The Tectonic Division And Evolution Of The Xilinhot Terrane

The northeast China located among the North China Craton,the Siberia Craton and the Pacific plate.This region was not only influenced by the collision of Paleo-Asian Ocean during the Paleozoic,but also influenced by the subduction of Pacific plate along the eastern margin of Asian Continent.The Xilinhot terrane of northeast China is located between the Siberia and North China Cratons and is bounded by the Hegenshan-Heihe suture to the north and the Solonker-Xar Moron suture to the south,so it plays a key role in understanding the tectonic evolution of the Paleo-Asian Ocean and the final collision between the Siberia and North China Cratons.Whether Precambrian basement occurs in the Xilinhot terrane or not remains an enigma.In this study,four samples of gneissic granites yielded weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 1371 ± 8.6 Ma,1369 ± 11 Ma,1391 ± 8.6 Ma,and 1360 ± 12 Ma,respectively.All zircon analyses of zircons give a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1375 ±5.5 Ma?n=155;MSWD=2.2?.Therefore,the Xilinhot complex is,at least in part,Mesoproterozoic.Geochemical study indicates that the samples are characterized by high contents of high field strength elements?e.g.,Nb = 7.2–20.4 ppm;Zr = 326–442 ppm?,10,000×Ga/Al values?2.6–3.5?,and Fe OT/Mg O values?4.3–4.9?.These features are comparable with those of A-type granites.We also focus on the Late Paleozoic sedimentary cover on the Precambrian basement.Samples of the Late Paleozoic formations yield detrital zircon U–Pb age populations of ².6 Ga,¹.9-1.7 Ga,¹.0-0.9 Ga,⁰.8 Ga,and ⁰.5 Ga.These populations are quite different from those of the North China Craton but similar to those of the Xing‘an and Songliao Blocks within the Central Asian Orogenic Belt.The youngest population of the Linxi formation shows a peak at ca.246 Ma,suggesting that the deposition of the Linxi Formation extended to the Early Triassic.Geochemical study indicates that these formations were generated in basins of passive continental margin.In the present study,we conclude that?1?the Xilinhot terrane is an ancient microcontinent with Mesoproterozoic basement and Late Paleozoic sedimentary cover,and not an Early Paleozoic accretionary complex as previously thought;?2?this terrane is probably the western part of the Songliao block and was likely originated from the Columbia Supercontinent;?3?in the Mesoproterozoic,the Xilinhot terrane was involved in the breakup of Columbia and located closed to the Greenland,Baltica,Congo,Siberia,and North China Cratons;and?4?in the Late Paleozoic,the Xilinhot terrane was influenced by the Early Triassic collision between the Siberia and North China Cratons.