Do supra-subduction zone ophiolites form by diffuse spreading of the forearc during subduction initiation? A Mariana - Troodos analogy
Abstract
The sinking of older and thicker oceanic plate within the deep Earth at subduction zones is one of the key components of plate tectonics on Earth. However, how subduction zones initiate has remained poorly understood. The long-standing view is that the rapid sinking of the nascent subducting plate in intra-oceanic systems generated extension that gave rise to large-scale stretching of the pre-subduction lithosphere in front of the trench. Forearc spreading further allowed the generation of basalticmantle melts, creating new oceanic crust right above the descending plate. However, because most spreading centers occur at some distance inboard of trenches (≥ 200 km), it has been questioned whether spreading can occur directly above a nascent, dehydrating slab. This view is challenged by observations of the southern Marianas, where diffuse spreading of the forearc crust right above a dehydrating slab (i.e. < 100 km from the trench) has taken place.Building upon this discovery of forearc spreading in the southern Marianas, we seek to further examine the forearc - ophiolite analogy to better comprehend the processes that occurred during subduction initiation. The geochemical similarities between the Troodos ophiolite (Cyprus), a relic of the Neo-Tethys Ocean, and the Southern Mariana forearc basalts implies that forearc spreading is a viable mechanism to create new oceanic crust in Troodos during subduction infancy.Because forearc spreading occurs directly above a dehydrating slab, we further propose that the pre-existing forearc lithosphere was diffusively stretched, and melting occurred over a broad region at the onset of subduction [1]. This resulted in the generation of new oceanic lithosphere in the forearc by a much more short-lived, diffuse mode of spreading - i.e. spatially and temporally unstable volcano-tectonic spreading centers - than observed at typical mid-ocean ridges and back-arc basin spreading centers.
[1] Martinez, F. et al. 2018, JGR, 2169-9356, doi: 2160.1002/2017JB014684.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T44A..02R
- Keywords:
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- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICSDE: 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 8140 Ophiolites;
- TECTONOPHYSICS