| Papers selected widely development in volcanic rocks of yixian formation in westernliaoning jianping horse factory region as the research object, on the basis of combiningprevious research results, find out the combination of volcanic rocks of yixian formationin the region characteristic, distribution, determine the age of volcanic rock formation,in-depth analysis of the geochemical features of volcanic rocks, discusses the nature of themagma source area of volcanic rocks, rock formation and tectonic background, for thewestern liaoning region early cretaceous volcanic activities and tectonic evolution historyprovides new data.1. The volcanic geological characteristics of yixian formationVolcanic rocks of yixian formation are mainly concentrated outcropped in the studyarea, southeast region roughly along the fault basin of north east to distribution, theexposed area of80km2, accounting for100%of the research area of Mesozoic volcanicrocks in the area. With complex composition of shallow celadon is the conglomerate,rhyolite, rhyolitic chip quality, and the crystal tuff, rhyolitic ignimbrite, black obsidian,trachyte dacite, rough surface, rough surface, the Ann tuff is given priority to, see a smallamount of andesite, scattered low limestone are in the clip. According to the profile willtest our and sampling research area is divided into three of yixian formation lithologicsection. 2. The volcanic chronology of yixian formation characteristicsZircon LA-ICPMS U-Pb dating, according to the results of two samples of rhyoliteformation ages were127.7+/-1.8124.3+/-1.8Ma, Ma, a black obsidian samples formage was122.3+/-1.4Ma, a coarse surface dacite samples form age was121.8+/-1.3Ma, a sample trachyte formation age was114.9+/-1.8Ma, the above five results showedthat the age of the volcanic rock samples ranged between127.7-114.9Ma, suggests thatduring the volcanic rock of yixian formation for the early cretaceous.3. The geochemical features of volcanic rocks of yixian formationVolcanic cycle of yixian formation can be divided into two volcanic cycle, and thefirst and the cycle of SiO2content is between64.66%~72.68%, Na2O and K2O and avalue of7.95%~9.15%, K2O/Na2O ratio between0.49~0.73, the sample Na2O <K2O,belongs to high potassium to pledge-potassium to pledge, terman index d=2.25~3. In64,. On the SiO2-K2O diagram, most of the samples into potassium XuanYan series(olive coarse andesite) range. In AFM graphical point fall on calcium alkali series. Thesecond and the cycle of SiO2content is between61.86%~69.48%, Na2O and K2O and avalue of7.83%~9.71%, K2O/Na2O ratio between0.65~0.93, the sample Na2O <K2O,belongs to the potassium to pledge, in the coarse surface of dacite terman index d=2.54~2.54, with a mean of3.15, belong to calc alkali rock series. Trachyte in terman index d=4.51~4.92, with a mean of4.70, belong to alkaline rock series. On SiO2-K2O diagram,most of the samples into potassium XuanYan series (olive coarse andesite) range, in AFMdiagram points behind the calc-alkaline series zone, has the obvious trend of rich alkali,show that magnesium rich alkali poor rock.The first cycle of volcanic rocks in the chondritic standardization of rare earthelements distribution diagram to present the patterns of distribution of right high left low,all the samples in Eu negative anomaly. Σ REE is172.48~250.54, LREE/HREE is14.29~22.63,(La/Yb)Nvalue range of19.47~31.95, the delta Eu value of0.45~0.97, theaverage is0.78, trace elements volcanic rocks in the primitive mantle standardized webshowed overall right curve characteristics, overall showed a significant enrichment in thegroup volcanic rocks in K, Rb, Li, Th, U, Y, Hf, Ta and other large ion lithophile elements; Strong loss of Nb, Ti, P high field strength elements, overall morphological characteristicsand geochemical characteristics of the lower continental crust.The second cycle of volcanic rocks in the chondritic standardization of rare earthelements distribution diagram to present the distribution of the right high left low mode.ΣREE is166.03~318.79, LREE/HREE is17.79~25.12,(La/Yb)Nvalue range of29.67~46.50, the delta Eu value is064~1.17, the average is0.94, trace elements volcanicrocks in the primitive mantle standardized web showed overall right curve characteristics,overall showed a significant enrichment in the group volcanic rocks in Rb, Li, Th, U, Y, Taand other large ion lithophile elements; Strong loss of Nb, P, Ti high field strengthelements, overall similar morphological characteristics and geochemical characteristics ofcontinental crust.4. The volcanic rocks in the source area of yixian formation properties and magmaevolution characteristicsVolcanic rocks have high silicon, alkali rich, poor calcium, magnesium, enrichmentof large ion lithophile elements, loss of high field strength elements and combination ofelements, which are the characteristics of the shell source magma. Volcanic rocks havestronger Eu negative anomaly, and most of the sample HREE distribution appeared mildconcave, show that magma source area of the residual mineral in the presence ofhornblende happened or hornblende separation and crystallization. In yixian cycle ofvolcanic rock material is mainly derived from partial melting of continental crust material,received a degree in the process of magma evolution on the earth’s crust materialcontamination.5. The structure of the volcanic rocks of yixian formation backgroundIn yixian cycle of the value of the first, second cycle of volcanic rocks of tau average35respectively81and24.39, volcanic rocks in orogenic belt of tau generally greater than10. The lg tau sigma-lg diagram shows that all the samples are projected area volcanicrocks in orogenic belts and its derived, alkaline and alkaline volcanic rocks zone. TheFeO*-MgO style-Al2O3diagram, in yixian cycle of first, second, the cycle of volcanicrocks in the projection point located in the central island region, expansionary reflect righteousness county cycle of volcanic activity in the lithosphere extensional tectonicenvironment, the in conformity with the yanshan region geological structure background.In yixian cycle of volcanic rock is the product of yanshan intraplate orogeny, formed in theintracontinental lithosphere stretch tectonic environment... |
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