Zircon U-Pb isotope age and Hf isotope composition of the Ea H’leo granite in Dak Lak area

Abstract

Convergent processes between South China plate and Indochina plate caused numerous granitic rocks in the Kontum massif, including the Ea H’leo granit which is assigned to the middle Triassic Van Canh complex. However, Choosing the analysis method and isotopic system plays a crucial role in determining the formation age of granit, especially in the areas where have diverse tectonic activities. With zircon U-Pb-Hf isotopes, we determine the formation age and propose the genesis of the Ea H’leo granit in this research. Ea H'leo granites have medium to large grain, commonly contain pink K-feldspar minerals, distributed in two large bodies in the northeast and southwest of Ea H'leo district, Dak Lak province. Ea H'leo granite has a major mineral composition including plagioclase (30-35%; oligoclase), orthoclase (25-35%), quartz (20-30%), biotite (5-7%) and hornblende (< 5%). Secondary minerals include zircon, apatite, sphen, and ore minerals. With the above mineral combination, Ea H'leo granite has the characteristics of I-granite. The Th/U ratio of the zircons ranges from 0.10 to 1.72, with an average of 0.8 demonstrating that these zircons are of magma origin. Partial melting of Paleoproterozoic crustal materials may be the forming mechanism for Ea H'leo I-granite formation as reflected by Hf from -11.1 to -7.7, average -9.9; TDM2 model age = 1.76 - 1.97 Ga. Formation age of U-Pb zircon by LA-ICP-MS method of Ea H'leo granite gives the result of 250 - 233 Ma, and this granite is the result of magmatic activity related to the Indosinian orogeny.