Periodic Reporting for period 1 - SUBIMAP (SUBduction Initiation at Magma-poor rifted margins: an Atlantic Perspective)
Reporting period: 2022-01-01 to 2023-12-31
Subduction initiation is a key process in the Wilson cycle. How it unfolds remains a glaring unknown in our understanding of the evolution of the Earth’s oceans and mountain belts. Tectonic inheritance acquired at passive margins imposes a major control on contractional reactivation and how subduction zones may form and propagate in Atlantic-type oceans. In particular, magma-poor rifted margins seem to share characteristics that may localize compressional deformation and lithospheric rupture. This project aims to study contractional deformation that precedes and/or accompanying subduction initiation and the role of inherited structures on the reactivation of passive margins using qualitative and quantitative constraints derived from examples along the southern North Atlantic rifted margins, coupled with geodynamic models of subduction initiation. The study region encompasses a number of reactivated magma-poor rifted margins that preserve different stages of the Wilson cycle. We will first map different Alpine styles and stages of margin reactivation along the Iberian Atlantic margins and interpret the first-order rift structure along selected sections along the Newfoundland margin. Direct observations will be used to constrain kinematic reconstructions of the spatial and temporal evolution of Iberian Atlantic margins during Alpine reactivation.The identified key rift parameters that control reactivation will then be tested and explored using numerical geodynamic models. The project will also involve the characterisation and mapping of intraplate deformation and subduction-related structural domains along evolving and nascent subduction trenches along the Sulu and Celebes Seas in SE Asia, located in the Pacific Ocean. SE Asia is a valuable setting to study intraplate deformation and subduction initiation and propagation in a convergent setting constrained by the evolution of propagating arcs, in contrast and complementary to the Iberian Atlantic margins, which represents a unique fossilized example to study intraplate deformation and subduction initiation affecting pristine archetypal magma-poor margins. In conjunction, the data available along SE Asia and along the southern North Atlantic will enable the development of a comprehensive and unique global study of the onset of convergent tectonics and the closure of Earth´s oceans, with fundamental implications for the study of natural hazars, such as eartquakes. Outcomes will provide further insights into fundamental geological systems and will be of broad interest to other communities working on active rifts, mid-ocean ridges, subduction zones, and collisional orogens.
The work done during the Outgoing Phase of the project included managing procedures as part of the Work Package-1, the development of the Observational Part as part of the Work Package-2, teaching of 2 lectures for the fourth-year/senior course EASC 4420 at Memorial Unversity of Newfoundland as part of Work Package-5, and science communication, with 6 contributions to international meetings, 5 presentations at Memorial University of Newfoundland, and 3 interviews on the media as part of Work Package-6.
The Observational part of the project focused on the characterisation of the structure of the North Iberian and West Iberian margins in the Atlantic Ocean and the Sulu Sea in the Pacific Ocean, based on the seismo-stratigraphic and geological interpretation of the compiled 2D seismic reflection profiles. We mapped the tectonic and gravitational structures and the rift- and orogenic-related seismo-stratigraphic horizons and units and depocenters in order to identify and describe different styles and stages of contractional deformation and the first-order rift structure. In order to date the depocenters and tectonic structures, we tied boreholes to seismic data creating Time to Depth charts using velocity logs in key areas. We also selected and interpreted some seismic profiles along the Newfoundland margin that provide pristine extensional templates. The MSCA fellow was also involved in the acquisition of reflection and refraction/wide angle seismic profiles along the West Iberian margin during the ATLANTIS marine research campaing.
We focused primarily on our results along the toe of the continental slope along the North Iberian margin. This area is unique along the Atlantic Ocean because it preserves a buried and fossilized accretionary wedge that developed during the initial underthrusting phases that mark subduction initiation, and underthrusting affected both transitional basement and oceanic crust. Our observations show an incipiently southward-subducted oceanic basement separated by a megathrust from an overlying buried accretionary prism, supporting incipient immature aborted Alpine subduction of oceanic crust at the western North Iberian margin. At the central part of the margin, however, we identified overthrust basement that led to basement thickening, and thrust and folded basement and sediments. We also built a unique time cross-section from the Bay of Biscay that illustrates multiple stages of the Wilson cycle in one location. It shows structural evidence resulting from the complete extensional cycle and the beginning of the convergent phases of the Wilson cycle, enabling the discussion of the preservation of different stages of the Wilson cycle and, ultimately, the opening and closure of oceans. As a result, we drafted 2 manuscripts to submit in the following months.
We focused secondly on the results along the NW Sulu Sea. Our observations define the Piedra-Blanca and Rasa structural domains, separated by the NW-Sulu-Break structure, NW-SE and NE-SW trending accommodation zones that may link rift segments with distinctive deformation patterns, and thrusting and folding in the Piedra-Blanca domain and mudflows in the Rasa domain during the contractional basin reactivation. As a result, we submitted a manuscript. We have also characterised the structure and evolution of the Sulu, North Sulawesi and Cotobato trenches, developed along the Sulu and Celebes seas.
The Observational part of the project focused on the characterisation of the structure of the North Iberian and West Iberian margins in the Atlantic Ocean and the Sulu Sea in the Pacific Ocean, based on the seismo-stratigraphic and geological interpretation of the compiled 2D seismic reflection profiles. We mapped the tectonic and gravitational structures and the rift- and orogenic-related seismo-stratigraphic horizons and units and depocenters in order to identify and describe different styles and stages of contractional deformation and the first-order rift structure. In order to date the depocenters and tectonic structures, we tied boreholes to seismic data creating Time to Depth charts using velocity logs in key areas. We also selected and interpreted some seismic profiles along the Newfoundland margin that provide pristine extensional templates. The MSCA fellow was also involved in the acquisition of reflection and refraction/wide angle seismic profiles along the West Iberian margin during the ATLANTIS marine research campaing.
We focused primarily on our results along the toe of the continental slope along the North Iberian margin. This area is unique along the Atlantic Ocean because it preserves a buried and fossilized accretionary wedge that developed during the initial underthrusting phases that mark subduction initiation, and underthrusting affected both transitional basement and oceanic crust. Our observations show an incipiently southward-subducted oceanic basement separated by a megathrust from an overlying buried accretionary prism, supporting incipient immature aborted Alpine subduction of oceanic crust at the western North Iberian margin. At the central part of the margin, however, we identified overthrust basement that led to basement thickening, and thrust and folded basement and sediments. We also built a unique time cross-section from the Bay of Biscay that illustrates multiple stages of the Wilson cycle in one location. It shows structural evidence resulting from the complete extensional cycle and the beginning of the convergent phases of the Wilson cycle, enabling the discussion of the preservation of different stages of the Wilson cycle and, ultimately, the opening and closure of oceans. As a result, we drafted 2 manuscripts to submit in the following months.
We focused secondly on the results along the NW Sulu Sea. Our observations define the Piedra-Blanca and Rasa structural domains, separated by the NW-Sulu-Break structure, NW-SE and NE-SW trending accommodation zones that may link rift segments with distinctive deformation patterns, and thrusting and folding in the Piedra-Blanca domain and mudflows in the Rasa domain during the contractional basin reactivation. As a result, we submitted a manuscript. We have also characterised the structure and evolution of the Sulu, North Sulawesi and Cotobato trenches, developed along the Sulu and Celebes seas.
From the integration of the tectonic structures that we observed along transitional basement along the North Iberian margin, published velocity and tectonic models, and geodynamically modelled lithospheric shear zones, we discuss three different tectonic scenarios accounting for contractional deformation along the transitional basement. Two scenarios support the localisation of contractional deformation at the base of the crust with the formation of lithospheric shear zones and a third scenario suggests, on the contrary, that there was intraplate deformation in the absence of a clearly imaged plate boundary. Variations in the basement nature and rheology, such as the occurrence of serpentinization fronts, and thickness changes, may have constrained the type and distribution of contractional structures.
Along the Sulu Sea, our observations show that mudflow in the Rasa Domain and thrusting and folding of thinned magmatic basement in the Piedra-Blanca domain of the NW Sulu Sea accommodated intraplate deformation during the basin contractional reactivation. Our results suggest that the end of widespread contraction along the NW Sulu Sea in the Late Miocene may be linked to subduction initiation along the SE Sulu Sea mainly because the nucleation of a megathrust and the development of the Sulu Trench may have focused contractional deformation.
Along the Sulu Sea, our observations show that mudflow in the Rasa Domain and thrusting and folding of thinned magmatic basement in the Piedra-Blanca domain of the NW Sulu Sea accommodated intraplate deformation during the basin contractional reactivation. Our results suggest that the end of widespread contraction along the NW Sulu Sea in the Late Miocene may be linked to subduction initiation along the SE Sulu Sea mainly because the nucleation of a megathrust and the development of the Sulu Trench may have focused contractional deformation.