Abstract
A comparative study of the zircon composition and texture in granites of a three-stage Late Cretaceous magmatism in the Chaun area, Chukotka, Russia, was conducted in biotite granites (BG), quartz monzonites-monzogranites (MG), and zinnwaldite granites (ZG). The significance of the study entails determining the mineralogical indicators of similar granitoids in areas of multi-stage petrogenesis. It is shown that in the rock series of Northern Chukotka, BG → MG → ZG, a morphological evolution of zircon takes place: a reduction in size, elongation, a growing complexity of the crystallography, and an individual texture. In later generations of zircon, as a result of the recrystallization and metasomatism, rare-metal overgrowths, defects in the crystal structure, pores and fissures, and mineral inclusions appear, whereas the crystal-face indices and patterns become more complicated. We can observe the geochemical evolution of zircon: a gradual change in the concentration of trace elements (Hf, U, Y, Th, Nb, and Ti), rare earth elements (Yb, Er, and Dy, as well as Ce and Nd), and uncommon elements (Ca and Al). Rare elements (REE, Y, Hf, Nb, U, and Th) at the post-magmatic stage of the regional history acquired economic abundances. Zircon is therefore indicative of productive ore-magmatic systems.
Highlights
Many researchers have noted the evolution of rock-forming minerals in the granitoids of the Chukchi Peninsula
The grains of biotite granites (BG) zircon are surrounded by a metamict rim, enriched in isomorphic trace-elements and micro-inclusions of U, Th, Y, and HREE minerals (Figure 2a)
Morphology of Zircon of different stages of magmatism in Northern Chukotka clearly differs in Zircon in granitoids shape and texture and forms a generation series, which includes populations of three consecutive
Summary
Many researchers have noted the evolution of rock-forming minerals in the granitoids of the Chukchi Peninsula. The evolution of accessory minerals has not been studied. A number of common accessory minerals, such as zircon, is recognized to be indicators of granitoids petrogenesis conditions, as well as of their age [1,2,3]. The determination of the mineralogical indicators of granitoids is relevant in the regions of post-orogenic magmatism, where repeated formation of granitoids of similar age and composition, combined in large plutons, occurred. These regions include Northern Chukotka, which is characterized by the facies diversity of its synchronous granitoids and the similarity of its heterochronous rocks composition [4,5]. The paper conveys a comparative analysis of zircons from granitoids of three Late
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