Study On Characteristics Of Main Detrital Minerals In Modern Sediments Of The Hongze Lake Reach In The Huai River

The Huaihe River is located between the Yellow River and the Changjiang River.It is the natural boundary between the warm temperate semi-humid zone and the subtropical humid zone in eastern China.Although the Huaihe River is a medium-sized river,it also transports a large amount of terrestrial detrital materials to the sea.Its sediments carry many sources of information such as source rock genesis,watershed environment,climatic conditions,sedimentary environment,etc.,and contribute to the Changjiang River and even the eastern sea area of China.Attention should be paid to the study of the characteristics of detrital minerals in the lower reaches of the Huaihe River,which can establish an effective indicator of sediments in the Huaihe River source,analyze the formation process of the Changjiang River Delta,provide a scientific basis for the analysis of the source material of the continental shelf in China and the diffusion transport of sediments into the sea.Nowadays,there are few studies on the characteristics of sediments in the Huaihe River,especially the study of detrital mineral.There are few systematic compartion of sediment characteristics in the Huaihe River and the Changjiang River.In this paper,representative samples of surface sediments from the of the Hongze Lake Reach in the Huai River(9)and the Changjiang River estuary(9)were obtained by field sampling,using sieve-sedimentation method,heavy liquid separation method,multiple grains mineral identification method,and electronic exploration.Electron probe,ICP-OES and ICP-MS methods were used to comprehensively analyze the characteristics of grain size,detrital mineral and amphibole geochemical of the surface sediments in the Huaihe River,and to establish a reliable indicator for sedimentation of the Huaihe.Based on the characteristics of the sediments in the Changjiang River,the contribution characteristics of the Huaihe River to the Changjiang River and the two rivers endmember indicators were initially explored.The results show:(1)The average grain size of the Huaihe River sediments is between 1.54~6.37?,which is distributed from medium sand to fine silt.The silt is the main one.Most of the samples are medium sorted,showing a positive partial distribution and obvious metastatic properties.The average grain size of the sediments in the Changjiang River ranges from 3.14~6.25?,mostly are silty sediments.The sorting is generally medium,and the skewed distribution is dominated by positive bias.(2)The mineral composition changes with the change of particle size.The characteristics and content of detrital minerals in different fractions are different,especially in heavy minerals.At the coarse-grain end of<2.5?,there are few mineral species with small density.The flaky and platy minerals are enriched,the heavy minerals are mica+hornblende,and the characteristic mineral is limonite;as the grain size becomes finer,the number of heavy minerals increases,and the ratio is large,granular or self-shaped.Highly stable mineral enrichment,heavy mineral combination is amphibole+epidote+limonite,garnet is the characteristic mineral.Due to the difference in the thickness of the whole sediment,the content and type of light mineral particles of different grain sizes in the Huaihe River are different.In the sediments of the whole grain size,the mica content is very low,the quartz content is high,and the feldspar content is less than quartz;In the fine-grained sediments,mica content is high in<3?grain with reached nearly 100%.As the grain size became finer,the mica content fell drastically,and the quartz content increased sharply,occupying the main position.The trend of feldspar is similar to that of quartz,which is second to quartz.(3)The Huaihe River had identified about 30 kinds of heavy minerals and 9 kinds of light minerals.The heavy mineral content of the Huaihe River is 2.59%,which is slightly lower than that of the Changjiang River(2.76%).Compared with the Changjiang River,the content of the amphibole and stable minerals are relatively high,and the minerals of the epidote-group,micas,pyroxene-group and carbonates are lower in the Huaihe River;the combination of the heavy minerals of the Huaihe River is hornblende+epidote+limonite+garnet.The SM/UM ratio of heavy minerals in Huaihe River is about 0.1,M(the light mineral maturity index)>1,it shows that the stability and weathering degree are relatively weak.(4)Through the comparative analysis of the geochemical elements of hornblende in the Huaihe River(136)and the Changjiang River(95),their hornblende all belong to the calcic amphiboles,mainly composed of magncsiohornblende.Compared with the Changjiang River,the content of magncsiohornblende is relatively low in the Huaihe River.The high content of edenite and tschermakite is the characteristics of the Huaihe River.There are more pargasite,ferropargasite and magnesiohastingsite with high K and Na in the Huaihe River.Most of amphibole is derived from intermediate-acid igneous rocks,whicth from crust-mantle in the Huaihe River.In addition,almost all metamorphic amphibole is formed by medium\low pressure metamorphism in the Huaihe River.(5)Compare the geochemical elements of the amphibole in the Huaihe River and the Changjiang River,there are small difference the major elements,and large difference in the content of most trace elements and light rare earth elements between the two rivers.The relative standard deviation values of trace elements are very large,such as Sr,Mo,Cs,Th,U in the two grades of the Changjiang River;Ba,Sr,Li,Ni,Cs,Pb,Th,U in the two grades of the Huaihe River;the fine sand grades of the Changjiang River and the Huaihe River Ba,Sr,Zr,Li,Mo,Hf,Tl,Th and U;Sc,Rb,Cs,Pb and other elements in the coarse sand between the Huaihe River and the Changjiang River.The LREE content in the fine sand grade is higher than the coarse sand grained in the Huaihe River,and two grades of HREE content in Huaihe River are similar,but both are higher than the Changjiang River.There are both negative anomalies in the elements of the Eu,and the degree of loss is increased by the the Huaihe River fine sand-the Huaihe River coarse silt-the Changjiang River fine sand-the Changjiang River coarse silt.The ratios of(La/Lu)_N,(La/Yb)_N,(La/Sm)_N and La/Y in the fine sand grade can be used as the endmembers of the Changjiang and Huaihe Rivers.