| Based on the profile survey of Ruyiting in the west of Xiangshan,its rock formations will be further divided,this article will divide the Daguding group on Ruyiting group into Shuangfengling formation,then,taking rhyodacite as our research object for the study of rock geochemistry and petrography,the results show that it does not belong shoshonite,but belong to high-K calc-alkaline rhyodacite.Based on the study of rock geochemistry,Sr-Nd-Pb isotope,chronology,we will explore the characteristics of magma source,crystallization separation and evolution,the genetic classification of rocks and diagenetic tectonic environment further.The rhyodacite in the west of Xiangshan are poor phyritic texture structure which in a colour of dark purple.The phenocrysts are mainly plagioclase,quartz,a small amount of hornblende and biotite.The rhyodacite display a higher SiO2?range from 66.15%to 68.26%,the average value is 67.09%?,enriched in Alkali?K2O+Na2O=7.72%8.95%,the average value is 8.25%?,and enriched in K?K2O=4.79%5.45%,the average value is 5.04%?,but lack of Ca?CaO=1.49%2.89%,the average value is 2.13%?and Mg?MgO=0.68%0.95%,the average value is 0.82%?.Plotting within the field of sub-alkaline series in the TAS diagram and plotting within the field of tholeiite series in the FAM diagram,belonging to calc-alkalic rock series.Through CIPW,the results show that the content of Q is ranging from20.01 to 25.92?the average value is 23.69?,belonging to the rough dacite.DI is higher?DI=78.4984.53,the average value is 81.50?,SI on the low side?SI=4.857.4,the average value is 6.12?,showing that the rock formation has experienced a high differentiation in the process of evolution.The?REE is higher(?REE=284.40×10-6,the content of?HREE is ranging from25.73×10-66 to 31.38×10-6,the ratio of?LREE/?HREE ranges from 8.73 to 9.69,Eu has obvious negative anomaly,REE pattern is LREE enrichment type of right-wing.On the trace element spider diagram,the characteristics of trace element are enriched in LILE?Rb?Th?U?La?,and high field strength elements are depleted enormously?Ba?Nb?Ta?Ti?.In the discrimination diagram of A-type granites and K2O-Na2O,the element characteristics of type A granite is displayed.The value of(87Sr/86Sr)i is ranging from 0.7096 to 0.7109?the average value is 0.7103?,the value of(143Nd/144Nd)i is ranging from 0.511940 to 0.512056?the average value is0.51199133?,the value of(206Pb/204Pb)i is ranging from 18.326 to 18.408?the average value is18.367?,the value of(207Pb/204Pb)i is ranging from 15.638 to 15.697?the average value is15.667?,the value of(208Pb/204Pb)i is ranging from 38.652 to 38.870?the average value is38.763?,the value of?Nd?t?is ranging from-10.2 to-7.90?the average value is average-9.17?,the value of TDMM is ranging from 1648Ma to 1811Ma?the average value is 1741 Ma?,the value of TDM2M2 is ranging from 1574Ma to 1757Ma?the average value is 1676 Ma?,showing the characteristics rhyodacite having a melting crust partial basement metamorphic product.From the diagram,such as?Nd?t??Ma?,ISr-?Nd?t?,208Pb/204Pb-206Pb/204P,208Pb/204Pb-206Pb,and??-??,rhyodacite exhibit material from the basement metamorphic rocks,influenced by mantle derived materials is not obvious.In the discrimination diagrams of Nb-Y-3Ga and Nb-Y-Ce,rhyodacite falls into the scope of A2 type under tensional tectonic environment and the rhyodacite in the west of Xiangshan formed in the intraplate extensional tectonic environment be displayed in the diagrams of SiO2-TFeO/?TFeO?+?MgO??CaO-TFeO+MgO?Rb-Y+Nb?Yb-Ta?Y-Nb.SHRIMP zircon U-Pb dating results show that the age of 206Pb/238U varied from134.86 to 142.3Ma,the weighted average age values is 137.4Maħ1.1Ma,MSWD=1.3,the formation age of rhyodacite is the early cretaceous.The resource of high-K calc-alkaline rhyodacite in the west of Xiangshan are mainly from the earth's crust,in the early cretaceous,the earth's crust have occurred some partial melting in the environment of intraplate extensionaltectonic,magma eruptting from the earth's crust is formed through crystallizing differentiation in the process of rising. |
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