Scientists have detected two massive tears in the Arabian tectonic plate beneath southeastern Iran, providing a rare look at the transition from ocean subduction to continental collision.
A team led by researchers from the Chinese Academy of Sciences used a network of 69 seismic monitoring stations to map deep geological activity. The recordings, taken between March 2017 and September 2018, revealed the tears in the Arabian Plate: one horizontal where the Zagros collision zone meets the Makran subduction zone, and a smaller vertical tear nearer the surface by the Makran Trench.
The ruptures are caused by differences in rock density. One part of the plate, once part of the ancient Neo-Tethys Ocean, is an oceanic slab of heavier basalt being pushed under a neighbouring plate. The other part is continental rock, thicker but less dense, which resists subduction and instead forms mountains. That mismatch is creating the tears.
"The coexistence of these two tearing modes provides a rare snapshot of the short-lived early transition from oceanic subduction to continental collision," the researchers wrote in a study published in Nature Geoscience.
The models suggest the tears have been progressing for several million years and will likely eventually meet. "While the two tears initiate independently, the intervening continental-oceanic boundary segment is progressively consumed as tearing advances," the researchers wrote. "This progressive linkage is expected to eventually drive coalescence of the two tears."
The team said the oceanic lithosphere beneath the Makran subduction zone has continuously subducted to depths of at least 450 kilometres, while the continental lithosphere in the Zagros collision zone has subducted no deeper than 300 kilometres, causing east–southward slab tearing and detachment. The researchers also identified a second 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 next question for geologists is how the tears and their possible merging may affect volcanic activity in the region, and hot magma already appears to be filling some of the gaps caused by the ruptures.
Analysis
Why This Matters
- The discovery offers a rare direct observation of the final stages of an ancient ocean's disappearance and the collision of continents, part of the Wilson Cycle that describes how oceans form and vanish over millions of years.
- Understanding these processes helps refine models of plate tectonics and earthquake hazards in a seismically active region.
- The tears may eventually merge, with implications for future volcanic activity in Iran and the surrounding area.
Background
Tectonic plates are constantly moving, but on timescales far beyond human generations. The Arabian Plate is converging with the Eurasian Plate, creating the Zagros Mountains and the Makran subduction zone. The Neo-Tethys Ocean once lay between these landmasses and is now mostly consumed. The new study, published in Nature Geoscience, used seismic data from 69 stations to image the deep structure.
What to Watch
- Whether volcanic activity in the Makran region changes as the tears progress and magma intrudes into the gaps.
- Future seismic imaging studies that may confirm the expected coalescence of the two tears.
- Additional research into how these rupture dynamics affect earthquake and tsunami risk along the Iranian coast.
Checked
12 claims in this story checked against 1 source: 11 supported.
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- SupportedGiant tears were discovered in the tectonic plate beneath Iran.ScienceAlert: “Scientists Discover Two Enormous Tears in a Tectonic Plate Beneath Iran.”
- SupportedResearchers found two ruptures in the Arabian Plate, offering a rare glimpse of continents colliding.ScienceAlert: “The coexistence of these two tearing modes provides a rare snapshot of the short-lived early transition from oceanic subduction to continental collision”
- SupportedThe research team was led by researchers from the Chinese Academy of Sciences.ScienceAlert: “Researchers led by a team from the Chinese Academy of Sciences have now found extensive evidence of two giant tears”
- SupportedThe researchers used a network of 69 seismic monitoring stations.ScienceAlert: “the researchers used a network of 69 different seismic monitoring stations to detect the vibrations coming from distant earthquakes.”
- SupportedThe recordings were taken between March 2017 and September 2018.ScienceAlert: “The recordings, taken between March 2017 and September 2018, revealed the two tears”
- SupportedOne tear is horizontal where the Zagros and Makran zones meet, and a smaller vertical tear is nearer the surface by the Makran Trench.ScienceAlert: “one horizontal (where the Zagros collision zone meets the Makran subduction zone), and a smaller vertical one, closer to the surface (by the Makran Trench).”
- Partly supportedDifferences in rock density caused the ruptures.ScienceAlert: “That second tear is more due to the movement of the plates than the differences between the oceanic and continental rock, the researchers suggest”
- SupportedThe researchers wrote: “The coexistence of these two tearing modes provides a rare snapshot of the short-lived early transition from oceanic subduction to continental collision,”ScienceAlert: “"The coexistence of these two tearing modes provides a rare snapshot of the short-lived early transition from oceanic subduction to continental collision," write the researchers in their published paper.”
- SupportedThe models indicate that the tears have been progressing for several million years and are likely eventually to meet.ScienceAlert: “These rips in the plates have been progressing for several million years, according to the study models, and those same models indicate that it's likely that they'll eventually meet each other.”
- SupportedThe researchers wrote: “While the two tears initiate independently, the intervening continental-oceanic boundary segment is progressively consumed as tearing advances,” and “This progressive linkage is expected to eventually drive coalescence of the two tears.”ScienceAlert: “"While the two tears initiate independently, the intervening continental-oceanic boundary segment is progressively consumed as tearing advances," write the researchers. "This progressive linkage is expected to eventually drive coalescence of the two tears."”
- SupportedThe oceanic lithosphere beneath Makran has subducted to at least 450 kilometres, while the continental lithosphere in Zagros has subducted no deeper than 300 kilometres, resulting in east–southward slab tearing and detachment.ScienceAlert: “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”
- SupportedA second tear probably began at the junction between the Makran Trench and transform boundary and propagated southward as the continental plate advanced northward.ScienceAlert: “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.”