Barium-bearing potassium feldspars of muscovite pegmatites

Afonina, G. G.; Makagon, V. M.; Shmakin, B. M.

doi:10.1080/00206817409471871

Cited by 2 publications

(2 citation statements)

References 5 publications

(1 reference statement)

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“…Carvalho et al., ; Markl & Bucher, ; Markl, Ferry, & Bucher, ). This is consistent with the presence of hyalophane (Ba‐rich K‐feldspar; Figure d,e) in the melt pseudomorphs, which is typically associated with high‐ P pegmatites (Afonina, Makagon, & Shmakin, ; Qu, Guo, Lai, Peng, & Liu, ) and/or carbonic or saline fluids (Pandur, Kontak, & Ansdell, ). Therefore, the aggregates are likely to have pseudomorphed the final proportions of melt or fluid within the high‐strain zones.…”

Section: Discussionsupporting

confidence: 73%

The recognition of former melt flux through high‐strain zones

Stuart

Piazolo

Daczko

2018

Journal Metamorphic Geology

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High‐strain zones are potential pathways of melt migration through the crust. However, the identification of melt‐present high‐strain deformation is commonly limited to cases where the interpreted volume of melt “frozen” within the high‐strain zone is high (>10%). In this contribution, we examine high‐strain zones in the Pembroke Granulite, an otherwise low‐strain outcrop of volcanic arc lower crust exposed in Fiordland, New Zealand. These high‐strain zones display compositional layering, flaser‐shaped mineral grains, and closely spaced foliation planes indicative of high‐strain deformation. Asymmetric leucosome surrounding peritectic garnet grains suggest deformation was synchronous with minor amounts of in situ partial melting. High‐strain zones lack typical mylonite microstructures and instead display typical equilibrium microstructures, such as straight grain boundaries, 120° triple junctions, and subhedral grain shapes. We identify five key microstructures indicative of the former presence of melt within the high‐strain zones: (a) small dihedral angles of interstitial phases; (b) elongate interstitial grains; (c) small aggregates of quartz grains with xenomorphic plagioclase grains connected in three dimensions; (d) fine‐grained, K‐feldspar bearing, multiphase aggregates with or without augite rims; and (e) mm‐ to cm‐scale felsic dykelets. Preservation of key microstructures indicates that deformation ceased as conditions crossed the solidus, breaking the positive feedback loop between deformation and the presence of melt. We propose that microstructures indicative of the former presence of melt, such as the five identified above, may be used as a tool for recognising rocks formed during melt‐present high‐strain deformation where low (<5%) volumes of leucosome are “frozen” within the high‐strain zone.

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Section: Discussionsupporting

confidence: 73%

The recognition of former melt flux through high‐strain zones

Stuart

Piazolo

Daczko

2018

Journal Metamorphic Geology

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“…The disordering factor here is the entry of isomorphous components, which retard the ordering. As has been shown, Ba has this effect for KFS (Afonina et al, 1973), as do Rb and Cs (Gordiyenko and Kamentsev, 1967).…”

Section: Discussionmentioning

confidence: 80%

Effects of rubidium and cesium on the structural states of potash feldspars from rare-metal pegmatites

Afonina¹

1979

International Geology Review

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Barium-bearing potassium feldspars of muscovite pegmatites

Cited by 2 publications

References 5 publications

The recognition of former melt flux through high‐strain zones

The recognition of former melt flux through high‐strain zones

Effects of rubidium and cesium on the structural states of potash feldspars from rare-metal pegmatites

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