Marine geophysical investigation of the Chain Fracture Zone in the equatorial Atlantic from the PI‐LAB experiment

Abstract

The Chain Fracture Zone is a 300 km long transform fault that offsets the Mid Atlantic Ridge. We analysed new multibeam bathymetry, backscatter, gravity and magnetic data with 100 % multibeam bathymetric data over the active transform valley and adjacent spreading segments as part of the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI‐LAB) Experiment. Analyses of these data sets allow us to determine the history and mode of crustal formation and the tectonic evolution of the transform system and adjacent ridges over the past 20 M.y. We model the total field magnetic anomaly to determine the age of the crust along the northern ridge segment to better establish the timing of the variations in the seafloor fabric and the tectonic‐magmatic history of the region. Within the active transform fault zone, we observe 4 distinct positive flower structures with several en échelon fault scarps visible in the backscatter data. We find up to ‐10 mGal residual Mantle Bouguer Anomaly in the region of the largest positive flower structure within the transform zone suggesting crustal thickening relative to the crustal thinning typically observed in fracture zones in the Atlantic. The extensional/compressional features observed in the Chain Transform are less pronounced than those observed further north in the Vema, St Paul and Romanche and may be due to local ridge segment adjustments.

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Identifiers

ORCID for Nicholas Harmon: orcid.org/0000-0002-0731-768X

ORCID for Saikiran Tharimena: orcid.org/0000-0002-1841-1911

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