Attività tettonica recente nel Massiccio del Pollino suggerita dallo studio di speleotemi fratturati

Abstract

Fractures or anomalies along the growth axis of spelaeothems may yield valuable information on suspected tectonically active regions, when more conventional deformation markers are absent. Radiometric dating of deformed spelaeothems provides a record of continuous motion, once the tectonic nature of deformation has been assessed. Deformed spelaeothems were collected in caves of an about 20 km long stretch of the southern border of the Pollino carbonate Massif, in Northern Calabria (Southern Italy). Contrary to conterminous regions, lack of evidence of active tectonics and significant historical seismicity induced to consider this area seismically quiescent. The cave systems are aligned along-strike of a through-going fault system (Pollino Line), where recent paleoseismoiogical investigations indicated late Pleistocene and Holocene earthquake-induced slips. The investigated caves exhibit a very recent transition from phreatic to vadose conditions and are tectonically displaced from their primary spelaeo-genic and morphologic setting. This suggests a differential uplift of the carbonate block and a recent tectonic sinking of the karst base-level. At least two growing generations of spelaeothems have been distinguished on a morphological and structural basis. A recurrent east-southeast shift of growth axes of younger spelaeothems was observed in all sites, which is consistent with the overall Quaternary kinematics of this region and also of the Crati area which is more to the South. Preliminary dating indicates activity in the late Pleistocene (40 ka) and Holocene. The lack of concretion growth observed between about 40 ka and 10 ka might be preliminarily related to a reduced water supply during the glacial maximum. This is consistent with observations in continental Europe and North America, but differs from the nearby sites of the Tyrrhenian coast of Italy so as to suggest periglacial conditions at low-moderate elevations near the sea in the Pollino Massif.