摘要
宽坪杂岩是连接北秦岭构造带和华北板块的重要岩石-构造单元之一,其物质组成和变质变形特征可为探讨北秦岭构造带与华北板块构造关系及演化提供重要证据。本文在已有研究基础上,对宝鸡-眉县-洛南一带宽坪变碎屑岩进行了系统的岩石学、矿物学和碎屑锆石U-Pb年代学研究。结果表明,宽坪碎屑岩最年轻碎屑锆石年龄峰值为~550Ma,最主要碎屑锆石年龄集中区为~2.5Ga和1.0~0.9Ga,次要年龄集中区为1.3~1.0Ga和850~750Ma。通过与周缘可能物源区的年代学特征对比揭示,宽坪碎屑岩物源主要来自北秦岭新元古代花岗岩与秦岭岩群副片麻岩,部分来自南秦岭和扬子板块北缘新元古代花岗岩以及太古宙基底岩系,缺乏华北板块物质;宽坪碎屑岩的碎屑锆石年龄谱特征与南侧的二郎坪碎屑岩近乎一致,暗示两者可能形成于同一沉积盆地。相平衡模拟结果显示,洛南红土岭宽坪杂岩含石榴子石石英片岩记录了顺时针P-T演化轨迹,峰期变质条件为P=7.17~7.92kbar,T=557~563℃,形成于大陆碰撞过程。结合前人报道宽坪杂岩~440Ma的变质年龄,我们认为在早志留世时期宽坪和二郎坪沉积盆地闭合,北秦岭构造带与华北板块碰撞形成现今的构造格局,在此之前北秦岭构造带与华北板块不具有亲缘性。
As one of the most important petro-tectonic units connecting the North Qinling Belt(NQB)and the North China Craton(NCC),the composition and metamorphism of the Kuanping Complex can provide important constrains for the tectonic evolution of the NQB and the relationship between the NQB and the NCC.In this contribution,we conducted petrography,mineral chemistry and LAICP-MS zircon U-Pb dating on the metaclastic rocks from the Kuanping Complex in Baoji-Meixian-Luonan areas.Detrital zircon U-Pb dating yields the youngest magmatic ages of~550 Ma,two dominant age groups at~2.5 Ga and 1.0~0.9 Ga,and two sub-dominant age groups at 1.3~1.0 Ga and 850~750 Ma,respectively.Comparing the detrital zircon age spectrum with all possible clastic provenances,it is suggested that the provenances of the Kuanping clastic rocks were mainly the Neoproterozoic granite and gneisses in the NQB,and subordinately the Neoproterozoic granite and the Archean basement rocks in the South Qinling Belt(SQB)and the Yangtze Craton(YZC),rather than rocks in the NCC.And the Kuanping clastic rocks display almost the same age spectrum with that of the Erlangping clastic rocks,indicating that they were probably formed in the same sedimentary basin.Phase equilibrium modelling predicts that the garnet-bearing quartz schist from Luonan area underwent a clockwise P-T path with peak P-T conditions of 7.17~7.92 kbar and 557~563℃,suggesting a continental collision tectonic environment.Together with the reported metamorphic age of~440 Ma for the Kuanping Complex,we proposed that the closure of the Kuanping-Erlangping sedimentary basin occurred at the Early Silurian,which resulted in the collision of the NQB and the NCC.Before that,the NQB has not any tectonic affinities with the NCC.
作者
王海杰
陈丹玲
任云飞
朱小辉
宫相宽
WANG HaiJie;CHEN DanLing;Ren YunFei;ZHU XiaoHui;GONG XiangKuan(State Key Laboratory of Continental Dynamics,Department of Geology,Northuest Uninersity,Xi'an 710069,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第5期1489-1507,I0011-I0017,共26页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41972058、41802056)资助。
