Petrology and zircon chronology of the Dorolj granite in Hinggan League, Inner Mongolia

Abstract：Located in the southern part of the Da Hinggan Mountains of Inner Mongolia，Dorolj granite lies on the superimposition position between ancient Asian tectonic domain, Mongol-Okhotsk tectonic domain and West Pacific plate tectonic domain. The rocks have preserved large amounts of tectonic and magmatic signatures of two orogenic events, and hence Dorolj granite is an ideal object for studying the orogenic process, evolution and post-orogenic superimposition and transformation. Dorolj granite is composed of four units, i.e., medium-fine grained monzonitic granite, coarse-medium grained monzonitic granite, syenogranite, and medium-fine grained biotite-bearing monzonitic granite. Major elements show that Dorolj granite belongs to peraluminous high K calc-alkaline rock series, and is characterized by high silicon, high alkali, peraluminous nature and low calcium. The biotite is the main dark mineral, and P2O5 decreases with increasing SiO2. These characteristics indicate that the Dorolj plutons belong to the I-type granite. The authors tried to probe into the petrology and chronology of the Dorolj granite using the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results show that the medium-fine grained monzonitic granite located on the northern side has the emplacement age of (132±0.3)Ma, whereas the syenogranite granite located in the middle part has the emplacement age of (213±1)Ma with (238±2)Ma zircon xenocrysts, indicating that there existed an early magma activity. In addition, the syenogranite located on the western side has the emplacement age of (131±1)Ma with (150±1)Ma zircon xenocrysts. Dorolj magmatic ages have a large span and can be divided into three ranges: (1) the late Triassic (213 Ma); (2) the late Jurassic (150 Ma); (3) Early Cretaceous (130 Ma). These three episodes of magma indicate an extensive environment without any subduction events. Based on the age data obtained by the authors, the Dorolj granites lack magmatism of Jurassic period. It is thus held that the Dorolj granites had nothing to do with the Mengentaolegai silver-polymetallic deposit.