AGE AND SOURCE CHARACTERISTICS OF THE YUZHNOE AND ULAN-UDE REE-FLUORITE OCCURRENCES ASSOCIATED WITH CARBONATITE MAGMATISM (WESTERN TRANSBAIKALIA, RUSSIA)

Abstract

The article presents new data on the age and isotopic (Sr, Nd) characteristics of the Yuzhnoe and Ulan-Ude REE-fluorite occurrences, paragenetically related to alkaline carbonatite magmatism. Age estimates of the fluorite-containing rocks were obtained from bastnaesites using U-Th-Pb (LA-ICP-MS) method and are 130.2±1.1 and 136.6±1.9 Ma for the Yuzhnoe and Ulan-Ude occurrences, respectively. The ƐNd(T) values of the bastnaesites vary from –7.41 to –6.08 for the Yuzhnoe occurrence and from –4.28 to –2.67 for the Ulan-Ude occurrence. The Yuzhnoe carbonatites are characterized by 87Sr/86Sr(I) ratios ranging from 0.705883 to 0.706011, and 87Sr/86Sr(I) ratios obtained for the Ulan-Ude bastnaesite-fluorite rocks are ranging from 0.70683 to 0.70687. The age estimates are consistent with the published geochronological data on alkaline carbonatite magmatism of the Central Asian orogenic belt related to Late Mesozoic intraplate magmatism and rifting. Isotopic Sr-Nd signatures of bastnaesite, as well as of the Yuzhnoe carbonatites and the Ulan-Ude bastnaesite-fluorites, indicate that their source rocks came from the enriched lithospheric mantle.

Keywords

• carbonatite magmatism
• bastnaesite-fluorite rocks
• nd and sr isotope composition
• u-th-pb dating
• central asian orogenic belt
• late mesozoic magmatism