大同火山活动在区域沉积中的记录和阶段性历史研究

发布时间：2018-05-04 00:41

本文选题：大同火山 + 湖相沉积　；参考：《地理学报》2017年09期

【摘要】：大同火山活动的阶段性历史是一个尚未被揭示清楚的地学问题。野外实地考察及室内磁化率、化学成分、粒度和古地磁的测定结果显示:古湖滨处水平层理发育的火山碎屑层存在4个不同倾角的倾斜;古湖近岸处的湖相沉积层中含有4层火山碎屑层;古湖深处的湖相沉积层中出现4个磁化率显著正异常的层位,且这些层位粒度都较粗;古湖岸上的黄土沉积中出现3个磁化率为峰值、Rb/Sr比值为谷值的层位;古湖深处湖相沉积剖面中存在B/M和Jaramillo磁极性界限。据此进一步分析后认为:(1)湖相沉积剖面中的磁化率显著正异常层位、黄土沉积中的高磁化率—低Rb/Sr比值层位可能是混入了大量火山灰物质;它们是区域火山活跃期的记录。(2)系列沉积剖面特征指示区域火山活动曾经历4个活跃期,每个活跃期期间有多次密集的火山喷发。(3)4个活跃期的年代大约为早于0.90 Ma BP(第一活跃期)、~0.47 Ma BP(第二活跃期)、~0.31 Ma BP(第三活跃期)和~0.09 Ma BP(第四活跃期);黄土沉积中还记录了区域北部有一个发生于~0.19 Ma BP的活跃期。此外,区域湖相沉积中所记录的4个火山活跃期都出现在湖退时期,平静期出现在湖侵时期。
[Abstract]:The periodic history of Datong volcanic activity is a geological problem that has not been revealed clearly. The field investigation and indoor magnetic susceptibility, chemical composition, granularity and paleomagnetism results show that there are four tilt angles in the volcanic clastic beds developed horizontally along the ancient lakeshore; There are four volcanic clastic layers in the lacustrine sedimentary layer near the ancient lake, four layers with obvious positive magnetic susceptibility anomaly in the lacustrine sedimentary layer in the depth of the ancient lake, and all of these layers have coarse granularity. In the loess deposits on the ancient lake shore, there are three horizons whose magnetic susceptibility is the peak value and the RB / Sr ratio is the valley value, and there are B / M and Jaramillo magnetic polarity boundaries in the lacustrine sedimentary profile of the paleolake depth. Based on the further analysis, it is concluded that the magnetic susceptibility in the lacustrine sedimentary profile is significantly positive anomalous, and the high susceptibility to low Rb/Sr ratio horizon in loess sediments may be mixed with a large amount of volcanic ash. They are the records of the regional volcanic active period.) the sedimentary profile features of the series indicate that the regional volcanic activity has gone through four active periods. The age of 4 active periods is about 0.90 Ma BP (the first active period is 0.47 Ma BP (the second active period is 0.31 Ma BP) and the second active period is 0.09 Ma BP (the fourth active period; the loess sediments). An active period occurred at 0.19 Ma BP in the northern part of the region was also recorded. In addition, the four volcanic active periods recorded in the regional lacustrine sediments occurred in the receding period and in the calm period during the transgression period.
【作者单位】：上海师范大学旅游学院地理系;
【基金】：国家自然科学基金项目(41371021)~~
【分类号】：P317;P512.2

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