Forced subduction initiation recorded in the sole and crust of the Semail Ophiolite of Oman

Abstract

Subduction zones are unique to Earth and fundamental in its evolution, yet we still know little on the causes and mechanisms of their initiation. Numerical models suggest far-field forcing may cause subduction initiation at weak pre-existing structures, whereas inferences from modern subduction zones suggest initiation through spontaneous lithospheric gravitational collapse. Measuring the time lag between initial lower plate burial and incipient extension in the upper plate should prove diagnostic in characterizing the subduction initiation mode. In modern systems, rocks that directly recorded initial lower plate burial should be found at the subduction interface and are inaccessible. Here we investigate a fossil system, the archetypal Semail ophiolite of Oman, which expose both lower and upper plate relics of incipient subduction stages. We show that burial of the lower plate predated upper plate extension and formation of Semail oceanic crust by at least 8 Myr, using geochronology of lower and upper plate material. Such a time lag requires far-field forced subduction initiation and provides for the first time unequivocal, direct evidence for a subduction initiation mechanism in the geological record.

Breakup Without Borders: How Continents Speed Up and Slow Down During Rifting

“…Eocene plate motion change is contemporaneous with the initiation of major new intraoceanic subduction zones across a wide region of the western Pacific presently represented by the Izu-Bonin-Mariana and Tonga-Kermadec systems (Gurnis et al, 2004). The details of earlier subduction initiations are less clear, but mid-Cretaceous subduction initiation within the Tethys ocean (Guilmette et al, 2018;Maffione et al, 2017) could be connected to increases in rift velocity within the South Atlantic and between Australia and Antarctica. Our model results allow us to propose the far-field effect of rift acceleration and breakup in the North Atlantic and Eurasia Basin (∼55 Myr ago) as an alternative, plausible catalyst for distal, almost contemporaneous changes in plate boundary configuration and force balance.…”

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

“…First, when assuming a shared tectonic history of the ophiolites despite their differences, the age difference may imply that suprasubduction forearc spreading at the Californian margin does not reflect subduction initiation. Recently, Guilmette et al () showed a 8‐ to 10‐Myr delay between subduction initiation and upper plate extension in the Oman ophiolite, and Maffione and van Hinsbergen () argued that in the Balkan region, the East Vardar SSZ ophiolites may have formed as much as ~70 Myr after subduction initiation. However, Lu/Hf ages of Franciscan metamorphic sole garnets, argued by Guilmette et al () to record prograde mineral growth during subduction initiation, are ~169 Ma (Anczkiewicz et al, ).…”

“…Recently, Guilmette et al () showed a 8‐ to 10‐Myr delay between subduction initiation and upper plate extension in the Oman ophiolite, and Maffione and van Hinsbergen () argued that in the Balkan region, the East Vardar SSZ ophiolites may have formed as much as ~70 Myr after subduction initiation. However, Lu/Hf ages of Franciscan metamorphic sole garnets, argued by Guilmette et al () to record prograde mineral growth during subduction initiation, are ~169 Ma (Anczkiewicz et al, ). Alternatively, between ~220 and ~170–165 Ma, the trench north of Vizcaíno may have been offset westward to an intraoceanic setting along a transform fault.…”

Subduction Initiation During Collision‐Induced Subduction Transference: Numerical Modeling and Implications for the Tethyan Evolution

“…Thus, the timing of collision is a bit varied among different studies (Aitchison et al, 2007;DeCelles et al, 2014;Najman et al, 2010;Searle, 2019;Yin & Harrison, 2000;Zhu et al, 2015). On the other hand, the geological records for SI are even more complex (Guilmette et al, 2018;Hall, 2018;Pandey et al, 2019;Parlak et al, 2019;Patriat et al, 2019;Searle, 2019;Stern, 2004;Stern et al, 2012). The emplacement of magmatic rock is generally later, by several million years, than the exact time of SI (Arculus et al, 2019;Hall, 2018;Shervais et al, 2019).…”