Geology And Geochemistry Of The Granites From Daheishan Area, Lvchun County, Yunan Province

Granite contains important information of crustal evolution and crust-mantleinteraction. And granite-related ore deposits are of great value to the development ofsociety. Therefore, geologists pay close attention to granites. In this thesis, we taketwo granite bodies (Jinchanghe and Niuzhi) from Daheishan Area as the researchsubjects, and based on the petrology, geochemistry and geochronology, we discusstheir genesis and tectonic background. Research area locates at Daheishan Area,Lüchun County, western of Yunan Province, southwest of China. Yunnan is stronglyaffected by Indian-Eurasian collision, as well as the Pacific plate. Eastern Yunanbelongs to fold belt of continental margin hyperplasia of Yangtze block, while theWestern Yunnan belongs to multi-island-arc basin system of Tethys.Major oxides data show them are depleted in K, enriched in Na and saturated inAl. High A/CNK value suggests that they are peraluminous granites. REE and traceelements show that large ion lithophile elements (Ba, Sr) and some of REE (La, Ceand Nd) are enriched, while the Rb, Th, Ta, Pr, P and Ti are depleted. Jinchanghegranite is+δEu, while the Niuzhi is slightly–δEu. δCe are not noticeable.LA-ICP-MS Zircon U-Pb geochronology show that Jinchanghe granite porphyryformed at264.7±1.3Ma（n=30，MSWD=2.3）while Niuzhi Monzonitic graniteporphyry formed at263.5±1.7Ma（n=29，MSWD=4.3）. Both formed at middlePermian, and belong to late Hercynian-early Indosinian.Jinchanghe granite was controlled by crustal anatexis which was started bymantle diapirism. High crust-mantle interaction led to Jinchanghe granite containingmore mantle information. Niuzhi granite contained more crustal informationsuggesting that sedimentary materials (metamorphic greywacke and slate) contributing to the magma. Tectonic background analysis proved that Jinchanghegranite formed at pre-collision stage while the Niuzhi at sync-collision stage. Thisimplies that the collision betweem Lvchun-Mojiang Arc Island and continent was ashort and rapid process.