Linking hematite (U-Th)/He dating with the microtextural record of seismicity in the Wasatch fault damage zone, Utah, USA
Linking hematite (U-Th)/He dating with the microtextural record of seismicity in the Wasatch fault damage zone, Utah, USA
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将赤铁矿 (U-Th)/He 定年与美国犹他州瓦萨奇断层破坏带的地震活动微观结构记录联系起来
作者：
A. Ault;P. Reiners;James P. Evans;S. Thomson
直接测定断层滑动年代的技术很少，限制了解释地震活动岩石记录的能力。赤铁矿通常存在于断层带中，可进行（U-Th）/He测年，并且滑动面赤铁矿可通过剪切加热事件和/或重结晶而复位。犹他州（美国）瓦萨奇断层下盘破坏带的有光泽的赤铁矿覆盖的断层表面，显示出赤铁矿碎裂的证据，并保存上新世赤铁矿（U-Th）/He测年。寄主片麻岩的磷灰石（U-Th）/He和裂变径迹数据表明，下盘去顶约1.2 km。4.5 MA.内部可再生的，但不同的赤铁矿（U-Th）/He日期4.5马和年轻的孤立位置上一个单一的故障表面不反映环境冷却。我们假设，这些日期，以及相关的彩虹色和退火晶体纹理，文件快速冷却摩擦产生的热量在小地震滑动事件之间的约。4.5 2.5Ma。因此，赤铁矿（U-Th）/He测年提供了潜在的破译与滑动10 5 - 10 6年的时间尺度上的岩石记录中的热异常。
Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity. Hematite is commonly found in fault zones, amenable to (U-Th)/He dating, and slip surface hematite may be reset by shear heating events and/or recrystallization. Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. Apatite (U-Th)/He and fission track data from the host gneiss indicate footwall unroofing through ∼2 km by ca. 4.5 Ma. Internally reproducible but disparate hematite (U-Th)/He dates 4.5 Ma and younger from isolated locations on a single fault surface do not reflect ambient cooling. We hypothesize that these dates, and associated iridescence and annealed crystal texture, document rapid cooling from friction-generated heat during small seismic slip events between ca. 4.5 and 2.5 Ma. Thus, hematite (U-Th)/He dating offers the potential to decipher thermal anomalies in the rock record associated with slip on 10 5 –10 6 yr time scales.