High Stress Deformation and Short-Term Thermal Pulse Preserved in Pyroxene Microstructures From Exhumed Lower Crustal Seismogenic Faults (Lofoten, Norway)
High Stress Deformation and Short-Term Thermal Pulse Preserved in Pyroxene Microstructures From Exhumed Lower Crustal Seismogenic Faults (Lofoten, Norway)
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DOI：
10.1029/2021jb023616
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发表时间：
2022-07-01
影响因子：
3.9
通讯作者：
Menegon, L.
中科院分区：
文献类型：
--
作者：
Campbell, L. R.;Menegon, L.
除非存在高孔隙流体压力，否则在强无水下陆壳中发生地震破裂需要高的脆性破坏应力。提出的几种机制在深度产生高应力意味着瞬态加载驱动的应力变化的频谱，范围从高度局部化的应力放大到地壳规模的应力转移。现场和模拟研究提出了高达GPa量级的高瞬态应力，但由于同震损伤和滑动的叠加，从地质记录中往往难以提取瞬态破裂前载荷的证据。然而，局部保存的变形微观结构，指示晶体塑性和脆性变形与地震周期在下地壳提供了机会，以限制变形的进展之前，期间和之后的破裂，包括应力和温度的演变。在这里，辉石显微结构的详细研究表征了短期演化的高应力变形和温度变化经历了前和期间的下地壳地震破裂。辉石是从挪威北方罗弗敦的剥露麻粒岩相地层中记录的下地壳地震的含假玄武玻璃断层和破坏带中取样的。渐进序列的微观结构表明本地化的高应力（在GPa水平）预破裂负荷容纳低温塑性，随后由同震粉碎式破碎和随后的晶粒生长触发的短期热脉冲与摩擦滑动。因此，高达GPa级的瞬时高应力（包括差应力和剪切应力）导致干燥下地壳中的地震成核可以在自然界中发生，并保存在断层岩石微结构中。
Earthquake rupture in strong, anhydrous lower continental crust requires high brittle failure stresses unless high pore fluid pressures are present. Several mechanisms proposed to generate high stresses at depth imply transient loading driven by a spectrum of stress changes, ranging from highly localized stress amplifications to crustal-scale stress transfers. High transient stresses up to GPa magnitude are proposed by field and modeling studies, but the evidence for transient prerupture loading is often difficult to extract from the geological record due to overprinting by coseismic damage and slip. However, the local preservation of deformation microstructures indicative of crystal-plastic and brittle deformation associated with the seismic cycle in the lower crust offers the opportunity to constrain the progression of deformation before, during and after rupture, including stress and temperature evolution. Here, detailed study of pyroxene microstructures characterizes the short-term evolution of high-stress deformation and temperature changes experienced before and during lower crustal earthquake rupture. Pyroxenes are sampled from pseudotachylyte-bearing faults and damage zones of lower crustal earthquakes recorded in the exhumed granulite facies terrane of Lofoten, northern Norway. The progressive sequence of microstructures indicates localized high-stress (at the GPa level) prerupture loading accommodated by low-temperature plasticity, followed by coseismic pulverization-style fragmentation and subsequent grain growth triggered by the short-term heat pulse associated with frictional sliding. Thus, up to GPa-level transient high stress (both differential and shear) leading to earthquake nucleation in the dry lower crust can occur in nature, and be preserved in the fault rock microstructure.