Литосфера (Dec 2017)
Mineralogy of the inclusions and age of zircon from granite basement of Verkhnerechensk area (Yamal peninsula)
Abstract
The study of minerals-prisoners in accessory zircons is gradually evolving into an important geological-petrological task. Such a study can show not only the earliest mineral rock association, but also evaluate the “sealed” mineral paragenesis of zircon, which in turn indicates whether the accessory zircon is native to the host rock or redeposited (alien). In the present work, the mineralogy of zircon from granitoids of the crystalline basement of the Verkhnerechensk oil-exploration area (the southern part of the Yamal Peninsula, Western Siberia) has been studied. Granitoids are represented by homogeneous light gray fine-grained variety of biotite-quartz-feldspar composition and refer to monzoleucogranite, which formed over the sedimentary substrate, most likely under conditions of late orogenic surrounding. The time of magmatic intrusion and crystallization of granites according to the data of U-Pb dating of zircon (measurements carried out on the ion microprobe SHRIMP-II) is estimated as Late Permian (254.0 ± 3.0 (MSWD = 1.6) Ma). It is established that inclusions in zircon are represented by various minerals - fluorapatite, titanite, monazite-(Ce), albite, quartz, chamosite and calcite. The last two minerals, apparently, were not formed together with zircon, but are later secondary minerals formed as a result of the propylization of the rock. The time of secondary changes in the granitoid supposedly occurred in the Late Triassic, as one of the zircons gave a U-Pb dating of 204.7 ± 2.6 Ma. In general, accessory zircons and mineral inclusions contained in them belong to the “granite” association, and, apparently, are native to the enclosing monzoleucogranite.
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