Evidence for symmetric extension and exhumation of the Yaounde nappe (Pan-African fold belt, Cameroon)
METADATA ONLY
Loading...
Author / Creator
Date
2003-04
Publication Type
Journal Article
ETH Bibliography
yes
Citations
Altmetric
METADATA ONLY
Data
Rights / License
Abstract
It is commonly assumed that the Yaounde nappe was deformed and emplaced onto the Congo craton during two compressional Pan-African deformation phases (D₁ and D₂). A detailed field and microstructural study of the mica schists, gneisses and pyriclasites of the Yaounde nappe in the Yaounde area was carried out and it appeared, however, that the D₂ deformation phase more likely corresponds to a major N-S and moderate E-W ductile pure shear extension, rather than compression. This was inferred from the study of various strain indicators, including the geometry of shear zones, the shape of boudins, the shape of pressure shadows, the orientation of deformed veins, of fold axes, the mineral lineations, as well as the preferred orientation pattern of quartz c-axes. The P-T conditions pertaining during this extensional phase were variably recorded by the mica schists (675 °C and 9 kbar), gneisses (800 °C and 12 kbar) and pyriclasites (750 °C and 10 kbar). Pure shear extension turned into minor top-to-the-south simple shear at lower temperature during retrogression into the greenschist facies. We therefore suggest that the syn-D₂ extension associated with subsequent uplift and erosion led to (Pan-African) exhumation of the Yaounde nappe. The D₁ phase of deformation is poorly known due to strong D₂ phase overprinting. However, the high P-T conditions indicated by the metasedimentary rocks in the area suggest that D₁ was compressional. The peak conditions of the related prograde metamorphism correspond to D₁-D₂ transition at the amphibolite-granulite interface. We propose that D₁ and D₂ respectively represent the compressional and extensional phases of a Pan-African tectono-metamorphic cycle within the Yaounde nappe. © 2003 Elsevier Ltd. All rights reserved.
Permanent link
Publication status
published
External links
Editor
Book title
Journal / series
Volume
36 (3)
Pages / Article No.
215 - 231
Publisher
Elsevier
Event
Edition / version
Methods
Geographic location
Date collected
Date created
Subject
Cameroon; Pan-African orogeny; Exhumation; Granulites; Extension tectonics
Organisational unit
Notes
Received 5 February 2002, Accepted 12 March 2003.