Diagenesis and Metamorphism of Clay Minerals in the Helvetic Alps of Eastern Switzerland

Abstract

Abstract--Helvetic sediments from the northern margin of the Alps in eastern Switzerland were studied by clay mineralogical methods. Based on illite "crystallinity" (Ktibler index), the study area is divided into diagenetic zone, anchizone and epizone. Data on the regional distribution of the following index minerals are presented: smectite, kaolinite/smectite mixed-layer phase, kaolinite, pyrophyllite, paragonite, chloritoid, glauconite and stilpnomelane. Isograds for kaolinite/pyrophyllite and glauconite/stilpnomelane are consistent with illite "crystallinity" zones. Using the ordering of mixed-layer illite/smectite, the diagenetic zone is subdivided into three zones. The illite domain size distribution was analyzed using the Warren-Averbach technique. The average illite domain size does not change much within the diagenetic zone, but shows a large increase within the anchizone and epizone. The average illite bo value indicates conditions of an intermediate-pressure facies series.The Helvetic nappes show a general increase in diagenetic/metamorphic grade from north to south, and within the Helvetic nappe pile, grade increases from tectonically higher to lower units. However, a discontinuous inverse diagenetic/metamorphic zonation was observed along the Glarus thrust, indicating 5-10 km of offset after metamorphism. In the study area, incipient metamorphism was a late syn-to post-nappe-forming event.

Distribution of authigenic albites in a limestone succession of the Helvetic Domain, eastern Switzerland

“…The section of Nissibach contains abundant crystals of large size (200 µm in average), whereas at Milchbach they are smaller (max 130 µm and 80 µm in average) and only occur in the 2 m-thick limestone bed of the Schilt-Kalk. The presence of authigenic albite is not reported in previous studies of the region (Kugler 1987;Wang et al 1996), suggesting a geographically very restricted occurrence.…”

“…The components required for albite formation according to the isochemical model, are present in the sediments of Nissibach and Milchbach. Moreover, deep burial transformations of the clay minerals during Alpine orogenesis (Wang et al 1996) could have provided the chemical components for albite authigenesis. However, this model does not explain the restricted occurrence of authigenic albite in the region and its general scarcity.…”

“…The burial history of the region was reconstructed by Wang et al (1996) using illite crystallinity, the presence of index minerals, and the ordering of illite/smectite. In the studied area, clay mineral assemblages indicate deep burial diagenesis close to the anchizone boundary, suggesting burial temperatures around 200°C (Merriman & Frey 1999).…”

Major and trace-element composition and pressure–temperature evolution of rock-buffered fluids in low-grade accretionary-wedge metasediments, Central Alps

“…For chlorite, the values from Thusis are lower than the boundary of anchizoneepizone and indicate clearly epizone conditions. Most studies placed the anchizone-epizone boundary between 270 and 350°C (Á rkai et al 2000Frey 1987b;Merriman and Frey 1999;Wang et al 1996). The KI results from Schiers (0.29) point to a lower grade compared with Thusis and are characteristic for high anchizone conditions (subgreenschist facies, 250-280°C; Mullis et al 2002).…”

Influência da pressão e temperatura na cristalinidade da illita em sequências Proterozoicas: Norte do Distrito Federal e Goiás, Brasil

“…As transformações da esmectita para illita e desta para muscovita, condicionadas pelo aumento de temperatura e pressão, começaram a ser mais detalhadamente estudadas a partir da década de 1960, com o intuito de definir a zona diagenética e a anquizona (Kübler 1968;Dunoyer de Segonzac 1969;Hower et al 1976;Boles & Franks 1979;Singer & Müller 1983;Hillier 1989;Velde & Vasseur 1992;Leoni et al 1996;Wang et al 1996;Dudek & Srodon 2003;Srodon et al 2009), bem como o limite do metamorfismo de baixo grau (Kisch 1983;Frey 1987;Jahren & Aagard 1992;Árkai et al 1996;Warr & Nieto 1998;Jaboyedoff et al 2001;Lee & Lee 2001;Abad et al 2003;Kamp 2008), inclusive quando há influência de esforço tectônico (Hoffman & Hower 1979;Eslinger & Sellars 1981;Piqué 1982;Akande & Erdtmann 1998;Poyatos et al 2001).…”