Reliability of very low-grade metamorphic methods to decipher basin evolution: Case study from the Markstein basin (Southern Vosges, NE France)

Potel, Sébastien; Maison, Tatiana; Maillet, Marine; Sarr, Anta‐Clarisse; Doublier, Michael P.; Trullenque, Ghislain; Mählmann, Rafael Ferreiro

doi:10.1016/j.clay.2016.10.003

Cited by 11 publications

(3 citation statements)

References 47 publications

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“…average 8.996; standard deviation 0.003) are very similar in the lower and upper formations of the Pulo do Lobo belt. Thus, the b parameter is consistently homogeneous and reflects very low phengite substitution in mica, as expected at low-pressure settings (Potel et al, 2006(Potel et al, , 2016, near the intermediate pressure gradient boundary (Guidotti and Sassi, 1986).…”

Section: Pressure Conditionssupporting

confidence: 66%

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary belt (SW Iberian Variscides)

Pérez-Cáceres¹,

Poyatos²,

Vidal³

et al. 2019

Preprint

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Abstract. The Pulo do Lobo belt is one of the units related to the orogenic suture between the Ossa-Morena and the South Portuguese zones in the SW Iberian Variscides. This metasedimentary unit has been classically interpreted as a Rheic subduction-related accretionary prism formed during the pre-Carboniferous convergence and eventual collision between the South Portuguese Zone (part of Avalonia) and the Ossa-Morena Zone (peri-Gondwanan terrane). Discrete mafic intrusions also occur in the dominant Pulo do Lobo metapelites, related to an intraorogenic Mississippian transtensional and magmatic event that had a significant thermal input. Three different approaches have been applied to the Devonian/Carboniferous phyllites and slates of the Pulo do Lobo belt in order to study their poorly known low-grade metamorphic evolution. X-Ray diffraction (XRD) was used to unravel the mineralogy and measure crystallographic parameters (illite crystallinity and K-white mica b-cell dimension). Compositional maps of selected samples were obtained from electron probe microanalysis, which allowed processing with XmapTools software, and chlorite semi-empirical and thermodynamic geothermometry was performed. Thermometry based on Raman spectroscopy of carbonaceous material (RSCM) was used to obtain peak temperatures. The microstructural study shows the existence of two phyllosilicate growth events at the chlorite zone, the main one (M1) related to the development of a Devonian foliation S1, and a minor one (M2) associated with a crenulation cleavage (S2) developed at middle/upper Carboniferous time. M1 entered well into epizone (greenschist facies) conditions. M2 conditions were at lower temperature, reaching the anchizone/epizone boundary. These data accord well with the unconformity that separates the Devonian and Carboniferous formations of the Pulo do Lobo belt. The varied results obtained by the different approaches followed, combined with microstructural analysis, are indicative of different snapshots of the metamorphic history. Thus, RSCM temperatures are higher in comparison with the other methods applied, which is interpreted as reflecting a faster reequilibration during the short-lived thermal Mississippian event. Regarding the metamorphic pressure, the data are very homogeneous (very low celadonite content in muscovite and low values of K-white mica b-cell dimension), indicating a low-pressure gradient, which is unexpected in a subduction-related accretionary prism.

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Section: Pressure Conditionssupporting

confidence: 66%

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary belt (SW Iberian Variscides)

Pérez-Cáceres¹,

Poyatos²,

Vidal³

et al. 2019

Preprint

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“…The measured b-cell parameters of K-white mica (in a short range between 8.991 and 9.002 Å; average 8.996; standard deviation 0.003) are very similar in the lower and upper formations of the Pulo do Lobo domain. Thus, the b parameter shows little variation and reflects very low phengite substitution in mica, as expected in low-pressure settings (Potel et al, 2006(Potel et al, , 2016 near the intermediate pressure gradient boundary (Guidotti and Sassi, 1986).…”

Section: Pressure Conditionssupporting

confidence: 54%

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary domain (SW Iberian Variscides)

Pérez-Cáceres

Poyatos²,

Vidal

et al. 2020

Solid Earth

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Abstract. The Pulo do Lobo domain is one of the units exposed within the orogenic suture zone between the Ossa-Morena and the South Portuguese zones in the SW Iberian Variscides. This metasedimentary unit has been classically interpreted as a Rheic subduction-related accretionary prism formed during pre-Carboniferous convergence and eventual collision between the South Portuguese Zone (part of Avalonia) and the Ossa-Morena Zone (peri-Gondwanan terrane). Discrete mafic intrusions also occur within the dominant Pulo do Lobo metapelites, related to an intra-orogenic Mississippian transtensional and magmatic event that had a significant thermal input. Three different approaches have been applied to the Devonian–Carboniferous phyllites and slates of the Pulo do Lobo domain in order to study their poorly known low-grade metamorphic evolution. X-ray diffraction (XRD) was used to identify the mineralogy and measure crystallographic parameters (illite “crystallinity” and K-white mica b-cell dimension). Compositional maps of selected samples were obtained from electron probe microanalysis, which allowed for processing with XMapTools software, and chlorite semiempirical and thermodynamic geothermometry was performed. Thermometry based on Raman spectroscopy of carbonaceous material (RSCM) was used to obtain peak temperatures. The microstructural study shows the existence of two phyllosilicate growth events in the chlorite zone, the main one (M1) related to the development of a Devonian foliation S1 and a minor one (M2) associated with a crenulation cleavage (S2) developed in middle–upper Carboniferous times. M1 entered well into epizone (greenschist facies) conditions. M2 conditions were at lower temperature, reaching the anchizone–epizone boundary. These data accord well with the angular unconformity that separates the Devonian and Carboniferous formations of the Pulo do Lobo domain. The varied results obtained by the different approaches followed, combined with microstructural analysis, provide different snapshots of the metamorphic history. Thus, RSCM temperatures are higher in comparison with the other methods applied, which is interpreted to reflect a faster re-equilibration during the short-lived thermal Mississippian event. Regarding the metamorphic pressure, the data are very homogeneous: very low celadonite content (0 %–10 %) in muscovite (and low values of K-white mica b-cell dimension; 8.995 Å mean value), indicating a low pressure–temperature gradient, which is unexpected in a subduction-related accretionary prism. Highlights A multidisciplinary approach has been applied to study the metamorphism of the Pulo do Lobo metapelites. Devonian metamorphism entered epizone conditions. Carboniferous metamorphism reached the anchizone–epizone boundary. The inferred low-pressure gradient is incompatible with a subduction-related accretionary prism.

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“…Samples were crushed with an agate pestle and mortar. Clay mineral separation was conducted using the techniques described by Potel et al (2016). To minimize the effect of possible detrital clay minerals, we avoided long grinding processes (<30 s) and repeated the settling procedure for the ≤2 μm fraction twice.…”

Section: Methodsmentioning

confidence: 99%

Low-grade evolution of clay minerals and organic matter in fault zones of the Hikurangi prism (New Zealand)

et al. 2018

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Clay minerals and organic matter occur frequently in fault zones. Their structural characteristics and their textural evolution are driven by several formation processes: (1) reaction by metasomatism from circulating fluids; (2)in situevolution by diagenesis; and (3) neoformation due to deformation catalysis. Clay-mineral chemistry and precipitated solid organic matter may be used as indicators of fluid circulation in fault zones and to determine the maximum temperatures in these zones. In the present study, clay-mineral and organic-matter analyses of two major fault zones – the Adams-Tinui and Whakataki faults, Wairarapa, North Island, New Zealand – were investigated. The two faults analysed correspond to the soles of large imbricated thrust sheets formed during the onset of subduction beneath the North Island of New Zealand. The mineralogy of both fault zones is composed mainly of quartz, feldspars, calcite, chabazite and clay minerals such as illite-muscovite, kaolinite, chlorite and mixed-layer minerals such as chlorite-smectite and illite-smectite. The diagenesis and very-low-grade metamorphism of the sedimentary rock is determined by gradual changes of clay mineral ‘crystallinity’ (illite, chlorite, kaolinite), the use of a chlorite geothermometer and the reflectance of organic matter. It is concluded here that: (1) the established thermal grade is diagenesis; (2) tectonic strains affect the clay mineral ‘crystallinity’ in the fault zone; (3) there is a strong correlation between temperature determined by chlorite geothermometry and organic-matter reflectance; and (4) the duration and depth of burial as well as the pore-fluid chemistry are important factors affecting clay-mineral formation.

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Reliability of very low-grade metamorphic methods to decipher basin evolution: Case study from the Markstein basin (Southern Vosges, NE France)

Cited by 11 publications

References 47 publications

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary belt (SW Iberian Variscides)

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary belt (SW Iberian Variscides)

Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary domain (SW Iberian Variscides)

Low-grade evolution of clay minerals and organic matter in fault zones of the Hikurangi prism (New Zealand)

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