Structural and chemical resetting processes in white mica and their effect on K-Ar data during low temperature metamorphism

Akker, Ismay Vénice; Berger, Alfons; Zwingmann, Horst; Todd, Andrew; Schrank, Christoph; Jones, Michael W. M.; Kewish, Cameron M.; Schmid, Timothy; Herwegh, Marco

doi:10.1016/j.tecto.2020.228708

Cited by 19 publications

(21 citation statements)

References 58 publications

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“…Note that these authors interpreted in situ 40 Ar/ 39 Ar ages in a similar low‐grade phyllite from the Sierra Alhamilla as the age of the H P /L T event around 48 Ma. These low‐grade phyllites experienced peak‐temperature conditions around 300°C (Martínez‐Martínez & Azañón, 1997; Platt et al., 2005), too low to permit substantial growth of new white micas from former mica precursors (Akker et al., 2021; Hueck et al., 2020; Sanchez et al., 2011). Also, fission‐tracks ages from zircon with admittedly lower opening/closure temperature than the 40 Ar/ 39 Ar system (Fission‐tracks Tc zircon is comprised between 260 and 360°C; Bernet, 2009; Guedes et al., 2013; Tagami & Shimada, 1996) appear largely unreset in the same area.…”

Section: Discussionmentioning

confidence: 99%

⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

et al. 2022

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How the dynamics of subducting lithospheric slabs interferes with crustal deformation in the upper plates of convergence zones is a major question in plate-kinematic and crustal-scale restorations. This question is particularly well illustrated in the Betic-Rif orogen (western Mediterranean) which results from complex interactions between the Africa and Iberia plates during their convergence and deep-seated slab dynamics (

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Section: Discussionmentioning

confidence: 99%

⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

et al. 2022

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“…Taken together, the diagenetic and low-grade metamorphic processes discussed above contributed to the Sr isotopic equilibration of the flysch units. Recently, Akker et al (2021b) evaluated the grain-size dependent isotopic resetting of the K-Ar system for white micas from the IFUs and found that the system is only partially reset, except for the southernmost part of the study area (T max ≈ 330 °C), where the grain-size fraction of ≤0.8 μm is nearly reset. We therefore propose that the Rb-Sr system was also only partially reset and that the late-stage Sr isotopic evolution of the pore fluid was dominated by the interaction with silicates rather than with the bulk rock, which would have required a higher metamorphic grade and full recrystallization of the sediments.…”

Section: A Strontium Isotope Ratios and Pore Fluid Evolutionmentioning

confidence: 99%

Tracing wedge-internal deformation by means of strontium isotope systematics of vein carbonates

et al. 2022

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Radiogenic strontium isotopes (87Sr/86Sr) of vein carbonates play a central role in the tectonometamorphic study of fold-and-thrust belts and accretionary wedges and have been used to document fluid sources and fluxes, for example, along major fault zones. In addition, the 87Sr/86Sr ratios of vein carbonates can trace the diagenetic to metamorphic evolution of pore fluids in accreted sediments. Here we present 87Sr/86Sr ratios of vein carbonates from the Infrahelvetic flysch units of the central European Alps (Glarus Alps, Switzerland), which were accreted to the North Alpine fold-and-thrust belt during the early stages of continental collision. We show that the vein carbonates trace the Sr isotopic evolution of pore fluids from an initial seawater-like signature towards the Sr isotopic composition of the host rock with increasing metamorphic grade. This relationship reflects the progressive equilibration of the pore fluid with the host rock and allows us to constrain the diagenetic to low-grade metamorphic conditions of deformation events, including bedding-parallel shearing, imbricate thrusting, folding, cleavage development, tectonic mélange formation and extension. The strontium isotope systematics of vein carbonates provides new insights into the prograde to early retrograde tectonic evolution of the Alpine fold-and-thrust belt and helps to understand the relative timing of deformation events.

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“…A fundamental observation in nature is that metasomatic fluids are more efficient at mobilizing isotopes than temperature (e.g., [60][61][62][63][64][65]). Kinetic rate constants for fluid mediated transport of solutes are orders of magnitude larger, with significantly smaller activation energies than thermally driven diffusion (e.g., [66]).…”

Section: The Effects Of Fluid Interaction and Closed-system Behaviourmentioning

confidence: 99%

Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

Spikings

Popov

2021

Minerals

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The 40Ar/39Ar method applied to K-feldspars and muscovite has been often used to construct continuous thermal history paths between ~150–600 °C, which are usually applied to structural and tectonic questions in many varied geological settings. However, other authors contest the use of 40Ar/39Ar thermochronology because they argue that the assumptions are rarely valid. Here we review and evaluate the key assumptions, which are that (i) 40Ar is dominantly redistributed in K-feldspars and muscovite by thermally-driven volume diffusion, and (ii) laboratory experiments (high temperatures and short time scales) can accurately recover intrinsic diffusion parameters that apply to geological settings (lower temperatures over longer time scales). Studies do not entirely negate the application of diffusion theory to recover thermal histories, although they reveal the paramount importance of first accounting for fluid interaction and secondary reaction products via a detailed textural study of single crystals. Furthermore, an expanding database of experimental evidence shows that laboratory step-heating can induce structural and textural changes, and thus extreme caution must be made when extrapolating laboratory derived rate loss constants to the geological past. We conclude with a set of recommendations that include minimum sample characterisation prior to degassing, an assessment of mineralogical transformations during degassing and the use of in situ dating.

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Structural and chemical resetting processes in white mica and their effect on K-Ar data during low temperature metamorphism

Cited by 19 publications

References 58 publications

⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

Tracing wedge-internal deformation by means of strontium isotope systematics of vein carbonates

Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

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Structural and chemical resetting processes in white mica and their effect on K-Ar data during low temperature metamorphism

Cited by 19 publications

References 58 publications

40Ar/39Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

40Ar/39Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

Tracing wedge-internal deformation by means of strontium isotope systematics of vein carbonates

Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

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⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)

⁴⁰Ar/³⁹Ar Age Constraints on HP/LT Metamorphism in Extensively Overprinted Units: The Example of the Alpujárride Subduction Complex (Betic Cordillera, Spain)