Garnet granulites of Sutam River middle current sutam river (Aldan Shield) as possible indicators of metamorhosed and tectonically displaced Post-Hadean weathering crust

2017

Литосфера, Vol 17, Iss 6, Pp 5-22 (2017)

The article discusses the problem of the nature of high-alumina garnet granulites from Sutam River (Aldan Shield). The studies revealed that the majority of detrital grains have U-Pb age of up to 1.92 Ga; however the zircon grain of 3.94 Ga has been for the first time discovered in Russia. This age is estimated as the upper limit of the Hadean eon. The goals of the present studies were to reveal the petrogenesis of garnet granulites and to find out the origin of the Hadean zircon in these garnet granulites and the mechanisms of injection diapirism of garnet granulite body to the upper horizons of the crust. The comparison of garnet granulites and middle crust showed that the granulites are enriched in the whole spectrum of rare earth elements (except of Eu) as well as Al2O3, U, Th and are depleted in Na, Ca и Sr (the most mobile elements). This in combination with other geochemical indicators suggested the granulite protolith as an upper part of the allite zone of middle crust weathering, formed in arid climate. The Hadean zircon grain is regarded as having been captured from the granites of middle crust. The diapirism of garnet granulites (with the captured Hadean zircon) proceeded during the Paleoproterozoic thermotectogenesis of the Aldan shield which were accompanied by the horizontal propagation of deep-seated granite-anorthosite tectonic flows from the plume’s center to its periphery. During the movement of these flows the fragments of the lower and middle crust were shifted both laterally and vertically. When they moved vertically they were discretely intruded in the upper granite-gneiss crust (1.83-1.82 Ga) under high pressure. The 3.94 Ga zircon is comparable with the Hadean zircons from Acasta orthogneiss (Canadian shield, 4.03-3.94 Ga, SHRIMP and ID-TIMS).

article

English
Russian

A.N. Zavaritsky Institute of Geology and Geochemistry, 2017.

алданский щит, гранатовые гранулиты, средняя кора, выветривание, сравнительные геохимия, петрогенезис, геохронология, тектоника, aldan shield, garnet granulites, middle crust, weathering, comparative geochemistry, petrogenesis, geochro-nology, tectonics, Engineering geology. Rock mechanics. Soil mechanics. Underground construction, TA703-712