Palaeostress and neotectonic analysis of sheared conglomerates: Southwest Alps and Southern Apennines

Geometrical and mechanical characteristics of the deformation of poorly cem ented conglomerates are described, Using striated pebbles for analysis of p alaeostresses, it is crucial to distinguish radial striation patterns. whic h result from deformation of the matrix around a rigid pebble. from unidire ctional striation patterns that represent sheer zones crossing the conglome ratic material. Examples of palaeostress determinations from striations of the latter type are given for extensional settings (Provence) and compressi onal settings (Southern Apennines, Southwest Alps). Their comparison with f ault analyses in brittle rocks that underlie the conglomerates validates th eir usefulness for palaeostress analyses and suggests that some conglomerat es behave as materials containing pre-existing surfaces of mechanical aniso tropy that fail by sliding on some suitable oriented surfaces. These exampl es show that sheared conglomerates can be used for stratigraphic dating of the deformation, for studies of syndepositional deformation and for neotect onic analysis. (C) 2001 Elsevier Science Ltd. All rights reserved.