Evaluating Along-strike Variations in Surface Uplift of the Andes: Constraints from Molecular Paleoaltimetry in the Eastern Cordillera of Colombia

哥伦比亚东部科迪勒拉的古植物学指标表明，在过去的600万年里，海拔迅速上升了1.5？2.5公里。需要独立的古测高指标来确定安第斯山脉北部的抬升时间和速度。与许多热带地区一样，缺乏应用氧同位素古海拔测量所需的适当碳酸盐或硅酸盐矿物。幸运的是，对富含有机物质的沉积物和古土壤的广泛保存，为测试两个新的古高度计提供了一个极好的机会。第一个古高度计利用保存在树叶蜡中的氚同位素的变化来重建稳定同位素随海拔变化的速率。第二，MBT/CBT古温度计(基于支链四醚环化(CBT)指数和支链四醚甲基化(MBT)指数的古温度计)，利用土壤中细菌产生的不同的四醚类脂的云母比例(这是年平均温度的敏感函数)来重建温度随海拔递减率的变化。这两个独立的古高度计将同时应用于高海拔和低海拔地点，提供多个记录，可以进行比较，以确定变化是地表抬升还是气候变化的结果。这些数据将与年代地层学结果相结合，以确定地表抬升的时间和速率。最近基于氧同位素和古植物学指标的模型认为，安第斯山脉中部的阿尔蒂普诺高原在大约10至6 Ma之间，地表快速抬升约2.5公里。这种快速的抬升速度导致了这样的说法，即点状抬升是由于先前通过广泛的水平缩短而增厚的下部岩石圈的剥离或对流移除造成的。据估计，安第斯山脉中部的总缩短约为200？350公里。在安第斯山脉北部，古植物学古海拔测量估计显示，晚新生代海拔也有类似的快速上升，尽管哥伦比亚东部科迪勒拉的地壳缩短不超过60公里。然而，像安第斯山脉中部一样，东科迪勒拉山脉的变形自始新世以来一直在进行，这表明安第斯山脉中部和北部都有一个更渐进的均衡隆升历史。确定在没有广泛的水平缩短的情况下是否发生了快速隆升，将有助于揭示目前正在进行的关于隆升机制和隆起造山带支撑的争论。

Paleobotanical proxies for the Eastern Cordillera of Colombia suggest a rapid rise in elevation of 1.5?2.5 km over the past 6 million years. Independent paleoaltimetry proxies are needed to determine the timing and rate of uplift in the northern Andes. As in many tropical locations, the appropriate carbonate or silicate minerals needed to apply oxygen isotope paleoaltimetry are missing. Fortunately, extensive preservation of organic-rich deposits and paleosols affords an excellent opportunity to test two new paleoaltimeters. The first paleoaltimeter exploits the variation in deuterium isotopes preserved in leaf waxes to reconstruct the lapse rate of stable isotopes with elevation. The second, the MBT/CBT paleo-thermometer (paleothermometer based on the Cyclisation of Branched Tetraether (CBT) index and Methylation of Branched Tetraether (MBT) index), utilizes the proportions of distinct moites of tetraether lipids produced by bacteria in soils (which are a sensitive function of mean annual temperature) to reconstruct the temperature versus elevation lapse rate. The two independent paleoaltimeters will be applied at both high- and low-elevation sites, providing multiple records that can be compared to determine if variations are the result of surface uplift or climate change. These data will be combined with chronostratigraphic results to determine the timing and rate of surface uplift.Recent models based on oxygen isotope and paleobotanical proxies posit rapid surface uplift of approximately 2.5 km for the Altiplano plateau in the central Andes between about 10 and 6 Ma. This rapid rate of uplift has led to suggestions that punctuated uplift resulted from delamination or convective removal of lower lithosphere previously thickened by extensive horizontal shortening. Estimates of total shortening in the central Andes are about 200?350 km. In the northern Andes, paleobotanical paleoaltimetry estimates show a similarly rapid late Cenozoic rise in elevation, although crustal shortening in the Eastern Cordillera of Colombia does not exceed 60 km. Nevertheless, like the central Andes, deformation in the Eastern Cordillera was ongoing since the Eocene, which would suggest a more gradual isostatic uplift history for both the central and northern Andes. Determining whether rapid uplift occurred in the absence of extensive horizontal shortening will shed light on the ongoing debate over the mechanisms of uplift and support of elevated orogens.