内蒙古阿拉善地块渣尔泰群的物源分析:区域地层限定和构造意义OA

The Zhaertai Group of the Alxa block is usually considered part of the Mesoproterozoic rift system of the North China block.However,the depositional age and provenance analysis of the Zhaertai Group have remained poorly constrained,hindering a definitive understanding of the affinity of the Alxa block's tectonic affinity.This study employs heavy mineral analysis and detrital zircon U-Pb dating to characterize the provenance of the Zhaertai Group,constrain its depositional age,and clarify the Alxa block's affiliation.The Shujigou,Zenglongchang,and Agulugou formations are characterized by distinct heavy mineral assemblages of zircon-rutile-ilmenite,tourmaline-zircon,and magnetite-zircon,respectively,suggesting derivation primarily from crystalline magmatic source rocks.Detrital zircon U-Pb dating yields maximum depositional ages of<1820 Ma for the Shujigou Formation,<951 Ma for the Zenglongchang Formation,and<1080 Ma for the Agulugou Formation.These chronological results indicate that the Zhaertai Group was deposited during the Neoproterozoic,not the Mesoproterozoic as previously assumed.The detrital zircon age spectra reveal that the～2.5 Ga,～1.95 Ga,and～1.8 Ga grains were sourced from the underlying Archean and Paleoproterozoic basement of the Alxa block.In contrast,the abundant～1.0 Ga zircons are interpreted as being derived from a distal source,potentially the Laurentian continent,reflecting inputs driven by Neoproterozoic tectonic activity.A comparison of regional detrital zircon age spectra and rock assemblages reveals distinct formation ages.Although the Zhaertai and Langshan groups in the Alxa block are Neoproterozoic,the correlative Zhaertai and Huade groups in the North China block are Mesoproterozoic.The Bayan Obo Group exhibits an intermediate Meso-to Neoproterozoic depositional age,allowing for correlation with other strata of similar age.A comprehensive analysis of the provenance of the Zhaertai Group in the Alxa block and comparative rocks in the North China block demonstrates that the Alxa block was the western extension of the North China block during the Neoproterozoic.