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蚀变俯冲板块和上覆地幔中的稳定和不稳定剪切
作者:小柯机器人 发布时间:2023/5/18 10:34:37


美国得州农工大学Prakash, Abhishek及其课题组报道了碳酸盐岩和中深度地震活动,蚀变俯冲板块和上覆地幔中的稳定和不稳定剪切。这一研究成果发表在2023年5月15日出版的国际学术期刊《美国科学院院刊》上。

课题组人员称,基于蚀变板的蛇纹石化脱水和脆化或窄细粒橄榄岩剪切带中的粘性剪切不稳定性,碳酸盐岩透镜体中的热剪切不稳定性增加了中等深度地震活动的潜在机制。俯冲板块和上覆地幔楔中的橄榄岩可能会与来自海水或地幔深处的含CO2流体发生反应,形成碳酸盐矿物和含水硅酸盐。镁碳酸的有效粘度高于蛇纹石的有效粘度,并且明显低于H2O和橄榄石的有效粘度。

然而,在俯冲带的温度和压力下,镁碳酸盐可能比含水硅酸盐延伸到更深的地幔。蚀变下降,地幔橄榄岩中的应变率可能局限于板块脱水后的碳酸盐岩层中。基于实验确定的蠕变定律,与地震断层面的地震速度相当,一个简单的碳酸盐地层剪切加热和热敏蠕变模型预测了应变率高达10/s的稳定和不稳定剪切应变条件。这种机制,超过了俯冲带蛇纹石的稳定性,提供了一种通过脱水脆化产生地震的替代方法,并应用于汤加俯冲带和日本东北的双重瓦达蒂-贝尼奥夫地震带的中等深度的地震中。

据悉,基于剪切定位、剪切加热和在一个改变下降的海洋板块上覆地幔楔中的薄层碳酸盐岩层内的失控蠕变,课题组人员评估了一个俯冲带中等深度地震的模型。

附:英文原文

Title: Carbonates and intermediate-depth seismicity: Stable and unstable shear in altered subducting plates and overlying mantle

Author: Prakash, Abhishek, Holyoke, Caleb W., Kelemen, Peter B., Kirby, Stephen H., Kronenberg, Andreas K., Lamb, William M.

Issue&Volume: 2023-5-15

Abstract: A model for intermediate-depth earthquakes of subduction zones is evaluated based on shear localization, shear heating, and runaway creep within thin carbonate layers in an altered downgoing oceanic plate and the overlying mantle wedge. Thermal shear instabilities in carbonate lenses add to potential mechanisms for intermediate-depth seismicity, which are based on serpentine dehydration and embrittlement of altered slabs or viscous shear instabilities in narrow fine-grained olivine shear zones. Peridotites in subducting plates and the overlying mantle wedge may be altered by reactions with CO2-bearing fluids sourced from seawater or the deep mantle, to form carbonate minerals, in addition to hydrous silicates. Effective viscosities of magnesian carbonates are higher than those for antigorite serpentine and they are markedly lower than those for H2O-saturated olivine. However, magnesian carbonates may extend to greater mantle depths than hydrous silicates at temperatures and pressures of subduction zones. Strain rates within altered downgoing mantle peridotites may be localized within carbonated layers following slab dehydration. A simple model of shear heating and temperature-sensitive creep of carbonate horizons, based on experimentally determined creep laws, predicts conditions of stable and unstable shear with strain rates up to 10/s, comparable to seismic velocities of frictional fault surfaces. Applied to intermediate-depth earthquakes of the Tonga subduction zone and the double Wadati–Benioff zone of NE Japan, this mechanism provides an alternative to the generation of earthquakes by dehydration embrittlement, beyond the stability of antigorite serpentine in subduction zones.

DOI: 10.1073/pnas.2219076120

Source: https://www.pnas.org/doi/10.1073/pnas.2219076120

期刊信息
PNAS:《美国科学院院刊》,创刊于1914年。隶属于美国科学院,最新IF:12.779
官方网址:https://www.pnas.org