The sedimentary record of ultrahigh-pressure metamorphism: a perspective review

Schönig, Jan; Eynatten, Hilmar von; Meinhold, Guido; Lünsdorf, Nils Keno

doi:10.1016/j.earscirev.2022.103985

Cited by 6 publications

(6 citation statements)

References 272 publications

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“…Possibly, due to their limited size, they escaped re-equilibration and preserved the original features of the trapping time. Similar microtextures are described in the Lago di Cignana Unit by Taguchi et al, (2021), in the Chasterian Unit by Manzotti et al (2022) and by Schönig et al (2022) in detrital coesite-bearing rocks deposed in sedimentary basins worldwide. A consistent shift in the Raman spectra (Figure 4e and Table S1) is found as a proof of the residual strain preserved in the elastic isolated inclusions (Murri et al, 2018 and references therein).…”

Section: Discussionsupporting

confidence: 68%

A new UHP unit in the Western Alps: First occurrence of coesite from the Monviso Massif (Italy)

Ghignone

Scaramuzzo

Bruno

et al. 2023

American Mineralogist

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The Western Alps are one of the most studied exhumed subduction-accretionary complexes worldwide. Ultra-high pressure (UHP) metamorphism has been documented therein since the 1980's. We now report the first discovery of coesite in the meta-ophiolitic suite of the Monviso Massif, corresponding to the fourth UHP unit defined on the Western Alps. Previous petrographic studies and results from thermodynamic modelling already suggested that these Alpine units may have experienced UHP metamorphism, but no occurrences of index minerals, such as coesite, have been reported to date. The newly discovered coesite inclusions from the Monviso Massif occur as intact single crystals (10-60 µm) hosted by garnet. The observations suggest that they have escaped re-equilibration, and maintained all the original features from the trapping time. The reduced size of the crystals and the lack of re-equilibration significantly differ from the typical textural features This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Section: Discussionsupporting

confidence: 68%

A new UHP unit in the Western Alps: First occurrence of coesite from the Monviso Massif (Italy)

Ghignone

Scaramuzzo

Bruno

et al. 2023

American Mineralogist

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“…Much of the recent dating has followed the newly developed methods of petrochronology (Kohn et al, 2017). In an important advance during the last few years, HP and UHP metamorphism has been confirmed at some localities based on detrital garnets and their mineral inclusions (Schönig et al, 2022). As a result, our community has enjoyed a golden age of quantification of P -T , developed better links between P -T and age, and made estimates of time-integrated rates of cooling and exhumation.…”

Section: Thermobarometry Petrochronology and Detrital Materialsmentioning

confidence: 97%

Some thoughts about eclogites and related rocks

Brown

2023

Eur. J. Mineral.

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Abstract. The past 40 years have been a golden age for eclogite studies, supported by an ever wider range of instrumentation and enhanced computational capabilities, linked with ongoing developments in thermobarometry and geochronology. During this time, we have made robust estimates of pressure–temperature (P–T) conditions; determined ages related to the prograde, metamorphic peak and retrograde stages; and calculated time-integrated rates of cooling and exhumation for eclogites and related rocks, including blueschists, from orogenic belts worldwide. Improvements to single mineral thermometers and new developments in elastic barometry using inclusions of one mineral in another (e.g. quartz and/or zircon in garnet), coupled with ongoing innovations in petrochronology and diffusion modelling, presage a new age for eclogite studies in which detailed quantification of metamorphic conditions and timescales will be linked to an improved understanding of processes at all scales. Since the turn of the century, numerical modelling of subduction zone and rock exhumation processes has become increasingly important. As a result, subduction and exhumation are quite well understood, but the volume of continental crust subducted to and returned from mantle conditions and the amount lost to the mantle are largely unknown. We have generated sufficient data to investigate the spatiotemporal distribution of metamorphism and secular change but not without controversy in relation to the rare occurrence of orogenic eclogites and the absence of blueschists prior to the late Neoproterozoic and the emergence of plate tectonics on Earth. Since the turn of the century, the assumption that metamorphic pressure is lithostatic has come under increasing scrutiny. Whether local variations in stress extrapolate to the crustal scale and, if so, whether the magnitude of the calculated deviations from lithostatic pressure can be generated and sustained in mechanically heterogeneous rock units remains contentious. Could the paradigm of subduction of continental lithosphere to mantle depths be simply an artefact of the lithostatic assumption? Fluid cycling in subduction zones and understanding the role of fluids in the generation of intermediate-depth earthquakes remain important topics of current research. Dry (H2O-absent) conditions are unlikely around the peak of ultrahigh-pressure (UHP) metamorphism or during exhumation, due to dehydroxylation of nominally anhydrous minerals and breakdown of hydrous minerals at P–T conditions in the realm of supercritical fluid and hydrous melt. Indeed, the presence of melt may be necessary to facilitate the exhumation of HP and UHP tectonometamorphic rock units. Finally, our ability to interrogate inclusions in superdeep diamonds should lead to a better understanding of how the deep interior and surface are linked in the context of Earth as a fully coupled system.

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“…Automated cosmic ray correction, background subtraction, spectral averaging/smoothing, and principal component analysis were performed using the WITec Project software. This method enables the confident identification of most inclusions ≥ 4 µm, as well as smaller inclusions for strong Raman scattering phases like quartz, coesite, rutile, and diamond (Schönig et al, 2022).…”

Section: Hyperspectral Imaging Of Inclusion-bearing Garnetmentioning

confidence: 99%

“…(3) mineral inclusion analysis of the detrital garnet grains by hyperspectral Raman imaging (n = 2669). Particularly, the analysis of mineral inclusions in detrital garnet is a powerful tool to detect the extent of eclogite-facies and ultrahighpressure metamorphic rocks by mineralogical evidence, relying on unequivocal indicator minerals like omphacite, coesite, and diamond (Schönig et al, 2022). This has been successfully applied in the Western Gneiss Region of Norway (Schönig et al, 2018a, b), the central Saxonian Erzgebirge (Ore Mountains) of Germany (Schönig et al, 2019(Schönig et al, , 2020(Schönig et al, , 2021a, and the D'Entrecasteaux metamorphic complex of Papua New Guinea (Baldwin et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Detrital garnet petrology challenges Paleoproterozoic ultrahigh-pressure metamorphism in western Greenland

Schönig¹,

Benner²,

Meinhold

et al. 2023

Eur. J. Mineral.

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Abstract. Modern-style plate tectonics is characterised by the global operation of cold and deep subduction involving blueschist facies and ultrahigh-pressure metamorphism. This has been a common process since the Neoproterozoic, but a couple of studies indicate similar processes were active in the Paleoproterozoic, at least on the local scale. Particularly conspicuous are extreme ultrahigh-pressure conditions of ∼ 7 GPa at thermal gradients < 150 ∘C GPa−1 proposed for metamorphic rocks of the Nordre Strømfjord shear zone in the western part of the Paleoproterozoic Nagssugtoqidian Orogen of Greenland. By acquiring a large dataset of heavy minerals (n = 52 130) and garnet major-element composition integrated with mineral inclusion analysis (n=2669) from modern sands representing fresh and naturally mixed erosional material from the metamorphic rocks, we here intensely screened the area for potential occurrences of ultrahigh-pressure rocks and put constraints on the metamorphic evolution. Apart from the absence of any indications pointing to ultrahigh-pressure and low-temperature–high-pressure metamorphism, the results are well in accordance with a common Paleoproterozoic subduction–collision metamorphic evolution along a Barrovian-type intermediate temperature and pressure gradient with a pressure peak at the amphibolite–granulite–eclogite-facies transition and a temperature peak at medium- to high-pressure granulite-facies conditions. In addition, we discuss that all “evidence” for ultrahigh-pressure metamorphism proposed in the literature for rocks of this area is equivocal. Accordingly, the Nordre Strømfjord shear zone is not an example of modern-style plate tectonics in the Paleoproterozoic or of very low thermal gradients and extreme pressure conditions in general.

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The sedimentary record of ultrahigh-pressure metamorphism: a perspective review

Cited by 6 publications

References 272 publications

A new UHP unit in the Western Alps: First occurrence of coesite from the Monviso Massif (Italy)

A new UHP unit in the Western Alps: First occurrence of coesite from the Monviso Massif (Italy)

Some thoughts about eclogites and related rocks

Detrital garnet petrology challenges Paleoproterozoic ultrahigh-pressure metamorphism in western Greenland

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