Extrusives Of Maimecha-Kotui Western Area

Extrusive volcanic rocks are developed extensively in the northern part of the Maimecha-Kotui province along the margin of the mid-Siberian platform with the Taimyr depression (Fig. 110) in the vicinity of the Guli complex (No. 2). The overall sequence is a thick one and a number of distinct suites can be recognised (Fig. 111, inset diagram). The Aridiansk and Pravoboyarsky suites lie on middle Palaeozoic rocks, which are predominantly limestones. The Pravoboyarsky rocks, from 250 to 400 m thick, are basic pyroclastics and the 250-500 m thick Aridiansk suite comprises ultramafic alkaline rocks. At the base of the Aridiansk succession there is 25-50 m of alkaline ultrabasic tuffs above which are flows of melanephelinite, melilitite, olivine melanephelinite, limburgite and alkaline picrite with occasional layers of tuffs and gravels. Above these two suites are rocks of the Kogotsky suite the lower sequence (300-400 m) of which consists of basalts with the upper 350-500 m thick sequence formed mainly of trachybasalts and trachyandesitic basalts, but also including flows of dacite, trachyte, andesite, olivine melanephelinite and nephelinite. The uppermost Delcan suite is divided into two sequences. The 545 m thick lower sequence consists of melanephelinite and melilitite, most of which contain olivine, mela-analcimite, limburgite, augitite, alkaline picrite, basanite and tephrite. The upper sequence is 300-500 m in thickness and sharply divided from the lower by a horizon of trachytes. It consists principally of rocks of the trachybasalt-trachyte series but there are also flows of ultrabasic foidites, subalkaline picrite, andesite, trachyrhyolite and trachytic ignimbrites. At the mouth of the Delcan River the Delcan suite is overlain by high Mg ultrabasic lavas and tuffs (meimichites) which extend for more than 20 km along the right bank of the Meimecha River. Analyses of the melilite-bearing rocks, including REE and other trace elements, are presented and discussed by Gladkikh (1991).