K-Ar, delta O-18 and REE constraints on the genesis of ammonium illite from the Harghita Bai hydrothermal system, Romania

• Tipo: Artigo em Revista Científica Internacional
• Data: 2010

Autores

Clauer, N (Autor) Outra; Liewig, N (Autor) Outra; Bobos, I (Autor) FCUP

Revista

Título: Clay Minerals

Vol. 45 Nº 3

Páginas: 393-411

ISSN: 0009-8558

Editora: Walter De Gruyter

Indexação

ISI Web of Knowledge - 9 Citações

Scopus - 10 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-003-31G

DOI: 10.1180/claymin.2010.045.3.393

Abstract (EN): Ammonium illite and ammonium illite-smectite mixed layers, together with potassium illite, smectite and minute amounts of kaolinite were identified in hydrothermally altered andesite rocks from the Harghita Bai area of the Eastern Carpathians, Romania. K-Ar dating and oxygen isotope tracing, as well as rare-earth elemental analyses were made to provide new information on the timing and crystal-chemical processes characterizing the crystallization and further evolution of these illite-type mineral phases. The combined results suggest the occurrence of hydrothermal activity in two distinct episodes with nucleation of two generations of illite-type particles of different chemistry and morphology. About 9.5 Ma ago, potassium illite crystallized in alteration halos of the porphyry Cu system, probably at a temperature of similar to 270 degrees C from fluids having a delta O-18 of similar to 2.9 parts per thousand (V-SMOW). Associated smectite seems to have precipitated slightly later in external alteration halos at a similar temperature, but from fluids depleted in alkalis and with a different delta O-18. Alternately, ammonium-rich illite-smectite mixed layers formed very recently, less than similar to 1 million years ago at a temperature of similar to 90 degrees C from fluids of probable meteoric origin that altered the previously crystallized potassium illite, resulting in the crystallization of a new generation of ammonium illite-smectite mixed layers. Evidence of this dissolution-precipitation process is provided by a significant increase in the delta O-18 of the mixed-layer structures and by a significant change in their REE contents and distribution patterns. Occurrence of potassium in the ammonium-rich mixed layers probably relates to the progressive alteration of the first-generation potassium illite and a discrete concomitant take up of released K by the new NH4-rich interlayers of the ammonium mixed layered sequence.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 19