CAJ | 학술논문

对川陕交界地区刘家坪花岗岩岩体进行了系统的锆石 U-Pb 年代学和地球化学研究,重点讨论了岩体的成因及其构造意义。测试结果显示,刘家坪花岗岩加权平均年龄值为825.9±7.8 Ma,属新元古代中期；岩石低 K富 Na,显示硅过饱和,w(SiO2)%平均为75.32,并伴有过 Al 质特征；稀土元素丰度较低,∑REE 为(182.13~243.76)×10-6,平均为197.29×10-6,显示 LREE 富集、HREE 相对亏损的特征,稀土元素球粒陨石配分模式图表现为右倾“海鸥”型,并且具有明显的 Eu 负异常(δEu 平均为0.57)；微量元素中 Nb/Ta、Rb/Sr 的结果及 Mg#值综合显示岩浆来源主要为下地壳物质的部分熔融。岩石具有 A 型花岗岩特征,形成于碰撞期后的伸展构造背景,据此推测碧口地块与扬子地块在825 Ma 之前曾发生碰撞造山作用。两者的拼合模式为从北东到南西的剪刀式拼合。
대천협교계지구류가평화강암암체진행료계통적고석 U-Pb 년대학화지구화학연구,중점토론료암체적성인급기구조의의。측시결과현시,류가평화강암가권평균년령치위825.9±7.8 Ma,속신원고대중기；암석저 K부 Na,현시규과포화,w(SiO2)%평균위75.32,병반유과 Al 질특정；희토원소봉도교저,∑REE 위(182.13~243.76)×10-6,평균위197.29×10-6,현시 LREE 부집、HREE 상대우손적특정,희토원소구립운석배분모식도표현위우경“해구”형,병차구유명현적 Eu 부이상(δEu 평균위0.57)；미량원소중 Nb/Ta、Rb/Sr 적결과급 Mg#치종합현시암장래원주요위하지각물질적부분용융。암석구유 A 형화강암특정,형성우팽당기후적신전구조배경,거차추측벽구지괴여양자지괴재825 Ma 지전증발생팽당조산작용。량자적병합모식위종북동도남서적전도식병합。
The Liujiaping granite intrusion is located in Sichuan-Shaanxi border area.The study of the zircon U-Pb geochronology and the geochemistry of the granite aim at discussing its formation and tectonic significance.The results show that the crystallization age of the granite is 825.9±7.8 Ma,which belongs to the mid-Neoproterozoic.The geochemistry analysis shows that the intrusion is low in potassium and rich in sodium and silica (with the average SiO2 being 75. 32%),with peraluminous characteristics.The abundance of the ∑ REE varies in the range of (182.13-243.76 )× 10 -6 ,with 1 97.29 × 10 -6 on average,which shows an enrichment of the LREE and a depletion of the HREE.Chondrite-normalized REE patterns are of the right sea-gull oblique type with the δEu being 0.57,showing a significant negative Eu anomaly.The results of the Nb/Ta,Rb/Sr and Mg# show that the magmatic rocks of this region originated from the partial melting of the lower crust.With the characteristics of A type granites,the rock formed in the post-collision extensional tectonic setting,which indicates a collision had occurred between the Eastern Bikou terrane and the Yangtze block before 825Ma.The jointing mode of the two blocks is scissors joint from northeast to southwest.