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The Moon's mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang'e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: ∼ 0.3 × high-K KREEP; ∼ 5 μg/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation (<70 % fractional crystallization) and significant assimilation of KREEP materials during magma transit and eruption cannot account for the ITE contents and ratios or radiogenic isotope compositions (e.g., εNd initial of + 8 to + 9 and εHf initial of + 40 to + 46) of the CE-5 basalts; instead, partial melting of their mantle source played a dominant role. The Chang'e-5 basalt is a chemically evolved low-Ti mare basalt (Mg# of ∼ 34) with enriched KREEP-like ITE compositions but high long-term time-integrated Sm/Nd and Lu/Hf ratios, which represent a hitherto unsampled type of mare basalt. It formed by melting of an augite-rich mantle source (late-stage magma ocean cumulates containing > 30–60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (∼1–1.5 modal %, equivalent to 0.2–0.3 μg/g Th in the mantle source). The voluminous mare basalts making up the Em4/P58 unit (>1500 km3) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366–18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way. [ABSTRACT FROM AUTHOR]

Carbonate melts play an essential role in the deep carbon cycle between Earth's surface and interior. Most previous studies proposed that the source of carbonate melt resulted from the recycling of subducted oceanic slabs. Recent studies on orogenic rocks show that continental subduction may also deliver carbonate sediments into the deep mantle. However, these rocks usually have undergone complex geological processes and strong modifications during exhumation. Here we report evidence of continental subduction-triggered carbonate metasomatism of the lithospheric mantle from a suite of mantle xenoliths entrained by the Cenozoic Qixia basalts from the southeastern North China Craton (NCC). Both petrological (the same variation of mineral modal content as in carbonate melt-peridotite reaction experiments, the replacement of olivine and orthopyroxene by clinopyroxene, and the presence of apatite) and geochemical (high Ca/Al, La N /Yb N , and low Ti/Eu ratios in clinopyroxene) evidence show mantle xenoliths record obvious signals of carbonated silicate melt metasomatism. The high 87Sr/86Sr ratios of 0.7094–0.7100 in clinopyroxene of these xenoliths indicate that the carbonated silicate melt was derived from subducted continental crust rather than oceanic crust and asthenosphere mantle. The carbonated silicate melt could be produced by carbonate dissolution during continental subduction or resulted from the partial melting of the diapiric carbonate-rich sediments. An estimation suggests a carbon input flux of 14 ± 7 Mt yr−1 associated with the Yangtze continental subduction, approximately 20–50% of the estimated total carbon input flux of the global oceanic subduction. It is therefore important to include the contribution of continental subduction when deciphering deep carbon recycling and its effects. • Qixia mantle xenoliths from North China Craton suffered carbonate metasomatism. • Carbonated silicate melt was derived from the subducted Yangtze Block. • Continental subduction plays an essential role in the deep carbon cycle. • Input flux of 14 ± 7 Mt. C yr−1 is estimated during Yangtze continental subduction. [ABSTRACT FROM AUTHOR]

Formation of ultramafic cumulate rocks at the arc root serves as a key process to understanding the deep evolution of arc magma and crustal growth. However, the arc root cumulates are easy to delaminate due to their high density, making limited field exposure. Here, we conducted comprehensive petrographic observations and geochemical analysis of typical ultramafic rocks (peridotites and pyroxenites) in an ophiolitic mélange from the central Beishan orogenic belt in the southern Central Asian Orogenic Belt (CAOB). Petrographic evidence shows that these rocks exhibit characteristic adcumulate and mesocumulate textures with intercumulus minerals such as olivine, orthopyroxene, and clinopyroxene. The mineral characteristics of ultramafic rocks, including olivine and orthopyroxene with lower NiO (0.10–0.33 wt% and 0.03–0.09 wt%, respectively) and Mg# (81–87 and 86–88, respectively), clinopyroxene with higher CaO (19.0–24.7 wt%), and spinel with lower Mg# (0–49), are distinct from those of mantle rocks but resemble cumulates. Both whole rock and calculated equilibrium melt exhibit the compositions of island arc magma characterized by enrichment in large ion lithophile elements (e.g., Cs, U, Pb, and Sr) and depletion in high field strength elements (e.g., Nb, Ta, Zr, Hf, and Ti). The covariation of high Mg# and low SiO 2 in whole rocks is akin to typical arc root cumulates from classic island arcs (e.g., Kohistan and Talkeetna). The positive zircon ε Hf (t) values (+13 to +16) and calculated crystallization pressure of 0.9–1.1 GPa (∼30–40 km) support the formation of ultramafic cumulates in a juvenile island arc setting. These findings imply that most ultramafic rocks in the central Beishan orogenic belt are arc root cumulates instead of the mantle portion of an ophiolitic mélange. Fractional crystallization models suggest that arc root cumulate formation may have influenced the evolution of intermediate-felsic rocks in this area, and that the differentiation of hydrous arc magma played a crucial role in large-scale crustal growth in the southern CAOB during the early Paleozoic. • Ultramafic rocks show cumulate textures and island arc geochemical features. • These rocks are arc-root cumulates, not the mantle portion of an ophiolitic complex. • The crystallization of cumulates promotes intermediate-felsic rock formation. • Hydrous arc magma differentiation has a critical role in crustal growth in the CAOB. [ABSTRACT FROM AUTHOR]

Sulfides are accessory phases in lunar rocks but are important for understanding lunar interior processes as well as impacts on the lunar surface. Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. The Chang'e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in the northern Oceanus Procellarum. Here we study chemical and sulfur isotopic compositions (δ34S V-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with low abundances of Ni, Co, and Cu (e.g., Ni < 0.04 wt% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites are late-stage crystallization products from the highly evolved CE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal (12–36 wt% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites with noticeably higher Ni abundances (mostly > 0.2 wt% with Ni/Co of 1–3) and reconcile with the addition of meteoritic materials into the impact melts. The δ34S V-CDT of large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65 ‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slight decrease in δ34S (by ∼ 1 ‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34S of troilites in CE-5 basaltic fragments (0.35 ± 0.25 ‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21 ‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼ 0.5 ‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S (0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur contents supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon. [ABSTRACT FROM AUTHOR]