欧龙布鲁克山全吉群砂砾岩地球化学特征及地质意义

Geochemical Composition of Glutenite from Quanji Group in Oulongbuluke Mountain Outcrop and its Geological Significance

欧龙布鲁克地块全吉群下部的下部砂砾岩段(Pt3qna)样品与石英砂岩段(Pt3qnb)样品在主量元素、微量元素等方面存在明显差异。石英砂岩段(Pt3qnb)样品除Si O2、V、Zr、Hf含量高于砂砾岩段(Pt3qna)样品外,其余元素明显低于砂砾岩段(Pt3qna)样品。该套碎屑岩沉积于南倾的被动大陆边缘盆地,碎屑物质均来自于中元古界达肯大阪群。鱼卡-沙柳河裂陷槽裂陷的不同阶段以及古气候环境的差异是造成欧龙布鲁克地块全吉群砂砾岩岩石学类型、地球化学特征巨大差异的直接原因。新元古代早期,鱼卡-沙柳河构造带形成裂谷,随后裂陷槽逐渐扩张,研究区构造活动逐渐趋于稳定,自下而上,全吉群陆源碎屑岩成分成熟度及结构成熟均明显增高。化学蚀变指数(CIA)的大幅度变化表明研究区受新元古代早期低纬度冰川事件的影响,下部砂砾岩段(Pt3qna)极低的CIA值是"雪球地球"在研究区的表现;石英砂岩段(Pt3qnb)极高的CIA值所反映的湿热古气候环境则是研究区该时期处于低纬度的正常表现。

There is a marked difference between major elements and trace elements in the lower part of glutenite segment（Pt3qna） and quartz sandstone（Pt3qnb） from the Quanji group Oulongbuluke block. Major and tract elements in quartz sandstone（Pt3qnb） samples except for Si O2, V, Zr, and Hf contents were higher than those in glutenite segment（Pt3qna） samples, and the remaining elements are visibly lower than those in glutenite segment（Pt3qna） samples. The clastic sedimentary rocks deposited in the passive continental south dipping margin, and the detrital material comes from the middle Proterozoic Dakendaban group. Different rifting stages of the rift trough and differences of ancient climate and environment are the direct causes for the great difference in glutenite lithology types and geochemical characteristics of the Quanji group Oulongbuluke block. In the Early Neoproterozoic, the Yuka-Shaliuhe tectonic belt formed the rift. Subsequently, the rift trough gradually expanded, tectonic activity in the study area gradually stabilized, terrigenous clastic rock compositional maturity and structural maturity of Quanji group also significantly increased. Large variation in the CIA index shows that the study area has been affected by low latitude glaciation events. Low number of CIA in the lower part of glutenite segment（Pt3qna） is the expression of ＂Snowball Earth＂ in the study area; high CIA number of quartz sandstone（Pt3qnb） reflects the hot and humid paleoclimate environment, which is a normal performance of the study area in the low latitude.