毛乌素沙地现代流动沙丘沙的矿物成分

对毛乌素沙地16个现代流动沙丘沙样品矿物分析结果进行归纳与研究.结果显示:(1)毛乌素沙地现代流动沙丘沙轻矿物占绝对优势,平均含量为94.8%,以石英、长石为主;重矿物所占比例很小,平均含量为1.6%,但种类较多,共含22种重矿物.(2)重矿物中2/3以上属硅酸盐类矿物,其含量前三的为角闪石、绿帘石、石榴子石;(3)重矿物以不稳定矿物和较稳定矿物占较高比例,绝大多数为硅酸盐类矿物,分别为100%和98.75%;(4)重矿物中硬矿物和极硬矿物含量高达80.17%,分别为61.57%和18.60%.结果还显示,轻矿物石英/长石含量比值(平均值为6.10)和重矿物矿物风化系数(平均值3.89)都较高,重矿物中造岩矿物(平均值26.7%)含量占近1/3.由此,并考虑到高含量的硬-极硬的重矿物的存在,表明其沉积时属于气候干冷、生物化学风化作用较弱的强风沙流环境.本文除证明了高含量的不稳定矿物和较稳定矿物与气候干旱具有本质上的联系外,还说明了干旱环境下沙丘沙中多种类、高含量的硬-极硬矿物的存在,极大地抑制了物理风化和生物化学两个方面的风化的难度,从而使其向土壤化根本逆转也很难.即使沙丘得以固定,由于其丘体的这种矿物组分,仍然难以消除潜在沙漠化的客观存在,故土地沙漠化引起生态环境的退化实际上也与沙丘沙碎屑矿物的物理性质具有本质上的联系.因此,干冷多风的气候条件及其导致的沙丘沙所具有的物质组成的特殊性应该是土地沙漠化的两个不可或缺的原因.

Mineral Composition of Sand Particles of Modern Mobile Sand Dunes in the Mu Us Sandy Land

Mineral composition of 16 modern mobile sand dunes sand particle samples from Mu Us Sandy Land was analyzed. Results show that: (1) Light minerals dominate in content, with 94.8% on average and the principal compositions are quartz and feldspar; In these samples little heavy minerals exist, with average 1.6%, but number of mineral species is various, with about 22 kinds. (2) More than 2/3 of heavy minerals are silicate minerals, and the TOP 3 are amphibole, epidote and garnet in content. (3) Unstable minerals and relatively stable minerals account for a big proportion in heavy minerals. In this two kinds of mineral assemblages, silicate minerals occupy absolute advantage, respectively 100% and 98.75%. (4) Hard minerals and ultrahard minerals in heavy minerals totally reach up to 80.17%, respectively 61.57% and 18.60%. The results also show high Q/TF ratio (average 6.10) in light minerals and high HW value (average 3.89) in heavy minerals. Rock-forming minerals (average 26.7%) account for nearly 1/3 in heavy minerals. Therefore, given the high content of hard and ultrahard heavy minerals, all these indicate that the dune sand particles was deposited in the dry-cold climate with strong wind-sand flow environment and weak biological and chemical weathering. The discussion of this paper on mineral components of sans particles of modern mobile sand dunes in Mu Us Sandy Land not only proves the essential relationship between the arid climate and the high content of unstable minerals and relatively stable minerals, but also shows the existence of various kinds and high content of hard and ultrahard minerals greatly inhibits both physical weathering and biochemical weathering and makes it difficult to reverse to pedogenesis fundamentally. Even though the dunes can be fixed, it is still difficult to eliminate the objective existence of potential desertification because of such mineral components of the dunes, so the degeneration of ecological environment resulted from desertification has essential relationship with the physical properties of clastic minerals in dune sand. Therefore, the dry-cold and windy climate conditions and its resulted special material composition in dune sand are the two essential causes of land desertification.