The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition

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Marco E. Ciriotti
Messaggi: 25818
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition

Messaggio da Marco E. Ciriotti » sab 04 mag, 2019 15:16

Prossima pubblicazione.

Referenza:
▪ Jin, S., Xu, H., Wang, X., Zhang, D., Jacobs, R., Morgan, D. (2019): The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition. Acta Crystallographica, 75, (in press).

Synopsis:
The metastable incommensurate structure of basaltic plagioclase phenocryst varies with the composition and cooling rate of the host rock, which may enable scientists to quantitatively study the thermal history of volcanic rocks in new ways.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 25818
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition

Messaggio da Marco E. Ciriotti » lun 12 ago, 2019 12:43

Pubblicazione effettuata.

Referenza:
▪ Jin, S., Xu, H., Wang, X., Zhang, D., Jacobs, R., Morgan, D. (2019): The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition. Acta Crystallographica, B75, 643-656.

Abstract:
Four basaltic phenocryst samples of plagioclase, with compositions ranging from An48 (andesine) to An64 (labradorite), have been studied with single‐crystal X‐ray and neutron diffraction techniques. The samples were also subjected to a heating experiment at 1100°C for two weeks in an effort to minimize the Al–Si ordering in their structures. The average and the modulated structures of the samples (before and after the heating experiment) were compared, in order to understand the mechanism of the phase transition from the disordered C\bar 1 structure to the e‐plagioclase structure. A comparison between the structures from neutron and X‐ray diffraction data shows that the ⟨T—O⟩ distance does not solely depend on the Al occupancy as previously thought. A dramatic decrease of the Al–Si ordering is observed after heating at 1100°C for two weeks for all four samples, with an obvious change in the intensities of the satellite reflections (e‐reflections) in the diffraction pattern. Evident changes in the modulation period were also observed for the more calcic samples. No obvious change in the Ca–Na ordering was observed after the heating experiment. An in situ heating X‐ray diffraction experiment was carried out on the andesine sample (An48) to study the change in the satellite intensity at high temperature. A dramatic weakening of the satellite peaks was observed between 477°C and 537°C, which strongly supports the displacive nature of the initiation of e2 ordering. Rigid‐Unit Mode (RUM) analysis of the plagioclase structure suggests the initial position of the e‐reflections is determined by the anti‐RUMs in the framework.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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