INITIAL SR-87-SR-86 RATIOS OF THE KIRWAN VOLCANICS OF DRONNING MAUD LAND - COMPARISON WITH THE KIRKPATRICK BASALT, TRANS-ANTARCTIC MOUNTAINS

A series of lava flows from Mountain B (6°13.9′W, 74°06.9′S) of the Kirwan Escarpment in Dronning Maud Land, Antarctica, is composed of tholeiite basalts of Jurassic age. Their chemical compositions are similar to those of Jurassic basalts elsewhere in Dronning Maud Land but differ from those of the Kirkpatrick Basalt of the Transantarctic Mountains. The basalts on Mountain B contain 50.39% SiO2, 9.7 ppm Rb, 174.4 ppm Sr, have a Rb/Sr ratio of 0.057, and a K/Rb ratio of 417. Their average initial 87Sr 86Sr ratio is 0.7044 ± 0.0010 (1σ) which suggests that the magma from which they formed could have been derived from the upper mantle without extensive contamination with 87Sr and other elements. These results confirm earlier suggestions that the Jurassic basalts of Dronning Maud Land differ significantly from the Kirkpatrick Basalt and the Ferrar Dolerite of the Transantarctic Mountains. These differences in chemical and Sr-isotopic composition may be related to tectonic activity and magma formation during the break-up of Gondwanaland. © 1979.