Titanian clinohumite formation in the Zermatt-Saas ophiolites, Central Alps

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Titanian clinohumite (Ti-Chu) represents a stable constituent of the greenschist facies assemblage antigorite (Atg)-forsterite (Fo)-diopside (Di)-magnetite (Mag) in serpentinites of the Zermatt area, Central Switzerland. The...

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Bibliographic Details
Published in:Mineralogy and petrology 1998-03, Vol.64 (1-4), p.1-13
Main Authors: Rahn, M. K., Rahn, K.
Format: Article
Language:English
Subjects:
Geology
High temperature
Lithosphere
Metamorphism
Minerals
Plate tectonics
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Summary:(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Titanian clinohumite (Ti-Chu) represents a stable constituent of the greenschist facies assemblage antigorite (Atg)-forsterite (Fo)-diopside (Di)-magnetite (Mag) in serpentinites of the Zermatt area, Central Switzerland. The red-brown fluorine-free mineral occurs as small grains within pseudomorphs after primary clinopyroxene, small corroded relics of which are still present. The clinopyroxene (Cpx) replacement by Ti-Chu can be described by a schematic reaction... The reaction transfers the CaTiAl^sub 2^O^sub 6^ component from primary Cpx to Ti-Chu, Al is transferred into antigorite. The Fe-pyroxene component is oxidized to magnetite, and pure, nearly stoichiometric diopside recrystallized as a new greenschist facies pyroxene in the serpentinite. Ti-Chu probably formed during oceanic metamorphism, based on the nature of the Ti-Chu forming reaction and the observed textures, (i.e. hydration of the oceanic lithosphere before subduction-related high-pressure metamorphism). According to recent experimental data, the stability field of Ti-Chu extends to higher temperatures than found for antigorite above a pressure of 2.3 GPa. Consequently, the phase remains stable at P-T conditions suggested for the early-Alpine subduction-related metamorphism of the area. Ti-Chu is proposed to have formed during oceanic metamorphism, and remained stable during subsequent early-Alpine subduction and later meso-Alpine greenschist facies overprint. A younger generation of coarse Ti-Chu formed under greenschist facies conditions and is found in late hydrothermal veins together with pure diopside and magnetite.[PUBLICATION ABSTRACT]
ISSN:0930-0708
1438-1168
DOI:10.1007/BF01226561