Inter-relationships between deformation partitioning, metamorphism and tectonism

Bell, T. H.; Rieuwers, Mark Thomas; Cihan, M.; Evans, Thomas Philip; Ham, A.P.; Welch, Peter W.

doi:10.1016/j.tecto.2012.06.014

Cited by 19 publications

(5 citation statements)

References 37 publications

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“…Other samples in Sifnos experienced an apparently smaller overstep and grew 3-5 cm crystals over ~8 Myr (Dragovic et al 2015). In the regionally metamorphosed Eastern Vermont terrane (geographically near the samples described by Bell et al (2013) and Spear et al (2014)), garnet crystals nucleated after a ~35 ˚C overstep (Dragovic et al 2018) and then grew up to ~2.5 cm in diameter in 3.8 ± 2.2 Myr during regional metamorphism (Gatewood et al 2015). In the Cascades Crystalline Core, garnet experienced ~30-40ºC of overstepping and then grew over a period of < 6 Myr (Stowell et al 2011).…”

Section: Discussionmentioning

confidence: 90%

“…Sample AV26A is from the Pomfret Dome, southeastern Vermont (Bell et al 2013). It formed during the Appalachian Taconic Orogeny, when over-thrusting of thick tectonic sheets resulted in porphyroblast nucleation at 550ºC and 8.0 kbar, consistent with 30ºC and 1.5 kbar of overstepping (Bell et al 2013). Analysis of inclusion trail geometries reveals that garnet only nucleated and grew during the start of crenulation-forming deformation events and nucleation was controlled by microlithologic domains developed during deformation (Bell et al 2013).…”

Section: Examples With Apparent Overstepping (>10ºc and 05 Kbar)mentioning

confidence: 92%

Section: Examples With Apparent Overstepping (>10ºc and 05 Kbar)mentioning

confidence: 92%

“…In general, samples with lower bulk rock MnO content display the least apparent overstepping of garnet nucleation. Figure 9 shows TEC and MSC versions of a T-X MnO diagram for sample AV26A (Bell et al 2013) in which the x axis ranges from 0 to 0.2 wt.% MnO, with other components fixed in the ratio reported by Bell et al (2013). The temperature at which garnet stability is first calculated scales inversely with the bulk rock MnO content.…”

Section: The Role Of X Mno In Pseudosection Calculationsmentioning

confidence: 99%

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The (chemical) potential for understanding overstepped garnet nucleation and growth

Nagurney

Caddick

Dragovic

et al. 2021

American Mineralogist

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Overstepping of porphyroblast-forming reactions has been shown to occur in regional, contact, and subduction zone metamorphism, calling into question the paradigm that metamorphic mineral reactions occur at or very close to thermodynamic equilibrium. These overstepped reactions result from the fact that nucleation and growth of new phases requires a thermodynamic driving force, or a departure from equilibrium. We use phase equilibria modeling to elucidate the energetic consequences of overstepped garnet nucleation and growth by comparing the chemical potentials of garnet-forming oxide components (MnO, CaO, FeO, MgO, Al 2 O 3) in two sets of calculations: one in which Gibbs free energy is minimized and one in which the minimization proceeds under identical conditions but in the forced absence of garnet. We focus on twelve examples from the literature which have previously described garnet nucleation as minimally overstepped (garnet nucleation at the P-T of initial garnet stability) or garnet nucleation as more substantially overstepped (garnet nucleation at P-T conditions greater than initial garnet stability). For a small P-T interval above nominal garnet-in reactions, differences in the chemical potentials between the two calculations are commonly minimal. In all 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: Discussionmentioning

confidence: 90%

Section: Examples With Apparent Overstepping (>10ºc and 05 Kbar)mentioning

confidence: 92%

Section: Examples With Apparent Overstepping (>10ºc and 05 Kbar)mentioning

confidence: 92%

Section: The Role Of X Mno In Pseudosection Calculationsmentioning

confidence: 99%

See 2 more Smart Citations

The (chemical) potential for understanding overstepped garnet nucleation and growth

Nagurney

Caddick

Dragovic

et al. 2021

American Mineralogist

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“…Such a microstructural pattern has in many places been interpreted as a result of polyphase pre‐D3 deformation‐porphyroblast growth (Bell & Sanislav, ; e.g. Bell et al ., ). These geometrical relationships are interpreted as a result of rigid body rotation of a staurolite porphyroblast within an incompetent weak matrix during the F3 folding.…”

Section: Discussionmentioning

confidence: 99%

Tectonometamorphic evolution of an intracontinental orogeny inferred from P–T–t–d paths of the metapelites from the Rehamna massif (Morocco)

Schulmann

Chopin

Štípská

et al. 2016

Journal Metamorphic Geology

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New petrographic and microstructural observations, mineral equilibria modelling and U/Pb (monazite) geochronological studies were carried out to investigate the relationships between deformation and metamorphism across the Rehamna massif (Moroccan Variscan belt). In this area, typical Barrovian (muscovite to staurolite) zones developed in Cambrian to Carboniferous metasedimentary rocks that are distributed around a dome‐like structure. First assemblages are characterized by the presence of locally preserved andalusite, followed by prograde evolution culminating at 6 kbar and 620 °C in the structurally deepest staurolite zone rocks. This Barrovian sequence was subsequently uplifted to supracrustal levels, heterogeneously reworked at greenschist facies conditions, which was followed locally by static growth of andalusite, indicating heating to 2.5–4 kbar and 530–570 °C. The 206Pb/238U monazite age of 298.3 ± 4.1 Ma is interpreted as minimum age of peak metamorphic conditions, whereas the ages of 275.8 ± 1.7 Ma and 277.0 ± 1.1 Ma date decompression and heating at low pressure, in agreement with previous dating of Permian granitoids intruding the Rehamna massif. The prograde metamorphism occurred during thickening and associated horizontal flow in the deeper crust (S1 horizontal schistosity). The horizontally disposed metamorphic zones were subsequently uplifted by a regional scale antiform during ongoing N–S compression. The re‐heating of the massif follows late massive E–W shortening, refolding and retrograde shearing of all previous fabrics coevally with regionally important intrusions of Permian granitoids. We argue that metamorphic evolution of the Rehamna massif occurred several hundred kilometres from the convergent plate boundaries in the interior of continental Gondwanan plate. The tectonometamorphic history of the Rehamna massif is put into Palaeozoic plate tectonic perspective and Late Carboniferous reactivation of (Devonian)–Early Carboniferous basins formed during stretching of the north Gondwana margin and formation of the Palaeotethys Ocean. The inherited heat budget of these magma‐rich basins plays a role in the preferential location of this intracontinental orogen. It is shown that rapid transition from lithospheric stretching to compression is characterized by specific HT type of Barrovian metamorphism, which markedly differs from similar Barrovian sequences along Palaeozoic plate boundaries reported from Variscan Europe.

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Channel flow extrusion model to constrain dynamic viscosity and Prandtl number of the Higher Himalayan Shear Zone

Mukherjee

2012

Int J Earth Sci (Geol Rundsch)

115

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Inter-relationships between deformation partitioning, metamorphism and tectonism

Cited by 19 publications

References 37 publications

The (chemical) potential for understanding overstepped garnet nucleation and growth

The (chemical) potential for understanding overstepped garnet nucleation and growth

Tectonometamorphic evolution of an intracontinental orogeny inferred from P–T–t–d paths of the metapelites from the Rehamna massif (Morocco)

Channel flow extrusion model to constrain dynamic viscosity and Prandtl number of the Higher Himalayan Shear Zone

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