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首页> 外文学位 >Melange a trois: Metamorphic controls on recycling and mass transfer within subduction zones.
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Melange a trois: Metamorphic controls on recycling and mass transfer within subduction zones.

机译：混合物：在俯冲区内再循环和传质的变质控制。

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摘要

This dissertation comprises three studies that provide new constraints and theories for our understanding of mass-transfer within subduction zones. Within Chapter 1, we examine the geochemical zoning of metamorphic garnets produced by prograde metamorphism of Tethyan MORB within the western Italian Alps. Metamorphism peaked within the coesite-eclogite facies, and we use these garnets to investigate the record of mineral reactions occurring during subduction. We find that anomalous patterns of growth zoning in garnets are consistent with the decomposition of coexisting titanite + clinozoisite, a dehydration reaction that is a likely candidate to mobilize key tracers from the metamorphic system to volcanic arcs. Using existing and new geothermobarometric constraints, we are able to reconstruct the apparent depth-interval of this reaction during metamorphism; this new approach to the metamorphic record preserved in eclogites allows for a more complete view of point-to-point mass transfer occurring within the subduction system. Chapters 2 and 3 are a pair of studies bearing upon the geochemical evolution of the melange matrix of the Catalina Schist, California. Melange matrix formed through the synergistic effects of deformation and metasomatism to produce hybridized rock types from sediment, basalt, and peridotite protoliths. Elemental systematics are largely dominated by mechanical mixing; however, numerous elements are highly controlled by the stability relationships of key host minerals buffered by the evolving bulk composition of melange zones. Sr-Nd isotope systematics appear to be dominated by mechanical mixing trajectories. In contrast to these systems recording mechanical mixing, Pb and B isotope ratios do not preserve mechanical mixing arrays, despite elemental systematics consistent with mixing. B isotope ratios are consistent with existing models for fluid flow in the complex, where lower-grade melange is an appropriate source for fluids, while higher-grade samples preserve the signature of evolved fluids progressing towards the mantle wedge. Pb isotope ratios are largely indistinguishable as a function of metamorphism and are more radiogenic than all constrained compositions input to the Catalina subduction zone, suggesting fractionation of the U-Th-Pb system during metamorphism due to mineral reactions.
机译：本论文包括三项研究，为我们对俯冲带内传质的理解提供了新的约束和理论。在第1章中，我们研究了意大利西部阿尔卑斯山特提斯MORB的超前变质作用所产生的变质石榴石的地球化学分区。在变质岩-榴辉岩相中，变质作用达到顶峰，我们用这些石榴石研究俯冲过程中发生的矿物反应的记录。我们发现，石榴石中生长分区的异常模式与共存的钛铁矿+斜长石分解是一致的，脱水反应可能是将主要示踪物从变质系统转移到火山弧的一种可能的候选方法。使用现有的和新的地热大气法约束，我们能够在变质过程中重建该反应的表观深度区间。这种保存在榴辉岩中的变质记录的新方法可以更完整地了解俯冲系统内发生的点对点传质。第2章和第3章是对加利福尼亚Catalina Schist混杂岩基质的地球化学演化的一对研究。通过变形和交代作用的协同作用形成的混杂基质，从沉积物，玄武岩和橄榄岩原石中产生混杂的岩石类型。元素系统主要由机械混合控制。然而，许多元素受到关键主体矿物稳定性关系的高度控制，而主体关系受混杂区不断变化的整体组成缓冲。 Sr-Nd同位素系统学似乎主要由机械混合轨迹控制。与这些记录机械混合的系统相反，尽管元素系统与混合相一致，但Pb和B同位素的比率却不能保留机械混合阵列。 B同位素比与现有的复杂流体模型相吻合，其中低品位的混杂物是合适的流体源，而高品位的样品则保留了向地幔楔发展的演化流体的特征。铅同位素比率在很大程度上不能根据变质作用来区分，并且比所有输入到卡塔利娜俯冲带的受约束成分具有更高的放射成因，这表明由于矿物反应，在变质过程中U-Th-Pb系统的分离。

著录项

  • 作者

    King, Robert L.;

  • 作者单位

    Lehigh University.;

  • 授予单位 Lehigh University.;
  • 学科 Geology.; Mineralogy.; Geochemistry.
  • 学位 Ph.D.
  • 年度 2006
  • 页码 171 p.
  • 总页数 171
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;矿物学;地质学;
  • 关键词

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