Pre-Variscan evolution of the eclogitised mafic rocks from the Helvetic basement of the Central Alps

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doi: 10.1127/ejm/7/1/0057
Authors:Biino, Giuseppe G.
Author Affiliations:Primary:
Mineralogisch-Petrographisches Institut, Bern, Switzerland
Volume Title:Fourth international eclogite conference
Volume Authors:Morten, Lauro, editor
Source:European Journal of Mineralogy, 7(1), p.57-70; Fourth international eclogite conference, Fuscaldo, Italy, Sept. 6-9, 1993, edited by Lauro Morten. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:1995
Note:In English. 66 refs.; illus., incl. geol. sketch map
Summary:In the Gotthard and Tavetsch units of the central Swiss Alps, a late Proterozoic oceanic stage is inferred from the chemistry of some of the mafic and ultramafic rocks; the closure of this oceanic domain involved both accretion and subduction. Convergent tectonics were also responsible for both supra-subduction magmatism and high-P metamorphism. Wedge and arc sequences experienced several phases of metamorphism after the supra-subduction gabbroic intrusions. The oldest metamorphic event had lawsonite as key mineral phase; during the prograde path, lawsonite was replaced by kyanite + zoisite + quartz, and a higher-T eclogite assemblage formed (∼ 650-700°C). The stable assemblage at peak T wasgarnet-omphacite-kyanite-quartz-zoisite-hornblende-ilmenite-magnetite-pyrite-rutile; estimated T and minimum P at this stage are ∼700-750°C, 1.8 GPa. The eclogitic event occurred during the Ordovician. A subsequent granulite-facies event is characterized bygarnet-diopside-orthopyroxene-oligoclase-quartz-hornblende-ilmenite-magnetite-pyrite-titanite; this assemblage yields T of 600-700°C and P of ∼ 0.8 GPa. Hydration and partial melting of the metasediments accompanied the subsequent unroofing and cooling. [R.A.H.]
Subjects:Basement; Eclogite; Facies; Gabbros; Granites; Granulite facies; High pressure; High-grade metamorphism; Hydration; Igneous rocks; Intrusions; Island arcs; Lawsonite; Mafic composition; Metamorphic rocks; Metamorphism; Migmatites; Mineral assemblages; Neoproterozoic; Ordovician; Orogeny; Orthosilicates; P-T conditions; Paleozoic; Partial melting; Plate collision; Plate tectonics; Plutonic rocks; Precambrian; Pressure; Proterozoic; Silicates; Sorosilicates; Subduction; Upper Precambrian; Variscan Orogeny; Alps; Central Alps; Central Europe; Europe; Gotthard Massif; Graubunden Switzerland; Lepontine Alps; Switzerland; Tavetsch; Evolution; Igneous activity
Coordinates:N460000 N473000 E0090000 E0073000
Abstract Numbers:95M/3705
Record ID:1995021741
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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