Collaborative Research: Surface Uplift and Climate Change in the Southern Altiplano: Evaluating Mechanisms for Surface Rise and the Effects of Tectonics on Climate

这项研究将研究中新世的气候和海拔历史的安第斯高原相结合的一种新的碳酸盐环境地质温度计，基于结块的碳-12和氧-18成键彼此在碳酸盐矿物晶格，与传统的分析土壤碳酸盐，湖泊碳酸盐和化石哺乳动物牙齿的稳定同位素组成。先前在安第斯高原的研究，估计古海拔的基础上古植物学数据，三角洲的沉积碳酸盐氧-18，和新的成团同位素方法。然而，这些研究通过假设一个与今天相似的基准面气候来估计海拔，并利用今天的海拔、年平均表面温度和大气沃茨的三角洲氧-18之间的关系。这种假设是不确定性的来源，除非蒸汽源的温度或起始组成可以被约束。这项研究的一部分将建立一个低海拔的气候记录，从Subandes的古海拔记录从高原可以比较。通过这种方法，将通过对Subandes观测到的气候长期变化进行校准来提取更准确的海拔记录。重要的是，这种新方法将使研究整个高原，包括其干旱的南半部，它抵制了仅根据表面碳酸盐的三角洲氧-18来确定古海拔的尝试。随着安第斯山脉表面隆起幅度的空间和时间变化的更好分辨率，这项研究的更广泛意义将是理解导致山区地表隆起的过程，包括地壳和地幔岩石圈的增厚和致密岩石圈的移动，岩石圈下部增厚最近对北方高原海拔历史的研究表明，地表快速抬升（300万年约3公里）发生在中新世晚期，晚于上地壳褶皱和断层造成的主要地壳增厚。在安第斯山脉的宽度上，在大于5度的纬度范围内，有类似年龄的地表隆升的证据，表明地幔岩石圈的去除是地表隆升的重要机制。然而，独立的数据只预测地幔岩石圈去除在南部高原和普纳。沿着安第斯山脉走向的地表隆起的时间和幅度的文件将阐明这些过程的综合作用以及它们的区域范围。这项工作的其他更广泛的影响是研究造山运动对区域气候的影响。该项目将研究从中新世中期到最近，高原不同纬度地区以及安第斯山脉东侧从低海拔到高海拔地区气候的空间变化，以评估地表隆起对当地气候的潜在影响。对中新世晚期到现代大型食草动物牙齿釉质的初步研究表明，这些动物是在地表水中生活的，其成分与现代降雨相似。这些数据将延伸到中新世中期，以评估晚中新世到现代的降雨模式是否是区域地表抬升的结果。此外，在低海拔和高海拔降水量的时间变化将进行评估，以测试的假设，晚中新世高原表面隆起迫使气候变化，表现为低海拔降雨量的增加，同时减少高海拔降雨量。这项研究将提供一个新的和广泛适用的方法来重建过去的气候和古海拔模型，通过聚集的碳-12和氧-18古测温法重建过去的温度和传统的稳定同位素研究重建模式的降水。

This study will examine the Miocene climate and elevation history of the Andean plateau by combining a new carbonate environmental geothermometer, based on clumping of carbon-12 and oxygen-18 into bonds with each other in the carbonate mineral lattice, with conventional analyses of the stable isotope compositions of soil carbonates, lake carbonates, and fossil mammal teeth. Previous studies in the Andean plateau have estimated paleoelevations based on paleobotanical data, the delta oxygen-18 of sedimentary carbonates, and the new clumped isotope method. However, these studies estimate elevation by assuming a base level climate similar to today, with today's relationships among altitude, mean annual surface temperature, and the delta oxygen-18 of meteoric waters. This assumption is a source of uncertainty unless the temperature or starting composition of the vapor source can be constrained. Part of this study will establish a low elevation climate record from the Subandes against which the paleoelevation records from the Altiplano can be compared. By this approach, a more accurate record of elevation will be extracted by calibrating against secular variations in climate observed in the Subandes. Importantly, this new approach will allow study of the entire plateau, including its arid southern half, which has resisted attempts to determine paleoelevation based on delta oxygen-18 of surface carbonates alone.With a better resolution of the spatial and temporal variation in the magnitude of surface uplift of the Andes, the broader significance of this study will be an understanding of processes that lead to surface uplift of mountain belts, including thickening of crustal and mantle lithosphere and removal of dense, thickened lower lithosphere. Recent studies of the elevation history of the northern Altiplano suggest that rapid surface uplift ( approximately 3 km in 3 million years) occurred in the late Miocene, postdating major crustal thickening by upper crustal folding and faulting. There is evidence of similar-age surface uplift across the width of the Andes for over greater 5 degrees of latitude, implicating the removal of mantle lithosphere as an important mechanism for surface uplift. However, independent data have only predicted mantle lithosphere removal in the southern Altiplano and Puna. Documentation of the timing and magnitude of surface uplift along strike in the Andes will shed light on the combined roles of these processes as well their regional extent.Additional broader impacts of this work are to examine the effects of mountain building on regional climate. This project will examine the spatial variations in climate from middle Miocene to recent over different latitudes in the Altiplano, as well as from low to high elevation along the eastern flank of the Andes, to evaluate the potential influence of surface uplift on local climate. A pilot study of the tooth enamel of late Miocene to modern large, water-dependent grazers shows that these animals were ingesting surface water similar in composition to modern rainfall. These data will be extended back to the middle Miocene to evaluate whether the Late Miocene to modern pattern of rainfall resulted from regional surface uplift. In addition, temporal changes in low elevation and high elevation precipitation amount will be evaluated to test the hypothesis that late Miocene surface uplift of the Altiplano forced climate change that was manifested by an increase in low elevation rainfall amount and a simultaneous decrease in high elevation rainfall amount. This study will provide a model for a new and widely applicable approach to reconstructing past climates and paleoelevation through the clumped carbon-12 and oxygen-18 paleothermometry method to reconstruct past temperatures and conventional stable isotope studies to reconstruct patterns of precipitation.