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Clay Minerals

Journal of Fine Particle Science


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1471-8030
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Coexistence of pyrophyllite, I-S, R1 and NH4+-rich illite in Silurian black shales (Sierra de Albarracín, NE Spain): metamorphic vs. hydrothermal origin

1 / I. Subías1

1Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain

Citation Information: Clay Minerals. Volume 45, Issue 3, Pages 383–392, ISSN (Online) 1471-8030, ISSN (Print) 0009-8558, DOI: https://doi.org/10.1180/claymin.2010.045.3.383, March 2016

Publication History

Received:
2009-07-03
Revised:
2010-03-03
Published Online:
2016-03-23

Abstract

A set of Silurian black shales from Sierra de Albarracín (NE Spain) corresponding to two different sections was studied to determine the relative influence of diagenesis, igneous activity, and regional tectonics on the clay-mineral genesis. The coexistence of pyrophyllite, I-S interstratifications (R1), ammonium-rich illite, potassium illite, kaolin, and chlorite is not the result of prograde evolution during diagenesis - very low-grade metamorphism. Three different stages may be inferred: (1) sedimentation of black shales (Aeronian, Lower Silurian, to basal Ludfordian, Upper Silurian) and the subsequent diagenetic process producing the coexistence of quartz, illite, kaolinite, organic matter, etc.; (2) intrusion of andesitic sills producing hydrothermal alteration and crystallization of pyrophyllite, ammonium-rich illites, smectite, I-S R1 phases and jarosite; and (3) and folding of shales and sills and development of penetrative schistosity during the late Variscan leading to illite and paragonite recrystallization reaching the anchizone grade.

Keywords: ammonium illite; pyrophyllite; black shales; Iberian Range; Spain

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