A structural geologic traverse through the Northern Apennines from  Rapallo to Bettola (N. Italy)

W.A. van Wamel; A.J. Bons; R.C.M.W. Franssen; W. van Lingen; W. Postuma; A.C.A. van  Zutphen

W.A. van Wamel Instituut voor Aardwetenschappen te Utrecht, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
A.J. Bons lnstituut voor Aardwetenschappen te Utrecht, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
R.C.M.W. Franssen lnstituut voor Aardwetenschappen te Utrecht, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
W. van Lingen lnstituut voor Aardwetenschappen te Utrecht, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands;
W. Postuma lnstituut voor Aardwetenschappen te Utrecht, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
A.C.A. van Zutphen British Petroleum Exploratie Maatschappij Nederland b. v., Catsheuvel 61, Den Haag, The Netherlands

Abstract

Four nappes have been distinguished in the Ligurian units of the N. Apennines between Rapallo and Bettola. The uppermost Antola Nappe is non-metamorphic. It contains a rock sequence of distant origin, that has been folded during one single phase of deformation. The immediately underlying Lavagna Nappe shows signs of very low-grade metamorphism. The constituent rock sequences originate from the Internal Ligurian Basin and have been subjected to polyphase folding and thrusting. Contrary to all later folding, the first folding phase (Fr) produced large-scale isoclinal folds that originally had a SW facing. These seem to have formed in an accretionary wedge, associated with a NE inclined subduction zone. The Mélange Nappe underlies the Lavagna Nappe. It is non-metamorphic in the area studied and contains rocks from the Bracco Zone (Ridge) and the External Ligurian Basin. Synsedimentary deformation is common in the Mélange Nappe. This nappe is also characterized by the occurrence of large-scale isoclinal recumbent folds with a NE facing. Together with gravitational sliding and spreading phenomena, this isoclinal recumbent folding seems to have been coherent with the gliding of the rock sequences, now incorporated in the Mélange Nappe, off a NE slope. The Canetolo Nappe is the lowermost thrust unit treated in this paper. It is non-metamorphic and the constituent rocks originate from the Subligurian Basin. After one phase of internal folding, the Canetolo Nappe was coupled together with the earlier stacked nappes. This pile of nappes overthrust the Tuscan units in a NE direction.