Morphological And Element Geochemical Characteristics And Provenance Significance Of Muscovite In Estuaries Of The Yellow River And Yangtze River

Hundreds of millions of tons of terrigenous detrital from the Yellow River and the Yangtze River are continuously imported into the Eastern Marginal Sea of China each year,which has become an important terrigenous sedimentation sink.The sediments flowing into the sea are important carrier and link for the study of land-sea interactions.Sediments contain a lot of information about the origin of source rocks,drainage basin conditions,climatic conditions,sedimentary environment,etc.,which are good indicators for provenance analysis,and are important research objects for sediment source analysis.At present,there have been many studies using single minerals to analyze sediment provenance and apply them to the study of the provenance of the Yellow River and the Yangtze River.Muscovite is not only a heavy mineral,but also an important light mineral.Muscovite has a high content in the Yellow River and the Yangtze River.Muscovite has strong resistance to weathering and belongs to a relatively stable mineral.It records environmental information during the mineral formation process.Moreover,the special flake structure of muscovite results in significant difference in its shape factor from spherical particles,as well as special hydraulic behavior.However,there is a lack of discussion on the difference between the morphological of muscovite and other granular detrital minerals in hydraulic sedimentation,and there are few studies on the provenance of the Yellow River and Yangtze River sediments based on the geochemical characteristics of muscovite.In this paper,surface sediment samples from the Yellow River estuary,Yangtze River estuary and Nantong coastal areas were obtained through field sampling and treated in the laboratory one by one.The detrital mineral samples were obtained by using water sieving method and heavy liquid separation method,and then the light microscope was used to observe the light and heavy mineral characteristics of the samples from the Yellow River and the Yangtze River estuaries.Then heavy liquid separation method,jigging method and magnetic separation method are used to select pure muscovite.The quality and weight must meet the experimental test requirements,and then use the 3D digital microscope to measure the length,width and thickness of the muscovite.Finally,ICP-OES and ICP-MS were used to detect the elemental geochemical content of muscovite,and their geochemical characteristics were analyzed to find out the indicators that can identify the provenance of the Yellow River and the Yangtze River.The experimental results and research conclusions can be summarized as follows:(1)The analysis of the characteristics of the light and heavy minerals composition in the Yellow River and the Yangtze River estuaries shows that the heavy mineral assemblage of the Yellow River estuary is dominated by hornblende-limonite-epidote.The content of garnet,limonite,ilmenite,magnesite,actinolite,epidote,tourmaline,zircon,hematite and other minerals in the heavy minerals of the Yellow River estuary is higher and significantly higher than that of the Yangtze River estuary.The content of hornblende,siderite,zoisite,diopside,sphene and debris in the Yangtze River estuary is significantly higher than that in the Yellow River estuary.The light minerals in the Yellow River and the Yangtze River estuaries are dominated by quartz and feldspar,and the average content of quartz in the Yellow River estuary is lower than that of the Yangtze River estuary,and the content of calcite and dolomite is higher than that of the Yangtze River estuary.(2)The analysis of the mineral and content characteristics of muscovite in the Yellow River and the Yangtze River estuaries shows that most of the clastic muscovite of two estuaries is flaky,and the color is mostly colorless and transparent,and mostly sub-circular.The muscovite in the Yellow River estuary has a higher roundness than the Yangtze River estuary.The size of the samples from the Yellow River estuary is concentrated in the range of 3.5?5.0?,and the size of the samples from the Yangtze River estuary is mostly distributed in the range of 3.5?6.0?.The white mica in the two estuaries is high in light minerals and low in heavy minerals.The content of white mica varies greatly among the grain sizes.Muscovite in the Yellow River estuary sample is relatively enriched within 1.5?4.0?,and that in the Yangtze River estuary sample is enriched in1.5?3.5?.There is a significant peak shift between the high muscovite content and the grain size of the high-frequency sediments.The difference is between 1.5??2.5?in the Yellow River estuary and 1.5?3.0?in the Yangtze River estuary.(3)The statistical analysis of particle size and thickness of muscovite shows that the difference between the average particle size of muscovite of the same size in the Yellow River and the Yangtze River estuaries is small,but the difference between particle size and thickness is large.The average thickness of Muscovite with different particle sizes is less than 15?m,and the thickness tends to increase with the increase of particle size.The relationship between the shape and diameter-thickness of quartz and feldspar is relatively stable,while muscovite is easily peeled into thin sections due to a group of extremely complete cleavage,so the relationship between diameter-thickness is prone to large changes.In order to further discuss the sedimentary composition of the two,we introduced the shape factor of diameter-thickness ratio.According to calculations and statistics,the diameter-thickness ratio of the muscovite in the Yellow River estuary is concentrated between 5?60,and the diameter-thickness ratio of the muscovite in the Yangtze River estuary is slightly larger and concentrated between 10?70.The diameter-thickness ratio of quartz and feldspar is smaller than that of muscovite,which is concentrated in the range of 3?20.(4)Using the diameter-thickness ratio,calculate and compare the difference in volume when the particle size of muscovite and quartz and feldspar are the same,the difference in the deposition rate when the particle size are the same,and the difference in the particle size when the deposition rate are the same.The hydraulic deposition characteristics of other granular detrital minerals of muscovite are analyzed.The volume of muscovite in the Yellow River estuary is about 16%?55%of the volume of felsic with the same particle size,and the volume of muscovite in the Yangtze River estuary is about13%?41%of the volume of felsic with the same particle size.When muscovite has the same particle size as quartz and feldspar,the deposition rate of muscovite in the Yellow River estuary is about 0.03?0.19 times that of quartz and feldspar,and the Yangtze River estuary is the Yangtze River estuary is about 0.03?0.11 times.When the deposition rate of muscovite and quartz and feldspar is equal,the size of muscovite is larger than that of quartz and feldspar.The difference between the particle size of muscovite and the felsic in the Yellow River estuary is about 1.25-2.25?,and the difference between the Yangtze River estuary is about 1.75?2.5?,this value may be larger in actual situations.Therefore,when the particle size is the same,the volume of muscovite is much smaller than that of felsic,and its deposition rate is much lower than that of felsic.When the particle size is the same,the particle size of muscovite is much larger than that of quartz and feldspar.Therefore,large-size muscovite often coexists with fine-grained argillaceous deposits.(5)The analysis of geochemical element content in the Yellow River estuary,the Yangtze River estuary and Nantong coast shows that among the major elements,muscovite in the Yellow River estuary,the Yangtze River estuary and Nantong coast have obvious characteristics of high Al₂O₃ and K₂O,and the content of the Yangtze River estuary and Nantong coast is higher than that of the Yellow River estuary.Among the trace elements,the lithophile elements Ba and Rb have a higher content.The content of V,Cr and Sr in muscovite of Nantong coast is higher than that of the Yangtze River and the Yellow River estuaries,and the Yellow River estuary is the lowest.The content of Zr,W,Be,Hf,Ta,Tl,Th,U in muscovite in the Yellow River estuary is higher than that in the Yangtze River estuary and Nantong coastal,and the difference between two regions is very small.Among the rare earth elements,except that the content of Eu in the Yellow River estuary is lower than that of the Yangtze River estuary and Nantong coastal,the content of other elements in the Yellow River estuary is higher than that in the Yangtze River estuary and Nantong coastal.Both the characteristic values of rare earth elements and the REE distribution pattern diagram show that the detrital muscovite from the Yellow River estuary,the Yangtze River estuary and Nantong coastal all show significant enrichment of light rare earths(LREE),and Eu has a positive anomaly.(6)Using analysis methods such as correlation coefficient,cluster analysis,principal component score matrix and relative deviation,the provenance indicators of sediments in the Yellow River and the Yangtze River estuaries were extracted from muscovite major elements,trace elements and rare earth elements.The results show that there is a good correlation between the major elements TFe₂O₃ and MnO and K₂O and Mg O,and the standard deviation of TFe₂O₃/MnO and K₂O/Mg O is relatively small,and the relative deviation is large.They can be used as major elements indexes for distinguishing the provenance identification of the Yellow River and the Yangtze River.Be,V,Zr,Hf,Ta,Tl,U,W can be used as trace element indicators for identification of the provenance of the Yellow River and the Yangtze River.The standardized values of chondrites of detrital muscovite in rare earth elements and the characteristic parameter values of rare earth elements?REE,?LREE,?HREE,?Y,Sm/Nd can also be used as important indicators for provenance identification.Using these provenance identification indicators to identify the provenance of the Nantong coastal samples,it shows that the provenance identification indexes of Nantong coastal detrital muscovite is closer to the Yangtze River,so most of the detrital muscovite comes from the Yangtze River.