Myrmekite — one hundred years later

Phillips, Evan R.

doi:10.1016/0024-4937(74)90029-2

Cited by 66 publications

(35 citation statements)

References 47 publications

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“…The two main hypotheses for myrmekite development are those of replacement reactions (Becke, 1908) and solid-state exsolution (Schwantke, 1909). These ideas and variations thereon have been summarized and discussed in &tail by Sturt (1970), Widenfalk (1972), Smith (1974) and Phillips (1974;1980). In Schwantke's lattice diffusion model, a change in solid composition m u m in response to elastic strain gradients, but requires a relatively long time to accomplish (see also Bayly, 1987).…”

Section: Discussionmentioning

confidence: 99%

“…Binns (1966), Parslow (1971), Bhattacharyya (1971) and Phillips & Carr (1973) among others. Summaries of these early works are given in Ashworth (1972), Phillips (1974) and Smith (1974). More recently, a correlation between mynnekite growth and crystal-plastic deformation has been suggested by several workers including Hanmer (1982), Tullis (1983), Watts & Williams (1983), Vernon, S i p n (1983; 1985), Hibbard (1987), LaTour (1987) and LaTour & Barnett (1987).…”

Section: Introductionmentioning

confidence: 99%

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Evidence for deformation‐induced K‐feldspar replacement by myrmekite

Simpson

Wintsch

1989

Journal Metamorphic Geology

302

156

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Several examples of deformation-induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths, namely a muscovite-poor S-C mylonite and a single foliation, muscovite-poor mylonitic gneiss. Back-scattered SEM and conventional optical microscopy show that in both rock types, syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of &feldspar grains that faced the local inferred incremental shortening direction for the mylonite.Myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction.The replacement of K-feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains. We suggest that the ambient temperature, pressure and chemical activities were such that the replacement reaction was favoured, but the addition of extra strain energy along the high-pressure sides of the grains localized the reaction at these sites. This energy could arise from elastic strain, or strain associated with tangled dislocations or twin boundaries. The relative roles of stress and strain energy concentrations in driving the replacement reaction are not known, but both were probably important.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evidence for deformation‐induced K‐feldspar replacement by myrmekite

Simpson

Wintsch

1989

Journal Metamorphic Geology

302

156

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“…The development of microperthite is more intense in smaller K-feldspar crystals, often only at the grain edges. Myrmekite aggregates are generally welldeveloped, and the marginal types as described by Phillips (1974) are predominant, in their planar and bulbous varieties. Subgrain rotation in progressively recrystallized grains is uncommon, and seems to be restricted to a few larger crystals.…”

Section: Tablementioning

confidence: 98%

Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr–Nd–Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil

Florisbal

Bitencourt

Janasi

et al. 2012

Lithos

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“…Familiar examples of symplectite formation involving composition change are myrmekites, where a vermicular intergrowth of sodic plagioclase and quartz replaces K-feldspar (Phillips 1974;Abart et al 2014) pseudoleucites, where vermicular nepheline-Kfeldspar intergrowths pseudomorphically replace leucite (Gittins et al 1980); scapolite-quartz symplectites replacing K-feldspar (Harley and Santosh 1995) or scapolite-clinopyroxene symplectites replacing garnet (Abart et al 2001).…”

mentioning

confidence: 99%

Synthesis of monticellite–forsterite and merwinite–forsterite symplectites in the CaO–MgO–SiO2 model system: influence of temperature and water content on microstructure evolution

Remmert

Heinrich

Wunder

et al. 2017

Contrib Mineral Petrol

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Homogeneous single crystals of synthetic monticellite with the composition Ca 0.88 Mg 1.12 SiO 4 (Mtc I) were annealed in a piston-cylinder apparatus at temperatures between 1000 and 1200• C , pressures of 1.0-1.4 GPa, for run durations from 10 min to 24 h and applying bulk water contents ranging from 0.0 to 0.5 wt% of the total charge. At these conditions, Mtc I breaks down to a fine-grained, symplectic intergrowth. Thereby, two types of symplectites are produced: a first symplectite type (Sy I) is represented by an aggregate of rod-shaped forsterite immersed in a matrix of monticellite with end-member composition (Mtc II), and a second symplectite type (Sy II) takes the form of a lamellar merwinite-forsterite intergrowth. Both symplectites may form simultaneously, where the formation of Sy I is favoured by the presence of water. Sy I is metastable with respect to Sy II and is successively replaced by the latter. For both symplectite types, the characteristic spacing of the symplectite phases is independent of run duration and is only weeakly influenced by the water content, but it is strongly temperature dependent. It varies from about 400 nm at 1000• C to 1200 nm at 1100• C in Sy I, and from 300 nm at 1000 • C to 700 nm at 1200• C in Sy II. A thermodynamic analysis reveals that the temperature dependence of the characteristic spacing of the symplectite phases is due to a relatively high activation energy for chemical segregation by diffusion within the reaction front as compared to the activation energy for interface reactions at the reaction front. The temperature dependence of the characteristic lamellar spacing and the temperature-time dependence of overall reaction progress have potential for applications in geo-thermometry and geo-speedometry.

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Myrmekite — one hundred years later

Cited by 66 publications

References 47 publications

Evidence for deformation‐induced K‐feldspar replacement by myrmekite

Evidence for deformation‐induced K‐feldspar replacement by myrmekite

Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr–Nd–Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil

Synthesis of monticellite–forsterite and merwinite–forsterite symplectites in the CaO–MgO–SiO2 model system: influence of temperature and water content on microstructure evolution

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