Search results for "Crenulation"
showing 4 items of 4 documents
Flame foliation: Evidence for a schistosity formed normal to the extension direction
2007
Abstract Foliations are normally thought to develop approximately parallel to the XY-plane of the finite strain ellipsoid, i.e., perpendicular to the main shortening direction. We present a new type of schistosity named “flame foliation” that forms orthogonal to the main extension direction, approximately parallel to the YZ-plane of finite strain. Flame foliation consists of anastomosing biotite-rich selvedges overprinting S1 in pelitic layers of metaturbitites in NW Namibia. The biotite crystals in the selvedges are peculiar because they are oriented oblique or orthogonal to the flame foliation itself and parallel to the previous S1 cleavage, a feature no other foliation shows. In some cas…
Tectonic evolution of the southern Kaoko belt, Namibia
2002
Abstract The tectonic evolution at the junction of the Panafrican Kaoko and Damara belts is well recorded in the siliciclastic and carbonate successions of the Neoproterozoic Zerrissene turbidite system, metamorphosed to the biotite zone of the greenschist facies. The structures in the turbidites are attributed to two main deformational events. The older one generated two continuous folding phases, D1 and D2, and the younger one resulted in D3 deformation. D1, of dominant E–W shortening, caused upright kilometre-scale folds with well-developed axial planar cleavage, N–S trending axial planes and subhorizontal axes. This phase graded into D2 that refolded the first folds coaxialy and develop…
Polymetamorphism and ductile deformation of staurolite-cordierite schist of the Bossost Dome: indication for Variscan extension in the Axial Zone of …
2003
The Bossòst dome is an E–W-trending elongated structural and metamorphic dome developed in Cambro-Ordovician metasedimentary rocks in the Variscan Axial Zone of the central Pyrenees. A steep fault separates a northern half-dome, cored by massif granite, from an E–W-trending doubly plunging antiform with granitic sills and dykes in the core to the south. The main foliation is a flat-lying S1/2 schistosity that grades into a steeper-dipping slaty cleavage at the dome margins. Three major deformational and two metamorphic phases can be differentiated. S1/2 schistosity is an axial planar cleavage to W-vergent recumbent folding that probably occurred in mid-Westphalian time. Peak regional metamo…
Porphyroblasts and Reaction Rims
1998
A volume of rock involved in deformation and metamorphism will continuously undergo changes in structure and mineral content. This chapter treats mineral growth and replacement structures and the way in which their geometry can be used to reconstruct tectonic history. Two types of informative structures are treated: porphyroblasts and reaction rims.