秦岭沙河湾Ⅰ型花岗岩岩石学、矿物学特征及岩浆形成的温压条件  

Petrology and Mineralogy of the I-type Granites and Temperature-Pressure Conditions for Magma Formation in the Shahewan Rock Mass of the Qinling

作　　者：刘春花[1] 吴才来[1] 雷敏[1] 秦海鹏[1] 李名则[1] 

机构地区：[1]大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037

出　　处：《地质与勘探》2013年第4期595-608,共14页Geology and Exploration

基　　金：中国地质调查局项目(1212011120160、1212010611803、1212010711816);国家自然科学基金创新群体项目“青藏高原大陆动力学及资源环境效应”(40921001)联合资助

摘　　要：南秦岭沙河湾岩体紧临商丹断裂南侧,是具有环斑结构的似斑状-粗粒结构石英二长岩。本文通过化学全分析、偏光显微镜、电子探针(EPMA)、扫描电镜(SEM)对沙河湾岩体的岩石学和矿物学特征进行了研究,并对岩浆形成的温压条件与构造背景进行了讨论。结果表明,主量元素SiO2=66.40%～70.08%,Al2O3=14.36%～14.95%,Fe2O3=0.93%～1.73%,FeO=1.22%～1.65%,CaO=1.94%～2.78%,Na2O+K2O=7.88%～8.56%,K2O/Na2O=1.02～1.11,δ﹤3.3,为高钾钙碱性的过铝质I型花岗岩类;ΣREE平均151×10-6,LREE/HREE平均13.63,(La/Yb)N平均20.54,δEu平均0.89,δCe平均0.95,表明其轻稀土富集,重稀土亏损,Eu和Ce异常不明显,球粒陨石标准化配分曲线为右倾型,亏损Nb、Ce、Zr、Ti等高场强元素,略富Ba、K、Sr等大离子亲石元素;主要造岩矿物为石英、斜长石(更(奥)长石-钠长石)、钾长石、镁角闪石和镁质黑云母,副矿物为锆石、榍石、磁铁矿、钛铁矿和少量的石榴石等;初始岩浆温度平均755～780℃;角闪石和斜长石结晶温度约621～623℃;岩浆侵位深度约4km,压力约1.26×108Pa,具有壳幔混源的特点;沙河湾石英二长岩形成于中温、富水、中氧逸度的环境。The Shahewan rock mass, located in the southern Shangdan fault of the south Qinling, predominantly consists of quartz monzonite with the porphyroid-coarse grained texture. This paper studies the petrological and mineralogical characteristics, and discusses the magma-forming P-T conditions and the tectonic settings of the Shahewan rock mass, through petrologcial observations, chemistry total analysis, electronprobe microanatyses （EPMA） and scanned electron microscope （SEM） methods. The result demonstrates that the Shanhewan quartz monzonite belongs to high-K calc-alkaline I-type gran- ite, with its SiO2 content varying from 66.40% to 70.08% ,the A1203 content 14.36% - 14.95% ,the Fe2O3 content 0.93% - 1.73% ,the FeO content ranging from 1.22% to 1.65% , the CaO content 1.94% -2.78% ,the（ Na2O ＋ K2O）content 7.88% - 8.56% , the K2O/Na2O ratio 1.02 - 1.11 and the values of 6 less than 3.3. The average LREE/HREE ratio is 13.63 ; the average （La/Yb）N ratio is 20.54 ; the average 6Eu and 6Ce are 0.89 and 0.95. The REE content averages 151×10^-6 ,which is enriched in LREE and shows HREE depletion and slight negative Eu and Ce anomalies. In addi- tion, the chondrite-normalized REE pattern of quartz monzonite belongs to the rightist type. Furthermore, the quartz monzonite is slightly rich in large ion lithophile elements such as Ba, K and Sr and depleted in high field strength elements such as Nb, Ce, Zr and Ti. The major rock-forming minerals are quartz, plagioclase（ oligoclase to albite）, K-feldspar, magnesiohornblende and magnesian biotite, whereas the accessory minerals include mainly zircon, sphene, magnetite, ilmenite and small amount of garnet. The average temperature of the initial magma is 755 -780℃ and the crystallization temperature of the magma is 621 -623℃. The depth of the magma emplacement is about 4 km and the pressure is about 1.26 × 10^8pa. The material source has crust mantle mixed characteristics. The Shahewan quartz monzonite might have been formed in a setting with features

关 键 词：花岗岩类 岩石学 矿物学 P—T条件 秦岭 沙河湾 

分 类 号：P618.65[天文地球—矿床学] P581[天文地球—地质学]