东秦岭地区早古生代的二郎坪群海相火山沉积建造中广泛发育有硅质岩建造, 这些硅质岩形成于同一时代但因后期成岩演化而产生了结晶程度和有序度的差异。 鉴于此, 选择西峡、 嵩县、 南召三地的二郎坪群硅质岩进行了常量元素地球化学特征及有序度的研究。 研究结果表明, 该硅质岩的SiO2含量为84.75%～94.12%、 平均89.09%, SiO2/(K2O+Na2O)值26.69~114.78、 平均65.67, SiO2/Al2O3值10.48~61.52、 平均30.58, 它们极好的吻合大陆边缘环境的热水沉积硅质岩特征; Raman分析结果表明, 硅质岩在该研究中的特征Raman位移有394, 464, 465和467 cm-1, 石英的特征峰经高斯拟合后的FWHM值按照“嵩县→南召→西峡”逐渐降低, 这反映了嵩县、 南召、 西峡的硅质岩有序度和结晶程度依次逐渐升高。 然而, 硅质岩中SiO2含量分别为嵩县地区87.36%最低, 南召地区硅质岩89.57%其次, 西峡地区硅质岩90.35%最高。 据此, 常量元素中SiO2的含量与有序度之间存在同步递增的趋势, 这反映硅质岩内石英的SiO2含量和有序度在成岩过程中增大的同时还可能存在对杂质元素的“剔除作用”。 然而, 这种成岩演化中的杂质剔除作用应该并不是导致硅质岩全岩常量元素含量差异的决定性因素。 在研究中, Raman光谱分析极好的揭示了二氧化硅的有序度, 这可能是探究硅质岩后期成岩演化的重要手段。

Siliceous rocks were extensively distributed in the marine volcanic sedimentary formation of Erlangping Group in the Early Paleozoic in eastern Qinling area. These siliceous rocks formed in the same age, but had differences in the degree of crystallization and order because of the late diagenetic evolution. In the present study, the major elements and order degree of the siliceous rocks were studied, which were from the Erlangping Group in Xixia area, Songxian area and Nanzhao area of eartern Qinling orogenic belt. As shown in the results, the siliceous rocks contained SiO2 with percentage between 84.75% and 94.12% and average of 89.09%. The SiO2/(K2O+Na2O) values were from 26.69 to 114.78 with 65.67 as its average, and the values of SiO2/Al2O3 were from 10.48 to 61.52 with average of 30.58. These above characteristics excellently agreed with the geochemical characteristics of hydrothermal siliceous rocks, which deposited in the continental margin environment. In the Raman analytical results, the quartz contributed to the characteristic Raman shifts at 394, 464, 465 and 467 cm-1. In the results of Gaussian fitting the degrees of order increased with the order of siliceous rocks of Songxian area, Nanzhao area and Xixia area, which were witnessed by the descending in FWHM values of quartz in the siliceous rocks of Songxian area, Nanzhao area and Xixia area orderly. Disagreeing with the FWHM values of Gaussian fitting, the silica contents of the siliceous rocks had a rising trend of Songxian (87.36%), Nanzhao (89.57%), Xixia area (90.35%), which meant a descending in impurity elements with the order of Songxian area, Nanzhao area and Xixia areas. According to this, there was high agreement between lower crystallinity degree and higher purity of silica, and this denoted that the rising in order degree of silica would result in lower impurity in siliceous rocks. Although the crystallinity degrees could change with the influences of temperature, pressure and its natural property, the impurity elements decreased with the rising in crystallinity degrees of silica. Although there was excluding of impurity elements during the increase in degrees of crystallinity and order, the key factor for the diversities of major elements in siliceous rocks was not likely to be the excluding of impurity elements during the increase in the crystallinity degrees in silica. In this study, the Raman analysis exhibited to be an effective way to understand the degree of order for the silica of the siliceous rocks, which would be a potential way to study the subsequent diagenetic evolution of siliceous rocks.