Genesis Of Phlogopite From Pusyerka Jadaitite,Polar Urals,Russia

Jadeitite is a kind of high pressure and low temperature metamorphic rock,which not only has important significance,but also is a kind of jewelry and jade jewelry material.Jadeite with better texture is also known as jade,and has high commercial value.The Pusyerka jadeite deposit in the Ural Syum-Keu peridotite in Polar Urals has been studied by petrographic observation,mineral chemical composition analysis and ⁴⁰Ar-³⁹Ar geochronology.The results show that jadeite,pyroxene are the main minerals of Polar Urals jadeitite,and there are also a small amount of phlogopite,amphibole and zeolite minerals.Jadeite and omphacite are showing mostly of granular and prismatic texture with subhedral and anhedral.The average chemical composition of jadeite is w(Si O₂)=58.44%,w(Al₂O₃)=22.46%,w(Na₂O)=13.89%,w(Ca O)=2.02%,w(Mg O)=1.45%,w(Fe O)=0.92%.Phlogopite is showing mostly of dark gray,flaky texture.It is veined into jadeitite fissures.Under the microscope,the phlogopite is colorless and flaky.The interference color is light green under cross-polarized light.The average chemical composition of phlogopite is w(Si O₂)=42.64%,w(Al₂O₃)=14.24%,w(Mg O)=24.46%,w(Fe O)=3.76%,w(K₂O)=8.99%.⁴⁰Ar-³⁹Ar geochronological experiments show that the age of phlogopite in the Polar Ural jadeitite is(355±2)Ma.Combined with mineralogical,petrological and previous geochronological evidence,jadeitite can be considered as the product of multi-phase fluid activity in the subduction zone.Jadeitite is produced in the orogenic belt formed by subduction of oceanic crust,so the age of the formation of jadeite also indicate the time of the happened of subduction.