On the Stability of Talc in Subduction Zones: A Possible Control on the Maximum Depth of Decoupling Between the Subducting Plate and Mantle Wedge

Peacock, Simon M.; Wang, Kelin

doi:10.1029/2021gl094889

Cited by 28 publications

(19 citation statements)

References 40 publications

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“…A lack of extensively talc‐altered serpentinite in subduction zones (Deschamps et al., 2013; Peters et al., 2017a) would likely affect the strength of the plate interface and the physical mechanisms controlling the coupling‐decoupling depth in subduction zones. Owing to its high‐pressure stability and rheological properties, the breakdown of talc has been suggested to reflect the downdip transition from a decoupled shear zone to a fully coupled plate interface (Peacock & Wang, 2021). Our thermodynamic calculations suggest that the formation of talc at the expense of serpentine by Si‐metasomatism (via the reaction: antigorite + 30SiO 2( aq ) = 16talc + 15H 2 O ( l ) ) may be more limited during subduction when compared with low pressure Si‐metasomatism such as in oceanic settings where lower SiO 2( aq ) activities suffice to drive talc alteration.…”

Section: Discussionmentioning

confidence: 99%

Fluid‐Mediated Mass Transfer Between Mafic and Ultramafic Rocks in Subduction Zones

Codillo

Klein

Dragovic

et al. 2022

Geochem Geophys Geosyst

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Metasomatic reaction zones between mafic and ultramafic rocks exhumed from subduction zones provide a window into mass‐transfer processes at high pressure. However, accurate interpretation of the rock record requires distinguishing high‐pressure metasomatic processes from inherited oceanic signatures prior to subduction. We integrated constraints from bulk‐rock geochemical compositions and petrophysical properties, mineral chemistry, and thermodynamic modeling to understand the formation of reaction zones between juxtaposed metagabbro and serpentinite as exemplified by the Voltri Massif (Ligurian Alps, Italy). Distinct zones of variably metasomatized metagabbro are dominated by chlorite, amphibole, clinopyroxene, epidote, rutile, ilmenite, and titanite between serpentinite and eclogitic metagabbro. Whereas the precursor serpentinite and oxide gabbro formed and were likely already in contact in an oceanic setting, the reaction zones formed by diffusional Mg‐metasomatism between the two rocks from prograde to peak, to retrograde conditions in a subduction zone. Metasomatism of mafic rocks by Mg‐rich fluids that previously equilibrated with serpentinite could be widespread along the subduction interface, within the subducted slab, and the mantle wedge. Furthermore, the models predict that talc formation by Si‐metasomatism of serpentinite in subduction zones is limited by pressure‐dependent increase in the silica activity buffered by the serpentine‐talc equilibrium. Elevated activities of aqueous Ca and Al species would also favor the formation of chlorite and garnet. Accordingly, unusual conditions or processes would be required to stabilize abundant talc at high P‐T conditions. Alternatively, a different set of mineral assemblages, such as serpentine‐ or chlorite‐rich rocks, may be controlling the coupling‐decoupling transition of the plate interface.

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Section: Discussionmentioning

confidence: 99%

Fluid‐Mediated Mass Transfer Between Mafic and Ultramafic Rocks in Subduction Zones

Codillo

Klein

Dragovic

et al. 2022

Geochem Geophys Geosyst

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“…The changes in the rheological properties and stress states of materials along the plate interface may manifest themselves as seismicity, such as slow slip events (Beroza & Ide, 2011; Rubin, 2008). The pressure‐sensitive breakdown of talc into secondary mineral assemblage has recently been suggested to control the extent of mechanical coupling along the plate interface (S. M. Peacock and Wang, 2021). Therefore, illuminating the conditions that facilitate talc formation at high P‐T conditions is important in assessing its importance in plate interface processes.…”

Section: Introductionmentioning

confidence: 99%

Preferential Formation of Chlorite Over Talc During Si‐Metasomatism of Ultramafic Rocks in Subduction Zones

Codillo

Klein

Marschall

2022

Geophysical Research Letters

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Talc formation via silica‐metasomatism of ultramafic rocks is believed to play key roles in subduction zone processes. Yet, the conditions of talc formation remain poorly constrained. We used thermodynamic reaction‐path models to assess the formation of talc at the slab‐mantle interface and show that it is restricted to a limited set of pressure–temperature conditions, protolith, and fluid compositions. In contrast, our models predict that chlorite formation is ubiquitous at conditions relevant to the slab‐mantle interface of subduction zones. The scarcity of talc and abundance of chlorite is evident in the rock record of exhumed subduction zone terranes. Talc formation during Si‐metasomatism may thus play a more limited role in volatile cycling, strain localization, and in controlling the decoupling‐coupling transition of the plate interface. Conversely, the observed and predicted ubiquity of chlorite corroborates its prominent role in slab‐mantle interface processes that previous studies attributed to talc.

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“…Due to its weak mechanical properties, talc is likely to affect phenomena related to shearing and mechanical interactions, such as the decoupling‐coupling transition in subduction zones (Agard et al., 2018; Peacock & Wang, 2021; Wada et al.. 2008) and seismicity proficiency at faults (Lockner et al., 2011). Seismic features of ETS have been recorded in subduction zones (Obara, 2002; Rogers & Dragert, 2003) as well as along large transform faults such as the San Andreas and Alpine faults (Shelly, 2017; Wech et al., 2012).…”

Section: Discussionmentioning

confidence: 99%

High‐Pressure Mechanical Properties of Talc: Implications for Fault Strength and Slip Processes

2023

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The hydrous mineral talc is stable over a relatively large P‐T field and can form due to fluid migration and metamorphic reactions in mafic and ultramafic rocks and in faults along plate boundary interfaces. Talc is known to be one of the weakest minerals, making it potentially important for the deformation dynamics and seismic characteristics of faults. However, little is known about talc's mechanical properties at high temperatures under confining pressures greater than 0.5 GPa. We present results of deformation experiments on natural talc cylinders exploring talc rheology under 0.5–1.5 GPa and 400–700°C, P‐T conditions simulating conditions at deep faults and subducted slab interface. At these pressures, the strength of talc is highly temperature‐dependent where the thermal weakening is associated with an increased tendency for localization. The strength of talc and friction coefficient inferred from Mohr circle analysis is between 0.13 at 400°C to ∼0.01 at 700°C. Strength comparison with other phyllosilicates highlights talc as the weakest mineral, a factor of ∼3–4 weaker than antigorite and a factor of ∼2 weaker than chlorite. The observed friction coefficients for talc are consistent with those inferred for subducted slabs and the San Andreas fault. We conclude that the presence of talc may explain the low strength of faults and of subducted slab interface at depths where transient slow slip events occur.

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On the Stability of Talc in Subduction Zones: A Possible Control on the Maximum Depth of Decoupling Between the Subducting Plate and Mantle Wedge

Cited by 28 publications

References 40 publications

Fluid‐Mediated Mass Transfer Between Mafic and Ultramafic Rocks in Subduction Zones

Fluid‐Mediated Mass Transfer Between Mafic and Ultramafic Rocks in Subduction Zones

Preferential Formation of Chlorite Over Talc During Si‐Metasomatism of Ultramafic Rocks in Subduction Zones

High‐Pressure Mechanical Properties of Talc: Implications for Fault Strength and Slip Processes

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