Study on the Order Degree and Geochemical Characteristics of Major Elements of Siliceous Rock in Eastern Qinling Area, China
Lü Ming-da1, LI Hong-zhong2*, ZHAO Ming-zhen3, MA Zhan-wu4, YANG Zhi-jun5, LIANG Jin5
1. School of Earth and Space Sciences, Peking University, Beijing 100871, China 2. Key Laboratory of Mineral Resource, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 3. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China 4. College of Civil Engineering, Beifang University of Nationality, Yinchuan 750021, China 5. Department of the Earth Science of Sun Yat-sen University, Guangzhou 510275, China
Abstract：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.
吕明达1，李红中2*，赵明臻3，马占武4，杨志军5，梁 锦5 . 东秦岭地区硅质岩的有序度及常量元素地球化学特征研究 [J]. 光谱学与光谱分析, 2014, 34(11): 3005-3010.
Lü Ming-da1, LI Hong-zhong2*, ZHAO Ming-zhen3, MA Zhan-wu4, YANG Zhi-jun5, LIANG Jin5. Study on the Order Degree and Geochemical Characteristics of Major Elements of Siliceous Rock in Eastern Qinling Area, China. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2014, 34(11): 3005-3010.
