We investigated the tectonothermal history of the Lesser Himalayan sediments (LHS), which are tectonically overlain by the Higher Himalayan Crystalline. Fission‐track dating and the track length measurement of detrital zircons obtained from the Kuncha nappe and the Lesser Himalayan autochthonous sediments in western central Nepal revealed northward cooling of the nappe and possible downward heating of the autochthon by the overlying hot nappe. Nine zircon fission‐track (ZFT) ages of the nappe showed northward‐younging linear distribution from 11.6 Ma in the front at Tamghas, 6 Ma in the central at Naudanda, and 1.6 Ma in the northernmost point at Tatopani. Thermochronological invert calculation of the ZFT length elucidated that the Kuncha nappe gradually cooled down (30 °C/Myr) at the front and rapidly cooled down (120 °C/Myr) at the root zone. In contrast, the ZFT age of the Chappani Formation, located just beneath the Kuncha nappe in the central part, demonstrated a totally reset age of 6.8 Ma, whereas the Virkot Formation, structurally far from the nappe, yielded a partially reset age of 457.3 Ma. This suggests that the LHS underwent downward heating, resulting in a thermal print on the upper part of the LHS; however, the thermal effect was not sufficient to anneal ZFT totally in the deeper part. Presently, the nappe cover is eroded and denuded from this area. Detrital zircons from the Chappani Formation in Tansen area to the south of the Bari Gad Fault did not show any evidence of annealing, suggesting that nappe never covered the LHS distributed to the south of the fault.

中文翻译：

---

贡恰纳皮斯的北向冷却和小喜马拉雅自噬体的向下加热分布在山顶。尼泊尔中西部安纳布尔纳峰

我们调查了小喜马拉雅沉积物（LHS）的构造热历史，这些沉积物在构造上被高喜马拉雅结晶覆盖。从尼泊尔西部中部昆察（Kuncha）推覆和小喜马拉雅自生土沉积物中获得的碎屑锆石的裂变径迹测距和道长测量表明，该推覆带向北冷却，并且上覆的热推覆层可能使自噬体向下加热。纳普的9个锆石裂变径迹（ZFT）年龄呈北向线性分布，从坦加斯前缘的11.6 Ma，瑙丹达中部的6 Ma和塔托巴尼的最北端的1.6 Ma。ZFT长度的热年代学反演表明，Kuncha尿布的前部逐渐冷却（30°C / Myr），而根部区域迅速冷却（120°C / Myr）。相比之下，恰帕尼组的ZFT年龄位于中部昆卡岩浆之下，显示出完全复位的年龄为6.8 Ma，而维科特组在构造上远离该尿布，产生的部分复位年龄为457.3 Ma。 。这表明LHS受到向下加热，从而在LHS的上部形成热敏打印；然而，热效应不足以完全在更深的部分进行ZFT退火。目前，该区域的尿布被腐蚀和剥落。Bari Gad断层以南Tansen地区Chappani组的碎屑锆石没有显示出任何退火迹象，这表明推覆层从未覆盖分布在断层以南的LHS。结果表明，完全复位年龄为6.8 Ma，而维科特组在构造上与尿布相距较远，部分复位年龄为457.3 Ma。这表明LHS受到向下加热，从而在LHS的上部产生热敏打印；然而，热效应不足以完全在更深的部分进行ZFT退火。目前，该区域的尿布被腐蚀和剥落。Bari Gad断层以南Tansen地区Chappani组的碎屑锆石没有显示出任何退火迹象，这表明推覆层从未覆盖分布在断层以南的LHS。结果表明，完全复位年龄为6.8 Ma，而维科特组在构造上与尿布相距较远，部分复位年龄为457.3 Ma。这表明LHS受到向下加热，从而在LHS的上部形成热敏打印；然而，热效应不足以完全在更深的部分进行ZFT退火。目前，该区域的尿布被腐蚀和剥落。Bari Gad断层以南Tansen地区Chappani组的碎屑锆石没有显示出任何退火迹象，这表明推覆层从未覆盖分布在断层以南的LHS。在LHS的上部形成热敏打印；然而，热效应不足以完全在更深的部分进行ZFT退火。目前，该区域的尿布被腐蚀和剥落。Bari Gad断层以南Tansen地区Chappani组的碎屑锆石没有显示出任何退火迹象，这表明推覆层从未覆盖分布在断层以南的LHS。在LHS的上部形成热敏打印；然而，热效应不足以完全在更深的部分进行ZFT退火。目前，该区域的尿布被腐蚀和剥落。Bari Gad断层以南Tansen地区Chappani组的碎屑锆石没有显示出任何退火迹象，这表明推覆层从未覆盖分布在断层以南的LHS。