The Cima D'Asta Complex (CDC) is a composite intrusive body of Permian age, outcropping in the eastern sector of the Southern Alps (Italy), close to the Valsugana Line. It consists of a main pluton of prevailing monzogranitic rocks and subordinate granodiorites and tonalites, and satellite mafic-intermediate masses of quartz norite-diorite to tonalitic composition. Both granitoids and mafic-intermediate rocks show petrological, geochemical and isotopic (Sr and Nd) evidence of interaction between felsic and mafic magmas. Granites from the main pluton have lower incompatible element abundances and initial Sr isotopic compositions, but higher ϵNd values (0.7076–0.7082 and ϵNd= −4.4 to −5.1) than granodiorites (0.7081–0.7092, ϵNd= −4.8 to −5.8) and tonalites (0.7092–0.7094; ϵNd= −6.6 to −6.2), which exclude a simple fractional crystallization model linking these intrusions. On the other hand the satellite bodies show a wider range of Sr and Nd isotopic compositions (0.7071–0.7111; ϵNd= −5.4 to −6/8) not related to their elemental abundances. Such a feature rules out both an evolution by closed system fractional crystallization (FC) and xrustal assimilation plus fractional crystallization (AFC) from mafic-intermediate to felsic lithotypes. Mingling and/or mixing between mafic and felsic magmas with concurrent variable degree of fractional crystallization in a multicompartmental reservoir, at the mantle-crust transition zone, appears to be the most reliable process for the genesis of the CDC.
Polygenetic nature of the Cima d'Asta intrusive complex, Southern Alps, Italy. Inferences from petrological, geochemical and isotopic (Sr and Nd) data.
MACERA, PATRIZIA;
1994-01-01
Abstract
The Cima D'Asta Complex (CDC) is a composite intrusive body of Permian age, outcropping in the eastern sector of the Southern Alps (Italy), close to the Valsugana Line. It consists of a main pluton of prevailing monzogranitic rocks and subordinate granodiorites and tonalites, and satellite mafic-intermediate masses of quartz norite-diorite to tonalitic composition. Both granitoids and mafic-intermediate rocks show petrological, geochemical and isotopic (Sr and Nd) evidence of interaction between felsic and mafic magmas. Granites from the main pluton have lower incompatible element abundances and initial Sr isotopic compositions, but higher ϵNd values (0.7076–0.7082 and ϵNd= −4.4 to −5.1) than granodiorites (0.7081–0.7092, ϵNd= −4.8 to −5.8) and tonalites (0.7092–0.7094; ϵNd= −6.6 to −6.2), which exclude a simple fractional crystallization model linking these intrusions. On the other hand the satellite bodies show a wider range of Sr and Nd isotopic compositions (0.7071–0.7111; ϵNd= −5.4 to −6/8) not related to their elemental abundances. Such a feature rules out both an evolution by closed system fractional crystallization (FC) and xrustal assimilation plus fractional crystallization (AFC) from mafic-intermediate to felsic lithotypes. Mingling and/or mixing between mafic and felsic magmas with concurrent variable degree of fractional crystallization in a multicompartmental reservoir, at the mantle-crust transition zone, appears to be the most reliable process for the genesis of the CDC.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
