Terrane Geodynamics: From Pre-Collision to Post-Collision
Abstract
Ocean lithosphere is not homogeneous but is punctuated by topographic and bathymetric highs—terranes (oceanic plateaus, microcontinents, seamounts etc.)—which can vary in size from tens to several hundreds of kilometres. Terranes are in motion together with their host tectonic plate to subduction zones, where they collide and accrete to the overriding plate or subduct into the mantle. Less known here is the tectonic development of terranes prior to their arrival at a subduction boundary and the controlling parameters of their fate at the plate boundary. We set up a series of numerical geodynamic experiments to understand which parameters can control terrane subduction and/or accretion, how terranes deform prior to collision/subduction, and what geodynamic events can occur during the whole pre- to post-collisional period. The test parameters are convergence rate (0 to 4 cm/yr), terrane size (120 to 600 km), terrane crustal thickness (15 to 30 km), terrane crust type (oceanic or continental), and density difference between mantle lithosphere and asthenosphere (30 to 50 kg/m3). All these parameters are tested in ocean-ocean (intra-oceanic) and ocean-continent subduction settings yielding a full set of 288 experiments. Our experiment results show that the tendency of terranes to subduct is proportional to increasing imposed convergence rates. Conversely, terranes tend to resist subduction and accrete partly or fully with the overriding plate when crustal thickness and/or terrane size are increased. An intriguing outcome of our experiments is that terranes can undergo significant extensional deformation prior to collision/subduction owing to the slab-pull force. The retrograde P-T-t graphs and extension factors from our models document these extensional phases. The experiment results are compared to the geophysical and petrological data from contemporary and accreted terranes located in the Pacific Ocean and Tethyan sutures. Our intra-oceanic subduction experiments yield diverse syn- and post-collisional geodynamic events such as ablative subduction and subduction polarity change, and the latter is compared to the geodynamic evolution of the Caribbean plate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMU010...13G
- Keywords:
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- 0810 Post-secondary education;
- EDUCATION;
- 0815 Informal education;
- EDUCATION