Coppaelite or Cupaelite

The term Coppaelite (or Cupaelite) derives form the small town of Coppaeli di Sotto, near Rieti, Umbria, Central Italy. Coppaelites are a variety of melilitites consisting of almost equal amounts of pyroxene and melilite with variable amounts of phlogopite and kalsilite but no olivine. A kamafugitic rock and now regarded as a kalsilite phlogopite melilitite.

Cupaello volcano

Fig.1: Geological sketch map of the coppaelite lava flow outcrop. From F.Stoppa (1995).

The Cupaello volcano, consisting of a pyroclastic apron overlain by a lava flow, is located along the eastern border fault of the Rieti basin, Central Italy. This basin forms part of a wider system of NNW-SSE trending asymmetric grabens and normal faults, Pliocene to Pleistocene in age. Cupalello is part of the Late Pleistocene Umbria-Latium ultra-alkaline district (ULUD) or Intra Appennine Province which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province along the most peripheral belt of the Tyrrhenian extensional tectonic system.

The Cupaello occurrence comprises a small eruptive vent, located on the eastern marginal fault of the Rieti graben, from which a kalsilite melilitite (coppaelite) lava flow emanated. Nearby, a sequence of carbonatitic pyroclastic rocks is preserved. Ash tephra deposits preserved around the vent are several meters thick and comprise angular lapilli and abundant chert lithics which are overlain by spatter scoria. The 750 m long melilitite flow occupies a river valley and quarrying operations have exposed the underlying carbonatitic pyroclastic rocks.
The pyroclastic sequence comprises, from bottom to top, a massive ashfall tephra succeeded by a massive carbonatitic lapilli-ash tuff, at the base and top of which are thin, coarser ash-lapilli surge layers. These are covered by a pyroclastic breccia composed of bombs of melilitite supported by a micritic carbonate matrix. Slump structures occurring in the breccia and injections of tephra into the overlying melilitite flow suggest that the breccia was unconsolidated at the time of its emplacement. ³⁹Ar-⁴⁰Ar dating of a kalsilite concentrate from the melilitite lava and a 99% pure phlogopite concentrate from the underlying pyroclastics yielded a maximum age of 639 ka.

The Summit lava is dark grey in colour with bluish reflections, and prominent flow lamination, characterized by cm-size amygdales commonly filled with euhedral zeolites, chlorite and apophyllite. Corroded phlogopite and clinopyroxene phenocrysts megacrystsup to cm-size are frequent in the aphanitic groundmass. Light-colored, sygmoidal veinlets up to cm-size composed of merlinoite, apatite, khibinskite, magnetite are common. These are associated with metasomatic zones closely matching the vein geometry. In this section, the rock comprises euhedral diopside, melilite and phlogopite phenocrysts in an intersertal groundmass of kalsilite, potash feldspar microliths and glass. Following Le Maitre et al. (1989), the rock is classified as a Kalsilite-phlogopite melilitite

There is a general agreement that the magmatism from the internal zones of Apennines has been generated in anomalous mantle sources, which have been affected by metasomatic enrichment in incompatible elements. However, the nature and timing of mantle metasomatic processes are still debated. Two conflicting hypotheses have been proposed for the genesis of Intra Appennine Province magmas. One suggests source contamination by marly sediments, whereas an alternative hypothesis invokes metasomaticmodification by deep mantle material. Mantle contamination by marly sediments requires subduction processes. These could have occurred as a consequence of convergence between the Adriatic plate and the Apennine chain.

Such a hypothesis is supported by the presence of a vertical body with high seismic wave velocities beneath the Northern Apennines . This body cuts the asthenosphere and has been interpreted as a relict slab of the Adriatic plate.
Other hypotheses emphasize the coexistence of kamafugites and carbonate-rich rocks, suggesting that these represent a typical association of melilitites and carbonatites, of the same type as those observed in the Virunga province, East Africa. In the view of this hypothesis, the Intra Appennine Province rocks represent a magmatism emplaced in a intra-continental rifting zone .

Bibliography

Le informazioni contenute in questa pagina sono tratte da:
• F. Stoppa, A. Cundari "A new Italian carbonatite occurrence at Cupaello (Rieti)and its genetic significance". Contrib Mineral Petrol (1995) 122: 275–288
• A. Peccerillo "Plio-Quaternary Volcanism in Italy: Petrology, Geochemistry, Geodynamics"

Photo
Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)
Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)
Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)
Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)
Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)
Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)
Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 2x (Field of view = 7mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 2x (Field of view = 7mm)	Phlogopite crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 10x (Field of view = 2mm)
Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 10x (Field of view = 2mm)	Phlogopite and Diopside crystals embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 10x (Field of view = 2mm)	Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 10x (Field of view = 2mm)
Diopside and phlogopite crystal. Coppaelite from Cupaello (Italy). PPL image, 10x (Field of view = 2mm)	Diopside and phlogopite crystal embedded in a Kalsilite (gray) melilite groundmass. Coppaelite from Cupaello (Italy). XPL image, 10x (Field of view = 2mm)