Kaczmarek, M.-A.Muntener, OthmarRubatto, Daniela2015-12-071432-0967http://hdl.handle.net/1885/28007The U-Pb ages and the trace element content of zircon U-Pb along with major and trace element whole rock data on gabbroic dikes from the Lanzo lherzolitic massif, N-Italy, have been determined to constrain crustal accretion in ocean-continent transition zones. Three Fe-Ti gabbros were dated from the central and the southern part of the massif providing middle Jurassic ages of 161 ± 2, 158 ± 2 and 163 ± 1 Ma, which argue for magmatic activity over few millions of years. Zircon crystals are characterized by high but variable Th/U ratios, rare earth element patterns enriched in heavy rare earths, pronounced positive Ce and negative Eu-anomalies consistent with crystallization after substantial plagioclase fractionation. The zircon trace element composition coupled with whole rock chemistry was used to reconstruct the crystallization history of the gabbros. A number of gabbros crystallized in situ, and zircon precipitated from trapped, intercumulus liquid, while other gabbros represent residual liquids that were extracted from a cumulus pile and crystallized along syn-magmatic shear zones. We propose a model in which the emplacement mechanism of gabbroic rocks in ocean-continent transition zones evolves from in situ crystallization to stratified crystallization with efficient extraction of residual liquid along syn-magmatic shear zones. Such an evolution of the crystallization history is probably related to the thermal evolution of the underlying mantle lithosphere.Keywords: accretion; crystallization; dike; emplacement; gabbro; Jurassic; magmatism; ocean-continent transition; plagioclase; rare earth element; shear zone; thermal evolution; trace element; uranium-lead dating; zircon; Eurasia; Europe; Italy; Southern Europe Lanzo massif; Oxyde gabbros; Peridotite; Piemont-Ligurian ocean; SHRIMP; Trace element geochemistry; U-Pb dating; Zircon200810.1007/s00410-007-0243-32015-12-07