Informace o publikaci

Titanite composition and SHRIMP U-Pb dating as indicators of post-magmatic tectono-thermal activity: Variscan I-type tonalites to granodiorites, the Western Carpathians



Rok publikování 2019
Druh Článek v odborném periodiku
Časopis / Zdroj Geologica Carpathica
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Klíčová slova titanite; I-type granites; Zr-in-titanite thennometry; LA-ICP-MS analyses; SHRIMP U-Pb dating; Western Carpathians
Popis Titanite belongs to the common accessory minerals in Variscan (similar to 360-350 Ma) metaluminous to slightly peraluminous tonalites to granodiorites of I-type affinity in the Tatric and Veporic Units, the Western Carpathians, Slovakia. It forms brown tabular prismatic-dipyramidal crystals (similar to 0.5 to 10 mm in size) in association with quartz., plagioclase, and biotite. Titanite crystals commonly shows oscillatory, sector and convolute irregular zonal textures, reflecting mainly variations in Ca and Ti versus Al (1-2 wt. % Al2O3, 0.04-0.08 Al apfu), Fe (0.6-1.6 wt. % Fe2O3, 0.02-0.04 Fe apfu), REE (La to Lu+ Y: 54.8 wt. % REE2O3, <= 0.06 REE apfu), and Nb (up to 0.5 wt. % Nb2O5, <= 0.01 Nb apfu). Fluorine content is up to 0.5 wt.% (0.06 F apfu). The compositional variations indicate the following principal substitutions in titanite: REE3++ Fe3+= Ca-2+Ti4+, 2REE(3+)+ Fe2+ = 2Ca(2+) Ti4+, and (Al,Fe)(3+)+ (OH, F)(-) = Ti4++O2-. The U-Pb SHRIMP dating of titanite reveal their Variscan ages in an interval of 351.0 +/- 6.5 to 337.9 +/- 6.1 Ma (Tournaisian to Visean); titanite U-Pb ages are thus similar to 5 to 19 Ma younger than the primary magmatic zircon of the host rocks. The Zr-in-titanite thermometry indicates a relatively high temperature range of titanite precipitation (similar to 650-750 degrees C), calculated for assumed pressures of 0.2 to 0.4 GPa and a(TiO2)=0.6-1.0. Consequently, the textural, geochronological and compositional data indicate relatively high-temperature, most probably early post-magmatic (subsolidus) precipitation of titanite. Such titanite origin could be connected with a subsequent Variscan tectono-thermal event (similar to 340 +/- 10 Ma), probably related with younger small granite intrusions and/or increased fluid activity. Moreover, some titanite crystals show partial alteration and formation of secondary titanite (depleted in Fe and REE)+allanite-(Ce) veinlets (Sihla tonalite. Veporic Unit), which probably reflects younger Alpine (Cretaceous) tectono-thermal overprint of the Variscan basement of the Western Carpathians.

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