Metamorphic reaction rates at ∼650–800 °C from diffusion of niobium in rutile
Metamorphic reaction rates at ∼650–800 °C from diffusion of niobium in rutile
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DOI：
10.1016/j.gca.2013.12.015
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发表时间：
2014-04
影响因子：
5
通讯作者：
A. Cruz‐Uribe;M. Feineman;T. Zack;M. Barth
中科院分区：
文献类型：
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作者：
A. Cruz‐Uribe;M. Feineman;T. Zack;M. Barth
量化变质反应发生速率的能力对于评估在各种动态环境中实现和保持平衡的程度至关重要。在这里，我们研究了金红石置换过程中的角闪岩相叠印的榴辉岩，石榴角闪岩和斜长岩从卡塔利纳岛，加利福尼亚州，挪威的特罗姆瑟推覆体，中国的北柴达木盆地，和墨西哥的Guichicovi复杂。通过激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）测定，微量元素浓度分布在金红石镶边的钛铁矿，揭示了铌分区的金红石，我们解释为从金红石-钛铁矿边界的铌反扩散的结果。我们提出了新的基于场的反应速率，从晶界速度计算，这反过来又是使用一维扩散模型计算的铌反扩散到金红石在670-770 °C的温度范围内的钛置换。我们的数据是一致的，或略快于以前的区域变质作用的基于字段的反应速率的估计，并扩展了温度和成分范围，区域变质反应速率已知。
The ability to quantify the rates at which metamorphic reactions occur is critical to assessing the extent to which equilibrium is achieved and maintained in a variety of dynamic settings. Here we investigate the kinetics of rutile replacement by titanite during amphibolite-facies overprinting of eclogite, garnet amphibolite and anorthosite from Catalina Island, CA, the Tromsø Nappe, Norway, the North Qaidam terrane, China, and the Guichicovi Complex, Mexico. Trace element concentration profiles across rutile rimmed by titanite, as determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), reveal Nb zoning in rutile that we interpret as the result of Nb back-diffusion from the rutile–titanite boundary. We present new field-based reaction rates calculated from grain boundary velocities, which in turn were calculated using a 1-D diffusion model for Nb back-diffusion into rutile during titanite replacement over the temperature range 670–770 °C. Our data are consistent with or slightly faster than previous estimates of field-based reaction rates for regional metamorphism, and extend the temperature and compositional range over which regional metamorphic reaction rates are known.