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首页> 外文期刊>GSA Bulletin >The role of the mantle during crustal extension: Constraints from geochemistry of volcanic rocks in the Lake Mead area, Nevada and Arizona
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The role of the mantle during crustal extension: Constraints from geochemistry of volcanic rocks in the Lake Mead area, Nevada and Arizona

机译：地幔在地壳扩展中的作用：内华达州和亚利桑那州米德湖地区火山岩地球化学的限制

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摘要

One of the fundamental questions in areas of large-magnitude extension and magmatism is the role of the mantle in the extension process. The Lake Mead area is ideally suited for developing models that link crustal and mantle processes because it contains both mantle and crustal boundaries and it was the site of large-magnitude crustal extension and magmatism during Miocene time. In the Lake Mead area, the boundary between the amagmatic zone and the northern Colorado River extensional corridor parallels the Lake Mead fault system and is situated just to the north of Lake Mead. This boundary formed between 11 and 6 Ma during, and just following, the peak of extension and corresponds to a contact between two mantle domains. During thinning and replacement of the lithospheric mantle in the northern Colorado River extensional corridor, the lithospheric mantle in the amagmatic zone remained intact. Contrasting behavior to the north and south of this boundary may have produced the mantle domain boundary. The domain to the north of the boundary is characterized by mafic lavas with a lithospheric mantle isotopic and geochemical signature (Nd = -3 to -9; 87Sr/86Sr = 0.706-0.707). To the south of the boundary in the northern Colorado River extensional corridor, lavas have an ocean island basalt (OIB)-mantle signature and appear to have only a minor lithospheric mantle component in their source (Nd = 0 to +4; 87Sr/86Sr = 0.703-0.705). Mafic lavas of the northern Colorado River extensional corridor represent the melting of a complex and variable mixture of asthenospheric mantle, lithospheric mantle, and crust. Pliocene alkali basalt magmas of the Fortification Hill field represent the melting of a source composed of a mixture of asthenospheric mantle, high U/Pb (HIMU)-like mantle, and lithospheric mantle. Depth of melting of alkali basalt magmas remained relatively constant from 12 to 6 Ma during, and just after, the peak of extension but probably increased between 6 and 4.3 Ma following extension. Miocene and Pliocene low Nd and high 87Sr/86Sr magmas and tholeiites at Malpais Flattop were derived from a lithospheric mantle source and were contaminated as they passed through the crust. The shift in isotopic values due to crustal interaction is no more than 4 units in Nd and 0.002 in 87Sr/86Sr and does not mask the character of the mantle source. The change in source of basalts from lithospheric mantle to asthenospheric mantle with time, the OIB character of the mafic lavas, and the HIMU-like mantle component in the source are compatible with the presence of rising asthenosphere, as an upwelling convective cell, or plume beneath the northern Colorado River extensional corridor during extension. The Lake Mead fault system, a major crustal shear zone, parallels the mantle domain boundary. The Lake Mead fault system may locally represent the crustal manifestation of differential thinning of the lithospheric mantle.
机译：大范围 扩展和岩浆作用的基本问题之一是地幔在扩展 过程中的作用。米德湖地区非常适合开发将地壳和地幔过程联系起来的 模型，因为它包含地幔和地壳边界的 ，并且它是大震级 中新世时期的地壳伸展和岩浆作用。在 米德湖地区，岩浆带与 北部科罗拉多河伸展走廊之间的边界平行于 米德湖断层系统，位于在 米德湖的北部。在 以及紧随其后的延伸峰之间，该边界形成在11和6 Ma之间，并且对应于两个地幔域之间的 接触。在北科罗拉多河支流扩展走廊上的岩石圈地幔变薄和替换期间，静磁区的岩石圈地幔保持不变。在此 边界的北部和南部的相反行为可能产生了地幔区域边界。边界以北的域 的特征是镁铁质熔岩 具有岩石圈地幔同位素和地球化学特征 （ Nd = -3至-9； 87 Sr / 86 Sr = 0.706-0.707）。在科罗拉多河北部延伸走廊的 边界的南部， 熔岩具有海洋岛玄武岩（OIB）-地幔特征，并且 出现在在其源中 仅具有较小的岩石圈地幔成分（ Nd = 0至+4; 87 Sr / 86 Sr = 0.703-0.705）。科罗拉多河北部延伸走廊的黑手党 熔岩代表了软流圈地幔，岩石圈地幔和地壳的复杂且可变的混合物的熔化。设防山场的上新世碱性玄武岩 岩浆代表由软流圈地幔，高U / Pb（HIMU）混合物组成的源的熔化 状地幔和岩石圈地幔。碱玄武岩岩浆融化的深度 在12〜6 Ma期间及之后一直保持相对恒定 ，但在此之后不久，延伸峰可能会增加延展期为6和4.3 Ma。 中新世和上新世低 Nd 和高 87 Sr / 86 Sr岩浆和黄hole石Malpais Flattop的 来自岩石圈地幔源 ，并且在穿过地壳时受到污染。地壳相互作用引起的同位素值 移动 在 Nd 中不超过4个单位，在 87 Sr中不超过0.002个单位/ 86 Sr，并且不掩盖 地幔源的字符。 玄武岩的来源随着时间的变化从岩石圈地幔变为软流圈地幔，镁铁质熔岩的OIB特征以及类似HIMU的 地幔源中的组成部分与上升的软流层的存在 ，上升流的对流单元或科罗拉多河北部延伸走廊 下的 泡沫兼容延期。米德湖断层系统是主要的地壳 剪切带，与地幔域边界平行。米德湖 断层系统可能局部代表了岩石圈地幔差异性变薄的地壳表现。

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  • 来源
    《GSA Bulletin》 |1993年第12期|1561-1575|共15页
  • 作者

    DAN L. FEUERBACH; EUGENE I. SMITH; J. D. WALKER; J. A. TANGEMAN;

  • 作者单位

    Center for Volcanic and Tectonic Studies, Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada 89154;

    Center for Volcanic and Tectonic Studies, Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada 89154;

    Isotope Geochemistry Laboratory Department of Geology University of Kansas, Lawrence, Kansas 66045;

    Isotope Geochemistry Laboratory Department of Geology University of Kansas, Lawrence, Kansas 66045;

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