A set of lamprophyric dykes, cutting thè Paleozoic phyllitic base-ment of thè Southern Alps, near Calceranica (Trento) have been studied. Their minerai assemblage is rather homogeneous and dominantly consists of salitic clinopyroxene, alkali feldspar, plagioclase, olivine, opaques, apatite and variable amounts of kaersutite; primary carbonate ocelli are often present. These Na-alkaline lamprophyres can be classified as monchiquites. Petrological and geochemical characteristics of this magmatism are consistent with an anorogenic within-plate origin, and small degrees of partial melting of a metasomalized and H2O-CO2 enriched subcontinental lithospheric mantle. The 39Ar/4"Ar dating, carried out on a kaersutite concentrate, gave an age of 71 ± 2 Ma, in excellent agreement with K/Ar and Rb/Sr ages obtained on Corvara - Val Badia monchiquite lamprophyres (68 ± 1 and 69.8 ± 3 Ma, respectively). On a regional scale, analogous magmatic activity occurs in Sardinia, Spain and France at thè Upper Cretaceous-Paleocene boundary. This confirms thè existence at that lime of an anorogenic Na-alkaline lamprophyric magmatism widespread, although quantitatively very scarce, along thè paleoeuropean and paleoafrican stable Continental margins.
Age and nature of lamprophyric dykes at Calceranica (Trento)
MONESE, Alessandro;SIENA, Franca;VACCARO, Carmela
1994
Abstract
A set of lamprophyric dykes, cutting thè Paleozoic phyllitic base-ment of thè Southern Alps, near Calceranica (Trento) have been studied. Their minerai assemblage is rather homogeneous and dominantly consists of salitic clinopyroxene, alkali feldspar, plagioclase, olivine, opaques, apatite and variable amounts of kaersutite; primary carbonate ocelli are often present. These Na-alkaline lamprophyres can be classified as monchiquites. Petrological and geochemical characteristics of this magmatism are consistent with an anorogenic within-plate origin, and small degrees of partial melting of a metasomalized and H2O-CO2 enriched subcontinental lithospheric mantle. The 39Ar/4"Ar dating, carried out on a kaersutite concentrate, gave an age of 71 ± 2 Ma, in excellent agreement with K/Ar and Rb/Sr ages obtained on Corvara - Val Badia monchiquite lamprophyres (68 ± 1 and 69.8 ± 3 Ma, respectively). On a regional scale, analogous magmatic activity occurs in Sardinia, Spain and France at thè Upper Cretaceous-Paleocene boundary. This confirms thè existence at that lime of an anorogenic Na-alkaline lamprophyric magmatism widespread, although quantitatively very scarce, along thè paleoeuropean and paleoafrican stable Continental margins.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
