How to interact between mantle and crustal components in the subduction zone?

May 24, 2019

The initiation of plate subduction on Earth may occur before 3 billion years ago or even Hadean. Subduction is the core process of plate tectonics, which gradually lead to the co-evolution of hydrosphere, atmosphere and biosphere with solid Earth, and realizes the material circulation and energy exchange between the spheres. According to the different tectonic attributes of the subduction zone, it can be divided into different mantle environments of oceanic-oceanic, oceanic-continental and continental-continental subduction zones. The mantle sections of supra-subduction zone (SSZ) ophiolites and mantle-wedge-type (MWT) orogenic peridotites represent the mantle fragments from oceanic and continental lithosphere in subduction zones, respectively. They are essential targets to study the crust-mantle interaction in subduction zones. The SSZ ophiolites can record melt/fluid-rock interaction, metamorphism, deformation, concentration of metallogenic elements and material exchange between crust and mantle, during the stages from the generation of oceanic lithosphere at spreading centers to the initiation, development, maturation and ending of oceanic subduction at continental margins. The MWT orogenic peridotites reveal the history of strong metamorphism and deformation during subduction, the multiple melt/fluid metasomatism, and the complex cycling of crust-mantle materials, during the subduction/collision and exhumation of continental plates.

The paper entitled "Subduction-zone peridotites and their records of crust-mantle interaction " was recently published in 2019(7) issue of Science China: Earth Sciences, written by Professor Zheng Jianping, China University of Geosciences (Wuhan). This study summarizes research progresses in terms of subduction-related peridotite massifs in the world, reveals the complex deformation and metamorphism process, the interaction of melt/fluid with crust-mantle rocks and the material circulation process in different stages of subduction zones from generation to maturity and even to extinction.

Along the slab/mantle interface in a subduction zone, strong and complex physical mixing, the exchange of crust-mantle materials and melt/fluid activities occur between the subducting slab and the mantle wedge. These processes can cause the large-scale tectonism, metamorphism, magmatism and mineralization along convergent plate boundaries. The mantle wedge is an important unit of a subduction-zone system. This wedge-shaped mantle is located between the subducting slab and the overlying crust, and connects the processes of material cycling and crust-mantle interaction in the Earth's interior. The crust-mantle physical interactions in the subduction channel are mainly manifested in the formation me?lange complexes by mechanical mixing of various rocks, the cracks and shear zones in mantle wedge peridotites, the plastic/brittle deformation in rocks and minerals, and the hydration of mantle wedge peridotites, which results in an important influence on the physical properties of rocks such as density, magnetism and velocity. The major way of element exchange and material cycling between crust and mantle in a subduction zone is through chemical interactions between melts/fluids and mantle wedge rocks. Within the silicatic rock-water system under different pressures and temperatures, the melts/fluids in subduction zones can be divided into the aqueous fluids, the hydrous melts and the supercritical fluids. These crust-mantle physical interactions mainly control the geometry and tectonic associations of orogen and mantle wedge, and also constrain the physical space for crust-mantle chemical interaction. Macro- and micro-scale deformation plays an important "catalyzed" role in metamorphism, melt/fluid activities and metasomatism within the crust-mantle interface of a subduction zone.
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This research was funded by the National Natural Science Foundation of China (Grant Nos. 41520104003 & 41873032).

See the article:

Shi X F, Liu S F, Lin C F. 2019. Growth structures and growth strata of the Qianjiadian Basin in the western Yanshanfold and thrust belt, North China. Science China Earth Sciences, 62(7): 1092-1109

https://doi.org/10.1007/s11430-018-9346-6http://engine.scichina.com/doi/10.1007/s11430-018-9346-6

Science China Press

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