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• The Altun block, Qilian block, North Qaidam and East Kunlun block show strong affinity in the Meso-Paleoproterozoic. • The assembly of Rodinia in AQK may start as early as 1030 Ma with a peak convergent time of ∼918 Ma. • The initial breakup of Rodinia in AQK may have started from 860 Ma until to 660 Ma with the peak time of ∼765 Ma. • The separation of AQK from the South China craton may occur until the opening up of Qilian ocean after 660 Ma. The Altun-Qilian-Kunlun Mountain (AQK), located on the northeastern margin of the Qinghai-Tibet Plateau, experienced multiple Neoproterozoic magmatic and metamorphic events which are correlated to the Rodinia supercontinent history. Here we present results from a systematic petrologic, geochemical, and zircon U Pb and Hf isotopic study on Neoproterozoic granitoids and mafic rocks from the AQK. In conjunction with a review of the available age data, we divide the early Neoproterozoic magmatism in AQK into two stages: the first stage at ca. 1030–846 Ma and the second stage at ca. 860–660 Ma. The new Lu Hf isotopic data coupled with published Lu Hf and Sm Nd results indicate that the stage 1 mafic rocks were mainly derived from a depleted mantle source with minor contamination with crustal materials or subducted sediments. The stage 2 mafic rocks were mainly derived from the depleted mantle with limited crustal contamination. Combined with whole-rock geochemical compositions and Sr Nd isotopic data, the stage 1 granitic magmas are inferred to have been derived from reworked Paleoproterozoic-Mesoproterozoic crust and the stage 2 granitoid magmas mainly came from reworked continental crust with minor mantle magma input. The AQK experienced arc magmatism in a compressional environment on an active continental margin during the late Mesoproterozoic-early Neoproterozoic (1030–846 Ma), followed by rift-related magmatism in an extensional setting in the middle to late Neoproterozoic (860–660 Ma). Similarities in basement compositions, magmatism and metamorphism between the Qilian block (QL) and surrounding blocks suggest that the AQK was with a composite block at early Neoproterozoic. The assembly of AQK started as early as 1030 Ma with peak convergence at ca. ∼918 Ma. The initial breakup might have started from 860 Ma and lasted until to 660 Ma with the peak at ca. ∼765 Ma. These timings correspond well with those of the assembly and breakup of the Neoproterozoic supercontinent Rodinia. The breakup of AQK from the South China Craton might have occurred in the late Neoproterozoic, not until the opening of the Qilian ocean at around 660 Ma. [ABSTRACT FROM AUTHOR]

Abstract The North Qaidam ultra-high pressure (UHP) metamorphic belt in the northern Tibetan Plateau is considered as a typical Alpine-type UHP metamorphic belt due to the Early Paleozoic subduction of the Qaidam Block beneath the Qilian Block. The well-preserved Paleozoic metatexite migmatite, diatexite migmatite, felsic sheet/dyke and anatectic granite in the North Qaidam UHP metamorphic belt provide us with an excellent opportunity to study the generation, transport and final fate of crustal melt and geodynamic processes associated with orogenesis. Based on structural relationships, petrology, geochronology, whole-rock geochemistry and Sr Nd isotope data, the Early Paleozoic anatexis during oceanic subduction to continental collision in the North Qaidam UHP metamorphic belt can be further divided into three stages of development ~470 Ma, 446–428 Ma and 432–420 Ma. The first-stage granitic leucosomes are rich in K, poor in Na with low Sr/Y and enrichment of large ion lithophile elements (LILEs), which were probably derived from partial melting of ancient felsic gneiss in continental arc circumstances during oceanic subduction. The second-stage Na-rich leucosomes and tonalite plutons are characterized by high Na, Sr, Sr/Y and La/Yb and low heavy rare earth elements (HREEs), with positive ε Nd (t) values of 0.1–4.3 and zircon ε Hf (t) values of 8.3–10.2, similar to typical tonalite-trondhjemite-granodiorites (TTGs). These TTG-like magmas were produced through partial melting of newly emplaced gabbroic rocks with arc affinity under high-pressure (HP) granulite-facies conditions in a thickened lower crust during continental collision. The volumetrically significant migrated plutons evolved from TTG-like melt will become segments of continental crust and contribute to crustal growth, with partial residual products of HP granulite and/or garnet pyroxenite to the mantle by delamination. The third stage of anatexis was preserved in both migmatitic UHP gneiss and eclogite in the Xitieshan and Luliangshan terranes. The Kfs-rich felsic leucosomes inside UHP gneisses in the third stage are characterized by high alkali contents and low mafic component with FeO T + MgO + TiO 2 <2%. In trace element distribution diagrams, these Kfs-rich leucosomes exhibit parallel patterns to their host gneisses but lower element contents and slightly positive Eu and Sr anomalies. The Pl-rich leucosomes within the retrograde eclogite have geochemical features as follows: (1) rich in CaO, Na 2 O and poor in K 2 O, with Na 2 O/K 2 O ratios >2.0; (2) high La/Yb and Sr/Y, and low Y and HREEs; (3) high Al 2 O 3 and low Mg# values; and (4) enriched in LILEs(e.g., Rb, Ba, K, Sr, Pb) and poor in high field strength elements (HFSEs). Partial melting of UHP eclogite and felsic gneiss during the initial retrogression stage with Pl-rich and Kfs-rich leucosome formation was triggered by dehydration melting involving predominant zoisite and muscovite. The anatectic melts from partial melting of deeply subducted UHP gneiss have accumulated and migrated outside the deeply subducted crustal slice in the form of syn -collisional plutons. The melt evolution from the leucosomes produced at the early exhumation stage to syn-collisional granitoids produced at the late exhumation, might contribute greatly to the exhumation of the North Qaidam UHP metamorphic belt from mantle depths to the lower crustal levels. [ABSTRACT FROM AUTHOR]