湘中包金山礦區(qū)花崗閃長斑巖的鋯石U-Pb年齡、Hf-O同位素組成及其地質(zhì)意義

魯玉龍，彭建堂，陽杰華，李玉坤，陳憲佳，周 溪，李干龍

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湘中包金山礦區(qū)花崗閃長斑巖的鋯石U-Pb年齡、Hf-O同位素組成及其地質(zhì)意義

魯玉龍1, 3，彭建堂1, 2，陽杰華2，李玉坤1，陳憲佳1，周 溪1, 3，李干龍3

(1. 中南大學(xué)地球科學(xué)與信息物理學(xué)院有色金屬成礦預(yù)測教育部重點實驗室，長沙 410083；2. 中國科學(xué)院地球化學(xué)研究所礦床地球化學(xué)國家重點實驗室，貴陽 550002；3. 湖南省有色地質(zhì)勘查局二總隊，湘潭 411102)

包金山金礦床是近年在湘中地區(qū)探獲的以金為主的多金屬礦床，其成礦與印支晚期巖漿活動關(guān)系密切。利用高精度SIMS鋯石U-Pb定年方法得到礦區(qū)兩條花崗閃長斑巖年齡分別為(225.1±1.5) Ma和(223.3±1.4) Ma，在誤差范圍內(nèi)一致，屬印支晚期大規(guī)模巖漿活動的產(chǎn)物；礦區(qū)兩條花崗閃長斑巖的176Hf/177Hf值均集中分布在0.2825附近，對應(yīng)的Hf()值介于?5.9~3之間，平均為?3.98，兩階段模式年齡DM2為0.96~1.45 Ga，平均為1.35 Ga；δ18O值為0.824%~0.973%；Hf-O同位素研究表明花崗閃長斑巖主要為中元古代下地殼巖石重熔形成，且有部分幔源物質(zhì)參與成巖作用；與紫云山花崗巖體對比分析，表明兩者為同源巖漿演化的產(chǎn)物，且間接指示包金山金礦成礦時間為227~223 Ma；花崗閃長斑巖形成于多板塊匯聚的動力學(xué)背景，為印支地塊向北擠壓和太平洋板塊向西俯沖共同作用的結(jié)果。

SIMS 鋯石U-Pb年齡；Hf-O同位素示蹤；花崗閃長斑巖；包金山礦床；湘中

隨著一系列典型印支期成礦年齡的確認(rèn)，如荷花坪錫多金屬礦((224±1.9) Ma)[1]、云頭界鎢鉬多金屬礦((216.8±7.5) Ma)[2]、錫田錫鉛鋅多金屬礦((212.8±3.0) Ma)[3]，華南印支期的成礦作用越來越值得重視。在湘中地區(qū)，金屬(多金屬)礦床多分布于印支期花崗巖體周邊，如白馬山雜巖體附近的古臺山石英脈型金銻礦[4]和高家坳微細(xì)浸染型金礦床[5?6]；天龍山巖體附近的大新破碎蝕變巖夾石英脈型金礦[7]；芙蓉巖體附近的廖家坪金銻鎢礦；紫云山巖體附近的包金山金礦等；其成礦與印支期的巖漿活動有著密切的關(guān)系。

白馬山?龍山?紫云山隆起帶為湘中重要的金多金屬成礦帶，其上的金屬礦床主要賦存于受巖漿上侵穹窿作用形成的放射狀或環(huán)狀斷裂中[7?11]。包金山金礦位于該成礦帶的東段(見圖1(b))，為典型的受紫云山穹窿環(huán)狀斷裂和地層聯(lián)合控制的礦床，以石英脈型為主，其成礦流體屬巖漿期后熱液，與礦區(qū)內(nèi)的花崗閃長斑巖有著密切聯(lián)系[12?19]。但是以往地質(zhì)工作對于礦區(qū)內(nèi)花崗閃長斑巖的研究還處于空白，嚴(yán)重制約了對該區(qū)成礦作用的認(rèn)識。

本文作者在野外實地調(diào)查的基礎(chǔ)上，通過高精度 SIMS 鋯石 U-Pb 測年及鋯石原位 Hf-O同位素分析，精確構(gòu)建區(qū)內(nèi)花崗閃長斑巖脈的年代學(xué)格架，深入探討了花崗閃長斑巖的源區(qū)特征及其形成的動力學(xué)背景，不僅為研究紫云山地區(qū)成巖成礦作用奠定了基礎(chǔ)，而且有助于進(jìn)一步研究華南地區(qū)早中生代構(gòu)造?巖漿演化過程。

1 礦區(qū)地質(zhì)概況

包金山金礦床位于湘中盆地的東緣，紫云山巖體北側(cè)3 km處。在大地構(gòu)造位置上，該區(qū)處在揚子地塊與華夏地塊的對接帶(見圖1(a))，長期以來經(jīng)歷了復(fù)雜的構(gòu)造巖漿活動，并伴有大規(guī)模的金屬成礦活動。礦區(qū)出露的地層為元古代板溪群馬底驛組淺變質(zhì)巖系，賦礦地層為第二段傾向北的鈣質(zhì)板巖夾鈣質(zhì)條帶狀板巖及灰?guī)r透鏡體。礦區(qū)主構(gòu)造線方向為近東西向(見圖2)，以斷裂構(gòu)造為主，近東西向斷裂為紫云山穹窿環(huán)狀斷裂的一部分；近南北向、北東向及北西向破礦斷裂。區(qū)內(nèi)花崗閃長斑巖分布廣泛，但產(chǎn)出面積較小，多為脈狀，呈NW走向，傾向北東。本區(qū)主成礦期與印支晚期中酸性巖漿的熱液活動有關(guān)[16?18]。礦區(qū)內(nèi)的花崗閃長斑巖與礦體相互穿插，在其轉(zhuǎn)彎處常有富礦體存在，其對成礦具有重要的疊加改造作用，并為成礦物質(zhì)活化運移及礦體的進(jìn)一步富集提供了熱量和能量，并提供了部分的成礦物質(zhì)[13, 17?19]。圍巖蝕變以絹云母化、硅化、黃鐵礦化與金成礦的關(guān)系最為密切。

本區(qū)金礦以石英脈型為主，主要有脈狀和筒狀兩類礦體。其中脈狀礦體多呈群脈雁形排列，走向NW，傾向SW，傾角45°~67°。該類礦體走向延伸較短，一般在20 m左右，傾向延深相對較長，礦體厚度0.2~2.0 m。筒狀礦體的走向和傾向與脈狀礦體相近，但規(guī)模相對較大，厚度幾米到十幾米，傾向延深可達(dá)百米。金礦化主要位于石英脈與圍巖的接觸部位，近圍巖的石英脈內(nèi)常見明金，金品位變化較大。

圖1 湘中區(qū)域地質(zhì)略圖

圖2 包金山礦區(qū)地質(zhì)略圖

2 巖石巖相學(xué)特征

通過系統(tǒng)的野外地質(zhì)觀察及鏡下顯微鑒定分析，本次所采集的樣品均為花崗閃長斑巖。巖石呈灰黑色，斑狀結(jié)構(gòu)，塊狀構(gòu)造(見圖3(a)和(b))，其淺色礦物為長石、石英，暗色礦物以黑云母為主，斑晶含量約20%~25%，主要由長石(15%~20%)和石英(5%~8%)組成，基質(zhì)含量約75%~80%，主要由它形粒狀石英、長石和黑云母。副礦物主要為鋯石、磁鐵礦等。長石主要是斜長石、次為正長石。長石常沿邊緣、粒間發(fā)生不同程度的絹云母化，整體蝕變強烈，長石可呈殘余狀產(chǎn)出，局部甚至全部蝕變?yōu)榻佋颇付Ａ粼L石的晶體外形(見圖3(d)、(e)和(f))；石英分布零星，主要呈橢圓狀、圓狀以斑晶的形式分布，集合體粒度一般0.5~1.5 mm(見圖3(c)和(e))。

3 樣品采集及測試分析

用于鋯石測年研究的花崗閃長斑巖樣品共有2件，樣品BJS-1采自鉆孔，樣品BJS-2采自10中段的44線附近，樣品均未發(fā)生風(fēng)化。

3.1 鋯石U-Pb年齡測定

鋯石的挑選由河北省廊坊市誠信地質(zhì)服務(wù)有限公司完成，樣品破碎至0.3 mm以下，用人工淘洗和電磁選方法富集鋯石，再在雙目鏡下精選鋯石，未使用任何化學(xué)藥劑。將精選的鋯石用無色透明環(huán)氧樹脂固定并進(jìn)行拋光，使內(nèi)部暴露，進(jìn)行透射光和反射光下照相，并用陰極發(fā)光掃描電子顯微鏡照相，以了解鋯石的內(nèi)部結(jié)構(gòu)，系統(tǒng)對比的基礎(chǔ)上選出最理想的供分析的鋯石顆粒。鋯石陰極發(fā)光(CL)內(nèi)部結(jié)構(gòu)照相在中國科學(xué)院地質(zhì)與地球物理研究所Cameca電子探針儀器上完成，分析電壓為50 kV，電流為15nA。鋯石U-Pb定年在中國科學(xué)院地質(zhì)與地球物理研究所離子探針實驗室的Cameca IMS-1280型二次離子質(zhì)譜儀(SIMS)上進(jìn)行，詳細(xì)的分析流程見文獻(xiàn)[20]。鋯石樣品的Pb/U比值用標(biāo)準(zhǔn)鋯石 TEMORA 2(417 Ma)[19]的ln(206Pb/238U)與ln(238U16O2/238U)之間的線性關(guān)系校正[22]；Th和U含量用標(biāo)準(zhǔn)鋯石91500[23]計算；普通Pb用測量的204Pb進(jìn)行校正；用現(xiàn)代地殼的平均Pb同位素組成[24?25]作為普通Pb組成進(jìn)行校正。單點分析的同位素比值及年齡誤差為1(為絕對誤差)，U-Pb平均年齡誤差為95%置信度。

3.2 鋯石原位Hf、O同位素分析

鋯石微區(qū)原位Hf同位素分析在中國地質(zhì)大學(xué)(武漢)地質(zhì)過程與礦產(chǎn)資源國家重點實驗室(GPMR)利用激光剝蝕多接收杯等離子體質(zhì)譜(LA-MC-ICP-MS)完成。激光剝蝕系統(tǒng)為GeoLas 2005 (Lambda Physik，德國)，配備了信號平滑裝置，使用氦氣作為載氣，并引入少量氮氣來提升元素的靈敏度[26]。詳細(xì)儀器操作條件和分析方法參照文獻(xiàn)[27]。鋯石樣品自身的Yb用于干擾校正[28]；179Hf/177Hf = 0.7325和173Yb/171Yb= 1.132685[29]用于計算Hf和Yb的質(zhì)量分餾系數(shù)Hf和Yb；179Hf/177Hf 和173Yb/171Yb的比值用于計算Hf(Hf) 和Yb (Yb)的質(zhì)量偏差；使用176Yb/173Yb=0.79639[29]來扣除176Yb對176Hf的同量異位干擾；使用176Lu/175Lu=0.02656[30]來扣除干擾程度相對較小的176Lu對176Hf的同量異位干擾；采用 Yb 的質(zhì)量分餾系數(shù)Yb來校正Lu的質(zhì)量分餾行為。分析數(shù)據(jù)的離線處理(包括對樣品和空白信號的選擇、同位素質(zhì)量分餾校正)采用軟件ICP-MS Data Cal完成[31]。

鋯石微區(qū)原位 O 同位素分析在中國科學(xué)院地質(zhì)與地球物理研究所離子探針實驗室的Cameca進(jìn)行。將做過SIMS鋯石U-Pb定年的樣品靶再次磨去約5 μm，以消除前期在U-Pb 定年時造成的氧污染，詳細(xì)的分析流程參見文獻(xiàn)[20]。儀器質(zhì)量分餾校正采用 91500 鋯石標(biāo)準(zhǔn)，其中 91500 標(biāo)準(zhǔn)鋯石的18O= 0.99%[32]，測量的18O/16O比值通過VSMOW值 (18O/16O= 0.0020052)校正后，加上儀器質(zhì)量分餾校正因子IMF即為該點的δ18O值：(18Ο)=((18O/16O)M/0.0020052?1)×100%；IMF= (18O)M(standard)?(18O)VSMOW；18OSample=(18O)M+IMF。

圖3 花崗閃長巖巖相學(xué)特征

4 分析結(jié)果

4.1 鋯石U-Pb年齡

供U-Pb同位素定年的2件花崗閃長斑巖樣品中的鋯石呈灰色長柱狀或短柱狀，顆粒較大，長度100~200 μm，長寬比一般為1.5~4，晶體自形程度較好，大部分具有清晰韻律環(huán)帶結(jié)構(gòu)(見圖4)，并且鋯石的Th/U比值主要介于0.10~0.90之間(見表1和表2)，具有巖漿鋯石的特點[33]。利用Isoplot[34]繪制鋯石的諧和曲線及諧和年齡的投影圖(見圖5)，數(shù)據(jù)點多分布在諧和線上或在諧和線附近呈線狀分布，表明所測的鋯石顆粒在形成后U-Pb同位素體系是封閉的，基本未發(fā)生U或Pb的加入和丟失[35?37]。

樣品BJS-1進(jìn)行了25個點的定年分析，其中有4個測點(8、15、17、18)年齡為離群值，其余21個測點206Pb/238U數(shù)據(jù)得到加權(quán)平均年齡(225.5±3.3) Ma(95%置信度，MSWD=0.21)，諧和年齡為(225.1±1.5) Ma(95%置信度，MSWD=0.40)(見圖5(a))。

圖4 包金山金礦床花崗閃長斑巖鋯石CL圖像及分析點位圖

圖5 包金山金礦床花崗閃長斑巖鋯石U-Pb年齡諧和圖

樣品BJS-2進(jìn)行了25個點的定年分析，其中有4個測點(1、9、18、21)年齡為離群值，其余21個測點206Pb/238U數(shù)據(jù)得到的加權(quán)平均年齡為(223.5±3.2) Ma(95%置信度，MSWD=0.25)，諧和年齡為(223.3±1.4) Ma(95%置信度，MSWD=1.9)(見圖5(b))。

因此，包金山礦區(qū)兩條花崗閃長斑巖的形成年齡分別為(223.3±1.4) Ma 和(225.1±1.5) Ma，其形成時間在誤差范圍內(nèi)一致，屬印支晚期的產(chǎn)物。

4.2 鋯石的Hf、O同位素組成特征

對樣品BJS-1的鋯石進(jìn)行微區(qū)原位Hf同位素分析，初始176Hf/177Hf比值為0.282494~0.282729之間，平均為0.282538，對應(yīng)的Hf()為?5.3~3(見圖6(a))，平均為?3.4，兩階段模式年齡DM2為0.96~1.41 Ga，平均為1.32 Ga。鋯石微區(qū)原位O同位素分析，18O為0.824%~0.973%(見圖6(b))，平均為0.907%。

對樣品BJS-2的鋯石進(jìn)行微區(qū)原位Hf同位素分析，初始176Hf/177Hf比值為0.282286~0.282592，平均為0.282498，對應(yīng)的Hf()為?5.9~?2.3(見圖6(a))，平均值?4.5，兩階段模式年齡DM2為1.25~1.45 Ga，平均為1.37 Ga。鋯石微區(qū)原位O同位素分析，18O為0.866%~0.948%(見圖6(b))，平均為0.916%。

對花崗閃長斑巖樣品BJS-1和BJS-2的鋯石顆粒(包括定年的鋯石)進(jìn)行了微區(qū)原位Hf-O同位素測定，分析結(jié)果分別見表3和4。

5 討論

5.1 成巖年代及意義

本實驗中采用高精度SIMS鋯石U-Pb測年方法獲得的包金山礦區(qū)花崗閃長斑巖年齡為(225.1±1.5) Ma 和(223.3±1.4) Ma，在誤差范圍內(nèi)一致。其與臨近的紫云山花崗巖體(鋯石SIMS U-Pb(227.0±2.2)~ (225.2±1.7) Ma[38]；鋯石LA-ICP-MS U-Pb(222.5±1.0) Ma~(222.3±1.8) Ma[39])、歇馬花崗巖體(鋯石SHRIMP U-Pb(218±3) Ma[40]；鋯石SHRIMP U-Pb(214.1±5.9) Ma[41])以及與區(qū)域上的南岳花崗巖體(鋯石LA-ICP-MSU-Pb(215.5±1.5) Ma[42]、溈山花崗巖體(黑云母Rb-Sr(227.0±13) Ma和(221.9±5.8) Ma[43])、大神山花崗巖體(鋯石LA-ICP-MS(224.3±1.0) Ma[44])、白馬山花崗巖體(鋯石LA-ICP-MS U-Pb(224.3±2.4) Ma、(221.4±4.0) Ma和(226.6±4.1) Ma[45])的成巖時限基本一致，表明礦區(qū)內(nèi)花崗閃長斑巖屬于印支晚期(230~200 Ma)大規(guī)模巖漿活動的組成部分[37, 46]。該類花崗閃長斑巖在區(qū)域上廣泛發(fā)育，在紫云山巖體主體花崗巖中也偶見出露，其與紫云山巖體應(yīng)屬同期不同階段的產(chǎn)物，形成時間應(yīng)略晚于后者。

表1 包金山礦區(qū)花崗閃長斑巖樣品BJS-1鋯石U-Pb(SIMS)分析結(jié)果

表2 包金山礦區(qū)花崗閃長斑巖樣品BJS-2鋯石U-Pb(SIMS)分析結(jié)果

Test method: SIMS; Test unit: Beijing Nano SIMS Lab, Institute of Geology and Geophysics, Chinese Academy of Sciences.

圖6 包金山金礦床花崗閃長斑巖的Hf和O同位素組成

表3 包金山金礦床花崗閃長斑巖BJS-1鋯石Hf-O同位素分析結(jié)果

包金山金礦產(chǎn)于紫云山巖體入侵形成的環(huán)狀斷裂內(nèi)，那么其成礦時間不會早于紫云山巖體的侵位時間；而花崗閃長斑巖脈穿插包金山礦脈，表明包金山成礦不會晚于花崗閃長斑巖的形成時間。因此，包金山成礦時間應(yīng)介于紫云山巖體((227.0±2.2)~(225.2±1.7) Ma[38])和包金山花崗閃長斑巖((225.1±1.5) Ma 和(223.3±1.4) Ma)侵位時間之間，即227~223 Ma。

5.2 巖漿源區(qū)及意義

對花崗閃長斑巖鋯石原位Hf-O同位素數(shù)據(jù)統(tǒng)計(見圖6)，其Hf-O同位素的組成基本相似，基本可以重疊。初始176Hf/177Hf值均集中分布在0.2825附近，對應(yīng)的Hf()值在?5.9~3.0之間，平均為?3.98；兩階段模式年齡DM2為0.96~1.45 Ga，平均為1.35 Ga；18O值為0.824~0.973%之間，均大于地幔18O值((0.53±0.03)%)[47]；在Hf()-U/Pb Age圖解中(見圖7(a))，樣品點主要落于下地殼區(qū)域，表明花崗閃長斑巖為中元古代下地殼巖石重熔形成。而在18O-Hf()圖解中(見圖7(b))，Hf-O同位素完全落在以大容山過鋁質(zhì)花崗巖為代表的地殼端元區(qū)域以外，表明源區(qū)有幔源巖漿的加入，且加入地幔物質(zhì)的比例至少可達(dá)20%[48?49]。樣品BJS-1的12號測點，初始176Hf/177Hf比值較大，對應(yīng)其年齡計算的Hf()值為3.0(見表3和4)，其可能為幔源物質(zhì)參與的結(jié)果。與臨近的紫云山巖體相比，兩者的Hf同位素組成基本相同，分布范圍和峰值基本一致(見圖6(a))；兩者的O同位素組成也基本相似，不過花崗閃長斑巖18O值的峰值略高一些(見圖6(b))，這可能是由于花崗閃長斑巖后期發(fā)生蝕變的結(jié)果。在圖7中，花崗閃長斑巖與紫云山花崗巖落于同一區(qū)域，表明兩者為同源的 特征。

表4 包金山金礦床花崗閃長斑巖樣品BJS-2鋯石Hf-O同位素分析結(jié)果

Zirons Hf isotopic: LA-MC-ICP-MS, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan) Airons Hf Isotopic; Beijing nano SIMS Lab, Institute of Geology and Geophysics, Chinese Academy of Sciences.

因此，本文作者認(rèn)為區(qū)內(nèi)花崗閃長斑巖由中元古代下地殼巖石熔融，與幔源巖漿形成的殼、?；旌蠋r漿源區(qū)演化而來，其與紫云山花崗巖體應(yīng)屬于同源巖漿不同演化階段的產(chǎn)物。

5.3 動力學(xué)背景探討

在華南地塊內(nèi)印支晚期花崗巖的逐漸確認(rèn)，尤其是一系列印支晚期 A 型花崗巖的發(fā)現(xiàn)，如湖南的錫田巖體、浙江的大爽巖體、江西蔡江巖體和福建高溪巖體等[39, 50?55]，對于華南印支晚期花崗巖形成于地殼伸展構(gòu)造體制的認(rèn)識已經(jīng)成為共識。但對于華南印支期花崗巖形成的動力學(xué)背景還存在分歧，部分學(xué) 者[44, 53?60]認(rèn)為印支運動期間(約260 Ma)，印支地塊向北擠壓，與華南地塊發(fā)生碰撞，導(dǎo)致地層加厚，之后10~20 Ma發(fā)生熱?應(yīng)力松弛作用，進(jìn)入伸展階段，地殼減壓熔融，進(jìn)而形成花崗巖。LI等[61]認(rèn)為，在中二疊世(約280 Ma)太平洋板塊西緣轉(zhuǎn)為活動大陸邊緣，開始向華南地塊俯沖，到三疊世華南地塊發(fā)生造山運動，之后進(jìn)入伸展?減薄構(gòu)造背景，地殼熔融形成花崗巖[62]。從印支期華南地塊內(nèi)的構(gòu)造變形來分析，其以NE-NNE向的褶皺及逆沖推覆構(gòu)造為主，單純印支地塊引起的南北向的擠壓應(yīng)力很難解釋這些構(gòu)造的形成。這些構(gòu)造的形成應(yīng)與同期東部太平洋板塊的俯沖有著密切的關(guān)系。

圖7 包金山金礦床花崗閃長斑巖εHf(t)?U/Pb圖解(a)和δ18O?εHf(t)圖解(b)

所以，本文作者認(rèn)為華南印支期應(yīng)該屬于多板塊匯聚的動力學(xué)背景，其構(gòu)造變形和同期花崗巖的形成應(yīng)為印支地塊向北擠壓和太平洋板塊向西俯沖共同作用的結(jié)果。

6 結(jié)論

1) 包金山礦區(qū)兩條花崗閃長斑巖鋯石SIMS U-Pb 年齡分別為(225.1±1.5) Ma和(223.3±1.4) Ma，在誤差范圍內(nèi)一致，其與印支晚期(230~200 Ma)大規(guī)模的巖漿活動時限一致，并間接的指示了包金山成礦時間為227~223 Ma，屬典型印支晚期成礦。

2) 花崗閃長斑巖由中元古代下地殼巖石重熔與部分幔源巖漿組成的殼、幔混合巖漿源區(qū)演化而來，其與紫云山巖體為同源不同演化階段的產(chǎn)物。

3) 花崗閃長斑巖形成于多板塊匯聚的動力學(xué)背景，為印支地塊向北擠壓和太平洋板塊向西俯沖共同作用的結(jié)果。

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(編輯 龍懷中)

Zircon U-Pb ages and Hf-O isotopes of granodiorite -porphyry in Baojinshan mining area and their geological significance

LU Yu-long1, 3, PENG Jian-tang1, 2, YANG Jie-hua2, LI Yu-kun1, CHEN Xian-jia1, ZHOU Xi1, 3, LI Gan-long3

(1.Key Laboratory of Non-ferrous Metals Metallogenic Prediction, Ministry of Education,School of Geosciences and Info-physics, Central South University, Changsha 410083, China;2. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry,Chinese Academy of Sciences，Guiyang 550002, China;3. The Second Corps of Nonferrous Geological Prospecting Bureau in Hunan Province,Geological Exploration Institute, Xiangtan 411102, China)

Baojinshan gold deposit is Au-dominated polymetallic deposit discovered recently in central Hunan, its mineralization is considered to be closely related to the magmatic activities in late Indosinian. High accuracy SIMS zircon U-Pb age determination was used in this study to obtain the ages of two granodiorite-porphyry dykes at (225.1±1.5) Ma and (223.3±1.4) Ma, indicating that this deposit was the product of extensive magma activity in late Indosinian. The176Hf/177Hf values of two granodiorite-porphyry dykes intensively distributed around 0.2825, with the correspondingHf() ranged from ?5.9 to 3, averaging ?3.98. The TDM2model age was estimated from 0.96 GPa to 1.45 Ga, averaging 1.35 Ga; the18O value of granodiorite-porphyry ranged from 0.824% to 0.973%. Hf-O isotope analysis shows that the granodiorite-porphyry is mainly formed by the rock remelting of Mesoproterozoic lower crust, and mantle-sourced materials are considered to participate the diagenesis. Contrastive analysis on the granodiorite-porphyry in Baojinshan with Ziyunshan granite suggests that both of them are the products of comagmatic evolution, which indirectly indicates that the metallogenetic time of Baojinshan gold deposit ranges in 227?223 Ma. The granodiorite-porphyry is formed under the multi-plates convergent dynamics background, and affected by the northward squeeze of Indochina Block and westward subduction of Pacific Plate.

SIMS U-Pb zircon dating; Hf-O isotopes tracing; granodiorite-porphyry; Baojinshan gold deposit; central Hunan Province

Project (41473043, 41272096) supported by the National Natural Science Foundation of China

2016-06-17; Accepted date: 2016-10-25

PENG Jian-tang; Tel: +86-13787787177; E-mail: jtpeng@126.com

10.19476/j.ysxb.1004.0609.2017.07.16

1004-0609(2017)-07-1441-14

P588.121；P597.3

A

國家自然科學(xué)基金資助項目(41473043，41272096)

2016-06-17；

2016-10-25

彭建堂，教授，博士；電話：13787787177；E-mail：jtpeng@126.com