金鸡岭产铀花岗岩体印支期侵位的岩浆动力学证据及其构造意义

通过对南岭西段金鸡岭花岗岩体地质-岩石地球化学特征研究,判明该岩体的侵位深度(7.5km)、围岩温度(270℃)及岩浆初始温度(950℃),建立起金鸡岭花岗岩体的数学计算模型,分别计算得出:金鸡岭花岗岩熔体侵位后,其初始温度降低至结晶温度所需的时间(Δtcol)为3.91Ma;由于结晶潜热释放而使结晶过程延长的时间(ΔtL)为2.92Ma;由于金鸡岭花岗岩体放射性元素含量(U——16.5×10-6,Th——51.3×10-6,K2O——4.82%)是世界平均花岗岩放射性元素含量(U——5×10-6,Th——20×10-6,K2O——2.66%)的3倍左右,金鸡岭花岗岩熔体侵位后产生的放射性成因热使结晶过程延长的时间(ΔtA)为34.5Ma,远长于按世界花岗岩平均放射性元素含量计算的ΔtA*(2.82Ma)。金鸡岭花岗岩体的侵位-结晶时差(ΔtECTD)为41.3Ma,结合锆石U-Pb年龄值(156Ma),通过反演计算得出金鸡岭花岗岩体侵位年龄值(tE)为197.3Ma,从而为该岩体属于印支期侵位提供了重要的岩浆动力学证据。

Magma-Dynamical Evidence for Indo-Sinian Emplacement of the Uranium-Bearing Jinjiling Granite Batholith and its Tectonic Implication

From the geological-geochemical features of Jinjiling granite batholith,the depth of emplacement（7.5 km）,the temperature of country rocks（270 ℃）and the initial temperature of the melt（950 ℃）during it emplacement are obtained.With these parameters a mathematic calculating model for the emplacement age of Jinjiling granite batholith is established in this paper.Model calculation results suggest that the cooling period（Δtcol）for Jinjiling granite batholith from its initial temperature to crystallization temperature（600 ℃）was 3.91Ma,the prolongation period（ΔtL）caused by latent heat generated from crystallization was 2.92 Ma.Since the radioactive elements of Jinjiling granite batholith（U—16.5×10-6,Th—51.3×10-6,K2O—4.82%）are as high as 3 times of the average of the world granites（U—5×10-6,Th—20×10-6,K2O—2.66%）,the prolongation period（ΔtA）caused by radiogenic heat from the decay of these radioactive elements is 34.5 Ma which is much longer than the ΔtA value calculated for the world granites average（2.82 Ma）.Therefore,the time elapsed from the emplacement to the end of crystallization（ΔtECTD）should be the sum of Δtcol,ΔtL,and ΔtA,which was 41.3 Ma for Jinjiling granite batholith.In combination with zircon U-Pb age of the granite（156 Ma）which represents the crystallization age,the emplacement age of Jinjiling granite batholith（tE）is estimated to be 197.3 Ma.This suggests that the emplacement of Jinjiling granite melt was in the Indo-Sinian Period.