Serpentinites of the Zermatt-Saas ophiolite complex and their texture evolution |
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| Authors: | X-P Li M Rahn K Bucher |
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| Institution: | Department of Geology, School of Earth and Space Sciences, Peking University, Beijing 100871, China; Swiss Federal Nuclear Safety Inspectorate, 5232 Villigen-HSK, Switzerland; Institute of Mineralogy, Petrology und Geochemistry, University of Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany () |
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| Abstract: | The Zermatt‐Saas serpentinite complex is an integral member of the Penninic ophiolites of the Central Alps and represents the mantle part of the oceanic lithosphere of the Tethys. Metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean‐floor hydration, subduction‐related high‐pressure overprint, meso‐Alpine greenschist facies metamorphism, and late‐stage hydrothermal alteration. The early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures. The primary serpentine minerals were completely replaced by antigorite. The stable assemblage in subduction‐related mylonitic serpentinites is antigorite–olivine–magnetite ± diopside. The mid‐Tertiary greenschist facies overprint is characterized by minor antigorite recrystallization. Textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high‐pressure metamorphism of up to 2.5 GPa and 650 °C. The Zermatt‐Saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth. |
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| Keywords: | antigorite ophiolite serpentinite textures Zermatt-Saas |
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