Ferrimuscovite and celadonite substitutions in muscovite from Fe3+-rich low-grade psammitic rocks (Northern Apennines, Italy)

doi:10.1016/0024-4937(89)90005-4

Lithos

Volume 23, Issue 3, August 1989, Pages 201-208

https://doi.org/10.1016/0024-4937(89)90005-4 Get rights and content

Abstract

Electron microprobe and wet-chemical data of muscovites from pyrophyllite- or K-feldspar-bearing Fe³⁺-rich rocks of the Verrucano metasediments are reported. A close relationship has been found between muscovite composition and bulk-rock chemistry. The extent of celadonite and ferrimuscovite substitutions increases progressively from pyrophyllite- to K-feldspar-bearing samples.

The mutual cation substitutions reveal: (1) an almost ideal Tschermak substitution; (2) a close positive correlation between the (Mg + Fe²⁺) and Fe³⁺ contents; and (3) a negative correlation between the octahedral and interlayer occupancies.

The extent of celadonite and ferrimuscovite substitutions of muscovite from magnetite-bearing rocks has been constrained at moderate pressure in low-temperature metamorphism.

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Vectors to ore in replacive volcanogenic massive sulphide deposits of the northern Iberian Pyrite Belt: Major and trace element mineral chemistry
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In more proximal areas, the primary minerals are illite-smectite mixed-layer clays or illite (Giorgetti et al., 2006; Lackschewitz et al., 2004). The paragonite-muscovite system has been largely investigated, whereas it is still unclear how ambient conditions control compositions in the muscovite-celadonite system – for example total Fe content, Fe/(Fe + Mg), or Fe3+/Fe2+ (e.g. Baldelli et al., 1989; Guidotti, 1984; Guidotti et al., 1994a; Guidotti et al., 1994b; Guidotti and Sassi, 1998; Keller et al., 2005). Although pressure is known to have an extensive effect in the Tschermak substitution – which tends to increase with it (Guidotti 1984, Guidotti et al., 1994a; Guidotti and Sassi, 2002)-, since all investigated white micas equilibrated at similarly low pressures (Tornos, 2006), the effect of this intensive parameter has not been considered.
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Chlorite is predominantly clinochlore in composition, with chamosite restricted to the centre of the hydrothermal system. In regionally altered lithologied it is characterized by a constantly low Al and Al^IV at variable Fe/(Fe + Mg); in rocks influenced by the hydrothermal system it presents higher Al^IV and total Al, and a progressive increase in Al, Al^IV and Fe/(Fe + Mg) towards its core.
Regional carbonates consist of calcite, with additional dolomite forming in proximal rocks. Iron content in dolomite increases towards the centre of the hydrothermal system, with ankeritic compositions becoming dominant.
Systematic variations in Ba, Cs, Li, Pb, Rb, Sn, Sr, Tl and Zn have been observed in white micas consistent with a proximal-distal transition (vector). Trends in chlorite have been less well characterized due to analytical limitations, although variations have been observed in the contents of As, Co, Li and Zn.
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Ferrimuscovite and celadonite substitutions in muscovite from Fe3+-rich low-grade psammitic rocks (Northern Apennines, Italy)

Abstract

Sediment. Geol.

Verrucano: a tecto-facies of the Alpine Mediterranean Southern Europe

Mem. Soc. Geol. Ital.

Significance of phengitic micas from low grade schists

Am. Mineral.

Regional distribution of Al-silicates nd metamorphic zonation in the low-grade Verrucano metasediments from the Northern Apennines, Italy

J. Metamorphic Geol.

Geochemistry and mineralogy of detritic rocks from “Verrucano” type-sequences of Northern Apennines (Monti Pisani and Punta Bianca), Italy

Rend Soc. Ital. Mineral. Petrol.

Sudoite, a rock forming mineral in Verrucano of the Northern Apennines (Italy) and the sudoite-chloritoid-pyrophyllite assemblage in prograde metamorphism

Contrib. Mineral. Petrol.

Sudoite, di/trioctahedral chlorite: a stable low-temperature phase in the system MgOAl2O3SiO2H2O

Contrib. Mineral. Petrol.

Coexisting paragonite and quartz in sillimanitic rocks from New Mexico

Am. Mineral.

Micas in metamorphic rocks

Ferrimuscovite and celadonite substitutions in muscovite from Fe³⁺-rich low-grade psammitic rocks (Northern Apennines, Italy)

Sudoite, di/trioctahedral chlorite: a stable low-temperature phase in the system MgOAl₂O₃SiO₂H₂O