LuHf geochronology is a powerful method to constrain the temporal evolution of geological systems. Traditional application of this dating method requires time-consuming chemical separation of the parent (¹⁷⁶Lu) and daughter (¹⁷⁶Hf) isotopes that is commonly accompanied by loss of textural context of the analysed minerals. In contrast, In-situ (laser-ablation based) LuHf geochronology offers a number of advantages including rapid analysis with high spatial resolution, as well as control on textural relationships of the analysed mineral. However, laser-ablation based LuHf geochronology has been hindered by isobaric interferences of ¹⁷⁶Yb and ¹⁷⁶Lu on ¹⁷⁶Hf that have effectively masked reliable determination of ¹⁷⁶Lu and ¹⁷⁶Hf. We present a methodology that resolves these interferences using LA-ICP-MS/MS (laser ablation tandem inductively coupled mass spectrometry) and NH₃ gas to separate Hf from Lu. Both Lu, Yb, and Hf react with NH₃ to form a variety of product ions. By measuring high order reaction products (e.g. Hf(NH)(NH₂)(NH₃)₃⁺), we demonstrate that ¹⁷⁶Hf can be measured interference-free from ¹⁷⁶Lu and ¹⁷⁶Yb with sufficient sensitivity to yield useful geochronological age data.

The novel in-situ LuHf technique has been successfully applied to a variety of Palaeozoic and Precambrian-aged garnet, apatite and xenotime samples, including published reference materials. The resulting age uncertainties are as low as ~0.5% (95% conf. interval). The technique has the potential to obtain spatially-resolved LuHf ages in garnet-bearing samples that would be difficult to obtain by conventional techniques. The method also offers the opportunity for rapid “campaign style” geochronology in complex terrains that record poly-metamorphic histories. In apatite, the expected higher closure temperature of the LuHf system compared to the commonly used UPb system allows high-temperature thermal history reconstructions. In addition, LuHf dating of apatite allows dating of samples with low U and high common Pb (e.g. mafic and low-grade metamorphic rocks and ore deposits). Furthermore, apatite tends to incorporate little to no common Hf, allowing single grain ages to be calculated, which opens new doors for detrital provenance studies. In situ LuHf dating of xenotime offers an additional avenue to UPb dating, and may be particularly beneficial to dating of rare earth element ore deposits that often have complex temporal records of development.

鲁铪同位素年代学的约束地质系统的时间演变的有效方法。这种测年方法的传统应用要求费时的化学分离母体（¹⁷⁶ Lu）和子体（¹⁷⁶ Hf）同位素，这通常伴随着所分析矿物的质地缺失。相比之下，Lu Hf原位（基于激光烧蚀）年代学具有许多优势，包括具有高空间分辨率的快速分析以及对所分析矿物的纹理关系的控制。然而，基于激光烧蚀的Lu Hf年代学已受到¹⁷⁶ Yb和¹⁷⁶ Lu对^176的等压干涉的阻碍。有效掩盖了¹⁷⁶ Lu和¹⁷⁶ Hf的可靠测定的Hf。我们提出了一种使用LA-ICP-MS / MS（激光烧蚀串联电感耦合质谱）和NH ₃气体从Lu中分离出Hf的方法来解决这些干扰的方法。Lu，Yb和Hf均与NH ₃反应形成各种产物离子。通过测量高阶反应产物（例如Hf（NH）（NH ₂）（NH ₃）₃ ⁺），我们证明可以从¹⁷⁶ Lu和¹⁷⁶ Yb不受干扰地测量¹⁷⁶ Hf，并具有足够的灵敏度以产生有用的地质年代数据。

新颖的原位Lu Hf技术已成功应用于各种古生代和前寒武纪的石榴石，磷灰石和xenotime样品，包括已发表的参考材料。最终的年龄不确定性低至〜0.5％（95％置信区间）。该技术具有在含石榴石的样品中获得空间分辨的Lu Hf年龄的潜力，而这是常规技术难以获得的。该方法还为记录多亚变历史的复杂地形中的快速“运动风格”年代学提供了机会。在磷灰石中，与常用的U Pb系统相比，Lu Hf系统的预期更高的关闭温度可实现高温热历史重建。另外，鲁磷灰石的Hf测年可以对低U和高Pb的样品（例如镁铁质和低品位的变质岩和矿床）进行测年。此外，磷灰石倾向于掺入很少甚至没有普通的Hf，从而可以计算单个晶粒的年龄，这为碎屑物源研究打开了新的大门。Xenotime的Lu Hf原位定年提供了U Pb定年的另一种途径，并且对于通常具有复杂的时间变化记录的稀土元素矿床定年可能特别有利。