La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

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Marco E. Ciriotti
Messaggi: 31292
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Messaggio da Marco E. Ciriotti » lun 12 set, 2022 8:53

Referenza:
▪ Vichi, G., Perna, M.G., Ambrosio, F.A., Rosatelli, G., Daniele, C., Broom-Fendley, S., Valdykin, N.V., Zaccaria, D., Stoppa, F. (2023): La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy. Mineralogy and Petrology, 117, (in press).

Abstract:
Very primitive ultramafic igneous rocks occur at Mt. La Queglia (Abruzzo, Italy). They form a strongly deformed sill–dyke system now tilted vertically. These rocks were initially classified as alnöite and, subsequently, have been suggested to be a carbonatitic olivine melilitite. However, further investigation and interpretation of these rocks is needed due to the presence of hand-specimen-scale textural variation suggesting a complex petrogenesis. We study the texture, mineral chemistry, and whole-rock geochemistry to define three main rock-types. (1) A brecciated rock with an ocellar texture composed of calcite pseudomorphs after olivine and melilite, plus fresh diopside in a groundmass of mica, aegirine, garnet, calcite, apatite, perovskite, titanate and chlorite. Zoned ocelli in this rock show an amoeboid shape, agglutination, and menisci typical of a plastic state. (2) A quenched rock showing a spinifex texture containing long feathery phenocrysts of cpx and mica suspended in a groundmass of nepheline, aegirine, apatite, Ti–rich magnetite, plus abundant calcite and some K-feldspar and zeolites. (3) A coarse-grained rock is composed of calcite plus intergranular glauconite, a mixture of spinel mineral group and Ti–rich magnetite, accessory barite, pyrite, and chabazite-K. The igneous rocks at Mt. La Queglia show extreme SiO 2 -undersaturation (33.5–37.3 wt% SiO 2 ), high MgO contents and TiO 2 /Al 2 O 3 ratios. Rock-type 1 has a lower Mg number Mg# = 100 × [Mg/(Mg + Fe ²⁺ )], higher Ca number Ca# = 100 × [Ca/(Ca + Mg)], high Cr (up to 720 ppm) Ni (up to 379 ppm), higher rare earth elements (REE) contents as well as La/Lu ratio, compared to rock-type 2. Perovskite and chromite accumulation seems an important agent during rock differentiation. Rock-type 3 shows REE cross-over with rock-type 2 suggesting light (L)REE concentration in a carbothermal residuum. Mt. La Queglia rocks are an end-member compared to other Upper Cretaceous and Paleogene Italian lamprophyres, suggesting a low degree of melting of a HIMU (a colloquialism for “high-μ”; referring to mantle domains with high ²³⁸ U/ ²⁰⁴ Pb) garnet-bearing mantle source.
Marco E. Ciriotti

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TOSATO FABIO
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Re: La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Messaggio da TOSATO FABIO » lun 12 set, 2022 12:26

Interessante per una regione, Abruzzo, non molto ricca di minerali.
Tosato Fabio
"Il vero viaggio di scoperta non consiste nel cercare nuove terre, ma nell'avere nuovi occhi." M. Proust
Noi siamo anche quello che non siamo riusciti ad essere.
Sic transit gloria mundi.

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Alessio73
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Iscritto il: mar 24 lug, 2007 10:35
Località: Ancona

Re: La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Messaggio da Alessio73 » lun 12 set, 2022 13:44

Beh il problema è che alcune zone interessanti sono in zona parco. Anche questa ovviamente.
Tanto per dire ci sono due zone con delle anomalie radioattive, una delle quali ha l' aggravante... è in una grotta carsica.
Socio AMI Delegato Marche-Abruzzo

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Marco E. Ciriotti
Messaggi: 31292
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Messaggio da Marco E. Ciriotti » mar 03 ott, 2023 11:24

Pubblicazione effettuata.

Referenza:
▪ Vichi, G., Perna, M.G., Ambrosio, F.A., Rosatelli, G., Daniele, C., Broom-Fendley, S., Valdykin, N.V., Zaccaria, D., Stoppa, F. (2023): La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy. Mineralogy and Petrology, 117, 505–528.
Marco E. Ciriotti

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