(1. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院，長沙410083；
2. 湖南省地質(zhì)調(diào)查院，長沙 410116；
3. 中國科學(xué)院地球化學(xué)研究所 地球內(nèi)部物質(zhì)高溫高壓院重點實驗室，貴陽 550081)
摘 要: 研究了新疆可可托海3號偉晶巖脈多個結(jié)構(gòu)帶中鋯石U-Pb定年及鋯石Hf同位素組成，旨在厘定3號偉晶巖脈形成及巖漿-熱液演化的時限，探討巖漿形成的物源特征及大地構(gòu)造背景。鋯石的BSE、CL特征顯示，可可托海3號脈巖漿結(jié)晶鋯石普遍遭受了蛻晶化、流體交代和不同程度重結(jié)晶等作用。鋯石的LA-ICP-MS U-Pb定年結(jié)果顯示，3號偉晶巖脈巖鐘體部分中II帶、IV帶和V帶以及緩傾斜部分中II帶分別形成于(211.9±3.2)、(214.9±2.1)、(212±4.1)和(212.0±1.8) Ma，指示巖漿階段時限從~220 Ma至215 Ma，巖漿-熱液過渡階段時限從215 Ma至209 Ma，熱液階段時限從209 Ma至195 Ma。3號偉晶巖脈巖鐘體部分中IV帶和V帶鋯石Hf同位素組成變化于+1.25~+2.39之間，二階段模式年齡變化于1103~1173 Ma之間，指示形成3號偉晶巖脈的巖漿很可能與中亞造山帶在三疊紀(jì)為陸-陸碰撞后的伸展構(gòu)造背景下導(dǎo)致加厚下地殼沉積物減壓熔融有關(guān)。
關(guān)鍵字: 鋯石U-Pb定年；Hf同位素組成；可可托海3號脈
（1. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;
2. Hunan Institute of Geological Survey, Changsha 410116, China;
3. Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 55081, China）
Abstract:This study presents zircon U-Pb dating and Hf isotope of the several textural zones of the Koktokay No.3 pegmatite, so as to declare the intrusion age and evolution time limitation of the pegmatite, and explore the geochemical characteristics of the source and tectonic setting of the pegmatite-forming magma. The results show that zircons from the studied pegmatite are commonly suffered from metamictization, fluid metasomatism and recrystallization based on back-scattered electron (BSE) and catholuminescence (CL) images. The result of zircon LA-ICP-MS U-Pb dating shows that the formation ages of II, IV and V zones from the “cupola” part and II zone from the plate part of the Koktokay No.3 pegmatite are (211.9±3.2), (214.9±2.1), (212.0±4.1) and (212.0±1.8) Ma, respectively, indicating that the time limitations for magmatic stage, magmatic-hydrothermal stage and hydrothermal stage last from about 220 Ma to 215 Ma, from 215 Ma to 209 Ma, and from 209 Ma to 195 Ma. The zircon Hf isotopic compositions of IV and V zones from the cupola part of the pegmatite are varied in a narrow range (in the range of +1.25~+2.39), with two-stage model ages of 1103-1173 Ma, suggesting that the petrogenesis of the pegmatite-forming magma was probably associated with decompression melting of thickened lower crust under continent-continent post-collisional extensional setting of the Central Asia Organic Belt (CAOB) in Triassic.
Key words: zircon U-Pb dating; Hf isotope; Koktokay No.3 pegmatite
