Taking thermochron samples together with Meinert Rahn high above the Magadino plain and Lago Maggiore

Current Ceneri project (funded by the FWF, start 2020)

Abstract

Collisional mountain belts frequently exhibit asymmetric patterns regarding accommodation of deformation expressed e.g. by abrupt along- and across-strike changes in collisional structure and post-collisional kinematics. A prime example of such a highly asymmetric pattern are the Central European Alps, where the Insubric Line separates high-grade amphibolite facies rocks in the north (Penninic Lepontine dome) from lowermost greenschist facies rocks (Southalpine crystalline basement) in the south. The proposed research project seeks to develop an understanding of the syn- to post-orogenic evolution of the Insubric Line, a key segment of the Periadriatic Fault System, through time and in three spatial dimensions. The long-term nature and timing of movement and denudation along and across this important fault system are critical to any tectonic model of late Alpine transpressional collision, but remain poorly understood owing to a lack of detailed geochronologic and structural data and their linking, particularly south of the fault line.

A combination of multiple established and emergent thermochronometric systems sensitive to a broad range of temperatures and time scales, will be applied aiming at (1) deciphering the vertical faulting history and the late landscape evolution of the Insubric Line based on low-temperature thermochronology data (U/Th-He and fission track methods on zircon and apatite as well as apatite 4He/3He thermochronometry) and their thermokinematic modelling, and (2) constraining the timing of brittle fault activity with LA-ICP-MS dating on slickensides hosted within the fault zone.

Dense sampling is proposed for a set of four extended (up to 20 km; three surface, one tunnel profile from the recently drilled Ceneri base tunnel) and two short (appr. 1 km) horizontal profiles across the fault line as well as two vertical profiles in the immediate vicinity of the fault, on which thermochronometric methods shall be applied. U-Pb dating of synkinematically formed minerals from the Insubric Line, in conjunction with structural fieldwork is proposed to connect information on exhumation with information on the hitherto poorly understood strike-slip motion. Since the applied low-temperature thermochronological methods also bear the potential to constrain valley formation processes, the formation of the Magadino plain, area of fault movement, fluvial and glacial incision, shall be investigated to link syn- with late- to post-orogenic processes. Such approach shall allow the construction of a time-constrained brittle evolutionary model for the Insubric Line. Such a model is expected to provide a valuable benchmark to test previously published models on the Alpine evolution along the suture zone of the orogen.

The project will build upon collaboration with several colleagues from the same department, the Universities of Göttingen, Frankfurt, Freiburg, Berlin, Tübingen, in Germany and the University of California, Berkeley in the USA.

Field work in fall 2021 with M. Rahn (left), C. v. Hagke (right) and Axel Gerdes – taking samples at Passo San Jorio