Subduction zone initiation (SZI) is a critical stage of the Wilson cycle. While our understanding of the mechanisms, and the sequence of events that precede and postdate SZI is growing, our models are limited to observations from a few prominent case studies.
To recover a geologic record of recent SZI, ocean exploration has proven very valuable; the most complete geologic evidence so far was extracted by diving and drilling into the Izu-Bonin-Mariana (IBM) plate margin. Similarly, the onshore record of the Semail ophiolite has been recovered by drilling (OmanDP). Consequently, our knowledge about SZI events from the perspective of direct geologic observation is based on this one single active and one fossil subduction zone, and is therefore likely biased towards the processes preserved in these specific SZI events.
Supra-subduction zone ophiolites and their underlying metamorphic soles provide valuable information about the occurrence, timing, and duration of ancient SZI events. Metamorphic soles in particular represent the ancient subduction interface and record the very first stages of subduction evolution; therefore, their ages are the most direct constraint on the onset of subduction.
Building on the subduction initiation database (https://www.szidatabase.org/), Derya Gürer from the Heidelberg University in Germany and her colleagues highlight focus regions for future Land-2-Sea drilling efforts that have the potential to recover the upper and lower plate geological records in form of supra-subduction zone ophiolites and their underlying metamorphic soles, respectively. Recovering and unravelling these unique tectono-metamorphic records is essential to constraining the timing, sense and conditions of subduction initiation.
