Seismic evidence for double slab tears at the Neo- Tethyan subduction, collision transition (published in Nature Geoscience, 4 November 2026).
An international team led by researchers from the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), including Haiqiang Lan, Ling Chen, and colleagues, with collaborators from Iran, France, and elsewhere, used seismic tomography to image two distinct tears in the subducting slab beneath the Zagros- Makran transition zone in southeastern Iran (near the Strait of Hormuz).
Key findings
- In the Makran subduction zone (east), oceanic lithosphere of the Neo- Tethys continues to subduct continuously to depths of at least ~450 km. It shows a long (~300 km) low-angle segment in the forearc that steepens beneath the volcanic arc.
- In the Zagros collision zone (west), continental lithosphere of the Arabian Plate reaches only ~300 km depth. A remnant of ancient oceanic slab lies beneath it, separated by a gap of roughly 100 km.
These contrasts indicate two slab tears with different mechanisms:
- Nearly horizontal (east- southward) tear and detachment under Zagros: Driven by buoyancy contrast. The denser oceanic portion continues sinking while the more buoyant continental portion resists, tearing along the ocean–continent transition and creating a slab window that separates the shallower continental slab from the deeper oceanic remnant.
- Vertical tear near the junction of the Zagros- Makran transition boundary (associated with the Zendan– Minab– Palami fault system) and the Makran trench: Marked by a low- velocity anomaly separating oceanic and continental slabs. It is interpreted as having initiated at the trench- transform junction and propagated southward (~200 km so far), triggered by the continued northward advance of the Zagros collision front that lengthens the transition boundary (rather than classic trench- retreat models). It may have started ~8 Ma.
The coexistence of these two modes offers a rare snapshot of the short- lived early stage of the transition from oceanic subduction to continental collision in the closing Neo- Tethys (part of the Wilson Cycle).
The tears are expected to eventually coalesce, potentially leading to rapid slab rollback. They may also influence regional tectonic deformation and magmatism (e.g., linked to volcanic rocks of varying ages and compositions in the area).
Methods
The team deployed a broadband seismic array (main and auxiliary lines) in the transition zone, recording data from March 2017 to September 2018.
They combined this with regional stations to obtain ~57,000 multi- frequency P- and S- wave travel-time residuals and applied finite- frequency travel- time tomography to build a 3D upper- mantle velocity model.
This work provides direct seismic constraints on deep processes during the subduction- to- collision transition that are often hard to observe.
The evolutionary model (from ~25 Ma to present and a possible future stage) is illustrated in the paper and related press materials.
The Neo- Tethys Ocean (also called Neotethys) opened in the late Paleozoic–early Mesozoic and closed diachronously during the Cenozoic through progressive continental collisions between Gondwana- derived blocks (Africa- Arabia, India, Australia) and Eurasia.
This formed the Alpine- Zagros- Himalayan orogenic belt. Closure was not simultaneous; it progressed from west to east in stages, with remnants of oceanic lithosphere still subducting in places like the Makran today.
Opening and Early Evolution
- Early Permian (~290- 270 Ma): Rifting of Cimmerian microblocks (parts of present-day Turkey, Iran, Tibet, etc.) from the northern margin of Gondwana initiated the Neo- Tethys as an eastward- opening oceanic embayment between Laurasia (north) and Gondwana (south).
- Late Permian- Early and Middle Triassic (~260- 240 Ma): Seafloor spreading expanded the ocean. Opening of the Yarlung Zangbo segment (Tibet) is constrained to ~250- 243 Ma.
- Late Triassic (~230- 200 Ma): Most Cimmerian microblocks collided with the southern Eurasian margin, closing the older Paleo- Tethys. This initiated northward subduction of Neo- Tethys oceanic lithosphere beneath Eurasia (e.g., in the Zagros sector, Late Triassic- Early Jurassic).
Subduction continued through the Jurassic- Cretaceous, producing arcs (e.g., Urumieh- Dokhtar in Iran, Gangdese in Tibet), ophiolite obduction (especially Late Cretaceous), and intra- oceanic arcs in some segments.
Cenozoic Closure Timeline (Diachronous)
Closure involved initial soft collision (continental margins meeting, often with ongoing oceanic subduction nearby), hard collision, slab break-off/tearing, and final marine regression.
Himalayan- Tibetan segment (India- Eurasia):
- Initial collision: ~65- 59 Ma in the central Himalaya (possibly progressing to 55- 50 Ma westward/eastward).
- Commonly cited main collision and suturing: ~55- 50 Ma (or ~50- 40 Ma in some records). This closed the eastern Neo- Tethys along the Indus- Yarlung suture.
- Ongoing post- collisional convergence and deformation continue today.
Southeastern Zagros– Makran transition (focus of the recent seismic study):
- Southeastern Zagros collision is one of the youngest: younger than ~25 Ma (Miocene), with some estimates of hard collision or major deformation in the last 10- 20 Ma.
- Oceanic lithosphere continues to subduct under the Makran (to ≥450 km depth).
- The recent Nature Geoscience study (2026) images double slab tears here as a snapshot of the early subduction- to- collision transition: a near- horizontal tear (detachment under Zagros, linked to buoyancy contrast, within roughly the last 10 Ma) and a vertical tear (initiated ~8 Ma near the Zendan- Minab- Palami transform boundary, propagating southward ~200 km).
- Marine- continental transition in eastern Zagros foreland is highly diachronous (as young as 8- 1 Ma in places).
Final seaway closure (Tethyan Seaway connecting Indian Ocean to Mediterranean/Paratethys):
- Stepwise: Partial restriction ~20- 19 Ma; further isolation ~15- 14 Ma or 13.8 Ma; permanent closure of the last marine connections by ~14- 12 Ma (middle-late Miocene), driven by Arabia- Eurasia convergence plus eustatic sea- level changes.
- Paratethys (isolated remnant) persisted longer and largely dried by the Pliocene (~5 Ma).
Broader Context and Ongoing Processes
- Closure rates and styles varied: India- Eurasia involved faster, longer convergence (~50- 60 mm/yr post- 50 Ma, with 1,000- 2,000 km of under- thrusting); Arabia- Eurasia was slower (~20- 30 mm/yr) with less penetration (~150 km).
- Slab tearing, break- off, and rollback are key processes during the transition, influencing magmatism, uplift (e.g., Iranian and Tibetan plateaus), and deformation. The Zagros- Makran area uniquely preserves both oceanic subduction and young continental collision side- by- side.
- Remnants: The Mediterranean, Black Sea, Caspian Sea, and residual Makran subduction are modern leftovers.
Timings remain debated due to diachroneity, differing definitions of “initial collision” (soft vs. hard), and methods (sedimentary records, magmatism, paleomagnetism, tomography).
The 2026 seismic study provides new deep- earth constraints specifically for the young southeastern Iranian transition.
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Seismic evidence for double slab tears at the Neo- Tethyan subduction–collision transition
The transition from oceanic subduction to continental collision is a critical stage in the Wilson Cycle, but deep processes (especially slab detachment) remain poorly observed. The authors present seismic tomographic images interpreted as evidence for two distinct slab tears beneath southeastern Iran, where the Neo- Tethys Ocean is still closing.
- In the Makran subduction zone (east), oceanic lithosphere has continuously subducted to ≥450 km depth.
- In the Zagros collision zone (west), continental lithosphere reaches no deeper than ~300 km, producing east- southward slab tearing and detachment.
- A second (vertical) tear likely initiated at the junction of the Makran Trench and the transform boundary (Zendan- Minab- Palami fault system) and has propagated southward as the continental plate advances northward.
The coexistence of these two tearing modes provides a rare snapshot of the short- lived early transition from oceanic subduction to continental collision.
Key Figures (from page)
- Fig. 1: Map of the study area showing major geological units, seismic stations, volcanoes, and plate motions.
- Fig. 2: Tomographic P- wave velocity model.
- Fig. 3: 3- D iso- surface plots of the Vp model with topography.
- Fig. 4: Evolutionary model of the plates in the ocean– continent transition (OCT) zone (stages from ~25 Ma to present and a possible future stage involving fast slab rollback).
Data & Methods Notes
- Data: Broadband seismic array (deployed ~2017- 2018) and regional stations → ~57,000 multi- frequency P- and S- wave travel- time residuals.
- Method: Finite- frequency travel- time tomography for 3- D upper- mantle velocity structure.
- Model availability: Mantle velocity model at https://doi.org/10.12197/2024GA017; travel- time data at https://doi.org/10.12197/2026GA028.
- Code: Third- party finite- frequency tomography software (available on request from developer Shu- Huei Hung).
The full article is behind a paywall and subscription (Nature Portfolio). Free access is typically available via institutional login or purchase.
Press releases and secondary summaries (e.g., from the Chinese Academy of Sciences, Phys.org, EurekAlert) expand on the two tears’ mechanisms (buoyancy- driven near- horizontal tear under Zagros vs. transform-boundary- driven vertical tear), timing estimates (~8 Ma onset for the vertical tear), and implications for regional deformation and magmatism.
Paper: Seismic evidence for double slab tears at the Neo- Tethyan subduction–collision transition
Journal: Nature Geoscience
DOI: 10.1038/s41561-026-02129-4
Provided: Chinese Academy of Sciences
Published: 4 November 2026
Authors: Haiqiang Lan,
Gaoshan Guo,
Ling Chen,
Morteza Talebian,
Lingkai Meng,
Xiaofeng Liang,
Bo Wan,
Yang Chu,
Yaguang Chen,
Sebastien Chevrot,
Jianfeng Yang,
Frederic Mouthereau,
Yifan Gao,
Zimu Wu,
Xu Wang,
Naeim Mousavi &
Jimin Sun
Abstract
The transition from oceanic subduction to continental collision is a key stage in the Wilson Cycle. Yet, key processes governing this transition remain unclear owing to sparse observations of structure at depth. One such process is detachment of the subducting slab, which influences both deformation and magmatism in the overriding plate. Here we present seismic tomographic images that we interpret as evidence for two slab tears beneath southeastern Iran, where the Neo-Tethys Ocean is closing. Specifically, we show that in the Makran subduction zone, the oceanic lithosphere has continuously subducted to depths of at least 450 km, whereas in the Zagros collision zone to the west, the continental lithosphere has subducted no deeper than 300 km, resulting in east–southward slab tearing and detachment. We further identify another slab tear that probably initiated at the junction between the Makran Trench and the transform boundary and has propagated southward as the continental plate advances northward. The coexistence of these two tearing modes provides a rare snapshot of the short-lived early transition from oceanic subduction to continental collision.
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