皖北新元古代刘老碑组页岩的地球化学特征及其地质意义

从安徽北部新元古代刘老碑组页(泥)岩中采集了11个样品。地球化学分析表明,研究区南部的淮南和凤阳页岩样品SiO₂、TiO₂、Al₂O₃、K₂O、TFeO和CaO含量分别为55.28%、0.87%、15.60%、2.99%、4.01%和5.83%,接近页岩平均值,只是CaO含量稍高。北部宿县地区页岩样品SiO₂、TiO₂、Al₂O₃、K₂O、TFeO和CaO含量分别为57.01%、1.82%、20.97%、4.85%、3.31%和0.57%,与南部地区相比,TiO₂和K₂O含量显著偏高,是其2.1倍和1.6倍。刘老碑组页岩REE总量平均为219×10^-6,LREE富集,La/Yb为14.2(9.8～18.6),Eu负异常,Eu/Eu^*为0.60(0.54～0.63),但是北部页岩有更高的REE总量(295.8×10^-6)和La/Yb比值(17.8)。微量元素分析表明,北部页岩中Sc、V、Zr、Nb和Th较高,南部Co和Pb较高。但是南部和北部却有比较一致的La/Sc(2.29±0.15)、Th/Sc(0.69±0.06)和La/Th(3.29±0.20)比值。La-Th-Sc和Th-Sc-Zr/10判别图清楚地表明,刘老碑组页岩形成于大陆岛弧构造环境,岛弧可能位于研究区的南部边缘。北部页岩明显偏高的TiO₂和Al₂O₃含量以及化学风化指数(CIW)表明北部沉积物的源区经历了更强烈的风化作用。

GEOCHEMICAL CHARACTERISTICS AND IMPLICATIONS OF NEOPROTEROZOIC SHALES FROM THE LIULAOBEI FORMATION IN NORTH ANHUI

samples were collected from Neoproterozoic shales (mudstones) of the Liulaobei Formation (LF) in north Anhui.In south part of the studied area including the Bagongshan and Songji profiles in Huainan and Fengyang respectively,concentrations of major elements SiO₂,TiO₂,Al₂O₃,K₂O,TFeO and CaO were 55.28%,0.87%,15.60%,2.99%,4.01% and 5.83% respectively,similar to the average shale,with CaO being some higher.In Suxian area,the north part of the studied area,SiO₂,TiO₂,Al₂O₃,K₂O,TFeO and CaO were 57.01%,1.82%,20.97%,4.85%,3 31% and 0.57% respectively,with TiO₂ and K₂O being higher,and 2.1 and 1.7 times as large as the south shales.The analysis showed LREE being 219×10^-6 on average (14315×10^-6～32118×10^-6),with LREE enriched (La/Yb=14.2) and negative Eu anomalie (Eu/Eu^*=0 60).The north shales had higher LREE (295.8×10^-6) and La/Yb (17.8) than that of the south shales.On basis of trace element analysis,Sc,V,Zr,Nb and Th were higher in the north shales,while Co and Pb were higher in the south shales,and both of the shales had unanimous ratios of La/Sc (2.29±0.15),Th/Sc (0.69±0.06) and La/Th (3.29±0.20).La-Th-Sc and Th-Sc-Zr/10 discriminatory diagrams suggested that LF shales were formed in a tectonic setting of continental island arc,and the island arc might locate south margin of the studied area.REE and trace element data supported the conclusion further.The chemical index of weathering (CIW) as well as TiO₂ and Al₂ O₃ concentrations reflected a more intense weathering in the provenances of the shales in north part.