Growth and erosion rates of the East Carpathians volcanoes constrained by numerical models: Tectonic and climatic implications

The East Carpathian volcanic range experienced an along-arc, Late Miocene to Quaternary migration of eruptive activity during its ~11 Ma-long activity. Here, a novel and complex methodology is presented that yields new geochronological and geomorphological constraints on the evolution of the 20 volcanic edifices. New unspiked K-Ar ages either constrain their lifespan (6.79 ± 0.10–6.47 ± 0.09 Ma for Seaca-Tătarca; 5.47 ± 0.08–4.61 ± 0.07 Ma for Vârghiş) or date the youngest volcanic activity (central Călimani). In parallel, numerical reconstructions of volcanic paleo-topographies were performed to quantify their shape at the end of their construction stage. The inferred initial volcano size shows a wide range (3 to 592 km3), making up the four main successive volcanic segments (910, 880, 279 and 165 km3 for Călimani, Gurghiu, North Harghita and South Harghita segment, respectively) totalizing 2200 km3 and an average growth rate of 200 km3/Ma at range-scale. At the volcano-scale, with only consideration to their respective time spans (i.e. avoiding repose periods), growth rate is characterized by two major trends: a moderate growth rate (137 km3/Ma) for the older volcanoes (11–3.6 Ma) followed by a lower growth rate (28 km3/Ma) obtained for the Plio-Quaternary volcanoes. Comparing reconstructed and current topographies yielded a total eroded volume of 524 ± 125 km3, defining averaged denudation of 22% and a 20 m/Ma erosion rate. Erosion rates for major climatic periods were computed, which highlight the contrasting climatic contexts since 11 Ma. The highest erosion rate (38 m/Ma) occurred during transitional moderate subtropical-continental climate period (9.5–8.2 Ma). An intermediate erosion rate (14 m/Ma) characterized a moderate continental climate period (8.2–6.8 Ma) when conditions became less humid. The lowest erosion rate (7 m/Ma) reflects the prevailing continental but occasionally semi-arid climate (6.8–5.8 Ma). The highest erosion rate (28 m/Ma) was obtained for Plio-Quaternary times during the interglacial/glacial cycles. Such a quantitative morphometric and geochronological approach demonstrates its efficiency to study volcanic dynamism, including both constructional and erosional processes, through time.