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Abstract Mechanisms of lithospheric transformation beneath the North China Craton (NCC) were widely discussed, but the northern NCC was less studied compare to the eastern part. In this research, In-situ major and trace element and Sr isotopic compositions of spinel peridotite and pyroxenite xenoliths carried by the Yangyuan Tertiary basalt were analyzed to constrain subduction style of the Paleo-Asian oceanic plate (PAOP) and its influence on the northern NCC. These xenoliths were classified into dunite, pyroxenite, and two groups of lherzolites according to their petrography and chemical features. The petrography and mineral chemistry suggest that the dunite, pyroxenite, and Group 1 lherzolites are residues of partial melting which experienced subsequent hydrous metasomatism. Correlations between 87Sr/86Sr with the Zr/La and Zr/Nb ratios in clinopyroxenes from these xenoliths suggest that the metasomatic agents should be fluids derived from the subducted PAOP. Mineral Rb Sr isochron of the pyroxenite show that the minimum age of the metasomatism event should be 295 ± 38 Ma. Major element compositions of minerals in the Group 2 lherzolites are more fertile compare to the dunite and Group 1 lherzolites. Clinopyroxenes in these xenoliths exhibit LREE-depleted REE patterns with relatively high HREE contents and 87Sr/86Sr ratios (0.70403–0.70482). Chemical zonations are preserved in several clinopyroxenes with incompatible elements depleted from core to rim, which should be the results of melt depletion after metasomatism. Patches of silica-rich glasses were present along the grain boundaries. These glasses have sediment-like Pb isotopic compositions and trace elements distribution patterns and thus are supposed to represent the melt from recycled sediments. Combined with geophysical and tectonic evidences, we propose that roll-back of the southward low-angle subducted PAOP in the late stage of subduction contributed to remelting of the PAOP subduction-modified mantle wedge beneath the northern NCC. Highlights • The Yangyuan basalt-borne xenoliths record subduction related metasomatism • Rb Sr isochron gives the minimum age of 295 ± 38 Ma for the metasomatism event. • Slab roll-back resulted in remelting of the subduction-modified mantle wedge. • Patches of silica-rich glass were derived from the subducted sediment diapirs. [ABSTRACT FROM AUTHOR]

Three types of carbonates have been found in the Miocene basalt in the Dongbahao area (Inner Mongolia), including wide veins and veinlets of carbonate in basalt and carbonates in peridotite xenoliths. Except for the dolomitic zonation in the basalt, all of the carbonates are calcite. Despite their different appearances, they share almost identical geochemical characteristics of low LILE (low large ion lithophile element), HFSE (high field strength element), and REE (rare earth elements) contents (ΣREE = 0.51–137 ppm); negative Ce anomalies; and low Ce/Pb ratios (0.51–74.5). Moreover, they show high δ 18 O SMOW values (20.95–22.61‰) and 87 Sr/ 86 Sr ratios (0.7087 ± 0.0003 (1σ, n = 17)). These characteristics indicate a sedimentary precursor for these carbonates. However, the occurrence and petrographic characteristics imply an igneous origin for the carbonates rather than a hypergene process. Further, the trace element compositions of the silicate melt and carbonate melt in the calcite-dolomite-silicate zonations fall on the same variation lines in the plots of Y-Ho, La-Yb, Li-Pb and Ba-Cu. It is suggested that these melts could have evolved from one magma system or could have been equilibrated. Given the partition coefficients of REEs and alkali elements (Cs, Rb, and K) between the carbonate melt and silicate melt, it can be inferred that these melts could have been formed from a primary H 2 O-Si-bearing Mg-Ca-carbonate melt by an immiscibility process at 1–3 GPa. Considering the southward subduction of the Paleo-Asian ocean along the northern margin of the North China Craton (NCC), these carbonate melts could have been derived from the melting of subducted sedimentary carbonate rocks. Interestingly, these carbonates have quite depleted carbon isotopic compositions (δ 13 C PDB = −8.23‰ to −11.76‰) but moderate δ 18 O SMOW values, implying coupled H 2 O-CO 2 degassing during subduction and/or recycling to the Earth’s surface. Low-δ 13 C PBD carbonates appearing at the global scale may suggest an underestimated path of CO 2 emission back to the atmosphere. [ABSTRACT FROM AUTHOR]

High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U–Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO 2 contents ranging from 48.7 to 63.2 wt.%, high Mg # values of 63–75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87 Sr/ 86 Sr ratios of 0.70417–0.70457, ε Nd (t) values from − 0.4 to 5.0, and ε Hf (t) values from 5.1 to 11, as well as zircon ε Hf (t) values from − 9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker–Xra Moron–Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian–Early Triassic. [ABSTRACT FROM AUTHOR]