滇西腾冲地块芒章花岗岩年代学、岩石地球化学、锆石Hf同位素组成及其地质意义  

Geochemistry,U-Pb dating and Hf isotope characteristics of Mangzhang granite in Tengchong block

作　　者：王硕 方乙[1,2] 唐晓源 代君瑶 王孟旭 WANG Shuo;FANG Yi;TANG Xiaoyuan;DAI Junyao;WANG Mengxu(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation,Ministry of Natural Resources,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]西南石油大学地球科学与技术学院,四川成都610500 [2]成都理工大学自然资源部构造成矿成藏重点实验室,四川成都610059

出　　处：《沉积与特提斯地质》2025年第1期187-199,共13页Sedimentary Geology and Tethyan Geology

基　　金：自然资源部构造成矿成藏重点实验室开放基金(gzck202004)。

摘　　要：位于三江特提斯构造带的腾冲地区中生代—新生代岩浆活动频繁,发育大量花岗岩。本文通过对腾冲地块的芒章花岗岩进行岩相学、全岩地球化学、锆石U–Pb年代学及Hf同位素分析,探讨其岩石成因及地质意义。结果表明,区内岩石以正长花岗岩为主要类型,具有高硅(74.41%~76.55%)、富钾(K_(2)O/Na_(2)O值均大于1)、过铝质(A/CNK=1.34~1.48)特征,属于S型花岗岩。Eu、Sr等元素强烈负异常,Rb、Pb等元素明显富集,同时在芒章地区古近纪花岗岩Al_(2)O_(3)/(MgO+Fe O)–CaO/(MgO+FeO)图解中,样品投点分别落于变质泥质岩、变质杂砂岩和富黏土源岩区域内。研究样品具有变化范围较小的锆石ε_(Hf)(t)值为-9.14~-7.73,对应的二阶段模式年龄(t_(DM2))值为1699~1613 Ma。测得锆石U–Pb加权平均年龄为(49.81±0.35)Ma,表明岩浆侵位时间属于早始新世。上述特征表明区内花岗岩可能是中元古代变质基底发生部分熔融的产物,来源于古老富黏土的变质泥质岩及部分变质杂砂岩。结合前人研究成果,认为研究区内正长花岗岩与拉萨地块广泛发育的60~50 Ma、50~40 Ma的岩浆岩一致,形成于同碰撞环境,表明腾冲内部具有同碰撞特征的花岗岩是该时期印度板块与腾冲–拉萨地块俯冲碰撞活动的响应。The Tengchong area,situated within the Sanjiang Tethys tectonic belt,exhibits frequent Mesozoic-Cenozoic magmatic activity and a significant presence of granite.This study investigates the petrogenesis and geological significance of Mangzhang granite in the Tengchong block through petrography,whole rock geochemistry,zircon U-Pb chronology,and Hf isotope analyses.The results show that the main types of rocks in this area are syenite granite with high SiO_(2) contents(from 74.41%to 76.55%)and high potassium abundances(K_(2)O/Na_(2)O ratio is greater than 1),peraluminous(A/CNK value varies from 1.34 to 1.48),and belong to S-type granite.Eu and Sr are strongly negative anomalies,Rb and Pb are obviously enriched.At the same time,in the Al_(2)O_(3)/(MgO+FeO)−CaO/(MgO+FeO)diagram of Paleogene granite in the Mangzhang area,the samples fall in the metamorphic argillaceous rocks,metamorphic gritstone,and clay-rich source rocks.Zircon ε_(Hf)(t)values in this study range from-9.14 to-7.73,corresponding to a two-stage model age(tDM2)of 1699-1613 Ma.The weighted average age of zircon U-Pb is(49.81±0.35)Ma,indicating that the magma emplacement time belongs to the early Eocene.The above characteristics suggest that the granite in this area may be the product of partial melting of the Mesoproterozoic metamorphic basement,which is derived from the ancient clay-rich metamorphic argillaceous rocks and some metamorphic greywackes.Combined with previous research results,it is believed that the syenite granite in the study area,as well as the 60-50 Ma and 50-40 Ma magmatic rocks that widely developed in the Lhasa block formed in the same collision environment,which indicating that the Eocene granite with the characteristics of the same collision in Tengchong is a response to the subduction and collision between the Indian plate and Tengchong-Lhasa block in this period.

关 键 词：花岗岩类 锆石U–Pb年代学 地球化学 锆石HF同位素 腾冲地块 

分 类 号：P597.3[天文地球—地球化学] P548[天文地球—地质学]