TY  - GEN
Y1  - 2011///
TI  - Long-term landscape evolution, cooling and exhumation history of Variscan rocks in the western Cantabrian Mountains (NW Spain)
N2  - The present study introduces the first comprehensive regional research of apatite-fission track (AFT) and apatite (U-Th-Sm)/He(AHe) thermochronology including state-of-the-art 3D thermokinematic modelling of longterm landscape evolution in the western termination of the Cantabrian Mountains (NW Spain). The study sets out to analyse and interpret thermochronological data to constrain the pattern and history of cooling and exhumation in the NW Iberian Massif. This allows to better resolve the potential coupling of tectonic and climatic events and their impact on long-term landscape evolution. In terms of  tectonic evolution the Cantabrian Mountains are a well-studied area, providing a well-suited domain to examine the impact of tectonic events on the topography. The mountains reach elevations of more than 2,600 m along the northern coast of Spain and are composed of a Variscan crustal section uplifted in the course of Cenozoic shortening along the northern Iberian Plate. Since the end of the Variscan orogeny in Late Palaeozoic, the Iberian Massif was affected by two major tectonic episodes, (1) Mesozoic rifting that lead to continental break-up by 115 Ma and opening of the Atlantic and Bay of Biscay to the West and North, and (2) limited convergence along the Bay of Biscay margin from Middle Eocene times onwards. The study constrains the pattern and history of exhumation within the Paleozoic bedrock and Variscan intrusions over the past c. 250 Ma. Thirty-five AFT samples reveal ages from 246.7 (26.9) to 68.1 (5.0) Ma, with mean track lengths between 10.4 (1.2) and 12.6 (1.8)µm. Six AHe samples range in age from 70.6 (5.2) to 114.4 (14.2) Ma. Timetemperature path modelling of the data indicates that continuous cooling at different rates took place during the main tectonic events that affected the area. A rapid cooling event that ended by Late Jurassic corresponds to topographic decay during unroofing of the Variscan orogen and the break-up of Pangea, and is responsible for the largest amount of exhumation at a rate of c. 0.3 km/Ma. Samples in Galicia cooled contemporaneously with rifting in the North Atlantic and Bay of Biscay during Late Jurassic to Early Cretaceous at exhumation rates of c. 0.25 km/Ma. By about 80 to 100 Ma most samples cooled below 60 °C, indicating that regional denudation has not exceeded c. 1.7 km since then, for geothermal gradients ? 27 ºC/km and a surface temperature of 15 °C. An extensive, low relief area in Central Galicia underwent very slow exhumation (0.02 km/Ma) since post-rift stage (80 to 100 Ma), and is interpreted as the remains of a pre-Eocene paleolandscape. Surface uplift of a ridge next to the northern coastline since late Middle Eocene caused minor exhumation during activation of the North Iberian margin. This ridge that reaches heights up to 1,000 m seems to be associated to reactivation of an inherited 60 to 80 Ma old escarpment. An average exhumation rate between 0.02 to 0.07 km/Ma reflects latest denudation as the new mountainous relief developed since incipient subduction along the northern Iberian Margin by 46 Ma due to shortening associated with convergence along the northern Iberian Plate. Reasonable estimates on the initial maximum mean elevation of the area after the end of the Variscan orogeny are determined between 2,400 and 3,400 m by 3D thermokinematic modelling. The strong coincidence between timing of major tectonic events and changes in topography and exhumation rates suggest that the major controlling factor of landscape evolution in this area is tectonic forcing while climatic effects have probably only a second order impact.
ID  - heidok11667
A1  - Grobe, René Wilhelm
AV  - public
KW  - Thermochronologie 
KW  -  Apatit-Spaltspur 
KW  -  3D thermokinematische Modellierung low-temperature thermochronology 
KW  -  long-term landscape evolution 
KW  -  Cantabrian Mountains 
KW  -  apatite fission-track 
KW  -  3D thermokinematic modelling
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/11667/
ER  -