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Phlogopite from the Serre ultramafic rocks, Central Calabria, Southern Italy

¹ Dipartimento di Mineralogia e Petrologia, Università di Padova, Corso Garibaldi 37, I–35137 Padova, Italy
² Dipartimento di Scienze della Terra, Università "G. D’ Annunzio" Chieti, Via dei Vestini 30, I–66013 Chieti Scalo, Italy
³ Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Piazza di Porta S. Donato 1, I–40126 Bologna, Italy

^* E-mail: giovanna{at}dmp.unipd.it

A 6–7 meter thick phlogopite-bearing peridotite "body" interlayered within a 200 m thick sequence of layered metagabbro and pyroxene-bearing felsic granulite outcrops in the Serre Massif, southern sector of the Calabrian Peloritan Arc (southern Italy). Phlogopite occurs throughout the whole peridotitic body, but in different modal amounts and in various textural sites.

It occurs as Type-I, isolated and oriented grains in textural equilibrium with the other phases, either in the peridotite or in included orthopyroxenite veins; Type-II, in a kind of mèlange, as millimetric smearings of flakes which separate anastomosing phlogopite-rich and orthopyroxene-rich peridotitic portions; Type-III, in centimetric phlogopitite layers alternating with phlogopite-rich layers.

The phlogopite has mg values [mg = Mg/(Mg+Fe)] in the range 0.90 to 0.94. It also shows appreciable variations of TiO², Cr²O³ and BaO contents, i.e., 1.26–2.44, 0.21–1.35, 0.15–2.02 wt%, respectively.

The primitive mantle-normalized REE pattern of Type-I phlogopite shows a steep negative slope from La to Eu, followed by a slight Gd positive anomaly and a moderately positive slope from Tb to Lu. The REE patterns of Types-II and -III show negative slopes from La to Lu, but the Type-II pattern displays a marked Eu negative anomaly, and Type-III phlogopite has lower M- and HREE contents.

The trace element spider diagrams show a generally decreasing trend in elemental amounts, in accordance with decreasing incompatibility, with evident K, Pb, Mo, P, Sn and Ti positive anomalies.

The occurrence of phlogopite in peridotite from the Serre Massif probably indicates that the rocks underwent a severe metasomatic event in upper mantle and/or lower crust-mantle boundary conditions.

Key-words: phlogopite, ultramafic rocks, Serre Massif, Calabrian Peloritan Arc, mineral chemistry, metasomatism..