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首页> 外文学位 >The origin and evolution of the deep lithosphere beneath continental arcs: Constraints from lower crustal and mantle xenoliths from the Sierra Nevada, California.
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The origin and evolution of the deep lithosphere beneath continental arcs: Constraints from lower crustal and mantle xenoliths from the Sierra Nevada, California.

机译：大陆弧下方深层岩石圈的起源和演化：来自加利福尼亚内华达山脉下部地壳和地幔异岩的约束。

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摘要

Lower crustal and upper mantle xenoliths from the Sierra Nevada continental arc in California, USA reveal a complex P-T-X-t (pressure-temperature-composition-time) evolution of the deep lithosphere. Metasedimentary xenoliths, despite high quartz contents, preserve granulite-facies equilibration conditions, necessitating transport from the surface into the lower crust. U-Pb and Hf isotope data on detrital zircon in the metasediments support continental underthrusting coeval with the peak of arc magmatism. Mantle xenoliths, represented by spinel and garnet-bearing spinel peridotites, indicate that shallow (spinel-facies), high-degree melt residues underwent thickening, cooling, and metamorphism into refertilized garnet peridotites that equilibrated below 800 °C and ca. 3 GPa. The source of refertilizing melts appears to be the mantle wedge itself, rather than the subducting slab based on mass-balance models and oxygen isotopes. Textural disequilibria, particularly Al-depletion haloes between orthopyroxene and exsolved garnet in peridotites, are diagnostic features related to cooling and increasing pressure. Diffusion modeling indicate that such disequilibria formed within 6 to 8 Ma. Coupled Lu-Hf and Sm-Nd age data on garnet pyroxenites show a significant lag between closure of the two chronometers in a lower crustal pyroxenite, but negligible difference in the deepest websterites. As a whole, the Sierran xenolith data provide insights into the origin and evolution of a mature continental arc, particularly highlighting the importance of thickening in both the crust and mantle lithosphere.
机译：来自美国内华达山脉内陆弧线的下地壳和上地幔异岩显示了深岩石圈复杂的P-T-X-t（压力-温度-合成时间）演化。尽管沉积物中的石英岩含量很高，但它们仍保留了粒岩相的平衡条件，因此必须将其从地表运输到下地壳。变质沉积物中碎屑锆石的U-Pb和Hf同位素数据支持了大陆弧下冲断带，并具有弧岩浆作用峰值。以尖晶石和含石榴石的尖晶石橄榄岩为代表的地幔异岩表明，浅（尖晶石相），高度熔体残留物经历了增稠，冷却和变质作用，转变为在800°C和ca以下平衡的精制石榴石橄榄岩。 3 GPa。溶化熔体的来源似乎是地幔楔本身，而不是基于质量平衡模型和氧同位素的俯冲板。质地不平衡，尤其是橄榄岩中邻苯二茂和溶解石榴石之间的Al贫化晕圈是与冷却和压力增加相关的诊断特征。扩散模型表明这种不平衡在6至8 Ma内形成。石榴石辉石上的Lu-Hf和Sm-Nd年龄数据耦合显示，在较低的地壳辉石岩中，两个天文钟的闭合之间存在显着的滞后性，但最深的辉石岩中的差异可忽略不计。总体而言，Sierran异岩体数据提供了对成熟大陆弧的起源和演化的见解，尤其突出了在地壳和地幔岩石圈中增厚的重要性。

著录项

  • 作者

    Chin, Emily Joyce.;

  • 作者单位

    Rice University.;

  • 授予单位 Rice University.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 288 p.
  • 总页数 288
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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