Influence of plastic deformations in zircon on its chemical composition: Evidence from gabbroids of the spreading zone of the Mid-Atlantic Ridge, Markov trough, 6° N

Zircon is considered to be one of the most stableminerals of rocks and is the main mineral used for rockdating by the U–Pb method. Interest in study of thismineral has increased significantly during the past fewyears in the context of the possibilities discovered fordating individual grains on ion microprobes. Theproblem of interpretation of the dating resultsobtained has become more important.Determination of zircon genesis is based on thecrystal habit, zonation type, and geochemical peculiarities. It is not considered that the idiomorphicshape of the crystal is not always primary, but may beformed as a result of recrystallization. Study of themorphology and internal structure of zircon usingcathode luminescence (CL) demonstrated that thediversity of zircon morphology was controlled byrepeated structural metamorphic transformations ofthe parental magmatic rocks [1, 2].The chemical stability of zircon in the course ofstructural metamorphic transformations of magmaticrocks was considered in an example of this mineralfrom olivine gabbro from the slowly spreading IndianRidge. A link between the increase of the REE diffusion rate and plastic deformation of zircon crystals wasdemonstrated [3, 4]. However morphogenetic andgeochemical alterations of zircons resulting from deformations superposed on host rocks, i.e., zircon evolutionin oceanic floor rocks, have not been studied yet.Because of this, we performed a study of zirconfrom gabbroids of the axial part of the MidAtlanticRidge (MAR) previously dated by two methods:SHRIMPII [5] and laser ablation [6]. Zircon grainswere extracted from gabbroids of the lower oceaniccrust dredged from walls of the Markov deep trough(6° N) in the axial part of the MAR, in the 10th cruiseof R/V