江汉平原主要河流沉积物重矿物特征与物源区岩性的响应

通过对江汉平原主要河流沉积物的重矿物组合、特征矿物以及能够反映沉积物稳定状况、物源及成熟度的重矿物特征指数(ATi,GZi和ZTR)进行对比分析,发现在江汉平原范围内,长江和汉江及其长江主要支流的沉积物中重矿物特征具有显著的差异。长江的重矿物组合模型为：  锆石+绿帘石+辉石+绿泥石+金属矿物,特征矿物是锆石和辉石;   汉江的重矿物组合模型为：  绿帘石+角闪石+石榴石+绿泥石+金属矿物,特征矿物是角闪石、石榴石;   另外,清江、漳河、沮水和玛瑙河的重矿物组合及特征矿物也都完全不同。而且各水系的沉积物的重矿物特征与其源区的岩性分布显示出极好的相关性。研究表明在江汉平原利用重矿物特征及组合模型来进行物源示踪的方法开展水系演化研究是可行的。

HEAVY MINERAL CHARACTERISTICS OF RIVER SEDIMENTS IN JIANGHAN PLAIN AND ITS RESPONSE TO PROVENANCE ROCK TYPES

The Jianghan Plain,located at the middle Yangtze River and the lower Hanjiang River,is the main body of the middle and lower Yangtze River Plain. Heavy mineral samples were obtained from sediments of these main rivers in the Jianghan Plain to find the difference among sediments of the Yangtze River,main tributaries of the Yangtze River(Qingjiang River,Zhanghe River,Jushui River,and Manaohe River),and the Hanjiang River. The sampling locations are on the sandy floodplain before the rivers flew into the Jianghan Plain. This research was based on the analysis of characteristic minerals,heavy mineral assemblages,and index values：  ATi,GZi and ZTR. These three indices can reveal the stability,provenance,and the degree of maturation of the sediments. Our results show that there are obvious differences among heavy mineral characteristics of sediments from the Yangtze River,Hanjiang River,and other rivers in the Jianghan Plain. Heavy mineral assemblage of the Yangtze River is zircon epidote pyroxene chlorite metal minerals and its characteristic minerals are zircon and augite. The Hanjiang River is different from the Yangtze River with the heavy mineral assemblage of epidote garnet chlorite metal minerals and hornblende &; garnet as its characteristic minerals. The characteristic mineral assemblage of the Qingjiang River is Zircon garnet chlorite pyrite hematite and limonite ilmenite;  and the characteristic minerals are pyrite hematite and limonite ilmenite. The characteristic mineral assemblage of the Zhanghe River is zircon tourmaline sphene garnet leucoxene rutile anatase spinel and the characteristic minerals can be divided into two types：  stable minerals(such as zircon tourmaline sphene rutile)and unstable minerals(such as leucoxene anatase spinel). The characteristic mineral assemblage of the Jushui River is zircon epidote garnet leucoxene rutile hematite and limonite ilmenite magnetite,and the characteristic minerals are zircon epidote garnet hematite and limonite. The characteristic mineral assemblage of the Manaohe River is zircon epidote garnet leucoxene hematite and limonite,and the characteristic minerals are mainly epidote garnet hematite and limonite. The ATi value of the Yangtze River and Hanjiang River are above 86,the GZi value of the Yangtze River is about 30～38,while the Hanjiang is 89～93,showing remarkable differences. The ZTR value of the Yangtze River is higher than that of the Hanjiang River. The ZTR value,ATi value,and GZi value of the Qingjiang River are all low. The ATi value and GZi value of the Zhanghe River sediments are low,while its ZTR value is very high. The ZTR value of the Jushuihe River is quite high,indicating the maturation of its sediments while its ATi value and GZi value are low. The Manaohe River is situated in the Jianghan Plain. Because of its short length,the heavy mineral characteristic indices is not apparent. The analysis of characteristic minerals,heavy mineral assemblages,and index values show very good correlation between heavy mineral assemblage of sediments from different river systems and type of lithology distribution of the source rocks. This correlation indicates that heavy mineral assemblage of sediments are controlled by lithology distribution of the source rocks and is feasible to study the evolution of river systems in the Jianghan Plain through source tracing. Such a research can be carried out by the characteristics and assemblages of heavy minerals from very fine sand,because heavy mineral from river sediment mainly exist at this size fraction. The calculation results show that the transport capacity of hydrodynamic towards different heavy minerals is almost the same.