基于扫描电子显微镜的重矿物物源分析方法对比

doi:10.19657/j.geoscience.1000-8527.2022.032

摘要/Abstract

摘要：

重矿物继承了源岩特征,能够揭示沉积盆地与源区之间的源汇联系。扫描电镜(SEM)及自动矿物识别技术的发展,使得重矿物从人工显微镜下鉴定逐步走向自动化定量分析。本文在传统显微镜识别的基础上,分别应用扫描电镜-能谱仪/背散射成像(SEM-EDS/BSE)技术及综合矿物分析系统(TIMA)进行重矿物的鉴定和统计,对比总结不同分析方法的特点和适用性,并对准噶尔盆地西北缘中生代物源区进行初步探讨。结果表明,基于SEM的两种分析方法都可以很好地对各种重矿物进行厘定和统计:其中SEM-EDS/BSE对矿物的统计更加灵活;TIMA能够快速、准确得到多种矿物信息,但需注意蚀变矿物对原生矿物统计的影响。根据重矿物组合、重矿物成熟度(ZTR指数)及前人报道的U-Pb年龄、古水流数据,认为准噶尔盆地西北缘中生代物源主要来自扎伊尔山,其中晚三叠世—早侏罗世哈拉阿拉特山隆升并开始为克拉玛依与白砾山地区提供物源。

关键词: 重矿物统计, 扫描电子显微镜, 能谱仪, 背散射成像, 综合矿物分析系统, 物源分析

Abstract:

Heavy minerals inherit the characteristics of source rocks and can reveal the source-sink connection between the sedimentary basin and the source area. With the development of scanning electron microscope and automatic mineral identification technology, the identification of heavy minerals has gradually changed from manual microscope identification to automatic quantitative analysis. In this paper, on the basis of traditional microscope identification, scanning electron microscopy-energy dispersive spectrometer/backscatter electron (SEM-EDS/BSE) and Tescan Integrated Mineral Analyzer (TIMA) are used to identify and count heavy minerals. We also compared and summarized the characteristics and applicability of different analysis methods. Besides, the Mesozoic provenance area in the northwestern margin of Junggar Basin is preliminarily discussed. The results show that both analysis methods based on SEM can determine and count various heavy minerals well: SEM-EDS/BSE can be more flexible in the statistics of altered minerals; TIMA can quickly and accurately obtain a variety of minerals information, but caution should be exercised in the statistics of altered minerals. According to the heavy mineral assemblage, ZTR index, and previous U-Pb age and paleocurrent data, it is believed that the Mesozoic provenance in the northwestern margin of Junggar Basin mainly came from the Zaire Mountain, and the Halaalat Mountain uplifted and began to provide provenance for Karamay and Bailishan areas during the Late Triassic to Early Jurassic.

Key words: heavy mineral statistics, SEM, EDS, BSE, TIMA, provenance analysis

中图分类号:

TE121.3
P571

曹玉璐, 曾宇轲, 张元元. 基于扫描电子显微镜的重矿物物源分析方法对比[J]. 现代地质, 2023, 37(02): 475-485.

CAO Yulu, ZENG Yuke, ZHANG Yuanyuan. Comparision of Heavy Mineral Provenance Analysis Methods Based on SEM[J]. Geoscience, 2023, 37(02): 475-485.

图/表 8

图1 准噶尔盆地西北缘地质简图[30]

Fig.1 Simplified geologic map of the northwestern Junggar Basin[30]

图2 重矿物统计方法(仅计算阴影颗粒,修改自Mange等[8])

Fig.2 Heavy mineral statistical methods(Only the shaded grains are counted, modified from Mange et al[8])

图3 TIMA的4种扫描模式示意图(修改自Hrstka等[42];扫描矿物颗粒数为1万个,4种扫描模式下BSE像素为2.5 μm,能谱步长为5 μm;线扫描模式的线间距为30 μm)

Fig.3 Schematic diagram of four scan modes of TIMA(modified from Hrstka et al[42];the number of mineral particles scanned is 10000.In four scan modes, BSE pixels was 2.5 μm and dot spacing was 5 μm; The line spacing of TIMA Line mapping was 30 μm)

表1 样品XZ17-19、XZ17-10 TIMA和SEM-EDS重矿物数量百分含量(%)

Table 1 Heavy minerals of XZ17-19 and XZ17-10 in quantity percentage based on the TIMA and SEM-EDS(%)

样品号	分析方法	钛铁矿	石榴石	铬铁矿	磁铁矿/赤铁矿	榍石	锆石	金红石	白钛石	磷灰石	角闪石
	能谱法	28.5	23.3	17.0	13.1	9.0	2.8	2.4	2.0	1.9	-
XZ17-19	TIMA点阵模式	16.3	29.3	18.0	7.6	8.8	4.4	-	13.3	1.4	1.0
	TIMA点模式	21.7	29.7	17.1	12.6	13.7	2.0	0.9	-	1.3	-
	能谱法	56.3	21.9	1.8	6.8	4.3	3.9	3.6	-	1.4	-
XZ17-10	TIMA点阵模式	48.7	28.0	2.4	4.3	6.0	7.9	1.6	-	1.1	-
	TIMA点模式	51.2	27.0	2.3	5.1	5.0	2.7	5.6	-	1.2	-

图4 样品XZ17-19、XZ17-10 TIMA和SEM-EDS重矿物组分对比图(单位:%)

Fig.4 Comparision between compositions of heavy mineral components of XZ17-19 and XZ17-10 based on the TIMA and SEM-EDS(unit:%)

图5 样品XZ17-19钛铁矿蚀变现象((a)钛铁矿蚀变为白钛石的矿物颗粒展示;(b)单个矿物颗粒的钛铁矿蚀变特征,包括矿物相图、背散射图、Ti元素分布图、Fe元素分布图)

Fig.5 Alteration of ilmenite of XZ17-19

表2 准噶尔盆地西北缘中生代地层中重矿物组成及数量百分比(%)

Table 2 Heavy minerals assemblage and quantity percentage of Mesozoic strata in northwestern Junggar Basin(quantity percentage,%)

样品号	位置	层位	钛铁矿	锆石	磁铁矿/ 赤铁矿	石榴石
XZ17-106	铁厂沟	T₃b	-	0.7	74.3	-	6.4	-	-	-	-	-	18.7	-	-	-	100.0
XZ17-103	铁厂沟	J₁b	26.6	2.7	2.0	1.1	1.5	65.3	-	-	-	-	-	0.8	-	-	79.6
XZ17-104	铁厂沟	J₁s	-	-	70.7	-	-	-	-	-	-	-	2.3	-	26.0	-	100.0
XZ17-94	白砾山	T₃b	-	-	97.2	-	-	-	-	-	-	-	2.8	-	-	-	100.0
XZ17-96	白砾山	J₁b	2.3	51.6	-	36.6	5.7	-	-	2.8	-	-	-	1.0	-	-	59.2
XZ17-86	白砾山	J₂x	65.0	6.3	3.1	6.5	4.6	-	6.8	-	-	3.5	4.1	-	-	-	47.0
XZ17-03	克拉玛依	T₃x	93.1	4.8	2.1	-	-	-	-	-	-	-	-	-	-	-	100.0
XZ17-06	克拉玛依	J₁b	20.0	3.2	17.5	19.8	18.6	2.6	-	-	-	-	-	-	-	21.0	52.3
XZ17-09	克拉玛依	J₁s	-	-	47.1	29.4	-	-	-	-	-	-	-	-	-	23.5	0
XZ17-10	克拉玛依	J₁s	51.2	2.7	5.1	27	5.6	2.3	-	1.2	5	-	-	-	-	-	20.0

图6 准噶尔盆地西北缘中生代地层重矿物组合图 (单位:%)

Fig.6 Heavy mineral assemblages of Mesozoic strata in northwestern Junggar Basin(unit:%)

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