Sources of granitoids in the Tuva-Mongolian microcontinent and surrounding structures: Evidence from Pb, Nd, and O isotopic systematics |
| |
| Authors: | G V Ovchinnikova D P Krylov I K Kozakov V P Kovach N A Sergeeva |
| |
| Institution: | (1) Department of Geology and Geophysics, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia;(2) CRPG-CNRS, 15 rue Notre-Dame des Pauvres, B.P. 20, 54501 Vandoeuvre-lès-Nancy Cedex, France |
| |
| Abstract: | Newly obtained data on Pb isotopic ratios in feldspars from Early Proterozoic granitoids of the Sangilen block of the Tuva-Mongolian
microcontinent and Caledonian structures surrounding it, considered together with earlier data on the O and Nd isotopic systems,
indicate that ancient (approximately 2 Ga) crustal material mixed in the sources of granites of the Tuva-Mongolian microcontinent
with younger juvenile material. Positive ɛNd values of granitoids from the Bashkimugor and Chgargalant massifs are accounted for by processes of crustal contamination
during the interaction of the melt with crustal material. Similar Nd isotopic characteristics of granitoids in the Khoromnug
pluton were caused by the melting of the Late Riphean crust. In granitoids of the massifs in the Kaakhem and Eastern Tannuola
zones of the surrounding Caledonian structures, the involvement of juvenile material from oceanic crust increases away from
the Sangilen block. Granites in the junction zone between the Tuva-Mongolian microcontinent and surrounding structures display
evidence of the presence (up to 10–20%) of an ancient crustal component, and the melting history of granitoids in the Eastern
Tannuola zone is dominated by an Early Paleozoic juvenile component in combination with material similar to the Vendian ophiolites
of the Agardag-Erzin zone. An increase in the δ18O value, the 206Pb/204Pb ratio, and the TNd(DM) values within a single complex (from older to younger granitoid phases) is explained by the systematic involvement of
crustal material in the melting processes. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
