Tracking Deep Sediment Underplating in a Fossil Subduction Margin: Implications for Interface Rheology and Mass and Volatile Recycling

Tewksbury-Christle, Carolyn M.; Helper, M. A.

doi:10.1029/2020gc009463

Cited by 30 publications

(76 citation statements)

References 120 publications

(345 reference statements)

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“…Sediment prevalence at depth in the CMS interface shear zone, despite subducting along a sediment-poor, tectonically erosive margin, required stacking of thin incoming sediment packages through protracted underplating and entrainment (Tewksbury-Christle et al, 2021). Down-dip thickening observed in modern LVZs (Abers et al, 2009;Hansen et al, 2012;Toya et al, 2017) may be indicative of this progressive underplating process and may be independent of incoming sediment supply, contrary to previous assumptions (Hansen et al, 2012).…”

Section: Accepted Articlementioning

confidence: 70%

“…Here we focus on the middle sheet, for which both the upper and lower shear zone boundaries are preserved, allowing us to constrain shear zone thickness. Tewksbury-Christle et al (2021) documented two phases of strain localization within the middle sheet. An early stage of distributed deformation occurred over ∼3 km thickness of dominantly schist (94%) with minor mafic blueschist and serpentinite components (Figure 2c).…”

Section: An Exhumed Subduction Shear Zone In the Klamath Mountainsmentioning

confidence: 99%

“…1c) are plausible sources. In addition, the composition and viscosity of the interface control coupling between the overriding and downgoing plates, contributing to, for example, slab velocities (Behr & Becker, 2018), upper plate topography (e.g., Delph et al, 2021, trench behavior (Čížková & Bina, 2013), underplating and recycling of material to the mantle (Bialas et al, 2011;Tewksbury-Christle et al, 2021), and slab morphology (Čížková & Bina, 2013). The LVZ thus provides a possible window into the location and distribution of the subduction interface and the processes along it, which can be used to characterize modern subduction zones.…”

Section: Accepted Articlementioning

confidence: 99%

“…Previous work established the subduction context of the CMS and provided a structural framework for interpreting pulses of deformation and underplating through time (Helper, 1986;Tewksbury-Christle et al, 2021). We use estimates of shear zone width, occupy-…”

Section: Accepted Articlementioning

confidence: 99%

“…Following this stage of distributed deformation, introduction of km-scale serpentinite lenses to the subduction interface allowed for temporary strain localization in serpentinite to <10 m thickness proximal to the thrusts along which the lower CMS was assembled (Fig. 2b) (Helper, 1986;Tewksbury-Christle et al, 2021).…”

Section: Accepted Articlementioning

confidence: 99%

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Constraints From Exhumed Rocks on the Seismic Signature of the Deep Subduction Interface

Tewksbury-Christle

2021

Geophysical Research Letters

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Seismic velocities of a 3 km fossil subduction interface shear zone are comparable to Low Velocity Zones (LVZs) in modern subduction zones.• Accounting for fracture and mineral anisotropy in a sediment-dominated interface shear zone results in highly anomalous seismic velocities. 10• The LVZ represents the seismic signature of a distributed interface shear zone com-11 posed of mixed lithologies.

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Section: Accepted Articlementioning

confidence: 70%

Section: An Exhumed Subduction Shear Zone In the Klamath Mountainsmentioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

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Constraints From Exhumed Rocks on the Seismic Signature of the Deep Subduction Interface

Tewksbury-Christle

2021

Geophysical Research Letters

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Seismic and Episodic Slip Characteristics of Frictional-Viscous Subduction Megathrust Shear Zones

Gerya

Cannizzaro

Blass

2021

Preprint

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The deep roots of subduction megathrusts exhibit aseismic slow slip events, commonly accompanied by tectonic tremor. Observations from exhumed rocks suggest this region of the subduction interface is a shear zone with frictional lenses embedded in a viscous matrix. Here we use numerical models to explore the transient slip characteristics of finite-width frictional-viscous megathrust shear zones. Our model utilizes an invariant, continuum-based, regularized form of rate-and state-dependent friction (RSF) and simulates earthquakes along spontaneously evolving faults embedded in a 2D heterogeneous continuum. The setup includes two elastic plates bounding a viscoelastoplastic shear zone (subduction interface melange) with inclusions (clasts) of varying distributions and viscosity contrasts with respect to the surrounding weaker matrix. The entire shear zone exhibits the same velocity-weakening RSF parameters, but the lower viscosity matrix has the capacity to switch between RSF and viscous creep as a function of local stress state. Results show that for a range of matrix viscosities near the frictional-viscous transition, viscous damping and stress heterogeneity in these shear zones both 1) sets the 'speed limit' for earthquake ruptures that nucleate in clasts such that they propagate at slow velocities; and 2) permits the transmission of slow slip from clast to clast, allowing slow ruptures to propagate substantial distances over the model domain. For reasonable input parameters, modeled events have moment-duration statistics, stress drops, and rupture propagation rates that match natural slow slip events. These results provide new insights into how geologic observations from ancient analogs of the slow slip source may scale up to match geophysical constraints on modern slow slip phenomena.

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Quartz-in-garnet barometry constraints on formation pressures of eclogites from the Franciscan Complex, California

Cisneros

Platt

Anczkiewicz

2022

Contrib Mineral Petrol

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Determining pressure and temperature variations between high-pressure/low-temperature (HP–LT) eclogite blocks is crucial for constraining end-member exhumation models; however, it has historically been challenging to constrain eclogite pressures due to the high variance associated with this bulk-rock composition. In this work, we utilize quartz-in-garnet elastic barometry to constrain formation pressures of eclogites from the northern (Junction School, Ring Mountain, Jenner Beach) and southern Franciscan Complex (Santa Catalina Island). Multiple eclogite blocks from Jenner Beach are analyzed, and a single eclogite from the other localities. By comparing garnet growth conditions from within a single outcrop and between distinct outcrops, we evaluate the local and regional spatial distribution of P conditions recorded by eclogites. We compare the mean, median, and max pressures between different garnet zones and eclogites. Pressures sometimes exhibit systematic changes across garnet zones; however, some eclogites exhibit no systematic pressure variations across garnet zones. Pressures from northern Franciscan eclogites range from $$\sim $$ ∼ 1.4–1.8 GPa, at an estimated temperature of 500 $$^{\circ }$$ ∘ C; pressures from the Catalina eclogite range from $$\sim $$ ∼ 1.2–1.5 GPa, at an estimated temperature of 650 $$^{\circ }$$ ∘ C. Mean and maximum pressures of different eclogites from the northern Franciscan exhibit negligible differences (< 0.1 GPa). The results are inconsistent with models that propose exhumation of metamorphic blocks from different structural levels, and suggest that now exposed HP–LT eclogites from the northern Franciscan Complex may represent rocks that were coherently underplated, and exhumed from similar structural levels.

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Tracking Deep Sediment Underplating in a Fossil Subduction Margin: Implications for Interface Rheology and Mass and Volatile Recycling

Cited by 30 publications

References 120 publications

Constraints From Exhumed Rocks on the Seismic Signature of the Deep Subduction Interface

Constraints From Exhumed Rocks on the Seismic Signature of the Deep Subduction Interface

Seismic and Episodic Slip Characteristics of Frictional-Viscous Subduction Megathrust Shear Zones

Quartz-in-garnet barometry constraints on formation pressures of eclogites from the Franciscan Complex, California

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