Neoproterozoic Crustal Reworking and Growth in the Zhangbaling Uplift, Tan-Lu Fault Zone: Evidence from the Feidong Complex and Zhangbaling Group

摘要

Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block,preserving abundant information about crustal reworking and growth.Zircon U-Pb-Lu-Hf isotope analysis was performed on material from the Feidong Complex(FDC)and Zhangbaling Group(ZBLG)of the Zhangbaling Uplift,in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks,to further provide important data for understanding the mid-Neoproterozoic crustal evolution of the Northeast Yangtze Block.The amphibolite and gneissic granites in the Feidong Complex(FDC)gave similar protolith ages of 782-776 Ma.The synmagmatic zircons exhibited variable negativeεHf(t)values of-26.9 to-8.3.Early(ca.2.4 Ga)to late Paleoproterozoic(ca.2.0-1.9 Ga)inherited zircons were found in the gneissic monzogranite,with negativeεHf(t)values of-11.2 to-7.2,indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block.Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting-related mafic magmas.The quartz-keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754-727 Ma with highεHf(t)values of-2.0 to+5.6,indicating their derivation from the reworking of juvenile crustal materials.The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable^(206)Pb/^(238)U ages(871-644 Ma)with a peak age at 741±11 Ma andεHf(t)values of-4.3 to+5.3,which is consistent with those of the Xileng Formation,but distinct from the FDC,indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation.The mid-Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block,situated in different positions from the Susong Complex and the Haizhou Group.The transition from ancient to juvenile crustal sources for felsic magmatic rocks is attributed to gradually increased crustal extension during continental rifting.