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应用岩石学、矿物学、地球化学及岩浆物理学等的理论和方法，对苏州地区Ｉ型和Ａ型花岗岩的特征及成因进行了对比研究，得出以下主要结论：Ｉ型花岗岩为晚侏罗世火山弧压性环境产物，侵位较深；而Ａ型者为Ａ２型花岗岩，为早白垩世造山后张性环境产物，侵位较浅，具晶洞构造．Ａ型比Ｉ型花岗岩以酸度、碱度、Ａｌ，Ｆ含量高而Ｈ２Ｏ＋含量低，以ＲＥＥ及不相容元素丰度高，负Ｅｕ异常强，而ｗ（ＬＲＥＥ）／ｗ（ＨＲＥＥ）低为特色．Ａ型者矿物结晶顺序先浅色后暗色，暗色矿物以富铁贫镁、ＲＥＥ分配系数高及负Ｅｕ异常明显及长石富碱贫钙，而与Ｉ型花岗岩不同．Ａ型者副矿物４０余种，属锆石－褐帘石－萤石型，锆石结晶温度高，（１１０），（１１１）晶面发育；而Ｉ型者仅１０余种，属榍石－锆石－磷灰石型，锆石结晶温度低，（１００），（３１１）晶面发育．Ｉ型花岗岩为幔源岩浆与下地壳部分熔融岩浆混合及ＡＦＣ作用产物，而Ａ型花岗岩为残余下地壳（麻粒岩相）熔融后分离结晶产物，二者并非同源岩浆演化关系．Ａ型比Ｉ型岩浆来源浅，酸度大，含水少；故岩浆密度小，粘度大，上升慢，冷凝长．受密度筛影响，Ａ型花岗岩岩浆房及侵位深度小于Ｉ型
Based on the theories and methods of petrology, mineralogy, geochemistry and magmatic physics, the characteristics and origin of type I and type A granites in Suzhou area are comparatively studied. The main conclusions are as follows: Type I granite is Late Jurassic Epoch volcanic arc environment products, emplacement deeper; and A-type A2-type granite, the Early Cretaceous orogenic post-tensional environment product, shallow emplacement, with a cave structure. Type A than the Type I granite with high acidity, alkalinity, high Al and F content and low H2O + content, high REE and incompatible elements, strong negative Eu and low (HREE) w (LREE) / w Features. The type A mineral crystallizes in the order of light-colored and dark-colored. The dark-colored minerals are rich in iron and poor in magnesium, with high REE partition coefficient and obvious negative Eu anomaly, and feldspar-rich and poor-calcium, but different from type I granite. More than 40 types of A-type side minerals belong to the zircon-brownishidite-fluorite type. The crystallization temperature of zircon is high, (110) and (111) planes develop. For Type I, only 10 species are found, - zircon - apatite type, zircon crystallization temperature is low, (100), (311) crystal plane development. Type I granite is the product of mixed molten magma and AFC from the mantle magma and part of the lower crust, whereas Type A granites are the crystalline products separated from the remnant lower crust (granulite facies) after melting, which are not the same as the magmatic evolution. Type A is lighter than Type I magma and has a large acidity and low water content. Therefore, magma has low density, large viscosity, slow rise and long condensation. Affected by the density screen, type A granite magma chamber and emplacement depth less than type I