Recent faulting in the southern Arava, Dead Sea Transform: Evidence from single grain luminescence dating
Recent faulting in the southern Arava, Dead Sea Transform: Evidence from single grain luminescence dating
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DOI：
10.1016/j.quaint.2007.08.039
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发表时间：
2009-04
影响因子：
2.2
通讯作者：
N. Porat;G. Duller;R. Amit;E. Zilberman;Y. Enzel
中科院分区：
文献类型：
--
作者：
N. Porat;G. Duller;R. Amit;E. Zilberman;Y. Enzel
构造活动区的崩积物与断层有关，测年对于确定地震时间和评估地震危险性很重要。在极度干旱地区，放射性碳的有机质是稀缺的，选择的定年方法是发光法。然而，崩积沉积物很难确定年代，因为通常所涉及的运输距离很短，而且由此造成的沉积物漂白不完全。断层相关崩积沉积物的单颗粒和小等分测量可以分离出漂白良好的颗粒，并提供可靠的断层事件的年龄。以色列南部的埃拉特位于活跃的死海变换上，古地震数据对城市规划者至关重要。在Elat附近的Nahal Shehoret的晚更新世至全新世冲积扇内，对一个小的NNE向地堑进行了挖沟，以暴露最近活动的正断层，下盘上有一堆崩积楔。释光测年的样品采集于东部断层附近的冲积扇和5个崩积楔堆的踵部（距断层面不到1 m）和趾部（距断层面约1.2m）。将石英的单颗粒测量与石英和碱性长石（KF）的大（数千颗粒）和小（数百颗粒）单等分试样进行比较。KF使用红外受激发光（IRSL）信号和单等份添加剂量（SAAD）或单等份再生剂量（SAR）方案进行测量。使用光学受激发光（OSL）信号和SAR协议测量大等分试样和单个石英颗粒。大小等分试样的等效剂量值分散较大，且人群明显年轻。从楔形体的趾部采集的样品的石英大等分年龄范围为5200年至2600年，然而从接近断层的踵部采集的样品的年龄顺序相反，从底部的4300年到上部楔形体的13,000年。这是由于断层崖上较深和较老的岩层逐渐暴露和侵蚀，并伴随着持续的断层作用，以及较老的漂白较差的颗粒进入上部楔形体。只有单一的颗粒测量可以分离出一个独特的，小人口的颗粒完全漂白时，沉积，约会崩积楔之间的500和1300年。大等分年龄大大高估了时间的断层。单颗粒年龄记录了非常年轻的断裂事件，这可能与过去1500年的已知历史地震有关。
Colluvial sediments in tectonically active areas are associated with faults, and dating them is important for timing earthquakes and assessing seismic hazards. In hyperarid regions organic matter for radiocarbon is scarce, and the dating method of choice is luminescence. However, colluvial sediments are difficult to date due to the short transport distance that is commonly involved and the resulting incomplete bleaching of the sediment. Single grain and small aliquot measurements of fault-related colluvial sediments may isolate well-bleached grains and provide reliable ages of faulting events. Elat, southern Israel, lies on the active Dead Sea Transform and paleoseismic data are crucial for city planners. A small fresh-looking NNE trending graben within the late Pleistocene to Holocene alluvial fan of Nahal Shehoret near Elat was trenched to expose recently active normal faults with a stack of colluvial wedges on the footwalls. Samples for luminescence dating were collected near the eastern fault, from the alluvial fan and from the heels (less than 1m from the fault plane) and toes (∼2m away from the fault plane) of a stack of five colluvial wedges. Single grain measurements of quartz were compared with large (thousands of grains) and small (hundreds of grains) single aliquots of quartz and alkali feldspar (KF). KF was measured using the infrared stimulated luminescence (IRSL) signal and the single aliquot added dose (SAAD) or single aliquot regenerative dose (SAR) protocols. Large aliquots and single grains of quartz were measured using the optically stimulated luminescence (OSL) signal and the SAR protocol. Large and small aliquots show large scatter in equivalent dose values, with a distinct population of young ages. Quartz large aliquot ages of samples taken from the toes of the wedges range from 5200 to 2600 years, however the ages of samples taken from the heels, close to the fault, are in reversed order, from 4300 years at the base to 13,000 years at the upper wedge. This results from progressive exposure and erosion of deeper and older beds on the fault scarp with continued faulting, and incorporation of older poorly bleached grains into the upper wedges. Only single grain measurements could isolate a distinct, small population of grains that were fully bleached at the time of deposition, dating the colluvial wedges to between 500 and 1300 years. Large aliquots ages substantially overestimated the time of faulting. The single grain ages record very young faulting events which may be correlated with the known historical earthquakes of the past 1500 years.