Zircons in gabbroids from the axial zone of the mid-atlantic ridge: U-Pb age and 176Hf/177Hf ratio (Results of investigations by the laser ablation method)

Abstract

In recent decades the evolution of novel local methods of isotopic and elemental analysis such as massspectrometry of secondary ions (SHRIMP, SIMS) and laser ablation along with inductivecou� pled plasma massspectrometry (LA-ICP-MS), which allow highly sensitive analysis of separate grains of minerals, have promoted the geochronological investigation of young rocks from ocean floor within middleocean ridges (MORs). Knowledge on the age distribution of minerals along and around the rift val� leys of MORs, where the new oceanic crust presum� ably form, would favor better understanding of dynamics of the process and establishment of its gen� eral regularities and likely anomalies. The isotopic composition of hafnium, as well as that of neody� mium, are used to determine the geochemical proper� ties of minerals and rocks that in combination with the age data provide unique versatility information on their origin. Herein we present the results of isotopic study of zircons separated from gabbroids of the axial zone of the MidAtlantic Ridge (MAR). The samples were collected within the Markov Deep from the depths 3400-4300 m between