Periodic Reporting for period 2 - SUBIMAP (SUBduction Initiation at Magma-poor rifted margins: an Atlantic Perspective)
Période du rapport: 2024-01-01 au 2024-12-31
Subduction initiation is a key process in the Wilson cycle that remains, however, as a glaring unknown in Plate Tectonics. The reactivated magma-poor rifted margins of the southern North Atlantic preserve different fossilized stages of the Wilson cycle, representing a unique setting to study the role of pre-existing extensional structures on contractional reactivation and lithospheric rupture during subduction inception. The NW Pacific convergent margins, in the other hand, host several ongoing subduction initiation sites that allow for the study of the birth and evolution of active nascent subduction zones. This project focuses primarily on the study of the contractional deformation that precedes and/or accompanies subduction initiation, and the role of inherited structures on the reactivation of passive margins using qualitative and quantitative constraints derived from active examples in SE Asia and the fossilized reactivated Iberian Atlantic margins coupled with geodynamic models. Our measurements show that the Continent- Ocean Transition localises major tectonic structures and that the basement nature, structure and thickness condition the distribution of tectonic structures and the styles of contractional deformation. In active subduction zones, deformation propagates laterally and leads to a diachronic evolution of subduction initiation and progression that results in the record of different evolutionary stages along-strike. The mapping of major tectonic structures that localise contractional deformation during these successive evolutionary stages provides critical constraints for investigating natural hazards, such as earthquakes and tsunamis.
The SUBIMAP project encompassed a Project Managing Part, an Observational Part, a Reconstruction Part, a Geodynamic Part, a Teaching and Supervising Part, and a Communication and Outreach Part.
The Project Managing included the purchase of the equipment, the scientific and budget management, the organisation of trips and stays for scientific conferences, project meetings and Secondments, and the preparation and submission of a Data Management Plan and the Initial and Final Period Project Reports.
The Observational Part of the project based mainly on the seismo-stratigraphic and geological interpretation of compiled 2D seismic reflection profiles. We mapped tectonic and gravitational structures and the rift- and orogenic-related seismo-stratigraphic units and depocenters in order to identify styles and stages of contractional deformation and the first-order structure of the margins and basins.
Our main results along the North Iberian margin show major contractional tectonic structures affecting oceanic and transitional basement along the Continent-Ocean Transition. A southward-subducted oceanic basement separated by a megathrust from an overlying buried accretionary prism supports incipient immature aborted Alpine subduction of oceanic crust. However, we identified overthrust transitional basement that led to basement thickening, and thrust and folded transitional basement and sediments. These deformation styles affecting transitional basement may be compatible with the occurrence of modelled lithospheric shear zones or, on the contrary, with intraplate deformation. As a result, we submitted the conceptual manuscript “A unique fossilized onset of convergent tectonics in the Atlantic Ocean”. We also built a unique Bay of Biscay time cross-section that enabled the drafting of a manuscript discussing the preservation of different stages of the Wilson cycle in one location.
In the West Iberian margin, we mapped mild reactivation of pre-existing extensional faults and discrete folding and/or uplift, halokynetic-related structures along areas of the continental platform, and thrusts and folds. The distribution of newly formed thrusts and/or reactivation of pre-existing faults correlates with variations on the basement nature and/or thickness. In the NW Sulu Sea in SE Asia, mud flows and thrusting and folding affected distinctively two basin domains structured by accommodation zones that may link rift segments. As a result, we published the manuscript “Structure and Tectonic Evolution of the NW Sulu Sea (SE Asia)”. Our measurements in active propagating subduction zones in the convergent margins of SE Asia show diffuse thrusting and folding along the Continent-Ocean Transition that evolves laterally to plate decoupling, megathrust development, and formation and evolution of subduction-related structural domains during the birth of the subduction zones. As a result, we have been drafting a conceptual manuscript entitled “Subduction Initiation, Propagation and Progression recorded in the Sulu and Celebes Seas (SE Asia).
The Reconstruction Part consisted on training and development of deformable plate kinematic reconstruction aiming at understanding the temporal evolution of styles of reactivation affecting magma-poor rifted margins.
The Geodynamic Part involved training courses at the University of Mainz and an ongoing MSc thesis to run in-progress 2D thermomechanical numerical models simulating reactivation of passive margins. We used our observations along the North Iberian margin and available geophysical data to test the role of crustal thickness variations, serpentinization, and passive margin length on the development of different styles of contractional deformation at different scales.
The project investigations resulted in 4 lectures for undergraduate students, a project logo and sites on Social media, 1 published paper, 1 submitted paper, 8 presentations at international scientific meetings, 6 talks at seminars at the host institutions, and 2 media interviews.
The Project Managing included the purchase of the equipment, the scientific and budget management, the organisation of trips and stays for scientific conferences, project meetings and Secondments, and the preparation and submission of a Data Management Plan and the Initial and Final Period Project Reports.
The Observational Part of the project based mainly on the seismo-stratigraphic and geological interpretation of compiled 2D seismic reflection profiles. We mapped tectonic and gravitational structures and the rift- and orogenic-related seismo-stratigraphic units and depocenters in order to identify styles and stages of contractional deformation and the first-order structure of the margins and basins.
Our main results along the North Iberian margin show major contractional tectonic structures affecting oceanic and transitional basement along the Continent-Ocean Transition. A southward-subducted oceanic basement separated by a megathrust from an overlying buried accretionary prism supports incipient immature aborted Alpine subduction of oceanic crust. However, we identified overthrust transitional basement that led to basement thickening, and thrust and folded transitional basement and sediments. These deformation styles affecting transitional basement may be compatible with the occurrence of modelled lithospheric shear zones or, on the contrary, with intraplate deformation. As a result, we submitted the conceptual manuscript “A unique fossilized onset of convergent tectonics in the Atlantic Ocean”. We also built a unique Bay of Biscay time cross-section that enabled the drafting of a manuscript discussing the preservation of different stages of the Wilson cycle in one location.
In the West Iberian margin, we mapped mild reactivation of pre-existing extensional faults and discrete folding and/or uplift, halokynetic-related structures along areas of the continental platform, and thrusts and folds. The distribution of newly formed thrusts and/or reactivation of pre-existing faults correlates with variations on the basement nature and/or thickness. In the NW Sulu Sea in SE Asia, mud flows and thrusting and folding affected distinctively two basin domains structured by accommodation zones that may link rift segments. As a result, we published the manuscript “Structure and Tectonic Evolution of the NW Sulu Sea (SE Asia)”. Our measurements in active propagating subduction zones in the convergent margins of SE Asia show diffuse thrusting and folding along the Continent-Ocean Transition that evolves laterally to plate decoupling, megathrust development, and formation and evolution of subduction-related structural domains during the birth of the subduction zones. As a result, we have been drafting a conceptual manuscript entitled “Subduction Initiation, Propagation and Progression recorded in the Sulu and Celebes Seas (SE Asia).
The Reconstruction Part consisted on training and development of deformable plate kinematic reconstruction aiming at understanding the temporal evolution of styles of reactivation affecting magma-poor rifted margins.
The Geodynamic Part involved training courses at the University of Mainz and an ongoing MSc thesis to run in-progress 2D thermomechanical numerical models simulating reactivation of passive margins. We used our observations along the North Iberian margin and available geophysical data to test the role of crustal thickness variations, serpentinization, and passive margin length on the development of different styles of contractional deformation at different scales.
The project investigations resulted in 4 lectures for undergraduate students, a project logo and sites on Social media, 1 published paper, 1 submitted paper, 8 presentations at international scientific meetings, 6 talks at seminars at the host institutions, and 2 media interviews.
The project outcomes enable to advance our understanding of the structures and styles of deformation that develop prior to and during the initiation of subduction. Observations of fossilized Alpine contractional tectonics structures along the reactivated Iberian Atlantic margins suggest that the nature of the basement and its thickness variations are major constraints on the inversion of pre-existing faults and/or the formation of contractional structures and the development and spatial distribution of styles of contractional deformation. Our tectonic mapping of contractional structures and subduction-related structural domains in the Sulu and Celebes seas allowed for the definition and first-time characterisation of the tectonism of stages of diffuse contractional deformation, subduction initiation, propagation and progression. The results critically constrain the lateral propagation and diachronic evolution of subduction initiation that results in along-strike structural variability. The mapping of margin domains and tectonic structures localising deformation during passive margin reactivation and subduction initiation are critical to study natural hazards and perform data-based calculations of seismogenic and tsunamigenic potential of major tectonic structures that develop during these successive evolutionary stages. These unexplored issues and the results and training obtained from the SUBIMAP action guided the preparation and submission of two scientific proposals to high competitive calls. 6 potential scientific papers are expected to be published addressing the work and the results of SUBIMAP, as well as an associated master dissertation, and 2 additional contributions to scientific meetings.