17:15 〜 18:45
[SIT14-P05] Significance of Nacrite in Subducting Slabs: A Deep Earth Overview
キーワード：Subducting Slabs, Subduction Zone, Phyllosilicates, Nacrite, Kaolin group Minerals, Polytype of Kaolinite, Density Functional Theory, LLSVP, PIH, Tectonic Activity,Mantle Mechanism, Mars
The processes of magma ocean formation and solidification strongly influenced the earliest compositional differentiation of the terrestrial planets. Subsequently, this marked the starting point for cooling, which led to the onset of thermally driven mantle convection and plate tectonics. Mineral phases forming within the Earth’s mantle and core give an overview of the Earth’s formation history.
The transport of water from the subducting crust into the mantle is mainly dictated by the stability of hydrous minerals in subduction zones. Water penetrates the mantle, lowering the melting point of rocks to produce magma. These magmas rise and fill the space of lower pressure to cool and form a new crust. This crust undergoes tectonic downwelling during subduction and completes the cycle. An important part of the deep water cycle is the dehydration process in subduction zones, which controls whether water is transported into the deeper mantle or released from the slab. The thermal structure of subduction zones is the key to the dehydration of the subducting crust at different depths.
The properties of mineral phases present within provide a perspective as to how different mantle zones behave as it shows a heterogenetic behavior.
High-pressure and high-temperature experiments are extremely challenging, hence the Density Functional Theory (DFT) based computational studies are often helpful to understand deep geological processes. DFT provides a theoretical approach towards the stability of different minerals present within the interior of the earth and predicts the structural stability and physical properties, helping us better understand the deep-earth processes. We will primarily investigate the nacrite and its hydrated phase using quantum mechanical first-principles methods based on density functional theory as implemented in Quantum ESPRESSO and the VASP simulation package.
The scant information about occurrences of nacrite is not only related to the rareness of this species but is also due to the difficulty in identifying polytypes by conventional instrumental methods, especially where nacrite occurs in subordinate amounts or with other kaolin minerals. Clay minerals including nacrite are used in various industrial and environmental applications due to their unique physico-chemical properties such as high cation exchange capacity and specific surface area.
Water and aluminum incorporation has huge effects on the behavior of mantle rocks. One such category of water and aluminium-bearing minerals is clay minerals particularly kaolinite and its polytypes which can carry a huge percentage of water into the deep Earth through the subducting slabs. So naturally, a scenario of pressure-induced hydration is being created while subduction. Nacrite particularly undergoes irreversible pressure-induced hydration indicating remnants of water get stored within the layers. This water can be carried further down than the stability range of kaolinite. Therefore nacrite might play an important role in the anomalies observed in mantle behavior beyond the upper mantle. Understanding these groups of phyllosilicates would help us understand the aqueous processes that had taken place on Mars and also understand its early geological history which is very similar to Earth.
The stability ranges of the ambient and hydrated structure correspond to the various local low-velocity seismic layers within Earth indicating possible water-containing pockets in those zones. We will try to understand the structural changes associated with Nacrite as they undergo pressure-induced changes in subducting slabs through thermodynamics and electronic properties of Nacrite and its hydrated phase to understand their stability in the pressure-temperature conditions of the deep Earth.
The transport of water from the subducting crust into the mantle is mainly dictated by the stability of hydrous minerals in subduction zones. Water penetrates the mantle, lowering the melting point of rocks to produce magma. These magmas rise and fill the space of lower pressure to cool and form a new crust. This crust undergoes tectonic downwelling during subduction and completes the cycle. An important part of the deep water cycle is the dehydration process in subduction zones, which controls whether water is transported into the deeper mantle or released from the slab. The thermal structure of subduction zones is the key to the dehydration of the subducting crust at different depths.
The properties of mineral phases present within provide a perspective as to how different mantle zones behave as it shows a heterogenetic behavior.
High-pressure and high-temperature experiments are extremely challenging, hence the Density Functional Theory (DFT) based computational studies are often helpful to understand deep geological processes. DFT provides a theoretical approach towards the stability of different minerals present within the interior of the earth and predicts the structural stability and physical properties, helping us better understand the deep-earth processes. We will primarily investigate the nacrite and its hydrated phase using quantum mechanical first-principles methods based on density functional theory as implemented in Quantum ESPRESSO and the VASP simulation package.
The scant information about occurrences of nacrite is not only related to the rareness of this species but is also due to the difficulty in identifying polytypes by conventional instrumental methods, especially where nacrite occurs in subordinate amounts or with other kaolin minerals. Clay minerals including nacrite are used in various industrial and environmental applications due to their unique physico-chemical properties such as high cation exchange capacity and specific surface area.
Water and aluminum incorporation has huge effects on the behavior of mantle rocks. One such category of water and aluminium-bearing minerals is clay minerals particularly kaolinite and its polytypes which can carry a huge percentage of water into the deep Earth through the subducting slabs. So naturally, a scenario of pressure-induced hydration is being created while subduction. Nacrite particularly undergoes irreversible pressure-induced hydration indicating remnants of water get stored within the layers. This water can be carried further down than the stability range of kaolinite. Therefore nacrite might play an important role in the anomalies observed in mantle behavior beyond the upper mantle. Understanding these groups of phyllosilicates would help us understand the aqueous processes that had taken place on Mars and also understand its early geological history which is very similar to Earth.
The stability ranges of the ambient and hydrated structure correspond to the various local low-velocity seismic layers within Earth indicating possible water-containing pockets in those zones. We will try to understand the structural changes associated with Nacrite as they undergo pressure-induced changes in subducting slabs through thermodynamics and electronic properties of Nacrite and its hydrated phase to understand their stability in the pressure-temperature conditions of the deep Earth.