This study is concerned with the tectono‐thermal history of the Kathmandu nappe and the underlying Lesser Himalayan sediments (LHS) that are distributed in eastern Nepal. We carried out zircon fission‐track(ZFT) dating and obtained 16 ZFT ages from the eastern extension of the Kathmandu nappe, the Higher Himalayan Crystalline, Kuncha nappe, and the Main Central Thrust (MCT) zone. The ZFT ages of the frontal part of the Kathmandu nappe range from 13.0 ±0.8 Ma to 10.7 ±0.7 Ma and exhibit a northward‐younging tendency. These Middle Miocene ZFT ages indicate that the frontal part of the Kathmandu nappe remained at a temperature above 240 °C until the termination of its southward emplacement at 12–11 Ma. The ZFT ages of the LHS range from 11.1 ±0.9 Ma in the southern part of the Okhaldhunga Window to 2.4 ±0.3 Ma of the augen gneiss in the northern margin and also exhibit a northward‐younging age distribution. The ZFT ages show the northward‐younging linear distribution pattern (−0.16 Ma/km) along the across‐strikesection from the frontal part of the Kathmandu nappe to the root zone, without a significant age gap. This distribution pattern indicates that the Kathmandu nappe, the underlying MCT zone, and the Kuncha nappe cooled from the frontal zone to the root zone as a thermally united geologic body at a temperature below 240 °C. An older ZFT age (456.3 ±24.3 Ma), which was partially reset at the axial part of the Midland anticlinorium in the central part of the Okhaldhunga Window, was explained by downward heating from the “hot” Kathmandu nappe. The above evidence supported a model that southward emplacement of the hot Kathmandu nappe resulted in a thermal imprint on the upper part of the LHS; however, the lower part did not reach 240 °C.

中文翻译：

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在加德满都推覆带的东部延伸区，北向年轻的锆石裂变径迹年龄在13Ma至2Ma之间，而潜在的小喜马拉雅沉积物分布在Mt山的南部。珠穆朗玛峰

这项研究与加德满都推覆的构造-热史以及分布在尼泊尔东部的底层小喜马拉雅沉积物（LHS）有关。我们进行了锆石裂变径迹（ZFT）测年，并从加德满都推覆带的东部延伸，喜马拉雅高结晶线，昆察推覆带和主中心逆冲（MCT）带获得了16个ZFT年龄。加德满都尿布前部的ZFT年龄从13.0±0.8 Ma到10.7±0.7 Ma不等，呈北移趋势。这些中新世ZFT年龄表明，加德满都推覆带的前部一直保持在240°C以上的温度，直到在12-11 Ma处向南定位终止为止。LHS的ZFT年龄范围从Okhaldhunga窗南部的11.1±0.9 Ma到2.4±0。北部边缘的奥根片麻岩3 Ma，并且呈北向年轻年龄分布。ZFT年龄显示了从加德满都尿布的前部到根部的整个走向，北走向的线性分布模式（−0.16 Ma / km）。这种分布模式表明，加德满都的尿布，下层的MCT带和昆卡的尿布从额叶区域冷却到根部区域，成为温度低于240°C的热结合地质体。ZFT年龄较大（456.3±24.3 Ma），其在Okhaldhunga窗中央部分的Midland防潮层的轴向部分被重设，其原因是“热”的加德满都尿布向下加热。上述证据支持了这样一个模型，即热的加德满都尿布的向南置入会在LHS的上部造成热烙印。然而，下部未达到240℃。