Early Paleozoic Tectonothermal Evolution of the Khan-Khukhay Metamorphic Complex, Northern Mongolia

• Published in: Petrology 2023-10, Vol.31 (5), p.519-537
• Main Authors: Polyansky, O. P., Selyatitskii, A. Yu, Zinoviev, S. V., Babichev, A. V.
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Evolution; Gabbro; Geochemistry; Intrusion; Lava; Magma; Magma chambers; Massifs; Mathematical models; Metamorphism; Metamorphism (geology); Mineralogy; Modelling; Ordovician; Paleozoic; Parameters; Quartz; Reconstruction; Rocks; Thermomechanical analysis
• ISSN: 0869-5911; 1556-2085
• DOI: 10.1134/S0869591123050041

The paper presents a reconstruction of metamorphic stages in the Moren and Erzin metamorphic complexes in the Khan-Khuhay block of northern Mongolia. This reconstruction is used as a basis for discussing the general geodynamic history of the Sangilen terrain of the Tuva–Mongolia Massif. The calculated clockwise P–T path shows two stages of metamorphism: (1) collisional metamorphism at 9 kbar, 740°C; and (2) metamorphism related to a regional magmatic episode, at 6–7 kbar, 860–880°C. Geochemical and petrological features of rocks in the Khan-Khuhay block demonstrate that these rocks are similar to those of the metamorphic block of Western Sangilen in southeastern Tuva. Quartz monzodiorite intrusive bodies first found in the Khan-Khuhay block show geochemical features similar to those of Ordovician gabbro–monzodiorite intrusions in the western Sangilen. The Khan-Khuhay quartz monzodiorite intrusions may be small apophyses of an intermediate deep crustal magma chamber and could be a probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. The numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explains the heating in the thickened crust during collision by a higher (relative to the average crustal) radiogenic heat production of 1.52 μW/m 3 . Computer modeling indicates that the P–T parameters of the second metamorphic stage could be reached only with the involvement of magmatic heat from the monzodiorite intrusion. The P–T metamorphic parameters calculated using mineral thermobarometry, similarity of geochemical characteristics, and results of the thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution.