Structural architecture of the Western Alpine Ophiolites, and the Jurassic seafloor spreading tectonics of the Alpine Tethys

Abstract

We present a regional synthesis of the structural architecture and tectonic evolution of the Western Alpine Ophiolites (WAO), exposed in NW Italy. The WAO represent the remnants of Alpine Tethys (Ligurian–Piedmont Ocean) that opened between Europe and Adria, and developed in four stages from the Middle Jurassic to Early Cretaceous. Emplacement of gabbroic intrusions into the extending lithospheric mantle of Europe–Adria marked the main magmatic event (Stage 1). Coalescent shear zones in the fossil upper mantle form lithospheric-scale detachment faults, which led to the exhumation of upper mantle peridotites and gabbros on the seafloor, and extensive serpentinization (Stage 2). Detachment faults, and serpentinized peridotites–gabbros in their footwalls, represent preserved fossil oceanic core complexes within the WAO. Emplacement of ophiolitic breccias and basaltic lava flows marked the syn-extensional phase (Stage 3). Radiolarian chert and limestone were deposited unconformably on this syn-extensional volcanic–sedimentary sequence, marking the post-extensional phase (Stage 4). Magmatic ages of gabbroic intrusions and mafic–felsic dykes, and depositional ages of post-extensional sequences in the WAO constrain the timing of the opening of the Ligurian–Piedmont Ocean to the Middle Jurassic ( c. 170–168 Ma), followed by a tectonic quiescence stage in the Late Jurassic–Early Cretaceous. Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection' available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways