^a Istituto di Mineralogia, Petrografia e Geochimica, Università di Palermo, Italy

^b School of Earth Sciences, University of Melbourne, Australia

^c Instituto de Geociencias, Universidade de Sao Paulo, Brazil

^d Istituto di Mineralogia e Petrografia, Università di Trieste, Italy

^e Dipartimento di Mineralogia e Petrologia, Università di Padova, Italy

^f Facultad de Ciencias Exactas y Naturales, Universidad de Asunciòn, Paraguay

A swarm of at least 200, mainley NW-SE trending, dykes occurs in the Sapucai region and seems to be formed by two main lineages: tephrite to phonolite (and peralkaline phonolite) and alkali basalt to trachyphonolite. They are characterized by ubiquitous diopside to ferrosalite, consistently yielding Al enrichment trends; common olivine, Fo_81-69 in tephrites and alkaline basalts, and up to Fo₆₅ in phonolites; zoned megacrysts of hastingsitic hornblende (core) to kaersutite (rim), associated with accessory groundmass pargasite in tephrites and phonotephrites; K-rich hastingsite and K-rich ferroan pargasite in the phonolites. Accessory groundmass mica falls in the annite-phlogopite range, and consistently yields insufficient (Si + Al) to satisfy the expected T site occupancy of 8.00 a.f.u. Fe---Ti oxides are Ti-magnetite, rarely ilmenite or haematite. Phenocrystal, i.e. xenocrystal plagioclase is An_70-20, and An_74-42 in the tephrites and phonolites, respectively; coexisting groundmass microlites are An_22-14, associated with sodasanidine and sanidine. Feldspathoids include analcimized leucite and nepheline; accessories Ti-andradite and sphene.

The two main lineages, recognized by distinctive mineralogical variations, are consistent with the petrochemical variations. Complex interaction of discrete and independently evolving magma batches are indicated by intra- and/or interphase chemical variations, suggesting multiple equilibrations of the crystallizing phases under shallow level, volcanic pressure regime. The observed geochemical trends are quite similar to those of “Roman Region type magma” with the same negative anomalies of Ta, Nb, Zr and Ti. The most likely mantle source is a garnet-peridotite characterized by different enrichment in incompatible elements and which suffered low degree of partial melting (3–7%), which has geochemical and isotopic features distinct from those of the adjoining tholeiitic basalts (130 Ma) and nephelinites (61-39 Ma).

The similarities of the Sapucai dyke suite with Barton's “Roman Region type magma” supports the view that this magma type may not be formed as a result of orogenic and/or subduction-driven activity in this region. Therefore, a causal relationship of the latter activity with “Roman Region type magma” is not supported and remains questionable.