Early Mesozoic lamproites and monzonitoids of southeastern Gorny Altai: geochemistry, Sr–Nd isotope composition, and sources of melts

Abstract

Small intrusions of lamprophyres and lamproites (Chuya complex) and K-monzonitoids (Tarkhata and Terandzhik complexes) are widespread in southeastern Gorny Altai. Geochronological (U–Pb and Ar–Ar) isotope studies show their formation in the Early–Middle Triassic (~ 234–250 Ma). Lamproites have been revealed within two magmatic areas and correspond in geochemical parameters to the classical Mediterranean and Tibet orogenic lamproites. According to isotope data ((87Sr/86Sr)T = 0.70850–0.70891, (143Nd/144Nd)T = 0.512157–0.512196, 206Pb/204Pb = 17.95–18.05) and Th/La and Sm/La values, the Chuya lamproites and lamprophyres melted out from the enriched lithospheric mantle with the participation of DM, EM1, EM2, and SALATHO. The monzonitoid series of the Tarkhata and Terandzhik complexes are similar in petrographic and geochemical compositions but differ significantly in Sr–Nd isotope composition: The Tarkhata monzonitoids are close to the Chuya lamproites, whereas the Terandzhik ones show a higher portion of DM ((87Sr/86Sr)T = 0.70434–0.70497, (143Nd/144Nd)T = 0.512463–0.512487) in their source, which suggests its shallower depth of occurrence and the higher degree of its partial melting as compared with the derivates of the Chuya and Tarkhata complexes. The studied rock associations tentatively formed in the postcollisional setting under the impact of the Siberian superplume.

The Overmaraat-Gol Alkaline Pluton in Northern Mongolia: U–Pb Age and Preliminary Implications for Magma Sources and Tectonic Setting

“…Similar signatures of interaction were reported for many alkaline and carbonatite plutonic complexes of different ages in the western CAOB ( Figure 3). Simultaneous involvement of EM-type and mature continental crust material was inferred for Mesozoic intrusions in areas of thick lithosphere, such as Western Transbaikalia, Southern Mongolia, and Russian Altai [4,40,41], but not in the southwestern Hovsgol area and the Sangilen Plateau in southeastern Tuva (Korgeredaba pluton). Therefore, magma sources may differ even in adjacent areas.…”

“…εNd(t) vs. εSr(t) plot for the Overmaraat-Gol pluton and some other alkaline complexes from the western Central Asian Orogenic Belt: Paleozoic intrusions of the Sangilen Plateau, Vitim Plateau, Russian Altai (complex Edelveis), Kuznetsk Alatau, and basalts of the Minusa Basin (MBB), after[5][6][7][8][9]11,33,34]. Korgeredaba nepheline syenites (~295 Ma, SE Tuva), after[35,36] and Beltesin-Gol carbonatites (~480 Ma, Northern Mongolia), after[37,38]; Mesozoic intrusions of Southern Mongolia (Mushgai Khudag, Bayan Khoshuu), Western Transbaikalia (Oshurkovo, Arshan, Khaluta) and lamproites of the Russian Altai, after[37,[39][40][41]. White stars are average compositions of the North Asian (NA), Devonian (D), and Siberian (S, AB = alkali basalts) mantle plumes, after[18,34,42].…”

Geological History of the Great Altai: Implications for Mineral Exploration

“…In recent years more and more evidence of Permian-Triassic within-plate magmatism has appeared for the southern part of the area of the Siberian LIP. In addition to the well-known trap basalts in the Kuznetsk basin [99,100], the dyke swarms of lamprophyres and subalkaline diorites, and the intrusive massifs of subalkaline monzonites and syenites are described in the Altai region [97,101,102]. Permian-Triassic intrusions of granites and leucogranites, which are accompanied by dolerite and lamprophyre dykes, are also widely distributed within the Altai and adjacent regions [91,103,104].…”

Duration of Granitoid Magmatism in Peripheral Parts of Large Igneous Provinces (Based on 40ar/39ar Isotopic Studies of Altai Permian-Triassic Granitoids)

“…Granitoids are enriched in LILE, HFSE, REE and 'transitional' elements. According to [Krupchatnikov et al, 2015], they results from differentiation of lamprophyre magmas.…”