A retrograde monazite-forming reaction in bearthite-bearing high-pressure rocks

Scherrer, Nadim; Gnos, E.; Chopin, C. (2001). A retrograde monazite-forming reaction in bearthite-bearing high-pressure rocks Schweizerische Mineralogische Und Petrographische Mitteilungen, 81, pp. 369-378.

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Bearthite,Ca2Al[PO4](2)(OH),an aluminium phosphate that may contain up to similar to 10 wt% of light rare-earth elements (LREE) + Th, shows various breakdown textures in high-pressure metamorphic rocks. Two such reactions are described: (1) a pyrope-bearing kyanite-phengite-quartz (coesite) schist from the high-pressure Dora-Maira terrane, Italy, in which bearthite displays a symplectitic rim that consists of apatite + monazite; (2) a garnet-bearing muscovite-biotite gneiss of the Monte Rosa nappe, Italy, in which a symplectitic pseudomorph consisting of apatite + corundum + monazite occurs as an inclusion in allanite. In rocks with a high Al/Ca ratio, we suggest that bearthite is more stable than monazite as the LREE-bearing phase under high P/low T conditions (that is, a subduction zone environment). It breaks down to an assemblage of symplectitic monazite + apatite + corundum (or Al-silicate with free SiO2) during decompression. Bearthite that coexists with HREE-dominated minerals like xenotime does not show increased HREE contents. Because of its considerable Th-content, bearthite could be used to constrain the time of high-pressure metamorphism.

Item Type:

Journal Article (Original Article)


Bern Academy of the Arts
Bern Academy of the Arts > Institute Materiality in Art and Culture


Scherrer, Nadim0000-0002-6576-885X;
Gnos, E. and
Chopin, C.


Q Science > QE Geology






Nadim Scherrer

Date Deposited:

10 Feb 2021 15:27

Last Modified:

10 Feb 2021 15:27

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Additional Information:

Notes: 499YV Times Cited:5 Cited References Count:21 Date: 2001

Uncontrolled Keywords:

bearthite monazite metamorphic reaction EMPA LREE western alps orthogneisses metamorphism paragenesis amphibolite apatite





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