桂东北大宁岩体黑云母矿物学特征及其对成岩作用的指示  

Mineral feature of biotite in Da’ning rock mass in Northeast Guangxi and its indication of diagenesis

作　　者：刘雷[1] 刘风雷 蔡永丰 LIU Lei;LIU Fenglei;CAI Yongfeng(Ningxia Branch of China National Geological Exploration Center of Building Materials Industry,Yinchuan 750021,Ningxia,China;Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development ofNew Materials in Guangxi&Guangxi Key Laboratory ofHidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541006,Guangxi,China)

机构地区：[1]中国建筑材料工业地质勘查中心宁夏总队,宁夏银川750021 [2]桂林理工大学,广西有色金属隐伏矿床勘查及材料开发协同创新中心&广西隐伏金属矿产勘查重点实验室,广西桂林541006

出　　处：《矿产与地质》2020年第2期294-301,共8页Mineral Resources and Geology

基　　金：广西自然科学基金项目(编号:2018GXNSFBA281069)资助。

摘　　要：为了揭示桂东北大宁岩体的成岩特征,利用电子探针(EMPA)对大宁岩体花岗闪长岩中的黑云母展开了矿物化学成分分析研究。分析测试结果表明:花岗闪长岩中黑云母w(SiO2)为35.32%~37.54%,w(FeO^T)为21.33%~27.00%,w(MgO)为7.18%~10.00%,w(K2O)为9.75%~10.46%,w(Na2O)为0.06%~0.15%,w(Al2O3)为12.44%~14.02%,w(CaO)为0.01%~0.07%,整体表现出富铁贫镁、富钾贫钠、高铝低钙的特征。根据黑云母Fe^2+/(Fe^2++Mg)比值的不同,可将其分为两组,第一组为未蚀变的原生黑云母,具有较高的Mg/(Fe^2++Mg)比值(0.47~0.49)、结晶温度(723℃~731℃)、氧逸度(-13)、结晶压力(121~135MPa)和结晶深度(4.58~5.11km);第二组黑云母局部绿泥石化,具有较低的Mg/(Fe^2++Mg)比值(0.34~0.36)和结晶温度(678℃~687℃)。综合分析表明:大宁岩体花岗闪长岩形成于较高温压条件,其形成与壳-幔相互作用有关,可能为早古生代华南地区陆内造山作用的产物。The analysis of mineral composition has been carried out for biotite in granodiorite of Da’ning rock mass in Northeast Guangxi in order to reveal the diagenetic characteristics.Electron microprobe analysis(EMPA)result shows that in biotite of granodiorite,w(SiO2)is 35.32%-37.54%,w(FeO^T)is 21.33%-27.00%,w(MgO)is 7.18%-10.00%,w(K2O)is 9.75%-10.46%,w(Na2O)is 0.06%-0.15%,w(Al2O3)is 12.44%-14.02%and w(CaO)is 0.01%-0.07%.The overall feature is rich in iron,potassium,and aluminum,and is low in sodium,magnesium and calcium.According to the difference of Fe^2+/(Fe^2++Mg)ratio of biotite,it can be divided into two groups.The first group is unaltered native biotite,which has a high ratio of Mg/(Fe^2++Mg)(0.47-0.49),crystallization temperature(723℃-731℃),oxygen fugacity(-13),crystallization pressure(121 MPa-135 MPa)and crystallization depth(4.58-5.11 km).The second group biotite has a lower Mg/(Fe^2++Mg)ratio(0.34-0.36)and crystallization temperature(678℃-687℃)with a local chloritization.Comprehensive analysis shows that the granodiorite in the Daning rock mass is formed under high temperature and pressure condition,and its formation is related to the crust-mantle interaction,which may be the product of the intracontinental orogeny in the South China in the Early Paleozoic.

关 键 词：大宁岩体 矿物化学成分 花岗闪长岩 黑云母 桂东北 

分 类 号：P575[天文地球—矿物学]