The Indosinian granitoids in South China can be divided into two genetic types.One category is strongly peraluminous S-type granites,which is rich in peraluminous minerals,high SiO2,A12O3 and P2O5 contens,A/CNK values and enriched in Rb,U,Ta,Zr,Hf,obviously depleted in Ba,Sr,Nb and Ti in the primitive mantle-normalized trace element spider diagrams.The rocks are characterized by low REE contents (2REE <80×10-6) showing right dipping REE patterns with significant negative Eu anomalies in the chondrite-normalized REE patterns.The other category is metaluminous I-type granites bearing hornblende and other mafic minerals such as biotite,rich in SiO2,Na2O.In general,these two types of granites all show high ( Sr/ Sr)i values (0.710490 ~ 0.742118) and low eNd(t) values ( - 14.42--4.1).Nd model ages (2.09 ~ 1.63 Ga) of the granitic rocks indicate that the Indosinian granites are typically crust-derived.Molar CaO/( MgO + FeO)-molar Al2O2/( MgO + FeOT ) diagram shows that these granites are mainly derived from partial melting of metamorphic sandstone and met-amorphic mudstone mixed with a small amount of metamorphic basalt and metamorphic tonalite rocks.Indosinian granitoids were formed in interval extensional process of collision stage of early Mesozoic in South China.It could be inferred that Indosinian granites were emplaced in extensional tectonic environment after large-scale lithospheric decompression.%华南地区印支期花岗岩按照成因类型可分两类,第一类属强过铝质S型花岗岩,富含过铝质矿物,富SiO2、Al2O3和P2O5,高A/CNK值,微量元素原始地幔标准化分布型式图中富集Rb、U、Ta、Zr、Hf,亏损Ba、Sr、Nb、Ti；稀土元素球粒陨石标准化分布型式图中具显著的负Eu异常,稀土元素总量偏低(ΣREE ＜80×10-6)；第二类属准铝质Ⅰ型花岗岩,含角闪石等镁铁质矿物,富SiO2、Na2O.总体来说,这两类花岗岩具有高的(87Sr/86 Sr),值(0.710490～0.742118)和低εNd(t)值(- 14.42 ～ -4.1),Nd模式年龄(2.09 ～1.63 Ga)指示印支期花岗岩为典型的壳源型花岗岩.CaO/( MgO+ FeOT) - Al2O3/( MgO+ FeOT)(摩尔比)图解表明这些花岗岩主要来源于变质杂砂岩和变质泥岩的部分熔融,夹杂了少量变质玄武岩和变质英云闪长岩.华南印支期花岗岩形成于挤压加厚的地壳发生局部伸展-减薄时期,推断印支期发生了多期次的岩石圈挤压和拉张,花岗岩侵位于大规模岩石圈挤压后局部减压-伸展的构造环境中.
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