Noble Gas Studies of Groundwater Recharge and Residence Time in Semi-Arid Region: Contrasting the Western Mojave River Basin with Central Australia and the Kalahari Desert

在这项提案中，我们将对三个研究充分的半干旱地区的一系列地下水进行惰性气体研究。我们的目标有两个：首先，我们计划评估4He累积法在100s至50万年的年龄范围内准确估计地下水停留时间的潜力。这一办法将涉及利用若干不同的地下水测年技术(氚、14C和36Cl)进行相互校准，并将总数据库与先前为各个盆地开发的地下水流动模型相结合。一个重要特征将是确定三个研究区“地壳He通量”的性质及其量化，特别是因为一个地区，即西莫哈维河流域，位于构造活动的地壳上，而另外两个，即澳大利亚中部和博茨瓦纳，位于稳定的克拉通平台上。我们将集中精力计算这三个区域的长期古补给率--这是当前资源管理战略中至关重要的参数--但其他水力参数(例如，含水层渗透率也可以使用4He技术进行评估)。第二个目标是利用惰性气体丰度(Ne、Ar、Kr和Xe的浓度)来计算补给时的温度和环境条件。在每个研究区域，我们将选择4He和其他技术测年的水域，重点关注最后一次冰川时期。通过惰性气体与稳定同位素d18O和d2H之间的关系，我们计划确定过去补给区的(古)温度变化和其他局部影响(例如，水位上升)。通过与各自地区(美国、澳大利亚和博茨瓦纳)地质调查局的同事合作，我们将前所未有地获得研究区域的广泛地球化学和地球物理数据，为新样本采集提供后勤支持，提供关于最先进地下水软件的培训机会，以及在现实世界资源和地下水管理问题上的本地化专业知识。

0001133HiltonIn this proposal, we will conduct a noble gas study of a series of groundwaters from three well-studied semi-arid regions. The aims are twofold: first, we plan to assess the potential of the 4He accumulation method to accurately estimate groundwater residence times over a range of ages from 100s to 500,000 years. The approach will involve inter-calibration with a number of different groundwater dating techniques (tritium, 14C and 36Cl, and integration of the total database into previouslydeveloped groundwater flow models for the individual basins. An important feature will be ascertaining the nature of the 'crustal He flux' and its quantification in the three studied areas, particularly as one, the West Mojave River Basin, is situated on tectonically active crust while the other two, Central Australia and Botswanna, lie on stable cratonic platforms. We will concentrate on deriving long-term, paleo-recharge rates for the three regions-a parameter of vital importance to current resource management strategies-but other hydraulic quantities (e.g., aquifer permeability can be also assessed using the 4He technique.The second aim is to utilize the noble gas abundances (concentrations of Ne, Ar, Kr and Xe) to derive both temperatures and environmental conditions at the time of recharge. In each of the studied areas, we will select waters, dated by 4He and other techniques, to focus on the last glacial period. Through the relationship between noble gases and stable isotopes d18O and d2H, we plan to determine (paleo) temperature variations and other localized effects (e.g., rising water tables) characteristic of past recharge regions.Through collaboration with colleagues from the Geological Surveys of the respective regions (U.S., Australia and Botswanna), we will have unprecedented access to a wide range of geochemical and geophysical data on the regions of study, logistical support for new sample collection, training opportunities on state-of-the-art groundwater software, and localized expertise on real-world resource and groundwater management issues.