發(fā)布時(shí)間：2018-07-15 11:27

【摘要】：義敦島弧是位于松潘—甘孜褶皺帶和羌塘地體之間的三疊紀(jì)火山島弧。稻城巖體和海子山巖體分別為義敦島弧上出露的晚三疊世和白堊紀(jì)花崗質(zhì)巖體。結(jié)合巖石地球化學(xué),以及偏光顯微鏡和電子探針(EPMA)、掃描電鏡(SEM)對上述巖體進(jìn)行了系統(tǒng)的礦物學(xué)研究,結(jié)果表明:兩個巖體的主要造巖礦物為斜長石(中長石—更長石),鉀長石(正長石)、石英和黑云母(鐵葉云母—鐵質(zhì)黑云母),副礦物為鋯石、榍石、磁鐵礦和磷灰石等;黑云母的成分表明兩個巖體的源區(qū)均為殼幔混源。稻城巖體屬高鉀鈣堿性系列,具過鋁質(zhì)特征的花崗巖,海子山巖體為高鉀鈣堿性—鉀玄巖系列,同樣具過鋁質(zhì)特征。根據(jù)鋯元素飽和濃度溫度計(jì)和稀土元素飽和濃度溫度計(jì)對兩個巖體進(jìn)行了溫度限定,稻城巖體巖漿形成的平均上限溫度為783℃,海子山巖體巖漿形成時(shí)的平均上限溫度為844℃。結(jié)合前人研究結(jié)果,筆者等認(rèn)為稻城巖體為高分異I型花崗巖,可能為與揚(yáng)子克拉通有關(guān)的晚古元古代至早中元古代的下地殼物質(zhì),在甘孜—理塘洋向西俯沖和閉合之后的弧—陸同碰撞背景下,因幔源巖漿的底侵作用而發(fā)生部分熔融,同時(shí)伴有少量的虧損地幔成分加入,因密度上升至中上—上地殼深度侵位,并且侵位后經(jīng)歷了快速的冷卻過程,在侏羅紀(jì)之初冷卻至300℃以下;海子山巖體為與俯沖有關(guān)的造山后伸展環(huán)境下形成的白堊紀(jì)A2型花崗巖,巖漿來源同樣為地殼物質(zhì)伴有少量地幔物質(zhì)混合而成,且在地殼中侵位深度較淺,之后經(jīng)歷快速的冷卻過程。
[Abstract]:Yidun island arc is a Triassic volcanic island arc between Songpan-Ganzi fold belt and Qiangtang terrane. The Daocheng and Haizishan intrusions are late Triassic and Cretaceous granitic rocks respectively. Combined with rock geochemistry, polarizing microscope and electron probe (EPMA) and scanning electron microscope (SEM), a systematic mineralogical study of the rock mass was carried out. The results show that the major rock-forming minerals of the two bodies are plagioclase (mesopaglitic feldspar), potash feldspar (orthoclase), quartz and biotite (Ironite-ferric biotite), and accessory minerals such as zircon, sphene, magnetite and apatite. The composition of biotite indicates that the source regions of the two rocks are crust-mantle mixing. The Daocheng rock body belongs to the high-potassium calc-alkaline series, with peraluminous characteristics, and the Haizishan rock body is a high-potassium calc-alkaline-potash series, which is also peraluminous. According to zirconium saturation concentration thermometer and rare earth element saturation concentration thermometer, the average upper limit temperature of magma formation is 783 鈩，

本文編號：2123908