Abstract

The intrusive magmatic formations jion on Krong No complex are found by the geologists, the 1/50.000 geological map of Tây Sơn project described by Nguyễn Quang Lộc (editor-in-chief, 1992). Krong No complex formed the small blocks with outcrops of rock from some to tens km2. Its shaping is isometric and deformed. The Krong No complex was formed mainly along the faults, pass through formations of Jurassic sediment or sometimes pass through granodiorit of Đinh Quán formation (The Krong No region). In the study region, the granotoit of Ankroet formation was popular (Huỳnh Trung, 1984). The mainly petrographical composition are gabbro, gabbronorite. the mineral composition include: plagiocla No=55-68 (55%), clinopyroxen, orthopyroxen (0 - 10%), olivin (0 - 2%), hocblen (replace pyroxen), biotit (0 - 15%) is polychro matic: Ng = brown, Np = yellow-brown, apatit, miner. The chemical compo sition: SiO2 = 51 - 52%, TiO2 > 0.72%, Na2O = 2,90%, K2O = 1,29%. The micro elements such as: V = 0,02%, Ti = 0,5%, Mn = 0,1%, Co = 0,002%, Ni = 0,005%, Cr = 0,01%, Sn = 0,001%, Cu = 0,02%, Pb= 0,005%, Zn = 0,01% ... The instrutive formations of Krong No complex distributed in Đại Hiệp region (Lâm Đồng), Định Quán, Vũng Tàu, Cà Ná, Chứa Chan mountain (Xuân Lộc). They are arranged into the bimodal formation type which have the same age as granitoit Ankroet complex (131 million years).