| Summary: | The supracrustal sequence of the Rombak Basement Window, consisting of vocanic rocks and quartzites, was intruded by mafic dykes, mafic to intermediate plutons and variety of granitoid batholiths c. 1.8-1.7 Ga aga. The region has experienced amphiobolite-grade metamorphism, followed by retrogression to greenschist facies along Caledonian shear-zones.On the basis of their petrographic and geochemical characteristics the volcanic rocks can be divided into 3 suites: (1) high-Mg basalts; (2) mafic to felsic volcanites with fairly high potassium contents and with calc-alkaline affinities; and (3) low-potassium, calc-alkaline felsic volcanites. Based on major element geochemistry the evolution of the potassic volcanites is interpreted to have been controlled, in the case of mafic-intermediate varieties, by early fractionation of Fe, Mg-rich minerals, and by plagioclase crystallisation for the felsic varieties. Suites 2 and 3 are similar to associated granites and granodiorites in their chemical composition.It is concluded that the volcano-sedimentary and intrusive rocks were formed in an lower Proterozoic mature magmatic arc environment at the southern margin of a continent composed predominantly of Archean tonalitic granitoid rocks and Lower Proterozoic greenstone terranes. 36219
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