A METHOD OF DISCRIMINATING BETWEEN DIFFERENT TYPES OF MID-OCEAN RIDGE BASALTS AND CONTINENTAL THOLEIITES WITH THE NB1BZR1BY DIAGRAM

Abstract

Analyses of more than 1800 basaltic rocks from different geotectonic settings define a new discrimination diagram using the immobile trace elements Nb, Zr and Y. The diagram distinguishes between different types of mid-ocean ridge basalts (“MORB”, including “N-type MORB”, from normal mid-ocean ridges and “P-type MORB”, from plume-influenced regions), within-plate tholeiites (WPT), and within-plate alkali basalts (WPA). Volcanic arc basalts (VAB) plot within both WPT and N-type MORB fields and thus cannot be distinguished from these types. Ancient continental tholeiites which plot in the conventional Ti-1bZr-1bY diagram within the MORB/VAB field are clearly distinguished from N-type MORB.