The tectonic patterns of the Hercynian-Indosinian cycle in southeastern China can be divided into twotypes.The first type is the Hercynian-Indosinian eugeosynclinal system,which is situated on the outer sideof the Caledonian uplift belts.The second type is the Hercynian-Indosinian fault depression zone orsuperimposed basin system,which is developed on the basement formed by the Caledonian orogenicmovement.There are two genetically different series of granitoids corresponding to two tectonic settings inthe Hereynian-Indosinian tectonic regime of southeastern China.Among the transformation-series batholiths one of the largest in the Qinzhou Gulf geosyncline isknown as the Darongshan granite(NE-extending)with an outerop area of about 7000 km~2.The age ofemplacement determined by whole-rock Rb-Sr isochron method ranges from 223 to 263 m.y..corresponding to late Permian,with higher Sr initial ratios(0.7179—0.7274).The granite is chemically richin K_2O but poor in Na_2O with the atomic Na/K ratio<1.0 and the mole ratio Al_2O_3/(Na_2O+K_2O+CaO)>1.0.K-feldspars are usually predominated by medium to maximum microclines with a higher degree ofAl-Si ordering characterized by the concentration of Al in T_1 sites of the feldspars(t_1(o)=0.57—0.99).Biotites are often rich in Fe but poor in Mg,belonging to Fe-biotite or siderophyllite,with a lower MF value(Mg/(Mg+Fe~(3+)+Fe~(2+)+Mn)),normally<0.4,and a lower Fe~(3+)/Fe~(2+) ratio of 0.03—0.02 in theiroctahedron layers.This fact indicates that the oxidation degree of iron is relatively low in thetransformation-series granites as compared with the syntexis-series granitoids.Granitic batholiths of the syntexis series distributed along the fault belts in the Hercynian depressionsare usually more mafic,meta-aluminous granodiorites and smaller in size than those of the transformationseries,with an outcrop area of 1—200 km~2.The Taiping granodiorite,for instance,is situated on thesouthern side of the Lower Yangtze River depression.It was emplaeed 223 m.y.ago as dated by whole-rockRb-Sr isochron method,with an initial Sr ratio of 0.706.Petrochemically,it is characterized by Na/K>1.0(1.31),mole Al_2O_3/(Na_2O+K_2O+CaO)<1.0(0.95) and high Fe_2O_3/(Fe_2O_3+FeO)(0.47),evidentlydiffering from the transformation-series granites.K-feldspars are predominated by orthoclase with a lowerdegree of Si-Al ordering (t_(o)=t_(m)=0.30).Biotites are commonly rich in Mg in their octahedron layers(MF=0.42—0.50)with higher Fe~(3+)/Fe~(2+)ratios (0.36—0.51),indicating their formation under higheroxygen fugacity conditions.All this goes to prove that the syntexis-series granitoids were probably derivedfrom mafic igneous or metamorphic source rocks in the lower crust. The tectonic patterns of the Hercynian-Indosinian cycle in southeastern China China can be divided into twotypes. The first type is the Hercynian-Indosinian eugeosynclinal system, which is situated on the outer side of the Caledonian uplift belts. Second-type is the Hercynian-Indosinian fault depression zone orsuperimposed basin system, which is developed on the basement formed by the Caledonian orogenic motif. Here are two genetically different series of granitoids corresponding to two tectonic settings inthe Hereynian-Indosinian tectonic regime of southeastern China. Among the transformation-series batholiths one of the largest in the Qinzhou Gulf geosyncline isknown as the Darongshan granite (NE-extending) with an outerop area of ​​about 7000 km ~ 2.The age of impacted volume determined by whole-rock Rb-Sr isochron method ranges from 223 to 263 my.corresponding to late Permian, with higher Sr initial ratios (0.7179-0.7274). The granite is chemically richin K20 but poor in Na20 with the atomic Na / K ratio <1.0 and the mole ratio A1_2O_3 / (Na_2O + K_2O + CaO)> 1.0. K-feldspars are usually predominated by medium to maximum microclines with a higher degree of Al-Si alignment characterized by the concentration of Al in T_1 sites of the feldspars (t 1 (o) = 0.57-0.99). Biotites are often rich in Fe but poor in Mg, belonging to Fe-biotite or siderophyllite, with a lower MF value (Mg / (Mg + Fe 3+) ~ (2 +) + Mn)), normally <0.4, and a lower Fe ~ (3 +) / Fe ~ (2+) ratio of 0.03-0.02 in theiroctahedron layers. This fact indicates that the oxidation degree of iron is relatively is low in the transformation-series granites as compared with the syntexis-series granitoids. Granitic batholiths of the syntexis series distributed along the fault belts in the Hercynian depressionsare usually more mafic, meta-aluminous granodiorites and smaller in size than those of the transformationseries, with an outcrop area of ​​1-200 km ~ 2.The Taiping granodiorite, for instance, is situated on the southern side of the Lower Yangtze River depressio n.It waIt was characterized by Na / K> 1.0 (1.31), mole Al 2 O 3 / (Na 2 O + K 2 O + CaO) 1.0 (0.95) and high Fe 2 O 3 / (Fe 2 O 3 + FeO) (0.47), evidentlydifferingfrom the transformation-series granites.K-feldspars are predominated by orthoclase with a lowerdegree of Si-Al ordering (t_ (o) = t_ (m) = 0.30) .Biotites are commonly rich in Mg in their octahedron layers (MF = 0.42-0.50) with higher Fe ~ (3+) / Fe 2+ (0.36-0.51), indicating their formation under higheroxygen fugacity conditions .All this goes to prove that the syntexis-series granitoids were probably derivedfrom mafic igneous or metamorphic source rocks in the lower crust.