Abstract
The South Khangai volcanic region (SKVR) comprises fields of Late Mesozoic–Cenozoic volcanic rocks scattered over southern and central Mongolia. Evolution of the region from the Late Jurassic to the Late Cenozoic includes 13 successive igneous episodes that are more or less evenly distributed in time. Major patterns in the distribution of different-aged volcanic complexes were controlled by a systematic temporal migration of volcanic centers over the region. The total length of their trajectory exceeds 1600km.Principle characteristics of local magmatism are determined. The composition of igneous rocks varies from basanites to rhyolites (predominantly, high-K rocks), with geochemistry close to that of OIB. The rock composition, however, underwent transformations in the Mesozoic–Cenozoic. Rejuvenation of mafic rocks is accompanied by decrease in the contents of HREE and increase of Nb and Ta. According to isotope data, the SKVR magmatic melts were derived from three isotope sources that differed in the Sr, Nd, and Pb isotopic compositions and successively alternated in time. In the Early Cretaceous, the predominant source composition was controlled by interaction of the EMII- and PREMA-type mantle materials. The PREMA-type mantle material dominated quantitatively in the Late Cretaceous and initial Early Cenozoic. From the latest Early Cenozoic to Late Cenozoic, the magma source also contained the EMI-type material along with the PREMA-type.The structural fabric, rock composition, major evolutionary pattern, and inner structure of SKVR generally comply with the criteria used to distinguish the mantle plume-related regions. Analogous features can be seen in other regions of recent volcanism in Central Asia (South Baikal, Udokan, Vitim, and Tok Stanovik). The structural autonomy of these regions suggests that distribution of the Late Mesozoic–Cenozoic volcanism in Central Asia was controlled by a group of relatively small hot finger-type mantle plumes associated with the common hot mantle field of Central Asia.
Highlights
Volcanic eruptions within the Baikal rift of predominantly basaltic composition belong to numerous small-volume eruptions, which took place in Cenozoic in Central Asia
While the rocks of 4 Ma group show the reverse correlation between decreasing Mg# and increasing CaO/Al2O3 and SiO2, which is a characteristic of olivine, clinopyroxene and Ti-magnetite crystallization, the rocks of 8 Ma group show no correlations between these indexes with Mg#, CaO/Al2O3 and SiO2 in the ranges of 56–67 %, 0.44–0.55 and 50.3 до 52 wt. %, respectively
The rocks of the 4 Ma group are characterized by higher La/Yb (20–33) compared to the rocks of the 8 Ma group, where La/Yb are in the range of 15–18
Summary
Volcanic eruptions within the Baikal rift of predominantly basaltic composition belong to numerous small-volume eruptions, which took place in Cenozoic in Central Asia. The great majority of these eruptions occurred within the mobile belts in the southern framing of the Siberian craton Few of such eruptions have happened within the cratonic margin and these are of particular interest, because volcanic rock composition may provide insights on the composition of the cratonic lithosphere. The Uda river area with the size of ~2000 km located within the Biryusa block of the Siberian craton (Fig. 1) was a white spot in terms of precise geochemical and isotopic data for basalts. We provide such data for the first time
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