Geophysical‐Geochemical Modeling of Deep Crustal Compositions: Examples of Continental Crust in Typical Tectonic Settings and North China Craton
Geophysical‐Geochemical Modeling of Deep Crustal Compositions: Examples of Continental Crust in Typical Tectonic Settings and North China Craton
复制标题
DOI：
10.1029/2022jb025536
复制
发表时间：
2023-05
期刊：
影响因子：
--
通讯作者：
D. Cui;Jing‐Liang Guo;William J. Shinevar;Liang Guo;Wangchun Xu;Hongfei Zhang;Zhenyi Jin
中科院分区：
文献类型：
--
作者：
D. Cui;Jing‐Liang Guo;William J. Shinevar;Liang Guo;Wangchun Xu;Hongfei Zhang;Zhenyi Jin
深部陆壳的化学成分是了解陆壳形成和演化的关键。然而，限制现今深部大陆地壳的化学成分受到间接可达性的限制。本文提出了一种从观测到的地壳地震结构中约束地壳深部化学结构的模拟方法。我们编制了一套已发表的大陆地壳成分模型，以构建地震波速度与地壳中主要氧化物含量之间的函数关系。相平衡和压缩波速度（VP）的每一个组成模型的深度和温度范围内的地壳深部计算。在α-石英稳定性场范围内的条件下，获得了VP和地壳主要氧化物含量之间的稳健函数关系。根据这些关系，可以将地壳深部VP的观测值反演为给定地温地区的化学成分。我们为这个过程提供了一个MATLAB代码（CalcCrustComp）。应用该方法对全球典型构造背景下的地壳深部VP和华北板块（NCC）进行了成分约束。我们的模拟结果表明，俯冲相关和裂谷相关的构造环境中的下地壳可能比平台/盾牌和造山带更镁铁质。NCC地壳深部的低VP特征可以用中间地壳成分、较高的含水量和/或较高的温度来解释。该方法获得的化学结构可作为进一步识别地壳深部特征的参考模型。
The chemical composition of the deep continental crust is key to understanding the formation and evolution of the continental crust. Constraining the chemical composition of present‐day deep continental crust is, however, limited by indirect accessibility. This paper presents a modeling method for constraining deep crustal chemical structures from observed crustal seismic structures. We compiled a set of published composition models for the continental crust to construct functional relationships between seismic wave speed and major oxide content in the crust. Phase equilibria and compressional wave speeds (VP) for each composition model were calculated over a range of depths and temperatures of the deep crust. For conditions within the alpha(α)‐quartz stability field, robust functional relationships were obtained between VP and major oxide contents of the crust. Based on these relationships, observed VP of the deep crust can be inverted to chemical compositions for regions with given geotherms. We provide a MATLAB code for this process (CalcCrustComp). We apply this method to constrain compositions from deep crustal VP of global typical tectonic settings and the North China Craton (NCC). Our modeling results suggest that the lower crust in subduction‐related and rifting‐related tectonic settings may be more mafic than platforms/shields and orogens. The low VP signature in the deep crust of the NCC can be explained by intermediate crustal compositions, higher water contents, and/or higher temperatures. The chemical structure obtained by this method can serve as a reference model to further identify deep crustal features.