【摘要】 在乌鲁木齐河源海拔3800m以上的空冰斗内发育有黑色富Mn型岩石漆。运用特征元素浓度线扫描对岩石漆表面成分进行了分析,并探寻了岩石漆与下伏基岩在成因上的关系;电镜扫描实验发现典型的葡萄状一半葡萄状一片状的表面微形态序列。实验结果显示,岩石漆的物质成分不可能来源于下伏基岩,而是外部来源;粘土矿物在岩石漆形成过程中起到非常重要的作用;岩石漆表面出现蜂窝状的溶蚀孔洞,可能是近年来乌鲁木齐市及河谷后峡地区工业生产造成的酸性污染物传递到河源区对岩石漆化学腐蚀的结果。更多还原

【Abstract】 At the headwaters of the Urumqi River in the Tianshan Mountain, Mn-rich black rock varnish outcrops are scattered in an ice-free cirque with an elevation above 3 800 m a.s.l. In this paper, a suite of rock varnish samples which were cut into slices in the two directions that respectively runs parallel and vertically to the varnish surface are collected in the field. Vertically to the surface, the electronic probe line scanning analysis is applied to detect the contents of the major elements including Mn, Fe, Al, Ca, Mg, Si, etc. in the rock varnish. The experiment reveals that the Mn/Fe ratio varies in a range of 3:1-6:1. The scanning lines are set running vertically to the varnish surface to determine whether there is genetic relation between the rock varnish and the underlying substrate, which reveals that the rock varnish is of external origin. It is found that on the varnish-rock interface, completely different contents of elements Mn, Fe, Al, Si, Mg are shown toward the orientation to the varnish and to the bedrock. The typical varnish micromorphological continuum from lamellate pattern to semi-botryoidal and botryoidal patterns was observed with scanning electronic microscopy (SEM). The outlines of the typical botryoidal bodies are observed and described detailedly in the article. Distinct interface between the varnish and the underlying crystal is present likewise. In addition, the clay minerals may play an important role in the formation of the rock varnish. In the ice-free cirque, the factors affecting locally the growth of rock varnish, such as the temperature, precipitation, sunshine, humidity, alkalinity, organic matter content, and level of ambient dusts, appear to favor the formation of the Mn-rich black varnish. Alveolate caves carved on the varnish nodules ascribe to presumedly the acidic erosion from the acidic contamination in the Houxia region where several industrial factories are located. In the riverhead area of Urumqi River, pH value of the surface water and aerosol is neutral to mildly alkaline, which could not offer the obligatory acidic environment to the chemic erosion on the varnish surface. It is supposed that the atmospheric pollutants are transported to the headwaters of the Urumqi River upstream along the valley and sunk onto the varnish surface with precipitation.更多还原