青海省同仁地区上二叠统石关组上部火山岩的新发现及其地球化学特征和构造环境意义

寇晓虎; 朱云海; 张克信; 施彬; 罗根明

青海省同仁地区上二叠统石关组上部火山岩的新发现及其地球化学特征和构造环境意义

寇晓虎^{1, 2,},
朱云海¹,
张克信^{1, 2},
施彬¹,
罗根明¹

1.
中国地质大学地球科学学院, 湖北武汉430074
2.
中国地质大学地质过程与矿产资源国家重点实验室, 湖北武汉 430074

基金项目:

高等学校全国优秀博士学位论文作者专项资金项目 200228

中国地质调查局项目 200413000007

详细信息

作者简介:
寇晓虎(1980-), 男, 硕士生, 从事区域地质调查和火山岩岩石学研究.E-mail：xh_kou@sina.com

中图分类号: P588.1
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出版历程
- 收稿日期: 2006-06-11
- 刊出日期: 2007-01-25

Discovery and Geochemistry of Upper Permian Volcanic Rocks in Tongren Area, Qinghai Province and Their Tectonic Significance

1.
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
2.
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China

摘要

摘要: 青海省同仁地区位于秦、祁结合部, 构造演化历史悠久.在该区隆务河两侧广泛发育着二叠、三叠纪地层, 通过两套地层岩石组合分析, 我们认为晚二叠世晚期至早三叠世早期该区属于半深海浊积扇相沉积环境.在该区晚二叠世晚期地层中新发现一套火山岩, 火山岩的岩石组合主要为玄武岩、安山岩、玄武安山岩等.根据岩石的常量元素特征, 可以将本区火山岩分为两部分: 下部岩石的SiO₂含量为49.04%~52.43%, 平均为51.28%, TiO₂含量为0.67%~1.11%, 平均为0.9%, ALK值为2.64%~3.6%.通过常量元素投点图分析, 本组火山岩岩性偏基性, 属于拉斑玄武岩系列, 显示高钛玄武岩特征.上部岩石的SiO₂含量为56.25%~60.36%, 平均为58.76%, TiO₂含量为0.52%~0.63%, 平均为0.58%, ALK值在5.26%~5.54%之间.岩性偏中性, 属于钙碱性系列, 显示低钛玄武岩特征.火山岩的稀土元素也有明显差异, 下部稀土总量较低, ∑REE= (61.7~97.17) ×10^-6, (La/Lu)_N比值平均为3.07, 轻重稀土分馏不明显, 显示与过渡型洋中脊玄武岩相似的特征; 而上部稀土总量较高, ∑REE= (107.51~143.32) ×10^-6, (La/Lu)_N比值平均为7.78, 轻重稀土分馏明显, 稀土分配曲线显示与岛弧安山岩相似的特征.该区火山岩的微量元素比值蛛网图显示与岛弧钙碱性玄武岩-过渡类型玄武岩具有较强的相似性.构造环境判别显示出本区火山岩具有从拉张的过渡型洋中脊环境到闭合的岛弧环境的演化特征.
- 地球化学 /
- 火山岩 /
- 石关组 /
- 上二叠统 /
- 西秦岭
Abstract: Tongren area is located in the lower reaches of the Longwuhe River, east of Qinghai Province, which is between the West Qinling and South Qilian orogenic belts. Along the two sides of Longwuhe River broadly develops stratum in Permian and Triassic. Through the analysis of rock assemblages, this area is determined to be turbidite fan facies of hemipelagic from the end of Late Permian to the beginning of Early Triassic. Through the geological research, we found volcanic rocks in the Shiguan Formation of Upper Permian. The volcanic rock assemblage is mainly composed of basalts, basaltic andesites and andesites. According to the characteristics of the ordinary elements, the volcanic rocks can be divided into two parts. The lower part: SiO₂ content is 49.04%-52.43%, with the average of 51.28%; the TiO₂ content is 0.67%-1.11%, with the average of 0.9%; and the ALK value is 2.64%-3.6%.The rock type is mainly tholeiitic basalt series, with high titanium quantity. The upper part: SiO₂ content is 56.25%-60.36%, the average being 58.76%; The TiO₂ content is 0.52%-0.63%, the average being 0.58%; the ALK value is 5.26%-5.54%. The rock type is calc-alkaline series with low titanium quantity. REE distribution patterns of the volcanic rocks are different. The lower part has lower REE, with (La/Lu)_N average being 3.07, and its distribution patterns are consistent with those of transitional mid-oceanic ridge basalt. REE is rich in the upper part, especially the LREE. And its distribution patterns are similar to those of island arc andesite. The trace elements have the same characteristics, the distribution type of which is something like that of island arc basalt rock. Tectonic setting distinction reveals that the volcanic rocks of this area were formed in transitional mid-oceanic ridge basalt to island arc tectonic setting.
- geochemistry /
- volcanic rocks /
- Shiguan Formation /
- Upper Permian /
- West Qinling

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图 1 研究区大地构造位置

Fig. 1. Tectonic location of the research area

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图 2 青海省同仁地区上二叠统石关组(P₃s) 实测剖面图

1.长石石英砂岩; 2.泥质灰岩; 3.硅质灰岩; 4.玄武岩; 5.安山岩; 6.玄武安山岩; 7.钙质板岩

Fig. 2. Section of Shiguan Formation of Upper Permian in Tongren area, Qinghai Province

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图 3 ∑FeO/ (∑FeO+MgO) -TiO₂图(Serri et al., 1985)

HT.高钛玄武岩; LT.低钛玄武岩

Fig. 3. ∑FeO/ (∑FeO+MgO) -TiO₂ diagram

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图 4 同仁地区上二叠统顶部的火山岩AFM图(Irvine and Barger, 1971,图例同图 3)

T.拉斑玄武岩系列; C.钙碱性系列

Fig. 4. AFM diagram of Upper Permian volcanic rocks in Tongren area

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图 5 同仁地区上二叠统顶部的火山岩稀土元素分配曲线(图例同图 3)

Fig. 5. REE distribution patterns of Upper Permian volcanic rocks in Tongren area

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图 6 同仁地区上二叠统顶部的火山岩微量元素比值蛛网图(图例同图 3)

Fig. 6. Spider diagram of trace elements of Upper Permian volcanic rocks in Tongren area

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图 7 同仁地区上二叠统顶部的火山岩FeO_t-MgO-Al₂O₃ (a)、K₂O-TiO₂-P₂O₅ (b)、FeO^*/MgO-TiO₂ (c) 构造环境判别图(图例同图 3)

a图据Pearce et al. (1977); 1.岛弧扩张中心火山岩; 2.造山带火山岩; 3.洋中脊火山岩; 4.洋岛火山岩; 5.大陆火山岩; b图据从柏林和张儒瑗(1983); OTB.大洋拉斑玄武岩; CTB.大陆拉斑玄武岩; AB.碱性玄武岩; c图据Miyashiro (1975); IAT.岛弧拉斑玄武岩; MORB.洋中脊玄武岩; OIB.洋岛玄武岩

Fig. 7. FeO_t-MgO-Al₂O₃, K₂O-TiO₂-P₂O₅ and FeO^*/MgO-TiO₂ diagram of Upper Permian volcanic rocks in Tongren area

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表 1 同仁地区二叠纪火山岩化学分析结果(%)

Table 1. Chemical analysis results of Permian volcanic rocks in Tongren area

表 2 同仁地区二叠纪火山岩稀土元素分析结果(10^-6) 及球粒陨石标准化值

Table 2. Analysis results of REE and meteorite standardize of Permian volcanic rocks in Tongren area

表 3 同仁地区二叠纪火山岩微量元素分析结果(10^-6) 及MORB标准化值

Table 3. Analysis results of trace elements and MORB standardize of Permian volcanic rocks in Tongren area

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