Controls on solid-phase inclusion during porphyroblast growth: insights from the Barrovian sequence (Scottish Dalradian)

Farber, Katja; Caddick, Mark J.; John, Timm

doi:10.1007/s00410-014-1089-0

Cited by 13 publications

(13 citation statements)

References 53 publications

(96 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(). Although some investigations have reported chlorite‐bearing assemblages in the general vicinity (Farber et al., ), the textural descriptions and images presented of these rocks are suggestive of retrograde chlorite after biotite. Most samples show evidence of compositional layering with alternating muscovite‐ and quartzofeldspathic layers of a few millimetre thickness.…”

Section: Petrographymentioning

confidence: 77%

“…Such graphical techniques suggest that garnet and chlorite react in a discontinuous reaction (in KFMASH systems) to produce staurolite in regionally metamorphosed pelites. This involves the following reaction:

6 Grt + 13 Ms + 4.6 Chl = 2 St + 13 Bt + 23 Qz + 14.8 H_{2} O

(Farber et al., ).…”

Section: Discussionmentioning

confidence: 99%

“…6Grtþ13Msþ4:6Chl ¼ 2Stþ13Btþ23Qzþ14:8H 2 O (Farber et al, 2014). Based on this balanced reaction, the molar volumes of garnet and staurolite (Geiger & Feenstra, 1997;Holdaway, Mukhopadhyay, & Dutrow, 1995) and the modal mineralogy of the schists (Table 1), the formation of~3.7 vol.% staurolite in sample GR01 would be associated with consumption of more than 2.8 vol.% of the garnet previously present in the schist.…”

Section: Garnet Zoning Characteristicsmentioning

confidence: 91%

See 2 more Smart Citations

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Dempster

Piazza

Taylor

et al. 2017

Journal Metamorphic Geology

View full text Add to dashboard Cite

Metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase. Relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low‐temperature amphibolite facies metamorphic reactions. Garnet is widely assumed to be a reactant in staurolite‐isograd reactions, and the evidence for this has been assessed in the Late Proterozoic Dalradian pelitic schists of the Scottish Highlands. The 3D imaging of garnet porphyroblasts in staurolite‐bearing schists reveals a good crystal shape and little evidence of marginal dissolution; however, there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction. Staurolite forms directly adjacent to the garnet, and its nucleation is strongly associated with deformation of the muscovite‐rich fabrics around the porphyroblasts. “Cloudy” fluid inclusion‐rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet. Such cloudy garnet typically has a Mg‐rich, Mn‐poor composition and is interpreted to have formed during a coupled dissolution–reprecipitation process, triggered by a local influx of fluid. All garnet in the muscovite‐bearing schists present in this area is potentially reactive, irrespective of the garnet composition, but very few of the schists contain staurolite. The staurolite‐producing reaction appears to be substantially overstepped during the relatively high‐pressure Barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions. Fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history. The remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning. Such zoning in metamorphic garnet created during coupled dissolution–reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re‐equilibration. Fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists. In addition, the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history. However, the partial re‐equilibration of the porphyroblasts during coupled dissolution–reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions.

show abstract

Section: Petrographymentioning

confidence: 77%

6 Grt + 13 Ms + 4.6 Chl = 2 St + 13 Bt + 23 Qz + 14.8 H_{2} O

(Farber et al., ).…”

Section: Discussionmentioning

confidence: 99%

Section: Garnet Zoning Characteristicsmentioning

confidence: 91%

See 1 more Smart Citation

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Dempster

Piazza

Taylor

et al. 2017

Journal Metamorphic Geology

View full text Add to dashboard Cite

show abstract

“…During metamorphism, the growth of porphyroblasts often results in the entrapment of solid or fluid inclusions, which then provide important information about the rock's history (e.g. Farber et al, 2014;Yardley and Bodnar, 2014;Ferrero and Angel, 2018). Due to the differences in the elastic compressibility and thermal expansion coefficient between the inclusion and host, residual inclusion pressures may be preserved after exhumation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry

2020

View full text Add to dashboard Cite

Abstract. Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion to the thin-section surface. Criteria are provided to quantify how much of the expected residual pressure is modified due to these three mechanisms. An analytical solution is introduced to demonstrate the effect of inclusion depth on the residual pressure field when the inclusion is close to the thin-section surface. It is shown that for a quartz-in-garnet system, the distance between the thin-section surface and inclusion centre needs to be at least 3 times the inclusion radius to avoid pressure release. In terms of viscous creep, representative case studies on a quartz-in-garnet system show that viscous relaxation may occur from temperatures as low as 600–700 ∘C depending on the particular pressure–temperature (P–T) path and various garnet compositions. For quartz entrapped along the prograde P–T path and subject to viscous relaxation at peak T above 600–700 ∘C, its residual pressure after exhumation may be higher than predicted from its true entrapment conditions. Moreover, such a viscous resetting effect may introduce apparent overstepping of garnet nucleation that is not related to reaction affinity.

show abstract

“…An example of topotaxial intergrowth of staurolite and kyanite in thin section is shown in Figure g in a sample from the Glacier Creek aureole, British Columbia (D.R.M. Pattison, unpublished data), and a possible example is shown in Figure h in a sample from Glen Clova in the Scottish Barrovian zones (Farber, ; Farber, Caddick, & John, ). Intergrown staurolite and kyanite is anticipated, if their growth is contemporaneous, because the crystal structure of staurolite consists of Al 2 SiO 5 layers with the kyanite structure alternating with AlO–OH–2FeO layers (Ferraris, Makovicky, & Merlino, ; figure 1 of Wenk, ).…”

Section: Textures Of Staurolite–al2sio5 Mineral Assemblagesmentioning

confidence: 99%

Kinetic control of staurolite–Al₂SiO₅ mineral assemblages: Implications for Barrovian and Buchan metamorphism

Pattison

Spear

2018

Journal Metamorphic Geology

View full text Add to dashboard Cite

The distribution and textural features of staurolite–Al2SiO5 mineral assemblages do not agree with predictions of current equilibrium phase diagrams. In contrast to abundant examples of Barrovian staurolite–kyanite–sillimanite sequences and Buchan‐type staurolite–andalusite–sillimanite sequences, there are few examples of staurolite–sillimanite sequences with neither kyanite nor andalusite anywhere in the sequence, despite the wide (~2.5 kbar) pressure interval in which they are predicted. Textural features of staurolite–kyanite or staurolite–andalusite mineral assemblages commonly imply no reaction relationship between the two minerals, at odds with the predicted first development (in a prograde sense) of kyanite or andalusite at the expense of staurolite in current phase diagrams. In a number of prograde sequences, the incoming of staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is coincident or nearly so, rather than kyanite or andalusite developing upgrade of a significant staurolite zone as predicted. The width of zones of coexisting staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is much wider than predicted in equilibrium phase diagrams, and staurolite commonly persists upgrade until its demise in the sillimanite zone. We argue that disequilibrium processes provide the best explanation for these mismatches. We suggest that kyanite (or andalusite) may develop independently and approximately contemporaneously with staurolite by metastable chlorite‐consuming reactions that occur at lower P–T conditions than the thermodynamically predicted staurolite‐to‐kyanite/andalusite reaction, a process that involves only modest overstepping (<15°C) of the stable chlorite‐to‐staurolite reaction and which is favoured, in the case of kyanite, by advantageous nucleation kinetics. If so, the pressure difference between Barrovian kyanite‐bearing sequences and Buchan andalusite‐bearing sequences could be ~1 kbar or less, in better agreement with the natural record. The unusual width of coexistence of staurolite and Al2SiO5 minerals, in particular kyanite and andalusite, can be accounted for by a combination of lack of thermodynamic driving force for conversion of staurolite to kyanite or andalusite, sluggish dissolution of staurolite, and possibly the absence of a fluid phase to catalyse reaction. This study represents an example of how kinetic controls on metamorphic mineral assemblage development have to be considered in regional as well as contact metamorphism.

show abstract

Controls on solid-phase inclusion during porphyroblast growth: insights from the Barrovian sequence (Scottish Dalradian)

Cited by 13 publications

References 53 publications

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry

Kinetic control of staurolite–Al₂SiO₅ mineral assemblages: Implications for Barrovian and Buchan metamorphism

Contact Info

Product

Resources

About

Controls on solid-phase inclusion during porphyroblast growth: insights from the Barrovian sequence (Scottish Dalradian)

Cited by 13 publications

References 53 publications

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation

Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry

Kinetic control of staurolite–Al2SiO5 mineral assemblages: Implications for Barrovian and Buchan metamorphism

Contact Info

Product

Resources

About

Kinetic control of staurolite–Al₂SiO₅ mineral assemblages: Implications for Barrovian and Buchan metamorphism