TERTIARY PLUTONS MONITOR CLIMATE-CHANGE IN EAST GREENLAND

The deltaD values of amphibole and biotite in Tertiary plutons in cent ral eastern Greenland decreased by approximately 30% between 55 and 50 Ma and then increased by approximately 35parts per thousand between 5 0 and 43 Ma. The deltaD values of amphibole and biotite in the plutons range from -160parts per thousand to -123parts per thousand. These lo w values reflect isotopic exchange between the igneous rocks and hydro thermal fluids that were dominated by meteoric water. The changes in m ineral deltaD values between 55 and 43 Ma are explained most plausibly by shifts in the isotopic composition of meteoric waters that fed hyd rothermal recharge areas. At 50 Ma, uplift related to the Iceland mant le plume elevated hydrothermal recharge areas by 1-2 km. High-altitude , low-deltaD meteoric waters collected by the uplifted recharge areas caused the approximately 30parts per thousand decrease in mineral delt aD values between 55 and 50 Ma. The subsequent increase in mineral del taD values from 50 to 43 Ma corresponds to widening of the North Atlan tic Ocean and a change from continental to maritime climate. Thus Tert iary plutons in central eastern Greenland represent a network of paleo climate stations that monitored the deltaD of meteoric water during op ening of the North Atlantic Ocean basin.