ECLOGITE CLASTS OF THE TERTIARY PIEDMONT BASIN, LIGURIAN ALPS, ITALY: RB-SR GEO/THERMOCHRONOLOGIC CONSTRAINTS ON EXHUMATION RATES

The Voltri Massif (VM) and Tertiary Piedmont Basin (TPB), Ligurian Alps, Italy preserve a unique geologic relationship: eclogite-facies metamorphic rocks (VM) directly overlain by sediments containing eclogite clasts (TPB). In this setting, high-precision exhumation rates, not dependent on low-temperature thermochronology, can be determined by combining the P-T-t history of eclogite clasts and the depositional age of sediments. These rates directly inform tectonic models for the assembly of the Alps and the mechanisms by which high-pressure low-temperature metamorphic rocks are exhumed. Furthermore, TPB eclogites provide information on eroded units which previously overlied the VM. However, TPB eclogite clasts are particularly intractable to U-Pb and ⁴⁰Ar/³⁹Ar dating methods. This study presents new Rb-Sr based geochronologic data for VM eclogites and TPB eclogite clasts. New Oligo-Miocene white mica-whole rock Rb-Sr dates from metasedimentary clasts agree with previous U-Pb baddeleyite dates determined from the VM. Further analysis of mafic eclogites and screening of micas based on Si content will examine the effects of greenschist retrogression on reported Rb-Sr dates.