摘要
新元古代全球范围内出现了2次主要的冰期事件,分别是 Sturtian 冰期和 Marinoan 冰期。渝东南秀山地区发育与上述2次冰期对应的冰川沉积,分别为南沱组（Marinoan 冰期）和千子门组（Sturtian 冰期）。笔者通过对千子门组砂岩锆石运用 LA ICP MS 进行定年,测得其206 Pb/238 U年龄为736~2726 Ma,其中28个测点数据非常集中,在736~890 Ma,平均值为834 Ma。其最小值736 Ma 限定了 Sturtian 冰期千子门组的沉积起始时间,且与湘东南江口冰期起始时间（734±4）Ma 在误差范围内几乎一致,二者可以对比。而834 Ma 则记录了物源区与四堡—晋宁运动有关的岩浆活动。所有样品 ICV 值介于0.85~1.74（平均值为1.23）,表明黏土矿物较少,受再沉积作用的影响较小。同时其 CIA 值介于43~69（平均值为57）,表明千子门组沉积环境特征为寒冷、干燥,低程度化学风化。利用 SiO2 K2 O/Na2 O 和 K2 O/Na2 O SiO2/Al2 O3构造环境判别图解,结合稀土元素配分曲线,判定千子门组很可能形成于活动大陆边缘环境。
There are two major glacial events in Neoproterozoic globally,respectively the Sturtian glacial stage and Marinoan glacial stage.Corresponding glacialde posits develop in Xiushan area of Southeast Chongqing,respectively Nantuo formation and Qianzimen formation.ZirconLA ICP MS dating of Qianzimen sandstone obtains 206 Pb/238 U age of 736—2 726 Ma,in which the data of 28 measuring points concentrate between 736 and 890 Ma,with anaver age of 834 Ma.Minimum value of 736 Ma defines the sedimentary starting time of Qianzimen formation,which can be compared with Jiangkou glacial stage of southeastern Hunan started in 734±4 Ma,almost unanimously in the same error range.The age of 834 Ma records magmatism related to Sipu-Jin-ning orogeny movement in provenance.ICV numerical values of all samples being 0.85—1.74 （1.23 on average）show that clay minerals are less and Qianzimen formation is less affected by the redeposition.Meanwhile,CIA numerical values of the samples being 43—69 （57 on average）in-dicatethe sedimentation environment of Qianzimen formation is cold,dry and low degree of chem-ical weathering.SiO2 K2 O/Na2 OandK2 O/Na2 O SiO2/Al2 O3 discrimination diagrams and REE patternscurve indicate that Qianzimen formation is created in the active continental margin envi-ronment.
出处
《西北地质》
CAS
CSCD
2015年第2期95-103,共9页
Northwestern Geology
基金
地质大调查项目"重庆秀山锰矿整装勘查区关键基础地质研究"(12120114016201)"川滇黔关键地区区域地质调查"(12120113050300)联合资助
关键词
新元古界
千子门组
U-PB年龄
砂岩
雪球地球
渝东南
Neoproterozoic
Qianzimenformation
U-Pbages
sandstones
snowballearth
southeast Chongqing
