Tertiary plutons monitor climate change in East Greenland

The δD values of amphibole and biotite in Tertiary plutons in central eastern Greenland decreased by ∼30‰ between 55 and 50 Ma and then increased by ∼35‰ between 50 and 43 Ma. The δD values of amphibole and biotite in in the plutons range from -160‰ to -123‰. These low values reflect isotopic exchange between the igneous rocks and hydrothermal fluids that were dominated by meteoric water. The changes in mineral δD values between 55 and 43 Ma are explained most plausibly by shifts in the isotopic composition of meteoric waters that fed hydrothermal recharge areas. At 50 Ma, uplift related to the Iceland mantle plume elevated hydrothermal recharge areas by 1-2 km. High- altitude, low-δD meteoric waters collected by the uplifted recharge areas caused the ∼30‰ decrease in mineral δD values between 55 and 50 Ma. The subsequent increase in mineral δD values from 50 to 43 Ma corresponds to widening of the North Atlantic Ocean and a change from continental to maritime climate. Thus Tertiary plutons in central eastern Greenland represent a network of paleoclimate stations that monitored the δD of meteoric water during opening of the North Atlantic Ocean basin.