秦岭造山带中段中、新生代构造——热冷却过程

Tectono-thermal Cooling Process of the Central Qinling Orogenic Belt in the Meso-Cenozoic

以沙沟街—商丹断裂为界的南、北秦岭于中、新生代期间经历了不同的构造变形。采自秦岭造山带中段沙沟街韧性剪切带南北两侧岩体的^(40)Ar-^(39)Ar、MDD模式计算及磷灰石裂变径迹测量结果表明,秦岭造山带中新生代期间南北两侧表现出不同的冷却历史和抬升过程。北侧在140～118 Ma期间发生快速冷却,冷却速度为13℃/Ma;118～110 Ma期间相对缓慢冷却,其速度为0.83℃/Ma;100 Ma发生第二次快速冷却,速度为6.8℃/Ma。沙沟街韧性剪切带的南侧秦岭造山带除300～200Ma期间发生过快速冷却外,在180～90 Ma期间发生过快速冷却,其冷却速度为3℃/Ma。从118～90 Ma期间,南北秦岭具有类似的冷却过程。南北秦岭地区的岩体冷却过程的不同反映了秦岭造山带碰撞之后陆内造山隆升的不一致性,这与区内的构造作用过程相对应。

The northern and southern Qinling orogenic belts, separated by the Shagoujie—Shangdan fault, experienced different deformations during the Mesozoic-Cenozoic period. Using the cooling curves of K-feldspars obtained by the specific ^(40)Ar/^(39)Ar step heating procedure and multiple diffusion domain modeling (MDD model), together with the dating results of biotite, hornblende and apatite, this research determines the cooling history on both sides of the Shagoujie ductile shear zone. The results indicate that there are different cooling histories in the Meso-Cenozoic. The time of rapid cooling is 140～118 Ma with a cooling rate of 13℃/Ma in the north Qinling orogenic belt. But in the southern Qinling orogenic belt, the rapid cooling occurred during the periods of 300～200 Ma and 180～90 Ma. The different cooling histories of the southern and northern Qinling orogenic belts during 300～118 Ma indicate an inconsistent uplift of the orogenic belts after the intracontinental collision. But after 118 Ma, both southern and northern Qinling orogenic belts had the same cooling process.