CAJ | 학술논문

西南天山马达尔地区乌帕塔尔坎群硅质岩与玄武岩以逆冲断层接触产出,但其时代缺乏依据.本次研究的硅质岩中含有放射虫,经鉴定时代为D_3-C_1.11件硅质岩样品的SiO_2含量为88.80%～93.28%,Al_2O_3含量为2.02%～3.72% ,其中只有4件样品为纯硅质岩(SiO_2 的含量为91.0%～99.8%),所有样品的SiO_2/Al_2O_3值(23.84～46.11)远低于纯硅质岩(SiO_2/Al_2O_3=80～1 400),表明其含有较高比例的陆源泥质沉积物.Al/(Al+Fe+Mn)=0.57～0.72,Ce/Ce~*=0.90～1.21,显示出生物沉积硅质岩的特点.此外,其Al_2O_3/(Al_2O_3+Fe_2O_3)=0.64～0.77, V含量为10.92×10~(-6)～26.70×10~(-6), Cu含量为2.15×10~(-6)～34.10×10~(-6), Ti/V=25.53～44.93,∑REE为30.78×10~(-6)～59.26×10~(-6),平均值为45.46×10~(-6),(La/Yb)_N=0.88～1.33,平均值为1.09,(La/Ce)_N=0.81～1.12,介于洋盆沉积物和大陆边缘沉积物之间,反映其沉积环境为接近陆源的深水-半深水的沉积环境.Ceanom值均大于-0.1,为-0.06～0.08,并且出现Eu的负异常,推测岩石沉积时水体贫氧.结合区域地质特征推测,乌帕塔尔坎群硅质岩形成于南天山洋盆闭合期的小洋盆.
서남천산마체이지구오파탑이감군규질암여현무암이역충단층접촉산출,단기시대결핍의거.본차연구적규질암중함유방사충,경감정시대위D_3-C_1.11건규질암양품적SiO_2함량위88.80%～93.28%,Al_2O_3함량위2.02%～3.72% ,기중지유4건양품위순규질암(SiO_2 적함량위91.0%～99.8%),소유양품적SiO_2/Al_2O_3치(23.84～46.11)원저우순규질암(SiO_2/Al_2O_3=80～1 400),표명기함유교고비례적륙원니질침적물.Al/(Al+Fe+Mn)=0.57～0.72,Ce/Ce~*=0.90～1.21,현시출생물침적규질암적특점.차외,기Al_2O_3/(Al_2O_3+Fe_2O_3)=0.64～0.77, V함량위10.92×10~(-6)～26.70×10~(-6), Cu함량위2.15×10~(-6)～34.10×10~(-6), Ti/V=25.53～44.93,∑REE위30.78×10~(-6)～59.26×10~(-6),평균치위45.46×10~(-6),(La/Yb)_N=0.88～1.33,평균치위1.09,(La/Ce)_N=0.81～1.12,개우양분침적물화대륙변연침적물지간,반영기침적배경위접근륙원적심수-반심수적침적배경.Ceanom치균대우-0.1,위-0.06～0.08,병차출현Eu적부이상,추측암석침적시수체빈양.결합구역지질특정추측,오파탑이감군규질암형성우남천산양분폐합기적소양분.
The Wupataerkan Group is characterized by cherts in contact with basalts through a thrust fault in Madaer area, Southwest Tianshan Mountains. However, definite evidence on the age of the group is absent. Based on the radiolarians picked up from the cherts, the authors hold that they were formed in Late Devonian to Early Carboniferous. Eleven chert samples have the SiO_2 and Al_2O_3 content ranging respectively from 88.80% to 93.28% and from 2.02% to 3.72%. Four samples could be classified as pure cherts, which have SiO_2 content of 91.0%～99.8%. However, all samples have much lower SiO_2/Al_2O_3 ratios than the pure cherts (80～1 400). These values suggest that the cherts contain high ratios of continental margin materials in the sources. The Al/(Al+Fe+Mn) ratios of 0.57～0.72 and Ce/Ce~* ratios of 0.90～1.21 suggest that these cherts are genetically biological sediments. Moreover, the Al_2O_3/(Al_2O_3+Fe_2O_3) ratios are between 0.64 and 0.77, 10.92 ×10~(-6)～26.7×10~(-6) for V, and 2.15×10~(-6)～34.10×10~(-6) for Cu. The Ti/V ratios vary from 25.53 to 44.93. The cherts have a total REE concentration of 30.78×10~(-6)～59.26×10~(-6), averaging 45.46×10~(-6). The (La/Ce)_N ratios range from 0.81 to 1.12, between the typical ocean basin and the continental margin. In 100 Fe_2O_3/SiO_2 versus 100 Al_2O_3/SiO_2, Fe_2O_3/(100-SiO_2) versus Al_2O_3/(100SiO_2), Fe_2O_3/TiO_2 versus Al_2O_3/(Al_2O_3+Fe_2O_3) and (La/Ce)_N versus Al_2O_3/(Al_2O_3+Fe_2O_3) diagrams, the samples fall into the area of continental margin. All these geochemical characteristics suggest that the cherts were formed in a continental margin setting. The Ceanom values range from -0.06 to 0.08. The characteristics of Ceanom ＞-0.1 and significant negative Eu anomalies indicate that the sea water was in an anoxic environment during the deposition. In combination with regional geological setting, it could be inferred that the cherts of the Wupataerkan Group were formed in a small ocean basin, probably at the stage of closing of the South Tianshan ocean basin. The researchers have basically reached consistency on the basic process of tectonic evolution history in Southwest Tianshan Mountains. However, there are different opinions about the collision time between Karakum-Tarim plate and Kazakhstan-Junggar plate. The geochemical characteristics of cherts in Madaer show that the cherts got much continental clastic materials during their formation and that their sedimentary environment was a continental margin. The formation age of cherts is from Late Devonian to Early Carboniferous. Based on these results, it is inferred that the ocean basin experienced shrinking in Early Carboniferous. Moreover, the collision time of the two plates is likely to be Late Carboniferous.