Mantle and Lower Crust Exposed in Oceanic Ridges and in Ophiolites: Contributions to a Specialized Symposium of the VII EUG Meeting, Strasbourg, Spring 1993 (Petrology and Structural Geology Book 6)

This volume follows a Specialized Symposium on "Mantle denudation in slow spreading ridges and in ophiolites", held at the XII EUG Meeting in Strasbourg, spring 1993. During the meeting it was felt that the contribu­ tions to the Symposium justified a volume presenting its main scientific achievements. The present title of the volume shows that the center of inter­ est has slightly shifted with respect to the initial objective: in order to under­ stand the processes involved in accretion taking place at oceanic ridges, it is crucial to study the interaction between uppermost mantle and lower crust. The approach favored here is that of petrological and structural analysis of oceanic rocks in present-day oceanic ridges combined with similar studies in ophiolites. Rock specimen collected by submersibles or dredge hauls in oceanic ridge environments provide a "ground truth". However, except for areas such as the MARK (Mid-Atlantic Ridge ne ar Kane fracture zone) where, thanks to multiple submersible dives, the local geology is known with aprecision even better than in many onshore ophiolites, mutual rela­ tionships between uppermost mantle and lower crust are poorly known. In contrast, onshore ophiolites provide a necessary large-scale picture built up over many years of structural and petrological mapping. Front Matter....Pages i-v Introduction....Pages 1-2 Front Matter....Pages 3-3 An Ultramafic Lift at the Mid-Atlantic Ridge: Successive Stages of Magmatism in Serpentinized Peridotites from the 15°N Region....Pages 5-34 Gabbroic Dikelets in Serpentinized Peridotites from the Mid-Atlantic Ridge at 23°20’N....Pages 35-69 Mafic and Ultramafic Intrusions into Upper Mantle Peridotites from Fast Spreading Centers of the Easter Microplate (South East Pacific)....Pages 71-120 Front Matter....Pages 121-121 Plastic Deformation of Gabbros in a Slow-spreading Mesozoic Ridge: Example of the Montgenèvre Ophiolite, Western Alps....Pages 123-145 Pre-orogenic High Temperature Shear Zones in an Ophiolite Complex (Bracco Massif, Northern Apennines, Italy)....Pages 147-161 A Detailed Study of Mantle Flow away from Diapirs in the Oman Ophiolite....Pages 163-177 Front Matter....Pages 179-179 Non Steady-State Thermal Model of Spreading Ridges: Implications for Melt Generation and Mantle Outcrops....Pages 181-214 Back Matter....Pages 215-215 The processes involved in accretion taking place at oceanic ridges are approached here via petrological and structural analysis of oceanic rocks in present-day oceanic ridges, combined with similar studies based on ophiolites, and includes present cases of slow and fast oceanic spreading and inferred analogues in ophiolites. A complementary model study of cyclic oceanic activity reconciles the extreme cases of slowly and rapidly spreading ridges. In essence, based as it is on the analysis of `real rocks', this book on mantle-crust interactions reinforces the well-known contrast between processes taking place at slow and fast oceanic ridges. Audience: Contains valuable information for scientists interested in the nature and generation of the ocean floor in present-day oceanic ridges and in their ophiolite counterparts