Nature and evolution of hydrous lithospheric mantle beneath the eastern North China Craton: Implications for the heterogeneity of deep-Earth water cycling

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Water is an essential element for life and plays a pivotal role in shaping our planet. However, the behavior of water in relatively “dry” magmatic systems and its influence on crystallization processes remain enigmatic. This study delves into the micro-analytical examination of amphibole-bearing gabbroic intrusions in the northeastern North China Craton, exploring their petrogenetic relationship with contemporaneous amphibole-rich appinites. The majority of pressure data cluster at ~1.17–4.01 kbar, indicating that these crystallization processes occurred near the roof of a magma chamber at shallow crustal levels. The paragenetic assemblages comprising olivine (forsterite~72), clinopyroxene/orthopyroxene, bytownite (anorthite[An]~87), pargasite, and phlogopite denote a middle-pressure system characteristic of the olivine gabbro. The associations of clinopyroxene/orthopyroxene, andesine (An~45), and magnesio-hornblende record a shallow-pressure level for the gabbro. A peritectic relationship between clinopyroxene and amphibole suggests that the crystallization of amphibole in these gabbroic rocks is facilitated by a hydrous reaction involving water-rich residual melts and anhydrous pyroxene-dominated residues within a closed-system evolution. The source of the “damp” mantle, characterized by low water contents, is responsible for generating amphibole-bearing gabbroic rocks. The “wet” magma system, with high water contents, facilitates the crystallization of amphibole-rich appinites. Varying amounts of water from the shallow oceanic crust can be recycled into the deep upper mantle via the subduction of the Paleo-Pacific Plate, causing a heterogeneous hydrous lithospheric mantle. In conclusion, the coexistence of two distinct types of mafic intrusions, each defined by varying proportions of hydrous minerals, reveals the heterogeneity of deep-Earth water cycling.