Tectonic slicing and mixing processes along the subduction interface: The Sistan example (Eastern Iran)

Bonnet, Guillaume; Agard, Philippe; Angiboust, Samuel; Monié, Patrick; Jentzer, Michael; Omrani, Jafar; Whitechurch, Hubert; Fournier, Marc

doi:10.1016/j.lithos.2018.04.016

Cited by 33 publications

(20 citation statements)

References 98 publications

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“…Ukar & Cloos, 2014), the Rio San Juan Complex (Krebs et al., 2008, 2011) and the Sistan suture (e.g. Bonnet et al., 2018). This observation suggests that when sheet silicates such as serpentine, chlorite and talc are the dominant matrix phases at the subduction interface, materials may be transported differentially over large scales.…”

Section: Discussionmentioning

confidence: 99%

Assessing P‐T variability in mélange blocks from the Catalina Schist: Is there differential movement at the subduction interface?

Harvey

Penniston‐Dorland

Kohn

et al. 2020

Journal Metamorphic Geology

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In subduction‐related tectonic mélange, thermobarometry on individual blocks can in principle constrain the scale of lithological mixing along the subduction interface. Previous thermobarometric investigation of the tectonic amphibolite facies mélange unit in the Catalina Schist, Santa Catalina Island, California, USA, has suggested relatively limited mixing among blocks (≤12 km). Here we further investigate scales of mixing among metamorphically disparate (‘exotic’) blocks within epidote‐amphibolite and lawsonite‐blueschist facies mélange of the Catalina Schist using field and petrographic observations, Zr‐in‐rutile thermometry, and quartz‐in‐garnet elastic barometry. A new statistically based method is presented for calculating elastic barometry maximum pressures. The exotic blocks record peak metamorphic temperatures between 580 and 735°C and peak pressures between 1.16 and 1.65 GPa. Temperatures primarily fall in between those recorded by rocks in the amphibolite facies and epidote amphibolite facies units (643–735°C and 553–596°C respectively). The pressure estimates encompass those recorded by blocks from the amphibolite facies mélange (1.34–1.44 GPa), although the exotic blocks record a much larger range of pressures. The large range of recorded temperatures and pressures suggests that blocks within the epidote amphibolite unit were sourced from and mixed along a 20–30 km region of the subduction interface while an exotic block from the lawsonite blueschist facies unit appears to have been sourced from at least 70 km deeper than the unit it is hosted in. Metre‐ to kilometre‐scale variations in matrix mineral rheology likely control strain partitioning at the interface and permit differential transport of mélange blocks over variable length scales.

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Section: Discussionmentioning

confidence: 99%

Assessing P‐T variability in mélange blocks from the Catalina Schist: Is there differential movement at the subduction interface?

Harvey

Penniston‐Dorland

Kohn

et al. 2020

Journal Metamorphic Geology

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“…Importantly, synchronous bimodal recovery from 25 to 35 km and 70-80 km is observed in the Sistan (Bonnet et al, 2018), Sambagawa (Aoki et al, 2009) and Franciscan complexes (e.g., San Simeon and W.…”

Section: Preferential Depths For Recovery?mentioning

confidence: 94%

“…A slightly younger episode of deeper recovery from depths of 50-55 km (at 70-80 Ma; Seghin unit: Agard et al, 2006;Angiboust et al, 2016;Sapi-Shergol: Groppo et al, 2016) is recorded from the same subduction system. Interestingly, in the nearby Sistan subduction zone, a pulse of rock recovery along~150 km is documented at 85 Ma (Eastern Iran; Broecker et al, 2013;Angiboust et al, 2013;Bonnet et al, 2018): two types of mafic rocks returned from depths of 30-40 and~80 km are found as m-to 10 m-scale blocks in a serpentinite mélange. (2) In the Franciscan complex of California, despite N10,000 km of eastward subduction, rock recovery was limited.…”

Section: Evidence That Transient Changes In Mechanical Coupling Contrmentioning

confidence: 99%

The subduction plate interface: rock record and mechanical coupling (from long to short timescales)

Agard

Plunder

Angiboust

et al. 2018

Lithos

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207

294

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Short-and long-term processes at or close to the subduction plate interface (e.g.,mineral transformations, fluid release, seismicity and more generally deformation) might be more closely related than previously thought. Increasing evidence from the fossil rock record suggests that some episodes of their long geological evolution match or are close to timescales of the seismic cycle. This contribution uses rocks recovered (episodically) from subduction zones, together with insights from thermomechanical modelling, to provide a new dynamic vision of the nature, structure and properties of the plate interface and to bridge the gap between the mechanical behavior of active subduction zones (e.g.,coupling inferred from geophysical monitoring) and fossil ones (e.g., coupling required to detach and recover subducted slab fragments). Based on critical observations and an exhaustive compilation of worldwide subducted oceanic units (for which the presence near the plate interface, rock types, pressure, temperature, T/P gradients, thickness and timing of detachment can be assessed), the present study demonstrates how long-term mechanical coupling exerts a key control on detachment from the slab and potential rock recovery. Critical assessment of rock T/P characteristics indicates that these fragments can indeed be used as natural probes and provide reliable information on subduction interface dynamics down to~2.8 GPa. Rock clusters are identified at depths of 30, 55-60 and 80 km, with some differences between rock types. Data also reveal a first-order evolution with subduction cooling (in the first~5 Myr), which is interpreted as reflecting a systematic trend from strong to weak mechanical coupling, after which subduction is lubricated and mostly inhibits rock recovery. This contribution places bounds on the plate interface constitution, regular thickness (b300 m; i.e. where/when there is no detachment), changing geometry and effective viscosity. The concept of 'coupled thickness' is used here to capture subduction interface dynamics, notably during episodes of strong mechanical coupling, and to link long-and short-term deformation. Mechanical coupling depends on mantle wedge rheology, viscosity contrasts and initial structures (e.g.,heterogeneous lithosphere, existence of décollement horizons, extent of hydration, asperities) but also on boundary conditions (convergence rates, kinematics), and therefore differs for warm and cold subduction settings. Although most present-day subduction zone segments (both along strike and downdip) are likely below the detachment threshold, we propose that the most favorable location for detachment corresponds to the spatial transition between coupled and decoupled areas. Effective strain localization involves dissolution-precipitation and dislocation creep but also possibly brittle fractures and earthquakes, even at intermediate depths.

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“…This poor knowledge partly stems from the generally poor preservation of mature subduction interfaces: whenever reliably identified, the two sides are tectonically offset by later deformation ( Fig. 1d; e.g., Angiboust et al, 2014Angiboust et al, , 2015Bonnet et al, 2018).…”

mentioning

confidence: 99%

Slabitization: Mechanisms controlling subduction development and viscous coupling

Agard

Prigent

Soret

et al. 2020

Earth-Science Reviews

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Tectonic slicing and mixing processes along the subduction interface: The Sistan example (Eastern Iran)

Cited by 33 publications

References 98 publications

Assessing P‐T variability in mélange blocks from the Catalina Schist: Is there differential movement at the subduction interface?

Assessing P‐T variability in mélange blocks from the Catalina Schist: Is there differential movement at the subduction interface?

The subduction plate interface: rock record and mechanical coupling (from long to short timescales)

Slabitization: Mechanisms controlling subduction development and viscous coupling

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