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

在这个项目中，科学家们将调查美国东南部近海的深层沉积物和基岩，以更好地了解大西洋是如何在大约1.9亿年前开始开放的。早在侏罗纪，随着美国东南部的大陆边缘从非洲西北部裂开，大西洋开始形成。在中大西洋海脊开始适应海底扩张之前，裂谷通过地壳和岩石圈的机械拉伸发生，可能伴随着广泛的加热和火山作用。在这个大陆伸展阶段，古老的断层线和阿巴拉契亚基底的缝合线可能被重新激活，熔岩流可能填满了早期的裂谷盆地。目前尚不清楚这场火山活动是北美和非洲分裂的原因还是结果。这个问题可以通过新的海洋地球物理数据来解决，这些数据将涵盖从大陆架到邻近深海平原的部分边缘，距离约400公里。通过深层沉积物和基底的地震图像，科学家们可以确定卡罗莱纳海槽、卡罗莱纳海岸和布莱克高原上的基底断层和熔岩流之间的关系，这些海槽位于佐治亚州和佛罗里达州更南边的地方。大西洋大陆边缘的这两段特别令人感兴趣，因为布莱克高原比卡罗莱纳海槽宽得多。要么布莱克高原形成了一个大陆地壳区块，在大陆裂谷过程中没有太大的伸展，要么它是一个主要由超大陆盘古大陆破裂时形成的火山岩组成的高原。海洋地球物理考察将涉及两艘船，即R/V Marcus Langseth号和R/V Neil Armstrong号，以及将用于记录地震波以绘制海底地下室结构图的海底地震仪。调查小组将邀请其他大学的学生和职业早期科学家参与考察，并将组织两个短期课程，让职业早期科学家参与数据的分析和解释。虽然这项研究的重点是美国东南部边缘，但结果将为世界其他大陆边缘正在进行的和未来的研究提供参考。大陆裂谷之下的软流圈可以在存在深层热异常的情况下产生大量熔体，或者由于岩石圈变薄的减压而产生大量熔体。在这种背景下，岩石圈板块伸展与岩浆的产生和输送之间的相互作用还不是很清楚。科学家团队将对美国东南部裂谷边缘进行主动震源地震调查，以更好地了解大陆解体期间构造伸展和岩浆活动之间的反馈，以及大西洋中部海底扩张的开始。布莱克高原的大陆边缘比北侧的卡罗莱纳海槽边缘要宽得多，这表明大陆岩石圈的伸展和破裂在这两个相邻的裂谷段上的过程是不同的。地幔温度异常、地幔熔融和大陆岩石圈结构继承性的差异可能都影响了这两种截然不同的裂谷类型。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，布莱克高原盆地在解体之前比卡罗莱纳海槽盆地伸展得更宽。2)裂谷过程中，岩浆供给与布莱克高原地壳伸展同步，而南卡罗来纳海槽以下陆壳迅速变薄，没有广泛的岩浆活动。3)裂谷作用时，布莱克高原深部地幔明显高于卡罗莱纳海槽之下的地幔，这将影响岩石圈的流变性和地幔的熔融程度。为了评估与裂谷有关的过程如何影响地壳结构和沉积物地层学，科学小组将使用R/V Marcus Langseth收集大约4500公里的二维地震反射数据和900公里的海底地震仪折射数据。在这次考察中，来自国家仪器中心(OBSIC)的39个OBS将与R/V尼尔·阿姆斯特朗一起部署。地震速度和反射率的图像将为沉积地层、玄武岩流动和地壳规模断层的几何形状以及火成岩地壳的厚度和组成提供新的见解。活动震源地震数据和现有玄武岩样品的地球化学分析将被用来推断卡罗莱纳海槽和布莱克高原过去的变形和侵入壳和喷出壳的侵位。来自其他美国机构的学生和初出茅庐的科学家将被邀请在尼尔·阿姆斯特朗或马库斯·朗塞斯号R/V上从事海洋地震反射和折射数据的获取和分析。这些远洋学员将在地震反射和折射数据的采集和船上处理方面获得经验。此外，为期一周的关于OBS折射数据分析和多道地震(MCS)反射数据处理的短期课程将帮助培训参与者如何使用这些新的地震数据。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.