| 山东蓬莱史家沟西山火山碎屑岩风化壳元素地球化学特征 |
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| 引用本文：王集宁,蒙永辉,颜堂,姚英强,刘瑞峰,邹连庆,商婷婷,付娟.2018.山东蓬莱史家沟西山火山碎屑岩风化壳元素地球化学特征[J].地球学报,39(4):498-512. |
| DOI：10.3975/cagsb.2018.051501 |
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| 基金项目:中国地质调查局项目“华北地区重要地质遗迹调查(山东)”(编号: DD2017078);“山东省重要地质遗迹调查”(编号: 鲁财建指[2012]110号) |
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| 中文摘要:以山东蓬莱城西史家沟的西山火山碎屑岩风化壳为研究对象, 系统采集样品, 并测试了微量元素、主量元素、稀土元素以及黏土矿物等指标, 揭示了西山火山碎屑岩风化壳的元素地球化学特征, 讨论了风化壳的形成年代及其气候条件。史家沟火山碎屑岩风化壳源自基性-超基性玻屑凝灰岩母岩, CIA平均值为92.3, 总体上处于为强度风化水平, K、Na、Ca和Mg等元素淋失殆尽, 出现了脱硅富铝铁现象, 为轻稀土富集型风化壳。西山火山碎屑岩风化壳可分为两个喷发旋回, 大致以200 cm为界限, 在此以下第一旋回, 以上为第二旋回。第一旋回的CIA介于94.0~97.2之间, V、Rb、Sb、Mo、Li和Ga等微量元素出现淋失, 在213 cm处并出现了?REE、?LREE和?HREE的峰值、Ce的负异常, 蒙脱石化彻底, 风化壳呈现灰白色。第二旋回的CIA在86.3~89.2之间, 风化程度较第一旋回稍低, 微量元素和稀土元素垂直变化较小, 蒙脱石化并不完全彻底, 仍残留长石、赤铁矿和石英等原生矿物, 因而仍然呈现红色或淡红色。西山火山碎屑岩风化壳形成于中新世末到上新世, 为温暖湿润的亚热带环境; 中新世后的气候趋冷造成了两个旋回风化程度和元素地球化学特征的差异。 |
| 中文关键词:风化壳 地球化学 火山碎屑岩 气候 蓬莱 |
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| The Geochemical Characteristics of the Weathering Crust Originating from Volcaniclastic Rock in Xishan of Shijiagou, Penglai,Shandong Province |
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| Abstract:A total of 21 samples were collected in the weathering crust originating from volcaniclastic rock in Xishan of Penglai, Shandong Province, and were analyzed for major elements, trace elements, rare earth elements and clay minerals. The geochemical characteristics were revealed, and the age and the climate of crust formation were discussed. The weathering crust in Xishan originated from basic-ultrabasic vitric tuff with the average CIA of 92.3, and suffered from strong weathering. Most of K, Na, Ca and Mg were lost, and Al, Fe accumulation and desilicification were clearly found. The profile of Xishan could be divided into two eruptive cycles with the boundary at 200 cm. The first eruptive cycle is the horizon below 200 cm, and the horizon above 200 cm is the second eruptive cycle. The CIA of the first cycle ranges from 94.0 to 97.2, indicating that the first cycle is at the strong weathering level. The first cycle exhibits significant leaching of V, Rb, Sb, Mo, Li and Ga, and has the peak of ?REE, ?HREE, and ?LREE at 213 cm with the negative anomaly of Ce. The first cycle suffered from strong montmorillonitization, and shows gray and white color. The CIA of the second cycle varies between 86.3 and 89.2, lower than that of the first cycle; nevertheless, there exist some primary minerals, such as feldspar, hematite and quartz. It could be inferred that the weathering crust of Xishan occurred in Late Miocene and Pliocene with warm and humid climate, and the cooling trend resulted in the significant differences of weathering degree and geochemical characteristics between two eruptive cycles. |
| keywords:weathering crust geochemistry volcaniclastic rock climate Penglai |
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