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The Mongolian Altai Zone is a part of the extensive Cambrian–Ordovician accretionary system located at the junction of the Siberian craton to the north and Tarim and North China cratons to the south. It extends approximately 2,000 km from Russia to Mongolia and represents one of the critical elements for reconstructing the early Paleozoic geodynamics of the Central Asian Orogenic Belt (CAOB). The studied section comprises a succession of deformed low- and high-grade metasedimentary rocks characterised by dominant terrigenous components mixed with volcanogenic material. The detrital zircons analysis revealed two separate groups a) more mature siliciclastic sediments (mostly sandstones) with maximum depositional age of Cambrian–Ordovician (ca. 463–489 Ma; zircon U-Pb) and b) more juvenile greywacke type sediments with Ordovician–Silurian (ca. 438–446 Ma; zircon U-Pb) maximum depositional age. U-Pb ages of detrital zircons show Cambrian-Ordovician (εHf(t) values –24.8 to +16.0) and Late Archean to Neoproterozoic source (εHf(t) values –35.5 to +10.4) and are interpreted as derived from the Ikh Mongol continental arc and the Baydrag continent. The greywackes, in addition, contain Silurian detrital zircons, with εHf(t) values from –0.5 to +13, suggesting syn-depositional contribution of juvenile material from a nearby magmatic arc. Both types of sediments are affected by Devonian (ca. 369–382 Ma; zircon U-Pb) metamorphism and magmatism granites, as well as stroingly reworked during the Permian (ca. 271–296; zircon U-Pb) under various metamorphic conditions. Late Devonian granitoids associated with felsic migmatites, and their zircon εHf(t) values from –9.5 to +13.5, indicate extensive melting of the sedimentary pile. A Permian high-temperature metamorphism is associated with granodiorite intrusions (εHf(t) values from –22.0 to +12.6) that contain Devonian zircon xenocrysts, suggesting melting of a Devonian source. The tectonic evolution of the Mongolian Altai Zone can be discretized in four events from which the first two were related to early Paleozoic metamorphic and magmatic evolution. The third one is associated with crustal-scale detachment that exhumed the early Permian migmatite-magmatite core complex in the south. The whole edifice was later affected by significant Permian-Triassic horizontal N-S shortening leading to juxtaposition of contrasting crustal levels thereby forming “apparent” terrane structure of the Mongolian Altai Zone. The whole edifice is interpreted as a Cambrian to Silurian fore-arc, affected by Devonian syn-extensional deep crustal melting. In addition,the Permian anatectic zone is interpreted as a deep part of an inverted continental rift.

Fossil organisms of the Boreal Realm in the Tuva–Mongol Block (TMB) and Amuria Block (AMB) are commonly thought to have lived at mid to high latitudes during the Carboniferous Period; however, reliable paleomagnetic constraints have not been available previously to test this hypothesis. Here we report newly obtained combined paleomagnetic and geochronological results from the Upper Mississippian Gunbayan Formation in the AMB and the Lower Pennsylvanian Altan-Ovoo Formation in the TMB. Zircon U–Pb dating of tuff beds from the Gunbayan and Altan-Ovoo formations yield ages of 331.0 ± 2.7 and 315.5 ± 2.4 Ma, respectively. A total of 263 paleomagnetic specimens underwent stepwise thermal demagnetization. After removing the viscous remanent magnetizations of the recent geomagnetic field, stable high-temperature components (HTCs), carried by magnetite, were successfully acquired from 240 specimens. The HTCs of the Gunbayan Formation passed a fold test and a reversal test, and those of the Altan-Ovoo Formation passed a fold test, suggesting that they represent primary remanence magnetizations. We used the elongation/inclination method to test and correct for all the HTC directions of the clastic rocks of the studied formations. Their corresponding paleomagnetic poles are 46.0°N/320.0°E (A = 95 2.0 °) at ca. 330 Ma for the AMB and 43.5°N/355.9°E (A = 95 2.9 °) at ca. 315 Ma for the TMB. The updated paleomagnetic database indicates with certainty that both the TMB and the AMB were located in northern hemisphere low-latitude regions and close to the equator at ca. 330 Ma, suggesting that the Boreal Realm might have extended into the equatorial region at the onset of the large ice age of the Carboniferous. The paleobiogeographic characteristics and distribution of climate-sensitive lithologies indicate that this realm occupied a wide northern temperate belt during 330–315 Ma.