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

这项研究将通过将一种新的碳酸盐环境地质温度计与土壤碳酸盐、湖泊碳酸盐和哺乳动物牙齿化石的稳定同位素组成的常规分析相结合，研究安第斯高原的中新世气候和海拔历史。该温度计基于碳-12和氧-18在碳酸盐矿物晶格中相互聚集成键。安第斯高原以前的研究已经根据古植物学数据、沉积碳酸盐的三角洲氧-18和新的块状同位素方法估计了古海拔。然而，这些研究通过假设与今天类似的基准面气候来估计海拔，以及今天海拔、年平均表面温度和大气水的增量氧-18之间的关系。这一假设是一个不确定的来源，除非蒸汽源的温度或起始组成可以受到限制。这项研究的一部分将建立苏班德山脉的低海拔气候记录，以便与高原的古海拔记录进行比较。通过这种方法，通过根据在Subandes观测到的气候的长期变化进行校准，可以提取更准确的海拔记录。重要的是，这种新的方法将允许研究整个高原，包括其干旱的南半部，这一方法抵制了仅根据地表碳酸盐的增量氧-18来确定古海拔的尝试。随着对安第斯山脉表面隆起幅度的时空变化的更好分辨率，这项研究的更广泛意义将是理解导致山带表面隆起的过程，包括地壳和地幔岩石圈的增厚以及致密、增厚的下部岩石圈的移除。最近对阿尔蒂普兰诺北部高程史的研究表明，中新世晚期发生了快速的地表抬升(300万年约3公里)，表明主要地壳通过上地壳褶皱和断层作用而增厚。有证据表明，横跨安第斯山脉宽度超过5度纬度的地表隆起年龄相似，这意味着地幔岩石圈的移位是地表隆起的重要机制。然而，独立的数据只预测了南部高原和普纳地区的地幔岩石圈移动。记录沿安第斯走向的地表抬升的时间和幅度，将有助于阐明这些过程的综合作用及其区域范围。此外，这项工作的更广泛影响是考察造山对区域气候的影响。该项目将研究高原不同纬度从中新世中期到最近的气候空间变化，以及沿安第斯山脉东侧从低海拔到高海拔的空间变化，以评估地表隆起对当地气候的潜在影响。对中新世晚期的牙齿釉质到现代大型、依赖水的食草动物的初步研究表明，这些动物摄取的地表水成分与现代降雨相似。这些数据将追溯到中新世中期，以评估晚中新世至现代降雨模式是否是区域地表抬升的结果。此外，还将评估低海拔和高海拔降水量的时间变化，以检验晚中新世高原地表抬升强迫气候变化的假设，即低海拔降雨量增加，高海拔降雨量同时减少。这项研究将提供一种新的、广泛适用的方法来恢复过去的气候和古海拔，通过块状碳-12和氧-18古测温法来恢复过去的温度，并通过常规的稳定同位素研究来重建降水模式。

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.