Diagenesis Of Intermediate-acidic Intrusive Rock In The Luzong Areas, Anhui Province

The Luzong area is located in the middle and lower Yangtze River rift belt, which isan important part of the middle and lower Yangtze River metallogenic belt. With thenew deposits from Luzong areas were discovered and prospected in recent years,revealed the existence of the hidden intrusive plutons, which provides a clue forpetrogenesis and mineralization in this area. We need to improve and supplement thepetrogenesis and the mineralization of the Luzong areas. Based on the summarise ofprevious studies and by the means of detailed geological investigation and experimentalanalysis, such as microscope observation, electron probe microanalysis, LA-ICP-MSisotopic chronology, petrogeochemistry, This paper carrys out the research work onthese intrusive plutons that had not been previously investigated in Luzong areas andhighlight their petrogenesis and the relationship with the mineralization.Along the Huangmeijian-Jiangjunmiao-Dalingjiao and its western elongation, theLuzong area was divided into the northern region and southern region. The hiddenintrusive plutons in the north of the Luzong areas are Qingshuitang pluton, Liudunpluton, Qiaochong pluton, Niutoushan pluton, Lijiazhuang pluton, the intrusive plutonsoutcrop in the south of the Luzong areas Shadun pluton, Chuanshaoshi pluton,Qingshan pluton, Hejiaao pluton, Meilin pluton, Gutangchong pluton, Zhoujiashanpluton. The intrusive plutons in the north Luzong area are monzonite and syenite, andthe intrusive pluton in the south Luzong are quartz syenite and moyite. ThroughLA-ICP-MS zircon U-Pb dating methods, we determined the age of intrusive plutons inLuzong area, respectively, Qingshuitang pluton was133.2±1.4Ma, Liudun pluton was131.3±1.3Ma, Qiaochong pluton was131.0±1.4Ma, Niutoushan pluton was131.2±1.2Ma, Lijiazhuang pluton was130.9±1.2Ma, Shadun pluton(biotite quartzsyenite) was126.5±1.1Ma, Shadun pluton(quartz syenite) was126.5±1.5Ma,Chuanshaoshi marginal facies pluton was126.2±1.2Ma, Chuanshaoshi center plutonwas126.7±1.3Ma, Qingshan pluton was126.7±1.3Ma, Hejiaao pluton was126.9±1.4Ma, Meilin pluton was125.9±1.3Ma, Gutangchong pluton was126.7±1.4Ma,Zhoujiashan pluton was124.9±1.3Ma. The epoch of plutons in the Luzong area isbetween134and123Ma, they are all early Cretaceous. According to the epoch andgeological characteristics, the intrusive plutons in the Luzong area can be divided intotwo stages. The early stage formed diorite, monzonite-syenite distributes in the northpart of the Luzong area in134~130Ma. The late stage intrusions were quartz syenite and moyite, they mainly distributed in the south part of the Luzong areas and were formedin129~123Ma.The electron probe microanalysis of intrusions in Luzong district shows no perthitecontained in the north intrusion, but perthite usually occur in the south intrusion,plagioclase in intrusions in the north are mainly oligoclase and andesine (An is29~44),in the south intrusion are mainly albite (An is0~5). The north intrusion contains augitewhich is rarely occured in the southern intrusions, both north and south intrusionscontain calcium hornblende and magnesian biotite. Augite, hornblende and biotite aremantle-derived origin. Geochemical characteristics of intrusions shows that intrusionsin both north and south are enriched high field strength elements such as Zr, Hf andlarge ion lithophile element Rb, Th, K, Ce et al., and deplete high field strength elementTi, Ta, P et al., but the north intrusion Th, U content are obviously higher than the south.The north intrusion∑REE range is175.28×10－6ppm~321.58×10－6ppm, δEu is0.34~0.68, the ratio of LREE/HREE is10.59~17.50;The south intrusion∑REE range is191.82×10－6ppm~642.91×10－6ppm, δEu is0.25~0.71, the ratio of LREE/HREE is6.95~18.74; both of them have right deviation of light rare earth element enrichmentcharacteristic, and all of them shows negative Eu abnormity, indicate that fractionalcrystallization of plagioclase maybe exist during magma evolution process. The Hfisotope characteristics shows that εHf(t)of the north intrusion in Luzong basin range is-13.10~-5.78, εHf(t)<0, while the south intrusion εHf(t)range is-6.99~4.96.According to former research and this study, we consider that the intermediateintrusion in Luzong area have the same origin, magmatic source is enriched mantle, thenorth (early period) intrusions are located at compression-tension transitional tectonicsetting, the ancient lower crust has more participation in magmatic evolution, but thesouth (late period) intrusions located at intraplate extensional tectonic setting, theancient lower crust has less participation in magmatic evolution.