Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonic setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems
Nepheline-bearing gneisses from the 75 km2 Tambani body in the Mozambique Belt of southern Malawi, are miaskitic biotite-nepheline monzodiorites, reflecting an absence of K-feldspar, alkali amphiboles or pyroxenes, and contain euhedral zircon megacrysts up to 5 cm across. The zircons contain U = 1-1,860 ppm, Th = 0-2,170 ppm and Y = 400-1,100 ppm, and very low concentrations of all other measured trace elements except Hf (HfO2 = 0.53-0.92 wt. %). Cathodoluminescence images reveal oscillatory...[Show more]
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|Source:||Contributions to Mineralogy and Petrology|
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