Collaborative Research: Rift Dynamics during the Formation of the Carolina Trough and Blake Plateau

Lead PI: Dr. Anne Becel

Unit Affiliation: Marine and Polar Geophysics, Lamont-Doherty Earth Observatory (LDEO)

May 2022 - April 2023
North America
Project Type: Research

DESCRIPTION: 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.