Equilibrium and disequilibrium processes across the greenschist–amphibolite transition zone in metabasites

Starr, Paul G.; Pattison, David R.M.

doi:10.1007/s00410-019-1553-y

Cited by 12 publications

(2 citation statements)

References 66 publications

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“…A more continuous amphibole trend exists in tholeiitic igneous systems ( Figure 7); indeed, trace element analysis rather than major element composition had to be used by Coogan et al (2001) to discriminate igneous from metamorphic amphiboles in the MOR setting. No doubt amphibole phase relations are exceedingly complex with active debate about actinolite-hornblende transitions (Maruyama et al, 1983;Starr & Pattison, 2019) or amphibole-feldspar thermometry (Holland & Blundy, 1994). Note that the same Al 2 O 3 -SiO 2 anticorrelation is observed within a single thermal gradient experiment at constant pressure (Figure 7; Huang et al, 2009), indicating that temperature changes alone can produce the observed amphibole trend during the thermal gradient differentiation process.…”

Section: 1029/2019jb017654mentioning

confidence: 90%

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

Lundstrom

2020

JGR Solid Earth

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Melt compositions in equilibrium with quartz and albite at 0.1 GPa and temperatures from 819 to 330 °C are reported for cold seal experiments in the Na2O‐Al2O3‐SiO2‐H2O system. At 60–70 °C intervals, melt compositions continuously change from rhyolite‐like melts with <10 wt.% H2O at the quartz‐albite eutectic to melts of nearly endmember Na2Si2O5 having >30 wt.% H2O at 330 °C (vapor undersaturated). Melt Na2O increases while SiO2 and Al2O3 decrease down temperature. Experiments performed at T > 600 °C are vapor saturated with <9.9–21 wt.% H2O while those T < 600 °C are vapor undersaturated with 18–37 wt.% H2O. Because of the continuous change in the liquid's composition down temperature, all compositions can be called melts; in reality, their high water contents may also lead to being termed hydrous fluids. These results indicate that igneous processes continue to temperatures >300 °C below the haplogranite solidus. The water‐rich melts at low temperature have low viscosities and densities suggesting that they buoyantly ascend by reactive flow at low melt porosities (<5%). Formation of low‐temperature melt will occur along the sides of gabbro bodies of mid‐ocean ridges, resulting in large‐scale convection that removes heat from the lower crust. This circulation may move heat off axis influencing observed heat flow. Melt reaction processes result in silicic differentiates (plagiogranites) and formation of greenschist metabasalts. This frees calcium from silicate bonding, providing an important sink for CO2 in Earth's carbon cycle. Sr isotopes of the ocean crust change with ocean crust production rates indicating mid‐ocean ridge systems are a major control on Earth's climate over time.

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Section: 1029/2019jb017654mentioning

confidence: 90%

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

Lundstrom

2020

JGR Solid Earth

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“…These generate a first‐order transition at 600°C and the miscibility gap shown in Figure 8 and considerably widen the miscibility gap between albite and plagioclase at low temperatures. As discussed in Nord Jr. et al (1978) and Starr and Pattison (2019), whether the miscibility gap is a solvus or a binary loop is unresolved; our model assumes the latter.

\begin{array}{lcl} W_{normalan normalab} & = & 3.4 false(\pm 0.3 false) kJ \\ α_{an} & = & 1.00 false(fixed false) \\ α_{ab} & = & 0.64 false(\pm 0.02 false) \\ normalΔ G_{ab}^{mod} & = & - 1.746 + 0.002 T false(\pm 0.05 false) kJ \\ normalΔ G_{an}^{mod} & = & 10.00 false(\pm 0.05 false) kJ \end{array}

…”

Section: Testing and Application Of The 4tr Modelmentioning

confidence: 92%

A thermodynamic model for feldspars in KAlSi₃O₈−NaAlSi₃O₈−CaAl₂Si₂O₈ for mineral equilibrium calculations

Holland

Green

Powell

2021

Journal Metamorphic Geology

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Activity-composition (a-x) relations for feldspars for petrological calculations in KAlSi 3 O 8 ÀNaAlSi 3 O 8 ÀCaAl 2 Si 2 O 8 are calibrated using literature data for (i) plagioclase cation exchange experiments at 600 and 700 C, (ii) experimental ternary feldspar pairs at 880 À 900 C, (iii) the alkali feldspar solvus, and (iv) the dry melting loop for plagioclase. The results are tested against the calorimetric heat of solution data and the experimental pressures for plagioclase coexisting with grossular, wollastonite, and quartz. As the aim is to produce a-x relations suitable for petrological modelling, we do not attempt to model complex structural phenomena in feldspar, except where they appear to contribute significantly to the energetics of high-temperature mixing. Seven models were investigated, using various formulations of entropy of mixing together with the van Laar model for non-ideal mixing. The model (4TR) that most satisfactorily reproduces the experimental data is one in which Al and Si partially order onto the four tetrahedral sites, approximated by reducing the tetrahedral site entropy of mixing by a factor of 4. When combined with an ordered albite, this model allows a peristerite gap closing at 600 C at the albite composition. The resulting activity-composition relations for feldspar should be applicable in petrological phase equilibrium calculations over a large range of geologically relevant pressure and temperature.

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Metamorphism of Mafic Rocks

Bucher

2023

Springer Textbooks in Earth Sciences, Geography and Environment

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Equilibrium and disequilibrium processes across the greenschist–amphibolite transition zone in metabasites

Cited by 12 publications

References 66 publications

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

A thermodynamic model for feldspars in KAlSi₃O₈−NaAlSi₃O₈−CaAl₂Si₂O₈ for mineral equilibrium calculations

Metamorphism of Mafic Rocks

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Equilibrium and disequilibrium processes across the greenschist–amphibolite transition zone in metabasites

Cited by 12 publications

References 66 publications

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

Continuously Changing Quartz‐Albite Saturated Melt Compositions to 330 °C With Application to Heat Flow and Geochemistry of the Ocean Crust

A thermodynamic model for feldspars in KAlSi3O8−NaAlSi3O8−CaAl2Si2O8 for mineral equilibrium calculations

Metamorphism of Mafic Rocks

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A thermodynamic model for feldspars in KAlSi₃O₈−NaAlSi₃O₈−CaAl₂Si₂O₈ for mineral equilibrium calculations