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Quartz Vein Geochemistry Records Deformation Processes in Convergent Zones
Geochemistry, Geophysics, Geosystems ( IF 3.275 ) Pub Date : 2021-03-05 , DOI: 10.1029/2020gc009201
Hugues Raimbourg, Kristijan Rajič, Benjamin Moris‐Muttoni, Vincent Famin, Giulia Palazzin, Donald Fisher, Kristin Morell, Saskia Erdmann, Ida Di Carlo, Clément Montmartin

In several examples of subduction zones, we compared pairs of quartz veins formed either at the lower temperatures of the seismogenic zone (260°C or below), or at the higher temperatures of its downdip limit (∼330°C). All the veins analyzed here are mode I cracks that formed contemporaneously with the host‐rock main stage of deformation at peak burial conditions. Lower‐temperature veins show examples of quartz crystals with euhedral shapes and growth rims, while higher‐temperature veins contain crack‐seal microstructures. In the lower‐temperature realm, quartz growth rims have alternatingly either: (1) high cathodoluminescence (CL), CL‐blue color and high concentration in trace elements and fluid inclusions, or (2) low luminescence, CL‐brown color and low concentration in trace elements and fluid inclusions. In contrast, the quartz from higher‐temperature samples is homogeneously low luminescent and CL‐brown, except for very restricted domains of the crack‐seal microstructures where patches of CL‐blue quartz are present. The highly luminescent quartz contains high concentrations of aluminum and lithium, up to 3,000 and 400 ppm, respectively. Variations in Al and Li correlate well, so that Li appears as the main charge‐compensating cation for Al. We propose that the incorporation of Al and Li reflects the amplitude of the fluid pressure variations, which control crystal growth rates. Quartz geochemistry might therefore unravel the contrast between the seismogenic zone, where large fluid pressure variations are present, and its downdip limit, where fluid pressure variations are much more limited in amplitude.

中文翻译:

石英脉地球化学记录收敛带的变形过程

在几个俯冲带的例子中,我们比较了在地震成因带的较低温度(260°C或更低)或其下倾极限的较高温度(〜330°C)下形成的成对石英脉。此处分析的所有静脉均为I型裂缝,与峰值埋藏条件下的变形主岩体主要阶段同时形成。较低温度的矿脉显示的是具有共面体形状和生长边缘的石英晶体,而较高温度的矿脉则包含裂缝-密封的微观结构。在低温领域,石英生长轮缘交替出现:(1)高阴极发光(CL),CL蓝色和痕量元素和流体包裹体中的高浓度,或者(2)低发光,CL褐色和低发光微量元素和流体包裹体中的浓度。相比之下,来自高温样品的石英具有均一的低发光度和CL褐色,除了在裂纹密封微结构中存在CL蓝色石英斑片的非常有限的区域外。高发光石英包含高浓度的铝和锂,分别高达3,000和400 ppm。Al和Li的变化具有很好的相关性,因此Li似乎是Al的主要电荷补偿阳离子。我们建议铝和锂的结合反映了流体压力变化的幅度,从而控制了晶体的生长速率。因此,石英地球化学可能会揭开存在较大流体压力变化的地震发生带与其下倾极限(流体压力变化幅度受到更大限制)之间的对比度。
更新日期:2021-04-08
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