COMPARISON OF 2.1–1.6 Ga FAULT–LINE ALKALINE METASOMATIC ROCKS AND GRANITOIDS FROM REGIONAL FAULT ZONES ON THE SOUTHERN FRAMING OF THE SIBERIAN CRATON
L.V. Kushch, V.A. Makrygina
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Alkaline metasomatic rocks, granitoids, marginal suture of the platform, feathering faults, blastocataclasis, rare–metal mineralization
Abstract
The geologic position, development stages, age, and geochemical features of metasomatic and felsic igneous rocks along the southern edge of the Siberian craton are compared. The comparison shows that all the studied metasomatic rocks are confined to the faults feathering the main suture zone of the craton. From Biryusa zone in the southwest and farther northeast, from Primor’e zone to Davan shear zone and Katugino–Ayan zone in the Aldan area, the metasomatic rocks are of similar composition but show higher mineralization. The process begins with blastocataclasis (barren stage). During the second stage, ore-bearing (Nb, Zr, Hf, and REE) potassic solutions circulate along the blastocataclastic zones. They form metasomatic potassic rocks of the early alkaline stage, expressed subalkalic granitization. The next (acid) stage is marked by the formation of greisens with Sn, Be, Th, U, and W mineralization. The igneous stage might precede or follow the metasomatism. At the time of ongoing tectonic movements, it produces rapakivi–like granites rich in the same elements. Also, a huge volcanoplutonic belt develops along the craton edge during this time. The geochemical features of its felsic volcanics are close to those of the metasomatic rocks and granites. The age of all these rocks is within 2.1–1.6 Ga.
DOI: http://dx.doi.org/10.1016/j.rgg.2014.01.014
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