欧龙布鲁克地块新元古代早期冰川事件:来自CIA指数的证据

Early Neoproterozoic Glacier Event in Oulongbuluke Block:Evidence from CIA Index

采自欧龙布鲁克地块全吉山、欧龙布鲁克山两个剖面全吉群下部砂砾岩段（包括麻黄沟组与枯柏木组）样品ICV指数大多数〉1、或略〈1，这表明该套碎屑岩沉积是构造活动地带的初始沉积。底部冰成岩发育层段样品CIA指数大多数在53左右，向上CIA指数增大至67左右，反映新元古代早期研究区古气候整体转暖。底部层段样品极低的CIA值表明欧龙布鲁克板块新元古代早期主要发生寒冷气候条件下的低等程度化学风化，首次从CIA指数角度证实研究区存在新元古代早期极端寒冷气候事件，为研究区受新元古代早期“雪球地球”事件影响提供了更进一步的证据。通过对前人年代学研究的总结，将这套含有大量低CIA值碎屑岩的冰川沉积地层沉积年限约束在780±20～740±16Ma范围内，并认为其与国际上的Kaigas冰期及塔里木地区贝义西冰期相对应。

Most of the ICV results on the collectted glutenite samples from the bottom of Quanji group （including Mahuanggou Formation and Kubaimu Formation ）, Quanji mountain and Oulongbuluke mountain outcrops in Oulongbuluke block, greater than 1 or less than 1. That means the glutenite sedimentary in the bottom of Quanji group is an initial sedimentary formed in the district with intense tectonic activity. CIA indexes of glacial rock samples that preserved in the bottom of Quanji group mostly around 53, then increase up to around 65 vertically, that reflects the ancient climate turned to warmer as a whole. These extremely low CIA indexes manifest a low degree of chemical weathering in cold climate condition occurred during the Early Neoproterozoic epoch, that makes us confirm the Early Neoproterozoic cold weathering climate influenced the study area from the perspective of CIA index for the first time and give out a further evidence for the study area was under the control of ＂snowball earth＂. With the summary on the previous chronology studies, we limit sedimentation time of glacial deposit formation with a large number of low CIA indexes glutenites during 780 ± 20Ma to 740 ± 16Ma and correspond it to the international Kaigas glacial epoch and Beiyixi glacial epoch.