Study On The Amphibolites Of The Qinling Group And The Danfeng Group

The mafic rock in Heihe Qinling Group had undergone regional metamorphism betwween 400Ma and 420Ma.The zircons' ages from the later intrusive diabase dikes were similar with it.Zircons' trace element indicated that they could be attributed to the same basaltic magma.The major element of amphibole indicated the degree of metamorphism had been to high amphibolite facies,and metamorphic pressure was between 0.39Gpa and 0.56Gpa,metamorphic temperature was between 726? and 752 ?.The geochemical datas in Hubao River Danfeng Group and Chenhe Qinling Group indicated they were an island arc.Hf isotopes indicated in the late of Neoproterozoic source materials leaved depleted mantle to the crust.The zircons in amphibolite next to Shangzhou Nanqin reservoir had been sufferred obvious recrystallization,whose U-Pb ages were between 360Ma and 390Ma,mainly concentrated in?370Ma,and had a continental margin arc calc alkaline basalt geochemistry characteristic.The degree of metamorphism had been to high amphibolite facies,and metamorphic pressure was between 0.36 Gpa and 0.44Gpa,metamorphic temperature was between 657 ? and 676 ?.Hf isotopic characteristic was similar to Heihe Danfeng Group.Zhacai ditch amphibolite was in qinling group,whose width was greater than 2km,and had a typical characteristic of N-MORB.The degree of metamorphism had been to low amphibolite facies,and metamorphic pressure was between 0.2Gpa and 1.18Gpa,metamorphic temperature was between 642 ? and 707 ?.Most of the zircon ages concentrated between 1800Ma and 2000Ma.Hf isotopic model agea were similar to the U-Pb ages.The average of ?Hf(t)was 5.00,indicating that zircons were directly formed on the rocks in the mantle or mantle source rocks took part in crust anatexis after a short time in the crust.Qinling group might be a complex geological body which was based on the Paleoproterozoic crystalline basement and suffered reformation in late Early Paleozoic.