Isotopic composition of strontium and geologic history of the basement rocks of wright valley, southern victoria land, antarctica

Abstract

The Sr87/Sr86 ratios of whole-rock samples from the major units of the crystalline basement complex and from the tholeiitic sills of Jurassic age (Ferrar Dolerite) in Wright Valley range from 0.710 to 0.728. The isotopic composition of strontium released from these rocks by chemical weathering is compatible with an average Sr87/Sr86 ratio of 0.7149 in the brines of Lake Vanda, Wright Valley, that was reported earlier. Some strontium having Sr87/Sr86 ratios less than that of Lake Vanda probably originates as weathering products of the Ferrar Dolerite sills and of the marbles of the Asgard Formation as well as by import of marine strontium by meteoric precipitation. Whole-rock Rb-Sr age determinations indicate that the Wright Intrusives (Olympus granite-gneiss and Dais granite) approached isotopic homogenisation of strontium about 500 α 43 m.y. ago. A suite of rocks from the Victoria Intrusives (Vida granite and Vanda porphyry) was dated at about 480 α 44 m.y. The average initial Sr87/Sr86 ratios of the two suites are 0.7109 α 0.0007 and 0.7104 α 0.0008, respectively, which indicates that both magmas contained radiogenic Sr87 presumably derived from older sialic rocks in this area. These and previous age determinations and geologic field studies provide the basis for a tentative geologic history of the rocks of the crystalline basement complex. © 1974 Taylor & Francis Group, LLC.