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 d enudation rates using paramagnetic centers in quartz measured by electron s pin resonance (ESR) spectroscopy. These centers have a relatively low therm al stability. For cooling rates of 40 degrees and 1000 degrees C Myr(-1), e ffective 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 Gra nite, which has an emplacement age of similar to 2 Ma as measured by U/Pb a nalyses of zircons. One 1500 m core was taken from a drill hole into the do me 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 degree s C Myr(-1) for the lower core; the corresponding denudation rates are simi lar to 2.5 (upper core) and 5.5mm a(-1) (lower core). The shape of the temp erature profile of the lower core indicates recent erosion. When fitting th e 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 rang e of 500 degrees C Myr(-1), thus confirming the cooling rates estimated by ESR. However, the ESR denudation rates underestimate the erosion rate of th e 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 landsca pe dynamics for the past 10-1000 kyr and that in conjunction with U/Pb, fis sion track, and Ar/Ar analyses it will be possible to develop dynamic model s for Quaternary tectonic movements.