Geochemistry And Petrogenesis Of Wangxianling Compound Granitoid In Nanling Area

A large area of Mesozoic granites closely related to W,Sn,Nb,Ta and REE deposits is widely developed in the Nanling area of China.Among them,Yanshanian granite is the most widely distributed,and the associated tungsten and tin deposits are large in scale and large in number,and the degree of research is high.In contrast,the Indosinian rock mass is less distributed and the degree of research is relatively low.In this paper,Wangxianling compound rock is selected as an example to analyze the petrogenesis of the Triassic compound rock.Through field exploration,petrography,geochemistry,zircon U-Pb chronology,and Nd-Hf isotopes,etc.,the rock composition,stage,and source area properties were obtained,combined with the rock secondary mineral geochemistry,to reveal different rock differentiation and evolution processes.Wangxianling rock body is composed of Yanshanian and Indosinian rock bodies.The main part of Indosinian rock body is mainly composed of coarse tourmaline muscovite granite and fine tourmaline muscovite granite.The boundary between the two is not significant,showing a transitional contact.In addition,biotite granite,granite porphyry and other small-scale dykes or rock strains occur.The emplacement sequence of magmatic rocks is determined by zircon U-Pb geochronology: the age of coarse tourmaline muscovite granite is 237.8±3.5Ma,The age of strongly altered tourmaline granite is 238.5±3.5Ma,The mica granite intrudes 236.6±5Ma,the zircon U-Pb ages of these rocks are in the same range,and they belong to the products of Late Triassic magmatism.The corresponding?Hf(t)values are-11.8~-7.8?-17.8~-7.4?-16.1~-6.3,?Nd(t)values are-9.9~-11.1?-10.8~-11.1?-9.2~-10.8.The similar values of ?Hf(t)and ?Nd(t)indicate that these magmatic rocks come from the same magmatic event in the same source area.The trend of Ce/Sm and Yb/Gd values increasing simultaneously in zircon trace elements of tourmaline muscovite granite in Triassic granite and the low P and Y contents indicate the existence of separate crystallization of mree rich and P and Y-rich minerals such as apatite.On the other hand,the relative loss of LREE and th in the mica granite indicates that before zircon crystallization,the melt undergoes the separation crystallization of epidote/monazite,while the higher P content further determines that the epidote is the separation crystallization of epidote rather than P-rich monazite;the lower Nb,Ta content and Eu negative anomaly are more significant,indicating that it is affected by the separation crystallization of rutile and plagioclase.Although tourmaline muscovite granite and biotite granite are homologous at the same time,the variation of zircon trace elements accurately depicts the difference of magma separation and crystallization process.