The Dixie Valley fault bounds the east side of the Stillwater Range in west‐central Nevada and last ruptured in 1954. Offset basalts indicate that slip began more recently than ~14 Ma, and prior work has interpreted the southern segment as an active low‐angle normal fault. Oligocene igneous rocks in the southern Stillwater Range were steeply tilted during large‐magnitude extension prior to ~14 Ma. To refine the timing of early extension and the onset of slip on the Dixie Valley fault, we collected two transects of samples for apatite fission track, apatite and zircon (U‐Th)/He (AHe and ZHe), and apatite ⁴He/³He thermochronometry. Apatite fission track ages from the Oligocene IXL pluton indicate rapid cooling ~18–14 Ma, and AHe and ZHe ages from the Cretaceous La Plata Canyon pluton indicate rapid cooling ~16–19 Ma. We interpret these data to record cooling during rapid extension. AHe ages from the IXL pluton are ~6–8 Ma and record cooling during slip on the Dixie Valley fault. We modeled these ages and ⁴He/³He spectra from one sample as the result of cooling during exhumation of a tilted fault block at a constant extension rate. The model predicts slip on the Dixie Valley fault beginning ~8 Ma. Although it does not constrain the initial fault dip, the model illustrates how a low‐angle fault requires a higher extension rate to reproduce cooling ages. Consequently, we prefer a high‐angle southern Dixie Valley fault for strain compatibility with the high‐angle northern segment.

中文翻译：

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内华达州南部斯蒂尔沃特山脉和迪克西山谷新生代扩张的时间

迪克西谷断裂带在内华达州中西部的斯蒂尔沃特山脉的东侧，最后一次破裂是在1954年。偏移的玄武岩表明，滑移的发生始于约14 Ma以上，并且先前的工作已将南部段解释为活跃的低角度正常故障。斯蒂尔沃特山脉南部的渐新世火成岩在〜14 Ma之前的大幅度扩展过程中急剧倾斜。为了完善Dixie Valley断层的早期伸展时间和滑动开始，我们收集了两个样带，分别用于磷灰石裂变径迹，磷灰石和锆石（U‐Th）/ He（AHe和ZHe）和磷灰石⁴ He / ³他的测温仪。渐新世IXL岩体的磷灰石裂变径迹年龄表明快速冷却〜18-14 Ma，白垩纪拉普拉塔峡谷岩体的AHe和ZHe年龄表明迅速冷却〜16-19 Ma。我们解释这些数据以记录快速扩展过程中的冷却情况。IXL岩体的AHe年龄约为6-8 Ma，并在Dixie Valley断层滑移期间记录了冷却。我们模拟了这些年龄和⁴ He / ³由于以恒定的扩展速率挖掘倾斜的断层块期间的冷却结果，他从一个样品中得到光谱。该模型预测从约8 Ma开始在迪克西河谷断层上的滑动。尽管该模型不限制初始断层倾角，但该模型说明了低角度断层如何要求更高的扩展速率才能再现冷却年龄。因此，我们更喜欢大角度的南部迪克西河谷断层，因为它与大角度的北部段具有应变相容性。