摘要
为进一步约束南岭地区复式岩体的形成机制和成岩动力学背景,本次研究选取南岭中段贵东复式岩体的沙溪花岗岩进行了野外地质、岩石学、岩石和Sr-Nd同位素地球化学、锆石U-Pb测年和Hf同位素研究。综合前人资料,系统探讨了沙溪花岗岩的岩浆源区性质、岩石成因及其地质意义。锆石U-Pb定年结果显示,花岗岩形成于晚侏罗世(1535±0.6 Ma)。其主要成岩矿物包括石英、碱性长石和斜长石,次要矿物为黑云母和白云母,属典型的碱性岩。岩石的主-微量及稀土元素分析显示,其具有富硅w(SiO_(2))=73.70%~76.81%、富碱w(K_(2)O+Na_(2)O)=7.71%~9.25%、高钾w(K_(2)O)=5.16%~6.38%、低镁w(MgO)=0.27%~0.38%和里特曼指数δ=1.76~2.76,属高钾钙碱性-钾玄岩系列;其A/CNK=1.09~1.26,表现出弱铝质-过铝质的地球化学特征;强烈亏损Ba、Nb、Sr、P和Ti、La/Yb=10.13~24.25、轻稀土富集和负Eu异常(δEu=0.17~0.31),具典型的右倾“海鸥型”稀土配分模式,同时具较高的10000×Ga/A_(l)=2.70~3.31和低Y/Nb=0.71~1.10;锆石饱和温度的变化范围为777~831℃,平均值为799℃,显示出典型的A1-型花岗岩的地球化学特征。锆石的ε_(Hf)(t)=-7.66~-10.45,平均值为-9.10,Hf同位素的T_(DM)^(2)平均值为1.8 Ga;全岩的εNd(t)=-11.95~-14.06,平均值为-12.6,T_(DM)的平均值为1.9 Ga。Sr-Nd-Hf同位素特征表明,沙溪花岗岩岩浆来自古元古代下地壳变质沉积岩的部分熔融。综合区域地质背景认为,沙溪花岗岩是古元古代下地壳中变质沉积岩部分熔融的产物,形成于古太平洋板块俯冲过程导致的弧后伸展背景。
Based on a comprehensive synthesis of previous data,this study investigates the Shaxi granite from the Guandong composite rock mass in the central section of the Nanling Range through field geological surveys,petrological analysis,rock and Sr-Nd isotopic geochemistry,zircon U-Pb dating,and Hf isotope analysis.The objectives are to constrain the formation mechanism and tectonic setting of the granite,as well as to explore the nature of the magma source,petrogenesis,and geological significance of the Shaxi granite.The results indicate that the zircon U-Pb dating of the Shaxi granite yields an age of 153.5±0.6 Ma(Late Jurassic).Petrological analysis reveals that the primary magmatic minerals of the Shaxi granite consist of quartz,alkali feldspar,and plagioclase,with biotite and muscovite as accessory minerals,exhibiting characteristics of a typical alkaline rock.Geochemical analyses of major,trace,and rare earth elements demonstrate that the Shaxi granite is silica-rich(w(SiO_(2))=73.70%-76.81%),alkaline(w(K_(2)O+Na_(2)O)=7.71%-9.25%),high in potassium(w(K_(2)O)=5.16%-6.38%),low in magnesium(w(MgO)=0.27%-0.38%),and has a Rittmann index(0)of 1.76-2.76,suggesting it belongs to the high-potassium calc-alkaline to potassic basalt series.The A/CNK ratio of the Shaxi granite ranges from 1.09 to 1.26,indicating weakly aluminous to peraluminous geochemical characteristics.The granite exhibits strong depletion in Ba,Nb,Sr,P,and Ti,with La/Yb ratios ranging from 10.13 to 24.25,enrichment in light rare earth elements,and negative Eu anomalies(δEu=0.17-0.31),displaying a typical right-leaning"seagull-type"rare earth element distribution pattern.Additionally,it has a high 10,000×Ga/A_(l)ratio(2.70-3.31)and low Y/Nb ratios(0.71-1.10).The zircon saturation temperatures of the Shaxi granite range from 777 to 831℃(average 799℃),consistent with typical geochemical features of A1-type granite.The zircon&μ(t)values range from-7.66 to-10.45(average-9.10),with an average Hf isotope TpM age of 1.8 Ga,while the whole-rock ena(t)values range from-11.95 to-14.06(average-12.6),with an average Tpm age of 1.9 Ga.Analysis of Sr-Nd-Hf isotopic characteristics suggests that the magma of the Shaxi granite was derived from partial melting of metamorphosed sedimentary rocks in the Lower Proterozoic lower crust.Combined with the regional geological setting,the Shaxi granite is interpreted as the product of partial melting of Lower Proterozoic lower-crustal metamorphic sedimentary rocks,formed in a back-arc extensional environment induced by the subduction of the ancient Pacific Plate.
作者
李开智
向安平
钟凌林
唐尧
刘洪
欧阳渊
LI Kaizhi;XIANG Anping;ZHONG Linglin;TANG Yao;LIU Hong;OUYANG Yuan(Chengdu Institute of Environmental Geology and Resources Development Co.,LTD.,Chengdu,Sichuan 610218,China;Chengdu Center of China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu,Sichuan 610218,China;College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu,Sichuan 610059,China;College of Earth Sciences,Jilin University,Changchun,Jilin 130012,China)
出处
《矿物岩石》
北大核心
2025年第2期15-28,共14页
Mineralogy and Petrology
基金
广东省重要成矿区稀土资源评价项目(编号:2023-1)
西南三江成矿带战略性矿产调查项目(编号:DD20240070)。
关键词
岩石地球化学
A-型花岗岩
晚侏罗世
沙溪岩体
韶关
petrogenesis
A-type granite
late Jurassic
Shaxi pluton
Shaoguan area of Guangdong province
作者简介
第一作者:李开智,男,27岁,硕士研究生,地质工程专业,研究方向:矿产资源勘查与评价.E-mail:1421720950@qq.com;通信作者:向安平,男,38岁,高级工程师(博士),矿产普查与勘探专业,研究方向:矿产资源勘查与评价.E-mail:136095387@qq.com。
