Trace-element and Nd-isotope systematics in detrital apatite of the Po river catchment: Implications for provenance discrimination and the lag-time approach to detrital thermochronology
Trace-element and Nd-isotope systematics in detrital apatite of the Po river catchment: Implications for provenance discrimination and the lag-time approach to detrital thermochronology
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DOI：
10.1016/j.lithos.2017.08.006
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发表时间：
2017-10
期刊：
影响因子：
3.5
通讯作者：
M. Malusà;Jian‐Gang Wang;E. Garzanti;Zhi‐Chao Liu;I. Villa;H. Wittmann
中科院分区：
文献类型：
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作者：
M. Malusà;Jian‐Gang Wang;E. Garzanti;Zhi‐Chao Liu;I. Villa;H. Wittmann
碎屑热年代学常被用来用滞后时间方法评估整个造山带的演化阶段，即，在地层序列中保存下来的碎屑矿物颗粒的冷却和沉积年龄之间的差异。不同侵蚀源对最终沉积汇的影响受多种因素控制，包括短期侵蚀速率和侵蚀基岩的矿物肥力。在这里，我们使用磷灰石肥力数据和宇宙起源的侵蚀率在波河流域（阿尔卑斯山，亚平宁山脉）来计算预期的百分比磷灰石颗粒提供给现代波河三角洲的主要阿尔卑斯山和亚平宁侵蚀源。我们测试这些预测，通过使用先进的数据集的微量元素和Nd同位素的签名871磷灰石颗粒从14个现代砂样品，我们使用磷灰石裂变径迹数据来验证我们的地球化学方法的来源判别。我们发现不同来源的磷灰石颗粒在地球化学上是不同的。中阿尔卑斯山Lepontine穹丘的磷灰石表现出相对HREE富集，Ce和U浓度较低，147 Sm/144 Nd比值较高。派生的种源预算点占主导地位的磷灰石贡献Po三角洲从高生育力的Lepontine圆顶，符合独立预测的范围从cosmonuclide和矿物肥力数据。我们的研究结果表明，在最终的沉积物汇的单矿物记录可以在很大程度上由高肥力的源岩暴露在快速侵蚀的地区内的排水。这意味着，碎屑热年代学记录可能反映的过程中影响相对较小的部分造山系统正在审议。因此，一个可靠的方法来滞后时间分析将受益于一个独立的原产地歧视过时的矿物颗粒，这可能会允许熟练地重新考虑许多以前的解释碎屑热年代学数据集的造山带范围内的稳定状态。
Detrital thermochronology is often employed to assess the evolutionary stage of an entire orogenic belt using the lag-time approach, i.e., the difference between the cooling and depositional ages of detrital mineral grains preserved in a stratigraphic succession. The impact of different eroding sources to the final sediment sink is controlled by several factors, including the short-term erosion rate and the mineral fertility of eroded bedrock. Here, we use apatite fertility data and cosmogenic-derived erosion rates in the Po river catchment (Alps–Apennines) to calculate the expected percentage of apatite grains supplied to the modern Po delta from the major Alpine and Apenninic eroding sources. We test these predictions by using a cutting-edge dataset of trace-element and Nd-isotope signatures on 871 apatite grains from 14 modern sand samples, and we use apatite fission-track data to validate our geochemical approach to provenance discrimination. We found that apatite grains shed from different sources are geochemically distinct. Apatites from the Lepontine dome in the Central Alps show relative HREE enrichment, lower concentrations in Ce and U, and higher147Sm/144Nd ratios compared to apatites derived from the External Massifs. Derived provenance budgets point to a dominant apatite contribution to the Po delta from the high-fertility Lepontine dome, consistent with the range independently predicted from cosmonuclide and mineral-fertility data. Our results demonstrate that the single-mineral record in the final sediment sink can be largely determined by high-fertility source rocks exposed in rapidly eroding areas within the drainage. This implies that the detrital thermochronology record may reflect processes affecting relatively small parts of the orogenic system under consideration. A reliable approach to lag-time analysis would thus benefit from an independent provenance discrimination of dated mineral grains, which may allow to proficiently reconsider many previous interpretations of detrital thermochronology datasets in terms of orogenic-wide steady state.