阿尔泰南缘乌吐布拉克铁矿区花岗质岩石年代学及成因

Study on Chronology and Genesis of Granite in the Wutubulake Iron Deposit District,Southern Margin of Altay

本文对新疆阿尔泰南缘乌吐布拉克铁矿区斜长花岗岩和黑云母斜长花岗岩进行了锆石LA-ICP-MSU-Pb年龄测定,分别获得了385·6±2·3Ma(MSDW=0·13)和387·7±2·1Ma(MSDW=0·23)的谐和年龄,两者为中泥盆世早期同源岩浆侵入体。乌吐布拉克铁矿的形成与岩浆侵入活动密切相关,据此限定铁矿成矿时代略晚于388～386Ma,为中泥盆世早期成矿。乌吐布拉克斜长花岗岩与黑云斜长母花岗岩均具有高硅(SiO2=66·01%～79·14%)、富钠贫钾(Na2O>K2O)的特点。A/CNK{A/CNK=n(Al2O3)/[n(CaO)+n(Na2O)+n(K2O)]}值均小于1·1,表明两者为准铝质低钾花岗岩。微量元素表现为富集Th、Ta、Hf等高场强元素,亏损Rb、Ba、K、Sr、P大离子亲石元素。稀土元素表现为轻稀土相对富集,轻重稀土元素分馏明显(La/Yb)N=2·46～7·24,具有中等或强的Eu负异常。结合区域地质资料,认为乌吐布拉克矿区花岗岩形成于与板块俯冲有关的活动大陆边缘的陆缘弧环境中。

LA-ICP-MS U-Pb zircon dating on the plagiogranite and biotite plagiogranite from the Wutubulake iron deposit district,southern margin of Altay,Xinjiang,yielded concordant ages of 385.6～2.3 Ma（MSDW=0.13） and 387.7～2.1 Ma（MSDW=0.23）,indicates that the two comagmatic plutons were formed at the beginning of the Middle Devonian.The Wutubulake iron deposit is closely related to the magmatic intrusion,writers hereby confine the iron deposit formed at the beginning of the Middle Devonian appreciably later than 388-386 Ma.The Wutubulake plagiogranite and biotite plagiogranite are characterized by enrichment of silica（SiO2=66.01%-79.14%） and Na（Na2OK2O）.The A/CNK{A/CNK=n（Al2O3）/[n（CaO）＋n（Na2O）＋n（K2O）]} ratios are less than 1.1,indicates that both of them are weakly peraluminous.Geochemically,the Wutubulake granites are enriched in Th,Ta,Hf,but depleted in Rb,Ba,K,Sr,P.The REE patterns are characterized by enrichment of LREE[（La/Yb）N=2.46-7.24],with moderately or significantly Eu negative anomalies.In combination with previous studies,writers concluded that the Wutubulake plutons were formed in continental arc at active extensional continental margin setting related to the subduction of plate.