Ammonium-bearing micas in very low-grade metapelites: micro- and nano-texture and composition

Bauluz, B. (Universidad de Zaragoza) ; Nieto, F.

Resumen: The present study examines the micro- and nano-texture and composition of an ammonium-bearing and potassium micas in very-low grade metamorphic black Silurian shales from the SE Iberian Range (NE Spain). Two organic-rich shales were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), analytical electron microscopy (AEM) and electron energy loss spectroscopy (EELS). The XRD showed the presence of two populations of micas: pure K micas with d(001) = 9.98 angstrom and ammonium-bearing micas with larger d(001) values (10.08 angstrom and 10.05 angstrom). The latter values indicate NH4 contents between 13 and 29% in the interlayer, which was confirmed by IR. Interstratifications of smectite and mica layers in the mica packets were not detected by XRD and TEM. Mica packets with sizes ranging from 100 to 250 angstrom show disordered polytypes and (001) lattice fringes that reflect the presence of K- and NH4-bearing layers (9.9-10.2 angstrom). The combination of AEM and EELS analyses on powdered and lamellar samples indicates that micas have typical dioctahedral compositions with highly variable K contents. This variation in K is consistent with the presence of K and NH4 in the interlayers, even though the NH4 and K are not distributed homogeneously; rather they are segregated in nm-sized domains in the mica interlayer.

Idioma: Inglés

DOI: 10.1180/clm.2018.8

Año: 2018

Publicado en: CLAY MINERALS 53, 2 (2018), 105–116
ISSN: 0009-8558

Factor impacto JCR: 1.787 (2018)

Categ. JCR: CHEMISTRY, PHYSICAL rank: 104 / 148 = 0.703 (2018) - Q3 - T3
Categ. JCR: MINERALOGY rank: 15 / 29 = 0.517 (2018) - Q3 - T2
Categ. JCR: GEOSCIENCES, MULTIDISCIPLINARY rank: 114 / 195 = 0.585 (2018) - Q3 - T2

Factor impacto SCIMAGO: 0.415 - Geochemistry and Petrology (Q3)

Financiación: info:eu-repo/grantAgreement/ES/DGA/E45
Financiación: info:eu-repo/grantAgreement/ES/MINECO/CGL2013-46169-C2-1-P

Tipo y forma: Article (Published version)

Área (Departamento): Área Cristalografía Mineralog. (Dpto. Ciencias de la Tierra)