胡 娟,劉曉春,曲 瑋,崔建軍

中國地質(zhì)科學(xué)院地質(zhì)力學(xué)研究所,北京 100081

桐柏造山帶古元古代變質(zhì)基性巖的鋯石U-Pb年齡及其地質(zhì)意義

胡 娟,劉曉春*,曲 瑋,崔建軍

中國地質(zhì)科學(xué)院地質(zhì)力學(xué)研究所,北京 100081

桐柏造山帶位于秦嶺和大別造山帶之間,其北側(cè)對(duì)應(yīng)于北秦嶺中高級(jí)變質(zhì)雜巖,南側(cè)對(duì)應(yīng)于大別山高壓/超高壓變質(zhì)雜巖。鋯石U-Pb定年在一個(gè)榴輝巖中獲得其原巖侵位年齡和鋯石重結(jié)晶或生長年齡分別為(1961±23) Ma和(1949±51) Ma,在一個(gè)石榴角閃巖(退變榴輝巖？)中獲得其變質(zhì)年齡為(1936±26) Ma,表明這兩種基性巖石在二疊-三疊紀(jì)高壓變質(zhì)之前經(jīng)歷了古元古代變質(zhì)作用的影響。由桐柏—大別—蘇魯造山帶可利用的年代學(xué)資料確定,揚(yáng)子陸塊北緣發(fā)育的古元古代構(gòu)造熱事件可分為兩幕,第一幕發(fā)生在約1.97～1.93 Ga,可能與Columbia超大陸的聚合有關(guān); 第二幕發(fā)生在約1.85～1.82 Ga,或者代表Columbia超大陸匯聚的繼續(xù),或者是陸塊邊緣增生過程的結(jié)果。

古元古代; 兩幕變質(zhì); 揚(yáng)子陸塊; 桐柏造山帶

揚(yáng)子陸塊是中國大陸最重要的古老陸塊之一,了解其早期形成和演化歷史對(duì)充分認(rèn)識(shí)中國大陸地殼的組成、構(gòu)造格局的演變乃至全球構(gòu)造事件的對(duì)比均具有重要意義。近年來,在揚(yáng)子陸塊不同地區(qū)的巖石中發(fā)現(xiàn)了一系列2.0～1.8 Ga構(gòu)造熱事件的年代學(xué)記錄(凌文黎,1996; Maruyama et al.,1998; 周漢文等,1998; Qiu et al.,2000; 高山等,2001; Ling et al.,2001; Ayers et al.,2002; 吳元保等,2003; 夏群科等,2003; Chen et al.,2003a,b; Yang et al.,2003; 鄭永飛,2003; Bryant et al.,2004; Li et al.,2004; 沈其韓等,2005; Hacker et al.,2006; Liu et al.,2006;Zhang et al.,2006a,b,c; 趙風(fēng)清等,2006; Zheng et al.,2006; Wu et al.,2006,2008,2009; Liu et al.,2008a; Sun et al.,2008; 熊慶等,2008; 彭敏等,2009;張麗娟等,2011),其中基巖部分主要來自于揚(yáng)子陸塊北緣的黃陵背斜(崆嶺群)及其附近區(qū)域,以及大別—蘇魯造山帶中的黃土嶺麻粒巖,而碎屑鋯石的年代學(xué)信息則遍布揚(yáng)子陸塊。這有可能說明,至少揚(yáng)子陸塊的北緣已卷入到古元古代強(qiáng)烈造山作用之中。而且,與華北陸塊一樣,古元古代造山作用在揚(yáng)子陸塊早期基底形成過程中可能起到了重要作用。

桐柏造山帶西連秦嶺造山帶,東接大別—蘇魯造山帶(圖1),其北側(cè)發(fā)育與北秦嶺相似的古生代中高級(jí)變質(zhì)單元,南側(cè)則發(fā)育二疊紀(jì)末-三疊紀(jì)高壓變質(zhì)單元,屬于大別—蘇魯高壓/超高壓變質(zhì)帶的西延部分(Liu et al.,2008b,2010,2011)。同位素年代學(xué)研究表明,高壓變質(zhì)單元中的變質(zhì)沉積巖均含有古元古代巖漿巖或變質(zhì)鋯石的年齡峰值,但榴輝巖的原巖及其伴生的變質(zhì)酸性火成巖多形成于新元古代(Liu et al.,2008b,2010)。進(jìn)一步詳細(xì)的鋯石U-Pb定年在一個(gè)榴輝巖和一個(gè)石榴角閃巖(退變榴輝巖？)樣品中獲得了古元古代構(gòu)造熱事件的年齡記錄,這也是在揚(yáng)子陸塊基巖中獲得的不可多得的古元古代年代學(xué)信息。本文報(bào)道了兩種變質(zhì)基性巖(即鳳凰咀榴輝巖和武勝關(guān)石榴角閃巖)的鋯石 U-Pb同位素年代學(xué)結(jié)果,并結(jié)合桐柏造山帶以及整個(gè)揚(yáng)子陸塊中的同期年代學(xué)記錄來探討揚(yáng)子陸塊北緣古元古代構(gòu)造熱事件的意義,以期加深對(duì)揚(yáng)子陸塊早前寒武紀(jì)陸殼增生歷史與構(gòu)造演化過程的理解。

1 區(qū)域地質(zhì)背景

桐柏造山帶中的高壓變質(zhì)單元以桐柏雜巖為核心,向北為北部榴輝巖帶,向南為南部榴輝巖帶(圖2),這些構(gòu)造單元基本上可以與西大別高壓/超高壓變質(zhì)地體相對(duì)比(Liu et al.,2004a,b)。北部榴輝巖帶主要出露于鴻儀河—固廟—桐柏一帶,向東延伸到譚家河北部,在大地構(gòu)造部位上相當(dāng)于西大別地區(qū)的滸灣剪切帶,但缺少石炭紀(jì)榴輝巖。主要組成巖石為花崗質(zhì)糜棱巖、白云鈉長片麻巖、白云石英片巖和大理巖,榴輝巖及其退變產(chǎn)物石榴角閃巖以團(tuán)塊、透鏡體或不規(guī)則條帶產(chǎn)于白云鈉長片麻巖和大理巖中。南部榴輝巖帶主要出露于七尖峰花崗巖體以西的黑龍鎮(zhèn)—雙河鎮(zhèn)—大阜山一帶,向東延伸到蔡家河,相當(dāng)于西大別地區(qū)的紅安巖群。主要由一套變質(zhì)火山巖-沉積巖系組成,包括白云鈉長片麻巖、白云石英片巖和大理巖,榴輝巖也以團(tuán)塊、透鏡體或不規(guī)則條帶產(chǎn)于白云鈉長片麻巖和大理巖中。此外,該帶還產(chǎn)出有大量的變質(zhì)輝長巖和石榴角閃巖塊體,以大阜山變質(zhì)基性-超基性巖體為代表。北、南兩條榴輝巖帶的峰期變質(zhì)條件分別為530～610°C、1.7～2.0 GPa和 460～560°C、1.3～1.9 GPa(劉曉春等,2005; Liu et al.,2008b)。SHRIMP 鋯石U-Pb以及礦物-全巖Rb-Sr和Lu-Hf定年揭示榴輝巖的原巖形成于新元古代,而峰期變質(zhì)時(shí)代為晚二疊世(約 255 Ma)(Liu et al.,2008b; Cheng et al.,2011),明顯早于大別—蘇魯?shù)貐^(qū)的高壓/超高壓變質(zhì)巖(約240～220 Ma)。此外,在變質(zhì)沉積巖的碎屑鋯石中獲得2.49 Ga、1.93 Ga和1.85～1.82 Ga三個(gè)年齡峰值,反映其物源來自于古老的揚(yáng)子地塊。

桐柏雜巖的主體是已強(qiáng)烈糜棱巖化的粗?；◢徺|(zhì)片麻巖,其內(nèi)含有規(guī)模不等的細(xì)粒閃長質(zhì)-花崗質(zhì)片麻巖、斜長角閃巖、副片麻巖、大理巖和鈣硅酸鹽巖等捕擄體(包體),這些捕擄體與周圍的糜棱巖化花崗質(zhì)片麻巖一起發(fā)生了塑性變形。Liu等(2010)在這些變質(zhì)巖捕擄體中發(fā)現(xiàn)了退變榴輝巖,礦物反應(yīng)結(jié)構(gòu)和石榴石成分環(huán)帶指示其經(jīng)歷了綠簾角閃巖相、榴輝巖相和角閃巖相三個(gè)演化階段,由相關(guān)系推測(cè)榴輝巖相變質(zhì)作用的 P-T范圍位于＜700°C、＞1.2 GPa區(qū)域內(nèi)。對(duì)退變榴輝巖、石榴角閃巖和閃長質(zhì)-花崗質(zhì)片麻巖等變質(zhì)火成巖進(jìn)行的鋯石 U-Pb定年結(jié)果表明(Liu et al.,2010),這些變質(zhì)巖的原巖年齡介于 933 Ma和 742 Ma之間,而變質(zhì)時(shí)代為232～220 Ma。變質(zhì)沉積巖的碎屑鋯石則產(chǎn)生2960 Ma和1966 Ma兩組年齡數(shù)據(jù)。占絕對(duì)優(yōu)勢(shì)的花崗質(zhì)片麻巖是在早白堊世(約 140 Ma)侵位的,而非前人所認(rèn)為的新元古代(Kr?ner et al.,1993)。

2 樣品及分析方法

2.1 樣品描述

鳳凰咀榴輝巖(樣品 SHZ17-1)呈團(tuán)塊狀產(chǎn)于南部榴輝巖帶大理巖中,出露寬度約50 m (圖3a)。榴輝巖呈淡綠色,主要由石榴石(35%)、綠輝石(25%)、角閃石(20%)、多硅白云母(7%)、綠簾石(3%)、石英(10%)和少量金紅石+榍石組成(圖 3b)。斑狀變晶結(jié)構(gòu),變形明顯。石榴石變斑晶多呈渾圓狀,粒徑0.5～1.0 mm,含有大量的模糊狀包裹體,經(jīng)電子探針檢測(cè)主要是綠簾石,其次是石英,也有角閃石,一般具有凈邊結(jié)構(gòu)。綠輝石多呈細(xì)粒集合體狀,但個(gè)別顆粒稍大。角閃石也為細(xì)小集合體,與綠輝石平衡共生,背散射圖像分析顯示環(huán)帶狀結(jié)構(gòu)。多硅白云母葉片稍大,定向性不如其他柱狀礦物。綠簾石均為長柱狀,背散射圖像分析也顯示環(huán)帶狀結(jié)構(gòu)。金紅石顆粒較大者保存較好,較小者僅保留在榍石的核部。

武勝關(guān)石榴角閃巖(樣品 WSG01-4)呈 3 m ×10 m大小的透鏡體夾于桐柏雜巖的黑云斜長片麻巖中(圖 3c)。主要組成礦物是石榴石(30%)、角閃石(45%)、斜長石(20%)、石英(5%)和少量綠簾石、鈦鐵礦,未見單斜輝石和金紅石(圖3d)。石榴石均為它形,粒徑 0.5～1.0 mm,具有明顯的白眼圈構(gòu)造,由斜長石和少量角閃石構(gòu)成。石榴石內(nèi)含有分散狀包裹體,主要是石英、榍石和少量綠簾石。角閃石呈細(xì)粒集合體分布,可含有蠕蟲狀、它形的斜長石包體。斜長石呈斑塊狀,或與角閃石共存,或圍繞石榴石生長。石英顆粒稍大,可能與石榴石屬于同一期次。綠簾石有兩種產(chǎn)狀,其一是生長在鈦鐵礦邊緣,其二是呈充填脈狀,與少量綠泥石共存,代表晚期綠片巖相迭加。以上礦物結(jié)構(gòu)表明,武勝關(guān)石榴角閃巖可能是榴輝巖的退變產(chǎn)物。

2.2 分析方法

鋯石的分選和挑純由河北省區(qū)域地質(zhì)礦產(chǎn)調(diào)查研究所實(shí)驗(yàn)室完成。將待測(cè)鋯石顆粒制成環(huán)氧樹脂樣品靶,拋光至其中心部位。先進(jìn)行光學(xué)和陰極發(fā)光(CL)顯微結(jié)構(gòu)觀察和照相,并由電子探針分析檢測(cè)礦物包裹體的成分,在此基礎(chǔ)上選擇合適的鋯石顆粒和(或)區(qū)域進(jìn)行U-Pb年齡測(cè)定。鳳凰咀榴輝巖樣品 SHZ17-1的鋯石 U-Pb定年由中國地質(zhì)科學(xué)院地質(zhì)研究所北京離子探針中心SHRIMP Ⅱ完成。分析流程和原理參考 Compston等(1992)的有關(guān)描述,測(cè)試孔徑約為25～30 μm。用澳大利亞國家地質(zhì)調(diào)查局標(biāo)準(zhǔn)鋯石 TEM (417 Ma)進(jìn)行元素間分餾的校正,應(yīng)用澳大利亞國立大學(xué)地球科學(xué)學(xué)院標(biāo)準(zhǔn)鋯石SL13 (572 Ma,U含量238×10-6)標(biāo)定所測(cè)鋯石的U、Th和Pb含量。利用中國科學(xué)院地質(zhì)與地球物理研究所CAMECA IMS-1280二次離子質(zhì)譜儀(SIMS)對(duì)武勝關(guān)石榴角閃巖樣品 WSG01-4的鋯石進(jìn)行了U-Pb定年。鋯石 SIMS年齡測(cè)定的方法和原理與Williams (1998)的描述類似。仍使用標(biāo)準(zhǔn)鋯石SL13來標(biāo)定待測(cè)樣品的 U、Th和 Pb的含量,每測(cè)定 3個(gè)樣品點(diǎn)之后測(cè)定一個(gè)標(biāo)準(zhǔn)鋯石 TEM (417 Ma)點(diǎn),用來進(jìn)行不同元素間同位素分餾校正。數(shù)據(jù)處理采用SQUID1.03和ISOPLOT程序,利用實(shí)測(cè)的204Pb含量來進(jìn)行普通Pb校正。單個(gè)測(cè)點(diǎn)同位素年齡的誤差為1σ,加權(quán)平均年齡具95%的置信度。

3 地質(zhì)年代結(jié)果

3.1 鳳凰咀榴輝巖(樣品SHZ17-1)

榴輝巖樣品SHZ17-1中的鋯石多為不規(guī)則狀、渾圓狀或短柱狀,晶體大小在200～400 μm之間。陰極發(fā)光圖像顯示多數(shù)鋯石顆粒具有核-邊結(jié)構(gòu)(圖4a,b),核部呈條帶狀構(gòu)造,與輝長巖中的典型鋯石特征相似(Corfu et al.,2003); 邊部呈均勻的灰白色,似交代重結(jié)晶或變質(zhì)增生成因(Xia et al.,2009)。大部顆粒發(fā)育不規(guī)則的裂隙,其內(nèi)被強(qiáng)發(fā)光物質(zhì)充填,表明它們可能經(jīng)歷了流體改造。

在16顆鋯石上分析了18個(gè)點(diǎn),其中13個(gè)點(diǎn)位于核部,5個(gè)點(diǎn)位于邊部(表1)?？傮w來看,鋯石核的U 和 Th 含量較高,分別為 99×10-6～564×10-6和86×10-6～757×10-6,Th/U 比值也較高,為 0.75～1.34,進(jìn)一步說明它們?yōu)閹r漿成因; 鋯石邊部的 U和 Th含 量 相 對(duì) 較 低 , 分 別 為 46×10-6～69×10-6和29×10-6～41×10-6,Th/U 比值為 0.56～0.77,與典型的變質(zhì)成因鋯石(Th/U＜0.1)略有區(qū)別。兩個(gè)鋯石部位的U-Pb年齡未見明顯的差別,但邊部誤差偏大(圖5)。13個(gè)鋯石核部分析點(diǎn)給出的不一致線上交點(diǎn)年齡為(1961±23) Ma (MSWD = 1.5),可能代表了原始輝長巖的侵位時(shí)間; 不一致線的下交點(diǎn)年齡為(533±880) Ma,誤差大,因此不具有實(shí)際地質(zhì)意義。5個(gè)鋯石邊部分析點(diǎn)中,7.2的年齡數(shù)據(jù)明顯年輕,排除此點(diǎn),其它4個(gè)分析點(diǎn)的207Pb/206Pb加權(quán)平均年齡為(1949±51) Ma (MSWD = 0.042),可能代表鋯石重結(jié)晶或變質(zhì)增生的時(shí)間。

3.2 武勝關(guān)石榴角閃巖(樣品WSG01-4)

石榴角閃巖樣品 WSG01-4中的鋯石均為卵形或渾圓狀,粒徑一般為20～100 μm。陰極發(fā)光圖像揭示大多數(shù)鋯石顯示均勻的灰色,少數(shù)發(fā)育不明顯的面狀/扇狀環(huán)帶(圖 4c,d),顯然屬于變質(zhì)成因(Corfu et al.,2003)。有些鋯石顆粒發(fā)育一個(gè)非常狹窄的,不連續(xù)的強(qiáng)發(fā)光邊,可能反映了晚期生長。礦物包裹體比較發(fā)育,主要成分是角閃石、石英、磷灰石和榍石,但未見石榴石,說明鋯石與巖石基質(zhì)中礦物組合的形成時(shí)間可能并不一致。

在23顆鋯石上分析了23個(gè)點(diǎn)(表2)。總體來看,除個(gè)別分析點(diǎn)(如5.1)外,鋯石中的Th、U含量普遍較低(分別為 3.7×10-6～13.4×10-6和 0.1×10-6～2.9×10-6),Th/U 比值為 0.01～0.30,且絕大多數(shù)＜0.10,進(jìn)一步證明了它們的變質(zhì)成因(Williams et al.,1987; Gebauer et al.,1997; Rubatto et al.,2000)。所有23個(gè)分析點(diǎn)均位于不一致線上或其附近,證明其經(jīng)歷了不同程度放射性成因 Pb的丟失。23個(gè)分析點(diǎn)產(chǎn)生的上交點(diǎn)年齡為(1936±26) Ma(圖 6),下交點(diǎn)年齡為(116±210) Ma (MSWD=1.3),其中上交點(diǎn)年齡與207Pb/206Pb加權(quán)平均年齡(1932±26) Ma (MSWD=1.3),在誤差范圍內(nèi)一致,結(jié)合鋯石的內(nèi)部結(jié)構(gòu)和包裹體類型將其解釋為角閃巖相變質(zhì)作用的發(fā)生時(shí)代; 下交點(diǎn)年齡誤差范圍較大,因此不具有地質(zhì)意義。

4 討論與結(jié)論

本文在榴輝巖中獲得其原巖侵位年齡和鋯石重結(jié)晶或變質(zhì)增生年齡分別為(1961±23) Ma和(1949±51) Ma,在石榴角閃巖中獲得其變質(zhì)年齡為(1936±26) Ma,表明這兩種基性巖石經(jīng)歷了古元古代變質(zhì)作用的影響。在兩個(gè)樣品中均未獲得約255 Ma的榴輝巖相變質(zhì)年齡,可能緣于榴輝巖形成溫度較低而使鋯石未能重新生長,或生長邊太窄而無法測(cè)定,這種現(xiàn)象在桐柏—大別地區(qū)的中低溫榴輝巖中普遍存在(Liu et al.,2004a,2008b,2010)。在桐柏造山帶的變質(zhì)沉積巖中已報(bào)道了4組碎屑鋯石年齡,分別為(1966±22) Ma (樣品 WHD04-2,變質(zhì)年齡)、(1930±7) Ma (樣品 DFS06-1,巖漿年齡)、(1846±5) Ma (樣品 SHZ03-5,變質(zhì)年齡)和(1820±6) Ma (樣品 TB02-1,變質(zhì)年齡)(Liu et al.,2008b,2010),這些碎屑鋯石年齡數(shù)據(jù)與本文的基巖定年結(jié)果相吻合?？磥?在桐柏造山帶中記錄的古元古代構(gòu)造熱事件似可分為兩幕,第一幕發(fā)生在約1.97～1.93 Ga,第二幕發(fā)生在約 1.85～1.82 Ga,二者間隔約100 Ma。

實(shí)際上,在桐柏造山帶中獲得的古元古代兩幕年代學(xué)圖譜在大別—蘇魯造山帶不同類型的三疊紀(jì)超高壓變質(zhì)巖中也已識(shí)別出來。這些超高壓巖石包括榴輝巖、硬玉石英巖、大理巖和花崗質(zhì)片麻巖,時(shí)代主要集中在1.99～1.92 Ga和1.86～1.80 Ga (周漢文等,1998; Maruyama et al.,1998; Ayers et al.,2002;Chen et al.,2003a; 吳元保等,2003; 夏群科等,2003;Yang et al.,2003; Li et al.,2004; Hacker et al.,2006;Liu et al.,2006; Zheng et al.,2006; Wu et al.,2006,2008; Sun et al.,2008)。甚至在中生代花崗巖中也有類似的繼承鋯石的年代學(xué)記錄(Bryant et al.,2004)。在揚(yáng)子陸塊內(nèi)部,約2.0～1.93 Ga的古元古代變質(zhì)年齡信息主要來自于揚(yáng)子北緣的崆嶺群太古宙變質(zhì)基底及其周圍的新元古代沉積蓋層(Qiu et al.,2000;高山等,2001; Ling et al.,2001; 趙風(fēng)清等,2006;Zhang et al.,2006a,b,c; Liu et al.,2008a; Wu et al.,2009),尚未見第二幕變質(zhì)作用的年齡報(bào)道,但這一時(shí)期有基性或花崗質(zhì)巖漿的局部侵入(熊慶等,2008;彭敏等,2009; 張麗娟等,2011)。

現(xiàn)有同位素年代學(xué)資料表明,約2.0～1.93 Ga的巖漿活動(dòng)和變質(zhì)作用在揚(yáng)子陸塊北部廣泛發(fā)育,應(yīng)代表一次重要的碰撞造山事件。一般認(rèn)為,這一碰撞造山事件可能與元古代Columbia超大陸的聚合有關(guān)(Zhang et al.,2006a,b; Zheng et al.,2007; Wu et al.,2008,2009),并導(dǎo)致了揚(yáng)子陸塊早期基底的形成。出露于黃陵背斜的圈椅埫A型花崗巖和基性巖脈以及華山觀環(huán)斑花崗巖的侵入時(shí)代集中在約1.85 Ga (熊慶等,2008; 彭敏等,2009; 張麗娟等,2011),表明這一時(shí)期揚(yáng)子陸塊應(yīng)處于伸展構(gòu)造體制下,可能與Columbia超大陸的裂解有關(guān)(彭敏等,2009; 張麗娟等,2011)。然而,在桐柏—大別—蘇魯造山帶中還發(fā)育一期 1.86～1.80 Ga的構(gòu)造熱事件,有可能說明在揚(yáng)子陸塊北緣存在另一期造山作用。這期造山作用或者與華北陸塊中發(fā)育的同期古元古代碰撞造山帶的性質(zhì)相似(Zhao et al.,2003),代表Columbia超大陸匯聚的繼續(xù),或者是陸塊邊緣增生過程的結(jié)果。

致謝: 鋯石測(cè)年得到中國地質(zhì)科學(xué)院地質(zhì)研究所北京離子探針中心張維博士和中國科學(xué)院地質(zhì)與地球物理研究所李獻(xiàn)華研究員、李秋立博士、唐國強(qiáng)和劉宇工程師的協(xié)助,張建新研究員對(duì)論文提出了寶貴的修改意見,在此致謝！

高山,QIU Yu-min,凌文黎,MCNAUGHTON N J,GROVES D I.2001.崆嶺高級(jí)變質(zhì)地體單顆粒鋯石SHRIMP U-Pb年代學(xué)研究——揚(yáng)子克拉通＞3.2 Ga 陸殼物質(zhì)的發(fā)現(xiàn)[J].中國科學(xué)(D輯),31(1): 27-35.

凌文黎.1996.揚(yáng)子克拉通北緣元古宙基底同位素地質(zhì)年代學(xué)和地殼增生歷史: I.后河群和西鄉(xiāng)群[J].地球科學(xué),21(5):491-494.

劉曉春,婁玉行,董樹文.2005.桐柏山地區(qū)低溫榴輝巖變質(zhì)作用的P-T軌跡[J].巖石學(xué)報(bào),21(4): 1081-1093.

彭敏,吳元保,汪晶,焦文放,劉小池,楊賽紅.2009.揚(yáng)子崆嶺高級(jí)變質(zhì)地體古元古代基性巖脈的發(fā)現(xiàn)及其意義[J].科學(xué)通報(bào),54(5): 641-647.

沈其韓,耿元生,宋彪,萬瑜生.2005.華北和揚(yáng)子陸塊及秦嶺—大別造山帶地表和深部太古宙基底的新信息[J].地質(zhì)學(xué)報(bào),79(5): 616-627.

吳元保,陳道公,夏群科,涂湘林,程昊,楊曉志.2003.大別山黃土嶺麻粒巖中鋯石 LAM-ICP-MS微區(qū)微量元素分析和Pb-Pb定年[J].中國科學(xué)(D輯),33(1): 20-28.

夏群科,鄭永飛,葛寧潔,DELOULE E.2003.大別山北部黃土嶺片麻巖的鋯石U-Pb年齡和氧同位素組成: 古老的原巖和多階段歷史[J].巖石學(xué)報(bào),19(3): 506-512.

熊慶,鄭建平,余淳梅,蘇玉平,湯華云,張志海.2008.宜昌圈椅 埫A型花崗巖鋯石U-Pb年齡和Hf同位素與揚(yáng)子大陸古元古代克拉通化作用[J].科學(xué)通報(bào),53(22): 2782-2792.

張麗娟,馬昌前,王連訓(xùn),佘振兵,王世明.2011.揚(yáng)子地塊北緣古元古代環(huán)斑花崗巖的發(fā)現(xiàn)及其意義[J].科學(xué)通報(bào),56(1):44-57.

趙風(fēng)清,趙文平,左義成,李宗會(huì).2006.崆嶺雜巖中混合巖的鋯石U-Pb年齡[J].地質(zhì)調(diào)查與研究,29(2): 81-85.

鄭永飛.2003.新元古代巖漿活動(dòng)與全球變化[J].科學(xué)通報(bào),48(16): 1705-1720.

周漢文,劉穎,李獻(xiàn)華,游振東,索書田,鐘增球.1998.大別山黃土嶺中性麻粒巖石榴子石階段酸淋濾 Pb-Pb等時(shí)線年齡[J].科學(xué)通報(bào),43(22): 2434-2437.

References:

AYERS J C,DUNKLE S,GAO S,MILLER C F.2002.Constraints on timing of peak and retrograde metamorphism in the Dabie Shan ultrahigh-pressure metamorphic belt,east-central China,using U-Th-Pb dating of zircon and monazite[J].Chemical Geology,186(3-4): 315-331.

BRYANT D L,AYERS J C,GAO S,MILLER C F,ZHANG H F.2004.Geochemical,age,and isotopic constraints on the location of the Sino-Korean/Yangtze suture and evolution of the Northern Dabie complex,east central China[J].Geological Society of America Bulletin,116(5-6): 698-717.

CHEN D G,DELOULE E,CHENG H,XIA Q K,WU Y B.2003a.Preliminary study of microscale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks: ion probe in situ analyses[J].Chinese Science Bulletin,48(16): 1670-1678.

CHEN F K,GUO J H,JIANG L L,SIEBEL W,CONG B L,SATIR M.2003b.Provenance of the Beihuaiyang lower-grade metamorphic zone of the Dabie ultrahigh-pressure collisional orogen,China: evidence from zircon ages[J].Journal of Asian Earth Sciences,22(4): 343-352.

CHENG H,ZHANG C,VERVOORT J D,WU Y B,ZHENG Y F,ZHENG S,ZHOU Z Y.2011.New Lu-Hf geochronology constrains the onset of continental subduction in the Dabie orogen[J].Lithos,121(1-4): 41-54.

COMPSTON W,WILLIAMS I S,KIRSCHVINK J L,ZHANG Z,MA G.1992.Zircon U-Pb ages for the Early Cambrian time-scale[J].Journal of the Geological Society,London,149(2): 171-184.

CORFU F,HANCHAR J M,HOSKIN P W O,KINNY P.2003.Atlas of zircon textures[J].Reviews in Mineralogy and Geochemistry,53(1): 469-500.

GAO Shan,QIU Yu-min,LING Wen-li,MCNAUGHTON N J,GROVES D I.2001.Single zircon U-Pb dating of the Kongling high-grade metamorphic terrain: evidence for ＞3.2 Ga old continental crust in the Yangtze craton[J].Science in China (Series D),44(4): 326-335.

GEBAUER D,SCHERTL H P,BRIX M,SCHREYER W.1997.35 Ma old ultrahigh-pressure metamorphism and evidence for very rapid exhumation in the Dora Maira Massif,WesternAlps[J].Lithos,41(1-3): 5-24.

HACKER B R,WALLIS S R,RATSCHBACHER L,GROVE M,GEHRELS G.2006.High-temperature geochronology constraints on the tectonic history and architecture of the ultrahigh-pressure Dabie-Sulu Orogen[J].Tectonics,25: TC5006,doi: 10.1029/2005TC001937.

LI X P,ZHENG Y F,WU Y B,CHEN F K,GONG B L,LI Y L.2004.Low-T eclogite in the Dabie terrane of China:petrological and isotopic constraints on fluid activity and radiometric dating[J].Contributions to Mineralogy and Petrology,148(4): 443-470.

LING W L,GAO S,ZHANG B R,ZHOU L,XU Q D.2001.The recognizing of ca.1.95 Ga tectono-thermal event in Kongling nucleus and its significance for the evolution of Yangtze Block,South China[J].Chinese Science Bulletin,46(4): 326-329.

LING Wen-li.1996.Isotopic geochronology and crustal growth of Proterozoic basement along the northern margin of Yangtze craton: I.Houhe Group and Xixiang Group[J].Earth Science,21(5): 491-494(in Chinese with English abstract).

LIOU J G,ZHANG R Y,WANG X M,EIDE E A,ERNST W G,MARUYAMA S.1996.Metamorphism and tectonics of high-pressure and ultra-high-pressure belts in the Dabie-Sulu region,China[M]//YIN A,HARRISON M T.The Tectonic Evolution of Asia.Cambridge: Cambridge University Press:300-344.

LIU F L,GERDES A,LIOU J G,XUE H M,LIANG F H.2006.SHRIMP U-Pb zircon dating from Sulu-Dabie dolomitic marble,eastern China: constraints on prograde,ultrahigh-pressure and retrograde metamorphic ages[J].Journal of Metamorphic Geology,24(7): 569-589.

LIU X C,JAHN B M,CUI J J,LI S Z,WU Y B,LI X H.2010.Triassic retrograded eclogites and Cretaceous gneissic granites in the Tongbai Complex,central China: implications for the architecture of the HP/UHP Tongbai-Dabie-Sulu collision zone[J].Lithos,119(3-4): 211-237.

LIU X C,JAHN B M,DONG S W,LOU Y X,CUI J J.2008b.High-pressure metamorphic rocks from Tongbaishan,central China: U-Pb and40Ar/39Ar age constraints on the provenance of protoliths and timing of metamorphism[J].Lithos,105(3-4):301-318.

LIU X C,JAHN B M,HU J,LI S Z,LIU X,SONG B.2011.Metamorphic patterns and SHRIMP zircon ages of medium-to-high grade rocks from the Tongbai orogen,central China: implications for multiple accretion/collision processes prior to terminal continental collision[J].Journal of Metamorphic Geology,29(9): 979-1002.

LIU X C,JAHN B M,LIU D Y,DONG S W,LI S Z.2004a.SHRIMP U-Pb zircon dating of a metagabbro and eclogites from western Dabieshan (Hong'an block),China,and its tectonic implications[J].Tectonophysics,394(3-4): 171-192.

LIU X C,WEI C J,LI S Z,DONG S W,LIU J M.2004b.Thermobaric structure of a traverse across western Dabieshan:implications for collision tectonics between the Sino-Korean and Yangtze cratons[J].Journal of Metamorphic Geology,22(4): 361-379.

LIU X M,GAO S,DIWU C R,LING W L.2008a.Precambrian crustal growth of Yangtze craton as revealed by detrital zircon studies[J].American Journal of Science,308(4): 421-468.

LIU Xiao-chun,LOU Yu-xing,DONG Shu-wen.2005.P-T path of low-temperature eclogites from the Tongbaishan area[J].Acta Petrologica Sinica,21(4): 1081-1093(in Chinese with English abstract).

MARUYAMA S,TABATA H,NUTMAN A P,MORIKAWA T,LIOU J G.1998.SHRIMP U-Pb geochronology of ultrahigh-pressure metamorphic rocks of the Dabie Mountains,central China[J].Continental Dynamics,3: 72-85.

PENG Min,WU Yuan-bao,WANG Jing,JIAO Wen-fang,LIU Xiao-chi,YANG Sai-hong.2009.Paleoproterozoic mafic dyke from Kongling Terrain in the Yangtze Craton and its implication[J].Chinese Science Bulletin,54(6): 1098-1104.

QIU Y M,GAO S,MCNAUGHTON N J,GROVES D I,LING W L.2000.First evidence of ＞3.2 Ga continental crust in the Yangtze craton of south China and its implications for Archean crustal evolution and Phanerozoic tectonics[J].Geology,28(1):11-14.

RUBATTO D,GEBAUER D.2000.Use of cathodoluminescence for U-Pb zircon dating by ion microprobe; some examples from the Western Alps[M]// PAGEL M,BARBIN V,BLANC P,OHNENSTETTER D.Cathodoluminescence in Geosciences.Berlin: Springer: 373-400.

SHEN Qi-han,GENG Yuan-sheng,SONG Biao,WAN Yu-sheng.2005.New information from the surface outcrops and deep crust of Archean rocks of the North China and Yangtze Blocks,and Qinling-Dabie orogenic belt[J].Acta Geologica Sinica,79(5): 616-627(in Chinese with English abstract).

SUN M,CHEN N S,ZHAO G C,WILDE S A,YE K,GUO J H,CHEN Y,YUAN C.2008.U-Pb zircon and Sm-Nd isotopic study of the Huangtuling granulite,Dabie-Sulu belt,China:implication for the Paleoproterozoic tectonic history of the Yangtze craton[J].American Journal of Science,308(4):469-483.

WILLIAMS I S,CLAESSON S.1987.Isotopic evidence for the Precambrian provenance and Caledonian metamorphism of high grade paragneisses from the Seve Nappes,Scandinavian Caledonides.II.Ion microprobe zircon U-Th-Pb[J].Contributions to Mineralogy and Petrology,97(2): 205-217.

WILLIAMS I S.1998.U-Th-Pb geochronology by ion microprobe[M]// MCKIBBEN M A,SHANKS W C,RIDLEY W I,Eds.Applications of Microanalytical Techniques to Understanding Mineralizing Processes.Reviews of Economic Geology,7: 1-35.

WU Y B,GAO S,GONG H J,XIANG H,JIAO W F,YANG S H,LIU Y S,YUAN H L.2009.Zircon U-Pb age,trace element and Hf isotope composition of Kongling terrane in the Yangtze Craton: refining the timing of Palaeoproterozoic high-grade metamorphism[J].Journal of Metamorphic Geology,27(6):461-477.

WU Y B,ZHENG Y F,GAO S,JIAO W F,LIU Y S.2008.Zircon U-Pb age and trace element evidence for Paleoproterozoic granulite facies metamorphism and Archean crustal rocks in the Dabie Orogen[J].Lithos,101(3-4): 308-322.

WU Y B,ZHENG Y F,ZHAO Z F,GONG B,LIU X M,WU F Y.2006.U-Pb,Hf and O isotopes evidence for two episodes of fluid-assisted zircon growth in marble hosted eclogites from the Dabie Orogen[J].Geochimica et Cosmochimica Acta,70(14): 3743-3761.

WU Yuan-bao,CHEN Dao-gong,XIA Qun-ke,TU Xiang-lin,CHENG Hao,YANG Xiao-zhi.2003.In-situ trace element analyses and Pb-Pb dating of zircons in granulite from Huangtuling,Dabieshan by LAM-ICP-MS[J].Science in China (Series D),46(11): 1161-1170.

XIA Q X,ZHENG Y F,YUAN H L,WU F Y.2009.Contrasting Lu-Hf and U-Th-Pb isotope systematics between metamorphic growth and recrystallization of zircon from eclogite-facies metagranites in the Dabie orogen,China[J].Lithos,112(3-4):477-496.

XIA Qun-ke,ZHENG Yong-fei,GE Ning-jie,DELOULE E.2003.U-Pb ages and oxygen isotope compositions of zircons from gneiss of Huangtuling,Northern Dabie; old protolith and multi-stage evolution[J].Acta Petrologica Sinica,19(3):506-512(in Chinese with English abstract).

XIONG Qing,ZHENG Jian-ping,YU Chun-mei,SU Yu-ping,TANG Hua-yun,ZHANG Zhi-hai.2008.Zircon U-Pb age and Hf isotope of Quanyishang A-type granite in Yichang: signification for the Yangtze continental cratonization in Paleoproterozoic[J].Chinese Science Bulletin,54(3): 436-446.

YANG J S,WOODEN J L,WU C L,LIU F L,XU Z Q,SHI R D,KATAYAMA I,LIOU J G,MARUYAMA S.2003.SHRIMP U-Pb dating of coesite-bearing zircon from the ultrahigh-pressure metamorphic rocks,Sulu terrane,east China[J].Journal of Metamorphic Geology,21(6): 551-560.

ZHANG Li-juan,MA Chang-qian,WANG Lian-xun,SHE Zhen-bing,WANG Shi-ming.2011.Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance[J].Chinese Science Bulletin,56(3): 306-318.

ZHANG S B,ZHENG Y F,WU Y B,ZHAO Z F,GAO S,WU F Y.2006a.Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China[J].Precambrian Research,151(3-4): 265-288.

ZHANG S B,ZHENG Y F,WU Y B,ZHAO Z F,GAO S,WU F Y.2006b.Zircon U-Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China[J].Earth and Planetary Science Letters,252(1-2):56-71.

ZHANG S B,ZHENG Y F,WU Y B,ZHAO Z F,GAO S,WU F Y.2006c.Zircon isotope evidence for ≥3.5 Ga continental crust in the Yangtze craton of China[J].Precambrian Research,146(1-2): 16-34.

ZHAO Feng-qing,ZHAO Wen-ping,ZUO Yi-cheng,LI Zong-hui.2006.Zircon U-Pb ages of the migmatites from Kongling complex[J].Geological Survey and Research,29(2): 81-85(in Chinese with English abstract).

ZHAO G C,SUN M,WILDE S A,LI S Z.2003.Assembly,accretion and breakup of the Paleo-Mesoproterozoic Columbia supercontinent: records in the North China craton[J].Gondwana Research,6(3): 417-434.

ZHENG J P,GRIFFIN W L,O’REILLY S Y,ZHANG M,PEARSON N,PAN Y M.2006.Widespread Archean basement beneath the Yangtze craton[J].Geology,34(6): 417-420.

ZHENG Y F,ZHANG S B.2007.Formation and evolution of Precambrian continental crust in South China[J].Chinese Science Bulletin,52(1): 1-12.

ZHENG Yong-fei.2003.Neoproterozoic magmatic activity and global change[J].Chinese Science Bulletin,48(16): 1639-1656.

ZHOU Han-wen,LI Xian-hua,LIU Ying,YOU Zheng-dong,SUO Shu-tian,ZHONG Zeng-qiu.1998.Age of granulite from Huangtuling,Dabie Mountain: Pb-Pb dating of garnet by a stepwise dissolution technique[J].Chinese Science Bulletin,44(10): 941-944.

Zircon U-Pb Ages of Paleoproterozoic Metabasites from the Tongbai Orogen and Their Geological Significance

HU Juan,LIU Xiao-chun,QU Wei,CUI Jian-jun
Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing100081

The Tongbai orogen is situated at the junction between the Qinling and Dabie orogenic belts.Its northern part corresponds to the North Qinling medium- to high-grade metamorphic complexes,whereas the southern part belongs to the westward continuation of the Dabie HP/UHP metamorphic complexes.Zircon U-Pb dating reveals a protolith age of (1961±23) Ma and a zircon recrystallization or growth age of (1949±51) Ma for an eclogite,and a metamorphic age of (1936±26) Ma for a garnet amphibolite (retrograded eclogite?).These data suggest that these rocks might have suffered Paleoproterozoic metamorphism prior to Permian-Triassic HP metamorphism.Based on the available geochronological data from the Tongbai-Dabie-Sulu orogen,the authors have inferred the existence of two episodes of Paleoproterozoic tectonothermal events in northern Yangtze block.The first episode occurred at 1.97-1.93 Ga,probably related to the assembly of the Columbia supercontinent.The second episode took place at 1.85-1.82 Ga,resulting either from the protracted assembly of the Columbia supercontinent or from the accretionary orogenesis along the northern margin of the Yangtze block.

Paleoproterozoic; two metamorphic episodes; Yangtze block; Tongbai orogen

P597.3; P588.348 文獻(xiàn)標(biāo)志碼: A doi: 10.3975/cagsb.2012.03.04

本文由國家973項(xiàng)目(編號(hào): 2009CB825006)和中國地質(zhì)調(diào)查局國土資源大調(diào)查項(xiàng)目(編號(hào): 1212010711812)聯(lián)合資助。

2012-03-03; 改回日期: 2012-04-09。責(zé)任編輯: 張改俠。

胡娟,女,1981年生。博士研究生。主要從事變質(zhì)巖石學(xué)研究。E-mail: hujuan1314@163.com。

*通訊作者: 劉曉春,男,1962年生。研究員。主要從事巖石學(xué)研究。E-mail: liuxchqw@yahoo.com.cn。