A Late Jurassic A-type granitic-magmatic belt in the westernmost Northeast China and its tectonic implications

Abstract

The Late Jurassic tectonic environment of the Erguna-Xing'an blocks (in western Northeast China) remains poorly understood due to the complications arising from supposedly superimposed impacts on activities associated with the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean tectonic regimes. The present work investigated the latest Jurassic A-type granite (Chaganhada granite) in the southwestern Xing'an block. The Chaganhada granite was emplaced at 148 Ma. According to the observations made with the zircon saturation thermometer, the Chaganhada granitic magma has a greater magmatic temperature (>855 °C) than common I-S type granites. In addition, the geochemical characteristics of Chaganhada granite suggest the magmatic affinity of A1-type, which can be supported by high total alkalis contents (8.55%–9.50%), Zr + Nb + Ce + Y values (380–602 ppm), and 10,000*Ga/Al ratios (2.74–3.22), and low Y/Nb ratios. Low CaO + FeO + MgO + TiO2 values, CaO/(FeOt + MgO + TiO2) and K/Rb ratios and initial 87Sr/86Sr ratios (0.7048–0.7055), positive εNd(t) values (0.90–1.22), and zircon εHf(t) values (1.2–5.1) were also observed in the Chaganhada granite. Hence, the study suggests that the latest Jurassic Chaganhada A-type granite might have originated from the crustal quartz-feldspathic igneous sources. Additionally, we approximately restrict a NE-SW trending Late Jurassic A-type granitic magmatic belt in the westernmost part of NE China using data collected by this study as well as publicly available data related to zircon ages, geochemical compositions, and location of the igneous rocks in NE China. Based on the observations above, the current study infers that a Late Jurassic intense extension impacted the westernmost NE China, presumably associated with the orogenic collapse following the closure of the western part of the Mongol-Okhotsk Ocean.