IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
artículos
Título:
SHRIMP U-Pb zircon dating and REE geochemistry from Angolan kimberlites associated with the Lucapa structure.
Autor/es:
SANDRA E. ROBLES-CRUZ; MONICA P ESCAYOLA; BILL DAVIS; SIMON JACKSON; SALVADOR GALÍ; BLADIMIR PEROV; MANUEL WATANGUA; ANTONIO GOCALVES; JOAN CARLES MELGAREJO
Revista:
CHEMICAL GEOLOGY
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Lugar: Amsterdam; Año: 2012 vol. 310 p. 137 - 147
ISSN:
0009-2541
Resumen:
We present the first age determinations of zircon from the diamondiferous Catoca kimberlite
in northeastern Angola, the fourth largest kimberlite body in the world. The U-Pb ages were
obtained using a Sensitive High Resolution Ion Microprobe II (SHRIMP II) on zircon crystals derived from tuffisitic kimberlite rocks and heavy-mineral concentrates from the Catoca
kimberlite. The SHRIMP results define a single weighted mean age of 117.9 ± 0.7 Ma (Mean
square weighted deviation MSWD = 1.3). More than 90% of the results indicate a single age
population. There is no evidence for variable ages within single crystals, and no diffusional
profiles are preserved. These data are interpreted as the maximum age of the kimberlite eruption
at Catoca. The U/Th values suggest at least two different sources of zircon crystals. These
different populations may reflect different sources of kimberlitic magma, with some of the grains
produced in U- and Th- enriched metasomatized mantle units. This idea is consistent with the
two populations of zircon identified in this study. One population originated from a depleted
mantle source with low total REE (less than 25 ppm), and the other was derived from an
enriched source, likely from the mantle or a carbonatite-like melt with high total REE (up to 123
ppm).The tectonic setting of northeastern Angola is influenced by the opening of the south Atlantic,
which reactivated deep NE-SW-trending faults during the early Cretaceous. The eruption of the
Catoca kimberlite can be correlated with these regional tectonic events. The Calonda Formation
(Albian-Cenomanian age) is the earliest sedimentary unit that incorporates eroded material
derived from the diamondiferous kimberlites. Thus, the age of the Catoca kimberlite eruption is
restricted to the time between the middle of the Aptian and the Albian. The new interpretation
will be an important guide in future exploration for diamonds because it provides precise data on
the age of a diamond-bearing kimberlite pulse in Angola.