Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas
Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas
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DOI：
10.1016/j.epsl.2015.06.001
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发表时间：
2015-09
影响因子：
5.3
通讯作者：
O. Karakas;J. Dufek
中科院分区：
文献类型：
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作者：
O. Karakas;J. Dufek
构造伸展作用和岩浆作用常常协同作用，改变地壳的热、力学和化学结构。量化的影响，在地壳中的熔融关系的伸展和岩浆流量是根本的，以确定地壳熔融速率与分馏，岩浆停留时间，和大陆地壳在裂谷环境中的增长。为了了解地壳热演化的构造伸展和岩浆侵位的耦合控制，我们开发了一个数值模型，占在不同的伸展环境和热岩相过程。我们表明，岩浆流量施加的主要控制熔体的产生和构造伸展放大的熔体居住在地壳柱的体积。侵入伸展的地壳产生混合岩浆，其组成为：1）玄武岩部分结晶后残留的熔体（幔源熔体）和2）地壳部分熔融的熔体（地壳熔体）。在伸展地壳中，幔源熔体比地壳熔体更普遍，在一系列的岩浆流量，构造伸展速率，和岩浆水含量。在大多数情况下，地壳温度不会达到其固相线温度，以启动这些火成岩岩性的部分熔融。能量平衡计算表明，岩脉输送的总焓主要用于增加周围冷地壳的感热，对地壳熔化潜热贡献很小（最大地壳熔化效率为6%）。在下地壳，大部分条件下都形成了一个大面积的泥质区。上地壳结晶糊状物是由地质上合理的流量和时间尺度为10 - 6年的扩展速率的岩浆连续侵位产生的。增加构造效应和非线性熔体分数关系表明，维持上地壳部分熔融区域所需的岩浆通量在许多裂谷区域的岩浆通量估计范围内（10 - 4至10 - 3 km 3/年），至少比以前的模拟估计低一个数量级。我们的研究结果表明，构造的重要性，在增强熔体生产，成分和地壳演化活跃的岩浆系统。
Tectonic extension and magmatism often act in concert to modify the thermal, mechanical, and chemical structure of the crust. Quantifying the effects of extension and magma flux on melting relationships in the crust is fundamental to determining the rate of crustal melting versus fractionation, magma residence time, and the growth of continental crust in rift environments. In order to understand the coupled control of tectonic extension and magma emplacement on crustal thermal evolution, we develop a numerical model that accounts for extension and thermal-petrographic processes in diverse extensional settings. We show that magma flux exerts the primary control on melt generation and tectonic extension amplifies the volume of melt residing in the crustal column. Diking into an extending crust produces hybrid magmas composed of 1) residual melt remaining after partial crystallization of basalt (mantle-derived melt) and 2) melt from partial melting of the crust (crustal melt). In an extending crust, mantle-derived melts are more prevalent than crustal melts across a range of magma fluxes, tectonic extension rates, and magmatic water contents. In most of the conditions, crustal temperatures do not reach their solidus temperatures to initiate partial melting of these igneous lithologies. Energy balance calculations show that the total enthalpy transported by dikes is primarily used for increasing the sensible heat of the cold surrounding crust with little energy contributing to latent heat of melting the crust (maximum crustal melting efficiency is 6%). In the lower crust, an extensive mush region develops for most of the conditions. Upper crustal crystalline mush is produced by continuous emplacement of magma with geologically reasonable flux and extension rates on timescales of 10 6 yr. Addition of tectonic effects and non-linear melt fraction relationships demonstrates that the magma flux required to sustain partially molten regions in the upper crust is within the range of estimates of magmatic flux in many rifting regions (∼ 10− 4 to 10− 3 km 3/yr) and at least an order of magnitude lower than previous modeling estimates. Our results demonstrate the importance of tectonics in augmenting melt production, composition, and crustal evolution in active magmatic systems.