本科生深入参与研究，从而促进预期的社会成果。该项目旨在了解北美东部边缘地区的复兴，与非洲、南美、欧洲和北大西洋海岸相对完整的复兴事件相比，北美东部边缘地区的复兴几乎是未知的。初步资料（巴尔的摩峡谷槽沉积物通量增加；新罕布什尔州White Mountains的热年代学）表明，北美东部边缘至少发生了三次复兴事件：早白垩世（130-110 Ma）、晚白垩世（85-65 Ma）和中新-上新世（15-0 Ma）。其他大西洋边缘的结果强调了两个时期，晚白垩世和中新-上新世，在这两个时期，多个环大西洋边缘可能同步发生了年轻化。这种巧合的时机提出了一个问题：一个共同的强迫机制能否同时使多个被动边缘恢复活力？两种端元假说包括：(1)通过岩石圈长距离传播的横向应力，或(2)被动边缘（如动态地形）下的动态地幔应力。在大尺度上，关于哪些边缘同步恢复活力以及它们如何在几何上相互关联的完整图景可用于推断大西洋尺度的强迫机制。在局部尺度上，描绘北美东部边缘恢复的时空格局可能揭示应力取向或局部断裂机制，从而约束潜在的强迫机制。本项目使用这两种方法来澄清北美中东部边缘（新英格兰、纽约和新泽西）的裂谷后挖掘模式。研究小组将利用基岩钻孔岩芯中的磷灰石和锆石U-Th/He和磷灰石裂变径迹热年代学来确定时间分辨的挖掘历史，并利用重矿物微量元素组成和锆石和金红石的U-Pb定年以及巴尔的摩峡谷槽海上钻孔岩芯中的沉积物物源来确定沉积物物源。这两种方法是互补的；热年代学提供了某一点挖掘的时间和规模，而碎屑物源整合了广泛的可能来源区域，并且可以检测到太小而无法重置热时计的挖掘事件。

The eastern North American continental margin was established during the Jurassic Period (about 145 to 200 million years ago) during the opening of the Atlantic Ocean and is thought to have remained tectonically stable since that time. However, recent evidence suggests tectonically driven uplift and erosion events occurred between 100 and 130 and between 15 and 2 million years ago, long after the rift episode. Similar events have been recognized on the margins of other continents bordering the Atlantic. The objective of this project is to determine the timing and spatial distribution of these events in eastern North America with the goal of establishing the relationship with events on other continents and, ultimately, provide constraints on possible tectonic mechanisms to explain synchronous events. The project will advance desired societal outcomes by the development of a grade 9-12 earth science module in collaboration with local schools with class visits and visits to Middlebury and intensive involvement of undergraduate students in research.This project aims to understand rejuvenation of the Eastern North American margin, which remains virtually unknown compared to relatively well-documented rejuvenation events on the coasts of Africa, South America, Europe, and the north Atlantic. Preliminary data (increased sediment flux to the Baltimore Canyon Trough; thermochronology in the White Mountains, New Hampshire) suggest that at least three rejuvenation events occurred along the Eastern North American margin: Early Cretaceous (130-110 Ma), Late Cretaceous (85-65 Ma), and the Mio-Pliocene (15-0 Ma). Results from other Atlantic margins highlight two periods, the Late Cretaceous and Mio-Pliocene, in which rejuvenation may have occurred synchronously across multiple circum-Atlantic margins. This coincident timing raises the question of whether a common forcing mechanism can rejuvenate multiple passive margins at the same time? Two end-member hypotheses include: (1) lateral stresses transmitted long distances through the lithosphere, or (2) dynamic mantle stresses beneath passive margins (e.g. dynamic topography). On the large scale, a complete picture of which margins were synchronously rejuvenated and how they are geometrically related may be used to infer Atlantic-scale forcing mechanisms. On the local scale, delineating the spatiotemporal pattern of rejuvenation of the Eastern North American margin may reveal stress orientations or local fault mechanics, thus constraining the underlying forcing mechanism. This project uses both of these approaches to clarify the pattern of post-rift exhumation in the central Eastern North American margin (New England, New York, and New Jersey). The research team will determine time-resolved exhumation histories by using apatite and zircon U-Th/He and apatite fission track thermochronology in bedrock drill cores and sediment provenance using trace element composition of heavy minerals and U-Pb dating of zircon and rutile and provenance of sediments in offshore drill cores from the Baltimore Canyon Trough. These two approaches are complementary; thermochronology provides the timing and magnitude of exhumation at a point, whereas detrital provenance integrates a broad range of possible source regions and can detect exhumation events too small to reset thermochronometers.