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摘要:
玄武岩的地球化学成分与其产出构造环境密切相关,是研究地球深部物质组成与动力学过程的重要岩石。为了判别玄武岩形成的构造环境,前人根据玄武岩的地球化学特征建立了一系列构造判别图,然而这些判别图仅限于二维或三维判别。随着全球玄武岩样品地球化学数据的爆发性增长,这些构造判别图逐渐暴露出其局限性强、准确率较低的缺点。在地学与大数据结合发展的背景下,利用机器学习方法有利于更全面和深入分析数据,建立高准确率和高效率的构造环境判别模型。因此,本文利用GEOROC和PetDB数据库,经过一系列数据下载、处理等步骤,建立了全球现代大洋玄武岩数据集。通过支持向量机(SVM)和随机森林(RF)机器学习算法,训练出高准确率的高维判别模型。本文分析了不同机器学习算法和不同地球化学成分数据集对现代大洋玄武岩构造环境判别的影响,并将各个判别模型应用于蛇绿岩数据当中,探讨机器学习模型在判别古老大洋岩石圈(蛇绿岩)形成构造环境下的应用前景。这项工作为大洋玄武岩形成的构造环境判别提供了更高维度的判别手段,是大数据时代下机器学习如何在地球科学领域应用的一次有益尝试。
Abstract:The geochemical composition of basalt is closely related to the tectonic setting of the formation, thus basalt is an important window for viewing the deep Earth and the composition and geodynamic processes. To discriminate the tectonic setting of basalt formation, although a series of tectonic discrimination diagrams have been established based on the geochemical characteristics of basalt, those discrimination diagrams are limited to two-dimensional or three-dimensional data. With the explosive growth of global geochemical data of basalt, these discrimination diagrams show gradually the shortcomings of being local and inaccurate. Therefore, using machine learning methods is beneficial to analyze data multi-dimensionally and comprehensively, and to establish accurate and efficient discriminant models. A global modern oceanic basalt dataset was established by using GEOROC and PetDB databases through a series of steps from data downloading, training, and analyzing. The dataset was trained by the support vector machine (SVM) and random forest (RF) machine learning algorithms and a high-accuracy and high-dimensional discrimination model was built. In addition, the accuracies of different machine-learning algorithms training were analyzed against different geochemical composition datasets of modern oceanic basalt, and the discrimination models were applied to ophiolitic basalt to explore the application of machine learning models for ancient oceanic basalt. This work provided a higher-dimensional approach to discriminate oceanic basalt, and a successful attempt of using machine learning in earth science in the era of the big data.
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Key words:
- geochemistry /
- tectonic setting /
- machine learning /
- oceanic basalt
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表 1 SVM、RF算法下现代大洋玄武岩分类模型准确率
Table 1. Accuracy of modern oceanic basalt classification models using SVM and RF algorithms
Basic_Data M&TE ME TE RI Average SVM 0.94 0.949 0.979 0.952 0.975 0.959 RF 0.997 0.994 0.914 0.993 0.982 0.976 表 2 蛇绿岩中玄武岩构造环境预测准确率
Table 2. Prediction accuracy of ophiolite using SVM and RF algorithms
Basic_Data M&TE ME TE RI Average 细分类模型 SVM 0.206 0.235 0.059 0.294 0.206 0.200 RF 0.118 0.265 0.088 0.294 0.265 0.206 大类分类模型 SVM 0.765 0.824 0.765 0.794 0.765 0.783 RF 0.706 0.794 0.706 0.853 0.765 0.765 表 3 RF算法下各数据集的分类精确率、召回率与F1分数
Table 3. Classification accuracy, recall, and F1 score of each dataset using RF algorithm
BABB IAB MORB OPB OIB 数据集 精确率 1 1 0.99 1 0.99 Basic_Data 召回率 0.99 0.99 1 0.96 0.99 F1分数 0.99 0.99 1 0.98 0.99 精确率 1 0.99 0.99 0.98 0.99 M&TE 召回率 0.98 0.99 1 0.92 0.99 F1分数 0.99 0.99 0.99 0.95 0.99 精确率 0.82 0.84 0.9 0.92 0.91 ME 召回率 0.59 0.78 0.97 0.5 0.91 F1分数 0.69 0.81 0.93 0.65 0.91 精确率 0.99 0.99 0.99 0.98 0.99 TE 召回率 0.97 0.99 1 0.93 0.99 F1分数 0.98 0.99 0.99 0.96 0.99 精确率 0.96 0.97 0.99 0.99 0.98 RI 召回率 0.97 0.96 0.99 0.94 0.97 F1分数 0.97 0.96 0.99 0.96 0.96 表 4 特征重要性度量
Table 4. The feature importance metric
排名 特征 特征重要性度量 排名 特征 特征重要性度量 排名 特征 特征重要性度量 1 Pb208/Pb204 0.0997 19 Gd 0.0182 37 Ba 0.0013 2 Pb206/Pb204 0.0848 20 Pr 0.0157 38 Ni 0.0012 3 Sr87/Sr86 0.0845 21 La 0.0143 39 Sm 0.0011 4 Nd143/Nd144 0.0826 22 Nd 0.0124 40 Zr 0.0011 5 Ta 0.0689 23 Nb 0.0112 41 FeOT 0.0011 6 Li 0.0529 24 Dy 0.0108 42 SiO2 0.001 7 Ga 0.0492 25 Eu 0.0104 43 P2O5 0.0009 8 Cs 0.0458 26 Sc 0.0096 44 Al2O3 0.0009 9 Lu 0.0443 27 Ce 0.0072 45 K2O 0.0009 10 Pb 0.0432 28 Co 0.0063 46 K 0.0008 11 Tm 0.0352 29 Cu 0.0057 47 MgO 0.0008 12 Yb 0.03 30 Sr 0.0048 48 CaO 0.0006 13 U 0.0264 31 Zn 0.0046 49 Rb 0.0006 14 Tb 0.0209 32 Th 0.002 50 Y 0.0006 15 Pb207/Pb204 0.0204 33 Ti 0.0017 51 Mg# 0.0005 16 Er 0.0193 34 Cr 0.0017 52 Na2O 0.0005 17 Hf 0.0189 35 TiO2 0.0015 53 P 0.0004 18 Ho 0.0187 36 V 0.0014 54 MnO 0.0004 -
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