RESUMEN
This paper focuses on constraining the erosion rate in the area of the Allchar Sb-As-Tl-Au deposit (Macedonia). It contains the largest known reserves of lorandite (TlAsS2), which is essential for the LORanditeEXperiment (LOREX), aimed at determining the long-term solar neutrino flux. Because the erosion history of the Allchar area is crucial for the success of LOREX, we applied terrestrial in situ cosmogenic nuclides including both radioactive (26Al and 36Cl) and stable (3He and 21Ne) nuclides in quartz, dolomite/calcite, sanidine, and diopside. The obtained results suggest that there is accordance in the values obtained by applying 26Al, 36Cl, and 21Ne for around 85% of the entire sample collection, with resulting erosion rates varying from several tens of m/Ma to â¼165 m/Ma. The samples from four locations (L-8 CD, L1b/R, L1c/R, and L-4/ADR) give erosion rates between 300 and 400 m/Ma. Although these localities reveal remarkably higher values, which may be explained by burial events that occurred in part of Allchar, the erosion rate estimates mostly in the range between 50 and 100 m/Ma. This range further enables us to estimate the vertical erosion rate values for the two main ore bodies Crven Dol and Centralni Deo. We also estimate that the lower and upper limits of average paleo-depths for the ore body Centralni Deo from 4.3 Ma to the present are 250-290 and 750-790 m, respectively, whereas the upper limit of paleo-depth for the ore body Crven Dol over the same geological age is 860 m. The estimated paleo-depth values allow estimating the relative contributions of 205Pb derived from pp-neutrino and fast cosmic-ray muons, respectively, which is an important prerequisite for the LOREX experiment.
RESUMEN
Two morphologic settings in the northwestern Argentine prone to giant mountain-front collapse-deeply incised narrow valleys and steep range fronts bordering broad piedmonts-were analyzed through detailed investigations of fossil landslides and related fluvio-lacustrine sediments. Nine different rhyodactic tephra layers were defined by geochemical fingerprinting of glass, morphology of pumice, stratigraphic relationships, and mineralogy. The age of three tephra could be determined either directly by 40Ar/39Ar dating or relatively by 14C dating of associated sediments: Paranilla Ash (723+/-89 ka), Quebrada del Tonco Ash ( approximately 30 ka), and Alemanía Ash ( approximately 3.7 ka). These units permit correlation of several spatially separate landslide deposits. Landslide deposits in narrow valleys were generated in the late Pleistocene between 40 and 25 ka and in the Holocene since ca. 5 ka and correspond to periods characterized by increased humidity in subtropical South America. In contrast, the age of large landslides in piedmont regions is significantly greater but more difficult to define by tephrochronology. However, selected deposits from this second environment have cosmogenic nuclide exposure ages of 140-400 ka. Because of the large distance of the collapsed mountain fronts from eroding streams and because of important Quaternary displacement along the mountain-bounding faults, we suggest that strong, low-frequency seismic activity is the most likely trigger mechanism for most of the landslides in this environment.