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.

Text Scherrer_2001_369-378.pdf - Published Version Restricted to registered users only Available under License Publisher holds Copyright. Download (1MB) | Request a copy

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)
Division/Institute:	Bern Academy of the Arts Bern Academy of the Arts > Institute Materiality in Art and Culture
Name:	Scherrer, Nadim0000-0002-6576-885X; Gnos, E. and Chopin, C.
Subjects:	Q Science > QE Geology
ISSN:	0036-7699
Language:	English
Submitter:	Nadim Scherrer
Date Deposited:	10 Feb 2021 15:27
Last Modified:	10 Feb 2021 15:27
Related URLs:	Publication
Web of Science ID:	000172599300006
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
ARBOR DOI:	10.24451/arbor.13535
URI:	https://arbor.bfh.ch/id/eprint/13535