Subduction initiation in the Scotia Sea region and opening of the Drake Passage: When and why?

During evolution of the South Sandwich subduction zone, which has consumed South American Plate oceanic lithosphere, somehow continental crust of both the South American and Antarctic plates have become incorporated into its upper plate. Continental fragments of both plates are currently separated by small oceanic basins in the upper plate above the South Sandwich subduction zone, in the Scotia Sea region, but how fragments of both continents became incorporated in the same upper plate remains enigmatic. Here we present an updated kinematic reconstruction of the Scotia Sea region using the latest published marine magnetic anomaly constraints, and place this in a South America-Africa-Antarctica plate circuit in which we take intracontinental deformation into account. We show that a change in marine magnetic anomaly orientation in the Weddell Sea requires that previously inferred initiation of subduction of South American oceanic crust of the northern Weddell Sea below the eastern margin of South Orkney Islands continental crust, then still attached to the Antarctic Peninsula, already occurred around 80 Ma. Subsequently, between ~71–50 Ma, we propose that the trench propagated northwards into South America by delamination of South American lithosphere: this resulted in the transfer of delaminated South American continental crust to the overriding plate of the South Sandwich subduction zone. We show that continental delamination may have been facilitated by absolute southward motion of South America that was resisted by South Sandwich slab dragging. Pre-drift extension preceding the oceanic Scotia Sea basins led around 50 Ma to opening of the Drake Passage, preconditioning the southern ocean for the Antarctic Circumpolar Current. This 50 Ma extension was concurrent with a strong change in absolute plate motion of the South American Plate that changed from S to WNW, leading to upper plate retreat relative to the more or less mantle stationary South Sandwich Trench that did not partake in the absolute plate motion change. While subduction continued, this mantle-stationary trench setting lasted until ~30 Ma, after which rollback started to contribute to back-arc extension. We find that roll-back and upper plate retreat have contributed more or less equally to the total amount of ~2000 km of extension accommodated in the Scotia Sea basins. We highlight that viewing tectonic motions in a context of absolute plate motion is key for identifying slab motion (e.g., rollback, trench-parallel slab dragging) and consequently mantle-forcing of geological processes

Reconstructing lost plates of the Panthalassa Ocean

Compared to continental lithosphere, oceanic lithosphere has a limited lifespan at the Earth’s surface. As a result of its continuous subduction and formation at mid-ocean ridges, modern oceanic crust is almost nowhere older than ~200 Ma. This implies that the lithosphere that was underlying ancestral oceans, such as the Panthalassa Ocean surrounding Pangea during its culmination in late Paleozoic – early Mesozoic times, has (almost) all been lost to subduction. As a result, deep-time plate tectonic reconstructions rely primarily on geological, paleontological and paleomagnetic data from the continents. Such reconstructions portray the distribution of plates that host continents through geological time, but generally lack (or include only conceptual) plate motions and -geometry in the oceanic domains. In this thesis, approaches are developed and data is collected that improve deep-time global plate kinematic reconstructions of the Panthalassa Ocean through quantitative restoration of lost oceanic plates. First, all available data from oceanic lithosphere of the present-day descendant of the Panthalassa, the Pacific Ocean, that did not (yet) subduct is used. The oldest part of the Pacific Plate, which originated in Jurassic time, contains magnetic lineations in three orientations that constrain relative plate motions of three conceptual plates conjugate to the Pacific (Izanagi in the northeast, Farallon in the northeast and Phoenix in the south) back to ~190 Ma. In chapter 1, the plate tectonic configuration that led to the birth of the Pacific Plate is reconstructed. Second, the location and tectonic nature of the boundaries of the Panthalassa Ocean through time are defined, which relies on reconstruction of Pangea’s (and post-Pangea’s) external trenches relative to the surrounding continents, and involves the restoration of complex crustal deformation at subduction plate boundary zones. In chapters 2-5 regional reconstructions are presented of the Pacific margin of Mexico and Caribbean region. The third step involves the use of data from fully subducted lithosphere. This includes paleomagnetic and stratigraphic data from ‘Ocean Plate Stratigraphy’ materials that were scraped off during subduction and are now exposed in the circum-Panthalassa accretionary complexes. Furthermore, seismic tomographic images reveal the locations of subducted material in the mantle that are correlated to reconstructed intra-oceanic or continental margin subduction zones, thereby constraining the position of these subduction zones relative to the mantle. Chapters 6 and 7 present reconstructed Permian-Cretaceous plate motions of the Farallon, Izanagi and Phoenix plates based on paleomagnetic data from OPS remnants exposed in the accretionary prisms of Mexico, Costa Rica, Japan and New Zealand, as well as of an intra-oceanic subduction zone of which the remnant arc is exposed in Japan

Reconstructing lost plates of the Panthalassa Ocean

Compared to continental lithosphere, oceanic lithosphere has a limited lifespan at the Earth’s surface. As a result of its continuous subduction and formation at mid-ocean ridges, modern oceanic crust is almost nowhere older than ~200 Ma. This implies that the lithosphere that was underlying ancestral oceans, such as the Panthalassa Ocean surrounding Pangea during its culmination in late Paleozoic – early Mesozoic times, has (almost) all been lost to subduction. As a result, deep-time plate tectonic reconstructions rely primarily on geological, paleontological and paleomagnetic data from the continents. Such reconstructions portray the distribution of plates that host continents through geological time, but generally lack (or include only conceptual) plate motions and -geometry in the oceanic domains. In this thesis, approaches are developed and data is collected that improve deep-time global plate kinematic reconstructions of the Panthalassa Ocean through quantitative restoration of lost oceanic plates. First, all available data from oceanic lithosphere of the present-day descendant of the Panthalassa, the Pacific Ocean, that did not (yet) subduct is used. The oldest part of the Pacific Plate, which originated in Jurassic time, contains magnetic lineations in three orientations that constrain relative plate motions of three conceptual plates conjugate to the Pacific (Izanagi in the northeast, Farallon in the northeast and Phoenix in the south) back to ~190 Ma. In chapter 1, the plate tectonic configuration that led to the birth of the Pacific Plate is reconstructed. Second, the location and tectonic nature of the boundaries of the Panthalassa Ocean through time are defined, which relies on reconstruction of Pangea’s (and post-Pangea’s) external trenches relative to the surrounding continents, and involves the restoration of complex crustal deformation at subduction plate boundary zones. In chapters 2-5 regional reconstructions are presented of the Pacific margin of Mexico and Caribbean region. The third step involves the use of data from fully subducted lithosphere. This includes paleomagnetic and stratigraphic data from ‘Ocean Plate Stratigraphy’ materials that were scraped off during subduction and are now exposed in the circum-Panthalassa accretionary complexes. Furthermore, seismic tomographic images reveal the locations of subducted material in the mantle that are correlated to reconstructed intra-oceanic or continental margin subduction zones, thereby constraining the position of these subduction zones relative to the mantle. Chapters 6 and 7 present reconstructed Permian-Cretaceous plate motions of the Farallon, Izanagi and Phoenix plates based on paleomagnetic data from OPS remnants exposed in the accretionary prisms of Mexico, Costa Rica, Japan and New Zealand, as well as of an intra-oceanic subduction zone of which the remnant arc is exposed in Japan

The dynamic history of 220 Million Years of subduction below Mexico: A correlation between slab geometry and overriding plate deformation based on geology, paleomagnetism, and seismic tomography

Global tectonic reconstructions of pre‐Cenozoic plate motions rely primarily on paleomagnetic and geological data from the continents, and uncertainties increase significantly with deepening geological time. In attempting to improve such deep‐time plate kinematic reconstructions, restoring lost oceanic plates through the use of geological and seismic tomographical evidence for past subduction is key. The North American Cordillera holds a record of subduction of oceanic plates that composed the northeastern Panthalassa Ocean, the large oceanic realm surrounding Pangea in Mesozoic times. Here we present new paleomagnetic data from subduction‐related rock assemblages of the Vizcaíno Peninsula of Baja California, Mexico, which yield a paleolatitudinal plate motion history equal to that of the North American continent since Late Triassic time. This indicates that the basement rocks of the Vizcaíno Peninsula formed in the forearc of the North American Plate, adjacent to long‐lived eastward dipping subduction at the southern part of the western North American continental margin. Tomographic images confirm long‐lived, uninterrupted eastward subduction. We correlate episodes of overriding plate shortening and extension to flat and steep segments of the imaged slab. By integrating paleomagnetic, geological, and tomographic evidence, we provide a first‐order model that reconciles absolute North American plate motion and the deformation history of Mexico since Late Triassic time with modern slab structure