Glacioisostacy controls chemical and isotopic characteristics of tholeiites from the Reykjanes Peninsula, SW Iceland

We present chemical and isotopic data from Reykjanes Peninsula rift zone tholeiites which show dramatic changes during the past 20 kyr, effectively defining the 9–13 kyr BP period of fluctuations in glacioisostacy associated with the end of the Weichselian glaciation and the Younger Dryas readvance. During this period primitive lavas were erupted with `depletedʹ characteristics; low Nb/Zr, high 143Nd/144Nd, low 87Sr/86Sr, and low 206Pb/204Pb. We propose that the clustered eruption of these chemically and isotopically anomalous lavas is primarily a reflection of reduced crustal residence times for the parental magmas. These `depletedʹ magmas largely escaped crustal processes such as mixing, assimilation and fractional crystallisation which would overprint their distinctive chemical and isotopic characteristics. There is some evidence that the northern rift zone may also have been similarly affected during this period of rapid glacioisostatic readjustment. The parental melts to these depleted glacioisostatic lavas may only be produced during fluctuations in glaciation, or could be a normal component in all Iceland magmas.