Sequence and tectonic deformation process of metamorphic complex in the Larsemann Hills, East Antarctica

The Larsemann Hills are located on the eastern coast of the Prydz Bay in East Antarctica. Based on large-scale geological mapping, metamorphic complex in the Larsemann Hills was found to be layered orderly in general, and therefore, the Larsemann Group is established. The Larsemann Group is subdivided into 6 rock formations, and the protolith formation age is the Mesoproterozoic. The group has experienced the superposition of the Grenvillian and Pan-African metamorphism, and the metamorphic grade reached upper amphibolite facies to granulite facies. The main structural line in the Larsemann Hills is in the NEE-SWW strain, which generally constitutes a synclinorum structure verging to NEE. The distribution of several rock formations also shows the gradually younging from east to west. The NNW-SSE deformation of the structural line is obviously superimposed on the eastern Mirror Peninsula. The study shows that the Larsemann Group has suffered 6 periods of deformation, including the early Neoproterozoic Grenvillian period (D1), the late Neoproterozoic to early Paleozoic Pan-African periods (D2, D3, D4 and D5) and the Meso-Cenozoic extension (D6). The foliations presented in the rocks are actually the composite foliations of both the Grenvillian and Pan-African events, and the Pan-African event is demonstrated stronger than the Grenvillian event, which is rarely preserved in the gneisses. Constrained with both the metamorphic age of the Larsemann Group and the intrusion time of the Progress granite, it is believed that the D2~D5 deformations occurred during the span of 550~500 Ma. Thus, both the metamorphism and deformation features of rocks from the Larsemann Hills show that the Mesoproterozoic Larsemann Group have witnessed two orogenies of Grenvillian and Pan-African periods, respectively, and the breakup of the Gondwana.