燕山造山带中生代伸展构造特征及其板内造山意义研究

Based on the field mapping in key areas and reconnaissance along the master tectonic belts, the Mesozoic extensional tectonic framework in the middle and eastern part of the Yanshan orogenic belt has been identified following the integrated investigations of geometry, kinematics of extensional structures in the research area together with the geochronological analysis on the plutonic and volcanic rocks which bear age controls on the timing of deformation. The extensional tectonic framework in the area is characterized by a symmetric graben system with axis lying along the Jianping and Lingyuan counties of western Liaoning province southwestward to Pingquan and Kuancheng counties of Hebei province. The extensional deformation commenced early Cretaceous. It's proposed that a pure shear extensional model derived from the deep mantle process be more acceptable to explain the deformation of this extensional framework. .Most of the master extensional faults developed right behind the back of the existing thrusting front and underwent extensive deformation shorter after the ceasing of the thrusting deformation. It's reasonable to inferred the extensional tectonics as a post-thrusting extensional tectonics. The short time span between the compressive deformation and the following extensional deformation implies that the temperature at the Moho boundary be much higher than usual at least in middle and eastern part of the Yanshan belt during Mesozoic. Furthermore it might be sharing the same origin with the profound and widespread plutonism and volcanism in this area during the Mesozoic..A so-called "Indosinia" cross-section in the middle Yanshan belt often cited as a line of important evidence showing the early Mesozoic deformation in Yanshan area and North China has been disaffirmed in terms of the geochronological analysis in the conduction of this project. The 40Ar/39Ar age dating on the volcanic rocks right above the unconformity and the tectonic comparison with surrounding areas indicate that the deformation underneath the unconformity be formed from Later Jurassic to middle Early Cretaceous instead of pre-Early Jurassic. .

揭示燕山造山带中生代伸展构造的几何学与运动学、形成时代与活动期次，定量估算伸展构造变形量及其在造山带形成中的地位和作用。查明区内伸展构造与逆冲推覆构造及岩浆活动之间的相互关系，建立研究区伸展构造形成模式，为全面认识板内造山作用过程提供科学依据。.