Basement nature and origin of the Junggar terrane: New zircon U–Pb–Hf isotope evidence from Paleozoic rocks and their enclaves

Abstract

The question of whether the Junggar terrane in the central area of the Central Asian Orogenic Belt (CAOB) has a Precambrian basement is one of the hottest topics surrounding the tectonic evolution of the CAOB. Recent work shows that the Central Tianshan range has a Mesoproterozoic–Neoproterozoic basement. Here, we reported the SIMS U–Pb age and Hf isotopes of zircons from newly discovered dioritic gneiss and magnetite quartzite enclaves and their host diorite dike in the Taheir area, deformed Ordovician conglomerate in the Dazigou area, and mica gneiss relicts and their host granite in the Shuangchagou area in the Junggar terrane. The results reveal the following evidence: 1) the dioritic gneiss was metamorphosed from 2.52Ga diorite at approximately 1.88Ga, the magnetite quartzite interlayered with hornblende–plagioclase gneiss layers has an age of approximately 1.92Ga, and the inherited zircons from the diorite TH4-6 contain three zircon populations with upper intercept ages of approximately 3.06Ga, 1.98Ga and 1.89Ga; 2) the sienna and colorless zircon populations from the conglomerate reveal two magmatic rocks with ages of approximately 1.86Ga and 0.94Ga; and 3) the magmatic zircons that form mica gneiss have TDMC and TDM2 ages ranging from 1.2Ga to 2.08Ga, and the inherited zircons from the mica gneiss and granite in the Shuangchagou area contain five zircon populations with upper intercept ages of approximately 2.48Ga, 1.80Ga, 1.47Ga,1.14Ga and 0.96Ga.By combining the published U–Pb ages and Hf isotope data of zircons from the Junggar terrane, it is suggested that the Junggar terrane has three Precambrian basement units, including the 2.1–1.7Ga Taheir–Kalamaili–Dazigou reworked Archean crust, the 2.5–1.8Ga Shuangchagou–Luliang crust and the 1.86–1.7Ga Tianshan crust between the Aermantai subduction zone and south Tianshan suture. There is also the possibility of a 1.92Ga quartzite formation in the Taheir area, 1.9–1.8Ga orogen along the Taheir–Dazigou–Shuangchagou line, 1.47–1.40Ga granitoids in the Shuangchagou–Xingxingxia area, 1.2–1.0Ga magmatic rocks in the Dazigou–Shuangchagou area, a massive 1.0–0.9Ga magmatic–metamorphic rock belt along the Tianshan range and in the Shuangchagou–Dazigou area, and 0.8–0.6Ga magmatic rocks in the Taheir, Dazigou, Shuangchagou and Baluntai area. Regular arrangements of the three basement units and various sedimentary, magmatic and metamorphic belts indicate that the Precambrian Junggar terrane was possibly split from southern Laurentia near the Lake Superior region at 1.1Ga and adjacent to the Caborca region at 1.0–0.6Ga.