摘要
本文通过几何学与运动学等构造变形分析,勾勒出南秦岭佛坪地区龙草坪混合岩化片麻岩穹隆、佛坪县城片麻岩穹隆以及秧田坝—十里铺走滑剪切带的基本形态。同时,对该区混合岩、麻粒岩以及变形花岗岩进行了系统的岩石学与年代学研究。结果表明,混合岩的锆石具有明显的核-边结构,其中中色体年龄集中在(211.8±1.9)Ma,浅色体中锆石边部年龄为(203.7±1.6)Ma,而继承核部则显示了与本地区泥盆纪变质沉积岩中碎屑锆石一致的年龄谱系。麻粒岩的锆石也具有明显的核-边结构,核与边分别得到(201.5±7.0)Ma和(188.1±1.5)Ma的加权平均年龄。伟晶岩和细粒花岗岩样年龄分别为(200.4±2.0)Ma和(201.1±1.5)Ma,误差范围内一致。穹隆一带的副片麻岩和走滑剪切带南侧变质沉积岩分别得到(198.1±2.2)Ma和(196.1±2.1)Ma的变质年龄。佛坪县城片麻岩穹隆一带的变形花岗岩年龄为(205.5±3.0)Ma。综合以上构造变形与变质-深熔-岩浆作用的研究,我们构建了佛坪地区早中生代构造演化序列,并提出片麻岩穹隆侵位过程中得到了作为勉略带东侧部分的秧田坝—十里铺韧性走滑剪切带活动的促进。并认为南秦岭构造带至少在217~212Ma之前仍处于俯冲环境,于211~201Ma进入同碰撞背景,并于200~190Ma完成同碰撞向伸展体制的转变。
In this study, based on an analysis of geometry and kinematics, the authors outlined a framework of Longcaoping migmatitic gneiss dome, Foping County gneiss dome and Yangtianba–Shilipu strike-slip shear zone. This paper also presents a combined petrologic and geochronologic study of migmatites, granulites and deformed granitoids from Foping area in South Qinling belt. Zircons from migmatite show distinct core-rim structure. The mesosome of migmatite yielded a weighted mean age of (211.8±9) Ma, while the leucosome contains Late Triassic zircon rims with U-Pb age of (203.7±1.6) Ma and detrital zircon cores with age spectrum analogous to that of the Devonian metasedimentary rocks from Foping area. Zircons from granulite also show distinct core-rim structure, with U-Pb age of (201.5±7.0) Ma for the core and (188.1±1.5) Ma for the rim. The pegmatite and granite dikes recorded similar ages at (200.4±2.0) Ma and (201.1±1.5) Ma, while two gneisses yielded slightly younger ages at (198.1±2.2) Ma and (196.1±2.1) Ma. The deformed granite yielded a weighted mean age of (205.5±3.0) Ma. Combining the tectonic analysis with the study of metamorphism, anataxis and magmatism, the authors constructed an Early Mesozoic tectonic evolution sequence and put forward the opinion that the activation of the Yangtianba–Shilipu strike-slip shear zone facilitated the emplacement of gneiss domes. It is also held that the South Qinling belt was under a subduction setting prior to 217~212 Ma, collision setting in 211~201 Ma and post-collision setting during 200~190 Ma.
作者
刘志慧
陈龙耀
曲玮
胡娟
刘晓春
LIU Zhi-hui;CHEN Long-yao;QU Wei;HU Juan;LIU Xiao-chun(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081;School of Earth and Space Sciences,Peking University,Beijing 100871)
出处
《地球学报》
EI
CAS
CSCD
北大核心
2019年第4期545-562,I0001-I0009,共27页
Acta Geoscientica Sinica
基金
国家重点基础研究发展规划项目(编号:2015CB856104)
国家自然科学基金项目(编号:41872059
41472064)联合资助~~
