Characterization of deep weathering and nanoporosity development in shale—A neutron study
-
Lixin Jin
,
Gernot Rother
Abstract
We used small-angle and ultra-small-angle neutron scattering (SANS/USANS) to characterize the evolution of nanoscale features in weathering Rose Hill shale within the Susquehanna/Shale Hills Observatory (SSHO). The SANS/USANS techniques, here referred to as neutron scattering (NS), characterize porosity comprised of features ranging from approximately 3 nm to several micrometers in dimension. NS was used to investigate shale chips sampled by gas-powered drilling (“saprock”) or by hand-augering (“regolith”) at ridgetop. At about 20 m depth, dissolution is inferred to have depleted the bedrock of ankerite and all the chips investigated with NS are from above the ankerite dissolution zone. NS documents that 5-6% of the total ankerite-free rock volume is comprised of isolated, intraparticle pores. At 5 m depth, an abrupt increase in porosity and surface area corresponds with onset of feldspar dissolution in the saprock and is attributed mainly to peri-glacial processes from 15 000 years ago. At tens of centimeters below the saprock-regolith interface, the porosity and surface area increase markedly as chlorite and illite begin to dissolve. These clay reactions contribute to the transformation of saprock to regolith. Throughout the regolith, intraparticle pores in chips connect to form larger interparticle pores and scattering changes from a mass fractal at depth to a surface fractal near the land surface. Pore geometry also changes from anisotropic at depth, perhaps related to pencil cleavage created in the rock by previous tectonic activity, to isotropic at the uppermost surface as clays weather. In the most weathered regolith, kaolinite and Fe-oxyhydroxides precipitate, blocking some connected pores. These precipitates, coupled with exposure of more quartz by clay weathering, contribute to the decreased mineral-pore interfacial area in the uppermost samples.
These observations are consistent with conversion of bedrock to saprock to regolith at SSHO due to: (1) transport of reactants (e.g., water, O2) into primary pores and fractures created by tectonic events and peri-glacial effects; (2) mineral-water reactions and particle loss that increase porosity and the access of water into the rock. From deep to shallow, mineral-water reactions may change from largely transport-limited where porosity was set largely by ancient tectonic activity to kinetic-limited where porosity is changing due to climate-driven processes.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
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Articles in the same Issue
- Roebling Medal Lecture. The three partners of metamorphic petrology
- Relationship between structure, morphology, and carbon isotopic composition of graphite in marbles: Implications for calcite-graphite carbon isotope thermometry
- Crystal structure, mosaicity, and strain analysis of Hawaiian olivines using in situ X-ray diffraction
- Characterization of deep weathering and nanoporosity development in shale—A neutron study
- Structural water in ferrihydrite and constraints this provides on possible structure models
- Critical evaluation of the revised akdalaite model for ferrihydrite
- Neutron diffraction study of hydrogen in birnessite structures
- Pressless split-sphere apparatus equipped with scaled-up Kawai-cell for mineralogical studies at 10–20 GPa
- Dislocation microstructures in majorite garnet experimentally deformed in the multi-anvil apparatus
- Density of carbonated peridotite magma at high pressure using an X-ray absorption method
- Stability and bulk modulus of Ni3S, a new nickel sulfur compound, and the melting relations of the system Ni-NiS up to 10 GPa
- Far-infrared spectra of synthetic [4][(Al2-xGax)(Si2–yGey)](OH,OD,F)2-kinoshitalite: Characterization and assignment of interlayer Ba-Oinner and Ba-Oouter stretching bands
- High-temperature elasticity of polycrystalline orthoenstatite (MgSiO3)
- Anatomy of a metabentonite: Nucleation and growth of illite crystals and their coalescence into mixed-layer illite/smectite
- Zn-O tetrahedral bond length variations in normal spinel oxides
- A new thermodynamic analysis of the intergrowth of hedenbergite and magnetite with Ca-Fe-rich olivine
- Raman spectroscopic investigations of some Tl-sulfosalt minerals containing pyramidal (As,Sb)S3 groups
- A first record of strong structural relaxation of TO4 tetrahedra in a spinel solid solution
- The high-pressure behavior of orthorhombic amphiboles
- XAS determination of the Fe local environment and oxidation state in phonolite glasses
- Chemical variation and significance of micas from the Fregeneda-Almendra pegmatitic field (Central-Iberian Zone, Spain and Portugal)
- Light-induced molecular change in HgI2·As4S4: Evidence by single-crystal X-ray diffraction and Raman spectroscopy
- Low-temperature electron paramagnetic resonance studies on natural calumetite from Khetri copper mine, Rajasthan, India
- Chromatite and its Cr3+- and Cr6+-bearing precursor minerals from the Nabi Musa Mottled Zone complex, Judean Desert
- Hazenite, KNaMg2(PO4)2⋅14H2O, a new biologically related phosphate mineral, from Mono Lake, California, U.S.A.
- The fractional latent heat of crystallizing magmas
