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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 pluton of the South Qinling Mountains is close to the southern side of the Shangdan Fault, which is a plagioclase - coarse grain structure quartz monzonite with a ring - spot structure. In this paper, the petrographic and mineralogical characteristics of the Shahewan pluton were studied by chemical full analysis, polarized light microscopy, electron probe (EPMA) and scanning electron microscopy (SEM). The temperature and pressure conditions and tectonic setting of the magma were also studied discuss. The results showed that the main elements were 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% 7.89% ~ 8.56%, K2O / Na2O = 1.02 ~ 1.11 and δ <3.3, which are high-K calc-alkaline petrolatum type I granites with ΣREE average of 151 × 10-6 and LREE / Yb) N averaged 20.54, δEu averaged 0.89 and δCe averaged 0.95, indicating that the light rare earths are enriched, the heavy rare earths are depleted and the Eu and Ce anomalies are not obvious. The normalized distribution patterns of chondrite meteorites are right-inclined and depleted in Nb, Ce, Zr, Ti Such as Ba, K, Sr and other large ion lithophile elements; the main rock-forming minerals are quartz, plagioclase (more (Austria) feldspar - albite), potassium feldspar, magnesia horn flash Rock and magmatic biotite, and the accessory minerals are zircon, feldspar, magnetite, ilmenite and a small amount of garnet; the initial magmatic temperature is 755 ~ 780 ℃ on average; the amphibole and plagioclase crystallization temperature is about 621 ~ 623 ℃. The emplacement depth of the magma is about 4km and the pressure is about 1.26 × 108Pa, which has the characteristics of crust-mantle mixed source. The Shahewan quartz monzhangyan is formed in moderate temperature, rich water and moderate oxygen fugacity.