Cenozoic unroofing history of the Ladakh Batholith, western Himalaya, constrained by thermochronology and numerical modelling

The Ladakh Batholith is part of the Transhimalayan Plutonic Belt, which crops out north of the Indus Suture Zone. We propose that the exhumation history of the Ladakh Batholith is linked to the tectonic, magmatic and erosion history of the Karakoram terrane and SW Tibet. We present new multiple low-temperature thermochronometry data (zircon (U–Th)/He, apatite fission-track and apatite (U–Th)/He) to gain insight into the cooling history of the Ladakh Batholith and recognize key periods in the evolution of the region. From the Indus Valley northwards the ages decrease across the batholith for all three thermochronometers applied. A model is proposed in which magmatism in the Ladakh Batholith ceased in the Late Eocene and initial denudation was driven by topographic uplift caused by collision. Southward tilting of the batholith occurred in the Late Palaeogene. This tilting resulted in an asymmetric topography with increasing elevation to the north. Strong erosion occurred in this northern region whereas the southern margin was affected by northwards thrusting of the Indus Molasse. For the first time, clear temporal and spatial variations in exhumation rate are identified in this region, highlighting why sampling strategy is critical in documenting exhumation changes in active tectonic settings.

拉达克岩基（Ladakh Batholith）隶属于跨喜马拉雅岩浆岩带（Transhimalayan Plutonic Belt），该岩带出露于印度河缝合带（Indus Suture Zone）北侧。本研究提出，拉达克岩基的剥露历史与喀喇昆仑地体（Karakoram terrane）及西藏西南部的构造、岩浆活动及侵蚀演化历史紧密关联。本文发布了全新的多组低温热年代学数据，涵盖锆石（U–Th）/He、磷灰石裂变径迹及磷灰石（U–Th）/He测年数据，旨在深入解析拉达克岩基的冷却历程，并明确该区域演化的关键阶段。针对所采用的三类热年代学测年体系，研究发现自印度河谷向北横穿岩基时，测年年龄依次降低。本研究提出如下模型：拉达克岩基的岩浆活动于始新世晚期终止，初始剥蚀作用由碰撞引发的地形抬升驱动；古近纪晚期，岩基发生南向倾斜，由此形成北高南低的不对称地形。该区域北部经历了强烈侵蚀作用，而南部边缘则受印度斯磨拉石（Indus Molasse）北向逆冲作用影响。本研究首次在该区域识别出剥露速率的显著时空差异，这一发现清晰阐释了在活动构造环境中，采样策略为何对记录剥露变化至关重要。