Late Cretaceous-Cenozoic Exhumation History of the L(u|¨)liang Mountains,North China Craton:Constraint from Fission-track Thermochronology

<正>The Liiliang Mountains,located in the North China Craton,is a relatively stable block,but it has experienced uplift and denudation since the late Mesozoic.We hence aim to explore its time and rate of the exhumation by the fission-track method.The results show that,no matter what type rocks are,the pooled ages of zircon and apatite fission-track range from 60.0 to 93.7 Ma and 28.6 to 43.3 Ma,respectively;all of the apatite fission-track length distributions are unimodal and yield a mean length of～13μm;and the thermal history modeling results based on apatite fission-track data indicate that the time-temperature paths exhibit similar patterns and the cooling has been accelerated for each sample since the Pliocene(c.5 Ma).Therefore,we can conclude that a successive cooling,probably involving two slow(during c.75-35Ma and 35-5Ma) and one rapid(during c.5 Ma-0 Ma) cooling,has occurred through the exhumation of the Liiliang Mountains since the late Cretaceous.The maximum exhumation is more than 5 km under a steady-state geothermal gradient of 35℃/km.Combined with the tectonic setting,this exhumation may be the resultant effect from the surrounding plate interactions,and it has been accelerated since c.5 Ma predominantly due to the India-Eurasia collision.