低温热年代对黄陵隆起中新生代古地形的约束

低温热年代技术已经广泛应用于造山带的剥露作用和古地形演化的研究。本文对黄陵隆起进行了裂变径迹和(U-Th)/He热年代学研究,分析计算其隆升剥露速率和厚度,恢复黄陵隆起中新生代古地形。依据岩石样品冷却历史计算出的剥露速率以及剥露厚度结果,综合黄陵隆起现今地形起伏,均衡回弹作用以及古海平面变化情况,获得了黄陵隆起早侏罗世、早白垩世、晚白垩世、晚始新世以及现今5个时期的古地形变化情况。结果表明黄陵隆起地形表现为持续降低的趋势,并存在两期剧烈的隆升剥露阶段。分析认为,白垩纪(140~80 Ma±),黄陵隆起的快速隆升剥露作用与秦岭大别造山带大规模的挤压作用密切相关,晚始新世以来(40~0 Ma)黄陵隆起的快速抬升剥露作用则是对喜山期构造运动的响应。

Low-temperature Thermochronological Constraints on the Mesozoic-Cenozoic Paleotopograph in the Huangling Massif

Low-temperature thermochronology has widely been used to study the exhumation in the orogeny and the evolution of the paleotopograph. This paper studied the Mesozoic-Cenozoic exhumation rate, denudation thickness and paleotopographic evolution of the Huangling massif using fission track and (U-Th)/He data. Both the thermal history and the exhumation rate indicate that the Huangling massif experienced four evolution stages since the early Jurassic (ca. 200 Ma). They are (1) the slow cooling stage during Early Jurassic to Early Cretaceous (200~140 Ma) with exhumation rate of about 0.017 mm/a; (2) the rapid cooling stage during the Early Cretaceous to the Late Cretaceous (140~80 Ma), mainly cooled in 120~90 Ma, with average exhumation rate of about 0.22 mm/a; (3) the thermal stable stage from the Late Cretaceous to Late Eocene (80~40 Ma). In this period, most samples stayed in the partial annealing zoneand the average exhumation rate is 0.013 mm/a; (4) a new rapid cooling stage from Late Eocene to the present (40~0 Ma) with exhumation rate of 0.049 mm/a. Combining the exhumation results, current topography, balanced effects and the sea level changes, the palaeotopograph of the Late Triassic, Early Cretaceous, Late Cretaceous and Eocene was deciphered. The results show that the paleotopograph of the Huangling massif experienced a continuous decrease trend and existed two dramatic change stages. During the Cretaceous (140~80 Ma), the rapid uplift and exhumation of the Huangling massif was controlled by the large-scale compression coming from the Qinling-Dabie orogenic belt; the second rapid exhumation in the Huangling massif responded to the Himalayan movement since the Oligocene (40~0 Ma).