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濟南輝長巖巖漿演化過程: 來自熔體包裹體的證據(jù)

2016-07-02 03:20:37丁相禮任鐘元錢生平黃小龍陳林麗張銀慧洪路兵吳亞東
大地構(gòu)造與成礦學(xué) 2016年1期
關(guān)鍵詞:橄欖石

丁相禮, 任鐘元, 郭 鋒, 錢生平, 2, 張 樂, 黃小龍,陳林麗, 張銀慧, 洪路兵, 張 艷, 2, 吳亞東, 2

(1.中國科學(xué)院 廣州地球化學(xué)研究所, 同位素地球化學(xué)國家重點實驗室, 廣東 廣州 510640; 2.中國科學(xué)院大學(xué), 北京 100049; 3.中國科學(xué)院 青藏高原研究所, 北京 100101)

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濟南輝長巖巖漿演化過程: 來自熔體包裹體的證據(jù)

丁相禮1, 2, 3, 任鐘元1*, 郭 鋒1, 錢生平1, 2, 張 樂1, 黃小龍1,陳林麗1, 張銀慧1, 洪路兵1, 張 艷1, 2, 吳亞東1, 2

(1.中國科學(xué)院 廣州地球化學(xué)研究所, 同位素地球化學(xué)國家重點實驗室, 廣東 廣州 510640; 2.中國科學(xué)院大學(xué), 北京 100049; 3.中國科學(xué)院 青藏高原研究所, 北京 100101)

摘 要:本研究首次報道了早白堊世濟南輝長巖中橄欖石斑晶捕獲的熔體包裹體的研究結(jié)果。濟南輝長巖中橄欖石的Fo(60.3~74.6), Mn(2500~3500 μg/g), Ni(70~1349 μg/g), Fe/Mn比值(61.2~83.5), 與源區(qū)母巖為純的橄欖巖形成的熔體結(jié)晶出的橄欖石性質(zhì)不同, 可能與源區(qū)存在輝石巖的貢獻(xiàn)有關(guān)。橄欖石中熔體包裹體主量元素具有較大的變化范圍。熔體包裹體成分的標(biāo)準(zhǔn)礦物計算(CIPW)表明, MgO>10%的熔體包裹體為含有霞石和橄欖石標(biāo)準(zhǔn)礦物分子的硅不飽和熔體,MgO<10%時為含石英標(biāo)準(zhǔn)礦物分子的硅飽和熔體。橄欖石中包裹有輝石和斜長石, 說明巖漿演化過程應(yīng)該處于開放環(huán)境。熔體包裹體的(208Pb/206Pb)i和(207Pb/206Pb)i與MgO具有良好的負(fù)相關(guān)關(guān)系, 與SiO2具有良好的正相關(guān)關(guān)系, 以及熔體包裹體具有較高的SiO2特征表明巖漿演化過程中可能有下地殼長英質(zhì)組分的加入。熔體包裹體的Pb同位素落在EMI附近并向EMII延伸, 其源區(qū)可能有EMI和EMII的貢獻(xiàn), 熔體包裹體的主量元素成分說明其源區(qū)母巖可能有橄欖巖和輝石巖的貢獻(xiàn)。

關(guān)鍵詞:濟南輝長巖; 橄欖石; 熔體包裹體; Pb同位素

項目資助: NSFC重大研究計劃(91214202, 90714001)和“百人計劃”擇優(yōu)項目聯(lián)合資助。

0 引 言

華北克拉通是世界上最古老的的克拉通之一,記錄的最古老的下地殼捕擄體年齡約為3.8 Ga(Liu et al., 1992), 與世界典型的克拉通形成于太古代的年齡相似(Aulbach et al., 2004, 2005, 2007)。華北陸塊在古元古代東、西部陸塊的碰撞拼合作用之后形成穩(wěn)定的克拉通。基于華北中新生代地幔包體的巖石學(xué)、地球化學(xué)研究表明, 華北克拉通巖石圈地幔發(fā)生了大規(guī)模的減薄, 且?guī)r石圈地幔性質(zhì)發(fā)生了轉(zhuǎn)變。目前, 對于華北克拉通破壞這一事實基本上取得了共識, 但對于克拉通破壞的機制仍存在爭論。華北克拉通破壞的機制存在如下的爭論: 熱-機械化學(xué)侵蝕作用(Griffin et al., 1998; Menzies and Xu,1998; Fan et al., 2000; Guo et al., 2001; Xu, 2001; 范蔚茗和郭鋒, 2005; Menzies et al., 2007); 拆沉作用(鄧晉福等, 1994; Gao et al., 2002, 2004; Wu et al.,2003; Xu et al., 2006; Deng et al., 2007; Yang et al.,2008; Liu et al., 2008); 橄欖巖-熔體相互作用(Zhang et al., 2002, 2008; 張宏福等, 2004; Tang et al., 2006;張宏福, 2009); 巖漿提取作用(Chen et al., 2004); 巖石圈地幔水化(牛耀齡, 2005)以及地幔柱模式(Qian et al., 2015)。華北克拉通破壞的動力學(xué)背景或控制因素存在如下爭論: 東側(cè)太平洋板塊的俯沖作用(Griffin et al., 1998; 牛耀齡, 2005; Wu et al., 2005,2006; Zheng et al., 2006; Qian et al., 2015); 來自南側(cè)揚子板塊向華北板塊的俯沖碰撞作用(Menzies and Xu, 1998; Gao et al., 1998, 2004; Xu, 2001; Zhang et al., 2002; Xu et al., 2004, 2005; Wu et al., 2006;Yang et al., 2008); 印度板塊同歐亞大陸碰撞的遠(yuǎn)程影響(Menzies et al., 1993; Liu et al., 2004a); 多方位板塊俯沖(Zhang et al., 2003; Zhai et al., 2007)。

華北克拉通中生代巖漿活動是克拉通破壞的淺部響應(yīng), 因此研究克拉通的巖漿活動可以反演克拉通破壞過程中的巖漿演化過程。華北克拉通中生代以來發(fā)育了大規(guī)模的巖漿活動, 白堊紀(jì)之前的巖漿活動較少且大多數(shù)為酸性、中性巖漿活動, 而基性巖漿活動很少, 主要分布于克拉通的邊緣。到白堊紀(jì)巖漿活動的范圍和強度達(dá)到頂峰, 并在克拉通的腹地出現(xiàn), 酸性和基性巖漿均有出現(xiàn)?;詭r漿通常被認(rèn)為由地幔熔融形成, 因此可以用來反演地幔性質(zhì), 為此我們選擇對中生代基性巖石進(jìn)行研究。

華北克拉通研究已取得了豐富的成果, 但是前人研究主要集中在全巖主微量、同位素, 只有部分學(xué)者采用了單礦物成分及同位素分析。但是全巖只能記錄部分熔融形成的熔體經(jīng)歷一系列復(fù)雜的巖石學(xué)過程后(巖漿混合、結(jié)晶分異、巖漿去氣和圍巖的同化作用等)的成分變化(Sobolev, 1996; Sobolev et al., 2000; Ren et al., 2005; 劉建強和任鐘元, 2013),關(guān)于巖石成因方面的重要信息變得模糊或消失。而熔體包裹體是礦物在結(jié)晶的過程中捕獲的巖漿小滴,它可以記錄原生巖漿及其演化過程中的巖漿信息(Sobolev, 1996; Norman et al., 2002; Ren et al.,2005)。因此通過熔體包裹體的研究可以更有效制約華北克拉通的深部巖漿過程。

1 區(qū)域地質(zhì)背景

華北克拉通位于中國中-東部, 秦嶺-大別-蘇魯超高壓變質(zhì)帶的北側(cè), 東鄰太平洋板塊, 北部為中亞造山帶(圖1a)。以南北重力梯度線為界分為東部板塊和西部板塊, 兩者在早元古代(2.0~1.8 Ga)時發(fā)生碰撞, 形成中央造山帶(Zhao et al., 2001)。山東可以根據(jù)郯廬斷裂帶分為魯西和魯東兩部分, 魯西地區(qū)北臨渤海, 東南部與蘇魯高壓超高壓變質(zhì)帶相鄰。魯西地區(qū)在早白世堊沿郯廬斷裂帶發(fā)育了大規(guī)模的巖漿活動, 主要有濟南和沂南輝長巖侵入體(約130~134 Ma, Huang et al., 2012; Guo et al., 2013), 鄒平輝長巖類雜巖體(~128 Ma, Huang et al., 2012), 淄博閃長巖巖體(~128 Ma, 鐘軍偉和黃小龍, 2012)、棗莊龍寶山堿性巖體(~129 Ma, Huang et al., 2012)及費縣(~119 Ma, Gao et al., 2008)和方城(~125 Ma, Zhang et al., 2002)玄武巖。

濟南巖體位于華北克拉通東部的濟南-郭店一帶, 郯廬斷裂帶西側(cè), 為中-基性雜巖體, 主要巖石類型為輝長巖類、閃長巖類和正長巖類。主要侵位于奧陶系、石炭系、二疊系, 多數(shù)被第四系覆蓋, 露頭零星出露, 主體呈EW向展布, 長~45 km, 寬~20 km,總面積~464 km2, 以濟南地區(qū)出露最廣(山東省地質(zhì)礦產(chǎn)局, 1991)(圖1b)。根據(jù)巖體之間的穿插關(guān)系、巖石和礦物特征, 可以將濟南巖體劃分為三個期次,第一期為濟南巖體的主巖體包括匡山、標(biāo)山、鳳凰山、臥牛山、無影山等, 主要分布于濟南市區(qū)附近;第二期主要出露在沙溝、于山等地, 分布于郭店一帶; 第三期出露在藥山一帶。本文研究的樣品分布在匡山(09SD-2, 09SD-4)、標(biāo)山(09SD-15)和臥牛山(09SD-23), 它們均屬于濟南巖體的主巖體(圖1b)。濟南巖體的鋯石和斜鋯石U-Pb年齡為130~134 Ma (Guo et al., 2013), Huang et al. (2012)報道的鋯石U-Pb年齡為127.5±2.2 Ma。

圖1 華北克拉通構(gòu)造簡圖(a), 濟南巖體區(qū)域地質(zhì)簡圖和采樣點位置(b, 據(jù)Zhao et al., 2001; 山東省地質(zhì)礦產(chǎn)局, 1991)Fig.1 Simplified tectonic framework of the North China Craton (a), and geologic sketch map of the Jinan gabbros andsample locations (b)

2 樣品與測試方法

本文選取Guo et al. (2013)報道過橄欖石成分和O同位素的09SD-2、09SD-4、09SD-15和09SD-23四個樣品進(jìn)行熔體包裹體研究。四個樣品均為輝長巖, 采樣位置見圖1b。巖石薄片中可見有橄欖石、輝石、斜長石和鈦鐵礦, 部分橄欖石中包裹有輝石、斜長石, 輝石中包裹有斜長石(圖2)。四個樣品均比較新鮮, 橄欖石未發(fā)生蝕變。四個樣品的成分變化范圍為: SiO2(47.91%~49.75%), MgO(12.32%~14.67%),F(xiàn)eO(8.95%~12.14%), CaO(10.6%~11.09%), Al2O3(11.43%~12.1%), Na2O(1.62%~1.8%), K2O(0.28%~0.43%),TiO2(0.4%~0.74%)。Guo et al. (2013)已經(jīng)對全巖的主微量, 鋯石和斜鋯石的Hf、O同位素, 橄欖石成分及O同位素進(jìn)行了分析, 我們在其研究的基礎(chǔ)上對橄欖石成分及其中熔體包裹體成分進(jìn)行了分析, 并測試了橄欖石中熔體包裹體的Pb同位素組成。

我們對四個樣品分別進(jìn)行了粉碎, 并用去離子水進(jìn)行清洗, 105 ℃烘干。隨后篩選60~80目粉末樣約50 g, 雙目鏡下挑選新鮮橄欖石400粒。在QFM條件下對橄欖石進(jìn)行加熱, 加熱溫度為1180 ℃, 在加熱爐中持續(xù)加熱10 min, 取出, 在空氣中淬冷,使其中的熔體包裹體均一化。將加熱后的橄欖石鑲嵌在直徑約為1 cm的樹脂靶上, 對其進(jìn)行打磨、拋光, 使熔體包裹體出露在樹脂靶的平面上; 再將磨出包裹體的樹脂靶鑲嵌在直徑約為2.5 cm的樹脂靶上。以上實驗是在中國科學(xué)院廣州地球化學(xué)研究所(GIG-CAS)同位素地球化學(xué)國家重點實驗室熔體包裹體實驗室完成, 詳細(xì)的熔體包裹體的制備方法見Ren et al. (2005)。

橄欖石和熔體包裹體化學(xué)成分分析是在GIG-CAS同位素地球化學(xué)國家重點實驗室JEOL JXA-8100型電子探針上完成的。橄欖石化學(xué)成分的測試條件與Sobolev et al. (2007)方法相似, 具體條件為: 加速電壓為20 kV, 電流為300 nA, 束斑直徑2 μm。Mg、Si、Fe三種元素的計數(shù)時間為90 s, Ca 和Mn計數(shù)時間為120 s, Ni的計數(shù)時間為150 s。熔體包裹體化學(xué)成分的測試方法與Wang and Gaetani (2008)相似, 具體條件: 加速電壓為15 kV, 電流為20 nA, 束斑直徑為3 μm。分析過程中Na、K容易丟失, 為了降低這種丟失, 優(yōu)先對Na、K進(jìn)行分析。每一次換樣之后都對內(nèi)標(biāo)進(jìn)行測定來監(jiān)測儀器的運行狀態(tài)。數(shù)據(jù)采用 ZAF 修正法進(jìn)行修正, 采用美國SPI 公司的標(biāo)樣校正。為了監(jiān)控儀器的漂移效應(yīng),每批樣品測定前后需要測定監(jiān)控標(biāo)樣。其中橄欖石監(jiān)控標(biāo)樣的相對分析精度: 主量元素(MgO、FeO和SiO2)小于0.4%, 痕量元素(CaO、MnO和NiO)小于3%; 包裹體測試時玻璃監(jiān)控標(biāo)樣 JB-2 的相對分析精度: 大部分主量元素小于0.5%, MnO, K2O 和P2O5分別為5%, 1%和8%。

熔體包裹體的 Pb 同位素組成是在GIG-CAS同位素地球化學(xué)國家重點實驗室的激光剝蝕-多接受等離子體質(zhì)譜儀(LA-MC-ICPMS)上完成的。首先將上述已經(jīng)完成主量元素分析的熔體包裹體大靶重新進(jìn)行拋光, 拋除熔體包裹體表面殘余碳粉, 挑選出直徑大于40 μm的熔體包裹體重新制靶拋光, 然后將新靶置于超聲波清洗槽中分別用1%的稀HNO3和Milli-Q水各超聲2遍, 每次超聲10 min。超聲完成以后晾干置于一旁待測。激光工作參數(shù):激光波長193 nm, 束斑直徑45 μm; 頻率3 Hz; 能量80 mJ; 能量通量50%; 單點激光剝蝕時間為30 s;背景測試時間為30 s; 激光池載氣(He)流量, 80 ml/min;氮氣, 2 ml/min。測試過程中質(zhì)譜采用的接收器陣列同時接收了U、Th和Pb的信號強度, 根據(jù)測試的U/Pb和Th/Pb比值來校正U和Th放射性衰變對Pb同位素的影響, 詳細(xì)的分析方法見Zhang et al. (2014)。

3 結(jié) 果

3.1橄欖石化學(xué)成分

我們共獲得了四個樣品中的98個橄欖石數(shù)據(jù)和47個熔體包裹體數(shù)據(jù)。橄欖石的Fo介于60.3~74.6, 與Guo et al. (2013)報道的(57.8~73.1)相似。具有較低的CaO含量(<0.1%), 較低的Mn(2500~3500 μg/g), 較高的Ni(70~1349 μg/g), Fe/Mn比值在61~83(表1)。部分Fo較低(<66)的橄欖石中包裹有單斜輝石和斜長石(表2, 圖2)。

3.2橄欖石中熔體包裹體的化學(xué)成分

圖2 濟南輝長巖和熔體包裹體的顯微照片F(xiàn)ig.2 Micro-photographs of the Jinan gabbros and melt inclusions

橄欖石中熔體包裹體的主量元素(SiO2、FeO、CaO、Al2O3、Na2O、K2O)變化較大(表3), 但與MgO具有相關(guān)性(圖3), 而Ni、Mn、P及易揮發(fā)元素(S、F、Cl)與MgO無相關(guān)性。橄欖石中熔體包裹體的成分與全巖相比表現(xiàn)出更寬的變化范圍(圖3)。SiO2與MgO總體上呈現(xiàn)負(fù)相關(guān)關(guān)系。K2O(0.45%~2.16%)變化范圍較大, 且隨MgO降低而升高。當(dāng)MgO>10%時, FeO、CaO、Al2O3、TiO2基本不隨MgO變化而變化, 而MgO<10%時, FeO、CaO、TiO2與MgO呈正相關(guān), Al2O3與MgO呈負(fù)相關(guān)(圖3)。

3.3熔體包裹體Pb同位素

共測試了19個直徑>40 μm的熔體包裹體的Pb同位素。經(jīng)過U和Th衰變校正后的熔體包裹體Pb同位素: (208Pb/206Pb)i=2.0927~2.1742, (207Pb/206Pb)i= 0.8535~0.8984(表4), 與全巖Pb同位素組成基本落在同一趨勢上(圖4)。熔體包裹體和全巖的Pb同位素都落在EMI附近, 有向EMII延伸的趨勢。與全巖相比, 熔體包裹體的(208Pb/206Pb)i、(207Pb/206Pb)i具有更大的變化范圍且較全巖偏低。熔體包裹體的MgO與(208Pb/206Pb)i和(207Pb/206Pb)i呈負(fù)相關(guān), SiO2與(208Pb/206Pb)i和(207Pb/206Pb)i呈正相關(guān)(圖5)。MgO含量較高的熔體包裹體具有較低的(208Pb/206Pb)i和(207Pb/206Pb)i, 偏離EMI區(qū)域, EMII的貢獻(xiàn)較大。

表1 濟南輝長巖中橄欖石主量元素(%)電子探針分析結(jié)果Table 1 Major element compositions (%) of the olivine phenocrysts in the Jinan gabbros

表2 橄欖石中包裹的單斜輝石和斜長石的主量元素成分(%)Table 2 Major element compositions (%) of clinopyroxene and plagioclase hosted in olivine

表3 濟南輝長巖中橄欖石捕獲的熔體包裹體成分(%)Table 3 Compositions of olivine-hosted melt inclusions from the Jinan gabbros

續(xù)表3:

4 討 論

4.1分離結(jié)晶

濟南輝長巖中含有橄欖石、輝石和斜長石等礦物,部分巖石樣品具有較高的MgO(最高可達(dá)15%)。全巖Mg#(68.7~77.5)與其中結(jié)晶的橄欖石(Fo=60.3~74.6)不平衡, 這可能是礦物堆晶造成。部分巖石具有明顯的Eu正異常(δEu達(dá)1.66)和Sr正異常(圖6), 這可能與斜長石的堆晶有關(guān)。因此利用全巖成分變化來判斷其巖漿演化過程可能會存在一些問題。熔體包裹體是礦物在結(jié)晶的過程中捕獲的巖漿小滴, 它可以記錄被捕獲時巖漿的信息, 我們試圖通過橄欖石中熔體包裹體的成分來重現(xiàn)巖漿的結(jié)晶順序。我們測試的包裹體成分較全巖具有更高或更低的MgO, 這說明所捕獲的包裹體記錄了較原始和演化巖漿的信息, 能夠更好的重現(xiàn)巖漿演化過程。在熔體包裹體氧化物與MgO關(guān)系圖中(圖3)可以看出, MgO>11%時, FeO、CaO/Al2O3、Na2O/K2O基本不隨MgO變化而變化,CaO、Al2O3、TiO2、Na2O、K2O和SiO2與MgO呈弱的負(fù)相關(guān)性, 這說明MgO含量高于11%時, 只有橄欖石的分離結(jié)晶, 因為橄欖石基本不含Ca、Al、Na和K。當(dāng)只有橄欖石結(jié)晶時, 巖漿的MgO降低, Al,Ca, Na和K將升高。因此隨著橄欖石結(jié)晶殘余巖漿中的CaO/Al2O3、Na2O/K2O基本不變。而輝石和斜長石的結(jié)晶會導(dǎo)致CaO/Al2O3比值的變化, Na2O/K2O在斜長石開始結(jié)晶時降低。MgO>11%時, 全巖具有較高的Ni、Cr且變化較快, CaO與MgO呈弱的負(fù)相關(guān)也說明了只有橄欖石的分離結(jié)晶(Huang et al.,2012)。對于那些MgO<11%的樣品, CaO與MgO呈正相關(guān), 說明有單斜輝石的分離結(jié)晶。TiO2在MgO>10%時基本不變, 而在MgO低于10%時快速降低, 這可能是鈦鐵礦的分離結(jié)晶造成的, 在巖石薄片中也能觀察到鈦鐵礦晶體(圖2)。Na2O/K2O比值在MgO為10%時開始下降, 說明有斜長石開始分離結(jié)晶, 而熔體中的CaO/Al2O3比值及Al2O3持續(xù)上升可能是巖漿演化主要受單斜輝石的分離結(jié)晶控制。CaO 和CaO/Al2O3比值在MgO<8%時降低速度變緩, 同時Al2O3呈現(xiàn)下降趨勢, 可能是斜長石的大量分離結(jié)晶造成的, 而SiO2持續(xù)升高可能是有富硅熔體加入造成的。結(jié)合巖相學(xué)特征, 我們認(rèn)為濟南輝長巖的結(jié)晶順序為: 橄欖石→單斜輝石→鈦鐵礦→斜長石。

圖3 MgO與SiO2、FeO、CaO、CaO/Al2O3、K2O、TiO2、Na2O、Al2O3、Na2O/K2O關(guān)系圖(全巖數(shù)據(jù)來自于Guo et al. 2013; MI(melt inclusions). 熔體包裹體)Fig.3 Plots of MgO vs. SiO2, FeO, CaO, CaO/Al2O3, K2O, TiO2, Na2O, Al2O3and Na2O/K2O and for melt inclusions and whole rocks from the Jinan gabbros

圖4 熔體包裹體(207Pb/206Pb)i-(208Pb/206Pb)i關(guān)系圖(底圖據(jù) Saal et al. 1998; EMI, EMII, FOZO, HIMU和MORB端元組分據(jù)Yurimoto et al., 2004; 全巖數(shù)據(jù)來自于Zhang et al., 2004; Yang et al., 2012; 華北下地殼數(shù)據(jù)來自Liu et al., 2004b)Fig.4 (207Pb/206Pb)ivs. (208Pb/206Pb)idiagram for melt inclusions from the Jinan gabbros

4.2地殼混染

來源于地幔的巖漿在上升侵位過程中或在地殼巖漿房停留時很容易受到地殼的同化混染, 而侵入巖一般在巖漿房中的停留時間更長, 所以受到地殼同化混染的可能性更大。濟南輝長巖的Zr/Nb比值與εNd(t)和εHf(t)負(fù)相關(guān), 說明濟南輝長巖在巖漿演化過程中受到了高Zr/Nb比值的殼源物質(zhì)(如富鋯石的長英質(zhì)火成巖或沉積物)的同化混染(Guo et al.,2013)。濟南輝長巖具有負(fù)的εNd(t)值和低的87Sr/86Sr比值, 且虧損Th、U(圖6)和高的Th/U、Nb/Ta比值,低的87Sr/86Sr比值可以排除上地殼的混染。下地殼巖石具有低的Th和U 含量(Rudnick and Gao,2003)。女山麻粒巖包體具有高的 Nb/Ta、Zr/Hf和Th/U比值和低的εNd(t)和87Sr/86Sr 比值, 具有華北克拉通太古代基底物質(zhì)的性質(zhì), 可以用來代表華北克拉通中生代下地殼組分特征(Huang et al., 2004),因此濟南輝長巖可能受到了下地殼物質(zhì)的作用。濟南輝長巖具有低的放射性Nd-Pb同位素, 高的放射性Sr, 富集大離子親石元素, 虧損高場強元素(圖6),這些特征也說明其可能與下地殼物質(zhì)的加入有關(guān)(Zhang et al., 2004)。

圖5 熔體包裹體中Pb同位素與MgO和SiO2關(guān)系圖Fig.5 Plots of Pb isotope vs. MgO and SiO2for melt inclusions from the Jinan gabbros

表4 濟南輝長巖中熔體包裹體的Pb同位素組成Table 4 Pb isotope compositions of melt inclusions from the Jinan gabbros

圖6 濟南輝長巖微量元素原始地幔標(biāo)準(zhǔn)化蛛網(wǎng)圖(原始地幔值據(jù)McDonough and Sun, 1995; 濟南輝長巖數(shù)據(jù)來自Guo et al., 2013; 費縣玄武巖來自Gao et al., 2008)Fig.6 Primitive mantle normalized trace element spider diagram of the Jinan gabbros

我們對橄欖石中熔體包裹體數(shù)據(jù)進(jìn)行CIPW標(biāo)準(zhǔn)礦物計算, 結(jié)果顯示熔體包裹體中MgO>10%時有橄欖石和霞石標(biāo)準(zhǔn)礦物的存在, 為硅不飽和熔體;而MgO<10%時有石英標(biāo)準(zhǔn)礦物分子存在(圖7), 為硅飽和熔體, 因此濟南輝長巖的母巖漿在巖漿作用過程中由硅不飽和巖漿演變?yōu)楣栾柡蛶r漿。正常的結(jié)晶分異過程中硅不飽和熔體不能演化為硅飽和熔體(Tuttle and Bowen, 1958; Philpotts and Ague, 2009),只有硅飽和熔體的加入才會導(dǎo)致這種結(jié)果。濟南輝長巖中同時含有鋯石和斜鋯石。鋯石與橄欖石和斜鋯石中δ18O存在不平衡, 及εNd(t)、εHf(t)與δ18O負(fù)相關(guān)說明橄欖石結(jié)晶于硅不飽和的封閉體系, 而鋯石結(jié)晶于硅飽和的開放體系, 可能是下地殼富含δ18O的長英質(zhì)組分的加入造成的(Yang et al., 2012;Guo et al., 2013)。熔體包裹體的CaO/Al2O3、Na2O/K2O在硅不飽和巖漿中保持恒定也說明早期處于封閉體系。后期SiO2快速升高, 封閉體系中正常的分離結(jié)晶作用很難使SiO2如此快速的升高。部分Fo較低的橄欖石中包裹有輝石和斜長石礦物(表3, 圖2), 輝石中包裹有斜長石晶體(圖2d), 這說明巖漿可能經(jīng)歷了多期次的分離結(jié)晶, 封閉體系中橄欖石結(jié)晶早于輝石和斜長石, 只有處于開放體系中有新巖漿的注入, 導(dǎo)致橄欖石重新開始結(jié)晶, 初始巖漿中結(jié)晶的輝石和斜長石才有可能被包裹在橄欖石中, 因此濟南巖體可能經(jīng)歷了多期次巖漿注入或者地殼混染。熔體包裹體的MgO和SiO2與Pb同位素具有良好的相關(guān)性。MgO含量高的熔體包裹體具有較低的(208Pb/206Pb)i和(207Pb/206Pb)i(圖5a、b)。高M(jìn)gO含量Pb同位素組成更接近原生巖漿, 下地殼具有較高的(208Pb/206Pb)i和(207Pb/206Pb)i, 隨著地殼混染程度增加(208Pb/206Pb)i、(207Pb/206Pb)i升高。SiO2與Pb同位素的關(guān)系說明隨著地殼混染程度增加(208Pb/206Pb)i、(207Pb/206Pb)i升高, 熔體中SiO2含量升高逐步演變?yōu)楣栾柡蛶r漿。地殼混染程度的增加也會導(dǎo)致橄欖石多期次的結(jié)晶, 因此橄欖石中會包裹更早期次結(jié)晶的輝石和斜長石。

圖7 熔體包裹體標(biāo)準(zhǔn)礦物分子計算(Q(quartz). 石英;Ne(nepheline). 霞石)Fig.7 CIPW norm calculation for melt inclusions from the Jinan gabbros

4.3地幔源區(qū)特征

濟南輝長巖的全巖Pb同位素組成(206Pb/204Pb)i=16.56~17.018, (207Pb/204Pb)i=15.216~17.378,(208Pb/204Pb)i=36.29~36.94(Zhang et al., 2004; Yang et al., 2012)與EMI的Pb同位素組成相似(Zinder and Hart, 1986)。較全巖Pb同位素組成(208Pb/206Pb)i= 2.1678~2.1962, (207Pb/206Pb)i=0.9031~0.9192(Zhang et al. 2004; Yang et al. 2012), 橄欖石中熔體包裹體的Pb同位素(208Pb/206Pb)i=2.0927~2.1742, (207Pb/206Pb)i= 0.8535~0.8984, 具有更大的變化范圍。熔體包裹體Pb同位素說明其地幔源區(qū)有EMI的貢獻(xiàn)也可能有EMII的參與。熔體包裹體的207Pb/206Pb較全巖偏低, 可能是橄欖石中的熔體包裹體記錄了更加接近原生巖漿的Pb同位素組成, 而全巖Pb同位素組成可能受到后期同化混染的影響, 使其207Pb/206Pb比值升高。全巖Pb同位素只表現(xiàn)出EMI地幔源區(qū)特征, 掩蓋了EMII的貢獻(xiàn)。高M(jìn)gO的熔融包裹體具有更接近EMII的Pb同位素組成(圖4, 5), 說明其地幔源區(qū)有EMII參與, 隨地殼混染程度增加EMII特征逐漸被掩蓋。

輝石巖部分熔融形成的熔體結(jié)晶出的橄欖石具有低MnO、CaO含量、高NiO含量、高Fe/Mn比值的特征(Sobolev et al., 2005, 2007; Herzberg et al.,2014)。濟南輝長巖中橄欖石具有較低的CaO(<0.1%)含量, 可能是由于擴散作用造成的。Ca在橄欖石中為不相容元素, 而在單斜輝石中為相容元素, 侵入巖中橄欖石與輝石接觸, 橄欖石中Ca會擴散至輝石中, 導(dǎo)致橄欖石中CaO<0.1%(Kent, 2008)。Fo介于65~69的橄欖石的Fe/Mn、Ni與Fo>70的橄欖石不在同一演化線上, 這可能是鈦鐵礦結(jié)晶使Fe快速降低造成的。鈦鐵礦結(jié)晶會使熔體中Mn含量降低, 但同時有其他礦物(橄欖石、單斜輝石)大量結(jié)晶使熔體中Mn升高(圖8b)。鈦鐵礦的分離結(jié)晶會干擾源區(qū)母巖判別, 為此我們只選取Fo>70橄欖石來討論其源區(qū)巖性。Fo介于72~75的橄欖石中具有較低的Mn(2538~2716 μg/g), 較高的Ni(307~1349 μg/g)和高的Fe/Mn比值(69.5~73.4)(圖8)。Fo介于72~75的橄欖石的Mn恰好與夏威夷Loihi玄武巖基本落在同一趨勢線上(圖8b), 橄欖石的Ni含量與Mn的投圖結(jié)果一致(圖8c), 且其Fe/Mn比值剛好處于橄欖巖與輝石巖熔體的分界附近(圖8d)。Loihi玄武巖被認(rèn)為是橄欖巖和輝石巖部分熔融形成的(Sobolev et al., 2005), 因此濟南輝長巖中較早結(jié)晶橄欖石的Fo(72~75)與Mn、Ni及Fe/Mn的關(guān)系圖說明其源區(qū)不止有橄欖巖的貢獻(xiàn)也應(yīng)該有輝石巖的參與。

為了進(jìn)一步限定源區(qū)巖性, 我們試圖通過熔體包裹體成分來判斷源區(qū)母巖的巖性。具有較低MgO的熔體包裹體受結(jié)晶分異和同化混染的影響很難反映源區(qū)特征。MgO<8%時, SiO2和TiO2明顯偏離橄欖巖和輝石巖區(qū)域(圖9a、c), 這可能是下地殼長英質(zhì)組分加入的結(jié)果, 此外鈦鐵礦的分離結(jié)晶導(dǎo)致TiO2降低。MgO較高的熔體包裹體相對比較接近母巖漿組分, 受結(jié)晶分異和同化混染的影響較小, 能更好的反映源區(qū)特征。高M(jìn)gO的熔體包裹體基本都落在橄欖巖和輝石巖的重疊區(qū)域(圖9), 這一特征也說明其源區(qū)可能有橄欖巖和輝石巖的貢獻(xiàn)。

5 結(jié) 論

本文通過濟南輝長巖的橄欖石化學(xué)組成, 熔體包裹體主量元素及Pb同位素組成結(jié)合前人已發(fā)表全巖主微量元素和同位素數(shù)據(jù), 得出如下認(rèn)識:

(1) 濟南輝長巖由硅不飽和巖漿逐漸演化為硅飽和巖漿, 演化過程中巖漿體系不是封閉的, 有下地殼長英質(zhì)熔體的加入。

圖8 濟南輝長巖橄欖石斑晶的組成(底圖據(jù)Herzberg, 2011)Fig.8 Plots of Ca, Mn, Ni and Fe/Mn against Fo for the olivines from the Jinan gabbros

圖9 濟南輝長巖與超鎂鐵質(zhì)巖石高壓實驗產(chǎn)生的部分熔融體之間的比較Fig.9 Comparison of the Jinan gabbros with the high-pressure experimental partial melts of various ultramafic rocks

(2) 熔體包裹體Pb同位素較全巖更靠近EMII,尤其是高M(jìn)gO的熔體包裹體, 表明全巖Pb同位素是受到地殼混染后的成分, 因此濟南輝長巖的地幔源區(qū)有EMI和EMII的貢獻(xiàn), 全巖遭受同化混染后掩蓋了EMII的貢獻(xiàn)。

致謝: 衷心感謝中國科學(xué)院廣州地球化學(xué)研究所熊小林研究員和吉林大學(xué)葛文春教授兩位審稿專家對本文提出了建設(shè)性的意見和建議。此外, 吳蕾女士在橄欖石挑選, 加熱, 熔體包裹體制備及測試中給予悉心的指導(dǎo)和幫助, 我們在此向其表示衷心的感謝。

參考文獻(xiàn)(References):

鄧晉福, 莫宣學(xué), 趙海玲, 羅照華, 杜楊松. 1994. 中國東部巖石圈根去根作用與大陸活化——東亞型大陸動力學(xué)模式研究計劃. 現(xiàn)代地質(zhì), 8(3): 349-356.

范蔚茗, 郭鋒. 2005. 華北地區(qū)晚中生代鎂鐵質(zhì)巖漿作用及其地球動力學(xué)背景. 大地構(gòu)造與成礦學(xué), 29(1): 44-55.

劉建強, 任鐘元. 2013. 玄武巖源區(qū)母巖的多樣性和識別特征: 以海南島玄武巖為例. 大地構(gòu)造與成礦學(xué),37(3): 471-488.

牛耀嶺. 2005. 玄武巖漿起源和演化的一些基本概念以及對中國東部中-新生代基性火山巖成因的新思路. 高校地質(zhì)學(xué)報, 11(1): 9-46.

山東省地質(zhì)礦產(chǎn)局. 1991. 山東區(qū)域地質(zhì)志. 北京: 地質(zhì)出版社: 300-325.

張宏福, 英基豐, 徐平, 馬玉光. 2004. 華北中生代玄武巖中地幔橄欖石捕虜晶: 對巖石圈地幔置換過程的啟示. 科學(xué)通報, 49(8): 784-789.

張宏福. 2009. 橄欖巖-熔體相互作用: 克拉通型巖石圈地幔能夠被破壞之關(guān)鍵. 科學(xué)通報, 54(14): 2008-2026.

鐘軍偉, 黃小龍. 2012. 魯西早白堊世基性侵入巖的鋯石Hf同位素組成變化及其成因. 大地構(gòu)造與成礦學(xué),36(4): 572-580.

Aulbach S, Griffin W L, Pearson N J, O'Reilly S Y, Kivi K and Doyle B J. 2004. Mantle formation and evolution,Slave Craton: Constraints from HSE abundances and Re-Os isotope systematics of sulfide inclusions in mantle xenocrysts. Chemical Geology, 208(1): 61-88.

Aulbach S, Griffin W L. Pearson N J, O'Reilly S Y and Kivi K. 2005. Os-Hf-Nd isotope constraints on subcontinental lithospheric mantle evolution, Slave Craton (Canada). Geochimica et Cosmochimica Acta, 69: 284-295.

Aulbach S, Griffin W L, Pearson N J, O'Reilly S Y, Kivi K and Doyle B J. 2007. Lithosphere formation in the central Slave Craton (Canada): Plume subcretion or lithosphere accretion? Contributions to Mineralogy and Petrology, 154(4): 409-427.

Chen B, Jahn B M, Arakawa Y and Zhai M G. 2004. Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen, North China Craton,elemental and Sr-Nd-Pb isotopic constraints. Contributions to Mineralogy and Petrology, 148: 489-501.

Dasgupta R, Hirschmann M M and Smith N D. 2007. Partial melting experiments of peridotite+CO2at 3 GPa and genesis of alkalic ocean island basalts. Journal of Petrology, 48(11): 2093-2124.

Deng J F, Su S G, Niu Y L, Liu C, Zhao G C, Zhao X G,Zhou S and Wu Z X. 2007. A possible model for the lithospheric thinning of North China Craton: Evidence from the Yanshanian (Jura-Cretaceous) magmatism and tectonism. Lithos, 96: 22-35.

Falloon T J and Danyushevsky L V. 2000. Melting of refractory mantle at 1.5, 2 and 2.5 GPa under anhydrous and H2O-undersaturated conditions: Implications for the petrogenesis of high-Ca boninites and the influence of subduction components on mantle melting. Journal of Petrology, 41(2): 257-283.

Fan W M, Zhang H F, Baker J, Javis K E, Mason P R D and Menzies M A. 2000. On and off the North China craton,where is the Archean keel? Journal of Petrology, 41: 933-950.

Gao S, Zhang B R, Jin Z M, Kern H, Luo T C and Zhao Z D. 1998. How mafic is the lower continental crust? Earth and Planetary Science Letters, 161: 101-117.

Gao S, Rudnick R L, Carlson R W, McDonough W F and Liu Y S. 2002. Re-Os evidence for replacement of ancient mantle lithosphere beneath the North China craton. Earth and Planetary Science Letters, 198: 307-322.

Gao S, Rudnick R L, Yuan H L, Liu X M, Liu Y S, Xu W L,Ling W L, Ayers J, Wang X C and Wang Q H. 2004. Recycling lower continental crust in the North China craton. Nature, 432: 892-897.

Gao S, Rudnick R L, Xu W L, Yuan H L and Ling W L. 2008. Recycling deep cratonic lithosphere and generation of intraplate magmatism in the North China Craton. Earth and Planetary Science Letters, 270: 41-53.

Guo F, Fan W M, Wang Y J and Lin G. 2001. Late Mesozoicmafic intrusive complexes in North China Block,constraints on the nature of subcontinental lithospheric mantle. Physics and Chemistry of the Earth, 26: 759-771.

Guo F, Guo J T, Wang C Y, Fan W M, Li C W, Zhao L, Li H X and Li J Y. 2013. Formation of mafic magmas through lower crustal AFC processes—An example from the Jinan gabbroic intrusion in the North China Block. Lithos, 179: 157-174.

Griffin W L, Andi Z, O'Reilly S Y and Ryan C G. 1998. Phanerozoic evolution of the lithosphere beneath the Sino-Korean craton // Flower M F J, Chung S L, Lo C H and Lee T Y. Mantle Dynamics and Plate Interactions in East Asia. Washington: American Geophysical Union Monograph: 107-126.

Herzberg C. 2011. Identification of source lithology in the Hawaiian and Canary Islands: Implications for origins. Journal of Petrology, 52: 113-146.

Herzberg C, Cabral R A, Jackson M G, Vidito C, Day J M D and Hauri E H. 2014. Phantom Archean crust in mangaia hotspot lavas and the meaning of heterogenous mantle. Earth and Planetary Science Letters, 396: 97-106.

Hirose K and Kushiro I. 1993. Partial melting of dry peridotites at high pressures: Determination of compositions of melts segregated from peridotite using aggregates of diamond. Earth and Planetary Sciences Letters, 114: 477-489.

Hirschmann M M, Kogiso T, Baker M B and Stolper E M. 2003. Alkalic magmas generated by partial melting of garnet pyroxenite. Geology, 31: 481-484.

Huang X L, Xu Y G and Liu D Y. 2004. Geochronology,petrology and geochemistry of the granulite xenoliths from Nushan, east China: Implication for a heterogeneous lower crust beneath the Sino-Korean Craton. Geochimica et Cosmochimica Acta, 68: 127-149.

Huang X L, Zhong J W and Xu Y G. 2012. Two tales of the continental lithospheric mantle prior to the destruction of the North China Craton, Insights from Early Cretaceous mafic intrusions in western Shandong, East China. Geochimica et Cosmochimica Acta, 96: 193-214.

Kent A J R. 2008. Melt inclusions in basaltic and related volcanic rocks. Reviews in Mineralogy and Geochemistry, 69(1): 273-331.

Keshav S, Gudfinnsson G, Sen G and Fei Y. 2004. High-pressure melting experiments on garnet clinopyroxenite and the alkalic to tholefitic transition in ocean-island basalts. Earth and Planetary Sciences Letters, 223: 365-379.

Kogiso T and Hirschmann M. 2006. Partial melting experiments of bimineralic eclogite and the role of recycled mafic oceanic crust in the genesis of ocean island basalts. Earth and Planetary Sciences Letters,249: 188-199.

Kogiso T, Hirschmann M M and Frost D J. 2003. High-pressure partial melting of garnet pyroxenite: Possible mafic lithologies in the source of ocean island basalts. Earth and Planetary Sciences Letters, 216: 603-617.

Laporte D, Toplis M J, Seyler M and Devidal J L. 2004. A new experimental technique for extracting liquids from peridotite at very low degrees of melting: Application to partial melting of depleted peridotite. Contributions to Mineralogy and Petrology, 146: 463-484.

Liu D Y, Nutman A P, Compston W, Wu J S and Shen Q H. 1992. Remnants of greater-than-or-equal-to 3800 Ma crust in the Chinese part of the Sino-Korean Craton. Geology, 20: 339-342.

Liu M, Cui X J and Liu F T. 2004a. Cenozoic rifting and volcanism in eastern China: A mantle dynamic link to the Indo-Asian collision? Tectonophysics, 393: 29-42.

Liu Y S, Gao S, Yuan H L, Zhou L, Liu X M, Wang X C, Hu Z C and Wang L S. 2004b. U-Pb zircon ages and Nd, Sr,and Pb isotopes of lower crustalxenoliths from North China Craton: Insights on evolution of lower continental crust. Chemical Geology, 211: 87-109.

Liu Y S, Gao S, Kelemen P B and Xu W L. 2008. Recycled crust controls contrasting source compositions of Mesozoic and Cenozoic basalts in the North China Craton. Geochimica et Cosmochimica Acta, 72: 2349-2376.

McDonough W F and Sun S S. 1995. The composition of the earth. Chemical Geology, 120: 223-253.

Menzies M A, Fan W and Zhang M. 1993. Palaeozoic and Cenozoic lithoprobes and the loss of >120 km of Archaean lithosphere, Sino-Korean craton, China. Geological Society, London, Special Publications, 76: 71-81.

Menzies M A and Xu Y G. 1998. Geodynamics of the North China Craton // Flower M, Chung S L, Lo C H and Lee T Y. Mantle Dynamics and Plate Interactions in EastAsia. Washington: American Geophysical Union Monograph: 155-165.

Menzies M A, Xu Y G., Zhang H F and Fan W M. 2007. Integration of geology, geophysics and geochemistry: A key to understanding the North China Craton. Lithos,96: 1-21.

Norman M D, Garcia M O, Vadim S. Kamenetsky R L and Nielsen. 2002. Olivine-hosted melt inclusions in Hawaiian picrites: Equilibration, melting, and plume source characteristics. Chemical Geology, 183: 143-168.

Pertermann M and Hirschmann M. 2003. Anhydrous partial melting experiments on MORB-like eclogite: Phase relations, phase compositions and mineral-melt partitioning of major elements at 2-3 GPa. Journal of Petrology, 44: 2173-2201.

Pilet S, Baker M B and Stolper E M. 2008. Metasomatized lithosphere and the origin of alkaline lavas. Science,320: 916-919.

Philpotts A R and Ague J J. 2009. Principles of Igneous and Metamorphic Petrology. Cambridge University Press: 194-220.

Qian S P, Ren Z Y, Zhang L, Hong L B and Liu J Q. 2015. Chemical and Pb isotope composition of olivine-hosted melt inclusions from the Hannuoba basalts, North China Craton: Implications for petrogenesis and mantle source. Chemical Geology, 401: 111-125.

Ren Z Y, Ingle S, Takahashi E, Hirano N and Hirata T. 2005. The chemical structure of the Hawaiian mantle plume. Nature, 436: 837-840.

Rudnick R L and Gao S. 2003. Composition of the continental crust // Carlson R W. Treatise on Geochemistry 3, The mantle and core. New York: Elsevier: 1-70.

Saal A E. 1998. Pb isotopic variability in melt inclusions from oceanic island basalts, Polynesia. Science, 282: 1481-1484.

Schwab B E and Johnston A D. 2001. Melting systematics of modally variable, compositionally intermediate peridotites and the effects of mineral fertility. Journal of Petrology,42(10): 1789-1811.

Sobolev A V. 1996. Melt inclusions in minerals as a source of principle petrological information. Petrology, 4(3): 209-220.

Sobolev A V, Hofmann A W and Nikogosian I K. 2000. Recycled oceanic crust observed in ghost plagioclase within the source of Mauna Loa lavas. Nature, 404: 986-990.

Sobolev A V, Hofmann A W, Sobolev S V and Nikogosian I K. 2005. An olivine-free mantle source of Hawaiian shield basalts. Nature, 434: 590-597.

Sobolev A V, Hofmann A W, Kuzmin D V, Yaxley G M,Arndt N T, Chung S L, Danyushevsky, L V, Elliott T,F(xiàn)rey, F A, Garcia M O, Gurenko A A, Kamenetsky V S,Kerr A C, Krivolutskaya N A, Matvienkov V V,Nikogosian I K, Rocholl A, Sigurdsson I A,Sushchevskaya N M and Teklay M. 2007. The amount of recycled crust in sources of mantle-derived melts. Science, 316: 412-417.

Tang Y J, Zhang H F and Ying J F. 2006. Asthenosphere-lithospheric mantle interaction in an extensional regime: Implication from the geochemistry of Cenozoic basalts from Taihang Mountains, North China Craton. Chemical Geology, 233: 309-327.

Tuttle O F and Bowen N L. 1958. Origin of Granite in the Light of Experimental Studies in the System NaAlSi3O8-KAlSi3O8-SiO2-H2O. Geological Society of America Memoirs: 1-146.

Walter M J. 1998. Melting of garnet peridotite and the origin of komatiite and depleted lithosphere. Journal of Petrology, 39: 29-60.

Wang Z R and Gaetani G A. 2008. Partitioning of Ni between olivine and siliceous eclogite partial melt: Experimental constraints on the mantle source of Hawaiian basalts. Contributions to Mineralogy and Petrology, 156: 661-678.

Wasylenki L E, Baker M B, Kent A J R and Stolper E M. 2003. Near-solidus melting of the shallow upper mantle: Partial melting experiments on depleted peridotite. Journal of Petrology, 44: 1163-1191.

Wu F Y, Walker R J, Ren X, Sun D and Zhou X. 2003. Osmium isotopic constraints on the age of lithospheric mantle beneath northeastern China. Chemical Geology,196: 107-129.

Wu F Y, Lin J Q, Wilde S A, Zhang X and Yang J H. 2005. Nature and significance of the Early Cretaceous giant igneous event in eastern China. Earth and Planetary Science Letters, 233: 103-119.

Wu F Y, Walker R J, Yang Y H, Yuan H L and Yang J H. 2006. The chemical-temporal evolution of lithospheric mantle underlying the North China Craton. Geochimica et Cosmochimica Acta, 70: 5013-5034.

Xu Y G, Ma J L, Frey F A, Feigenson M D, Liu J F. 2005. Role of lithosphere-asthenosphere interaction in the genesis of Quaternary alkali and tholeiitic basalts from Datong, western North China Craton. Chemical Geology, 224: 247-271.

Xu Y G. 2001. Thermo-tectonic destruction of the Archaean lithospheric keel beneath the Sino-Korean Craton in China: Evidence, timing and mechanism. Physics and Chemistry of the Earth (A), 26: 747-757.

Xu Y G, Ma J L, Huang X L, Iizuka Y, Chung S L, Wang Y B and Wu X Y. 2004. Early Cretaceous gabbroic complex from Yinan, Shandong province: Petrogenesis and mantle domains beneath the North China Craton. International Journal of Earth Sciences, 93: 1025-1041.

Xu W L, Gao S, Wang Q H, Wang D Y and Liu Y S. 2006. Mesozoic crustal thickening of the eastern North China Craton: Evidence from eclogite xenoliths and petrologic implications. Geology, 34: 721-724.

Yang J H, Wu F Y, Wilde S A, Belousova E and Griffin W L. 2008. Mesozoic decratonization of the North China block. Geology, 36(6): 467-470.

Yang D B, Xu W L, Pei F P, Yang C H and Wang Q H. 2012. Spatial extent of the influence of the deeply subducted South China Block on the southeastern North China Block: Constraints from Sr-Nd-Pb isotopes in Mesozoic mafic igneous rocks. Lithos, 136: 246-260.

Yurimoto H, Kogiso T, Abe K, Barsczus H G, Utsunomiya A and Maryuama S. 2004. Lead isotopic compositions in olivine-hosted melt inclusions from HIMU basalts and possible link to sulfide components. Physics of the Earth and Planetary Interiors, 146: 231-242.

Zhang L, Ren Z Y, Nichols A R L, Zhang Y H, Zhang Y,Qian S P and Liu J Q. 2014. Lead isotope analysis of melt inclusions by LA-MC-ICP-MS. Journal of Analytical Atomic Spectrometry, 29: 1393-1405.

Zhang H F, Sun M, Zhou X H, Fan W M, Zhai M G and Yin J F. 2002. Mesozoic lithosphere destruction beneath the North China Craton: Evidence from major-,trace-element and Sr-Nd-Pb isotope studies of Fangcheng basalts. Contributions to Mineralogy and Petrology, 144: 241-253.

Zhang H F, Sun M, Zhou X H, Zhou M F, Fan W M and Zheng J P. 2003. Secular evolution of the lithosphere beneath the eastern North China Craton: Evidence from Mesozoic basalts and high-Mg andesites. Geochimica et Cosmochimica Acta, 76: 4373-4387.

Zhang H F, Sun M, Zhou M F, Fan W M, Zhou X H and Zhai M G. 2004. Highly heterogeneous late Mesozoic lithospheric mantle beneath the North China Craton: Evidence from Pb-Sr-Nd isotopic systematics of mafic igneous rocks. Geological Magazine. 141: 55-62.

Zhang H F, Goldstein S L, Zhou X H, Sun M, Zheng J P and Cai Y. 2008. Evolution of subcontinental lithospheric mantle beneath eastern China: Re-Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts. Contributions to Mineralogy and Petrology, 155: 271-293.

Zhai M G, Fan Q C, Zhang H F, Sui J L, Shao J A. 2007. Lower crustal processes leading to Mesozoic lithospheric thinning beneath eastern North China: Underplating,replacement and delamination. Lithos, 96: 36-54.

Zhao G C, Wilde S A, Cawood P A, Sun M. 2001. Archean blocks and their boundaries in the North China Craton,lithological, geochemical, tructural and P-T path constraints and tectonic evolution. Precambrian Research, 107: 45-73.

Zheng J P, Griffin W L, O'Reilly S Y, Yang J S, Li T F, Zhang M, Zhang R Y and Liu J G. 2006. Mineral chemistry of peridotites from Paleozoic, Mesozoic and Cenozoic Lithosphere, Constraints on mantle evolution beneath Eastern China. Journal of Petrology, 47: 2233-2256.

Zindler A and Hart S. 1986. Chemical geodynamics. Annual Review of Earth and Planetary Sciences, 14: 493-571.

Magmatic Processes Involved in Formation of the Jinan Gabbros:Evidence from Melt Inclusions

DING Xiangli1, 2, 3, REN Zhongyuan1*, GUO Feng1, QIAN Shengping1, 2, ZHANG Le1, HUANG Xiaolong1, CHEN Linli1, ZHANG Yinhui1, HONG Lubing1, ZHANG Yan1, 2and WU Yadong1, 2
(1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, China; 2. University of Chinese Academy of Sciences, Beijing 100049,China; 3. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China)

Abstract:We present the first analyses of major elements and Pb isotope compositions of olivine-hosted melt inclusions from the Jinan gabbros in the Early Cretaceous. The olivines in the Jinan gabbros display a relatively large compositional variation: Fo values vary from 60.3 to 74.6; Mn contents range from 2500- 3500 μg/g; Ni contents show a range of 70- 1349 μg/g and Fe/Mn ratios range from 61.2 to 83.5. Different from the olivine crystallized from partial melts of pure peridotite, the compositional variation of the olivine in the Jinan gabbros is consistent with the contribution of pyroxenite other than peridotite in the source. The melt inclusions hosted by the olivine crystals show a significant compositional variation. CIPW norm calculations indicate that melt inclusions with MgO>10% contain normative nepheline (Ne) and olivine (Ol), while melt inclusions with MgO<10% contain normative quartz (Q). The occurrence of clinopyroxene and plagioclase hosted in olivines suggests that the magmatic processes involved the formation of gabbro should be occurred in an open-system. The negative correlation between (208Pb/206Pb)i, (207Pb/206Pb)iand MgO, and positive correlation between (208Pb/206Pb)i, (207Pb/206Pb)iand SiO2, and high SiO2content of melt inclusions, indicate that felsic component from the lower crust may be involved in the magmatic processes. The Pb isotopic compositions of melt inclusions are close to EMI and extend towards an EMII-type isotopic composition,suggestive of the involvement of the EMI and EMII components during the formation of the Jinan gabbros. The CaO contents and major element compositions of melt inclusions are consistent with partial melting of the mixing of peridotite- and pyroxenite- sources.

Keywords:the Jinan gabbros; olivine; melt inclusions; Pb isotope

中圖分類號:P581

文獻(xiàn)標(biāo)志碼:A

文章編號:1001-1552(2016)01-0174-017

收稿日期:2015-01-27; 改回日期: 2015-03-20

第一作者簡介:丁相禮(1987-), 男, 碩士研究生, 巖石地球化學(xué)專業(yè)。Email: 991592435@qq. com

通信作者:任鐘元(1962-), 男, 研究員, 從事巖石學(xué)和地球化學(xué)方向研究。Email: zyren@gig.ac.cn

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