赤峰—开源断裂在赤峰西部地段的构造形迹及其演化特征

为研究赤峰—开源断裂在赤峰西部地段的性质,笔者在1∶5万朝阳地幅、姜家营子幅区调工作中,利用岩石学、岩石地球化学、LA—ICP—MS锆石U—Pb测年等方法,对构造控制的多期次侵入岩进行构造环境研究。结果表明,晚泥盆世二长花岗岩年龄为382. 8±2. 1 Ma,形成于同碰撞挤压环境;晚泥盆世超基性岩年龄为378. 4±3. 2 Ma,形成于碰撞后裂谷拉张环境;早二叠世二长花岗岩、石英闪长岩年龄分别为280. 1±1. 5 Ma、275. 7±1. 8 Ma,形成于同碰撞挤压环境;晚三叠世、早白垩世花岗斑岩年龄分别为206±25 Ma和128. 8±1. 3 Ma,形成于非造山伸展拉张环境。构造带上带状构造的野外地质调查发现构造带经历了3期韧性和1期脆性变形,分别为晚泥盆世至晚石炭世北东东向右行正斜滑韧脆性剪切(构造内花岗斑岩脉年龄374. 2±2. 6 Ma),早二叠世北东东向左行正斜滑韧性剪切(构造内花岗斑岩脉年龄270. 3±1. 7 Ma),晚三叠世北西西向左行正斜滑韧脆性剪切(构造内辉长岩年龄247. 53±7. 4 Ma)和中侏罗世至早白垩世北东和北西向脆性断裂。显示赤峰—开源断裂在赤峰西部地段表现为多期次挤压、间歇伸展,并以挤压造山为主的构造-岩浆岩带。

Structure style and evolution features in western district of Chifeng of Chifeng-Kaiyuan Fault

To study the properties of western Chifeng section of Chifeng-Kaiyuan fault, the petrology, rock geochemistry and LA-ICP-MS zircon U-Pb dating are undertaken during the geological mapping of 1:50000 Chaoyang and Jiangjiaying maps to explore the tectonic environment of multi-stage structurally controlled intrusive rocks. The results show that the age of the Late Devonian monzonitic granites is 382.8 ±2.1 Ma, which were formed in the syn-collisional compression environment. The age of ultrabasic Late Devonian rocks is 378.4±3.2 Ma, which were formed in the extensional environment of post-collisional rift. The ages of Early Permian monzogranite and quartz diorite are 280.1±1.5 Ma and 275.7±1.8 Ma respectively, which were formed in the syn-collisional and extruding environment. The ages of Late Triassic and Early Cretaceous granite porphyries are 206±25 Ma and 128.8±1.3 Ma respectively, which were formed in the non-orogenic stretching and extensional environment. The field geological investigation of the band structure on the tectonic belt shows that the tectonic belt has experienced three stages of ductile deformations and one stage of brittle deformation, namely, Late-Devonian to Late Carboniferous NEE-trending right-lateral oblique slip ductile shear (the age of the structural porphyry veins is 374.2±2.6 Ma), Early Permian NEE left-lateral ductile shear(the age of the structural porphyry veins is 270.3±1.7 Ma), Late Triassic NWW left-lateral oblique slip ductile shear (the age of the structural gabbro is 247.53±7.4 Ma) and Middle Jurassic to Early Cretaceous NE and NW brittle fault. The results show that the Chifeng-Kaiyuan Fault appears in the western part of Chifeng as a tectonic-magmatic belt with multiple stages of compressions and intermittent extensions and is dominated by extruding orogens.