Crustal evolution of alkali basalts: A case study of the Cenozoic Datong volcanoes, North China Craton

This dataset is used to study the crustal evolution of alkaline basalts from the Cenozoic volcanic group in Datong, Shanxi. The hypothesis is that the geochemical and mineralogical characteristics of these basalts provide crucial information on the differentiation and storage conditions of magma in the crust, revealing the magmatic evolution mechanisms during ascent and emplacement.
Data Collection Methods：
1.Point Counting Method: Modal mineral composition analysis of basalt thin sections was performed, providing quantitative data for olivine, clinopyroxene, plagioclase, and the matrix.
2.Electron Probe Microanalysis (EPMA): An electron probe was used to analyze the major elements of key mineral phases, including olivine, clinopyroxene, plagioclase, and the matrix. Probe conditions typically included an accelerating voltage of 15 kV and a beam current of 20 nA, ensuring precise measurements of mineral chemical compositions.
3.Whole-rock Major and Trace Element Analysis: Major elements were determined by X-ray fluorescence (XRF), and trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Standard and blank samples were used for calibration to ensure the accuracy of the data.
Key Findings：
1.Mineral Composition: The composition of olivine phenocrysts suggests fractional crystallization. The chemical composition of clinopyroxene indicates crystallization in evolved magmas. Compositional variations in plagioclase reflect dynamic conditions within the magma system. The presence of clinopyroxene-olivine-plagioclase glomerocrysts indicates magmatic mixing and storage processes.
2. Geochemical Trends: Whole-rock major element data reveal the alkaline nature of the basalts, while trace element data indicate significant magmatic differentiation. Differences in SiO2 and MgO content between Group 1 and Group 2 samples suggest varying degrees of magmatic evolution and storage depths.
3. Insights into Crustal Evolution: Mineral-melt equilibrium thermobarometry calculations show that Group 1 and 2 basalts crystallized in different magma chambers. Continuous magmatic replenishment may have driven the evolution of the volcanic conduit system, resulting in differing differentiation histories for the two groups.
These data help reconstruct the petrogenetic evolution of the Datong basalts, highlighting the role of fractional crystallization and magmatic replenishment within the crust, providing strong support for the evolution of alkaline basalts in the crust.
This dataset can be used for regional petrological comparisons, crustal evolution studies, and further crust-magma interaction modeling. Researchers should consider possible uncertainties in the analysis process and calibration standards to ensure accurate interpretation. This dataset provides significant support for volcanic petrology and regional crustal dynamics research.

本数据集用于研究山西大同新生代火山群碱性玄武岩的地壳演化过程。本研究提出假说：这些玄武岩的地球化学与矿物学特征，可为地壳内岩浆的分异作用与赋存条件提供关键信息，进而揭示岩浆上升就位过程中的演化机制。

数据采集方法：
1. 点计数法：对玄武岩薄片开展模态矿物组成分析，定量获取橄榄石、单斜辉石、斜长石及基质的组分数据。
2. 电子探针显微分析（Electron Probe Microanalysis, EPMA）：采用电子探针对橄榄石、单斜辉石、斜长石及基质等关键矿物相的主量元素进行分析。探针测试条件通常设置为加速电压15 kV、束流20 nA，以保障矿物化学成分测量的精准性。
3. 全岩主量与微量元素分析：主量元素采用X射线荧光光谱法（X-ray fluorescence, XRF）测定，微量元素则通过电感耦合等离子体质谱法（inductively coupled plasma mass spectrometry, ICP-MS）分析。实验中设置标准样品与空白样品进行校准，以保障数据准确性。

关键研究发现：
1. 矿物组成特征：橄榄石斑晶的组成特征指示了分离结晶作用；单斜辉石的化学成分表明其形成于演化后的岩浆中；斜长石的成分变化反映了岩浆系统内的动态环境；橄榄石-单斜辉石-斜长石聚晶的存在，指示了岩浆混合与赋存过程。
2. 地球化学演化趋势：全岩主量元素数据表明玄武岩具有碱性属性，而微量元素数据则显示岩浆经历了显著的分异作用。第1组与第2组样品的SiO₂与MgO含量差异，反映了二者岩浆演化程度与赋存深度的不同。
3. 地壳演化启示：矿物-熔体平衡温压计算结果显示，第1、2组玄武岩分别形成于不同的岩浆房内。持续的岩浆补给可能驱动了火山通道系统的演化，导致两组样品呈现差异化的分异历史。

本数据集有助于重建大同玄武岩的岩石成因演化过程，阐明分离结晶与地壳内岩浆补给作用的关键角色，为碱性玄武岩的地壳演化机制提供有力支撑。

本数据集可应用于区域岩石学对比、地壳演化研究以及进一步的壳-岩浆相互作用模拟。研究者需考量分析过程与校准标准中存在的潜在不确定性，以保障解读结果的准确性。本数据集为火山岩石学与区域地壳动力学研究提供了重要支撑。