Shengchang Ding, Mark J. Dekkers, Mingkun Li, Qi Zhao, Yi Yan, Zhaoyu Zhu
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引用次数: 0
摘要
措鄂岩心包含了措鄂湖(中国青藏高原,北纬31°24′-31°32′,东经91°28′-91°33′)的整个第四纪地层。在此,我们结合扫描电子显微镜和 X 射线能量色散光谱仪分析,对来自 CE 地核的 1,748 个样品进行了磁性研究。主要的磁性矿物似乎是磁铁矿和绿帘石。为进一步量化中欧地质中心岩芯中存在的绿泥石,对 84 个样本进行了更详细的岩石磁学分析,包括:电感(χ)与温度的关系、等温剩磁(IRM)采集曲线的矫顽力成分分析,以及一阶反转曲线(FORC)图的主成分分析。绿泥石含量和饱和 IRM 比感性(SIRM/χ)似乎呈指数关系。SIRM/χ 可用作绿泥石浓度指标。我们还提出了一种快速识别 CE 岩心中灰榴石的方法:当 SIRM/χ 增加,而无磁重力感应(χARM)仅缓慢增加时,样本中含有绿泥石。SIRM/χ < 15 kA/m 的样品也遵循这一关系。与传统使用的 SIRM/χ 参数相比,这种绿泥石检测方法的检测限更低。此外,它还比 FORC 分析法更快,因此特别适用于大量样品的分析。使用这种方法在 CE 岩芯中确定了 20 个含灰岩层。在目前可用的磁地层学中,CE 岩心中 Jaramillo 亚时空的位置是有争议的,这可能与该岩心区间中存在的绿帘石有关。
Rapid Identification of Greigite in Lacustrine Sediments Using SIRM/χ and χARM: Insights From the Cuo E Core, Tibetan Plateau, China
The Cuo E (CE) core contains the entire Quaternary stratigraphy of the CE Lake (31°24′–31°.32′ N, 91°28′–91°33′E, Tibetan Plateau, China). Here, we study the magnetic properties of 1,748 samples from the CE core, combined with scanning electron microscopy and X-ray energy dispersive spectrometer analysis on selected samples. The main magnetic minerals appear to be magnetite and greigite. To further quantify the presence of greigite in CE core, 84 samples were analyzed using rock magnetism in more detail including: susceptibility (χ) versus temperature, coercivity component analysis of acquisition curves of the isothermal remanent magnetization (IRM), and principal component analysis of the first-order reversal curve (FORC) diagrams. The greigite content and saturation IRM over susceptibility (SIRM/χ) appear to be exponentially related. SIRM/χ can be used as greigite concentration indicator. We also propose a rapid way to identify greigite in the CE core: When SIRM/χ increases and anhysteretic remanent susceptibility (χARM) increases only slowly, the sample contains greigite. Samples with SIRM/χ < 15 kA/m also follow this relation. This greigite detection method has a lower limit of detection than the traditionally used SIRM/χ parameter. It is also faster than FORC analysis and thus particularly suitable for analysis of large sample collections. Twenty greigite-bearing layers were identified in the CE core using this method. The location of the Jaramillo subchron in the CE core is controversial in the currently available magnetostratigraphy, possibly related to the presence of greigite in this core interval.
期刊介绍:
Marking AGU’s second new open access journal in the last 12 months, Earth and Space Science is the only journal that reflects the expansive range of science represented by AGU’s 62,000 members, including all of the Earth, planetary, and space sciences, and related fields in environmental science, geoengineering, space engineering, and biogeochemistry.