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The Mongolian micro‐continental fragments play an important geodynamic role in the Palaeozoic evolution of the Central Asian Orogenic Belt. However, the original provenance of individual blocks within the Nuna/Columbia and Rodinia supercontinents is not well constrained. In this work, we present zircon U–Pb and Lu–Hf isotopic data from the Mesoproterozoic to Neoproterozoic metamorphosed cover of the Baidrag Block in central Mongolia. These data reveal important maxima in the Neoarchean, Palaeoproterozoic and locally Neoproterozoic. Although the majority of the new data can be attributed to local sources within the basement of the Mongolian micro‐continental fragments, an important contribution of juvenile 2.0 Ga zircons is linked to the western margin of the Siberian Craton, and 1.5 Ga zircons are either directly derived from North Australia or indirectly recycled from sediments in NW Laurentia. [ABSTRACT FROM AUTHOR]

Abstract Sedimentological and detrital zircon provenance study of the Lower Palaeozoic Zuunnuruu, Tsetseg and Sagsai sedimentary formations was carried out in the eastern part of the Hovd Zone in western Mongolia. Sedimentological analysis has revealed two distinct and consecutive types of sedimentary environments. The Lower Ordovician–earliest Silurian sediments had dominantly volcano-sedimentary character, interpreted as reflecting deposition in a proximal part of a Pacific-type accretionary wedge. The upper, mainly Devonian part of the profile has generally siliciclastic flysch-like nature and indicates platform-type depositional setting related to the syn-extensional thinning of the accretionary wedge-system. Detrital zircon age populations of all the three studied formations uniformly show a dominant Neoproterozoic–Ordovician age group at ca. 560–460 Ma, a broad Neo- to Mesoproterozoic peak at ca. 1050–720 Ma, several minor Meso- to Palaeoproterozoic age clusters at ca. 1.4, 1.9 and 2.4 Ga and ca. 400–360 Ma peaks in the youngest Devonian formation. The early Palaeozoic part of the age spectra is interpreted as detritus mainly derived from the magmatic rocks of the Cambrian–Ordovician Ikh-Mongol Arc System within the nearby Lake Zone and the youngest ages from the neighbouring Devonian granites. The other sources were identified as more distal Tonian magmatic-arc complexes, Rodinia break-up-related volcanic rocks and basement of the Precambrian Zavkhan and Baidrag continental blocks even further east. The maximum sedimentary ages, determined by the youngest detrital zircons, shift the end of deposition of the Sagsai Formation at least to the latest Devonian. Nearly identical detrital zircon age spectra from Lower Palaeozoic sequences of the Hovd Zone and other parts of the Altai belt support an existence of a single giant accretionary complex developed along the entire outer margin of the Ikh-Mongol Arc System. The change in the sedimentary style suggests the latest Ordovician–earliest Silurian termination of magmatic-arc activity in the western Lake Zone, marking the onset of late Silurian–Devonian crustal extensional period in the Altai accretionary system. Graphical abstract Unlabelled Image Highlights • Ordovician deposition in the accretionary wedge in the Hovd Zone (HZ) • Early Palaeozoic subduction beneath the Zavkhan–Baydrag microcontinents • HZ belonged to the Altai accretionary complex bordering the Ikh-Mongol Arc System. • Magmatism in the Ikh-Mongol Arc System most likely terminated in early Silurian. • In the HZ followed Silurian–Devonian platform-type extension-related sedimentation [ABSTRACT FROM AUTHOR]

[Display omitted] • First report of 890–790 Ma metamorphism in the Baidrag supracrustal rocks, Mongolia. • Anticlockwise P-T path is inferred from Grt-Sil-Ky gneiss and Grt-St schist. • Metamorphism at 27–32 °C/km gradient is related to ca. 890–853 Ma extension. • Burial to 8–9 kbar at 18–22 °C/km is related to compression at ca. 835–815 Ma. • Supra-subduction switching caused by subduction relocation to Rodinia margin. The processes leading to the assembly of the Rodinia supercontinent through Grenvillian collisional orogeny are relatively well known. In contrast, accretionary orogenic processes occurring at the supercontinent periphery following Rodinia assembly are poorly understood. To fill this gap, we have identified metamorphic rocks in the Mongolia collage of the Central Asian Orogenic Belt, where numerous data testify for Meso- to Neoproterozoic magmatic reworking. The tectono-metamorphic evolution of the peri-Siberian tract of the Central Asian Orogenic Belt is mainly characterized by the late Proterozoic–early Cambrian (Baikalian) cycle. However, we document here a Tonian age metamorphism at the northern part of the Precambrian Baidrag block, previously considered as a typical example of the Baikalian metamorphic belt. This study incorporates zircon and in-situ monazite geochronology linked to P-T modelling of Grt-Sil-Ky migmatite gneiss and Grt-St micaschist. Grt-Sil-Ky gneiss records initial burial to the sillimanite stability field at ∼720 °C and 6.0 kbar followed by further burial to the kyanite stability field at ∼750 °C and ∼9 kbar and decompression to ∼650 °C and ∼8 kbar. The Grt-St schist records initial burial to the staurolite stability field at ∼620 °C and 6 kbar, followed by further burial to ∼590 °C and 8.5 kbar. The monazite data yield a continuum of 207Pb-corrected 238U/206Pb dates of ca. 926–768 Ma in the Grt-Sil-Ky gneiss, and ca. 937–754 Ma in the Grt-St schist. Based on monazite textural positon, internal zoning, and REE patterns, the time of prograde burial to 6.0 kbar under a thermal gradient of 27–32 °C/km is estimated at ca. 890–853 Ma. It is not clear whether such high-grade conditions prevailed until a phase of further burial under a geothermal gradient of 18–22 °C/km dated at ca. 835–815 Ma. The late monazite recrystallization at ca. 790 Ma is related to decompression. Additionally, monazite with dates of ca. 568–515 Ma occur as whole grains or as rims with sharp boundaries on Tonian monazite in Grt-St schist suggesting a minor Baikalian overprint. Metamorphic zircon rims with Th/U ratios of ∼ 0.01–0.06 in Grt-Sil-Ky gneiss with 877 ± 7 Ma age, together with lower intercepts of detrital zircon discordia lines in both Grt-Sil-Ky gneiss and Grt-St schist further support the Tonian age of high-grade metamorphism. The anticlockwise P-T evolution is interpreted as a result of thickening of a supra-subduction extensional and hot edifice – probably of back-arc or arc type. This kind of prograde metamorphism has so far only been described on the northern part of the Tarim block and was interpreted to be a result of initiation of peri-Rodinian subduction of the Mirovoi Ocean. The geodynamic consequences of a unique discovery of Tonian metamorphism are discussed in terms of tectonic switch related to initiation of peri-Rodinian oceanic subduction during supercontinent assembly, followed by strong mechanical coupling potentially related to onset of Rodinia dispersal. [ABSTRACT FROM AUTHOR]

New field, petrographic, geochemical and geochronological data from the Togtokhinshil Complex (western margin of the Lake Zone, Central Asian Orogenic Belt) reveal the presence of two separate Early Palaeozoic magmatic pulses: Mid-Ordovician and Late Devonian. The Mid-Ordovician (c. 460 Ma) magmatism produced various types of mafic plutonic rocks (gabbro-diorite suite) emplaced into the volcanosedimentary sequence of the Baatar Fm. Gabbros to gabbrodiorites have metaluminous and mostly low to normal-K calc-alkaline or possibly tholeiitic character. The majorand trace-element as well as Nd isotopic signatures suggest its magmatic-arc geotectonic setting and imply the derivation either exclusively from the mantle or in part from the juvenile mafic crust. The Late Devonian (c. 376 Ma) granite suite intruded the rocks of both the gabbro-diorite suite and the Baatar Fm. Granites are subaluminous and have a high-K calc-alkaline to shoshonitic character. Their magmatic arc-like geochemical signature is interpreted as inherited from the recycled arc-related crustal source. The granite suite seems a product of extensive mantle heat-induced crustal anatexis. The Depleted Mantle Nd model ages (c. 0.75 Ga) indicate derivation of the magmatic rocks of the both suites from relatively juvenile, and geochemically immature, sources. These results provide a clear evidence of the Mid-Ordovician arc-related magmatism in the western part of the Lake Zone. They thus prolong the assumed period of magmatic-arc activity and constrain onset of accretionary processes in this part of the Central Asian Orogenic Belt. The gabbro-diorite suite represents either part of a long-lived magmatic-arc or, more likely, a member of multiple island-arc system along the western margin of the Lake Zone. Newly described Late Devonian magmatism in the Togtokhinshil Complex provides further evidence of tectono-thermal event that was widespread in the Central Asian Orogenic Belt. The geodynamic cause for this event remains uncertain, but effects of lithospheric thinning and/or asthenospheric mantle upwelling are considered the most likely. [ABSTRACT FROM AUTHOR]

[Display omitted] • Western juvenile and eastern mature Ordovician arcs intruded the Altai wedge. • Late Ordovician–Silurian volcanic gaps were related to Altai wedge thickening. • An early Devonian back-arc formed in the western part of the Altai wedge. • Back-arc extension migrated to the east in the late Devonian. • This diachronous evolution resulted from lateral variations in subduction modes. The early Palaeozoic volcano–sedimentary evolution of the Khovd and Gobi-Altai zones of the Mongol–Altai Domain was investigated by quantitative petrographic analysis of sediments, whole-rock geochemistry of volcanic rocks, and U–Pb zircon dating. Three evolutionary stages were identified in the Khovd Zone: (1) Cambrian–mid Ordovician basaltic (Nb/Yb = 0.09–1.25) and rhyodacitic (Nb/Yb = 4.36) volcanism and sedimentation of immature greywackes in the fore-arc basin in front of the juvenile continental arc, (2) late Ordovician flysch-type sedimentation accompanied by a volcanic gap coincided with Barrovian metamorphism in footwall sequences reflecting a compressional stage, and (3) Silurian–Devonian within-plate bimodal volcanism (with a strong asthenospheric imprint; Nb/Yb = 4.45–20.34) followed by mature siliciclastic deposition interpreted as transformation of the former fore-arc region into a back-arc domain associated with HT metamorphism. In the Gobi-Altai Zone the three stages were: (1) Cambro–Ordovician marginal greywacke–sandstone succession adjacent to a mature continental arc (mafic rocks Nb/Yb = 0.71–4.36), (2) Silurian siliciclastic sedimentation associated with migration of the volcanic gap and Barrovian metamorphism, and (3) Lower Devonian deep-marine sedimentation followed by shallow-marine carbonate sedimentation, initially accompanied by calc-alkaline basalts (Nb/Yb = 0.74–4.57) and andesites to rhyolites (Nb/Yb = 0.69–4.87), evolving in the mid–late Devonian to within-plate alkali basalts (Nb/Yb = 11.05) thus reflecting back-arc basin development. These temporal and spatial variations in the Mongol-Altai Domain are interpreted as a diachronous sequence of retreating and advancing subduction modes instead of juxtaposition of suspect terranes as proposed in previous studies. [ABSTRACT FROM AUTHOR]