安徽金寨三仙山地区梅山群碎屑岩成分及其对物源区构造属性和地层时代的意义

Compositions of detrital rocks of the Meishan Group in Sanxianshan area of Jinzhai,Anhui Province:Significances of provenance tectonic attributes and the stratigraphic age

安徽金寨三仙山地区位于大别山北缘,该地梅山群主要为一套轻微变质的碎屑岩系。砂岩碎屑组分统计表明,砂岩类型主要为岩屑石英砂岩、岩屑石英杂砂岩,石英、长石、岩屑的平均含量为87.21%、1.67%、9.64%,杂基含量为15%;石英几乎全为单晶石英(95.79%),长石以斜长石为主,岩屑主要为沉积岩屑(75.49%),其次为变质岩屑(24.51%)。碎屑岩地球化学元素平均含量为:SiO_2(75.99%),Al_2O_3(11.96%),MgO(0.72%),CaO(0.10%),Fe_2O_3(4.02%),K_2O(1.70%),Na_2O(0.26%)。∑REE=170.49×10^(-6)(74.49×10^(-6)~309.42×10^(-6)),LREE/HREE=11.16(7.89~14.26),轻稀土略有富集,δEu=0.72(0.59~0.90),La/Yb=22.08(13.01~31.18),(La/Yb)_N=14.89(8.77~21.02),δCe=0.84(0.42~0.97)。碎屑岩地球化学特征指示三仙山地区梅山群母岩主要为古老沉积岩、长英质火山岩和古老变质基底,具有多重物源区。梅山群构造背景较复杂,主要为被动大陆边缘和活动大陆边缘,其次为大陆岛弧。三仙山地区梅山群碎屑岩的源岩成分、构造背景与商城—固始地区石炭系有很大差别,故其地层时代有待于进一步研究。

The detrital rocks of the Meishan Group in Sanxianshan area of Jinzhai is located at the northern margin of the Dabie Mountains, and are mostly composed of lithic quartz sandstones and lithic quartz greywacke. The average contents of quartz,feldspar and lithite are 87.21%, 1.67%, 9.64%, respectively. The quartz is mainly single crystal quartz （95.79%）, the feldspar is mainly plagioclase and the lithite is mainly sedimentary rock lithite （75.49%）, followed by the metamorphic lithite （24.51%）. The average contents of clastic rocks are Si02 75.99%,A120311.96%,MGO 0.72%, CaO 0.10%, Fe203 4.02%, K20 1.70%, Na20 0.26%, δREE= 170.49× 10-6（74.49×10^-6- 309.42×10-6） ,LREE/HREE = 11. 16（7.89- 14.26） ,light REE enrichment,δEu= 0. 72（0. 59-0. 90） ,SCe = 0. 84（0. 42-0. 97） ,La/Yb = 22.08 （ 13.01 -31. 18 ） , （La/Yb）N = 14.89 （8.77 -21.02 ）. The geochemical characteristics of the clastic rocks indicates that the source rocks of the Meishan Group were ancient sedimentary rocks, felsic volcanic rocks and ancient metamorphic basement and uncovers a complicated tectonic settings composed of mainly passive continental margin and active continental margin, followed by continental island-arcs. The both the Meishan Group in the Sanxianshan and the Carboniferous in Shangcheng-Gushi area have different composition of source rocks and tectonic setting, which might imply the both to have different geological ages.