T273 Advances in Mineral Sciences from Atomistic to Macro Perspectives II: Recognition of Dr. Nancy L. Ross, 2024 Roebling Medalist of the Mineralogical Society of America

Wednesday, 25 September 2024
1:30 PM - 5:30 PM
206B

THE STRUCTURE, PROPERTY, AND DETECTABILITY OF HYDROUS MINERALS IN SUBDUCTION ZONE SETTINGS

Paper number: T273-5
Program: Technical Sessions
Time: 2:20 PM – 2:35 PM

Authors

Abstract

Hydrous mineral phases play a vital role in transporting water into the deep Earth. Hydrous minerals in hydrated peridotite and hydrated sediments could be better understood in simplified MgO-SiO2-H2O (MSH) and Al2O3-SiO2-H2O (ASH) ternary systems respectively. The efficient transport of water is reliant both on the P-T path of the subducting slab and the concomitant presence of overlapping thermodynamic stabilities of relevant hydrous phases. Along warm geothermal gradients, there are often gaps between the P-T stability of low-pressure and high-pressure hydrous phases, leading to a thermodynamic “choke point”. Intermediate pressure minerals in the MSH ternary system, such as the 10 Å phase [Mg3Si4O10(OH)2.nH2O, n= no of water molecules in the interlayer region, typically, n= 2/3 to 2], are often stable at depths relevant to the “choke point” and allow for efficient transport of water. Similar to the 10 Å phase in the MSH system, the ASH system also exhibits pressure-induced hydration of kaolinite to super-hydrated kaolinite [Al2Si2O5(OH)4.nH2O]. Layered hydrous minerals are extremely anisotropic, with their interlayer region being the most compressible. Here we address the role of pressure in hydration and associated swelling of the interlayer region and present pressure-induced changes in the crystal structure of talc and kaolinite. We also examine the atomistic scale changes that prompt the crystal structure ready for interlayer hydration and their influence on the physical properties of these hydrous minerals which may be geophysically detectable at subduction zone conditions. Finally, I will demonstrate that some geophysical observations of low-velocity layers at the top of the subducting slabs could be explained by hydrous phases.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403064

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