Cenozoic topographic evolution of the Southern Central Andes foreland as revealed by hydrogen stable isotopes in hydrated volcanic glass
Cenozoic topographic evolution of the Southern Central Andes foreland as revealed by hydrogen stable isotopes in hydrated volcanic glass
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水合火山玻璃中氢稳定同位素揭示安第斯山脉中南部前陆新生代地形演化
DOI：
10.1016/j.epsl.2023.117991
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发表时间：
2023
影响因子：
5.3
通讯作者：
Hren, Michael T.
中科院分区：
文献类型：
--
作者：
Fennell, Lucas M.;Brandon, Mark T.;Hren, Michael T.
本文用同位素-古地形学方法研究了南中安第斯山脉及其以东35° S附近的前陆的地形演化。我们的分析是基于从Malargüe盆地55 - 10 Ma地层剖面采集的107个样品的水合火山玻璃和另外11个第四纪凝灰岩样品的δ 2 H测量。现代大气水样品（n= 197），这是用来表征现代的地形升降和降水同位素之间的关系的一个大型数据集的分析结果是支持的。我们的解释是由地形降水和同位素（OPI）程序，提供了一个完整的模拟潮湿的空气流在一个指定的三维地形和由此产生的冷凝和下降的雨和雪，以及与这些过程相关的同位素分馏。OPI模型在最小二乘意义上适合现代同位素数据，这提供了一种测试水分来源和计算降水同位素如何受气候变化影响的方法。从这些数据中可以得出三个重要结论：1）现代水同位素的OPI模拟表明，Malargüe研究区的降水完全来自潮湿的东北风。同位素分馏沿着这条风路发生在抬升科尔多瓦和圣路易斯的基底高点，并在最初上升的范围的东侧。偏西的潮湿空气能够通过山脉，但东侧的下坡气流意味着这个来源变得强烈欠饱和，因此该地区的降水受到抑制。2)我们的火山玻璃数据表明，自55 Ma至今，降水的氢同位素组成δ 2 H已经强烈亏损，亏损幅度为-50 ~90 ‰。造成这种消耗的唯一途径是通过湿风的上坡流和山脉东侧的相关降水。同位素分馏量在55 ~ 15 Ma期间保持相当稳定，与现代相似，这表明马拉圭以东的地形在这段时间内相当稳定。3)δ 2 H记录表明，在15 ~ 10 Ma之间，Malargüe的上风地形减小了约50%，然后在10 ~ 0 Ma之间又增加了相同的幅度。这一沉降事件与Paranense海侵相吻合，也预测了与纳斯卡板块俯冲相关的地幔流和动态地形的数值模拟。
We use the “isotope-paleotopography” method to resolve the topographic evolution of the Southern Central Andes and adjacent foreland to the east, at the latitude of 35° S. Our analysis is based on δ 2 H measurements from hydrated volcanic glass from 107 samples collected from a 55 to 10 Ma stratigraphic section in the Malargüe basin, and from an additional 11 samples of Quaternary tuffs. The results are supported by an analysis of a large dataset of modern meteoric water samples (n= 197), which are used to characterize the relationship between orographic lifting and precipitation isotopes in the modern. Our interpretations are guided by the Orographic Precipitation and Isotopes (OPI) programs, which provide a full simulation of the flow of moist air over a specified 3D topography and the resulting condensation and fall out of rain and snow, and the isotopic fractionation associated with these processes. The OPI model is fit, in a least-squares sense, to the modern isotope data, which provides a way to test for moisture sources and to calculate how precipitation isotopes would be influenced by variations in climate. There are three important conclusions from these data: 1) OPI modeling of modern water isotopes shows that precipitation at the Malargüe study area is derived solely from the moist northeasterly winds. The isotopic fractionation along this wind path occurs by lifting over the Córdoba and San Luis basement highs, and during the initial rise up the east side of the range. Westerly moist air is able to pass over the range, but downslope flow over the east side means that this source becomes strongly undersaturated, so precipitation from this source is suppressed in this area. 2) Our volcanic glass data indicate that the hydrogen isotopic composition of precipitation, δ 2 H, has been strongly depleted, by− 50 to− 90 per mil, since 55 Ma to present. The only way to produce this depletion is by upslope flow of moist winds and associated precipitation over the eastern side of the range. The amount of isotopic fractionation remains fairly constant and similar to modern for the interval from 55 to 15 Ma, which indicates that the topography to the east of Malargüe has been fairly steady during that time interval. 3) Our δ 2 H record indicates that between 15 and 10 Ma, the topography upwind of Malargüe decreased by about 50%, and then increased by the same amount between 10 and 0 Ma. This subsidence event coincides with the Paranense marine transgression, and is also predicted by numerical modeling of mantle flow and dynamic topography associated with subduction of the Nazca plate.
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DOI：
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发表时间：
2013
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DOI：
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发表时间：
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期刊：
Andean Tectonics
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