安徽省巢湖地区二叠纪栖霞组、孤峰组硅质岩地球化学特征对比及大地构造背景分析

摘要/Abstract

摘要：

为探讨下扬子地区二叠系硅质岩的硅质来源和形成背景,以巢湖地区二叠纪栖霞组和孤峰组硅质岩为研究对象,收集了前人大量有关栖霞组和孤峰组的研究成果和数据,并对采自栖霞组和孤峰组硅质岩样品进行了主量元素、微量元素、稀土元素测试。栖霞组、孤峰组硅质岩样品测试结果显示,硅质岩的稀土元素经北美页岩标准化后的配分曲线近似平坦型向左倾斜,有弱Ce负异常,且HREE弱富集,反映了热水沉积硅质岩的特征。研究区硅质岩样品的Al-Fe-Mn三角图中,样品投点分布较广,即Al比值变化范围较大,认为是岩浆在喷发过程中受硅-铝质陆壳混染作用的结果。结合沉积环境判别指标分析认为:栖霞组硅质岩沉积时期其沉积环境主要为大陆边缘环境;孤峰组硅质岩沉积时期其沉积环境为大陆边缘-海盆过渡环境。从栖霞组到孤峰组沉积时期,海侵规模不断变大,水体变深,海盆面积扩大,研究区在不同时期沉积环境存在差异。研究区栖霞组、孤峰组硅质岩的沉积与大陆边缘裂陷活动紧密相关。

关键词: 硅质岩, 海盆, 大陆边缘, 热水沉积, 巢湖地区

Abstract:

Aiming to discuss the origin and sedimentary background of Permian chert in Yangtze region, we took the siliceous rocks as samples from Qixia Formation and Gufeng Formation in Chaohu area, which located in the northern margin of the Yangtze block. In this study, we collected previous research data of these two formations and systematically analyzed major, trace and rare elements data of siliceous rocks collected from the two formations.Test results of samples which we got in this study show that rare earth elements (REEs) pattern curves lean slightly to the left, with slight Ce negative anomaly and HREE relative enrichment, reflects the characteristics of the hydrothermal chert.The points pitched on the Al-Fe-Mn diagram of Qixia Formation and Gufeng Formation siliceous rocks indicate that most of the samples are high in Al. In this paper,we proposed that magma suffered the contamination of the Si-Al rich continental crust during the eruption,with high Al ratio. Combined with diagrams of sedimentary environments we came to a conclusion that cherts in Qixia Formation and Gufeng Formation were deposited at continental margin, continental margin-ocean basin, respectively. From Qixia Period to Gufeng Period, transgression scale became large, the depth of seawater became large, the area of ocean basin expanded, which made sedimentary environment different.The siliceous rocks sedimentation in both Qixia Formation and Gufeng Formation was closely related to continental margin chasmic activities.

Key words: siliceous rock, ocean basin, continental margin, hydrothermal sedimentation, Chaohu area

中图分类号:

P588.2

加娜提古丽·吾斯曼, 周瑶琪, 姚旭, 许汉华, 方雪. 安徽省巢湖地区二叠纪栖霞组、孤峰组硅质岩地球化学特征对比及大地构造背景分析[J]. 现代地质, 2017, 31(04): 734-745.

JIANATIGULI Wusiman, ZHOU Yaoqi, YAO Xu, XU Hanhua, FANG Xue. Geochemical Characteristics Comparison and Tectonic Background Analysis of Siliceous Rocks from Qixia Formation and Gufeng Formation of Permian in Chaohu Area, Anhui Province[J]. Geoscience, 2017, 31(04): 734-745.

图/表 14

图1 巢湖地区区域地质图

Fig.1 Regional geological map of Chaohu area

图2 巢湖地区中二叠统硅质岩岩相照片 (a)巢湖平顶山剖面栖霞组硅质结核;(b) 巢湖平顶山剖面栖霞组串珠状硅质条带;(c)巢湖平顶山剖面孤峰组层状硅质岩与硅质泥岩互层;(d)巢湖龟山剖面栖霞组与孤峰组分界(红色虚线示意分界:线左侧为孤峰组地层,线右侧为栖霞组地层)

Fig.2 Lithofacies photos of Middle Permian siliceous rocks in Chaohu area

表1 巢湖地区栖霞组和孤峰组硅质岩主量元素分析(wB/%)

Table 1 Analysis of major elements of siliceous rocks in Qixia Formation and Gufeng Formation in Chaohu area (%)

样品编号	SiO₂	Al₂O₃	TiO₂	Fe₂O₃	MnO	MgO	CaO	Na₂O	K₂O	P₂O₅
CH-qx-2	94.32	0.60	0.028	0.335	0.002 1	0.070	0.99	0.042	0.15	0.017 7
CH-qx-3	95.04	0.42	0.020	0.145	0.001 1	0.180	1.01	0.040	0.13	0.016 1
CH-qx-4	94.24	0.21	0.053	0.065	0.001 8	0.680	1.97	0.030	0.11	0.016 2
CH-qx-5	95.58	0.18	0.007	0.052	0.000 8	0.091	1.30	0.025	0.07	0.015 6
CH-qx-6	95.86	0.33	0.011	0.090	0.001 3	0.025	1.13	0.013	0.10	0.014 6
CH-qx-7	96.32	0.20	0.008	0.076	0.000 7	0.027	1.01	0.012	0.14	0.015 5
CH-qx-8	93.98	0.20	0.008	0.038	0.000 8	0.014	0.06	0.010	0.11	0.014 6
CH-qx-9	82.56	0.23	0.009	0.090	0.009 0	0.650	7.38	0.019	0.10	0.022 4
CH-gf-1	94.62	0.60	0.025	0.189	0.001 6	0.110	0.98	0.023	0.34	0.046 9
CH-gf-2	94.44	0.67	0.027	0.204	0.001 0	0.067	0.33	0.041	0.13	0.047 2
栖霞组均值	93.49	0.30	0.020	0.110	0.000 0	0.22	1.86	0.020	0.11	0.016 6
孤峰组均值	94.53	0.64	0.030	0.200	0.000 0	0.09	0.66	0.030	0.24	0.047 0

表2 沉积环境值pH值及酸碱度与MnO/Fe比值关系

Table 2 The relationship between pH of the sedimentary environment and MnO/Fe ratio

沉积环境	酸性	弱酸性	中性	弱碱性	碱性
MnO/Fe	<0.013	0.013~0.016	0.016~0.026	0.026~0.055	>0.055
pH值	<5	5~6	6~7.8	7.8~9	>9

图3 巢湖地区中二叠统地层柱状图

Fig.3 Stratigraphic column of Middle Permian in Chaohu area

表3 巢湖地区栖霞组和孤峰组硅质岩稀土元素分析(wB/10-6)

Table 3 Analysis of rare earth elements of siliceous rocks from Qixia Formation and Gufeng Formation in Chaohu area (10-6)

样品编号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu
CH-qx-2	0.77	1.50	0.200	0.77	0.160	0.040	0.160	0.028	0.15	0.034	0.110	0.017	0.120	0.020
CH-qx-3	0.48	0.98	0.120	0.47	0.110	0.023	0.100	<0.02	0.10	0.016	0.055	0.0110	0.062	0.013
CH-qx-4	0.46	0.66	0.087	0.29	0.042	0.020	0.063	<0.02	0.07	0.013	0.048	<0.01	0.046	<0.01
CH-qx-5	0.26	0.43	0.070	0.22	0.055	0.018	0.065	<0.02	0.05	<0.01	0.045	<0.01	0.035	<0.01
CH-qx-6	0.30	0.51	0.074	0.29	0.029	0.020	0.063	<0.02	0.050	<0.01	0.038	<0.01	0.035	<0.01
CH-qx-7	0.43	0.82	0.100	0.31	0.060	0.015	0.045	<0.02	0.05	<0.01	0.038	<0.01	0.057	<0.01
CH-qx-8	0.07	0.16	<0.02	0.07	0.008	0.005	<0.02	<0.02	0.008	0.003	<0.02	<0.01	<0.03	<0.01
CH-qx-9	0.83	0.93	0.210	0.83	0.190	0.040	0.170	0.035	0.18	0.042	0.110	0.014	0.089	0.010
CH-gf-1	2.09	2.94	0.440	1.87	0.370	0.090	0.450	0.063	0.46	0.110	0.290	0.044	0.300	0.035
CH-gf-2	2.05	2.75	0.460	1.68	0.340	0.080	0.410	0.060	0.41	0.100	0.260	0.041	0.260	0.043
栖霞组均值	0.45	0.75	0.110	0.41	0.080	0.020	0.090	0.020	0.08	0.020	0.060	0.010	0.060	0.010
孤峰组均值	2.07	2.85	0.45	1.78	0.360	0.090	0.430	0.060	0.44	0.110	0.280	0.040	0.280	0.040

表4 巢湖地区栖霞组和孤峰组硅质岩微量元素分析(wB/10-6)

Table 4 Analysis of trace elements of siliceous rocks from Qixia Formation and Gufeng Formation in Chaohu area (10-6)

样品编号	Co	Ni	Cu	Th	U	U/Th
CH-qx-2	0.39	4.02	5.93	0.39	1.13	2.90
CH-qx-3	0.33	3.19	2.75	0.29	1.29	4.45
CH-qx-4	0.12	2.66	6.22	0.11	1.85	16.82
CH-qx-5	0.09	1.87	3.26	0.07	1.81	25.86
CH-qx-6	0.086	2.04	0.50	0.10	3.67	36.70
CH-qx-7	0.12	3.37	0.50	0.14	11.50	82.14
CH-qx-8	0.13	3.67	3.18	0.04	0.20	5.00
CH-qx-9	0.37	6.01	1.38	0.10	1.28	12.80
CH-gf-1	0.44	24.80	12.80	0.43	4.58	10.65
CH-gf-2	0.41	23.30	7.36	0.20	4.41	22.05

图4 栖霞组、孤峰组地层柱状图样品所对应的地球化学参数变化曲线图

Fig.4 Geochemical parameter curves of siliceous rock samples from Qixia Formation and Gufeng Formation in Chaohu area

图5 巢湖地区中二叠世层状硅质岩与非层状硅质岩Ce/Ce*、Eu/Eu*、(La/Yb)N、(La/Ce)N值分布图

Fig.5 Histograms showing Ce/Ce* variations(A),Eu/Eu* variations (B),(La/Yb)N ratios (C) and (La/Ce)N ratios(D) in different types of siliceous rocks from Middle Permian in Chaohu area

图6 巢湖地区栖霞组和孤峰组硅质岩样品REE配分模式图(北美页岩值据HASKIN等[25])

Fig.6 NASC-normalized REE patterns for siliceous rocks from Qixia Formation and Gufeng Formation in Chaohu area

图7 栖霞组和孤峰组硅质岩Fe-Mn-(Cu+Ni+Co)×10三角图[26] HD.热水沉积物区;ED.东太平洋中脊热水沉积物区;RH.红海热卤水沉积物区;HN.水成沉积物区

Fig.7 Fe-Mn-(Cu+Ni+Co)×10 diagram of siliceous rocks from Qixia Formation and Gufeng Formation[26]

图8 孤峰组(a)和栖霞组(b)硅质岩Al-Fe-Mn三角图[30]

Fig.8 Al-Fe-Mn diagrams for siliceous rocks from Gufeng Formation and Qixia Formation[30]

图9 研究区中二叠统硅质岩沉积环境判别图(底图据文献[24])

Fig.9 Discriminant diagrams of sedimentary environment for Middle Permian siliceous rocks

图10 中二叠世古陆分布图((a)据Kametaka M等[6]修改)和二叠纪硅质沉积优势区域分布图 ((b)据姚旭等[33],2013修改)及硅质岩成因模式图((c)据姚旭等[33],2013修改)

Fig.10 Middle Permian ancient continent distribution((a)modified from Kametaka M et al.[6], 2005) and Permian siliceous sedimentary dominant region((b) modified from Yao Xu et al.[33],2013) and silicalite formation model ((c) modified from Yao Xu et al.[33],2013)

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