Pb-Pb age and Sr isotopic characteristic of the Middle Riphean phosphorite concretions: The Zigaza-Komarovo Formation of the South Urals

Autor:	A. B. Kuznetsov, B. M. Gorokhovskii, G. V. Ovchinnikova, I. M. Vasil’eva, M. T. Krupenin, Igor M. Gorokhov, A. V. Maslov
Rok vydání:	2013
Předmět:	Isochron Riphean Geochemistry Mineralogy Phosphate Mantle (geology) Isotopic composition chemistry.chemical_compound Stratotype Phosphorite chemistry Earth and Planetary Sciences (miscellaneous) General Earth and Planetary Sciences Dissolution Geology
Zdroj:	Doklady Earth Sciences. 451:798-802
ISSN:	1531-8354 1028-334X
DOI:	10.1134/s1028334x13080047
Popis:	The Pb-Pb age of phosphorite concretions of the Zigaza-Komarovo Formation, which composes the intermediate horizons of the Riphean stratotype of the South Urals, was determined in fractions resulting from the stepwise dissolution of concretions in 0.1 N, 0.5 N, and 1 N HCl. The determination of the Sr isotopic composition in phosphate fractions was favorable for rejection the fractions polluted with extraneous material. On the 207Pb/204Pb-206Pb/204Pb diagram, the isochron based on 31 points corresponds to 1330 ± 20 Ma (MSWD = 1.12), which is in agreement with the stratigraphic position of the Zigaza-Komarovo Formation. The decreased μ2 value of 9.57 for the phosphorite concretions relative to that of the average earthly lead based on the Stacey-Kramers model (9.74) is related to the rocks with an admixture of mantle lead, which occur in the run-off area of the Zigaza-Komarovo sediments.
Databáze:	OpenAIRE
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