Linear correlations of lnP vs the thickness t of the TOT mica module and vs the ditrigonal distortion α are established by analyzing a population of 43 phengites for which an estimate of the crystallization pressure P independent of the Si content is available. The equations for the fitting regression lines are: lnP = -0.35(3)α + 5.0(3) (R 0.90, 26 observations) and lnP = -29(2)t + 293(22) (R 0.90, 43 observations). These correlations evidence the strict links involving genetic conditions, chemical composition and structural parameters c (represented by t) and α. In their turn, for the structural parameters the following correlation holds: t = 0.0110(9)α + 9.859(7) (R 0.92, 26 observations). The linear correlations of lnP, t and α vs the Si content have equations: lnP = 4.2(4)Si - 12(1) (R 0.86, 43 observations), t = -0.13(1)Si + 10.37(4) (R 0.87, 43 observations), and α = -12.7(9)Si + 50(3) (R 0.94, 26 observations). The observed dispersion of the data is mainly due to the uncertainty in the pressures estimated from mineral assemblages. The possibility of calculating P from a measure of c only does not overcome this type of uncertainty, but opens the possibility of estimating the crystallization pressure of phengites relics at nanoscale (e.g., by transmission electron diffraction).

Correlation between crystallization pressure and structural parameters of phengites

CURETTI, Nadia;FERRARIS, Giovanni;
2008

Abstract

Linear correlations of lnP vs the thickness t of the TOT mica module and vs the ditrigonal distortion α are established by analyzing a population of 43 phengites for which an estimate of the crystallization pressure P independent of the Si content is available. The equations for the fitting regression lines are: lnP = -0.35(3)α + 5.0(3) (R 0.90, 26 observations) and lnP = -29(2)t + 293(22) (R 0.90, 43 observations). These correlations evidence the strict links involving genetic conditions, chemical composition and structural parameters c (represented by t) and α. In their turn, for the structural parameters the following correlation holds: t = 0.0110(9)α + 9.859(7) (R 0.92, 26 observations). The linear correlations of lnP, t and α vs the Si content have equations: lnP = 4.2(4)Si - 12(1) (R 0.86, 43 observations), t = -0.13(1)Si + 10.37(4) (R 0.87, 43 observations), and α = -12.7(9)Si + 50(3) (R 0.94, 26 observations). The observed dispersion of the data is mainly due to the uncertainty in the pressures estimated from mineral assemblages. The possibility of calculating P from a measure of c only does not overcome this type of uncertainty, but opens the possibility of estimating the crystallization pressure of phengites relics at nanoscale (e.g., by transmission electron diffraction).
93
451
455
Phengites; crystallization pressure; pressure-structure correlation; ditrigonal distortion; mica module thickness
N. CURETTI; G. FERRARIS; G. IVALDI
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/22158
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