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首頁> 外文學(xué)位 >Kinetics of partial melting and melt-rock reaction in the Earth's mantle.
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Kinetics of partial melting and melt-rock reaction in the Earth's mantle.

機(jī)譯：地球地幔中部分熔融和熔融巖石反應(yīng)的動力學(xué)。

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Partial melting of the mantle occurs predominantly in the spinel lherzolite stability field, where pyroxenes are consumed to produce olivine and basaltic melt. The phase equilibria of this reaction are relatively well understood but the grain-scale processes through which pyroxenes undergo partial melting are not. With a combination of kinetic experiments and numerical modeling, I demonstrated that during partial melting of lherzolites of varying bulk compositions, lherzolites do not simply melt at equilibrium but go through a series of kinetic process that involve primarily dissolution and reprecipitation. The most important feature of these grain-scale processes is the reduction in equilibration times between melt and minerals by several orders of magnitude, suggesting that melting in the mantle might take place closer to equilibrium conditions than currently believed. These results are presented in Chapters 1, 2, and 4.;In Chapter 3, I explored the nature of the interface between peridotites and pyroxenites in the mantle to understand the mechanisms controlling the style and extent of chemical interaction between these two lithologies. The motivation behind this study is to determine the scale and evolution of heterogeneities in the Earth's mantle and to determine their role in basalt petrogenesis. My dissolution experiments demonstrated the existence of two melt-rock reaction regimes depending on whether the lherzolite is subsolidus or partially molten. At subsolidus conditions, dissolution is extremely slow and equilibration between the pyroxenite-derived melt and peridotite is unlikely. When the lherzolite is partially molten, the dissolution mechanism changes from simple dissolution to reactive dissolution (involving diffusive mixing, dissolution, and reprecipitation of several phases) and resulting in significant increase in equilibration and dissolution rates. Using these experiments I was able to derive kinetic parameters that I subsequently introduced into a reactive porous flow model where I explored the fractionation of incompatible trace elements during melt transport. The results of this simulation suggest that if enriched signals in ocean-floor basalt originate from pyroxenite-derived melts, then the melt migration rate through the uppermost mantle must be very fast (on the order of mm to cm/sec).
機(jī)譯：地幔的部分熔融主要發(fā)生在尖晶石鋰沸石穩(wěn)定場中，在那里輝石被消耗以產(chǎn)生橄欖石和玄武質(zhì)熔體。該反應(yīng)的相平衡是相對充分理解的，但是輝石經(jīng)歷部分熔融的晶粒度過程卻不是。通過動力學(xué)實(shí)驗(yàn)和數(shù)值模型的結(jié)合，我證明了在不同體積組成的鋰鐵礦的部分熔融過程中，鋰鐵礦不僅會在平衡狀態(tài)下簡單熔融，還會經(jīng)歷一系列主要涉及溶解和再沉淀的動力學(xué)過程。這些晶粒度過程的最重要特征是熔體和礦物之間的平衡時(shí)間縮短了幾個(gè)數(shù)量級，這表明地幔中的熔融可能比目前認(rèn)為的更接近平衡條件。這些結(jié)果將在第1章，第2章和第4章中介紹。在第3章中，我探索了地幔中橄欖巖和輝石巖之間的界面性質(zhì)，以了解控制這兩種巖性之間化學(xué)相互作用的方式和程度的機(jī)制。這項(xiàng)研究背后的動機(jī)是確定地球地幔中非均質(zhì)性的規(guī)模和演化，并確定它們在玄武巖成巖作用中的作用。我的溶出實(shí)驗(yàn)證明了兩種熔融巖石反應(yīng)機(jī)制的存在，這取決于鋰鐵礦是亞固相的還是部分熔融的。在低于固相線的條件下，溶解非常緩慢，并且源自輝石的熔體和橄欖巖之間的平衡不大可能。當(dāng)鋰鐵礦部分熔融時(shí)，溶解機(jī)理從簡單溶解變?yōu)榉磻?yīng)性溶解（涉及擴(kuò)散混合，溶解和幾個(gè)階段的再沉淀），從而導(dǎo)致平衡和溶解速率顯著提高。使用這些實(shí)驗(yàn)，我能夠得出動力學(xué)參數(shù)，隨后將其引入反應(yīng)性多孔流模型中，在該模型中，我探索了熔體運(yùn)輸過程中不相容的痕量元素的分離。該模擬結(jié)果表明，如果海底玄武巖中的富集信號來自輝石巖衍生的熔體，那么穿過最上地幔的熔體遷移速率必須非?？欤ê撩字晾迕?秒的量級）。

著錄項(xiàng)

  • 作者

    Cascio, Mauro Lo.;

  • 作者單位

    Brown University.;

  • 授予單位 Brown University.;
  • 學(xué)科 Mineralogy.;Geochemistry.
  • 學(xué)位 Ph.D.
  • 年度 2008
  • 頁碼 289 p.
  • 總頁數(shù) 289
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類 礦物學(xué);地質(zhì)學(xué);
  • 關(guān)鍵詞

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