Collaborative Research: Rift dynamics during the formation of the Carolina Trough and Blake Plateau

合作研究：卡罗莱纳海槽和布莱克高原形成过程中的裂谷动力学

• 批准号: 2112597
• 负责人: Harm Van Avendonk
• 金额: $ 81.92万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-05-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2112597&HistoricalAwards=false
• 关键词: Collaborative; Research; Rift; dynamics; during

In this project scientists will investigate the deep layers of sediments and bedrock offshore the southeastern United States to better understand how the Atlantic Ocean started opening approximately 190 million years ago. In Early Jurassic, the Atlantic Ocean began to form as the continental margin of the southeastern United States rifted from northwest Africa. Rifting occurred by mechanical stretching of the crust and lithosphere, potentially with extensive heating and volcanism, before the Mid-Atlantic Ridge started to accommodate extension by seafloor spreading. Old fault lines and sutures of the Appalachian basement may have been reactivated during this continental stretching phase, and lava flows may have filled the early rift basin. Whether this episode of volcanism was a cause or consequence of the breakup between North America and Africa is not yet clear. This question can be addressed with new marine geophysical data that will cover parts of the margin from the continental shelf to the adjacent abyssal plain, a distance of approximately 400 km. With seismic images of the deep sediments and basement, scientists can determine the relationship between basement faults and lava flows on the Carolina Trough, along the coast of the Carolinas, and Blake Plateau, farther south along Georgia and Florida. These two sections of the Atlantic continental margin are of particular interest because the Blake Plateau is much wider than the Carolina Trough. Either the Blake Plateau forms a block of continental crust that did not stretch much during continental rifting, or it is a plateau that largely consists of volcanic rock that formed during rupture of the supercontinent Pangea. The marine geophysical expedition will involve two vessels, the R/V Marcus Langseth and the R/V Neil Armstrong, and ocean-bottom seismometers that will be used to record seismic waves to map subseafloor basement structure. The investigating team will invite students and early-career scientists from other universities to participate in the expedition, and two short courses will be organized to engage early-career scientists in the analysis and interpretation of the data. Although this study focuses on the southeastern United States margin, results will inform ongoing and future studies at other continental margins worldwide. The asthenosphere beneath continental rifts can produce large volumes of melt in the presence of deep-seated thermal anomalies, or due to decompression beneath thinning lithosphere. The interactions between lithospheric plate extension and the generation and delivery of magma in this setting are not yet well known. The team of scientists will conduct an active-source seismic investigation of the rifted margins of the southeastern United States to better understand the feedbacks between tectonic extension and magmatism during continental breakup and the onset of seafloor spreading in the central Atlantic Ocean. The continental margin of Blake Plateau is much wider than the adjacent margin of Carolina Trough to the north, suggesting that extension and rupture of continental lithosphere progressed differently at these two adjoining rift segments. Differences in mantle temperature anomalies, mantle melting, and structural inheritance of the continental lithosphere may all have influenced these two contrasting styles of rifting. The investigators seek to address the following three hypotheses: 1) The Blake Plateau Basin stretched much wider than the Carolina Trough Basin before breakup due to a difference in lithospheric thickness. 2) During rifting, the magma supply kept pace with extension of Blake Plateau crust, whereas the continental crust rapidly thinned without extensive magmatism beneath the southern Carolina Trough. 3) At the time of rifting, the deep mantle beneath the Blake Plateau was significantly hotter than the mantle beneath Carolina Trough, which would affect the lithospheric rheology, and the degree of mantle melting. To assess how rift-related processes affected crustal structure and sediment stratigraphy, the science team will gather approximately 4500 km of 2-D seismic reflection data and 900 km of ocean-bottom seismometer (OBS) refraction data with the R/V Marcus Langseth. During this expedition, 39 OBSs from the national Instrument Center (OBSIC) will be deployed with the R/V Neil Armstrong. Images of seismic velocity and reflectivity will provide new insights into the sediment stratigraphy, the geometry of basalt flows and crustal-scale faults, and the thickness and composition of igneous crust. The active-source seismic data and geochemical analyses of existing basalt samples will be used to infer past deformation and the emplacement of intrusive and extrusive crust at the Carolina Trough and Blake Plateau. Students and early-career scientists from other US institutions will be invited to engage in the acquisition and analysis of marine seismic reflection and refraction data on the R/V Neil Armstrong or R/V Marcus Langseth. These sea-going participants will obtain experience in the acquisition and on-board processing of seismic reflection and refraction data. In addition, two week-long short courses on OBS refraction data analysis and on processing of multichannel seismic (MCS) reflection data from this project will help train the participants in the use of these new seismic data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在这个项目中，科学家将研究美国东南部的沉积物和基岩离岸的深层层，以更好地了解大西洋大约在1.9亿年前如何开始开放。在侏罗纪早期，大西洋开始形成，因为美国东南部的大陆边缘从西北非洲裂开。裂谷是由于地壳和岩石圈的机械拉伸而发生的，有可能在大西洋山脊开始通过海底扩散来容纳延伸之前，可能会带有广泛的加热和火山。在这个大陆伸展阶段，阿巴拉契亚地下室的旧断层线和缝合线可能已经重新激活，熔岩流可能已经填满了早期的裂谷盆地。这场火山主义是北美和非洲之间破裂的原因还是结果，尚不清楚。可以使用新的海洋地球物理数据来解决这个问题，该数据将涵盖从大陆架到相邻的深渊平原的边距的一部分，距离约400公里。有了深层沉积物和地下室的地震图像，科学家可以确定卡罗来纳州沿海的卡罗来纳州槽上的地下室断层和熔岩流之间的关系，以及沿乔治亚州和佛罗里达州南部的布雷克高原。大西洋大陆边缘的这两个部分特别有趣，因为布雷克高原比卡罗来纳州的槽宽得多。布雷克高原形成了大陆地壳的块，在大陆裂谷期间没有伸展太多，或者是高原，在很大程度上是由pangea破裂过程中形成的火山岩组成的。海洋地球物理探险将涉及两艘船只，即R/V Marcus Langseth和R/V Neil Armstrong，以及海底地震仪，它们将用于记录地震波以绘制地下室地下室结构。调查团队将邀请其他大学的学生和早期职业科学家参加探险活动，并将组织两个简短的课程，以吸引早期职业科学家参与数据的分析和解释。尽管这项研究的重点是美国东南部的利润率，但结果将为全球其他大陆边缘的持续和未来研究提供信息。 大陆裂谷下的软圈可以在存在深层热异常的情况下产生大量熔体，或者是由于岩石圈稀疏下的减压。在这种情况下，岩石圈板扩展与岩浆的产生和传递之间的相互作用尚不清楚。科学家团队将对美国东南部的裂痕边缘进行积极的地震调查，以更好地了解大陆分手期间构造延伸与岩浆主义之间的反馈，以及中央大西洋中部的海底扩散。布莱克高原的大陆边缘比北部的卡罗来纳州槽的相邻边缘宽得多，这表明在这两个相邻的裂谷段，大陆岩石圈的延伸和破裂的进展不同。大陆岩石圈的地幔温度异常，地幔融化和结构遗传的差异都可能影响了这两种对比风格的裂谷风格。研究人员试图解决以下三个假设：1）由于岩石圈厚度的差异，布雷克高原盆地在破裂前的宽度比卡罗来纳州的盆地宽得多。 2）在裂开期间，岩浆供应与布雷克高原外壳的延伸保持同步，而大陆地壳迅速变薄，而南部卡罗来纳州的槽下没有广泛的岩浆作用。 3）在裂谷时，布雷克高原下方的深陆壁比卡罗来纳州的槽下的地幔明显高，这将影响岩石圈的流变学和地幔熔化程度。为了评估与裂谷相关的过程如何影响地壳结构和沉积物地层，科学团队将使用R/V Marcus Langseth收集约4500 km的2-D地震反射数据和900 km的海底地震计（OBS）折射数据。在这次探险期间，将在R/V Neil Armstrong部署国家仪器中心（观察中心）的39次观察。地震速度和反射率的图像将为沉积物地层，玄武岩流和地壳尺度断层的几何形状以及火成岩壳的厚度和组成提供新的见解。现有玄武岩样品的主动源地震数据和地球化学分析将用于推断过去的变形，并在卡罗来纳州和布雷克高原对侵入性和膨胀的地壳的增压。来自美国其他机构的学生和早期职业科学家将被邀请参与R/V Neil Armstrong或R/V Marcus Langseth的海洋地震反思和折射数据的收购和分析。这些乘船参与者将获得地震反射和逆转数据的登机处理经验。此外，有关OBS折射数据分析和处理多通道地震（MCS）反射数据的两周短课程将有助于培训参与者使用这些新的地震数据。该奖项反映了NSF的法定任务，并通过该基金会的知识优点和广泛的criperia审查了NSF的法定任务，并通过评估值得评估。