Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA
Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA
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DOI：
10.1016/j.epsl.2017.04.020
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发表时间：
2017-08
影响因子：
5.3
通讯作者：
R. McDermott;A. Ault;James P. Evans;P. Reiners
中科院分区：
文献类型：
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作者：
R. McDermott;A. Ault;James P. Evans;P. Reiners
出土的断层记录了地震产生的温度。我们表明，瞬态升高的断层表面温度保存在岩石记录是可量化的，通过微观结构分析，断层岩石热年代学，和热力学建模。我们将这种方法应用于网络的镜像，小，赤铁矿涂层的断层表面的挖掘，孕震Wasatch断层带，UT，美国。多面体和叶状的赤铁矿晶体形态，加上赤铁矿（U-Th）/他的数据模式，从这些表面和主机岩石磷灰石（U-Th）/他的数据，最好的解释摩擦产生的热量在滑动界面几何粗糙。这些观测结果通知热机械模拟的摩擦接触处的闪热和由此产生的分数他损失超过生成的断层表面的时间-温度的历史。根据粗糙体的大小，> 1000 -1200° C的温度足以导致断层表面200 μm范围内的赤铁矿损失85-100%的He。空间隔离，高温显微织构意味着空间可变的热生成和衰变。我们的研究结果表明，粗糙体的闪热和相关的摩擦减弱可能会促进Wasatch赤铁矿断层镜上的小地震（Mw =-3至3）。我们认为，类似的热过程和由此产生的动力减弱可能会促进更大的地震。
Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U–Th)/He data patterns from these surfaces and host rock apatite (U–Th)/He data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time–temperature histories. Temperatures of>∼ 700–1200° C, depending on asperity size, are sufficient to induce 85–100% He loss from hematite within 200 μm of the fault surface. Spatially-isolated, high-temperature microtextures imply spatially-variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (M w≈− 3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes.