华北克拉通及兴蒙造山带地壳厚度演化:来自西拉木伦河沿岸碎屑锆石U-Pb年代学的证据OACHSSCD

In this study,LA-(MC)-ICP-MS technique was employed to conduct systematic U-Pb dating and Hf isotope analysis on detrital zircons from the floodplain sediments of the Xilamulum River.The results show that 1 561 valid detrital zircons are predominantly of magmatic origin,with their U-Pb ages exhibiting a distinct multi-peak distribution.The εHf(t)values of the zircons have a wide variation range and significant temporal differences:those from the Early Paleozoic are mainly negative,while those from the Late Paleozoic are predominantly positive.Based on the Eu anomaly characteristics of approximately 1 500 zircons,the crustal thickness evolution history of the North China Craton(NCC)and the Xingmeng Orogenic Belt(XMOB)was reconstructed,both of which display distinct phased characteristics.For the NCC:crustal thickening occurred during the Early Paleoproterozoic due to subduction and accretion;crustal thinning happened between 2.3～2.0 Ga as a result of faulting and extension;crustal thickness remained stable between 2.0～1.65 Ga owing to deep-seated magmatic activities(mainly metamorphism and intrusion in the deep crust);and magmatic activity was dormant between 1.65 Ga～500 Ma.For the XMOB:its crustal thickness fluctuated during the Paleozoic;continuous crustal thickening occurred between 500～350 Ma,controlled by the subduction of the Paleo-Asian Ocean lithosphere and the closure of the ocean basin;two episodes of crustal thinning took place during 340～280 Ma and 235～200 Ma,corresponding to the development of the Xingmeng Orogenic Belt in the Early Carboniferous and the formation of the Linxi depression under the basin-and-range tectonic setting in the Early-Middle Permian,respectively;rapid crustal thickening between 270～235 Ma indicates a tectonic transition from extension to contraction.