Low-temperature thermochronology in the Peruvian Central Andes: implications for long-term continental denudation, timing of plateau uplift, canyon incision and lithosphere dynamics

In Peru, the western edge of the 4.5 km high Western Cordillera is cut by a &gt;3 km deep canyon. To understand incision by the Cotahuasi–Ocoña River and the regional uplift history of this orogenic plateau capped by volcanic rocks, 26 crystalline rock samples were collected for low-temperature thermochronology from vertical profiles parallel and perpendicular to the canyon. Rock cooling histories confirm that most plateau denudation had occurred prior to 24 Ma but plateau incision peaked after <em>c</em>. 14–9 Ma in response to rapid surface uplift. The abrupt occurrence of a rock heating event is also detected during middle Miocene time. This was either a response to the emplacement of low-conductivity, regionally extensive ignimbritic caprock or a response to crustal-scale fluid circulation caused by wet melting of the overriding plate when magmatism resumed <em>c</em>. 24 Ma. The potential for thermochronology to provide information on past geothermal gradients is discussed, showing how it can be used as a proxy for understanding change in subducting slab dynamics, with oscillations in subduction angle having perhaps been the main on–off switch for magmatism in this Cordilleran setting.

在秘鲁境内，海拔4.5千米的西科迪勒拉山脉（Western Cordillera）西缘被一条深度超3千米的峡谷切割。为探究科塔瓦西-奥科尼亚河（Cotahuasi–Ocoña River）的下切作用机制，以及这套覆有火山岩的造山高原的区域隆升历史，研究人员沿平行于峡谷和垂直于峡谷的垂直剖面采集了26件结晶岩样品，用于低温热年代学（low-temperature thermochronology）测试分析。岩石冷却史结果证实，高原的绝大多数剥蚀作用发生于24百万年之前，但高原下切作用在约14–9百万年达到峰值，这一过程对应快速地表隆升事件。研究同时在中新世中期检测到一次突发性岩石加热事件，该事件可归因于两种可能的成因：一是区域广泛分布的低导电性火成碎屑盖层（ignimbritic caprock）的就位作用；二是约24百万年岩浆活动重新启动时，上覆板块（overriding plate）发生湿熔融，进而引发壳尺度流体循环。本文还探讨了热年代学（thermochronology）在重建古地热梯度方面的应用潜力，阐明其可作为理解俯冲板片动力学变化的代用指标；而俯冲角度的波动或许是该科迪勒拉构造背景下岩浆活动的主要触发开关。