Discovery of Eoarchean Meta-Dioritic Rocks in Anshan Area, China and Its Geological Significance

In the Anshan area of Liaoning Province, an occurrence area of the oldest rocks in the world, the meta-dioritic rock of Eoarchaean has recently been found as enclaves in the 3.8 Ga Dongshan banded trondhjemitic rock. It has relatively high contents of REE (w(ΣREE)=149.3×10-6) and unmarked LREE enrichment over HREE (wn(La)/wn(Yb)=6.99). Eight analyzed zircon grains yield a well-defined discordia with an upper intercept of 3.65 Ga. Some of the data points give an important information of more ancient zircon existence in the rock. The rock shows unusually low ε(Nd, 3.8 Ga) values of -1.15 to -1.24 and large tDM age of 4.15-4.16 Ga. The geological significance of the discovery is briefly discussed in this paper.