摘要
喜马拉雅造山带是研究板块构造的天然实验室,位于造山带核心部位的大喜马拉雅岩系是揭示碰撞造山过程和造山带演化的关键。本文主要对亚东地区大喜马拉雅岩系中的花岗质片麻岩进行了岩相学、锆石和独居石UTh-Pb年代学以及全岩主微量地球化学研究。野外和显微结构特征观察表明,花岗质片麻岩的矿物组合为斜长石+钾长石+石英+黑云母+石榴石,岩石发生了部分熔融,经历了高角闪岩相至麻粒岩相的变质作用。年代学和全岩地球化学研究表明,花岗质片麻岩的原岩包括新元古代(~800 Ma)的花岗闪长岩和志留纪(~440 Ma)的花岗岩,二者均在中新世(~16 Ma)发生了变质作用。新元古代花岗闪长岩具有负的εHf(t)值(-16. 4^-12. 2),地壳Hf模式年龄为3. 11~2. 79 Ga,说明其起源于古老下地壳物质的部分熔融。新元古代花岗闪长岩和志留纪花岗岩具有相似的弧花岗质岩石地球化学特征,即具有高场强元素Nb、Ta、P和Ti的负异常。本次研究表明大喜马拉雅岩系经历了多期构造热事件,其不仅记录了新生代的碰撞造山作用,还记录了与新元古代与罗迪尼亚超大陆演化相关的岩浆热事件以及古生代冈瓦纳大陆拼合后的周缘安第斯型造山作用。
The Himalayan orogenic belt is a natural laboratory for studying plate tectonics. Located at the core of the Himalayan orogen, the Greater Himalayan Sequence( GHS) is the key to revealing the collisional orogenesis and orogenic evolution. This paper presents the petrography, zircon and monazite U-Th-Pb chronology and geochemistry of the GHS granitic gneisses from the Yadong area. The field survey and microstructure show that these rocks have the mineral assemblage of plagioclase + K-feldspar + quartz + biotite + garnet, and have experienced a metamorphism of the upper-amphibolite to granulite facies with partial melting. Chronology and geochemistry indicate that the protoliths of granitic gneisses include the Neoproterozoic(~ 800 Ma) granodiorite and the Silurian(~ 440 Ma) granite, both of which experienced metamorphism in Miocene(~ 16 Ma). The Neoproterozoic granodiorite has negative εHf( t) values of-16. 4 ^-12. 2, and crust model ages tCDMof 3. 11 ~ 2. 79 Ga,suggesting that the rock was derived from partial melting of the ancient lower crust. The Neoproterozoic granodiorite and Silurian granite have similar geochemical characteristics to arc granitic rocks, with negative anomalies of high field strength elements Nb, Ta, P and Ti. The present study reveals that the Greater Himalayan Sequence has experienced multistage tectono-thermal events, including not only the Cenozoic collisional orogeny but also the Neoproterozoic magmatism associated with the evolution of the supercontinent Rodinia as well as the surrounding Andean orogeny after the Paleozoic formation of Gondwana.
作者
董昕
田作林
DONG Xin;TIAN Zuo-lin(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2019年第4期431-452,共22页
Acta Petrologica et Mineralogica
基金
国家自然科学基金项目(41872070)
国家留学基金项目(201809110024)
中国地质调查局地质调查项目(12120114022801,12120115026801,DD20160022,DD20160201)~~
