Characteristics And Significance Of Heavy Minerals And Zircons In Aeolian Loess In The South Of Qinling Mountains

South Piedmont of Qinling Mountain is a transition zone between the north subtropical and temperate zone, and is very sensitive to the response to climate change. The research of sediment source and environmental change has important significance for the study of global climate change. The widely developed and thick loess in the basin where in the south of Qinling Mountain and terraces of Hanjiang River was found through the field investigation. But the research about the material source of loess is controversial. This study took the Aeolian loess in the south of Qinling Mountain as the research object, and the composition characteristics of heavy mineral in the loess were analyzed. Difference of heavy minerals in loess in the north and south sides of Qinling Mountain was studied and the response mechanism was also studied. Took the different sediments in the south sides of Qinling Mountain as research objects, through the analysis of zircon U-Pb age composition in different sediment and comparisons with the Zircon U-Pb age composition in the wind sediment of North and south sides of Qinling Mountains, the sediment sources of the were discussed. The main results as follows:(1) There are 20 kinds of heavy mineral in the loess in the south side of Qinling Mountain, containing Zircon, Staurolite, Rutile, Anatase, Actinolite, Tournaline, Hematite, Leucoxene, Tremolite, Titanite, Garnet, Pyrrhotite, Ilmenite, Pyroxene, Apatite, Magnetite, common Hornblende, Allochite, Kyanite, Barite, Sillimanite and so on. The magnetite, hornblende, and ilmenite as dominant mineral, accounted for more than 60% of the total heavy mineral. While the stable mineral of Magnetite, Hematite and Limonite ore, Ilmenite, Leucoxene, Anatase and Garnet minerals accounted for about 47.95% of total heavy mineral. And they were the main mineral composition in the loess.(2) The comparison of heavy mineral distribution in the Malan loess and paleosol in the south side of Qinling Mountain were studied. The results showed that two kinds of heavy minerals were exactly the same, content was close, indicating the sediment source was consistent in the loess and paleosol. Unstable heavy mineral content in the loess layer was higher than the content in the Paleosol, but the stable heavy mineral content was lower. The R value was low and it showed that the sediment is strongly influenced by weathering and leaching during the period of Paleosol formation and the climate is warm and wet.(3)The heavy mineral species in the loess on the south and north sides of the Qinling Mountain had a good comparability. The dominant mineral species were similar to the stable mineral assemblage distribution and indicated that source area of the subject matter of loess sediment on the both sides of the Qinling Mountains was consistent. The stable mineral content in the loess on the south side of Qinling Mountain was higher than the content in the loess of the Loess Plateau. And this indicated that the climate in the south side of Qinling Mountain was warmer and wetter than the Loess Plateau's.(4) The Zircon age distribution of eolian sediments in the south side of Qinling Mountain was very similar and its distribution range was wide. The maximum Zircon age was older than 2Ga. The peak of Zircon content appeared in the 170-240Ma, 320-450Ma,490-530Ma and 560-820Ma. And the material source of loess and paleosol was consistent, indicating that the source of regional eolian sediments was stable and the the eolian accumulation was a stable deposition process.(5)In the sediment of south side of Qinling Mountain, the comparison of Zircon U-Pb age in the eolian sediment and it in the water deposited material showed that the distribution range of Zircon U-Pb age in the eolian sediment of Hanjiang valley was wide, the peaks of the number of Zircon were more and the old age was more, too. While Zircon U-Pb age in the water deposited material was young, and the peaks of the number of Zircon was less. They had difference in the Zircon U-Pb age composition and it showed that the source of the eolian sediment and the water deposited material was different. The source of eolian sediment was more complicated and extensive.(6) From the Zircon U-Pb age composition in the eolian loess debris in the north and south sides of Qinling Mountain, we concluded that the peaks and distribution range of them had a good contrast. The distribution range of Zircon U-Pb ages were all near 2.5Ga. Many groups Zircon ages appeared in the eolian sediment on the south side of Qinling Mountain were all peaks in the eolian sediment of Loess Plateau. And it indicated that two source areas had the overlap. The Zircon age composition showed that the Loess Plateau's distribution range was wide and the Zircon content appeared more peaks, reflecting the Loess Plateau region was near the source area and Reveals the source direction of the Aeolian Sediments in the south of Qinling Mountains.