The Nature And Significance Of The Late Neoarchean And Late Paleoproterozoic Tectono-thermal Events In The Southern Margin Of The Yinshan Block Of The North China Craton

The Yinshan Block comprises relatively complete late Neoarchean tonalite-trondhjemite-granodiorite(TTGs),greenstone belt rocks and granulite-charnockite associations,and is the key study area of the North China Craton during this period for the tectonic evolution.The Guyang and Wuchuan regions have been extensively studied due to their good basement exposures,but the researches in other area are relatively weak.Based on this,the petrologic,geochemical,geochronologic,and zircon Hf isotopic studies of the meta-granitic rocks and amphibolites from the Guyan-Wuchuan,Wulatezhongqi and Wulatehouqi area have been carried out In this paper,and the petrogenetic and tectonic backgrounds of different types of metamorphic magmatic rocks of the late Neoarchean in the three regions are preliminarily defined.The meta-granitic rocks in the Guyang-Wuchuan and Wulatezhongqi regions formed at 2491?2545Ma and metamorphosed at 2485Ma.Primitive-mantle-normalized trace-element diagrams show that the meta-granitic samples are depleted in Nb,Ta,Ti and HREE,and are enriched in Pb,Th,and U.The chondrite-normalized REE patterns show that the differentiations of light and heavy rare earth elements are moderate([La/Yb]_N=3.99?15.6),and the differentiations of heavy REEs are small([Gd/Yb]_N=1.28?2.74).The zircon Hf isotopic compositions(?_Hf(t)=+0.9?+7.1,t^C_DM=2.67?3.03Ga)indicate that the parent magma of the meta-granitic rocks originates from the recycling of the Meso-to Neo-archean crust,with the addition of a small amount of juvenile addition.The formation ages of the amphibolites in the Wulatehouqi area are 2495?2527Ma.Primitive-mantle-normalized trace-element diagrams show obvious depletions of Nb,Ta and Ti,and enrichments of Rb,Pb,Th and U.The chondrite-normalized REE patterns show that moderate differentiation of light and heavy REEs([La/Yb]_N=4.24?14.2)and relatively flat of heavy REEs([Gd/Yb]_N=1.81?2.19).The zircon Hf isotopic compositions(?_Hf(t)=+1.7?+6.3,t_DM1=2.62?2.73Ga)indicate that they originated mainly from the depleted mantle in the Neoarchean.In addition,The Khondalite belt locates in the western North China Craton and there have been disputes about the extension direction of its north boundary in the Dengkou area and its location in the Shetai area.In this contribution,we studied the mineral inclusions,U-Pb isotopes and trace elements of the metamorphic zircons from the granitic gneisses in the Dengkou area and the amphibolites in the Shetai area.U-Pb ages of the metamorphic zircons in the Denkou area are 1896±5 Ma and 1854±6 Ma,and their REE patterns are generally left-leaning.On the other hand,the metamorphic zircons of the ampbibolites in the Shetai area gave U-Pb ages of 1879±24 Ma and 1791±21 Ma in the south and 2473±6 Ma in the nouth,respectively and their REE patterns are also characteristic of left-leaning.Combined with the rock assemblage,the spatial distribution of metamorphic events in the late Neoarchean and Paleoproterozoic periods,and the previous research results,we can draw the following conclusions:(1)In Dengkou area,the boundary between Khondalite belt and Yinshan block is more likely to extend to the west,rather than to the southwest as previously believed.In Shetai area,the boundary should be distributed along Wuchuan-Guyang-Shetai,rather than the distribution along Wuchuan-Guyang-Wulatehouqi as previously believed.(2)The Late Neoarchean magmatic event in the southern margin of the Yinshan block was a subduction-related magmatic event,which was not limited to the Guyang-Wuchuan area,but extended to the Wulate Houqi area in the southwest by 400km.