Transpressional tectonics during the Variscan-Alpine cycle transition: supporting a multi-rifting model, evidence from the European western Southern Alps

Abstract. We delve into the transition between the Paleozoic Variscan cycle and the Meso-Cenozoic Alpine supercontinent cycle, both of which have played a pivotal role in shaping the central European-Mediterranean plate’s architecture. Our focus is on the European western Southern Alps (Varese Area, N Italy), where we documented the tectonic events occurred during this transition. Two main scenarios have been proposed so far for this transition: i) a single, long-lasting, Permo-Triassic rifting event, culminating in the opening of the Alpine Tethys, or ii) multiple, distinct rifting events, preceding the onset of the Alpine cycle. By means of a tectono-stratigraphic and thermochronological approach, we recognized a first early Permian rifting stage associated with magmatic activity, followed during the early-middle Permian by transpressive tectonics and regional-scale erosion that signal the end of the first cycle of crustal rifting. During the Middle Triassic, a second event initiated, which, we propose, marks the onset of the Alpine Tethys opening. This event could represent the stretching phase, which predates the well documented Upper Triassic crustal-thinning phase. Based on our findings, we propose that the Middle Triassic stretching phase represents the first stage of the Alpine Tethys rifting, thereby rejecting the hypothesis of a continuous Permo-Triassic long-lasting phase of extension.