Thermal and Structural History of the Pennine-Austroalpine Transition Zone, Alps (Eastern Switzerland)

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Large-scale structures in collisional mountain belts such as the Alps or Himalayas typically record shortening strains reflective of the collision of two continents. However, increasing evidence is emerging that some structures in these belts deform by extension (or stretching), a pattern opposite to the expectation. In some cases, the extension may be consequence of collapse of the high topography created by the collision. In this project, a research team from California Institute of Technology and Australian National University, will test if a major structure in the Alps deformed by extension. If so, the finding would shed new light on the complex processes that operate in major collisional mountain belts. The project would advance desired societal outcomes by: (1) full participation of underrepresented minorities in STEM through a high school mentoring program; (2) increased public scientific literacy and public engagement with science and technology through outreach activities; (3) development of a competitive STEM workforce through training of a graduate and an undergraduate student; and (4) increased partnerships through international collaboration. This project investigates the structural and low-temperature thermal history of the base of the Austroalpine allochthon in eastern Switzerland, representing the contact between the Adriatic microplate and various tectonostratigraphic units located along the southern margin of Europe. Published thermochronological and structural data in the region suggest that the fault may primarily be a normal fault, juxtaposing the allochthon against its structurally complex substrate, the Pennine Zone, at some point in early to mid-Tertiary time. In collaboration with the Australian National University, the research team will analyze eight transects across the southern part of the base of the allochthon in order to constrain the thermal histories of the Austroalpine and Penninic domains, and the structural transport direction(s) along and near the base. This project will constrain the cooling paths of from samples transects using (U-Th)/He and fission-track methods on apatite, zircon and where possible, titanite. The Australian National University group will constrain the cooling histories of the same samples, using white mica and potassium feldspar. This multiple-method approach across key contact zones will provide powerful new constraints on the origin and emplacement of the allochthon. A normal fault origin for the base of the allochthon (cold rocks emplaced over hot), if correct, will have first-order implications not only for the assembly of this iconic orogen, but for convergent orogens in general.