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The Lüliang Complex is located at the western margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks amalgamated to form the basement of the North China Craton. The complex consists of the Paleoproterozoic granitic plutons and meta-supracrustal rocks, of which the latter are subdivided into the Jiehekou, Lüliang, Yejishan, and Heichashan/Lanhe Groups. A meta-volcanic rock from the Yejishan Group gives a magmatic zircon U–Pb age of 2188 ± 48 Ma and ε Hf (t) values of + 0.06 to + 5.42. Based on the geochemical characteristics, four different ~ 2.2 Ga igneous rock suits have been identified in the Lüliang Complex. The calc-alkaline basalts and andesites show the geochemical features of typical ‘normal’ arc volcanics with pronounced LREE enrichments relative to HREE, negative Nb, Ta, P and Ti anomalies and ε Nd (t) values of − 2.69 to + 2.14. The adakitic rocks are characterized by high Na 2 O/K 2 O ratios, weak to positive Eu anomalies, positive Sr and Ba but negative Nb and Ti anomalies, and relatively clustered and near to zero ε Nd (t) values. The Nb-enriched basalts and andesites have higher Nb, Zr and TiO 2 contents, higher Nb/Ta (14.4–19.3) and Nb/U (20.6–23.2) ratios than the majority of arc basalts and andesites and relatively variable ε Nd (t) values (− 1.54 to + 3.02). The magnesian andesites are characterized by anomalously high MgO, Cr and Ni contents and have ε Nd (t) values of − 3.90 to + 1.17. The occurrence of adakitic rocks, Nb-enriched basalts and andesites and magnesian andesites has been described from many modern arcs featuring subduction of oceanic slab. Therefore, we suggest that similar mechanism may have played an important role in the production of the ~ 2.2 Ga igneous rocks in the Lüliang Complex and thus the final collision between the Eastern and Western Blocks along the TNCO must have happened at some time after ~ 2.2 Ga. [ABSTRACT FROM AUTHOR]

The Taihua Complex in the Xiaoqinling area of the southern Trans-North China Orogen (TNCO) records extensive magmatism during the early Paleoproterozoic. This contrasts with the tectono-magmatic quiescence recorded globally at this time. Based on zircon U−Pb geochronological and whole-rock geochemical data, the 2.36–2.30 Ga granitic gneisses in the Taihua Complex can be subdivided into three groups. Group-1 gneisses (2.36–2.33 Ga), mainly in the Dumutai area, are high-K 2 O granitoid rocks, which record the earliest magmatism. These rocks have fractionated rare earth elements (REE) patterns, marked negative Eu−Sr anomalies, and variable whole-rock ε Nd (t) (−1.67 to +2.41) and ε Hf (t) values (−0.89 to +3.41), and were likely derived by partial melting of a mixture of pre-existing tonalite–trondhjemite–granodiorite (TTG) and K-rich rocks with residual plagioclase in the source at high-temperature and low-pressure conditions. Group-2 gneisses (2.33–2.31 Ga), mainly in the Jialu and Xitongyu areas, are granitoid rocks that formed after the Group-1 gneisses. These rocks have less fractionated REE patterns, low La/Yb and Sr/Y ratios, and slightly positive to negative whole-rock ε Nd (t) (−3.91 to +2.00) and ε Hf (t) values (−7.99 to +0.87), which resulted from high-degree partial melting of ancient crust in an extensional setting. Group-3 gneisses (~2.30 Ga) are TTG rocks from the Bayuan area, which represent the youngest magmatism. These rocks have high La/Yb and Sr/Y ratios, high MgO, Cr, and Ni contents, and negative whole-rock ε Nd (t) (−1.71 to −1.67) and ε Hf (t) values (−0.57 to −0.10), which indicate derivation by partial melting of delaminated lower crust and interaction with mantle materials. Samples from all groups have variable zircon ε Hf (t 7/6) (−6.38 to +7.70) and δ18O values (3.97‰ − 6.79‰), indicative of a heterogeneous magmatic source. Most zircons have slightly positive to negative ε Hf (t 7/6) values, indicating significant reworking of ancient crustal materials and limited crustal growth during this period. The age, geochemistry, and petrogenesis of the studied granitoid rocks record orogenic collapse and a transition from post-collisional extension to crustal delamination in the early Paleoproterozoic. This followed late Archean subduction–collision–accretion processes in the southern NCC. • Gneisses of the Xiaoqinling Taihua Complex record extensive magmatism at ca. 2.3 Ga. • The Xiaoqinling Taihua gneiss protoliths were formed by reworking of lower crust. • The ca. 2.3 Ga magmatism in the southern NCC was related to orogenic collapse. [ABSTRACT FROM AUTHOR]

It is debated whether global-scale tectono-magmatic quiescence prevails on the Earth during the early Paleoproterozoic. The early Paleoproterozoic meta-mafic and intermediate rocks in the southwestern Yangtze Block of South China could provide an opportunity to constrain not only the tectonic evolution of the Yangtze Block itself but also augment our understanding of the global tectono-magmatic lull during the early Paleoproterozoic. Zircon U Pb geochronological study indicates that the meta-mafic rocks were emplaced at ca. 2.32 Ga, whereas the intermediate rocks were emplaced at ca. 2.35 Ga. These two lithologies are characterized by subduction-related whole-rock geochemical (such as depleted Nb, Ta and enriched Rb, K, Pb) and unradiogenic Nd Hf isotopic signatures (ε Hf (t) < 0, ε Nd (t) < 0), implying a derivation from a geochemically enriched lithospheric mantle modified by ancient subduction. Thermodynamic modeling further suggests that the intermediate rocks are products of the AFC process between mantle-derived basaltic magma and TTG-like basement rocks at shallow crustal levels. We interpret this as occurring within a post-orogenic extensional setting. Integrated with the published work, we further posit that the Yangtze Block experienced a tectonic regime transition from compressive orogenesis to post-orogenic extension during the early Paleoproterozoic, and the magmatic activities in several crustal blocks are still active until ~2.3 Ga and therefore places important constraints on the beginning of the tectono-magmatic lull. [Display omitted] • 2.35–2.32 Ga mafic-intermediate magmatism is identified in the SW Yangtze Block. • Mafic-intermediate rocks in this study were derived from the lithospheric mantle. • Tectonic transition from orogeny to post-orogenic extension at ~2.35 Ga in Yangtze. [ABSTRACT FROM AUTHOR]

Tectonic regimes took different forms worldwide during the early Paleoproterozoic, ranging from a slowing or halting of plate tectonics to vigorous subduction-related magmatism. A detailed study is conducted on the Delingha granitoid pluton in the Quanji Massif of northwestern China to reveal the crustal evolution of this Precambrian microcontinent and to provide potential insight on complex and heterogeneous evolutionary processes occurring in this period. The Delingha pluton was mainly composed of gneissic biotite granite and gneissic granodiorite, which formed at ca. 2.48 – 2.44 Ga and 2.38 – 2.35 Ga, respectively, as evidenced by LA-ICP-MS zircon U-Pb ages. The gneissic biotite granite exhibited high-K I-type granite affinities and variable zircon ε Hf (t) values (−12.9 −4.7) with a major peak of approximately 2.8 and a secondary peak of approximately 3.9, indicating that the source rock was dominated by heterogeneous mafic crustal materials. The gneissic granodiorite shows A-type granite affinities and a nearly unimodal distribution of zircon ε Hf (t) values (−3.1 −4.0, with a peak of approximately 1.5). These data indicate that the gneissic granodiorite was mainly sourced from Archean mafic igneous rocks. Our study suggests that the gneissic biotite granite formed in a subduction-related environment while the gneissic granodiorite formed in a post-collisional tectonic regime. Alongside previous studies on other Siderian granitoids in the Quanji Massif, we propose a tectonic evolution model, including (1) plate subduction occurring before 2.44 Ga; (2) a collision occurring from ca. 2.43 to ca. 2.40 Ga; (3) a post-collisional extension occurring from ca. 2.39 to ca. 2.32 Ga. This tectonic evolution reveals that the operation of plate tectonics continued during the Siderian and that a slowdown or pause might have occurred in the Quanji Massif after ca. 2.3 Ga. Unlabelled Image • A 2.48 – 2.44 Ga subduction-related granitoid was recognized in the Quanji Massif. • The A-type granitoid suggests a post-collision setting during 2.38-2.35 Ga. • An orogenic cycle from subduction to collision and then post-orogeny is revealed. [ABSTRACT FROM AUTHOR]