徐學(xué)純,張行行,鄭常青,崔芳華,高 源,高 峰
吉林大學(xué)地球科學(xué)學(xué)院,長(zhǎng)春 130061
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遼西楊家杖子侵入巖地球化學(xué)和年代學(xué)特征及其與成礦的關(guān)系
徐學(xué)純,張行行,鄭常青,崔芳華,高 源,高 峰
吉林大學(xué)地球科學(xué)學(xué)院,長(zhǎng)春 130061
遼西楊家杖子地區(qū)位于華北板塊北緣,燕山褶皺帶東段。該區(qū)侵入巖主要有4種類(lèi)型:中粗粒鉀長(zhǎng)花崗巖、斑狀鉀長(zhǎng)花崗巖、似斑狀鉀長(zhǎng)花崗巖和細(xì)粒角閃二長(zhǎng)巖。其中:主體巖石為中粗粒鉀長(zhǎng)花崗巖、斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖,均呈較大的巖基出露,沿北東向展布,鋯石U-Pb同位素測(cè)年結(jié)果顯示其形成于早侏羅世(181~188 Ma);細(xì)粒角閃二長(zhǎng)巖多呈巖墻或巖脈產(chǎn)出,近南北向展布,鋯石U-Pb同位素測(cè)年結(jié)果顯示其形成于晚三疊世(227 Ma左右)。巖石地球化學(xué)分析結(jié)果顯示:斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖屬于弱過(guò)鋁質(zhì)高鉀鈣堿性系列巖石;細(xì)粒角閃二長(zhǎng)巖屬于準(zhǔn)鋁質(zhì)高鉀鈣堿性系列巖石。斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖富集高場(chǎng)強(qiáng)元素Th、La、Nd、Hf和Gd,虧損高場(chǎng)強(qiáng)元素Ti、Ho和大離子親石元素Ba、Sr;細(xì)粒角閃二長(zhǎng)巖富集高場(chǎng)強(qiáng)元素Gd、Er和大離子親石元素Ba、Sr,虧損高場(chǎng)強(qiáng)元素Nb、Hf、Ti、Pr、Y、Yb。稀土配分模式圖均為右傾型,輕稀土元素分餾明顯,重稀土元素分餾不明顯。研究表明該區(qū)中生代巖漿作用主要發(fā)生在早侏羅世,且與著名的楊家杖子鉬礦有著密切的成因聯(lián)系,而晚三疊世巖漿作用相對(duì)較弱。
遼西;楊家杖子;侵入巖;地球化學(xué);年代學(xué);楊家杖子鉬礦
遼西楊家杖子地區(qū)位于華北板塊燕山褶皺帶東段,以斑巖-矽卡巖型鉬礦而著稱(chēng)。許多專(zhuān)家學(xué)者對(duì)遼西地區(qū)侵入巖的年代學(xué)[1-4]和巖石地球化學(xué)[2-3,5-11]特征,礦床地質(zhì)特征、控礦構(gòu)造、成礦流體、成礦機(jī)制及成礦年齡等[12-20]方面做過(guò)較詳細(xì)的研究,并取得了一些統(tǒng)一認(rèn)識(shí)。前人認(rèn)為EW向和NE、NNE向斷裂控制了蘭家溝斑巖型鉬礦、楊家杖子斑巖-矽卡巖型鉬礦等Au、Cu、Mo、Pb、Zn多金屬礦床[16,18-20],同時(shí)指出控礦巖體屬于高分異I型花崗巖[8-10],其黑云母K-Ar年齡、Rb-Sr等時(shí)線和鋯石U-Pb年齡為181~193 Ma[1-4],蘭家溝斑巖鉬礦的輝鉬礦、矽卡巖Re-Os模式年齡和等時(shí)線年齡為181.6~191.0 Ma[12-16,20],成巖和成礦時(shí)間均屬于早侏羅世。而目前對(duì)于遼西地區(qū)中生代所處構(gòu)造環(huán)境的認(rèn)識(shí)卻存在較大爭(zhēng)議:部分學(xué)者認(rèn)為華北板塊北緣在三疊紀(jì)末期即開(kāi)始受到古太平洋俯沖的影響[8],燕山早期庫(kù)拉板塊向歐亞板塊俯沖,巖漿活動(dòng)強(qiáng)烈[2,21-23];部分學(xué)者認(rèn)為中生代從晚三疊世開(kāi)始,華北板塊北緣處于西伯利亞板塊向南擠壓,古太平洋板塊向歐亞板塊俯沖的應(yīng)力帶中[15],進(jìn)入侏羅紀(jì)以來(lái),作用最強(qiáng)的是伊佐奈歧板塊朝NW方向運(yùn)移、俯沖到東亞大陸之下,初生的太平洋板塊則在南半球微弱地向SW方向俯沖[24-25];還有學(xué)者認(rèn)為華北板塊中生代大規(guī)模巖漿活動(dòng)與太平洋板塊的俯沖無(wú)關(guān),可能相當(dāng)于幾個(gè)不同時(shí)期發(fā)育的長(zhǎng)英質(zhì)大火成巖省,與中生代東亞超級(jí)地幔柱的活動(dòng)有關(guān)[26-27]。出現(xiàn)上述分歧的主要原因是對(duì)該區(qū)侵入巖的類(lèi)型、產(chǎn)出狀態(tài)及分布特征缺少系統(tǒng)的研究。
筆者通過(guò)詳細(xì)的野外考察和系統(tǒng)采樣,對(duì)該區(qū)不同類(lèi)型的侵入巖進(jìn)行了巖石地球化學(xué)分析和鋯石U-Pb同位素測(cè)年,分析了該區(qū)中生代侵入巖的年代學(xué)格架、巖石成因及其形成時(shí)的構(gòu)造背景,并探討了侵入巖與楊家杖子鉬礦的關(guān)系。
遼西楊家杖子地區(qū)位于華北板塊膠遼陸塊秦皇島巖漿弧區(qū)[28],燕山褶皺帶東段,錦西--青龍山和女兒河斷裂之間,從山海關(guān)--北鎮(zhèn)隆起到北票凹陷的過(guò)渡帶。區(qū)內(nèi)的太古宙地質(zhì)體主要由大面積的TTG雜巖和少部分表殼巖系構(gòu)成。這些太古宙TTG主要形成于25 億a左右,中元古代--古生代以穩(wěn)定克拉通內(nèi)的沉積建造為主,晚古生代--早中生代為前陸盆地沉積,石炭紀(jì)發(fā)育海相、海陸交互相沉積,二疊紀(jì)發(fā)育海陸交互相、陸相紅層和蒸發(fā)巖,在早、中三疊世連續(xù)發(fā)育陸相紅層沉積[29],缺少明顯的巖漿活動(dòng)。但是由于早石炭世晚期古亞洲洋板塊向華北板塊之下俯沖,華北北緣轉(zhuǎn)化為活動(dòng)大陸邊緣,該區(qū)發(fā)育大量閃長(zhǎng)巖-石英閃長(zhǎng)巖-花崗閃長(zhǎng)巖和一些島弧火山巖[28]。在東北地區(qū),古亞洲洋的最終閉合時(shí)間最晚可能發(fā)生在中三疊世,自此以后,華北板塊進(jìn)入到環(huán)太平洋構(gòu)造體系和蒙古--鄂霍茨克構(gòu)造體系的演化階段[30]。
楊家杖子地區(qū)出露的主體侵入巖有4種類(lèi)型:北東側(cè)的中粗粒鉀長(zhǎng)花崗巖、斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖,分布較廣;南西側(cè)的細(xì)粒角閃二長(zhǎng)巖,分布較少(圖1)。
圖1 楊家杖子鉬礦區(qū)地質(zhì)圖(據(jù)腳注①修編)Fig.1 Geological sketch map of Yangjiazhangzi molybdenum deposits(according to the footnote① revision)① 張梅生.遼寧省1∶25萬(wàn)錦西市幅區(qū)調(diào)修測(cè)報(bào)告.長(zhǎng)春:吉林大學(xué),2013.
2.1 野外產(chǎn)狀及分布
中粗粒鉀長(zhǎng)花崗巖(B002-1,肉紅色,中粗粒結(jié)構(gòu),塊狀構(gòu)造,正長(zhǎng)石體積分?jǐn)?shù)約為40%,粒徑3~6 mm,石英體積分?jǐn)?shù)約為30%,粒徑3~6 mm,斜長(zhǎng)石體積分?jǐn)?shù)約為20%,粒徑2~4 mm,黑云母體積分?jǐn)?shù)約為10%,粒徑2~3 mm,圖2a)出露在楊家杖子地區(qū)的北東一側(cè),以巖基形式產(chǎn)出,呈北東向展布,是該區(qū)分布最廣的侵入巖類(lèi)型。該巖體與古生界寒武系、奧陶系、石炭系直接接觸,在與寒武系、奧陶系灰?guī)r的接觸帶,出現(xiàn)大理巖化、角巖化、矽卡巖化等現(xiàn)象,與楊家杖子鉬礦關(guān)系密切。
斑狀鉀長(zhǎng)花崗巖(STTW-06,肉紅色,斑狀結(jié)構(gòu),塊狀構(gòu)造,基質(zhì)為微晶質(zhì)結(jié)構(gòu),斑晶主要為石英,粒徑1~5 mm,正長(zhǎng)石,粒徑2~8 mm,圖2b)和似斑狀鉀長(zhǎng)花崗巖(STTW-07,肉紅色,似斑狀結(jié)構(gòu),塊狀構(gòu)造,基質(zhì)為細(xì)粒顯晶結(jié)構(gòu),斑晶主要為石英,粒徑2~3 mm,正長(zhǎng)石,粒徑2~4 mm,斜長(zhǎng)石,粒徑2~3 mm,圖2c)出露在楊家杖子地區(qū)北東的大北嶺隧道一帶,以巖株形式產(chǎn)出,呈北東向展布,通過(guò)野外觀察和前人資料[4,20]分析,屬于中粗粒鉀長(zhǎng)花崗巖的邊緣相。該巖體與元古宇青白口系、霧迷山組和古生界寒武系、奧陶系直接接觸;在與寒武系、奧陶系灰?guī)r的接觸帶,出現(xiàn)大理巖化、角巖化、矽卡巖化等現(xiàn)象,并產(chǎn)有鐵礦, 與楊家杖子鉬礦關(guān)系密切。經(jīng)過(guò)吉科1井的鉆探驗(yàn)證*徐學(xué)純,張行行,黃明國(guó),等.吉科1井鉆探報(bào)告.長(zhǎng)春:吉林大學(xué),2013.,發(fā)現(xiàn)楊家杖子向斜底部為斑狀鉀長(zhǎng)花崗巖,表明其與地表出露的斑狀鉀長(zhǎng)花崗巖連為一體。
細(xì)粒角閃二長(zhǎng)巖(STTW-08,灰綠色,細(xì)粒結(jié)構(gòu),斜長(zhǎng)石體積分?jǐn)?shù)約為40%,正長(zhǎng)石體積分?jǐn)?shù)約為30%,角閃石體積分?jǐn)?shù)約為20%,黑云母體積分?jǐn)?shù)約為10%,粒徑1 mm左右,圖2d)出露在楊家杖子地區(qū)南西松樹(shù)卯一帶,以巖墻或巖脈形式產(chǎn)出,呈南北向展布,分布較少。該巖體與古生界寒武系、奧陶系、石炭系、二疊系和中生界三疊系直接接觸,與前兩個(gè)巖體未見(jiàn)直接接觸關(guān)系。該巖體還含有閃長(zhǎng)巖[4],本文采樣為細(xì)粒角閃二長(zhǎng)巖。
2.2 巖相學(xué)特征
中粗粒鉀長(zhǎng)花崗巖:肉紅色,中粗粒結(jié)構(gòu),塊狀構(gòu)造。主要礦物為條紋長(zhǎng)石(體積分?jǐn)?shù)為50%),半自形板狀,條紋結(jié)構(gòu)明顯,粒徑3~6 mm;石英(30%),他形粒狀,粒徑3~6 mm;斜長(zhǎng)石(15%),半自形板狀,粒徑2~4 mm;黑云母(5%),半自形片狀,粒徑2~3 mm(圖3a)。副礦物組合為磁鐵礦-鋯石-磷灰石-榍石。
斑狀鉀長(zhǎng)花崗巖:肉紅色,斑狀結(jié)構(gòu),基質(zhì)為微晶質(zhì)結(jié)構(gòu),塊狀構(gòu)造。斑晶主要為條紋長(zhǎng)石、微斜長(zhǎng)石、斜長(zhǎng)石、石英,基質(zhì)主要為細(xì)粒長(zhǎng)英質(zhì)。堿性長(zhǎng)石主要為條紋長(zhǎng)石,他形板狀,條紋結(jié)構(gòu)明顯,粒徑1.5~9.0 mm;微斜長(zhǎng)石少量,半自形板狀,有格子雙晶,粒徑0.5~2.0 mm;斜長(zhǎng)石,半自形長(zhǎng)板狀,粒徑0.5~2.0 mm;石英,他形粒狀,表面干凈,粒徑1~5 mm(圖3b)。副礦物組合為磁鐵礦-鋯石-磷灰石。
似斑狀鉀長(zhǎng)花崗巖:肉紅色,似斑狀結(jié)構(gòu),基質(zhì)為細(xì)粒顯晶結(jié)構(gòu),塊狀構(gòu)造。斑晶主要為石英、正長(zhǎng)石、斜長(zhǎng)石,基質(zhì)由0.2 mm左右的長(zhǎng)英質(zhì)組成。石英,他形粒狀,外形不規(guī)整,粒徑1.5~2.0 mm;正長(zhǎng)石,半自形長(zhǎng)板狀,粒徑1.5~4.0 mm;斜長(zhǎng)石,半自形板狀,大多發(fā)生了絹云母化蝕變,粒徑1.5~4.0 mm(圖3c)。副礦物組合為磁鐵礦-磷灰石。
細(xì)粒角閃二長(zhǎng)巖:深灰色,細(xì)粒結(jié)構(gòu),塊狀構(gòu)造。主要礦物為斜長(zhǎng)石、正長(zhǎng)石、角閃石和少量黑云母、石英。斜長(zhǎng)石(40%)半自形板狀,呈小聚合體分布,部分斜長(zhǎng)石發(fā)生了高嶺土化蝕變,粒徑0.2~0.6 mm;正長(zhǎng)石(30%)半自形板狀,粒徑0.2~0.6 mm;角閃石(15%)他形粒狀,粒徑0.2~0.4 mm;黑云母(10%)半自形片狀,粒徑0.2~0.4 mm;石英(5%)他形粒狀,粒徑0.2~0.5 mm(圖3d)。副礦物組合為磁鐵礦-磷灰石。
本文選取了斑狀鉀長(zhǎng)花崗巖、似斑狀鉀長(zhǎng)花崗巖、細(xì)粒角閃二長(zhǎng)巖3種巖石樣品進(jìn)行了主量元素、微量稀土元素和年代學(xué)測(cè)試。
巖石樣品由哈爾濱礦產(chǎn)資源監(jiān)督檢測(cè)中心進(jìn)行處理。首先將樣品進(jìn)行粗碎,然后研磨至200目以下。主量元素和微量元素的分析測(cè)試由哈爾濱礦產(chǎn)資源監(jiān)督檢測(cè)中心完成。主量元素采用電感耦合等離子體發(fā)射光譜儀(IC-OES)測(cè)定,微量元素采用等離子體質(zhì)譜儀(ICP-MS)測(cè)試完成。樣品的主量元素質(zhì)量分?jǐn)?shù)由36種涵蓋硅酸鹽樣品范圍的參考標(biāo)準(zhǔn)物質(zhì)雙變量擬合的工作曲線確定,基體校正根據(jù)經(jīng)驗(yàn)的Traill-Lachance程序進(jìn)行,分析精度優(yōu)于 1%~5%。樣品中微量元素質(zhì)量分?jǐn)?shù)則使用USGS標(biāo)準(zhǔn)W-2和G-2及國(guó)內(nèi)標(biāo)準(zhǔn)GSR-1、GSR-2和GSR-3來(lái)校正,其分析精度一般為2%~5%。具體實(shí)驗(yàn)步驟、測(cè)試條件及實(shí)驗(yàn)原理參考文獻(xiàn)[31]。巖石地球化學(xué)數(shù)據(jù)處理及作圖采用路遠(yuǎn)發(fā)[32]的Geokit和Geoplot軟件完成。
a. 中粗粒鉀長(zhǎng)花崗巖;b. 斑狀鉀長(zhǎng)花崗巖;c. 似斑狀鉀長(zhǎng)花崗巖;d. 細(xì)粒角閃二長(zhǎng)巖。圖2 楊家杖子地區(qū)侵入巖的野外照片F(xiàn)ig.2 Field photos of the three intrusive rocks in Yangjiazhangzi
a. 中粗粒鉀長(zhǎng)花崗巖;b. 斑狀鉀長(zhǎng)花崗巖;c. 似斑狀鉀長(zhǎng)花崗巖;d. 細(xì)粒角閃二長(zhǎng)巖。均為正交偏光。Pl. 斜長(zhǎng)石;Aks. 堿性長(zhǎng)石;Bt. 云母;Q. 石英;Hbl. 角閃石。圖3 楊家杖子地區(qū)侵入巖的鏡下照片F(xiàn)ig.3 Microscope photographs of the intrusive rocks in Yangjiazhangzi
測(cè)年樣品破碎和鋯石挑選由河北省廊坊區(qū)域地質(zhì)礦產(chǎn)調(diào)查研究所實(shí)驗(yàn)室完成。將樣品機(jī)械性粉碎至80目,進(jìn)行重力分選,利用礦物介電分選儀進(jìn)行磁選,然后經(jīng)重液分選,最后在雙目鏡下選擇透明無(wú)包裹體無(wú)裂隙、晶形好、顆粒較大的鋯石單礦物粘在雙面膠上,用無(wú)色透明的環(huán)氧樹(shù)脂固定,待環(huán)氧樹(shù)脂固化以后將鋯石拋光,使其內(nèi)部結(jié)構(gòu)剖面充分暴露,進(jìn)行陰極發(fā)光(CL)顯微圖像的采集。
鋯石測(cè)年由天津地質(zhì)礦產(chǎn)調(diào)查研究所同位素測(cè)試實(shí)驗(yàn)室采用LA-MC-ICP-MS法完成。分析儀器為T(mén)hermo Fisher公司制造Neptune型質(zhì)譜儀和美國(guó)ESI公司生產(chǎn)的UP193-FX ArF準(zhǔn)分子激光器,激光束斑直徑為35 μm,頻率8~10 Hz,激光器能量密度13~14 J/cm2。實(shí)驗(yàn)中采用動(dòng)態(tài)變焦擴(kuò)大色散可以同時(shí)接收質(zhì)量數(shù)相差很大的U-Pb同位素,從而進(jìn)行鋯石U-Pb同位素測(cè)定。采樣方式為單點(diǎn)剝蝕,數(shù)據(jù)采集選用一個(gè)質(zhì)量峰采集一點(diǎn)的跳峰方式,每完成4~5個(gè)樣品的測(cè)定,插入測(cè)標(biāo)樣一次。采用TEMORA作為外部標(biāo)準(zhǔn)鋯石,利用NIST612作為外標(biāo)計(jì)算鋯石樣品的U、Pb質(zhì)量分?jǐn)?shù),采用208Pb對(duì)普通鉛進(jìn)行校正。采用中國(guó)地質(zhì)大學(xué)劉勇勝[33]博士研發(fā)的ICPMSDataCal程序和Ludwig[34]的Isoplot程序進(jìn)行數(shù)據(jù)處理。
4.1 主量元素特征
STTW-08與文獻(xiàn)中閃長(zhǎng)巖、二長(zhǎng)巖均屬于松樹(shù)卯巖體,STTW-06、STTW-07與文獻(xiàn)中花崗巖均屬于楊家杖子巖體,下同。Ir.Irvine分界線,上方為堿性,下方為亞堿性,據(jù)文獻(xiàn)[34]。1.橄欖輝長(zhǎng)巖;2a.堿性輝長(zhǎng)巖;2b.亞堿性輝長(zhǎng)巖;3.輝長(zhǎng)閃長(zhǎng)巖;4.閃長(zhǎng)巖;5.花崗閃長(zhǎng)巖;6.花崗巖;7.硅英巖;8.二長(zhǎng)輝長(zhǎng)巖;9.二長(zhǎng)閃長(zhǎng)巖;10.二長(zhǎng)巖;11.石英二長(zhǎng)巖;12.正長(zhǎng)巖;13.副長(zhǎng)石輝長(zhǎng)巖;14.副長(zhǎng)石二長(zhǎng)閃長(zhǎng)巖;15.副長(zhǎng)石二長(zhǎng)正長(zhǎng)巖;16.副長(zhǎng)正長(zhǎng)巖;17.副長(zhǎng)深成巖;18.霓方鈉巖/磷霞巖/粗白榴巖?;◢弾r、閃長(zhǎng)巖和二長(zhǎng)巖數(shù)據(jù)據(jù)文獻(xiàn)[2,5-7,10]。圖4 w(Na2O+K2O)-w(SiO2)巖石分類(lèi)圖Fig.4 w(Na2O+K2O)-w(SiO2) rock classification diagram
從表1和參考文獻(xiàn)[2,5-7,10]數(shù)據(jù)可以得知:斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖中w(SiO2)較高,為68.89%~77.38%,w(Al2O3)為12.79%~15.34%,w(Na2O)為2.64%~4.91%,w(K2O)為4.16%~5.53%;閃長(zhǎng)巖和二長(zhǎng)巖中w(SiO2)較低,為51.40%~61.73%,w(Al2O3)較高,為14.84%~16.58%,w(Na2O)為4.06%~4.91%,w(K2O)為2.68%~4.17%。經(jīng)過(guò)w(SiO2)-w(Na2O+K2O)巖石分類(lèi)圖解投影(圖4),分別落入花崗巖區(qū)、閃長(zhǎng)巖區(qū)和二長(zhǎng)巖區(qū)。花崗巖A/CNK值為0.87~1.16,A/NK值為0.97~1.25;二長(zhǎng)巖和閃長(zhǎng)巖A/CNK值為0.42~0.68,A/NK值為1.55~1.69。從A/NK-A/CNK圖解(圖5a)可以看出,斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖屬于弱過(guò)鋁質(zhì)系列巖石,細(xì)粒角閃二長(zhǎng)巖屬于準(zhǔn)鋁質(zhì)系列巖石。從w(K2O)-w(SiO2)圖解(圖5b)可以看出,大多數(shù)巖石樣品落入高鉀鈣堿性系列,顯示巖石相對(duì)富鉀的特征。花崗巖分異指數(shù)(DI)較高,為86.61~96.67,堿度率(AR)為1.90~2.45,固結(jié)指數(shù)(SI)為0.21~5.96,具有高分異I型花崗巖的特點(diǎn);二長(zhǎng)巖和閃長(zhǎng)巖DI為50.75~67.19,AR為3.2~6.1,SI為23.83~36.72。
4.2 微量元素和稀土元素特征
從表2、文獻(xiàn)[2]數(shù)據(jù)和微量元素蛛網(wǎng)圖(圖6a)可以看出:原始地幔標(biāo)準(zhǔn)化曲線向右傾斜,斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖富集高場(chǎng)強(qiáng)元素Th、La、Nd、Hf和Gd,虧損高場(chǎng)強(qiáng)元素Ti、Ho和大離子親石元素Ba、Sr;細(xì)粒閃長(zhǎng)巖富集高場(chǎng)強(qiáng)元素Gd、Er和大離子親石元素Ba、Sr,虧損高場(chǎng)強(qiáng)元素Nb、Hf、Ti、Pr、Y、Yb。其中細(xì)粒角閃二長(zhǎng)巖Nb的虧損可能指示地殼物質(zhì)參與了巖漿過(guò)程,斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖Ti的虧損可能指示其經(jīng)歷了一定程度的分異演化[8]。
從表2、文獻(xiàn)[2]數(shù)據(jù)和稀土配分模式圖(圖6b)可以看出:球粒隕石標(biāo)準(zhǔn)化曲線均為右傾型,輕稀土元素分餾明顯,重稀土元素分餾不明顯。斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖的δEu為0.36~0.61,具有明顯負(fù)Eu異常;細(xì)粒角閃二長(zhǎng)巖和細(xì)粒閃長(zhǎng)巖的δEu為0.72~0.91,具有微弱負(fù)Eu異常。從表2中得出3種巖石的稀土元素總量w(∑REE)為(70.30~220.32)×10-6,∑LREE/∑HREE為7.58~16.10,LaN/YbN為7.49~32.32。
5.1 斑狀鉀長(zhǎng)花崗巖
侵入巖鋯石CL圖像見(jiàn)圖7,其中斑狀鉀長(zhǎng)花崗巖中的鋯石(圖7a)分析數(shù)據(jù)見(jiàn)表3。鋯石為半自形到自形,粒徑70~250 μm,長(zhǎng)寬比為1.2~2.5,一般長(zhǎng)柱狀,具有振蕩環(huán)帶,Th、U質(zhì)量分?jǐn)?shù)較高,Th/U值較大(一般>0.4)。根據(jù)鋯石標(biāo)型和內(nèi)部結(jié)構(gòu)特征,判斷其為巖漿鋯石,這些鋯石的年齡在181 Ma左右。利用這些數(shù)據(jù)繪制的年齡諧和圖如圖8a,b,加權(quán)平均年齡為(181.30±0.95) Ma,MSWD=1.70,代表了斑狀鉀長(zhǎng)花崗巖的侵位時(shí)間為早侏羅世。
花崗巖、閃長(zhǎng)巖和二長(zhǎng)巖數(shù)據(jù)據(jù)文獻(xiàn)[2,5-7,10]。圖5 A/NK-A/CNK圖解(a)和w(K2O)-w(SiO2)圖解(b)Fig.5 A/NK-A/CNK diagram(a) and w(K2O)-w(SiO2) diagram(b)
樣品編號(hào)SiO2TiO2Al2O3FeOFe2O3MnOMgOCaONa2OK2OSTTW0674.380.2113.490.251.160.050.240.524.284.13STTW0776.620.1012.790.080.700.010.070.253.784.72STTW0858.340.6616.583.371.390.105.184.864.113.26樣品編號(hào)P2O5燒失量總計(jì)A/CNKA/NKDISIARR1R2STTW060.060.5499.221.081.1794.152.394.002457336STTW070.010.5899.541.091.1396.670.794.742658284STTW080.320.9899.060.871.6159.0129.922.0515471123
注:主量元素質(zhì)量分?jǐn)?shù)單位為%。
標(biāo)準(zhǔn)化值據(jù)文獻(xiàn)[35];花崗巖和閃長(zhǎng)巖數(shù)據(jù)據(jù)文獻(xiàn)[2]。圖6 楊家杖子地區(qū)侵入巖的微量元素蛛網(wǎng)圖(a)和稀土配分模式圖(b)Fig.6 REE chondrite normalization(a) and trace elements spider pattern(b) of the intrusive rocks in Yangjiazhangzi
樣品編號(hào)CrRbBaThUNbTaLaSTTW062.415236414.591.08422.01.5035.31STTW072.712517824.111.37929.70.7118.82STTW08202.4105138013.592.5927.80.7248.57樣品編號(hào)CePrSrNdZrHfSmEuSTTW0670.756.51313222.481404.0513.4090.508STTW0724.183.8556013.041125.3141.9710.235STTW0893.1311.180130645.531904.3497.0321.996樣品編號(hào)TiGdTbDyYHoErTmSTTW0612593.3920.4272.24514.0100.4791.6070.259STTW075991.9770.2931.78511.6800.4001.4040.250STTW0839806.1410.6692.72512.2800.4621.4770.165樣品編號(hào)YbLu∑REELREEHREELREE/HREELaN/YbNδEuSTTW061.8140.287149.48138.9710.5113.2213.960.45STTW071.8030.28370.3062.108.207.587.490.36STTW081.0780.164220.32207.4412.8816.1032.320.91
注:微量、稀土元素質(zhì)量分?jǐn)?shù)單位為10-6,下角N為球粒隕石標(biāo)準(zhǔn)化值。
5.2 似斑狀鉀長(zhǎng)花崗巖
似斑狀鉀長(zhǎng)花崗巖中的鋯石分析數(shù)據(jù)見(jiàn)表3。鋯石為半自形到自形,粒徑50~180 μm,長(zhǎng)寬比值為1.2~2.8,一般長(zhǎng)柱狀,具有振蕩環(huán)帶,根據(jù)鋯石標(biāo)型和內(nèi)部結(jié)構(gòu)特征,判斷其為巖漿鋯石(圖7b)。這些鋯石的年齡在188 Ma左右,利用這些數(shù)據(jù)繪制的年齡諧和圖如圖8c,d,加權(quán)平均年齡為(188.78±0.86) Ma,MSWD=0.77,代表似斑狀鉀長(zhǎng)花崗巖的侵位時(shí)間為早侏羅世。
5.3 細(xì)粒角閃二長(zhǎng)巖
細(xì)粒角閃二長(zhǎng)巖中的鋯石分析數(shù)據(jù)見(jiàn)表3。鋯石為他形到半自形,粒徑40~130 μm,長(zhǎng)寬比值為2.0~1.3,一般為長(zhǎng)柱狀,根據(jù)鋯石標(biāo)型和內(nèi)部結(jié)構(gòu)特征,判斷其為巖漿鋯石(圖7c)。這些鋯石的年齡在227 Ma左右,利用這些數(shù)據(jù)繪制的年齡諧和圖如圖8e,f,加權(quán)平均年齡為(227.80±1.10) Ma,MSWD=1.90,代表細(xì)粒角閃二長(zhǎng)巖的侵位時(shí)間為晚三疊世。
根據(jù)楊家杖子地區(qū)侵入巖的地質(zhì)產(chǎn)狀關(guān)系和鋯石U-Pb年代學(xué)研究,總結(jié)了該區(qū)侵入巖侵位年齡及其成礦時(shí)代如表4。
6.1 侵入巖形成的構(gòu)造環(huán)境
從巖石化學(xué)成分來(lái)看,楊家杖子地區(qū)大部分花崗質(zhì)侵入巖樣品在w(Al2O3)-w(SiO2)、w(K2O)-w(SiO2)和R1-R2判別圖解(圖9、圖10)上,投在后造山期花崗巖區(qū),而細(xì)粒閃長(zhǎng)巖和細(xì)粒角閃二長(zhǎng)巖樣品大多投在碰撞后隆起期花崗巖區(qū);從空間分布來(lái)看,楊家杖子地區(qū)的斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖呈NE、NNE向展布,如果是受到西伯利亞板塊的影響其產(chǎn)狀應(yīng)該呈東西向而不是NE、NNE向,因此西伯利亞板塊的影響可能不是導(dǎo)致其形成的直接因素;從成巖年齡來(lái)看,楊家杖子地區(qū)侵入巖的成巖年齡為181~193 Ma[1-4],該時(shí)期為早侏羅世,此時(shí)古亞洲洋已經(jīng)閉合,華北板塊所處的構(gòu)造域發(fā)生轉(zhuǎn)換,古太平洋板塊向西俯沖[30];從古地磁資料來(lái)看,燕山期作用最強(qiáng)的是伊佐奈歧板塊朝NW方向運(yùn)移、俯沖到東亞大陸之下,初生的太平洋板塊則在南半球微弱地向SW方向俯沖[24-25]。所以該區(qū)斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖的形成可能是受到伊佐奈歧板塊的影響。
圖7 楊家杖子地區(qū)侵入巖鋯石CL圖像及測(cè)點(diǎn)Fig.7 CL images of zircon and analysis spot from the intrusive rocks in Yangjiazhangzi
筆者認(rèn)同陳衍景等[36]的觀點(diǎn),即楊家杖子地區(qū)的細(xì)粒角閃二長(zhǎng)巖和閃長(zhǎng)巖可能形成于華北板塊與蒙古地塊之間發(fā)生強(qiáng)烈的陸陸碰撞而導(dǎo)致的地殼擠壓、縮短、疊覆、隆起階段[36]。而斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖則屬于后造山期高分異I型花崗巖,可能與伊佐奈歧板塊朝NW方向俯沖到華北板塊有關(guān),形成于華北板塊邊緣的后造山階段。
6.2 侵入巖與成礦關(guān)系
NE、NNE向錦西--青龍山斷裂和女兒河斷裂控制了楊家杖子斑巖-矽卡巖型鉬礦床、蘭家溝斑巖型鉬礦床等礦床的空間分布。楊家杖子鉬礦床的賦礦地層為寒武系、奧陶系碳酸鹽巖,控礦巖體巖石類(lèi)型主要為中粗粒鉀長(zhǎng)花崗巖、斑狀鉀長(zhǎng)花崗巖、似斑狀鉀長(zhǎng)花崗巖等中生代中淺層酸性侵入巖,這些侵入巖為鉬礦床提供熱源、物源。在吉科1井巖心中見(jiàn)到的圍巖蝕變以鉀長(zhǎng)石化、碳酸鹽化、螢石化為主,礦石礦物組合主要有黃鐵礦、磁鐵礦、黃銅礦、方鉛礦、輝鉬礦等,脈石礦物主要為石榴子石、透輝石、透閃石、陽(yáng)起石等矽卡巖礦物組合。
表3 楊家杖子地區(qū)3種侵入巖LA-ICP-MS鋯石U-Pb測(cè)年數(shù)據(jù)
表3(續(xù))
a,b. 斑狀鉀長(zhǎng)花崗巖;c,d. 似斑狀鉀長(zhǎng)花崗巖;e,f. 細(xì)粒角閃二長(zhǎng)巖。圖8 楊家杖子地區(qū)侵入巖的鋯石U-Pb年齡諧和圖Fig.8 Zircon U-Pb concordant diagram of the intrusive rocks in Yangjiazhangzi
測(cè)試礦物/巖石測(cè)試方法年齡/Ma資料來(lái)源細(xì)粒角閃二長(zhǎng)巖鋯石UPb227.80±1.10本文二長(zhǎng)閃長(zhǎng)巖黑云母KAr年齡202①細(xì)粒閃長(zhǎng)巖鋯石UPb221±2[4]斑狀鉀長(zhǎng)花崗巖鋯石UPb181.30±0.95本文似斑狀鉀長(zhǎng)花崗巖鋯石UPb188.78±0.86本文似斑狀二長(zhǎng)花崗巖RbSr等時(shí)線187[1]似斑狀二長(zhǎng)花崗巖黑云母KAr年齡183[1]似斑狀二長(zhǎng)花崗巖RbSr等時(shí)線181~193[2]二長(zhǎng)花崗巖鋯石UPb188~189[4]似斑狀二長(zhǎng)花崗巖鋯石UPb182±2[4]輝鉬礦ReOs等時(shí)線181.6±6.5[12]矽卡巖ReOs等時(shí)線187±2[13]輝鉬礦ReOs模式年齡187~191[16]輝鉬礦ReOs模式年齡183±3[20]
①遼寧省區(qū)域地質(zhì)測(cè)量隊(duì).遼寧省K-51-(25)(錦西幅)和K-51-(31)(興城幅)1∶20萬(wàn)區(qū)域地質(zhì)調(diào)查報(bào)告.大連:遼寧省區(qū)域地質(zhì)測(cè)量隊(duì),1983.
1.地幔斜長(zhǎng)花崗巖;2.破壞性活動(dòng)板塊邊緣(板塊碰撞前)花崗巖;3.板塊碰撞后隆起期花崗巖;4.晚造山期花崗巖;5.非造山區(qū)花崗巖;6.同碰撞花崗巖;7.造山期后花崗巖?;◢弾r、閃長(zhǎng)巖和二長(zhǎng)巖數(shù)據(jù)據(jù)文獻(xiàn)[2,5-7,10]。圖10 R2-R1判別圖解Fig.10 R2-R1 discrimination diagram
通過(guò)研究區(qū)侵入巖的鋯石U-Pb年齡測(cè)試,可以得出:楊家杖子地區(qū)侵入巖分別由227 Ma的印支晚期和181~188 Ma的燕山早期兩期侵入巖組成,其中燕山早期的斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖與楊家杖子鉬礦等Au、Cu、Mo、Pb、Zn多金 屬礦床成礦時(shí)間密切相關(guān)[8],實(shí)驗(yàn)測(cè)得輝鉬礦Re-Os和矽卡巖Re-Os模式年齡和等時(shí)線年齡為181.60~191.00 Ma[12-16,20],與燕山早期侵入巖的成巖年齡(181~188 Ma)相近,驗(yàn)證了野外接觸關(guān)系。
1)楊家杖子地區(qū)侵入巖主要有中粗粒鉀長(zhǎng)花崗巖、斑狀鉀長(zhǎng)花崗巖、似斑狀鉀長(zhǎng)花崗巖、細(xì)粒角閃二長(zhǎng)巖4種類(lèi)型。其中,斑狀鉀長(zhǎng)花崗巖、似斑狀鉀長(zhǎng)花崗巖形成時(shí)間分別為(181.30±0.95) Ma、(188.78±0.86) Ma,均屬于弱過(guò)鋁質(zhì)高鉀鈣堿性系列巖石,為中粗粒鉀長(zhǎng)花崗巖的邊緣相;而細(xì)粒角閃二長(zhǎng)巖形成時(shí)代為(227.80±1.10) Ma,屬于準(zhǔn)鋁質(zhì)高鉀鈣堿性系列巖石。
2)侵入巖的鋯石U-Pb年齡研究表明,楊家杖子地區(qū)燕山早期斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖(181~188 Ma)與楊家杖子鉬礦Au、Cu、Mo、Pb、Zn等多金屬礦床有著密切的時(shí)間和成因關(guān)系。
3)楊家杖子地區(qū)的細(xì)粒角閃二長(zhǎng)巖和閃長(zhǎng)巖可能形成于華北板塊與蒙古地塊之間發(fā)生強(qiáng)烈陸陸碰撞而導(dǎo)致的地殼擠壓、縮短、疊覆、隆起階段。而斑狀鉀長(zhǎng)花崗巖和似斑狀鉀長(zhǎng)花崗巖屬于后造山期高分異I型花崗巖,可能與伊佐奈歧板塊朝NW方向俯沖到華北板塊有關(guān),形成于華北板塊邊緣的后造山階段。
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Geochemistry and Chronology Characteristics of the Intrusive Rocks and Its Relationship with Mineralization in Yangjiazhangzi Area, the Western Liaoning Province
Xu Xuechun,Zhang Xingxing,Zheng Changqing,Cui Fanghua,Gao Yuan,Gao Feng
CollegeofEarthSciences,JilinUniversity,Changchun130061,China
Yangjiazhangzi area in the Western Liaoning Province (Liaoxi) is located in the east section of Yanshan fold belt which is in the north rim of the North China craton. There are four main types of intrusive rocks in this area: medium-coarse grain moyites, porphyritic moyite, porphyaceous, and fine-grained hornblende monzonite. The main rock is porphyritic moyite and porphyaceous moyite,which appear as large batholiths,and distribute along the north-east. Zircon U-Pb isotope dating shows its emplacement mainly in 181-188 Ma. Fine-grained hornblende monzonite presents as a stock, and distribute along the north-south. Zircon U-Pb isotope dating shows its emplacement mainly in 227 Ma. Petrogeochemistry analysis results indicate that porphyritic moyite and porphyaceous moyite belong to weak peraluminous high k calc alkaline rock series. The fine-grained hornblende monzonite belongs to metaluminous high k calc alkaline rock series. Porphyritic moyite and porphyaceous moyite are rich in high field strength elements Th, La, Nd, Hf and Gd, and depleted of high field strength elements Ti, Ho and large ion lithophile elements Ba, Sr; fine-grained hornblende monzonite is rich in high field strength elements Gd, Er and large ion lithophile elements Ba, Sr, and depleted of high field strength elements Nb, Hf, Ti, Pr, Y, Yb. The chondrite-normalized REE patterns show that all the three rocks belong to the right slope type, the LREE fractionation is obvious, and the HREE fractionation is insignificant. Researches show that Mesozoic magmatism in this region mainly occurred in Early Jurassic, and had close genetic relation with the famous Yangjiazhangzi molybdenum deposits, but the Late Triassic magmatism was relatively weak.
Liaoxi;Yangjiazhangzi;intrusive rocks;geochemistry;chronology;Yangjiazhangzi molybdenum deposits
10.13278/j.cnki.jjuese.201503113.
2014-09-29
國(guó)土資源部公益性行業(yè)科研專(zhuān)項(xiàng)經(jīng)費(fèi)項(xiàng)目(201011083)
徐學(xué)純(1954--),男,教授,博士生導(dǎo)師,主要從事流體地質(zhì)學(xué)和變質(zhì)地質(zhì)學(xué)方面的研究,E-mail:xuxuechun@jlu.edu.cn。
10.13278/j.cnki.jjuese.201503113
P588.1
A
徐學(xué)純,張行行,鄭常青,等.遼西楊家杖子侵入巖地球化學(xué)和年代學(xué)特征及其與成礦的關(guān)系.吉林大學(xué)學(xué)報(bào):地球科學(xué)版,2015,45(3):804-819.
Xu Xuechun,Zhang Xingxing,Zheng Changqing,et al.Geochemistry and Chronology Characteristics of the Intrusive Rocks and Its Relationship with Mineralization in Yangjiazhangzi Area, the Western Liaoning Province.Journal of Jilin University:Earth Science Edition,2015,45(3):804-819.doi:10.13278/j.cnki.jjuese.201503113.