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

Codillo, Emmanuel; Klein, Frieder; Marschall, Horst R.

doi:10.1029/2022gl100218

Cited by 12 publications

(8 citation statements)

References 90 publications

(120 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Even though exhumed high-pressure mélange terranes display significant lithologic heterogeneity, hydrous minerals such as chlorite and amphibole are found ubiquitously and in large abundance in these terranes. These observations are supported by petrologic and thermodynamic modeling studies that suggested formation of chlorite and other hydrous minerals by fluid-mediated metasomatism of ultramafic and mafic rocks are likely pervasive along the plate interface Codillo et al, 2022aCodillo et al, , 2022bMori et al, 2014). This implies that buoyancy and diapirism are possible within the thermal stability limit of chlorite at ~850 °C (Lakey and Hermann, 2022;Pawley, 2003).…”

supporting

confidence: 56%

Mass transfer and chemical interactions in subduction zones

Codillo¹

View full text Add to dashboard Cite

Subduction zones are important sites of material recycling on Earth, with volatiles playing key roles in mass transfer processes and magma formation. This thesis investigates outstanding questions associated with a continuum of interrelated processes that occur as oceanic plates descend in subduction zones by integrating petrological and geochemical constraints from exhumed high-pressure rocks and erupted arc magmas, high pressure-temperature laboratory experiments, and thermodynamic calculations. Chapters 2 and 3 investigate the fluid-mediated reactions between mafic and ultramafic rocks at conditions relevant to the slab-mantle interface and show that Mg-metasomatism of mafic rocks to form chlorite-rich assemblages is favored and is likely more pervasive in subduction zones than in oceanic settings. Contrary to common belief, talc is unlikely to form in high abundance in ultramafic rocks metasomatized by Si-rich slabderived fluids. This means that talc-rich assemblages formed via Si-metasomatism along the slabmantle interface are less likely to be playing prominent roles in volatile transport, in facilitating slow-slip events, and in controlling the decoupling-coupling transition of the plate interface. Chapter 4 experimentally investigates the phase equilibria, melting, and density evolution of mélange rocks that formed by mixing and fluid-rock interactions. Results show that melting of mélanges is unlikely to occur along slab-tops at pressures ≤ 2.5 GPa. Accordingly, diapirism into the hotter mantle wedge would be required to initiate melting. The density contrast between mélanges and the overlying mantle would allow for buoyancy-driven diapirism at relatively low pressures and melting could subsequently occur in the hotter mantle wedge during ascent. However, diapir buoyancy may be limited at higher pressures due to the formation of abundant garnet especially in mélange rocks with peraluminous composition. Chapter 5 experimentally investigates the compositions of melts and mineral residues from melting of a mantle wedge hybridized with small amounts of mélange rocks to simulate an end-member scenario where solid mélange diapirs dynamically interact with the mantle wedge. Results from laboratory experiments show that melting of a mélange-hybridized mantle wedge can produce melts that display compositional characteristics similar to arc magmas. Finally, Chapter 6 presents new interpretations on the evolution of slab-to-mantle transfer mechanisms from subduction initiation to arc maturity. Analyses of published magma compositions from global arcs reveal that melting of mélange plays an increasingly important role in magma formation as slab-tops cool and arcs mature over time. This trend is attributed to the deepening of the decoupled plate interface during subduction where mélange zones can form more extensively and contribute to the melting process more significantly. Taken together, this thesis highlights (i) the dynamic connection between mechanical mixing of different lithologies and fluid-rock interactions along the slab-mantle interface, (ii) how these processes modify the petrophysical and geochemical properties of subducted materials, and (iii) how these processes collectively influence the mechanisms of slabto-mantle transfer, elemental cycles, and the formation of arc magmas worldwide.

show abstract

supporting

confidence: 56%

Mass transfer and chemical interactions in subduction zones

Codillo¹

View full text Add to dashboard Cite

show abstract

“…Talc may also be produced by the reaction of CO 2 with serpentinites (e.g., Okamoto et al., 2021); however, because of the lack of carbonate materials in sediments recovered from the Cocos plate (Watkins et al., 1982), we suggest that this is unlikely to be a significant process beneath Guerrero. Water is also expected to be the most abundant volatile comprising fluids released by the subducting slab, but solutes such as Al and Ca, in addition to Si, will also be present in these fluids (Codillo, Klein, & Marschall, 2022; Manning, 2004). The involvement of these elements could promote the growth of other minerals like chlorite, which was predicted to grow during some types of metasomatism based on reactive transport modeling (Codillo et al., 2022b), and is a common phase in metasomatic rocks exhumed from subduction zones that may be involved in the localization of deformation at the conditions of ETS (e.g., Hoover et al., 2022; Nishiyama et al., 2023; Ujiie et al., 2022).…”

Section: Discussionmentioning

confidence: 99%

“…New hybrid lithologies may also be produced through the physical mixing of various (potentially silica‐rich) lithologies that are juxtaposed at the subduction interface (e.g., Hoover et al., 2022; Penniston‐Dorland et al., 2014). Other studies of serpentinite metasomatism have employed reactive fluid flow models to predict the production of metasomatic minerals (e.g., Beinlich et al., 2020; Codillo, Klein, & Marschall, 2022). Codillo, Klein, and Marschall (2022) suggest that talc will not be a significant metasomatic product in subduction zones based on results of reactive transport modeling, but this is in contrast with geologic studies that indicate talc formation by silica metasomatism (e.g., Bebout & Barton, 1993; Hirauchi et al., 2020).…”

Section: Mechanisms Of Talc Productionmentioning

confidence: 99%

“…Other studies of serpentinite metasomatism have employed reactive fluid flow models to predict the production of metasomatic minerals (e.g., Beinlich et al., 2020; Codillo, Klein, & Marschall, 2022). Codillo, Klein, and Marschall (2022) suggest that talc will not be a significant metasomatic product in subduction zones based on results of reactive transport modeling, but this is in contrast with geologic studies that indicate talc formation by silica metasomatism (e.g., Bebout & Barton, 1993; Hirauchi et al., 2020). Rather than focusing on fluid compositions, our models simulate the alteration of rock compositions through advective silica transport specifically by focusing on the equilibrium mineralogy of varying bulk‐rock compositions.…”

Section: Mechanisms Of Talc Productionmentioning

confidence: 99%

See 1 more Smart Citation

Metasomatism and Slow Slip: Talc Production Along the Flat Subduction Plate Interface Beneath Mexico (Guerrero)

Lindquist,

Condit,

Hoover

et al. 2023

Geochem Geophys Geosyst

View full text Add to dashboard Cite

Talc‐rich rocks are common in exhumed subduction zone terranes and may explain geophysical observations of the subduction zone interface, particularly beneath Guerrero, Mexico, where the Cocos plate subducts horizontally beneath North America and episodic tremor and slow slip (ETS) occurs. We present petrologic models exploring (a) the degree of silica metasomatism required to produce talc in serpentinized peridotites at the pressure‐temperature conditions of the plate interface beneath Guerrero and (b) the amount of silica‐bearing water produced by rocks from the subducting Cocos plate and the location of fluid pulses. We estimate the volumes of talc produced by the advection of silica‐rich fluids into serpentinized peridotites at the plate interface over the history of the flat‐slab system. In the ETS‐hosting region, serpentinites must achieve ∼43 wt. % SiO2 to stabilize talc, but minor additions of silica beyond this produce large volumes of talc. Our models of Cocos plate dehydration predict that water flux into the interface averages 3.9 × 104 kg m−2 Myr−1 but suggest that only where subducting basalts undergo major dehydration reactions will sufficient amounts of silica‐rich fluids be produced to drive significant metasomatism. We suggest that talc produced by advective transport of aqueous silica alone cannot account for geophysical interpretations of km‐thick zones of talc‐rich rocks beneath Guerrero, although silica‐bearing fluids that migrate along the plate interface may promote broader metasomatism. Regions of predicted talc production do, however, overlap with the spatial occurrence of ETS, consistent with models of slow slip based on the frictional deformation of metasomatic lithologies.

show abstract

“…Bang et al (2021) used thermal models to study the stability of subducted glaucophane over Earth's thermal evolution. Codillo et al (2022) showed chlorite is preferentially formed over talc during Si-metasomatism of ultramafic rocks while also suggesting a limited rheological role of talc in determining the physical structure of subduction zones (as suggested to the contrary by Peacock and Wang, 2021). Martindale et al (2013) used models specific for the Marianas subduction zone to design experiments focusing on high-pressure phase relations of volcaniclastic sediments and demonstrated that these sediments contribute widely to the geochemical characteristics of Mariana arc magmas.…”

Section: Design and Interpretation Of Physical Experimentsmentioning

confidence: 99%

An introductory review of the thermal structure of subduction zones: I. Motivation and selected examples

Keken¹,

Wilson

2023

Preprint

View full text Add to dashboard Cite

The thermal structure of subduction zones is fundamental to our understanding of physical and chemical processes that occur at active convergent plate margins. These include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions that can release fluids. Computational models can predict the thermal structure to great numerical precision when models are fully described but this does not guarantee accuracy or applicability. In a pair of companion papers the construction of thermal subduction zone models, their use in subduction zone studies, and their link to geophysical and geochemical observations is explored. In part I the motivation to understand the thermal structure is presented based on experimental and observational studies. This is followed by a description of a selection of thermal models for the Japanese subduction zones.

show abstract

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

Cited by 12 publications

References 90 publications

Mass transfer and chemical interactions in subduction zones

Mass transfer and chemical interactions in subduction zones

Metasomatism and Slow Slip: Talc Production Along the Flat Subduction Plate Interface Beneath Mexico (Guerrero)

An introductory review of the thermal structure of subduction zones: I. Motivation and selected examples

Contact Info

Product

Resources

About