THE LAMBERT PROVINCE OF ALKALINE-BASIC AND ALKALINE-ULTRABASIC ROCKS IN EAST ANTARCTICA - GEOCHEMICAL AND GENETIC-CHARACTERISTICS OF IGNEOUS COMPLEXES

Alkaline igneous rocks occurring in the region of the Lambert Glacier (central East Antarctica) vary from the Early Paleozoic to Paleogene i n age and show a range of chemical compositions. These rocks crop out mainly in the Prince Charles Mountains and include Early Paleozoic lam proite dikes, Late Paleozoic subalkaline dolerites, alkali lamprophyre s, trachydolerites, and Mesozoic alkaline ultrabasic rocks and kimberl ites. The youngest among them are Paleogene alkali basaltoids. The maj ority of the complexes display similar structural, compositional, and genetic features, which allowed us to describe them collectively as th e Lambert province of basic and ultrabasic alkaline rocks. The close r elations of the igneous complexes are suggested by the resemblance of their morphology (dikes, small stocklike bodies, and occasional sills) , lithological composition, structural position, and origin. Polyphase intrusions are typical of most of the complexes. The saturation of ig neous melts with fluid was established in almost all of the complexes. Fluids were of primary importance for both the partial melting of sou rce regions and melt crystallization. The majority of rocks in the com plexes belong to the potassium series. With respect to geochemical and textural features, most of the rocks are classed as lamprophyres and a ''lamprophyre'' character is, therefore, postulated for the suite of alkaline rocks occurring in this territory. Dikes of alkaline lamprop hyres are also widespread in the Vestfold Hills, 400 km east of the Pr ince Charles Mountains, but their geologic setting and Proterozoic age did not allow us to group definitely them with the Lambert province. The mineral potential of the province is related to the stocklike bodi es of ultrabasic alkaline composition in the northern Prince Charles M ountains, more specifically, to tuffisites of the first intrusive phas e, which are facially homologous to lamproite breccias from Western Au stralia; the most promising may appear the southern part of the region .