Circum-Tethyan magmatic provinces, shifting continents and Permian climate change

Abstract

Plate tectonics plays a key role in shaping the long-term climate but on shorter time-scales large igneous provinces (LIPs) perturb the climate system through voluminous release of gases to the atmosphere. Three early Permian LIPs have been recognised globally, but geochronologic (283 to 276 Ma) and geochemical data reported here suggest a fourth, early Permian LIP (Zaduo) in North Qiangtang (central Tibet) that erupted at low southern latitudes along the eastern Tethyan margin. The late Paleozoic ice age (LPIA) lasted from about 330 to 260 Ma, but we argue here that increasing atmospheric CO2 levels and temperatures from ∼300 Ma – contemporaneous with a fast reduction in glacial frequency – was spearheaded by long-lasting circum-Tethyan LIP degassing. This process nearly ended icehouse conditions at ∼280 Ma with atmospheric CO2 levels (∼800 ppm) and tropical sea surface temperatures near glacial inception thresholds. The middle Permian (275-260 Ma) is characterized by a lowering of CO2 levels (∼400 ppm), which partly could have been related to enhanced weathering of juvenile LIP-lavas on short time-scales, but major changes in the Tethyan paleogeography, including the opening of the Neotethys from ∼275 Ma, led to the increase of exposed land in the Tethyan tropics during the middle Permian and thus enhanced silicate weathering and CO2 drawdown. Both the Emeishan LIP (∼260 Ma) and Siberian Traps (∼252 Ma) led to extraordinary climate perturbations, but the transition to a Triassic super-greenhouse we propose is linked to the radical reduction of Tethyan land areas within the tropics, at a time when the Central Pangean tropics was aridified, and that configuration led to the lowest global river runoff and silicate weathering efficiency for the entire Phanerozoic.