How are the Alpine ophiolites different from the Caledonian ophiolitic mélanges?

How are the Alpine ophiolites different from the Caledonian ophiolitic mélanges? Mohn,G., Jakob,J., and Andersen T.B. Both the Caledonian and Alpine belts preserve extensive exposures of ophiolitic sequences. These ophiolitic sequences have been variably interpreted to represent tectonic mélanges or vestiges of either supra-subduction zone spreading ridges or continent-ocean transition zones, among other hypotheses. In this regard, the Alpine ophiolites consist of serpentinised mantle, ophicalcites in relation with fluid circulation, minor magmatic intrusions, tectono-sedimentary breccias and deep-marine sedimentary systems. Such lithostratigraphic association is interpreted as the remnants of the former continent-ocean transition of the Alpine Tethys that formed during the final stage of the Mesozoic rifting. In comparison, several distinct ophiolitic belts can be identified in the Scandinavian Caledonides. The structurally uppermost ophiolitic assemblages are associated with magmatic arc complexes and have been related to an intra-oceanic subduction zone. Located in a structurally lower position, another ophiolitic belt has been recognized in between the continent-derived Jotun-Lindås-Dalsfjord nappe complexes and the Baltica continent. The structurally lower ophiolitic belt, previously recognized as a tectonic mélange, contains numerous solitary metaperidotite bodies embedded in micaschists that are locally associated with mafic rocks. This ophiolitic sequence also contains locally fossiliferous conglomeratic layers made of ultramafic materials. Recent studies already recognized the similarities with the Alpine ophiolites and reinterpreted these tectonic mélanges as the remnants of the former Continent-Ocean Transition of Baltica. In that perspective, the aim of this contribution is to compare and confront fundamental observations from the Alpine ophiolites with key localities of the Caledonides that are particularly well exposed in the Southern Caledonides (Vågåmo, Otta, Lesja areas). We will detail the similarities but also the differences between the Alpine and Caledonian ophiolites and critically discuss some implications for the architecture of the Pre-Baltica margin and its reactivation during the Caledonian orogeny.