Abstract In the western Huallaga basin, located in the Peruvian Subandes, a series of nine fluvial terraces with elevations of up to 160 m above current floodplain level (+FP) were formed against the Biabo anticline. The terraces are progressively more folded with age and terrace elevation and present growth strata, suggesting ongoing folding of the anticline. Optically and InfraRed Stimulated Luminescence (OSL and IRSL) dating of fluvial terrace sediments yielded ages of 10.8 ± 0.7 ka for the T2, 24.2 ± 2 ka for the T4 and 46 ± 9 ka for the T7 terrace. Uniform uplift rates of 2 mm a−1 for the past 46 ka were calculated. Terrace profiles and two new seismic profiles that cross the Biabo anticline longitudinally and transversally were used to calculate shortening rates of 2.6 mm a−1 for the anticline over the past 46 ka. Our calculations took into account potential contributions of detachment thrusting parallel to the Biabo fold and reverse tear faulting perpendicular to the fold tip as visible on the seismic sections. A maximum uplift rate of 0.62 mm a−1 due to reverse thrusting of the Bellavista tear fault for the past 46 ka could have contributed to the overall uplift of the Bellavista terraces. Based on trigonometric relationships, a reverse fault slip rate of 0.86 mm a−1 and an age of 137 ka were calculated for this fault. In the eastern part of the Huallaga basin, a series of two fluvial terraces were formed with elevations of 13–15 m and 30 m + FP and with OSL ages of 6.9 ± 0.7 ka for T1 and 30.2 ± 3.1 ka for T2. The interpretation of a third new seismic profile crossing the study area in combination with field observations and trigonometric relationships shows that the terraces were formed by a complex system of oblique ramp and strike-slip faulting resulting in uplift and shortening rates of 1 mm a−1 and 1.96 mm a−1 between 30.2 ka and 6.9 ka respectively; and uplift and shortening rates of 2 mm a−1 and 3.70 mm a−1 from 6.9 ka until the present. Reverse slip of the Shapaja oblique ramp, that was responsible for uplift of the terraces, was calculated at 2.19 mm a−1 for the period 30.2 to 6.9 ka and 4.15 mm a−1 from 6.9 ka until the present. Measured total slip in combination with the calculated slip rates allowed an age calculation of 181 ka for the Shapaja thrust ramp. Our inferences showed that the studied tectonic structures absorb most of the present-day deformation in the Huallaga basin. The calculated uplift and shortening rates are compatible with published, present-day crustal movement velocities, and Miocene to present shortening rates for various, studied sites of the tropical Subandes and suggest that it is deforming at a relatively uniform rate. The timing of sedimentation of the terrace sediments may have corresponded to periods of increased precipitation which occurred coeval with the Heinrich events of the Northern Hemisphere. Terrace records similar as ours have been described for other, tectonically highly active areas in the tropical Subandes, but not in the tectonically less active Amazonian lowlands. It is suggested that uplift rates of at least 1 mm a−1 are needed to preserve suborbital climate cycles as individual terraces. The tropical Subandes could therefore be a new key area to investigate the interactions between tectonics, suborbital climate forcing and fluvial response during the late Quaternary.

中文翻译：

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河流阶地作为秘鲁瓦拉加盆地晚第四纪拆离褶皱和蠕动逆冲断层的定量标志

摘要 在位于秘鲁苏班德斯的瓦拉加盆地西部，与比亚博背斜相对地形成了一系列海拔高达当前洪泛区水平（+FP）以上160 m的河流阶地。阶地随着年龄和阶地海拔高度和目前的生长地层逐渐折叠，表明背斜正在进行折叠。河流阶地沉积物的光学和红外激发发光（OSL 和 IRSL）测年得出的年龄为 T2 为 10.8 ± 0.7 ka，T4 为 24.2 ± 2 ka，T7 阶为 46 ± 9 ka。计算了过去 46 ka 的 2 mm a-1 的均匀抬升率。台地剖面和两个纵向和横向穿过比亚博背斜的新地震剖面被用来计算过去 46 ka 中背斜 2.6 mm a-1 的缩短率。我们的计算考虑了平行于 Biabo 褶皱的分离推力和垂直于地震剖面上可见的褶皱尖端的反向撕裂断层的潜在贡献。由于过去 46 ka 的 Bellavista 撕裂断层的反向推力，0.62 mm a-1 的最大抬升率可能有助于 Bellavista 阶地的整体抬升。根据三角关系，该断层的反向断层滑动率为 0.86 mm a-1，年龄为 137 ka。在瓦拉加盆地东部，形成了一系列两个河流阶地，海拔分别为 13-15 m 和 30 m + FP，OSL 年龄为 T1 为 6.9±0.7 ka，T2 为 30.2±3.1 ka。结合现场观测和三角关系对穿越研究区的第三个新地震剖面的解释表明，阶地是由斜斜坡和走滑断层的复杂系统形成的，导致抬升和缩短速率为1 mm a-1和 1.96 mm a-1 分别在 30.2 ka 和 6.9 ka 之间；从 6.9 ka 到现在，隆起和缩短率分别为 2 mm a-1 和 3.70 mm a-1。导致阶地抬升的 Shapaja 斜坡的反向滑移在 30.2 至 6.9 ka 期间计算为 2.19 mm a-1，从 6.9 ka 到现在计算为 4.15 mm a-1。测得的总滑移与计算的滑移率相结合，可以计算出 Shapaja 推力斜坡的年龄为 181 ka。我们的推论表明，所研究的构造结构吸收了瓦拉加盆地目前的大部分变形。计算出的隆起和缩短率与公布的当今地壳运动速度和中新世相一致，以显示热带苏班德斯各种研究地点的缩短率，并表明它以相对均匀的速度变形。阶地沉积物的沉积时间可能与北半球海因里希事件同时发生的降水增加时期相对应。在热带苏班德斯的其他构造高度活跃的地区也有与我们类似的梯田记录，但在构造不那么活跃的亚马逊低地则没有。建议至少需要 1 mm a-1 的抬升率才能将亚轨道气候循环保存为单独的阶地。因此，热带 Subandes 可能成为研究晚第四纪构造、亚轨道气候强迫和河流响应之间相互作用的新关键领域。