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Zircon U–Pb ages, geochemical data and Sr–Nd isotopic data are presented for volcanic rocks from the lower Permian Dashizhai Formation. These rocks are widely distributed in the south-eastern Central Asian Orogenic Belt in central Inner Mongolia, China. The volcanic rocks mainly consist of basaltic andesite and rhyolite, subordinate dacite and local andesite, and exhibit bimodal geochemical features. The results of zircon U–Pb dating indicate that the volcanic rocks formed during the early Permian (292–279 Ma). The mafic volcanic rocks belong to low-K tholeiitic to medium-K calc-alkaline series. These mafic volcanic rocks are also characterised by moderately enriched light rare earth element (LREE) patterns; high abundances of Th, U, Zr and Hf; negative Nb, Ta and Ti anomalies; initial 87 Sr/ 86 Sr ratios of 0.70514–0.70623; and positive ε Nd (t) values (+1.9 to +3.8). These features indicate that the mafic volcanic rocks were likely derived from the high-percentage partial melting of subduction-related metasomatised asthenospheric mantle. The felsic rocks show an A-type affinity, with enrichments in alkalis, Th, U and LREEs. The felsic rocks are depleted in Ba, Sr, Nb, Ta and Ti and exhibit moderately LREE-enriched patterns (La N /Yb N = 2.09–6.45) and strongly negative Eu anomalies (Eu/Eu ∗ = 0.04–0.25). These features, along with the positive ε Nd ( t ) values (+2.6 to +7.7) and young T DM2 ages (T DM2 = 435–916 Ma), indicate that the felsic rocks were likely derived from a juvenile crustal source that mainly consisted of juvenile mid-ocean ridge basalt -related rocks. The volcanic association in this study and in previously published work widely distributed in central Inner Mongolia. The observations in this study suggest that the lower Permian volcanic rocks formed in an identical tectonic environment. The regional geological data indicate that the bimodal volcanic rocks from the lower Permian Dashizhai Formation in the study area formed in an extensional setting that was likely related to post-collisional delamination. [ABSTRACT FROM AUTHOR]

The northern Alxa orogenic belt, a junction between the western and eastern Central Asian Orogenic Belt (CAOB), is not well understood, especially in its Carboniferous to Permian tectonic history. In this paper, an integrated study incorporating the geochronology, geochemistry, and isotopes of magmatic rocks and provenance analysis of clastic rocks is conducted to address the above issue. The zircon U Pb age data, both in this study and in previous studies, indicates that the Permian magmatic activities in the Alxa Block were intensive and peaked at ca. 276 Ma. The magmatic zircons yield negative ε Hf (t) values with a wide range, indicating their dominant derivation from the crustal reworking of the Alxa Block with the addition of juvenile materials. The Permian high-K to shoshonitic, I-type granitoids combined with the A-type granitoids/rhyolites were most likely formed in extensional settings. The late Carboniferous sandstones collected along the Badain Jaran fault yield a high proportion of early Paleozoic zircons peaked at ca. 429 Ma with both positive to negative Hf (t) values and a low proportion of Precambrian zircons with positive to negative Hf (t) values. Thus, their provenance were likely the Precambrian to Paleozoic rocks in the Alxa Block and in the terranes in the CAOB. The zircon age spectra with no indicators of Carboniferous zircons approximating their depositional age supports an extensional setting. The Permian A-type granites and volcanic rocks in the Alxa area have some geochemical affinity with the Permian alkaline granitoids in the eastern Tianshan–Beishan and central-north Inner Mongolia regions. These findings support the extension of the Gobi–Tianshan belt in the Alxa area. • The Permian magmatic rocks were predominantly reworked from the Alxa Block. • The clastic rocks were sourced from the Alxa Block and the terranes in the CAOB. • An extensional setting was proposed for the Alxa area. [ABSTRACT FROM AUTHOR]

Identifying the petrogenesis and geodynamic mechanism of the Early Permian igneous rocks widely distributed in the Inner Mongolia–Daxing'an Orogenic Belt (IMDOB) is crucial for understanding the tectonic evolution of the southeastern Central Asian Orogenic Belt. In this study, a combined study of petrology, geochronology, and geochemistry of Early Permian volcanic–plutonic rocks from the Uliastai continental margin, northern IMDOB, was conducted aiming to constrain their petrogenesis and tectonic setting. The U Pb zircon data for the magmatic zircons indicate that the Baoligaomiao Formation (BG Fm.) volcanic rocks, including felsic and mafic rocks, erupted at approximately 298–285 Ma, and quartz monzonite porphyries that intruded the BG Fm. were emplaced at approximately 292 Ma. The mafic volcanic rocks exhibit intraplate nature with basaltic compositions transitional between the calc-alkaline and shoshonite series. The geochemical behavior and isotopic data of these volcanic rocks reflect a depleted lithospheric mantle source metasomatized by fluids released from the stagnant slab. Felsic volcanics and quartz monzonite porphyries show affinities with A-type granites and are derived from the partial melting of juvenile crustal materials. Moreover, we suggest that the Early Permian magmatism formed in a post-collisional extensional setting, which is the continuation of the Late Carboniferous extension and was induced by the lithospheric collapse after the slab break-off of the Hegenshan Ocean. Notably, the felsic rocks formed after 290 Ma, with affinity changing from A 2 -type to A 1 -type granite, and approximately 288 Ma mafic volcanic rocks exhibited intraplate characteristics. These changes, combined with the development of coeval bimodal volcanic rocks and dike swarms, suggest that the tectonic setting at the end of the Early Permian in the northern IMDOB may have gradually transferred to an intraplate environment. • Mafic rocks were derived by melting of depleted lithospheric mantle. • Felsic rocks with depleted Hf isotopes record the reworking of juvenile crust. • They formed in a post-collisional setting after the closure of Hegenshan Ocean. • Tectonic setting transferred to an intraplate extension in the late Early Permian. [ABSTRACT FROM AUTHOR]