| Since the Archean, with the rifting and closuring, frequent and intense magmatic activities had happened in ZhongTiao Mountain, has gone through the magmatic activities of the pre Jiang Xian period, Jiang Xian period, period of XiYanghe stage and Yanshan period.XiYanghe group located in the slope zone and the north south area in Zhongtiao mountain, consisted of a set of thick andesite volcano lava, with a small amount of sedimentary rocks and volcanic. From bottom to top, this group formation is divided into XuShan group, JiDanping group and MaJiahe group.The author, on the basis of field observation, through petrology and geochemistry analysis of main、trace、rare earth element, discuss the reason of the volcanic rocks and tectonic environment, at the same time, through the macroscopic and microscopic observation, discuss the types and characteristics of andesite amygdala and evaluate its potential value. Mainly getting the following views: 1.XiYanghe group volcanic rocks in the whole was the color of grey purple, sage green, individual for brick red and purple. Mainly was no spot hidden crystalline structure, porphyritic structure was rare, almond-shaped structure was well developed. Rock types mainly included:andesite, basalt, andesite, rough surface, andesite basalt, basaltic andesite, dacite, rough surface, dacite and rhyolite, had both basic volcanic rocks and intermediate-acid volcanic rocks, mainly was neutral andesite.2.The overall characteristics of main elements of this group volcanic rocks was relatively with large changes in SiO2content, rich in FeO, K2O, while Al2O3, TiO2and MgO were low. K2O content was3.37%on average, which close to subduction zone activities. Characteristics of the main elements indicate that the elements of XiYanghe volcanic rocks are neutral and alkaline volcanics potassium, high potassium calc alkali-XuanYan series, formed in the predominantly squeezed active continental margin tectonic environment.3. The REE elements of this volcanic rocks were between103.66-442.12, w (LREE)/w (HREE) between4.85～9.88, LaN/YbN=5.68～11.05, the distribution curve of both basic and acid type rare earth element were right trend, characterized by light rare earth elements concentration, heavy rare earth element were relatively loss. XiYanghe group volcanic rocks were rich in large ion lithophile elements (LILE), especially the Ba, K, Rb, Th high concentrated, high field strength elements (HFSE) relatively lossed, such as Nb, Ta, Ti content were low, showing the geochemical affinity of island arc volcanic rocks. Main, trace element geochemical characteristics indicate that the XiYanghe group volcanic rocks formed in the active continental margin arc environment.4. In the early stages of the eruption, namely Xu Shan period-JiDanping period, volcanic rocks were widespread with the pillow structure, indicating this period was mainly underwater erupted; and to terminal, namely MaJiahe period, volcanic rock was in the development of columnar joints, may give priority to with onshore eruption.5. The amygdala ingredients of XiYanghe group volcanic rocks were mainly included:crystal, agate, chalcedony, opal, calcite, chlorite, the agate amygdala was more common among them. The amygdala was small, in the majority of0.5-1.5cm, withing the space of round sphere, ellipsoid, flat cake shape and irregular shape, color variety in white, gray, red, green and dark. The agate amygdala was mainly with cracks, impurities and loose pore, banded structure was not obvious; maily was implicit crystalline granular texture, fibrous and radial structure were rare, the micro porosity and the pore connectivity was poor, therefore, the agate amygdala of XiYanghe group don’t have potential economic value. |
PDF Full Text Request