Project

Alps; Erosion; Thermochronometry

Lead
Lay summary
This project is directed to the determination of the erosion of the Adamello intrusion in the southern Alps of Italy. The Adamello intrusion is 30 Million years old, but it has been brought to the Earth's surface much more recently. We will measure the cooling ages in the mineral apatite by measuring the Uranium, Thorium and Helium. The ratio of these elements gives us the time at which the mineral cooled below 100 degrees. In addition we will meaure a profile of helium across individual apatite grains to see how much helium has diffused out of the center of the grain compared to the rim.  This can give information on the cooling of the mineral down to temperatures of 40 degrees. By measuring apatite cooling ages and rates from throughout the Adamello, we can determine the pattern of cooling and thus the pattern of erosion of the surface. We will determine whether this erosion pattern implies control by tectonic processes or climatic processes, for example related to the onset of glacial erosion 1 to 2 million years ago.

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Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

This proposal is a continuation request to continue and complete a project which was originally funded by SNF through the TOPOEurope Eurocore program of the ESF. This project was part of the THERMO-Europe CRP comprising about 10 projects. The original CRP had as its aims, the addressing of the following questions:Can we document and quantify variations in erosion rates in, and/or sediment flux from, mountain belts through time and can we link these two measurements? What resolution can we achieve in the establishment of a record of erosion rates through time?Can we establish the timing of these variations with sufficient temporal and spatial resolution to enable correlation between different study areas?Can we use this information to discriminate climatic and tectonic forcings on the topographic evolution of the region?Can we reveal changes in topography due to changing rates and processes of erosion (e.g., increased relief due to valley carving)?Can we document and model the tectonic response to changing erosion rates and topography, and can we establish couplings in the system?This proposal is for a continuation of the work started in IP3 “Late stage exhumation of the Adamello Massif”, originally awarded to Dr. Cosca at the University of Lausanne, but transferred to the ETH Zurich on Dr. Cosca’s resignation from the University. Our results to date have been valuable and intriguing, but have opened up new questions and have been unhelpful in one regard; apatite (U-Th-Sm)/He and fission-track dating, although providing good constraints for exhumation in the late Miocene, have been unable to resolve rates of younger exhumation. Given our target of resolving variations in Plio-Pleistocene exhumation, this is problematic. However, this was not entirely unanticipated in the original project concept, and was the motivation for the proposed development of the apatite 4He/3He technique, although this was to be done in an independent project (Thermo-Europe IP6). Our results to date from the Adamello show that this technique is essential if we are to address the later exhumation rates. For this reason, the student in this project (Reverman) has shifted much of her effort to completing the 4He/3He instrumentation and obtaining suitable samples for its application.To this method, we can also add the new technique of OSL thermochronometry, which has been developed in our group in the last few years (Herman et al., 2010) This is a method based on luminescence of quartz or feldspar grains which have never been exposed to surface radiation. In this case, the luminescence has an Arrhenious relationship to temperature and thus can be used as a thermochronometer. The effective closure temperature for this system is about 32°C, making it the lowest temperature thermochronometer developed to date. This development was not anticipated when the original proposal was submitted, and it provides a potentially powerful tool to address the recent exhumation.The main justification for this proposal is to conduct more extensive application of apatite 4He/3He and OSL thermochronometry in the Adamello Massif. Samples will have been collected under the initial grant and we require only the student salary and some analytical expense support to complete the analyses.