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We report new U–Pb zircon age data, zircon in situ oxygen isotope, mineral chemistry, whole-rock geochemistry and Sr–Nd isotopic compositions from the Early Devonian ultrapotassic Gucheng pluton in the North China Craton, and discuss its petrogenesis. The Gucheng pluton is exposed in the northern part of the North China Craton and forms a composite intrusion, consisting of K-feldspar-bearing clinopyroxenite, clinopyroxene-bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene (Wo43–48En19–35Fs18–38), sanidine (An0Ab3–11Or89–97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in situ oxygen isotopes (δ18O = 5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the North China Craton. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the North China Craton facing the Palaeo-Asian Ocean. [ABSTRACT FROM AUTHOR]

The Zhangguangcai Range in the Xing'an Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ɛNd(t) values of 2.3–3.2 and positive ɛHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet- to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia. [ABSTRACT FROM AUTHOR]

The main rock types of the Boluonuo and Daguangding plutons are diorite, quartz diorite, tonalite, granodiorite, and subordinate plagioclase-bearing hornblendite and hornblende gabbro. Zircon SHRIMP U-Pb dating for a quartz diorite of the Boluonuo pluton suggests that the pluton was emplaced at about 296 ± 4 Ma. Plagioclase-bearing hornblendites show typical cumulative textures, which, in combination with their convex-upward REE patterns and the large variation of compatible elements such as Co, V and Sc, suggests that these hornblendites formed through accumulation of hornblende during magma evolution. Microgranular mafic enclaves (MMEs) are common in the Boluonuo and Daguangding intermediate to felsic plutons. Many plagioclase grains show compositional and textural disequilibrium, with calcium-rich cores (An) mantled abruptly by sodium-rich plagioclase (An). Whole-rock samples of the plutons are characterized by quite negative ɛ( t) values (−16.5 to −11.8) and ɛ( t) values (−22.5 to −16.8), and the ɛ( t) values are negatively correlated with silica contents. All these features suggest that the intermediate to felsic plutons formed through magma mixing of enriched mantle-derived, evolved basaltic magma with granitic, crustal melts, followed by fractional crystallization of mainly hornblende and small amounts of pyroxene, apatite and zircon. The hornblende-dominated fractionation contributed significantly to the adakite-like features of the intermediate to felsic plutons, like the high Sr and Sr/Y ratios and low Yb abundance. In addition, the Boluonuo and Daguangding plutons are highly enriched in LILEs (e.g., Ba and Sr), but depleted in HFSEs (e.g., Nb, Zr and Ti), which is typical of arc magmas. Therefore, the formation of Boluonuo and Daguangding plutons was probably related to the subduction of the Paleo-Asian oceanic slab beneath the North China Craton in the Paleozoic. [ABSTRACT FROM AUTHOR]

Abstract: The Fanshan ultramafic–syenitic complex is located on the northern margin of North China Craton, with zircon U–Pb ages of 220Ma. It is a concentrically zoned complex, with syenite in the core, surrounded by ultramafic rocks (clinopyroxenite, glimmerite) and garnet-clinopyroxene syenite, respectively, towards the rim. Diopside, biotite, orthoclase, melanite, magnetite and apatite are the major minerals, with subordinate sphene and calcite. Mineralogy, petrology and geochemical studies point to the formation of the complex through fractional crystallization and accumulation from a SiO2-undersaturated ultrapotassic alkaline-peralkaline parent magma that is characterized by high CaO, Fe2O3, K2O and fluid compositions (P2O5, CO2, H2O, F), and by high temperature and high oxygen fugacity. Rocks from the complex are highly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE; e.g., Rb, Ba, Sr), depleted in high field strength elements (HFSE; e.g., Nb, Ta, Ti), and show relatively homogeneous Sr–Nd isotopic compositions with initial 87Sr/86Sr=0.70513–0.70597 and εNd(t)=−5.8 to −5.3. The data suggest that the Fanshan complex originated from a phlogopite-clinopyroxenite-rich lithosphere mantle source that had previously been metasomatized by melts from carbonated oceanic crust above a subduction zone. Highly radiogenic Os isotope compositions (initial 187Os/188Os=0.299–2.449) suggest that the parent magma to the Fanshan complex has been contaminated by Precambrian mafic crustal rocks during magma emplacement in crustal levels. The occurrence of the Fanshan complex, together with many other ultramafic/alkaline plutons of similar ages, on the northern margin of the North China Craton suggests that the northern margin of the craton entered into a large-scale extensional regime in late Triassic after the final amalgamation between Mongolian microcontinent and the craton. [Copyright &y& Elsevier]

The North China Craton (NCC) represents one of the oldest and largest cratons in the earth with a nearly complete record of Precambrian history. In the northern part of the NCC, the earliest phase of alkaline magmatism occurred in discrete pulses in the Early and Middle Devonian; whereas the next episode of alkaline magmatism took place in the early Mesozoic. The Gucheng pluton is exposed in the northern part of the NCC and forms a composite intrusion, consisting of K‐feldspar–bearing clinopyroxenite, clinopyroxene–bearing syenite and alkali‐feldspar syenite. Mineral phases in these lithologies include clinopyroxene (Wo43‐48En19‐35Fs18‐38), sanidine (An0Ab3‐11Or89‐97), and subordinate titanite, andradite and Na‐feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in‐situ oxygen isotopes (δ18O=5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the NCC. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo‐Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. SHRIMP U‐Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean‐type continental margin evolution along the northern edge of the NCC facing the Palaeo‐Asian Ocean. [ABSTRACT FROM AUTHOR]

The Zhangguangcai Range in the Xing'an(Hinggan) Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island‐arc mafic rocks, the DBZG dolerite is characterized by high trace‐element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB‐type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ∊Nd(t) values of 2.3–3.2 and positive ∊Hf(t) values of 8.5–17.1. Trace‐element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet‐to spinel‐facies conditions. The occurrence of OIB‐like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back‐arc environment in the upper plate of a palaeo‐Pacific slab subducting W–NW beneath East Asia. [ABSTRACT FROM AUTHOR]

The upper-mantle section of the Yushigou ophiolite in the North Qilian Orogenic Belt consists mainly of moderately depleted harzburgite. New mineral and whole-rock major- and trace-element geochemical data show that these rocks could not have formed by simple partial melting of more enriched peridotites. The harzburgites contain high-Mg olivine (Fo = 91.0–92.2) and orthopyroxene (Mg# 91.4–92.6) accompanied by sparse high-Cr magnesium chromite (Cr# = 54.1–67.6) and clinopyroxene with low Al 2 O 3 (1.19–2.11 wt%) and TiO 2 (<0.02 wt%) contents. Most of the analysed samples exhibit depleted, U-shaped, chondrite-normalized rare earth element patterns, whereas primitive mantle-normalized PGE display flat patterns from Os to Pt with significant depleted in Pd. We propose that these peridotites underwent a multi-stage melting process beginning with 20%–25% partial melting of a mantle source beneath a mid-ocean ridge environment followed by second-stage partial melting and related refertilization in a supra-subduction zone tectonic setting, experience an additional 5%–10% melting, yielding a total of 25%–35% melting in the two episodes. TiO 2 enrichment (up to 0.09 wt%) of spinels in some of the harzburgites point to interaction between an already depleted mantle and various proportions of silicate melts with LREE-enriched, boninitic compositions in a forearc setting. Both the Re Os isotope and the PGE characteristics of the Yushigou harzburgites were controlled mainly by ancient depletion events. All the samples have low Re concentrations (0.006–0.228 ppb) and subchondritic Os isotopic compositions (0.11216–0.11979). The Re -depletion model ages (1.5–1.2 Ga) of the Yushigou harzburgites may record a period of Mesoproterozoic intracontinental rifting and formation of the original ocean basin in the North Qilian Orogenic Belt. • The upper mantle section of the Yushigou ophiolite comprises mainly harzburgite. • The Yushigou harzburgites experienced two-stages of depletion and refertilisation. • The harzburgites expericed melt metasomatism in a supra-subduction zone environment. • The high degree of partial melting resulted in significant PPGE depletion. • The harzburgites have subchondritic Os isotopic compositions and ancient modal age. [ABSTRACT FROM AUTHOR]