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The Central Asian Orogenic Belt (CAOB) is the world's largest Phanerozoic accretionary orogen and is the most important site for juvenile crustal growth in the Phanerozoic. In this work, we employed U-Pb zircon geochronology to identify the early and middle Mesozoic intraplate granitic intrusive events in the Chinese Altai segment of the southern CAOB in order to better understand the crustal architecture of the CAOB. We also used whole-rock geochemical, Sr-Nd isotopic and zircon Hf isotopic data to constrain the generation for these granitic rocks and to evaluate the implications for vertical crustal growth in this region. The Early Mesozoic granitic intrusions were emplaced between 220 and 200 Ma in the central Altai “microcontinental terrane” (also widely referred to as Units 2 and 3). The granites have shoshonitic and high-K calc-alkaline affinities and show the characteristics of differentiated I-type granite. The whole-rock initial 87Sr/86Sr ratios (0.7058-0.7128) and εNd(210) values (−0.6 to −4.3), as well as the zircon εHf(t) values (−4.0 to +5.0) and two-stage Hf model ages (0.94-1.52 Ga), suggest that the granitic magmas were produced from a mixed source with both mantle-derived and recycled crustal components. The middle Mesozoic granites were emplaced at ~150 Ma in the southern Altai “accretionary terrane” (Units 4 and 5). They show A-type characteristics with the REE tetrad effect and have positive εNd(151) whole-rock values of +1.0 to +5.2 and two-stage Nd model ages (TDM2) of 0.6 to 1.0 Ga. Zircon Hf data show positive zircon εHf(151) values of +1 to +8 and two-stage Hf model ages of 0.6 to 1.2 Ga. The Nd-Hf isotopic data suggest that the granitic magmas were derived from short-lived juvenile mantle-derived materials. Thus, the isotopic signatures of all the Mesozoic granites from the central (old terrane) and southern (young accretional terrane) Altai suggest that the basement of both terranes has retained its original nature. The data further imply

U-Pb dating of the Katugin peralkaline granite in Russia, to which it is suggested that rare-metal mineralisation was related, indicates a new rare-metal metallogenic epoch from about 2.2 to 2.05 Ga, linked to a global period of extension prior to early Proterozoic spreading and ocean formation., U-Pb dating of the Katugin peralkaline granite in Russia, to which it is suggested that rare-metal mineralisation was related, indicates a new rare-metal metallogenic epoch from about 2.2 to 2.05 Ga, linked to a global period of extension prior to early Proterozoic spreading and ocean formation.

The deposit's geology is outlined, the radiometric dating of the various intrusive rocks discussed and the geochemistry at different sample points in the orebody tabulated. Early pre-ore granite dykes, intruding the host gabbro-diorites, are cut by second-stage basites and third-stage syenite-granite dykes of the same age as the ore mineralisation. The major- and rare-element compositions of the basites, syenites and granites are compared with those of the leucogranitic massif and the magmatic and ore-forming process discussed., The deposit's geology is outlined, the radiometric dating of the various intrusive rocks discussed and the geochemistry at different sample points in the orebody tabulated. Early pre-ore granite dykes, intruding the host gabbro-diorites, are cut by second-stage basites and third-stage syenite-granite dykes of the same age as the ore mineralisation. The major- and rare-element compositions of the basites, syenites and granites are compared with those of the leucogranitic massif and the magmatic and ore-forming process discussed.

The Palaeozoic and Mesozoic granitoid intrusions are associated with the Yugodzyr Mo-W deposit and the Khaylias ore district plus a number of other tungsten or tin-tungsten occurrences. The Yugodzyr deposit consists of quartz-wolframite-molybdenite veins in Ordovician sediments surrounding a greisenised biotite-granite, while the Khaylias occurrences are associated with porphyritic granites of the Subshirotniy massif. The geochemistry of the Yugodzyr massif, Subshirotniy massif and adjacent Yuzhniy massif is compared and the results of Rb-Sr, U-Pb, Sm-Nd and Sr-Sr isotope studies are discussed., The Palaeozoic and Mesozoic granitoid intrusions are associated with the Yugodzyr Mo-W deposit and the Khaylias ore district plus a number of other tungsten or tin-tungsten occurrences. The Yugodzyr deposit consists of quartz-wolframite-molybdenite veins in Ordovician sediments surrounding a greisenised biotite-granite, while the Khaylias occurrences are associated with porphyritic granites of the Subshirotniy massif. The geochemistry of the Yugodzyr massif, Subshirotniy massif and adjacent Yuzhniy massif is compared and the results of Rb-Sr, U-Pb, Sm-Nd and Sr-Sr isotope studies are discussed.

The deposit lies in a graben that resulted from rifting during the early Mesozoic and contains a volcanic-intrusive suite of basalts and trachyrhyolites with granitoids. The deposit is hosted by effusive-breccia trachydacites and rhyolites that form part of the granotoid complex. Sampling found Be grades ranging from 3 087 to 8 616 g/t in the orebody, compared with 8.8-17.5 g/t Be in the adjacent granitoids 1-2 km away. The orebody was also enriched in SiO2, Fe2O3, Li, Th, U, Nb, Ta, Zr and V but depleted in alkaline elements, Ba, Cu, Ni and Cr. The geochemistry of the deposit and surrounding rocks is discussed in detail and compared with chondrite-normalised va;ues, while the results of isotope analysis are considered in relation to mid-ocea-ridge basalts, EM II enriched mantle and high U-Pb mantle., The deposit lies in a graben that resulted from rifting during the early Mesozoic and contains a volcanic-intrusive suite of basalts and trachyrhyolites with granitoids. The deposit is hosted by effusive-breccia trachydacites and rhyolites that form part of the granotoid complex. Sampling found Be grades ranging from 3 087 to 8 616 g/t in the orebody, compared with 8.8-17.5 g/t Be in the adjacent granitoids 1-2 km away. The orebody was also enriched in SiO2, Fe2O3, Li, Th, U, Nb, Ta, Zr and V but depleted in alkaline elements, Ba, Cu, Ni and Cr. The geochemistry of the deposit and surrounding rocks is discussed in detail and compared with chondrite-normalised va;ues, while the results of isotope analysis are considered in relation to mid-ocea-ridge basalts, EM II enriched mantle and high U-Pb mantle.