摘要
目前普遍认为,在早中生代华南与华北板块全面碰撞造山后,秦岭造山带在晚侏罗世-早白垩世经历了强烈的陆内造山作用。尤其在南秦岭的大巴山地区,发育了大规模逆冲推覆构造。然而,秦岭造山带其他构造单元对此次造山事件的响应尚不明确。北秦岭构造带内发育的晚侏罗世-早白垩世沉积地层,为探讨这一造山事件提供了理想的载体。本文以北秦岭南召地区马市坪盆地晚侏罗世-早白垩世地层为研究对象,开展了系统的磁组构和古地磁研究。磁组构结果表明,马市坪盆地的晚侏罗世-早白垩世地层发育NW向磁线理,表现出明显的初始变形组构以及铅笔状组构特征。结合区域地质分析,认为盆地发育时受NE-SW向压应力控制。古地磁研究获得了南召地区马市坪盆地晚侏罗世古地磁极(58.6°N、208.3°E、A_(95)=13.1°)以及早白垩世古地磁极(64.9°N、224.0°E、A_(95)=13.7°)。选取同时代华北板块稳定古地磁极为参考极,计算得到马市坪盆地自晚侏罗世以来相对华北板块发生了15.2°±11.8°的顺时针旋转,自早白垩世以来发生了13.7°±11.4°的顺时针旋转。结合前人研究成果,本文认为秦岭造山带在晚侏罗世-早白垩世经历了一次广泛以NE-SW向挤压为主的陆内造山运动。在NE-SW方向持续构造缩短的同时,造山带东部上地壳物质普遍向东侧向挤出,并经历较大规模的顺时针旋转。
Following the collisional orogeny during the Late Triassic,the Qinling Orogenic Belt underwent a prolonged and intense intracontinental evolutionary process from the Late Jurassic to the Early Cretaceous.The South Qinling orogen,particularly in the Daba Mountains,is characterized by large-scale overthrust nappe structures.However,the response of the other tectonic units within the Qinling orogen remains ambiguous.In the North Qinling orogen,the Late Jurassic-Early Cretaceous sedimentary strata provide an ideal framework for investigating intracontinental orogeny.Consequently,detailed magnetic fabric and paleomagnetic analyses were conducted on the Upper Jurassic and Lower Cretaceous strata of the Mashiping Basin in the Nanzhao area of the North Qinling orogen.The magnetic fabric results revealed NW-trending magnetic lineations,exhibiting distinct initial deformation fabrics and pencil-shaped fabric characteristics.Based on these findings,we propose that shortening primarily controlled the basin deformation,with the maximum principal stress oriented in the NE-SW direction.Paleomagnetic analysis yielded Late Jurassic paleomagnetic poles(58.6°N,208.3°E,A_(95)=13.1°)and Early Cretaceous paleomagnetic poles(64.9°N,224°E,A_(95)=13.7°)for the Nanzhao area.By comparing these results with the coeval reference poles of the North China Block,we identified a 15.2°±11.8°clockwise rotation after the Late Jurassic and a 13.7°±11.4°clockwise rotation after the Early Cretaceous in the study area relative to the North China Block.Integrating these findings with previous research,it is inferred that the Qinling orogen experienced widespread intracontinental orogeny dominated by NE-SW compression during the Late Jurassic-Early Cretaceous.Concurrently,the eastern Qinling Orogenic Belt underwent eastward extrusion and clockwise rotation relative to the South and North China blocks,while continuous structural shortening occurred along the NE-SW direction.
作者
任刘凡
梁文天
申琪
蒋凯
司国浩
李建刚
REN Liufan;LIANG Wentian;SHEN Qi;JIANG Kai;SI Guohao;LI Jiangang(Department of Geology,Northwest University,Xi’an 710069,Shaanxi,China;State Key Laboratory of Continental Evolution and Early Life,Xi’an 710069,Shaanxi,China)
出处
《大地构造与成矿学》
北大核心
2025年第4期884-899,共16页
Geotectonica et Metallogenia
基金
第二次青藏高原科考项目(2019QZKK0708)
国家重点研发计划(2023YFF0803500)
中国博士后科学基金资助项目(2023M742824)
国家资助博士后研究人员计划(GZC20232145)联合资助。
关键词
磁组构
古地磁学
构造旋转
晚中生代
北秦岭
magnetic fabric
paleomagnetism
tectonic rotation
Late Mesozoic
North Qinling
