ZIRCON U-Pb AGES, Hf ISOTOPIC CHARACTERISTICS AND THEIR IMPLICATIONS OF THE EARLY PALEOZOIC GRANITES IN THE NORTHEASTERN DA HINGGAN MTS., NORTHEASTERN CHINA

Abstract

The Paleozoic granites in the Ergun block, exposed in the northeastern Da Hinggan Mts., northeastern China, are of I-type. Zircon U-Pb dating by LA-ICPMS technique indicates that the Shibazhan, Neihe and Baiyinna plutons were emplaced with ages of 499 ± 1,500 ± 1 and 460 ± 1Ma; whereas the Chalabanhe pluton was formed by several pulses with age between 465-481 Ma. Considering other previously reported age data, it is proposed that the granitic magmatism in the northeastern Da Hinggan Mts. during the Early Paleozoic took place at 460-50OMa. Zircon Hf analyses conducted by LA-MC-ICPMS show that these granites have εHf(t) values of +1.5 ∼ +3.8 with Hf modal ages of 1.1 ∼ 1.4Ga, indicating that the crust in the Ergun block was extracted from mantle during Meso-Neoproterozoic, which is much different from the Xing'an block to the south, in that it shows a characterized Phanerozoic crustal age.