【摘要】 徐淮地区矽卡岩型矿床与早白垩世岩浆活动具有密切的成因联系，区内广泛分布的早白垩世岩浆岩是研究成岩成矿作用的极佳对象。本文重点对徐淮地区旗杆楼早白垩世花岗岩开展了岩相学、同位素年代学、全岩地球化学和锆石Hf同位素组成研究，并对旗杆楼铁矿中矽卡岩开展了岩相学和年代学研究。在此基础上，剖析了花岗岩的成因及其源区属性，探讨了旗杆楼花岗岩对矽卡岩型铁矿形成的制约作用。旗杆楼花岗岩锆石LA-ICP-MS U-Pb同位素定年结果指示其形成于105.4±0.9 Ma；矽卡岩中石榴石U-Pb同位素年龄为102.2±1.6 Ma，代表了旗杆楼铁矿的成矿年龄，表明其成岩成矿作用均发生于早白垩世晚期。旗杆楼花岗岩主要由斜长石、钾长石、石英等组成，其P₂O₅（0.14%～0.19%）、A/CNK（0.68～0.97）、（Na₂O+K₂O）/Ca O（2.11～6.53）和^TFe O/Mg O（1.13～2.54）均较低，与I型花岗岩的地球化学组成特征一致。花岗岩的锆石?_Hf（t）值为-18.3～-14.7，明显低于该地区早白垩世基性侵入岩及高镁埃达克岩，指示其源区可能为古老的基性下地壳，幔源物质的贡献较小。锆石Hf同位素组成相较于大别造山带埃达克岩，具有明显的亏损特征，暗示该地区早白垩世岩浆源区下地壳属性并非扬子克拉通下地壳，应该来源于华北克拉通基性下地壳的部分熔融。旗杆楼花岗岩具有低Sr(108.5×10^-6～460×10^-6)、Y(7.9×10^-6～10.8×10^-6)、Yb(0.79×10^-6～0.96×10^-6)、Sr/Y（10.05～44.23）和高（La/Yb）_N（10.96～54.53）的特征，表明其源区存在斜长石和石榴石的残余，对应于1.0～1.5 GPa的熔融压力。徐淮地区早白垩世岩浆作用由高镁埃达克质岩向I型花岗岩的转换，受控于早白垩世古太平洋的西向俯冲所引发的岩石圈减薄。此外，旗杆楼花岗岩的岩浆氧逸度(logf_O2=-18.76～-9.32)明显低于徐淮地区杨桥孜铜金矿成矿岩体的岩浆氧逸度(logf_O2=-15.10～-2.12)，综合分析认为，岩浆氧逸度及源区差异共同导致了旗杆楼铁矿与杨桥孜铜金矿成矿类型的不同。更多还原

【Abstract】 The skarn-type deposits of the Xuzhou-Huaibei area are closely related to the Early Cretaceous magmatism,and the Early Cretaceous magmatic rocks widely distributed in the area are excellent objects for studying igneous and ore-forming processes.This study focused on the investigation of petrography,isotopic chronology,whole-rock geochemistry,and Hf isotopic compositions of zircon from the Early Cretaceous granite of the Qiganlou region in the Xuzhou-Huaibei area.Additionally,we examined the petrography and geochronology of skarn from the Qiganlou Fe deposit.Based on the research above,we analyze the petrogenesis of these granites and their source area properties,and discuss the restricting effect of the Qiganlou granites on the formation of skarn type iron ore.Zircon LA-ICP-MS U-Pb isotopic dating results indicate that the Qiganlou granites formed at 105.4±0.9 Ma.The U-Pb isotopic age of garnet in the skarn is 102.2±1.6 Ma,representing the mineralization age of the Qiganlou Fe deposit.These results suggest that both the igneous and ore-forming activities occurred during the late Early Cretaceous.The Qiganlou granites are primarily composed of plagioclase,potassium feldspar,and quartz,with low P₂O₅ （0.14%～0.19%）,A/CNK （0.68～0.97）,（Na₂O+K₂O）/Ca O （2.11～6.53）,and ^TFe O/Mg O （1.13～2.54）,which is consistent with the geochemical characteristics of I-type granites.Zircon?_Hf（t） values of the Qiganlou granites range from-18.3 to-14.7,significantly lower than those of Early Cretaceous mafic intrusions and high-Mg adakites in this area,suggesting a probable origin from ancient mafic lower crust,with minor or without contribution of the mantle-derived materials.Zircon Hf isotopic compositions of the Early Cretaceous magmatic rocks in the Xuzhou-Huaibei area are significantly more depleted than those of the adakites in the Dabie orogenic belt,implying that the source of the Early Cretaceous magmatism in this area is not the lower crust of Yangtze Craton,but derived from partial melting of mafic lower crust of the North China Craton.The Qiganlou granites show the geochemical characteristics of low contents of Sr (108.5×10^-6～460×10^-6),Y (7.9×10^-6～10.8×10^-6),Yb (0.79×10^-6～0.96×10^-6),low ratio of Sr/Y （10.05～44.23）,and high ratio of （La/Yb）_N （10.96～54.53）,indicating the presence of residual plagioclase and garnet in the magmatic source area,corresponding to a melting pressure of 1.0～1.5 GPa.The transition from high-Mg adakites to I-type granites of the Early Cretaceous magmatism in the Xuzhou-Huaibei area is attributed to lithospheric thinning triggered by westward subduction of the Paleo-Pacific slab.Additionally,the magmatic oxygen fugacity (logf_O2=-18.76～-9.32) of the Qiganlou granites is notably lower than that of the metallogenic magmatic rocks (logf_O2=-15.10～-2.12) of the Yangqiaozi Cu-Au deposit in the Xuzhou-Huaibei area.Comprehensive analyses suggest that the differences in magmatic oxygen fugacity and magma source both contributed to the contrasting mineralization types between the Qiganlou Fe deposit and the Yangqiaozi Cu-Au deposit.更多还原