Nature and assembly of microcontinental blocks within the Paleo-Asian Ocean

Abstract

The microcontinental blocks in the CAOB include the combined NE China blocks (comprising the Erguna, Xing'an, Songliao and Jimusi-Khanka blocks) in the eastern segment of the CAOB, the Kazakhstan-Yili-Central Tianshan and Junggar blocks in the western segment of the CAOB, and the Tuva-Mongolia blocks and Beishan block in the central segment of the CAOB. The basement in these microcontinental blocks mainly consists of Archean to Paleoproterozoic crystalline rocks and/or Meso-Neoproterozoic granitoids and metamorphic complexes, indicating that most of the so-called blocks in the CAOB can be regarded as microcontinental fragments. Zircon age spectra from the eastern segment of the CAOB reveal four age peaks at 495 Ma, 780 Ma, 1825 Ma and 2600 Ma, which is similar to those recorded in the central and western segments of the CAOB. In addition, evidence of the global ‘Grenvillian’ tectonic event at 1000 Ma is also present in most blocks, indicating that the microcontinents in the CAOB have a common tectonic history. Furthermore, late Pan-African metamorphism at ~ 500 Ma affects all the microcontinents in the CAOB, with this granulite-facies event forming a single metamorphic belt that extends for > 1300 km across NE China, and named the “NE China Khondalite Belt” in the eastern segment of the CAOB. There is also a corresponding > 1000 km-long Sayang–Baikal orogenic belt along the southern margin of the Siberia Craton. We propose that the microcontinents of the CAOB originated as part of Rodinia along the global Grenville Orogenic Belt (1100–750 Ma). At 750–600 Ma, after the break-up of Rodinia, the various microcontinental blocks were located along the margin of Gondwana, close to the South China and Tarim cratons. At ~ 600 Ma, these blocks became detached from eastern Gondwana and, together with accreted complexes, drifted to the north (present-day co-ordinates) across the Paleo-Asian Ocean to the southern margin of the Siberia Craton, where collision took place during the late Pan-African. © 2017 Elsevier B.V.