Ridge Jumps and Mantle Exhumation in Back-Arc Basins

21 pages, 8 figures, 2 tables, supplementary material https://doi.org/10.3390/geosciences11110475.-- Data Availability Statement: The models run for this publication used ASPECT version 2.30-pre (master, commit d5995ea), deal.II 9.2.0, Trilinos 12.10.1, and p4est 2.2.0. The code and the main parameter files can be found in the repository at https://github.com/valemagni/aspect/tree/Magni_etal_2021_geosciences (assessed on 11 November 2021)
Back-arc basins in continental settings can develop into oceanic basins, when extension lasts long enough to break up the continental lithosphere and allow mantle melting that generates new oceanic crust. Often, the basement of these basins is not only composed of oceanic crust, but also of exhumed mantle, fragments of continental crust, intrusive magmatic bodies, and a complex mid-ocean ridge system characterised by distinct relocations of the spreading centre. To better understand the dynamics that lead to these characteristic structures in back-arc basins, we performed 2D numerical models of continental extension with asymmetric and time-dependent boundary conditions that simulate episodic trench retreat. We find that, in all models, episodic extension leads to rift and/or ridge jumps. In our parameter space, the length of the jump ranges between 1 and 65 km and the timing necessary to produce a new spreading ridge varies between 0.4 and 7 Myr. With the shortest duration of the first extensional phase, we observe a strong asymmetry in the margins of the basin, with the margin further from trench being characterised by outcropping lithospheric mantle and a long section of thinned continental crust. In other cases, ridge jump creates two consecutive oceanic basins, leaving a continental fragment and exhumed mantle in between the two basins. Finally, when the first extensional phase is long enough to form a well-developed oceanic basin (>35 km long), we observe a very short intra-oceanic ridge jump. Our models are able to reproduce many of the structures observed in back-arc basins today, showing that the transient nature of trench retreat that leads to episodes of fast and slow extension is the cause of ridge jumps, mantle exhumation, and continental fragments formation
This study was supported by the Research Council of Norway through its Centers of Excellence funding scheme, Project Number 223272 and made use of the UNINETT Sigma 2 computational resource allocation (Notur NN9283K and NorStore NS9029K). ICM and M. Prada had funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation, of the Spanish “Ministerio de Ciencia, Innovación y Universidades”. 2020–2023 (CEX2019-000928-S)