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Major, trace element and Sr–Nd–Pb isotopic data of basalts emplaced during 90–40 Ma in the North and Northeast China are compiled in this review, with aims of constraining their petrogenesis, and by inference the evolution of the North China Craton during the late Cretaceous and early Cenozoic. Three major components are identified in magma source, including depleted component I and II, and an enriched component. The depleted component I, which is characterized by relatively low 87 Sr/ 86 Sr (<0.7030), moderate 206 Pb/ 204 Pb (18.2), moderately high ε Nd (∼4), high Eu/Eu ∗ (>1.1) and HIMU-like trace element characteristics, is most likely derived from gabbroic cumulate of the oceanic crust. The depleted component II, which distinguishes itself by its high ε Nd (∼8) and moderate 87 Sr/ 86 Sr (∼0.7038), is probably derived from a sub-lithospheric ambient mantle. The enriched component has low ε Nd (2–3), high 87 Sr/ 86 Sr (>0.7065), low 206 Pb/ 204 Pb (17), excess Sr, Rb, Ba and a deficiency of Zr and Hf relative to the REE. This component is likely from the basaltic portion of the oceanic crust, which is variably altered by seawater and contains minor sediments. Comparison with experimental melts and trace element modeling suggest that these recycled oceanic components may be in form of garnet pyroxenite/eclogite. These components are young (<0.5 Ga) and show an Indian-MORB isotopic character. Given the share of this isotopic affinity by the extinct Izanaghi-Pacific plate, currently stagnated within the mantle transition zone, we propose that it ultimately comes from the subducted Pacific slab. Eu/Eu ∗ and 87 Sr/ 86 Sr of the 90–40 Ma magmas increases and decreases, respectively, with decreasing emplacement age, mirroring a change in magma source from upper to lower parts of subducted oceanic crust. Such secular trends are created by dynamic melting of a heterogeneous mantle containing recycled oceanic crust. Due to different melting temperature of the upper and lower ocean crust and progressive thinning of the lithosphere, the more fertile basaltic crustal component is preferentially sampled during the early stage of volcanism, whereas the more depleted gabbroic lower crust and lithospheric mantle components are preferentially sampled during a late stage. This model is consistent with a protracted destruction process of the lithosphere beneath eastern China. The presence of significant recycled oceanic crust components in the 90–40 Ma basalts highlights the influence of Pacific subduction on the deep processes in the North China Craton, which can be traced back at least to the late Cretaceous. This, along with the conjugation of crustal deformation pattern in this region with the movement of the Pacific plate, makes the Pacific subduction as a potential trigger of the destruction of the North China Craton. [ABSTRACT FROM AUTHOR]

Abstract: Hydrothermal fluid geochemistry and mineralization timing are two important factors in the genesis of a hydrothermal deposit. 40Ar/39Ar analyses of fluid inclusions not only provide time constraints for the mineralization but also help to clarify the K–Ca–Cl–Ar characteristics for the ore-forming fluids. In this study, six sphalerite samples collected from the Fankou lead–zinc sulfide deposit are investigated by 40Ar/39Ar in vacuo crushing. Gases liberated from the early and late crushing steps exhibit distinct Ar isotopic compositions and 40Ar/39Ar apparent ages. Argon released in the early steps has much higher 40Ar and 38ArCl and lower 37ArCa contents than those in the late steps. The significant excess Ar (40ArE) extracted in the early crushing steps shows a strong correlation with 38ArCl with very high 40ArE/38ArCl ratios. In contrast, those of the late steps mainly consist of atmospheric Ar and K-correlated radiogenic Ar with a constant 40ArR/39ArK ratio and the atmospheric initial 40Ar/36Ar ratio. As a result, all samples yield similar declining age spectra: the fore segments with anomalously old apparent ages decline quickly in the early crushing steps and the rear ones are flat with concordant apparent ages in the late crushing steps. The data points of the early steps define linear correlations in plots of 40ArNA/39ArK vs. 38ArCl/39ArK and 38ArCl/40ArNA vs. 39ArK/40ArNA (NA for non-atmospheric) and most yield ages of 240–230Ma. On the other hand, the data of the late steps always construct well-defined isochrons in the plots of 36ArA/40ArNA vs. 39ArK/40ArNA with consistent ages of ∼300Ma. We interpret that gases released in the early steps were from the secondary fluid inclusions (SFIs) due to their distribution characteristics along cracks leading to be easily extracted, and those released in the later steps represented the contribution of the primary fluid inclusions (PFIs). The initial 40Ar/36Ar ratios of SFIs, much higher than the modern atmospheric ratio, suggest that their fluids were most likely from deep sources. However, these ratios of PFIs, close to the modern atmospheric ratio, might imply that the ore-forming fluids were mainly meteoric. Accordingly, our results show that a major lead–zinc mineralization occurred at about 300Ma and a subsequent hydrothermal interruption at 240–230Ma. The sphalerite 40Ar/39Ar crushing results suggest that the ore-forming fluid might strongly interact with the sedimentary rocks resulting in the enrichment of ore deposit. [Copyright &y& Elsevier]