...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Contributions to Mineralogy and Petrology >Trace element and isotopic evidence for two types of crustal melting beneath a High Cascade volcanic center, Mt. Jefferson, Oregon
【24h】

Trace element and isotopic evidence for two types of crustal melting beneath a High Cascade volcanic center, Mt. Jefferson, Oregon

机译：高喀斯喀特火山中心下方两种类型的地壳融化的痕量元素和同位素证据。俄勒冈州杰斐逊

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Mt. Jefferson is an andesite-dacite composite volcano in the Cascade Range, the locus of andesite and dacite-dominated volcanism for at least 1 million years. A large trace element data set for Mt. Jefferson and its surrounding mafic volcanic platform effectively rules out any fractionation based model (FC or AFC) for the generation of Mt. Jefferson andesites. Several incompatible element (Zr, Nb, Y) concentrations decrease in the range from basalt to andesite, and then increase in the range from andesite to rhyodacite. Others (Ba, Rb, La, Th) remain constant or show a slight increase in the basalt to andesite range, with modest increases from andesite to rhyodacite. Systematic variations in highly incompatible element ratios such as Ba/La and Rb/Th suggest magma mixing dominates the trace element signatures. Rhyodacites are isotopically uniform (~(87)Sr/~(86)Sr = 0.70325-0.70343; ~(206)Pb/~(204)Pb = 18.75-18.85; ?~(18)O = 6.3 +- 0.3), whereas andesite and dacite are more variable (~(87)Sr/~(86)Sr = 0.70291-0.70353; ~(206)Pb/~(204)Pb = 18.59-18.86; ?~(18)O = 6.0 +- 0.6). Typical basaltic andesite has (~(87)Sr/~(86)Sr = 0.70326-0.70358; ~(206)Pb/~(204)Pb = 18.78-18.85; ?~(18)O = 5.9 +- 0.4). Sr-rich (> 1,000 ppm) basaltic andesite is more variable (~(87)Sr/~(86)Sr = 0.70300-0.70360; ~(206)Pb/~(204)Pb = 18.70-18.89; ?~(18)O = 5.9 +- 0.4). The data define mixing arrays with one end member at (~(87)Sr/~(86)Sr = 0.7029; ~(206)Pb/~(204)Pb = 18.59, another at rhyodacite, and a third at (~(87)Sr/~(86)Sr = 0.7036; ~(206)Pb/~(204)Pb = 18.89. The first end member is defined by Sr-rich (800-1,200 ppm) andesite with high Al_2O_3, and low K_2O, Ba, and Rb/Th; the third one by K_2O- and very Sr-rich (>2,000 ppm) shoshonite. Isotopic data for basalts in northern Oregon preclude any fractionation relationship between basalt and either rhyodacite or Sr-rich andesite (e.g., the minimum ~(206)Pb/~(204)Pb ratio in basalt is 18.83). Considered in light of geophysical models for the Cascades, these data suggest two types of crustal melting beneath the arc. Rhyodacite may be generated at 25-30 km depth by partial melting of arc basalt-like amphibolite at 850-900 deg C. Sr-rich andesite may be formed by partial melting of depleted MORB-like mafic granulite at 35-45 km depth at 1,000-1,100 deg C. Experimental and REF evidence supports these interpretations as does the restriction of Sr-rich andesite in the Cascades to the area south of the 100 mW/m~2 heat flow contour between Mt. Jefferson and Mt. Hood. Thick crust and high heat flow are necessary to produce such andesite.
机译：公吨。杰斐逊是喀斯喀特山脉的安山岩-达克特复合火山，这是安山岩和以达克特为主的火山活动的所在地，至少存在了一百万年。 Mt的大量痕量元素数据集。杰斐逊及其周围的镁铁质火山岩平台有效地排除了任何基于分馏的模型（FC或AFC）来生成Mt。杰斐逊安第斯山脉。几种不相容元素（Zr，Nb，Y）的浓度在从玄武岩到安山岩的范围内减小，然后在从安山岩到流纹岩的范围内增大。其他的（Ba，Rb，La，Th）保持不变，或者玄武岩到安山岩的范围略有增加，从安山岩到流纹岩的增加不大。 Ba / La和Rb / Th等高度不相容元素比率的系统变化表明，岩浆混合主导了痕量元素特征。菱锰矿是同位素均匀的（〜（87）Sr /〜（86）Sr = 0.70325-0.70343;〜（206）Pb /〜（204）Pb = 18.75-18.85;α〜（18）O = 6.3 +-0.3），而安山岩和钠长辉石更具可变性（〜（87）Sr /〜（86）Sr = 0.70291-0.70353;〜（206）Pb /〜（204）Pb = 18.59-18.86;α〜（18）O = 6.0 +- 0.6）。典型的玄武安山岩具有（〜（87）Sr /〜（86）Sr = 0.70326-0.70358;〜（206）Pb /〜（204）Pb = 18.78-18.85;α〜（18）O = 5.9 +-0.4）。富Sr（> 1,000 ppm）的玄武质安山岩更具变化性（〜（87）Sr /〜（86）Sr = 0.70300-0.70360;〜（206）Pb /〜（204）Pb = 18.70-18.89;α〜（18 O ＝ 5.9±0.4）。数据定义了一个混合数组，其中一个末端成员为（〜（87）Sr /〜（86）Sr = 0.7029;〜（206）Pb /〜（204）Pb = 18.59，另一个为流纹岩，第三个为（〜（ 87）Sr /〜（86）Sr = 0.7036;〜（206）Pb /〜（204）Pb = 18.89。第一端由富Sr（800-1,200 ppm）的安山岩定义，其中Al_2O_3高，K_2O低，Ba和Rb / Th;第三个是富含K_2O和非常富Sr（> 2,000 ppm）的菱铁矿。俄勒冈州北部玄武岩的同位素数据排除了玄武岩与流纹岩或富Sr安山岩之间的任何分馏关系（例如，玄武岩中的最小〜（206）Pb /〜（204）Pb比为18.83）。根据喀斯喀特山脉的地球物理模型考虑，这些数据表明弧下有两种类型的地壳融化。流纹岩可能在25-30通过在850-900摄氏度下部分熔化玄武岩样角闪石来形成3 km深度。富含Sr的安山岩可能是通过在1,000-1,100摄氏度下在深度35-45 km处耗尽的MORB样镁铁质粒岩的部分熔融而形成的。 REF证据支持这些梯级中富含Sr的安山岩限制在Mt.之间的100 mW / m〜2热流轮廓线以南的区域也是如此。杰斐逊山引擎盖。要生产这样的安山岩，必须有厚的地壳和高的热流。

著录项

相似文献

  • 外文文献
  • 中文文献
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号