Zircon in Polydeformed and Metamorphosed Precambrian Granitoids from the White Sea Tectonic Zone, Russia: Morphology, Cathodoluminescence, and U-Pb Chronology

Abstract

This paper presents U-Pb isotopic data and information on the morphology of zircons from the White Sea tectonic zone, Baltic Shield. These zircons were taken from early Precambrian intrusive rocks and their metamorphic products and have revealed patterns in zircon behavior and processes of repeatedly imposed deformation and metamorphism. This study is of particular interest to those involved with U-Pb dating of zircons from repeatedly deformed and metamorphosed igneous rocks. Zircon crystals from the igneous rocks were transformed from primary prismatic forms into ovoid-isometric shapes during deformation processes under granulite and high-temperature amphibolite facies. Crystal transformation occurred just after zircon crystallization during the intrusion of hypersthene diorites at 2728 Ma and the intrusion of hornblende granodiorites at 2416 Ma. Formation of new zircon generations in the hypersthene diorites is connected with fluid mobility as the result of granodiorite intrusion at 2416 Ma and ultramet...