Academic literature on the topic 'Continental margins'

ABSTRACT Submarine landscapes, like their terrestrial counterparts, are sculpted by autogenic sedimentary processes toward morphologies at equilibrium with their allogenic controls. While submarine channels and nearby, inter-channel continental-margin areas share boundary conditions (e.g., terrestrial sediment supply, tectonic deformation), there are significant differences between the style, recurrence, and magnitude of their respective autogenic sedimentary processes. We predict that these process-based differences affect the rates of geomorphic change and equilibrium (i.e., graded) morphologies of submarine-channel and continental-margin longitudinal profiles. To gain insight into this proposed relationship, we document, classify (using machine learning), and analyze longitudinal profiles from 50 siliciclastic continental margins and associated submarine channels which represent a range of sediment-supply regimes and tectonic settings. These profiles tend to evolve toward smooth, lower-gradient longitudinal profiles, and we created a “smoothness” metric as a proxy for the relative maturity of these profiles toward the idealized equilibrium profile. Generally, higher smoothness values occur in systems with larger sediment supply, and the smoothness of channels typically exceeds that of the associated continental margin. We propose that the high rates of erosion, bypass, and deposition via sediment gravity flows act to smooth and mature channel profiles more rapidly than the surrounding continental margin, which is dominated by less-energetic diffusive sedimentary processes. Additionally, tectonic deformation will act to reduce the smoothness of these longitudinal profiles. Importantly, the relationship between total sediment supply and the difference between smoothness values of associated continental margins and submarine channels (the “smoothness Δ”) follows separate trends in passive and active tectonic settings, which we attribute to the variability in relative rates of smoothness development between channelized and inter-channel environments in the presence or absence of tectonic deformation. We propose two endmember pathways by which continental margins and submarine channels coevolve towards their respective equilibrium profiles with increased sediment supply: 1) Coupled Evolution Model (common in passive tectonic settings), in which the smoothness Δ increases only slightly before remaining static, and 2) Decoupled Evolution Model (common in active tectonic settings), in which the smoothness Δ increases more rapidly and to a greater final value. Our analysis indicates that the interaction of the allogenic factors of sediment supply and tectonic deformation with the autogenic sedimentary processes characteristic of channelized and inter-channel areas of the continental margin may account for much of the variability between coevolution pathways and depositional architectures.

Understanding the conditions for forming new subduction zones at passive continental margins is important for understanding plate tectonics and the Wilson cycle. Previous models of subduction initiation (SI) at passive margins generally ignore effects due to the lateral transition from oceanic to continental lithosphere. Here, we use three-dimensional numerical models to study the possibility of propagating convergent plate margins from preexisting intraoceanic subduction zones along passive margins [subduction propagation (SP)]. Three possible regimes are achieved: (i) subducting slab tearing along a STEP fault, (ii) lateral propagation–induced SI at passive margin, and (iii) aborted SI with slab break-off. Passive margin SP requires a significant preexisting lithospheric weakness and a strong slab pull from neighboring subduction zones. The Atlantic passive margin to the north of Lesser Antilles could experience SP if it has a notable lithospheric weakness. In contrast, the Scotia subduction zone in the Southern Atlantic will most likely not propagate laterally.

Continental breakup along transform margins produces a sequence of (1) continent-continent, (2) continent-oceanic, (3) continent-ridge, and (4) continent-oceanic juxtapositions. Spreading ridges are the main sources of heat, which is then distributed by diffusion and advection. Previous work focused on the thermal evolution of transform margins built on 2D numerical models. Here we use a 3D FEM model to obtain the first order evolution of temperature, uplift/subsidence, and thermal maturity of potential source rocks. Snapshots for all four transform phases are provided by 2D sections across the margin. Our 3D approach yields thermal values that lie in between the previously established 2D end-member models. Additionally, the 3D model shows heat transfer into the continental lithosphere across the transform margin during the continental-continental transform stage ignored in previous studies. The largest values for all investigated quantities in the continental area are found along the transform segment between the two ridges, with the maximum values occurring near the transform-ridge corner of the trailing continental edge. This boundary segment records the maximum thermal effect up to 100 km distance from the transform. We also compare the impact of spreading rates on the thermal distribution within the lithosphere. The extent of the perturbation into the continental areas is reduced in the faster models due to the reduced exposure times. The overall pattern is similar and the maximum values next to the transform margin is essentially unchanged. Varying material properties in the upper crust of the continental areas has only a minor influence.