Early Mesozoic Bimodal Volcanic Sequences of Central Mongolia: Implications for the Evolution of the Khentey Segment of the Mongol–Okhotsk Belt

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Petrology Pub Date : 2024-12-05 DOI:10.1134/S0869591124700206
V. V. Yarmolyuk, A. M. Kozlovsky, V. M. Savatenkov, A. S. Novikova, Ts. Oyunchimeg
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Abstract

Volcanic sequences of bimodal basalt–trachyte–alkaline rhyolite character with alkaline granites are widespread in central Mongolia. They crop out in small sublatitudinal grabens scattered along the southern and western surroundings of the Khentey part of the Mongol–Okhotsk Belt. According to geochronological data, the bimodal magmatic activity continued from the latest Triassic to earliest Jurassic (at ∼220–195 Ma). Many rocks of the bimodal sequences contain high concentrations of alkalis and rare metals. Fractional crystallization was the leading process for enrichment of rare metals up to their ore-level concentrations in the most differentiated melts. Mafic magmas enriched relative to the OIB in most incompatible trace elements were parental for all rocks of these associations. At the same time, they show elevated Ba and depleted Ta and Nb contents, which indicate that a lithospheric mantle component was involved in their source. The Nd and Sr isotopic ratios of the rocks indicate that the magmas were derived from at least two sources, which are identified as enriched asthenospheric mantle and metasomatized subduction-modified lithospheric mantle. Bimodal magmatism in the Khentey segment of the Mongol–Okhotsk belt appeared ~30 Ma after collision caused by the closure of the Ada-Tsag branch of the Mongol–Okhotsk Ocean at about 250 Ma. Rifting affected the entire surroundings of the Khentey segment of the belt and controlled this magmatism. It was initiated by the collapse of the orogen with delamination of its keel caused the involvement of asthenospheric mantle in the Late Triassic–Early Jurassic magmatism of the region

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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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