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仙霞岩体是浙北和皖南交界区域明显受北东向学川-孝丰断裂构造带控制的大岩体,其内部岩性复杂,主要由早期中粒二长花岗岩、巨斑状二长花岗岩和晚期中粗粒正长花岗岩、细粒正长花岗岩组成,后期有大量细晶岩、石英正长岩、闪长玢岩、安山岩、辉绿岩等脉岩侵入。锆石U-Pb年龄数据显示早期二长花岗岩大约侵位于145.1~144.2Ma,晚期正长花岗岩大约侵位于131.7~130.8Ma,后期辉绿岩脉侵位于128.3Ma。两期岩石均具高SiO_2、高K_2O+Na_2O和低P_2O_5特征;早期二长花岗岩为准铝质、高钾钙碱系列岩石,稀土配分曲线强右倾,中等负Eu异常,富集Rb、Th、U、K,亏损Ba、Nb、Sr、P、Ti等特征;晚期正长花岗岩为准铝质-过铝质、钾玄岩系列岩石,稀土配分曲线弱右倾、强负Eu异常,同样富集Rb、Th、U、K,强亏损Sr、P、Ti等特征;均属高分异I型花岗岩类。两期岩石均具有相对高的(86Sr/87Sr)i值(0.70807~0.70988)和εNd(t)值(-8.87~-5.14),Nd二阶段模式年龄为1.36~1.65Ga。成岩可能与古太平洋板块俯冲角度的改变,构造背景由中晚侏罗世(165±5~145±5Ma)的挤压环境向早白垩世早期(145±5~125Ma)的伸展拉张环境转变有关,致使古老江南造山带地壳物质熔融并可能混染扬子岩石圈地幔物质形成的两期岩浆经高程度结晶分离作用先后侵位,也表明浙西北乃至华南地区晚中生代构造转换时间为145Ma左右,且在早白垩世发生了多期次伸展拉张作用。
The Xianxia granite is a large rock mass which is obviously controlled by the north-east Xuechuan-Xiaofeng fault tectonic belt. Its internal lithology is complicated and mainly consists of the early mesophase monzogranite, the maculiform monzonitic granite In the late stage, there are coarse-grained, normal-granite and fine-grained granitoid granites. Later, there are a large number of fine-grained rocks, quartz syenite, diorite porphyrite, andesite, diabase and other vein intrusions. Zircon U-Pb age data show that the early monzonitic granite invaded approximately 145.1-144.2Ma, the late-stage granodiorite invaded at 131.7-130.8Ma, and the later diabase dikes at 128.3Ma. Both of the two rocks are characterized by high SiO_2, high K_2O + Na_2O and low P_2O_5. Early-stage monzogranite is a quasi-aluminum and high-K calc-alkaline series of rocks. Rare earth distribution curves have strong right- U, K, loss of Ba, Nb, Sr, P, Ti and other characteristics. Late-stage orthoclase granites are quasi-aluminum-petrolatum series, and have a weakly right- Rb, Th, U, K, strong loss of Sr, P, Ti and other characteristics; are high I-type granite. Both rocks have relatively high values of (86Sr / 87Sr) i (0.70807-0.70988) and εNd (t) (-8.87-5.14), and the Nd two-stage model ages are 1.36-1.65Ga. The diagenesis may be related to the subduction angle of the Paleo-Pacific plate. The tectonic setting changes from the extensional environment of the mid-late Jurassic (165 ± 5 ~ 145 ± 5Ma) to the extensional extensional environment of the Early Cretaceous (145 ± 5 ~ 125Ma) , The two phases of magma formed by melting and melting the crustal material of the ancient Jiangnan orogenic belt and possibly mixing with the Yangtze lithosphere mantle material have intruded successively by high degree of crystallization separation and also indicate that the structural transition time of the Late Mesozoic in the northwestern Zhejiang and even in southern China is about 145 Ma, And in the Early Cretaceous occurrence of multi-stage stretching tension.