Late Palaeozoic magmatism in the eastern Tseel Terrane of SW Mongolia evidenced by chronological and geochemical data

Abstract

The eastern Tseel Terrane of SW Mongolia, which is an important part of the Central Asian Orogenic Belt (CAOB), contains a segment of imbricated sheets of Late Palaeozoic granites as well as a bimodal volcanic suite. Late Devonian (380-382 Ma) granites that are enriched in Th, U, and K and depleted in Nb, Ta, P, Ba, Sr, and Ti indicate arc magmatism and are low-K tholeiitic to medium-K calc-alkaline series. Zircon εHf(t) values are of +8.30 to +14.1, with crustal model ages of 0.83-0.48 Ga. The bimodal volcanic suite is composed of N-MORB basalt and 302 ± 2 Ma rhyolite having A 2 -type granite affinities, εHf(t) values ranging from +9.9 to +11.9, and crustal model ages from 0.69 to 0.59 Ga. The rhyolite mighthave originated from partial melting of juvenile lower crust, rather than fractional crystallization of coeval basaltic magma. Late Carboniferous (299-303 Ma) granites are medium-K to high-K calc-alkaline series, crosscutting carbonaceous siltstone, emplaced into the deformed volcanic rocks and are characterized by enrichment in K, Th, and U accompanied by depletion in Ba, Nb, Ta, Sr, P, and Ti in a primitive mantle-normalized diagram with εHf(t) values ranging from +6.05 to +10.6 and crustal model ages from 0.70 to 0.65 Ga. Thus, LA-ICP-MS zircon ages in combination with geochemical data document a phase of arc-related magmatism in the Tseel Terrane at 380-382 Ma. These rocks were subsequently deformed under low-grade metamorphic conditions and intruded by undeformed granites at c. 299-303 Ma. The coeval 302 Ma rhyolite in bimodal volcanic suite shows typical A 2 -type granitic geochemical affinities and probably documents a back-arc basin extensional environment, which was probably related to the roll-back of the Palaeo-Asian Oceanic Plate during the northward subduction under the Central Mongolia microcontinent.

Late Ordovician magmatic pulse in the Tugrug Group, the Gobi Altai Zone, SW Mongolia

“…On the other hand, early Carboniferous granitoids of the Chandman Massif in the northern Gobi Altai Zone were emplaced in the core of a migmatite-granite dome marking regional compression (Broussolle et al 2015;Lehmann et al 2017). In contrary, Hong et al (2020) interpreted late Carboniferous (303-298 Ma) plutons and rhyolites on the southern slopes of the Gichigeny Range east of our studied valley as A 2 type granites related to the extensional back-arc basin. Moreover, late Carboniferous Sagsai gabbro-monzonite pluton intruding the Tugrug Group west of the studied area has a within-plate geochemical signature (Buriánek et al 2016).…”

“…Granites in the metamorphic complex south of Bayanlig soum were dated as late Silurian (Helo et al 2006) or as middle Ordovician (Kröner et al 2017). Devonian plutonic protolith of the orthogneisses (Helo et al 2006;Demoux et al 2009;Burenjargal et al 2014;Hong et al 2020) common in metamorphic rocks of the Bodonch-Tseel Zone, was interpreted as a product of syn-extensional melting of the wedge sediments and volcanic rocks (Hanžl et al 2016;Sukhbaatar et al 2022). On the other hand, early Carboniferous granitoids of the Chandman Massif in the northern Gobi Altai Zone were emplaced in the core of a migmatite-granite dome marking regional compression (Broussolle et al 2015;Lehmann et al 2017).…”

Modes and geometry of crustal-scale detachment folding in hot orogens—Insights from physical modeling

“…Here, the gradient of ages for Mongol-Altai domes comprises a sequence of older intrusions (360 Ma-340 Ma) for the Chandmann dome (Lehmann et al, 2017). Meanwhile, younger intrusions are found in the Tseel domain (ca 300 Ma-240 Ma) (Hong et al, 2021;Sukhbaatar et al, 2022;Zhang et al, 2014) and the southern Bugat batholith (300 Ma-275 Ma) (Cai et al, 2015). The youngest ages are in the north Bugat pluton (215 Ma-206 Ma) (Cai et al, 2015).…”

“…Lehmann et al (2017) suggest that detachment folding may represent an important regime contributing for vertical differentiation and horizontal amalgamation within the orogenic systems on Earth. In particular, the Central Asian Orogenic Belt (CAOB), the largest accretionary complex on Earth, contains several kilometer-scale migmatitic to granulitic magmatic-metamorphic domes, e.g., the Chandmann dome (Lehmann et al, 2017); Bugat dome (Cai et al, 2015) or Tseel dome (Jiang et al, 2012;Burenjargal et al, 2016;Hong et al, 2021). These structures were initiated in response to the early formative stages (Silurian-Devonian) of the Mongol-Altai zone, and amplified during closing of the Mongol-Okhotsk oceanic domain during development of the Mongol-Hingan orocline in the Permian-Triassic (Jiang et al, 2016;Jiang et al, 2019;Krýza et al, 2021).…”

Geochronology and trace elements of zircon in the Southern Chinese Altay: Implications for tectonic setting

“…Moreover, the traceelement compositions of zircon also play an important role in tectonic setting studies and have been suggested as an indicator of zircon provenance (Belousova et al, 2002;Grimes et al, 2007Grimes et al, , 2009. The Central Asian Orogenic Belt (CAOB), which is one of the largest and longest-lived accretionary orogenic systems, has undergone complex geodynamic processes during the Phanerozoic continental growth of Central Asia (Hong et al, 2017(Hong et al, , 2020Li et al, 2017;Sengör et al, 1993;Windley et al, 2007;Xiao et al, 2009Xiao et al, , 2015. The Chinese Altay, a key segment of the CAOB, is an important region for studying the convergent processes and amalgamation of the Mongolian and Kazakhstan collage systems (Cai et al, 2016;Li et al, 2019;Liu et al, 2017;Xiao et al, 2015).…”