Progressive metamorphism in a crustal-scale shear zone; an example from the Léon region, North-west Brittany, France

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Authors:Jones, K. A.
Author Affiliations:Primary:
Cheltenham and Gloucester College of Higher Education, Department of Geography and Geology, Cheltenham, United Kingdom
Volume Title:Journal of Metamorphic Geology
Source:Journal of Metamorphic Geology, 12(1), p.69-88. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 0263-4929
Publication Date:1994
Note:In English. 67 refs.; illus. incl. 7 tables, geol. sketch maps
Summary:In this area a series of metasediments, Le Conquet schists and their higher grade equivalents, occur as tectonically emplaced screens within a sequence of foliated gneisses. The sequence exhibits a steep S right arrow N increase in grade from garnet- staurolite schist to sillimanite gneiss and sillimanite-K-feldspar migmatite. Phase relations, mineral zoning and the change in mineral compositions with progressive metamorphism are consistent with mineral growth proceeding through a series of continuous reactions. Textural evidence indicates that porphyroblast growth occurred as a result of episodic operation of these continuous reactions. The stability relations amongst Al2SiO5 polymorphs indicate a considerable evolution in P-T conditions during the period of reaction progress. P-T- deformation path trajectories are consistent with the metamorphism being the product of crustal thickening by overthrusting followed by extensional collapse during thermal relaxation accommodated in the development of a crustal-scale shear zone. [R.A.H.]
Subjects:Faults; Foliation; Metamorphism; Overthrust faults; Porphyroblastic texture; Prograde metamorphism; Shear zones; Textures; Transtension; Armorican Massif; Brittany; Europe; France; Western Europe; Leon France
Abstract Numbers:94M/3820
Record ID:1994006024
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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