ISOTOPE PROVINCES, MECHANISMS OF GENERATION AND SOURCES THE CONTINENTAL CRUST IN THE CENTRAL ASIAN MOBILE BELT: GEOLOGICAL AND ISOTOPIC EVIDENCE

Abstract

The available geological, geochronological and isotopic data on the felsic magmatic and related rocks from South Siberia, Transbaikalia and Mongolia are summarized to improve our understanding of the mechanisms and processes of the Phanerozoic crustal growth in the Central Asian mobile belt (CAMB). The following isotope provinces have been recognised: 'Precambrian' (T DM ¼ 3:3 – 2:9 and 2.5 –0.9 Ga) at the microcontinental blocks, 'Caledonian' (T DM ¼ 1.1– 0.55 Ga), 'Hercynian' (T DM ¼ 0.8 – 0.5 Ma) and 'Indosinian' (T DM ¼ 0.3 Ga) that coincide with coeval tectonic zones and formed at 570– 475, 420– 320 and 310– 220 Ma. Continental crust of the microcontinents is underlain by, or intermixed with, 'juvenile' crust as evidenced by its isotopic heterogeneity. The continental crust of the Caledonian, Hercynian and Indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments. The crustal growth in the CAMB had episodic character and important crust-forming events took place in the Phanerozoic. Formation of the CAMB was connected with break up of the Rodinia supercontinent in consequence of creation of the South-Pacific hot superplume. Intraplate magmatism preceding and accompanying permanently other magmatic activity in the CAMB was caused by influence of the long-term South-Pacific plume or the Asian plume damping since the Devonian.