Instantaneous healing of micro-fractures during coseismic slip: Evidence from microstructure and Ti in quartz geochemistry within an exhumed pseudotachylyte-bearing fault in tonalite
Instantaneous healing of micro-fractures during coseismic slip: Evidence from microstructure and Ti in quartz geochemistry within an exhumed pseudotachylyte-bearing fault in tonalite
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DOI：
10.1016/j.lithos.2016.03.011
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发表时间：
2016-06-01
期刊：
影响因子：
3.5
通讯作者：
de Wall, Helga
中科院分区：
文献类型：
--
作者：
Bestmann, Michel;Pennacchioni, Giorgio;de Wall, Helga
英云闪长岩Adamello岩体（南阿尔卑斯山）内的折返断层在深度上是地震性的，这一点由伪玄武玻璃体（凝固的摩擦引起的熔体）的存在所表明。在英云闪长岩的冷却过程中，早期形成的节理首先被与石英脉沉积相关的局部韧性剪切带（类似于500摄氏度）利用，后来被含假玄武玻璃的碎裂断层（类似于250-300摄氏度的环境温度）利用。在假玄武玻璃附近，寄主英云闪长岩的石英显示出遍布的薄（1-10 μ m宽）愈合微裂缝和沿沿着微剪切带的超细（1-2 μ m粒度）重结晶聚集体。在阴极发光（CL）下，愈合的微裂缝具有比主体“岩浆”石英更深的灰色阴影，这反映了Ti浓度（[Ti]）的变化，如NanoSIMS测量所示。[Ti]从CL-较轻的基质石英中的35-55 ppm变化到沿沿着CL-较暗的愈合微裂缝的10-13 ppm。这些[Ti]继承的超细重结晶聚集体，叠加在岩浆石英和愈合的微裂缝在高温瞬态有关的摩擦地震滑动。基于石英中的钛温度测量，我们推断微裂缝愈合发生在比断层的环境温度更高的温度（250-300摄氏度，0.2 GPa），其中[Ti]
Exhumed faults within the tonalitic Adamello pluton (Southern Alps) were seismic at depth as indicated by the presence of pseudotachylytes (solidified friction-induced melts). During cooling of tonalite, early-formed joints were first exploited by localized ductile shear zones associated with deposition of quartz veins (at similar to 500 degrees C), and later by pseudotachylyte-bearing cataclastic faults (at similar to 250-300 degrees C ambient temperature). Adjacent to pseudotachylytes, quartz of the host tonalite shows pervasive thin (1-10 mu m wide) healed micro-fractures and ultra-fine (1-2 mu m grain size) recrystallized aggregates along micro-shear zones. Under cathodoluminescence (CL) the healed micro-fractures have a darker gray shade than the host "magmatic" quartz that reflects a change in Ti concentrations ( [Ti]) as indicated by NanoSIMS measurements. [Ti] vary from 35-55 ppm in the CL-lighter host quartz to 10-13 ppm along the CL-darker healed micro-fractures. These [Ti] were inherited by the ultra-fine recrystallized aggregates that overprinted both the magmatic quartz and the healed micro-fractures during the high temperature transient related to frictional seismic slip. Based on Ti-in-quartz thermometry, we infer that micro-fracture healing occurred at higher temperatures than the ambient temperatures of faulting (250-300 degrees C at 0.2 GPa), for which [Ti]