Two-phase Neogene extension in the northwestern Basin and Range recorded in a single thermochronology sample
Two-phase Neogene extension in the northwestern Basin and Range recorded in a single thermochronology sample
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单个热年代学样本记录了西北盆地和山脉的两相新近纪伸展
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
P. Reiners
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文献类型：
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作者：
J. Colgan;D. Shuster;P. Reiners
我们使用磷灰石4He/3He、(U-Th)/He和裂变径迹热年代学相结合的方法，通过分析断层下盘华纳山脉的单个样品，确定了加州东北部奇谷断层的滑动年代。该样品为砾岩中的花岗岩碎屑，裂变径迹年龄为11.6±2.8 Ma，(U-Th)/He比值为3.02±0.52 Ma。地质关系表明，该样品在惊喜谷断层滑动期间出土前埋藏在约3.3公里深。裂变径迹年龄和长度数据表明，样品在14 Ma后开始折返之前已经完全重置(>；120°C)。一个等分的9个磷灰石颗粒被逐级加热进行4He/3He分析；对得到的4He分布的模拟表明，从80°C到~20°C的冷却发生在3-1 Ma之间。组合的4He/3He、(U-Th)/He和裂变径迹数据的一致时间-温度(t-T)解需要两个不同的冷却时期，这与惊喜谷断层上的非连续滑动一致。早期的冷却和断层滑动发生在14~8 Ma之间，之后是约3 Ma的较新的断层滑动。这一时间安排既符合当地的地质关系，也符合盆地和山脉省西缘断裂的区域时间安排。这些数据显示了联合裂变径迹、(U-Th)/He和4He/3He热计时数据从靠近地球9S表面的单个样品中提取低温t-T信息的分辨率。
We use a combination of apatite 4 He/ 3 He, (U-Th)/He, and fission-track thermochronology to date slip on the Surprise Valley fault in northeastern California by analyzing a single sample from the Warner Range in the footwall of the fault. This sample, a granitic clast from a conglomerate, yielded a fission-track age of 11.6 ± 2.8 Ma and a (U-Th)/He age of 3.02 ± 0.52 Ma. Geologic relationships indicate that this sample was buried to a depth of ~3.3 km prior to exhumation during slip on the Surprise Valley fault. Fission-track age and length data indicate that the sample was fully reset (>120 °C) prior to exhumation, which began sometime after 14 Ma. A single aliquot of nine apatite grains was step-heated for 4 He/ 3 He analysis; modeling of the resulting 4 He distribution indicates that cooling from >80 °C to ~20 °C occurred between 3 and 1 Ma. Interconsistent time-temperature ( t-T ) solutions to the combined 4 He/ 3 He, (U-Th)/He, and fission-track data require two distinct periods of cooling, consistent with non-continuous slip on the Surprise Valley fault. Early cooling and fault slip took place between 14 and 8 Ma, followed by more recent fault slip ca. 3 Ma. This timing is consistent with both local geologic relationships and with the regional timing of faulting along the western margin of the Basin and Range Province. These data demonstrate the resolving power of combined fission-track, (U-Th)/He, and 4 He/ 3 He thermochronometric data to extract low-temperature t-T information from a single sample close to Earth9s surface.