摘要
秦岭造山带是一条复合型大陆碰撞造山带,存在若干新元古代构造岩浆事件的遗迹,它们对深化认识南北秦岭汇聚-碰撞过程和Rodinia超大陆聚合具有重要意义。本文对南秦岭东部豆腐尖岩体英云闪长岩开展LA-ICP-MS锆石U-Pb年代学和全岩主微量元素地球化学研究。代表性样品的^(206)Pb/^(238)U加权平均年龄为860.7±6.0Ma,表明其形成时代为新元古代。岩石地球化学特征表现为高SiO_(2)(62.41%-68.89%)、高Al_(2)O_(3)(15.33%-17.33%),富Na_(2)O(4.23%-5.80%)和高Na_(2)O/K_(2)O比值(1.11-2.41),富Sr(>400×10^(-6)),低MgO(0.55%-2.08%),低Y(7.40×10^(-6)-18.20×10^(-6))、Yb(0.63×10^(-6)-1.62×10^(-6)),高Sr/Y比值(31.49-78.22),轻稀土元素显著富集[(La/Yb)_(N)>20],弱Eu正异常,具埃达克质岩特征。较高的K_(2)O含量(2.00%-4.31%)和低MgO以及显著的高La/Yb比值等特征指示,其具有典型高钾钙碱性埃达克质岩特征,很可能源于加厚下地壳的部分熔融,推测该岩体形成时南秦岭地壳厚度可能达到65 km。结合区域地质资料,认为豆腐尖岩体形成于陆-陆碰撞环境,是新元古代松树沟洋盆闭合后北秦岭和南秦岭碰撞造山的产物,是Rodinia超大陆聚合事件在该地区的岩浆响应。新元古代早期商南豆腐尖高钾钙碱性埃达克质岩的首次识别为限定南-北秦岭碰撞事件提供了有力约束。
The Qinling orogenic belt is a composite continental collision orogenic belt, which records Neoproterozoic tectono-magmatic events. It is of great significance for understanding the convergence and collision process of the North and South Qinling terranes, and the assemblageof Rodinia supercontinent. Zircon geochronology, whole-rock majorand trace elements geochemistry have been carried out for the Doufujian tonalites in the east of the South Qinling. Analyzed zircons yielded weighted mean ^(206)Pb/^(238)U age of 860.7±6.0 Ma, indicating magma emplaced in Neoproterozoic. The rocks werecharacterized by high SiO_(2)(62.41%-68.89%), Al_(2)O_(3)(15.33%-17.33%), Na_(2)O(4.23%-5.80%), and Na_(2)O/K_(2)O ratio(1.11-2.41). They are enriched in rich Sr(>400×10^(-6)), but low MgO(0.55%-2.08%), Y(7.40×10^(-6)-18.20×10^(-6)), Yb(0.63×10^(-6)-1.62×10^(-6)), with high Sr/Y ratio(31.49-78.22), they also significantly rich in light rare earth elements \[(La/Yb)_(N)>20], but show weak Eu positive anomaly. They have typical characteristics of adakite rocks. Their high K_(2)O content(2.00%-4.31%), low MgO and high La/Yb ratio indicate that the rocks are typical calc-alkaline adakiterocks. Parental magmas were likely originated from partial melting of the thickened lower crust, and the crust thickness of the South Qinling terrane may be up to 65 km.Combined with the regional geological data, it is suggested that the Doufujian tonalites were formed in a continental collision setting resulting from the collision between the North and South Qinling terranes after the closure of the Songshugou oceanic basin, and were the magmatic response of the Rodinia supercontinent aggregation. The first identification of the early Neoproterozoic calc-alkaline adakite provides a strong evidence for the South and North Qinling collision event.
作者
蔡文春
曾忠诚
赵鹏彬
杨宗永
李景晨
王明志
朱雪丽
张小明
CAI Wenchun;ZENG Zhongcheng;ZHAO Pengbin;YANG Zongyong;LI Jingchen;WANG Mingzhi;ZHU Xueli;ZHANG Xiaoming(Shaanxi Mineral Resources and Gieological Survey,Xi'an,710068;Shaanxi Institute of Geological Survey,Xi'an,710054;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing,100083;Institute of Gieochemistry,Chinese Acdemy of Sciences,Giuijyang,550081)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2021年第3期686-702,共17页
Acta Geologica Sinica
基金
陕西省公益性地质调查项目(编号20170103、20150103、20170102)
陕西省地质勘查基金项目(编号61201908335)联合资助成果。
关键词
埃达克质岩
U-PB年代学
新元古代
松树沟洋
碰撞造山
南秦岭
adakitic rocks
U-Pb chronology
Neoproterozoic
Songshugou oceanic basin
continental collision
South Qinling
