A new method for the estimation of cooling and denudation rates using paramagnetic centers in quartz:: A case study on the Eldzhurtinskiy Granite, Caucasus

We present a new method for the assessment of the most recent cooling and denudation rates using paramagnetic centers in quartz measured by electron spin resonance (ESR) spectroscopy. These centers have a relatively low thermal stability. For cooling rates of 40 degrees and 1000 degrees C Myr(-1), effective closure temperatures vary between 55 degrees and 82 degrees C (Ti center) and 49 degrees and 64 degrees C (Al center), respectively. Samples were collected from two cores that were drilled into the Eldzhurtinskiy Granite, which has an emplacement age of similar to 2 Ma as measured by U/Pb analyses of zircons. One 1500 m core was taken from a drill hole into the dome of the granite, a second core of 4000 m from a drill hole at the base of the Baksan Valley. Our results yield cooling rates of between 160 and 250 degrees C Myr(-1) for the upper core and between 570 degrees and 600 degrees C Myr(-1) for the lower core; the corresponding denudation rates are similar to 2.5 (upper core) and 5.5mm a(-1) (lower core). The shape of the temperature profile of the lower core indicates recent erosion. When fitting the temperature data with a two-dimensional heat-transfer model, we obtain a net denudation rate of similar to 10 mm a(-1) and cooling rates in the range of 500 degrees C Myr(-1), thus confirming the cooling rates estimated by ESR. However, the ESR denudation rates underestimate the erosion rate of the Baksan Valley because the geothermal gradient is not equilibrated between the surface and the depth of the annihilation temperatures, 950 and 1800 m for the Al and Ti centers, respectively. We conclude that ESR measurements of paramagnetic centers in quartz will allow the reconstruction of landscape dynamics for the past 10-1000 kyr and that in conjunction with U/Pb, fission track, and Ar/Ar analyses it will be possible to develop dynamic models for Quaternary tectonic movements.