MULTIPLE GEOCHEMICAL TRACES OF TWO TYPES OF INTERMEDIATE-BASIC VOLCANIC ROCKS IN XIARUO-TUODING AREAS, JINSHA RIVER COMBINATION ZONE, NORTHWEST OF YUNNAN PROVINCE, CHINA
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摘要: 应用常量元素、微量元素对火山岩进行构造环境、成因及岩源示踪时, 首先必须在宏观区域地质、地球化学调查基础上, 结合当时所形成的各类地质体岩石类型组合来恢复, 它是宏观构造环境判别的基础; 其次, 由于构造环境时空复杂性, 需采用“两结合”的研究方法, 一是多元地球化学信息示踪, 二是不同岩类的时空配套; 第三, 在选择判别图解时, 弄清前人图解的应用前提、适用范围和条件, 切忌乱套瞎投.在此思想指导下, 侧重对滇西北金沙江结合带霞若—拖顶地区两类中-基性火山岩进行了多元地球化学示踪, 获得了较好的效果: (1) 金沙江蛇绿混杂岩带东侧的基性火山岩产于大陆裂谷环境, 而西侧中-基性火山岩具岛弧火山岩特征; (2) 两者火山熔浆均源自富集地幔, 东侧来自均一的富集地幔, 而西侧富集地幔具不均一性; (3) 在此基础上讨论了它们形成的构造演化特征.Abstract: When using major and trace elements as a tool to trace tectonic settings, origins and magma sources of volcanic rocks, we must firstly reconstruct the elements on the bases of macro-regional geology and geochemical investigations, and of various kinds of rock-type assemblages in different geological bodies that occurred at that time. This reconstruction serves as the basis for the identification of the macro-tectonic settings. Secondly, we should adopt the research method characterized by the combination of the multiple geochemical information tracing with the temporal-spatial matching of various kinds of rock types, due to the temporal-spatial complexity of the tectonic settings. Thirdly, we should fully understand the application premises, ranges and conditions, so as to identify correctly the corresponding illustrations. On the basis of the three points mentioned above, this paper focuses on the multiple geochemical tracing of the two types of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas in the Jinsha River combination zone, Northwest of Yunnan Province, China. This research has already brought us the following three relatively excellent effects: (1) The basic volcanic rocks located on the eastern side of the Jingsha River ophiolitic mélange zone occurred in the continental-rift setting. However, the intermediate-basic volcanic rocks are characterized by the island-arc volcanic rocks on the western side of Jingsha River ophiolitic mélange zone. (2) The volcanic lava of the two types of volcanic rocks both originated from the lava-enriched earth mantle. Specifically, the volcanic rock on the eastern side originated from the homogeneous lava-enriched earth mantle, while those on the eastern side originated from the heterogeneous lava-enriched earth mantle. (3) Finally, the structural evolutionary characteristics of these volcanic rocks are discussed.
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图 1 滇西北金沙江结合带霞若—拖顶地区地质略图
1.三叠纪崔以比组; 2.晚二叠世奔子栏组; 3.早二叠世喀大崩组; 4.晚石炭世响姑岩组; 5.早石炭世申洛拱组; 6.灰岩; 7.中-基性火山岩夹碎屑岩; 8.玄武岩; 9.蛇绿混杂岩; 10.前志留纪变质杂岩; 11.各磨茸石英闪长岩—花岗闪长岩; 12.右行剪切糜棱岩带; 13.右行韧脆性剪切带; 14.主斜向走滑断层; 15.次斜向走滑断层; 16.倒转地层产状; 17.地层产状; 18.吉义独-各磨茸蛇绿混杂岩带; 19.晚石炭世—早二叠世裂谷带; 20.早—中三叠世岛弧带; 21.中咱地块; 22.地名; 23.采样点及编号; 24.工作区
Fig. 1. Geological sketch map of Xiaruo-Tuoding areas in Jinsha River combination zone, Northwest Yunnan Province
图 2 金沙江结合带霞若—拖顶地区两类中-基性火山岩构造环境的F1-F2和F2-F3图解判别
WPB.板内玄武岩; OFB.洋中脊玄武岩; CAB.钙碱性玄武岩; LKT.低钾(岛弧) 拉斑玄武岩; SHO.钾玄岩(投点编号见表 1).据Pearce, 1976, 见文献[7]
Fig. 2. F1-F2 and F2-F3 tectonic setting discrimination diagrams for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
图 3 不同构造环境玄武岩w (Ti) /w (Y) -w (Nb) /w (Y) 判别(据文献[8])
实线.洋脊玄武岩; 虚线.板内玄武岩; 点线.岛弧玄武岩.1.金沙江西侧中-基性火山岩; 2.金沙江东侧基性火山岩
Fig. 3. w (Ti) /w (Y) vs. w (Nb) /w (Y) diagrams for different tectonic settings discrimination for basalts
图 4 金沙江结合带霞若—拖顶地区中-基性火山岩以MORB标准化蜘网图
a.火山弧型玄武岩: 1.钙碱性; 2.拉斑质; 3.西侧中-基性火山岩平均值. b.板内玄武岩: 1.拉斑—碱性; 2.拉斑质; 3.东侧基性火山岩平均值. a, b中1, 2据文献[8]
Fig. 4. MORB normalized trace element spider diagrams for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
图 5 金沙江结合带霞若—拖顶地区中-基火山岩稀土配分模式
a.西侧(下), 东侧(上); b.东侧(样品编号见表 2)
Fig. 5. REE distribution patterns for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
图 6 金沙江结合带霞若—拖顶地区中-基性火山岩微量元素比值蜘网图
a.比值蜘网图; a1.西侧中-基性火山岩; a2.东侧基性火山岩. b. Nb标准化比值蜘网图(b1, b2同a1, a2)
Fig. 6. Trace element ratios and niobium normalized spider diagrams for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
表 1 金沙江结合带霞若—拖顶地区两类中-基性火山岩岩石化学成分
Table 1. Chemical compositions for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
表 2 金沙江结合带霞若—拖顶地区两类中-基性火山岩微量元素质量分数和比值
Table 2. Trace element mass fractions and their ratios for two kinds of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas of Jinsha River combination zone
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