Microtextures and the Origin of Muscovite-Kaolinite Intergrowths in Sandstones of the Utrillas Formation, Basque Cantabrian Basin, Spain

Abstract

Abstract--Muscovite-kaolinite intergrowths found in Albian sandstones of the Basque Cantabrian basin (northern Spain) were studied by optical, scanning and electron microscopy and electron microprobe analysis. Kaolinitization begins at grain edges, forming the characteristic fanned-out textures, and propagates toward the interior along the cleavages of muscovite. Kaolinite and muscovite occur as thick packets, being free of interlayering. Phase boundaries between both minerals show bidimensional crystallographic continuity, and no intermediate phases have been identified. The data obtained suggest that muscovite only supplied a template suitable for the epitactic crystallization of kaolinite, while A1 was available in sufficient amounts due to the dissolution of detrital K-feldspar. Very small packets of magnetite or maghemite showing a coherent orientation with the kaolinite crystals have been recognized, and could be responsible for the small Fe contents usually detected in electron microprobe analyses of kaolinite.Textural relationships between authigenic kaolinite and deformation microstructures in the intergrowths, combined with previous information about burial conditions, show that alteration proceeded during a late stage of the diagenetic history, related to the uplift of the studied materials as a result of the Alpine orogeny.

Growth and albitization of K‐feldspar in crystalline rocks in the shallow crust: a tracer for fluid circulation during exhumation?

“…4). Another is the growth of kaolinite within muscovite during diagenesis, resulting in deformation and displacement of the topotactic mica template (Arostegui et al . 2001).…”

“…It might be postulated that the (0 0 1) face of the sheet silicate grain provides a suitable substrate, similar to that proposed for the growth of kaolinite within muscovite (Arostegui et al 2001). However, there are several problems with this.…”

Outlining the thermal posdepositional evolution of the Ordovician successions of northwestern Argentina by clay mineral analysis, chlorite geothermometry and Kübler index.

“…Kaolinite also partly replaces detrital muscovite laths, showing displacive precipitation along the cleavage planes, leading to "fanning" along the edges of the mica flakes (Fig. 4c, below centre) (De Ros, 1998;Arostegui et al, 2001). Accessory phases include scarce apatite and rutile.…”

“…All these retrograde-diagenetic clay-minerals show a texture parallel or sub-parallel to the original metamorphic phyllosilicates. They are the result of epitaxial and/ or topotaxial reactions (e.g., Arostegui et al, 2001), therefore they inherit the same crystallographic orientation of the mother phases (Nieto et al, 1994; hence a distinction between metamorphic and retrograde phyllosilicates, based only on their orientation is impossible.…”

Progressive Formation of Halloysite From the Hydrothermal Alteration of Biotite and the Formation Mechanisms of Anatase in Altered Volcanic Rocks From Limnos Island, Northeast Aegean Sea, Greece

“…Banfield and Eggleton, 1990;Jiang and Peacor, 1991;Dong et al, 1998;Arostegui et al, 2001;Ece and Schroeder, 2007). Previous investigations revealed that micas can alter by weathering to both halloysite and kaolinite (e.g.…”