Globular Phyllosilicates of the Glauconite–Illite Series in the Cambrian and Ordovician Rocks of the Eastern Baltica (Northern Estonia, Western Lithuania, and Western Latvia)

IF 0.7 4区 地球科学 Q4 GEOCHEMISTRY & GEOPHYSICS Lithology and Mineral Resources Pub Date : 2023-04-18 DOI:10.1134/S002449022270002X
T. A. Ivanovskaya, B. A. Sakharov, T. S. Zaitseva
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Abstract

The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite–illite series (GPS) from the Lower Cambrian sequences of Northern Estonia and Western Lithuania, from the Middle Cambrian sequences of Western Latvia, and also from the Lower Ordovician sequences of Northern Estonia and Western Latvia are considered for the first time. Based on Al index (KAl = VIAl/[VIFe3+ + VIAl]) varying from 0.27 to 0.59, the globular phyllosilicates are attributed to the glauconite–illite series, most of which are represented by glauconites (the Al index is KAl = 0.27–0.46) and one sample, by Al-glauconite (KAl = 0.59). The K2O content in minerals is from 7.12 to 7.90%. The content of expandable layers (4–13%), their types (smectite, vermiculite), and the character of their alternation (R = 0, R = 2) were determined for the first time in the studied samples by simulation of experimental X-ray diffraction patterns from oriented specimens. Simulation of X-ray diffraction patterns obtained from unoriented specimens made it possible to determine the degree of three-dimensional order and mean values of the unit-cell parameter b (9.056–9.094 Å), as well as the distribution of their individual micaceous varieties. Based on these data, the microheterogeneity of the Cambrian and Ordovician GPSs was established and compared with the heterogeneity in the previously studied Riphean GPS (Drits et al., 2013). The obtained Rb-Sr и K‑Ar ages for the studied Middle Cambrian and Lower Ordovician samples, as well as the earlier published dates for the Lower Cambrian samples, are “rejuvenated” relative to age limits accepted for the Cambrian and Lower Ordovician (Gradstein et al., 2020). The relationship of the Cambrian and Lower Ordovician “rejuvenated” isotopic dates and the discovered GPS heterogeneity, as well as possible reasons for its occurrence, are discussed.

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波罗的海东部(爱沙尼亚北部、立陶宛西部和拉脱维亚西部)寒武系和奥陶系海绿石-伊利石系列中的球状层状硅酸盐
本文首次研究了爱沙尼亚北部和立陶宛西部下寒武统层序、拉脱维亚西部中寒武统层序以及爱沙尼亚北部和拉脱维亚西部下奥陶统层序海绿石-伊立石系列(GPS)的7个球状层状硅酸盐样品的矿物学、结构和晶体化学特征。从Al指数(KAl = VIAl/[VIFe3+ + VIAl])在0.27 ~ 0.59之间的变化来看,球状层状硅酸盐属于海绿石—伊利石系列,其中大部分为海绿石(Al指数为KAl = 0.27 ~ 0.46),有一个样品为Al-海绿石(KAl = 0.59)。矿物中K2O含量为7.12% ~ 7.90%。通过模拟取向试样的实验x射线衍射图,首次测定了试样中可膨胀层的含量(4 ~ 13%)、类型(蒙脱石、蛭石)及其变化特征(R = 0, R = 2)。模拟无取向样品的x射线衍射图,可以确定三维有序程度和单位胞参数b (9.056-9.094 Å)的平均值,以及它们的单个云母品种的分布。基于这些数据,建立了寒武系和奥陶系GPS的微观非均质性,并与之前研究的Riphean GPS的非均质性进行了比较(Drits et al., 2013)。所研究的中寒武统和下奥陶统样品的Rb-Sr - K - Ar年龄,以及之前公布的下寒武统样品的年龄,相对于寒武统和下奥陶统的公认年龄限制,都得到了“恢复”(Gradstein et al., 2020)。讨论了寒武系和下奥陶统“返青”同位素日期与GPS非均质性的关系及其可能的原因。
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来源期刊
Lithology and Mineral Resources
Lithology and Mineral Resources 地学-地球化学与地球物理
CiteScore
1.30
自引率
37.50%
发文量
29
审稿时长
>12 weeks
期刊介绍: Lithology and Mineral Resources is an international peer reviewed journal that publishes articles on a wide range of problems related to the formation of sedimentary rocks and ores. Special attention is given to comparison of ancient sedimentary rock and ore formation with present-day processes. The major part of the journal is devoted to comparative analysis of sedimentary processes on the continents and in oceans, as well as the genetic aspects of the formation of sedimentary and hydrothermal–sedimentary mineral resources. The journal welcomes manuscripts from all countries in the English or Russian language.
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