Abstract

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio K_Al = (^VIAl / (^VIFe³⁺ + ^VIAl) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 Å and K₂O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mössbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.

中文翻译：

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Ust-Il'ya组球状青绿岩的结构和晶体化学特征及Rb-Sr年龄（下里菲安，阿纳巴尔隆起）

摘要

首次从马根河（西伯利亚北部Anabar断块的西坡）下里菲安Ust-Il'ya地层的辉绿岩样品获得了矿物学，结构，晶体化学和同位素-地质年代学数据。已经确定，脆性青石岩的透镜状层中的青石岩（青石岩颗粒≥80％）包含两个混合层晶体，其中云母层（93％）与蒙脱石型（7％）或ver石交替-短程因数R = 3的金属层（7％）。比率K _Al =（^VI Al /（^VI Fe ³⁺ + ^VIAl）等于0.45可以将单位面积参数b = 9.065Å和K ₂的云母类矿物识别为青灰石O含量为8.29％。新数据与之前在马甘河断面以南65 km的科图坎河断面（伊利亚河口上方2.5 km）的Ust-Il'ya青绿岩的矿物学和晶体化学特征的比较表明，两者共同点和不同点。对来自不同岩性类型的岩石的Kotuikan青绿岩样品的晶体化学非均质性分析表明，组成青绿岩小球的单个云母品种的分布具有特殊性。结合了马格河断面的青水晶石的同位素测年，模拟八面体阳离子的分布以及比较穆斯堡尔光谱和红外光谱数据的结果。这种方法与矿物学和晶体化学分析相结合，有助于正确解释同位素数据的地层学意义。获得的结果为得出以下结论提供了依据：来自玛根断面的青绿岩的同位素日期（1474±21 Ma）与Ust-Il'ya组的较早的Rb-Sr和K-Ar测年（1485±以科图坎剖面的青灰石为基础，分别为13和1459±20 Ma）（Zaitseva等人，2016）。前者的值标志着沉积物早期成岩的阶段，适用于估算该地层的年龄。获得的结果为得出以下结论提供了依据：来自玛根断面的青绿岩的同位素日期（1474±21 Ma）与Ust-Il'ya组的较早的Rb-Sr和K-Ar测年（1485±以科图坎剖面的青灰石为基础，分别为13和1459±20 Ma）（Zaitseva等人，2016）。前者的值标志着沉积物早期成岩的阶段，适用于估算该地层的年龄。获得的结果为得出以下结论提供了依据：来自玛根断面的青绿岩的同位素日期（1474±21 Ma）与Ust-Il'ya组的较早的Rb-Sr和K-Ar测年（1485±以科图坎剖面的青灰石为基础，分别为13和1459±20 Ma）（Zaitseva等人，2016）。前者的值标志着沉积物早期成岩的阶段，适用于估算该地层的年龄。