A New Model for the Evolution of Oceanic Transform Faults Based on 3D Broadband Seismic Observations From São Tomé and Príncipe in the Eastern Gulf of Guinea. (27th November 2022)

• Record Type: Journal Article
• Authors: Thomas, Myron F. H.; Heine, Christian; van Itterbeeck, Jimmy; Ostanin, Ilya; Seregin, Andrey; Spaak, Michael; Morales, Tamara; Essink, Tess Oude
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 23:Number 11(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-27
• Subjects: oceanic crust -- transform faults -- PSDM seismic -- nodal basin -- Atlantic -- extension; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010351
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Oceanic Transform Faults are one of manifestations of the three major plate boundaries and a key tectonic feature of oceanic crust. They are broadly considered to accommodate strike‐slip displacement along simple vertical faults and to be largely without magmatic addition. We present the first observations from broadband 3D seismic of buried, Cretaceous‐aged transform faults in the Gulf of Guinea with complex internal architectures including crustal scale detachments and rotated packages of volcanics within oceanic crust. In the study area, several Oceanic Fracture Zones (OFZ) are described from Top Crust to Moho. OFZ scarps are observed to connect at depth with zones of low angle reflectivity which dip into the OFZ and perpendicular to the spreading orientation. At depth they detach onto the Moho, necking the adjacent crust in the manner of extensional shear zones. Thickly stacked and tilted reflectors, interpreted as extrusive lava flows, are common above the shear zones and infill up to 75% of the crustal thickness. The entire OFZ stratigraphy is overlain and sealed by late‐stage lavas that are continuous from the abyssal hills of the trailing spreading ridge. These insights demonstrate complexity previously only predicted in numerical simulations. We propose a model with extension at a high angle to the spreading orientation along a low angle shear zone that acts as a conduit for decompression related melt and volcanism. We conclude that oceanic transforms are non‐conservative and not simple strike slip fault zones, contradicting the conventional view. Plain Language Summary: Oceanic transform faults (OTFs) are one of three types of plate boundaries and an integral component of the seafloor fabric which is used to reconstruct the evolution of oceanic basins. They laterally offset active seafloor spreading ridges and record the geometrical configuration of past spreading ridges as the "train tracks of plate tectonics"—oceanic fracture zones. OTFs are regarded as "conservative"—simple vertical fault planes where no crustal material was added or destroyed, yet observational support for the 3D crustal‐scale architecture of these faults has been lacking. Here, we present observations from a proprietary, high‐resolution industry 3D seismic data set acquired in the Gulf of Guinea. We document, for the first time, the 3D architecture of these faults in Cretaceous‐aged oceanic crust (105–115 Million years old), now buried underneath more than 3 km of sediments and formed shortly after South America‐Africa breakup at center of the former Gondwana supercontinent. We show that oceanic transform faults have a complex 3D architecture, formed by a two‐stage process of extension/deformation and infilling through lava flows. Our work highlights that this type of plate boundary can no longer be regarded as simple conservative and supports similar conclusions from recent geodynamic models. Key Points: Oceanic transforms faults are interpreted from 3D Pre‐Stack Depth Migrated Seismic with a fidelity unavailable with standard methods For the first time, we document intra‐transform detachments and lava growth packages along 180 km high‐resolution seismic profiles and in 3D Inconsistent with a simple strike slip model this supports numerical model outcomes of oblique extension and two stage crustal accretion