CAJ | 학술논문

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。
신원고대전구범위내출현료2차주요적빙기사건,분별시 Sturtian 빙기화 Marinoan 빙기。투동남수산지구발육여상술2차빙기대응적빙천침적,분별위남타조(Marinoan 빙기)화천자문조(Sturtian 빙기)。필자통과대천자문조사암고석운용 LA ICP MS 진행정년,측득기206 Pb/238 U년령위736~2726 Ma,기중28개측점수거비상집중,재736~890 Ma,평균치위834 Ma。기최소치736 Ma 한정료 Sturtian 빙기천자문조적침적기시시간,차여상동남강구빙기기시시간(734±4)Ma 재오차범위내궤호일치,이자가이대비。이834 Ma 칙기록료물원구여사보—진저운동유관적암장활동。소유양품 ICV 치개우0.85~1.74(평균치위1.23),표명점토광물교소,수재침적작용적영향교소。동시기 CIA 치개우43~69(평균치위57),표명천자문조침적배경특정위한랭、간조,저정도화학풍화。이용 SiO2 K2 O/Na2 O 화 K2 O/Na2 O SiO2/Al2 O3구조배경판별도해,결합희토원소배분곡선,판정천자문조흔가능형성우활동대륙변연배경。
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.