柴北緣烏蘭地區花崗巖鋯石SHRIMP定年及其成因

吳才來, 雷 敏, 吳 迪, 李天嘯

1)中國地質科學院地質研究所, 北京 100037; 2)中國地質大學(北京), 北京 100083

柴北緣烏蘭地區花崗巖鋯石SHRIMP定年及其成因

吳才來1), 雷 敏1), 吳 迪2), 李天嘯2)

1)中國地質科學院地質研究所, 北京 100037; 2)中國地質大學(北京), 北京 100083

柴北緣烏蘭地區花崗巖鋯石SHRIMP U-Pb定年結果表明, 哈德森溝巖體的年齡為(413±3) Ma, 許給溝巖體的年齡為(254±3) Ma, 椅落山巖體的年齡為(251±1) Ma, 察汗諾巖體角閃閃長巖和花崗巖的年齡分別為(249±1) Ma和(248±2) Ma, 察汗河巖體年齡為(240±2) Ma, 曬勒克郭來巖體的花崗閃長巖和花崗巖年齡分別為(250±1) Ma和(244±3) Ma。從年齡上看, 這些花崗巖明顯地分為兩期: 早期屬早泥盆世(年齡為413 Ma), 形成的巖石組合為: 石英二長巖+堿長花崗巖; 晚期屬晚二疊世—早三疊世(年齡為254～240 Ma),又可進一步細分為254～251 Ma、250～248 Ma、244～240 Ma三次侵位, 對應的巖石組合為: 閃長巖+花崗閃長巖+花崗巖。巖石地球化學研究表明, 早期花崗巖類不僅富集大離子親石元素, 而且還富集部分高場強元素(Zr、Y、Nb等), 屬A型花崗巖; 晚期花崗巖類富集大離子親石元素, 虧損高場強元素, 屬I型花崗巖。早期花崗巖的87Sr/86Sr比值(0.710 8)和Nd模式年齡(T2DM=2.10 Ga)均高于晚期花崗巖(0.707 6～0.710 7, T2DM=1.41～1.58 Ga), 但晚期花崗巖的εNd(t)值(?11.6)低于早期花崗巖(?4.8 ～ ?6.8), 表明早期A型花崗巖可能起源于古元古代的大陸地殼, 而晚期I型花崗巖起源于中元古代地殼。結合區域地質構造特征, 我們認為,早期A型花崗巖的形成與祁連巖石圈拆沉導致歐龍布魯克陸塊北緣減薄、拉伸有關, 也標志著宗霧隆裂陷的開始; 而晚期I型花崗巖類的形成與宗霧隆洋殼向南俯沖于歐龍布魯克陸塊之下有關。

花崗巖; 鋯石SHRIMP定年; 歐龍布魯克陸塊; 宗霧隆構造帶; 烏蘭

柴北緣自1998年發現榴輝巖以來, 一直是地學界研究的熱點地區之一(Yang et al., 1998; 楊經綏等, 2000), 許多學者對區內的超高壓變質作用開展了深入的研究, 取得了許多重要成果(宋述光和楊經綏, 2001; Song et al., 2003a, b, 2005, 2006, 2009, 2011, 2014a, b; Yang et al., 2005; Zhang et al., 2005, 2008, 2009, 2010, 2014; Mattinson et al., 2006; 宋述光等, 2007, 2009, 2013; Chen et al., 2009; Yu et al., 2012, 2014)。在該區的榴輝巖及其圍巖片麻巖中發現了許多超高壓變質礦物如柯石英、金剛石和超高壓微結構(Liu et al., 1996, 2002; 楊經綏等, 2001; 張建新等, 2002; Song et al., 2005), 因此, 該區成為中國境內繼蘇魯—大別之后的又一條超高壓變質帶(楊經綏等, 2000; 陳丹玲等, 2005)。柴北緣地區呈北西向窄長帶狀從阿爾金山向東沿伸到鄂拉山, 約800 km(圖1),其南北分別被柴達木北緣斷裂和中祁連南緣斷裂(宗務隆—青海南山斷裂)所切, 北西端被阿爾金左行走滑斷裂所切, 東南端被哇洪山斷裂所切(陸松年等, 2002, 2004; 林慈鑾等, 2006)。柴北緣地區以NW向的魚卡—烏蘭斷裂為界分為南北兩個構造單元,南部構造單元為超高壓變質帶, 北部構造單元是歐龍布魯克陸塊(青海省地質礦產局, 1991)。近些年,對南部構造單元上的花崗巖做了較多的研究工作,并取得了許多成果, 特別是花崗巖的年代學研究方面取得了長足進展(吳才來等, 2001, 2004, 2007, 2008, 2010, 2014; 袁桂邦等, 2002; Xiao et al., 2004;孟繁聰等, 2005; 盧欣祥等, 2007; Yu et al., 2012; Song et al., 2014a)。然而, 柴北緣北部構造單元上的花崗巖定年及研究工作仍不多見。尤其是和都蘭超高壓地體相鄰的烏蘭地區, 出露眾多的花崗巖侵入體, 這些花崗巖體的時代及成因以及與都蘭地區乃至與柴北緣南部構造單元上花崗巖有何成因聯系、所反映的構造信息等問題仍不清楚。因此, 我們完成了烏蘭地區花崗巖類的詳細地球化學和年代學研究, 試圖對上述問題作一探討。

1 地質背景及巖體地質特征

柴北緣前寒武紀基底由一套中-高級片麻巖、角閃巖和片巖組成, 其上被早古生代奧陶紀火山巖和砂巖、灰巖覆蓋, 這是一套大陸活動邊緣的海相沉積。晚古生代地層由晚泥盆世陸相碎屑巖、火山巖和石炭紀淺海相沉積巖組成。侏羅紀和白堊紀含煤沉積地層覆蓋在晚古生代地層之上(青海省地質礦產局, 1991)。柴北緣北部構造單元沿烏蘭—德令哈—歐龍布魯克—全吉山—達肯大坂山一線分布, 由德令哈雜巖、達肯大坂群和新元古代巖群組成結晶基底, 其上被寒武—奧陶紀穩定的海相沉積巖所覆蓋(陸松年等, 2002, 2004; 辛后田等, 2002; 王惠初等, 2006); 南部構造單元沿都蘭北部的沙柳河—野馬灘—錫鐵山—綠梁山—魚卡—賽什騰山一線分布,是一條早古生代俯沖-碰撞雜巖帶, 由含榴輝巖的花崗質片麻巖和早古生代灘間山群島弧火山巖組成(陸松年等, 2002, 2004; 辛后田等, 2002; 王惠初等, 2006), 其上被泥盆紀磨拉石沉積巖不整合覆蓋。柴北緣北構造單元歐龍布魯克陸塊與中南祁連陸塊之間是土爾根大坂—宗霧隆—青海南山構造帶(簡稱宗霧隆構造帶)(彭淵等, 2016)(圖1)。宗務隆構造裂谷帶由石炭紀宗務隆群和早—中三疊世郡子河群組成, 兩者呈斷層接觸。宗務隆群包括土爾根大坂組和果可山組, 是一套半深海相復理石沉積和中酸性-基性火山巖系?？ぷ雍尤簩儆跍\海相碎屑巖和碳酸鹽巖沉積建造(青海省地質礦產局, 1991)。宗務隆構造帶的沉積建造向東可延至青海橡皮山一線, 被認為屬于華北陸塊南緣斜坡相沉積, 并與秦嶺—昆侖海盆相鄰(郭安林等, 2007, 2009)。

本文研究的花崗巖體主要分布在柴北緣北部構造單元歐龍布魯克微陸塊東部烏蘭地區(圖1), 與宗霧隆構造帶相鄰。從東到西分別為許給溝巖體、椅落山巖體、察汗諾巖體、察汗河巖體、哈德森溝巖體和曬勒克郭來巖體(圖2)。這些巖體長軸方向為NW向, 部分巖體由若干個NW向延伸的巖體復合而成, 形成不規則狀近EW向的巖基, 如椅落山巖體和曬勒克郭來巖體。巖體的巖石類型主要為角閃閃長巖、石英閃長巖、石英二長巖、花崗閃長巖和花崗巖。巖體的圍巖主要為晚古生代(C-T2)的灰色片巖、片麻巖、灰白色大理巖、變粒巖及綠色中基性火山巖, 其次有少量的早古生代(∈-O)凝灰巖、安山巖夾片巖、薄層大理巖、白云巖、石英巖、陽起透輝石巖等。

圖2 烏蘭地區花崗巖分布示意地質圖(據1/200 000烏蘭幅和天峻幅地質圖修編)Fig. 2 Geological sketch map showing distribution of granites in Wulan area (modified after 1/200 000 Geological Map of Wulan Sheet and Tianjun Sheet)

各巖體主要地質特征見表1, 主要巖石類型的巖石學特征見表2。

表1 各巖體地質特征Table 1 Geological characteristics of rock mass

表2 巖石學特征Table 2 Petrologic characteristics of rock mass

圖3 鋯石CL圖像Fig. 3 Cathodoluminescence (CL) images of zircons of the granites from Wulan area

2 鋯石SHRIMP定年

8個樣品鋯石SHRIMP U-Pb定年數據列于表3, 定年方法見吳才來等(2014)。

樣品CL05-82取自椅落山巖體花崗閃長巖。該樣品的鋯石為柱狀, 長寬比為1.5∶1～2∶1。CL圖像顯示, 大多數鋯石具有明顯的振蕩環帶, 反映了巖漿結晶鋯石的特點(Pidgeon et al., 1998; Corfu et al., 2003; Hoskin and Schaltegger, 2003)。少量的鋯石具有老的繼承性核, 如鋯石6、7號測點(圖3)。測定的9顆鋯石14個測點得出, U的含量變化于172×10-6到1 190×10-6之間, Th的含量變化于74×10-6到820×10-6之間, Th/U比值除老的繼承性鋯石核外,其余的均大于0.3(0.33～0.71)(表3)。該樣品除老的繼承性鋯石核(6、7號測點)的年齡為(430.2±3.4) Ma、(405.9±3.2) Ma外, 其余具有環帶結構的鋯石U-Pb年齡變化于(244.4±1.7) Ma到(267.6±2.9) Ma之間,計算平均年齡為(251.3±1.5) Ma(圖4), 代表鋯石的結晶年齡(圖4)。

續表3

圖4 柴北緣東段花崗巖鋯石207Pb/206Pb-238U/206Pb諧和圖及平均年齡Fig. 4207Pb/206Pb-238U/206Pb concordia diagram and average age of the granites from Wulan area

樣品CL05-84取自察汗諾巖體的角閃閃長巖,樣品中的鋯石大小不一, 但都呈柱狀, 長寬比為2:1～3:1。CL圖像顯示, 鋯石內部具有寬條帶狀、扇狀結構, 部分鋯石外圍具有環帶結構(圖3)。該樣品12顆鋯石測得的U、Th含量分別為176×10-6～520×10-6和160×10-6～960×10-6, Th/U比值變化于0.87到1.92之間(表3)。12個分析點得出U-Pb年齡變化于(244.8±2.9) Ma到(251.7±2.2) Ma之間, 得出平均年齡為(249.1±1.3) Ma, 與207Pb/206Pb-238U/206Pb諧和圖產生的交點年齡為(248.1±2.4) Ma, 在誤差范圍內與平均年齡一致(圖4)。

樣品CL05-85取自察汗諾巖體的花崗巖, 鋯石呈柱狀, 長寬比為1.5∶1～2∶1。CL圖像顏色較深, 鋯石具有環帶結構和板狀結構, 部分含有大小不同的礦物包裹體(圖3)。鋯石的U、Th含量較高, 變化較大, 分別為309×10-6～1 907×10-6和169×10-6～3 257×10-6, Th/U比值通常大于0.5, 變化于0.52～1.76之間(表3)。12顆鋯石分析得出U-Pb年齡變化于(236.4±3.3)～(425.9±3.1) Ma, 其中12號鋯石測點為老的繼承性核(年齡為(425.9±3.1) Ma), 其余鋯石測點得出平均年齡為(247.9±2.1) Ma, 解釋為鋯石的結晶年齡(圖4)。

圖5 鋯石CL圖像Fig. 5 Cathodoluminescence (CL) images of zircons of the granites from Wulan area

圖6 柴北緣東段烏蘭花崗巖鋯石207Pb/206Pb-238U/206Pb諧和圖及平均年齡Fig. 6207Pb/206Pb-238U/206Pb concordia diagram and average age of the granites from Wulan area

表4 柴北緣東段烏蘭花崗巖類化學成分Table 4 Chemical composition of the granites from Wulan area, eastern segment of North Qaidam

續表4

圖7 SiO2-(Na2O+K2O)圖Fig. 7 Diagram of SiO2-(Na2O+K2O) for the granites from Wulan area

樣品CL05-88取自曬勒克郭來巖體花崗閃長巖,樣品中的鋯石呈柱狀, 長寬比為1∶1～2∶1。CL圖像顯示出明顯的振蕩環帶(圖3)。鋯石的U、Th含量分別為231×10-6～554×10-6、120×10-6～438×10-6, Th/U比值大于0.5(變化于0.52～0.95之間)。14顆鋯石測年產生206Pb/238U年齡變化于(245.0±2.1) Ma到(254.4±1.9) Ma之間, 平均年齡為(249.9±1.4) Ma(圖4)。207Pb/206Pb-238U/206Pb諧和圖得出交點年齡為(250.2±1.3) Ma, 與平均年齡在誤差范圍內一致(圖4)。

樣品CL05-90取自哈德森溝花崗巖, 鋯石為柱狀, 長寬比為1∶1到2∶1之間。CL圖像顏色較深, 少量的鋯石可見同心環帶, 多數鋯石含有不規則的黑色團塊, 可能反映了后期流體沿裂隙的改造(圖 5)(Cherniak and Watson, 2000)。16顆鋯石分析結果表明, U、Th的含量分別為546×10-6～4 060×10-6、195×10-6～2 329×10-6, Th/U比值變化于0.32到1.89之間,分析得出平均年齡為(412.6±3.2) Ma(圖6),207Pb/206Pb-238U/206Pb諧和圖得出交點年齡為(412.4±3.5) Ma(圖6), 兩者非常一致, 代表巖體結晶年齡。

樣品CL05-92取自察汗河花崗閃長巖, 鋯石呈自形的短柱狀, 長寬比為1∶1～1.5∶1。CL圖像顯示出較好的振蕩環帶(圖5)。U、Th含量分別為131×10-6～644×10-6、108×10-6～530×10-6, Th/U比值大于0.5(變化于0.53到0.91之間)(表3)。除11號鋯石為老的捕獲鋯石(年齡為(2 474.4±26.8) Ma)外,其余12顆鋯石測年得出較為一致的結果, U-Pb年齡為(234.9±1.9)～(247.0±1.7) Ma, 平均為(240.3±2.3) Ma (圖6),207Pb/206Pb-238U/206Pb諧和圖年齡為(242.5±3.2) Ma(圖6), 在誤差范圍內與平均年齡一致, 代表巖體結晶年齡。

樣品CL05-93取自曬勒克郭來巖體的花崗巖,樣品中鋯石為柱狀, 鋯石長寬比為1.5∶1～2∶1。盡管鋯石的CL圖像顏色較深, 但部分鋯石仍具有明顯的振蕩環帶, 部分鋯石核部結構很復雜, 顯示出受到流體的改造(圖5)。測定結果表明, 鋯石的U、Th含量變化較大, 分別為184×10-6～5 733×10-6和102×10-6～16 707×10-6, Th/U比值變化于0.49和3.01之間(表3)。17顆鋯石測年得出206Pb/238U年齡變化于(209.6±1.1) Ma到(249.8±0.7) Ma之間, 除去受流體改造的鋯石, 得出平均年齡為(243.9±2.9) Ma(圖6),207Pb/206Pb-238U/206Pb諧和圖得出交點年齡為(236.2±7.8) Ma(圖6), 與平均年齡在誤差范圍內基本一致, 可解釋為巖體結晶的年齡(圖6)。

圖8 SiO2-Fe＊和MALI圖(據Frost et al., 2001; Frost and Frost, 2008; 圖例同圖7 )Fig. 8 Diagrams of SiO2-Fe＊ and SiO2-MALI for the granites from Wulan area (after Frost et al., 2001; Frost and Frost, 2008; symbols as for Fig. 7) Fe*=FeOT/(FeOT+MgO); MALI=Na2O+K2O-CaO

樣品CL9956取自許給溝花崗巖, 該樣品的鋯石呈長柱狀, 長寬比在2∶1到3∶1之間。CL圖像表明, 大多數鋯石具有明顯的振蕩環帶, 少數鋯石具有板狀結構(圖5), 這也是典型的巖漿鋯石(Pidgeon et al., 1998)。測試分析表明, 鋯石的U、Th含量分別為613×10-6～1 030×10-6、305×10-6～811×10-6, Th/U比值為0.44～0.94(表3)。該樣品9顆鋯石測年得出的年齡變化于(244.0±6.5)～(270.0±12.0) Ma, 計算平均年齡為(254.2±3.5) Ma, 代表鋯石的結晶年齡(圖6)。

圖9 A/CNK-A/NK圖(據Maniar and Piccoli, 1989; 圖例同圖7 )Fig. 9 Diagram of A/CNK-A/NK for the granites from Wulan area(after Maniar and Piccoli, 1989; symbols as for Fig. 7)

圖10 哈克圖解(圖10 g據Peccerillo and Taylor, 1976; 圖例同圖7 )Fig. 10 Harker diagrams for the granites from Wulan (Fig. 10g after Peccerillo and Taylor, 1976; symbols as for Fig. 7)

根據上面鋯石SHRIMP U-Pb定年結果, 烏蘭地區花崗巖類除哈德森溝巖體為(412.6±3.2) Ma(屬早泥盆世)外, 其余各巖體的年齡變化于254～240 Ma之間, 屬晚二疊—中三疊世。早期巖石組合: 石英二長巖+花崗巖; 晚期花崗巖進一步可劃分出三個侵入次序, 即(1)晚二疊(254～251 Ma), 主要為椅落山巖體和許給溝巖體; (2)早三疊(250～248 Ma), 主要為察汗諾巖體和曬勒克郭來西巖體; (3)中三疊(244～240 Ma), 主要為察汗河巖體和曬勒克郭來東巖體。巖石組合分別為: (1)石英閃長巖+花崗閃長巖+花崗巖; (2)角閃閃長巖+花崗閃長巖+花崗巖; (3)花崗閃長巖+花崗巖。

3 巖石地球化學

16個樣品分析了主量和微量元素, 定年樣品分析了Sr、Nd同位素, 數據分別列于表4、5。全巖及同位素分析方法見吳才來等(2014)。

3.1 主量和微量元素

早期花崗巖類石英二長巖、花崗巖具有60.72～73.37 wt％的SiO2, 13.23～18.07 wt％ Al2O3, 2.08～3.07 wt％ TFeO, 0.37～0.43 wt％ MgO, 0.52～2.2 wt％ CaO, 3.67～6.58 wt％ Na2O, 5.11～5.97 wt％ K2O; 晚期花崗巖類除樣品CL05-82-2(角閃閃長巖)外, 其余的具有64.97～77.69 (wt％)的SiO2, 12.30～16.40 wt％ Al2O3, 0.82～4.61 wt％ TFeO, 0.15～2.24 wt％ MgO, 0.56～5.04 wt％ CaO, 2.98～3.65 wt％ Na2O, 1.62～4.79 wt％ K2O。在硅堿圖上,早期花崗巖類樣品分別落入正長巖區和花崗巖區,晚期的石英閃長巖和花崗閃長巖主要投入花崗閃長巖區, 二長花崗巖和正長花崗巖主要投入花崗巖區,而樣品CL05-82-2落入輝長巖區(圖7)(Irvine and Baragar, 1971; Middlemost, 1994)。由圖7可見, 烏蘭地區侵入巖類主要為亞堿性系列巖石, 早期花崗巖類的全堿含量明顯高于晚期巖石(圖7), 且主要為堿鈣性-堿性的Fe質類型(圖8)。晚期巖石主要為鈣性-鈣堿性的Mg質類型, 少量的為Fe質類型(圖8)(Frost et al., 2001; Frost and Frost, 2008), 且隨著SiO2含量的增加, 巖石由準鋁質到弱過鋁質(圖9)(Maniar and Piccoli, 1989)(表4), 其中, 晚期第一、二次侵位的花崗巖類為準鋁質, 第三次侵位的巖石為弱過鋁質(圖9)。同時, 早、晚兩期花崗巖類隨硅的增加, K2O由中鉀(鈣堿性)到高鉀(高鉀鈣堿性)地增加, TiO2、Al2O3、TFeO (FeO+Fe2O3)、MgO、CaO和P2O5表現出規律性地減少, 但Na2O變化規律不同(圖10)。早期的Na2O變小, 晚期第一次花崗巖類幾乎不變, 其余各次巖石的Na2O增加。

圖11 花崗巖類微量元素蛛網圖(原始地幔值據McDonough and Sun, 1985; 樣品號同表1)Fig. 11 Primitive mantle-normalized trace-element spider diagrams(normalized values after McDonough et al., 1985; sample numbers as for Table 1)

早期的花崗巖類不僅富集大離子親石元素(LILE)如K、Rb、La和Th, 而且也富集高場強元素(HFS)如Sc、Y、Zr、Hf和Nb(表4), 晚期花崗巖類則富集大離子親石元素, 相對虧損高場強元素(表 4)。在微量元素蛛網圖上, 早期花崗巖類具有非常明顯的Ba、Nb、Sr、P和Ti負異常(圖11); 晚期花崗巖類具有相似的微量元素原始地幔標準化模型,即Nb、P、Ti具有負異常(圖11), 而Sr具有弱的正異常到弱的負異常, 與早期花崗巖具有明顯的Sr負異常不同(圖11)(McDonough and Sun, 1985)。

圖13 花崗巖類稀土元素球粒隕石標準化圖(稀土球粒隕石值據Boynton, 1984; 樣品號同表3)Fig. 13 Chondrite-normalized REE patterns for the granites (normalized values after Boynton, 1984; sample numbers as for Table 3)

3.2 稀土元素

花崗巖類稀土總量變化于73.35×10-6到740.89×10-6之間(表4), 早期花崗巖類具有最高的稀土總量(480.57×10-6～740.89×10-6), 且隨著SiO2含量的增加, 稀土總量降低(表4); 晚期各次花崗巖類稀土總量變化范圍分別為: 73.35×10-6～130.94×10-6、87.6×10-6～214.59×10-6、82.01×10-6～203.54×10-6(表4), 第一、二次花崗巖類稀土總量隨SiO2增加而升高, 但第三次花崗巖類降低(圖12a, 表4)。兩期花崗巖類的稀土總量與Zr的含量成正相關, 表明鋯石可能是稀土元素的主要載體礦物(圖12b, 表4)。所有樣品均富集輕稀土元素, LREE/HREE比值變化于5.25～25.27之間(表4)。相對而言, 晚期各次花崗巖類各樣品的輕重稀土比值變化較大, 分別為5.25～18.02、6.34～25.27、6.14～14.55, 早期花崗巖類為10.00～12.03。球粒隕石標準化模型表明, 早期花崗巖類具有明顯的負Eu異常(δEu=0.11～0.15), 晚期花崗巖類大多數不具有Eu負異常和少數具有弱的負Eu異常, δEu分別為0.63～1.15、0.35～0.95、0.30～0.80。各期次花崗巖類樣品具有相似的稀土配分曲線, 且基本平行(Boynton, 1984)(圖13)。相比較而言, 各期次巖石樣品的輕稀土元素分異明顯, 重稀土元素分異不明顯,即早期巖石的(La/Sm)N為4.68～5.61, (Gd/Yb)N為1.76～2.62; 晚期各次巖石的(La/Sm)N為2.48～7.21、3.50～9.06、3.75～8.17, (Gd/Yb)N為1.19～2.08、1.19～2.65、0.98～2.01。

3.3 Sr、Nd同位素

選擇部分定年樣品做全巖Sr、Nd同位素分析,結果見表5。

圖14 柴北緣烏蘭花崗巖類(87Sr/86Sr)i-εNd(t)圖解Fig. 14 Isotopic (87Sr/86Sr)i-εNd(t) diagram of the granites from Wulan area

表5 柴北緣東段烏蘭花崗巖類Sr-Nd同位素分析Table 5 Sr-Nd isotopic analyses of the granites from Wulan area in eastern section of Northern Qaidam

圖15 花崗巖成因類型判別圖解(據Whalen et al., 1987; 圖例同圖7 )Fig. 15 Discrimination of granite genetic-types (after Whalen et al., 1987; symbols as for Fig. 7)A-A型花崗巖; I, S & M-I型、S型和M型花崗巖; FG-分異的I型花崗巖; OGT-世界I型、S型和M型花崗巖A-A-type granite; I, S & M-I-type, S type and M type granite; FG-fractionated I-type granite; OGT-world I-type, S-type and M-type granite

由表5可見, 烏蘭早期花崗巖類比晚期花崗巖類具有較高的(87Sr/86Sr)i、較大的T2DM和較低的εNd(t)值, 早期花崗巖的(87Sr/86Sr)i、T2DM、εNd(t)值分別為0.710 99、2.10 Ga、–11.6, 晚期花崗巖的分別為: 0.707 567～0.710 691、1.41～1.58 Ga、–4.8 ～ –6.8(表5)。圖14中, 早期花崗巖落入澳大利亞拉克蘭(Lachlan)I型和S型花崗巖區域之下(Keay et al., 1997; Serhat and Goncuoglu, 2007), 但晚期花崗巖類樣品落入I型花崗巖區(圖14)。

4 討論

4.1 花崗巖成因類型

研究表明, 烏蘭早期花崗巖類(413 Ma)巖石組合為石英二長巖+花崗巖, 這些巖石不僅富集大離子親石元素, 而且還富集部分高場強元素(Zr、Y、Nb等), 稀土元素配分曲線以明顯的負Eu異常為特征(圖13a), 具有A型花崗巖的地球化學特征(圖15a, b, c, d)。按張旗等(2010)的劃分方案, 這組花崗巖類似于華南A型花崗巖, 以低Sr高Yb為特征(圖16)。同時, 本期花崗巖類具有較高的10 000×Ga/Al (＞2.6, 2.7～3.6, 平均為3.15)、Zr(277×10-6～380×10-6)和Zr+Nb+Ce+Y(＞350×10-6, 586×10-6～815×10-6, 平均為700.5×10-6)值和較低的MgO(0.37～0.43 wt％)、Ba(151×10-6～250×10-6)和Sr(59.8×10-6～63.0×10-6)的含量, 還具有明顯的Eu負異常(0.11～0.15)(Whalen et al., 1987)和明顯的Ba、Sr、P、Eu、Ti虧損(表4,圖11, 13), 這些都是A型花崗巖的特征。巖石中沒有堿性暗色礦物和巖石的A/CNK=0.85～1.06, 表明其屬準鋁質-鋁弱飽和的A型花崗巖(King et al., 1997)。負的Ti、P、Eu異?？赡芘c含Ti礦物相(如鈦鐵礦和金紅石)、磷灰石、斜長石和/或鉀長石的分異有關。鉀長石的分餾還可能產生Eu、Ba的同時負異常(Wu et al., 2003)。實驗巖石學和鋯石飽和溫度證明(Clemens et al., 1986), A型花崗巖不可能由I型花崗巖分異產生, 因為A型花崗巖需要非常高的溫度(Wu et al., 2003)。從花崗巖的Sr、Yb含量來看, 烏蘭早期A型花崗巖類似于華南南嶺A型花崗巖(圖16)。

烏蘭晚期花崗巖類巖石組合為閃長巖+花崗閃長巖+二長花崗巖, 其中, 第一次侵入的花崗巖類ASI變化于0.97～1.04之間, 平均為1.0, 第二次的為0.81～1.00, 平均為0.95, 第三次的為1.01～1.08, 平均為10.5, CIPW標準礦物計算結果, 前兩次的花崗巖幾乎不出現剛玉, 但第三次花崗巖出現0.6％～1.21％的剛玉?？梢? 第一、二次花崗巖屬準鋁質, 而第三次花崗巖屬鋁弱過飽和型。三次巖石隨SiO2含量的增加, P2O5含量明顯地呈線性減少,反映了I型花崗質巖漿的演化特點。三次巖石的元素地球化學以富集大離子親石元素, 虧損高場強元素為特征(圖11), 稀土元素以富集輕稀土、且輕稀土分異明顯重稀土分異不明顯、不具有或具有弱的負Eu異常為特征(圖13), 表現出島弧I型花崗巖類地球化學屬性。另外, 三次花崗巖類的微量元素原始地幔標準化曲線(圖11)和稀土元素球粒隕石標準化曲線(圖13)相同或相似, 表明它們具有相同或相似的物質來源和巖漿演化過程。在圖16中, 三次花崗巖樣品的Sr、Yb投點位于張旗等(2010)劃分的埃達克型、閩浙型、喜馬拉雅型和華南型花崗巖的過渡區域, 表現出由埃達克型到閩浙型/喜馬拉雅型向華南型過渡的I型花崗巖特征(圖16)。此外, 晚期花崗巖類Sr、Nd同位素特征與澳大利亞拉克蘭褶皺帶I型花崗巖相似(圖14), 也表明其具有I型花崗巖的地球化學屬性。

圖16 花崗巖Yb-Sr圖解(據張旗等, 2010; 圖例同圖7 )Fig. 16 Yb-Sr diagram of granites (after ZHANG et al., 2010; symbols as for Fig. 7)

4.2 花崗質巖漿起源

實驗巖石學證明, 在非常寬的溫度、壓力條件下, 多種源巖的部分熔融均可以產生花崗質熔體(Rapp et al., 1991; Wolf and Wyllie, 1994; Rapp and Watson, 1995; Patino Douce and Johnston, 1996, 1998; Winther, 1996; Skjerlie and Patino Douce, 2002), 熔體成分的變化取決于初始熔融物質的成分、熔融的溫度和壓力、初始物質的含水量(Jogvan et al., 2006),如泥質的沉積巖部分熔融可以產生強烈富鋁和富鉀的熔體, 硬砂巖的部分熔融可以產生中等到強烈富鋁的花崗閃長巖/花崗巖熔體, 玄武質巖石的部分熔融可以產生云英質-奧長-花崗閃長質熔體(Rapp et al., 1991; Sen and Dunn, 1994; Wolf and Wyllie, 1994; Rapp and Watson, 1995; Winther, 1996)?？梢?只要源巖含水或存在含水相的礦物, 部分熔融就可以產生花崗質熔體(Patino Douce and Johnston, 1996, 1998)。研究表明, 柴北緣北部構造單元歐龍布魯克地塊出露的基底變質表殼巖可以劃分為2個類型:第I類變質表殼巖的T2DM=2.57～2.83 Ga, εNd(t)=–1.18～2.08, 應屬有幔源物質混入的變質陸源沉積巖; 第II類變質表殼巖的T2DM=1.61～2.17 Ga, εNd(t)為高的正值(7.23～15.12) (陳能松等, 2007a, b)。烏蘭早期花崗巖類的(87Sr/86Sr)St為0.710 80, (143Nd/144Nd)st為0.511 514, εNd(t)為–11.6, T2DM2.10 Ga, 晚期各次侵位的花崗巖類Sr、Nd同位素比值相似, 即(87Sr/86Sr)St變化于0.707 57～0.710 69,(143Nd/144Nd)st為0.511 965～0.551 207 4, εNd(t)為–4.8～ –0.68, T2DM為1.41～1.58 Ga, 可見, 它們與歐龍布魯克基底兩類表殼巖的Sr、Nd同位素特征不同, 表明它們不可能來自暴露地表的前寒武紀變質巖系的部分熔融。通常認為A型花崗巖在地殼伸展期間,伴隨著地幔源巖漿為地殼深熔作用提供熱源, 殼源物質部分熔融形成的(Clemens et al., 1986; Ostendorf et al., 2014)。因此, King(1997)認為準鋁質A型花崗巖是殼內部分熔融形成的。根據(87Sr/86Sr)St、(143Nd/144Nd)St同位素值和T2DM年齡, 結合它們的巖石地球化學特征, 我們認為, 烏蘭早期的花崗巖類可能起源于古元古代的陸殼物質, 而晚期的花崗巖類起源于中元古代的陸殼物質, 并可能混合了幔源成分。

4.3 花崗巖形成的構造環境

宗霧隆構造帶北邊以青海南山斷裂為界與中南祁連地塊相隔, 南邊以宗霧隆南緣斷裂為界與柴北緣歐龍布魯克地塊相鄰, 向西延至阿爾金斷裂,向東分離西秦嶺與南祁連造山帶(圖1)。宗霧隆構造帶與鄂拉山構造帶地質特征及演化過程十分相似,可能是由于西秦嶺沿共和坳拉谷強烈斜向碰撞柴達木—歐龍布魯克地塊, 造成了印支期宗務隆構造帶東段造山隆升及強烈的巖漿活動(彭淵等, 2016)。柴達木東緣花崗巖漿-火山活動帶稱為鄂拉山構造帶,該構造帶上苦?！愂蔡辽呔G構造混雜巖帶中玄武巖的40Ar/39Ar年齡為(368.6±1.4) Ma(張智勇等, 2004), 說明洋盆從晚泥盆世—早石炭世開始打開,到中石炭世—早二疊世形成了有限的洋盆, 烏蘭地區歐龍布魯克陸塊北部邊緣泥盆紀A型花崗巖的出現, 是對這一構造事件的響應。受西秦嶺向西擠出以及華南地塊向北俯沖碰撞的共同影響, 晚二疊世—中三疊世洋盆向西斜向俯沖, 洋盆閉合收縮(孫延貴, 2004), 形成了鄂拉山構造帶上年齡為220～200 Ma(Rb-Sr、K-Ar、U-Pb)的巖體(孫延貴等, 2001; 孫延貴, 2004; 李玉曄, 2008; 李永祥等, 2011)。鄂拉山構造巖漿帶巖漿巖主體屬于高鉀鈣堿性花崗閃長巖, 形成于板塊碰撞及碰撞后階段, 是西秦嶺地塊沿共和坳拉谷向柴達木地塊下斜向強烈俯沖碰撞的產物(張森琦等, 2000; 孫延貴等, 2001;孫延貴, 2004; 李玉曄, 2008)。對比宗務隆構造帶與鄂拉山構造帶內侵入巖特征, 兩者具有相同的巖漿巖類型, 相似的構造成因, 均為印支期構造巖漿活動的產物。

除本文報道的兩期花崗巖外, 前人也報道過宗霧隆構造帶上天峻南山花崗巖、青海湖南花崗巖、二郎洞二長花崗巖的鋯石U-Pb年齡均為印支期,加上天峻南山果可山組超鎂鐵質-鎂鐵質蛇綠巖地體(Rb-Sr年齡(318±3) Ma)的發現(王毅智等, 2001)以及天峻南山等島弧型高鉀鈣堿性I型花崗巖的產出(郭安林等, 2009), 認為宗霧隆構造帶是一條具有完整構造旋回的印支期造山帶(王毅智等, 2001; 郭安林等, 2009)。

圖17 花崗巖類La/Yb-Th/Yb構造環境判別圖解(據Condie, 1989; 圖例同圖7 )Fig. 17 Geochemical compositions of two episodes of the granites from Wulan area plotted in the tectonic setting discrimination diagrams (after Condie, 1989; symbols as for Fig. 7)

Gorton和Schandl(2000)收集了世界上26個不同地方的花崗巖和中酸性火山巖的地球化學資料,利用不相容元素Ta、Th和Yb的豐度和比值, 有效地區分出大洋島弧、活動大陸邊緣和板內火山巖帶三種不同的構造環境。其中板內火山巖帶的資料來自冰島、埃塞俄比亞和新墨西哥的瓦勒斯火山, 大陸活動邊緣的有希臘、智利、阿根廷、日本、墨西哥、阿拉斯加和湯加—克馬德克及伊豆小笠原弧(Tonga–Kermadec and Izu–Bonin arcs), 大洋島弧的有呂宋島(Luzon arc)。三種構造環境中火成巖的Th逐步富集主要歸因于弧的成分增加, Th/Ta比值1～6是板內火山巖帶, 6～20是活動大陸邊緣, ＞20～90的是大洋島弧(Gorton and Schandl, 2000)。烏蘭地區早期花崗巖類的Th/Ta比值為27.1～29.4, 平均為28.25,晚期的變化較大, 為7.5～51.4, 平均15.17, 可見,本區早期A型花崗巖類Th/Ta比值高于活動大陸邊緣火成巖, 而和大洋島弧區火成巖的相似, 這可能與花崗巖產出的位置和源巖有關。從圖2可以看出,該A型花崗巖產在歐龍布魯克陸塊的北部邊緣, 哇洪山左行走滑斷裂穿過巖體, 可能是該斷裂的走滑拉分作用, 導致混入了洋殼成分的古元古代陸殼發生部分熔融, 形成了類似大洋島弧火成巖Th/Ta比值的A型花崗巖。晚期花崗巖類除個別樣品外, 所有樣品的Th/Ta比值落入活動大陸邊緣區的范圍內。從Th/Yb-La/Yb圖解(Condie, 1989)來看, 本區兩期花崗巖類樣品投點主要落在大陸邊緣弧的范圍內(圖17), 也說明兩期花崗質巖漿活動發生在活動大陸邊緣, 在Muller和Groves(1994)的圖解上, 本區早期花崗巖類落入板內區(圖18a), 晚期的花崗巖類落入與弧相關的區域內; 在圖18b上, 兩期次花崗巖類的樣品投點均落入與弧相關的大陸和碰撞后區域(圖18b); 在Gorton和Schandl(2000)圖解中,兩期花崗巖投點均落入大洋弧和活動大陸邊緣區域(圖18c), 反映了兩期巖漿作用的構造環境與活動大陸邊緣相關。這與兩期花崗巖體分布在歐龍布魯克微陸塊北部邊緣的地質事實相吻合。

圖18 Y-Zr (a)、Zr/Al2O3-TiO2/Al2O3 (b)和Th/Yb-Ta/Yb (c)構造判別圖解(據Muller and Groves, 1994; Gorton and Schandl, 2000; 圖例同圖7 )Fig. 18 (a) Y-Zr, (b) Zr/Al2O3-TiO2/Al2O3and (c) Th/Yb-Ta/Yb geotectonic discrimination diagrams (after Muller and Groves, 1994; Gorton and Schandl, 2000; symbols as for Fig. 7)

綜上所述, 烏蘭地區泥盆紀A型花崗巖的出現,標志著歐龍布魯克北緣宗霧隆裂谷作用的開始, 到晚石炭世(Rb-Sr年齡(318±3) Ma)開始出現宗霧隆洋盆(王毅智等, 2001), 晚二疊世—中三疊世洋殼向南俯沖, 形成一系列中酸性火山巖和青海湖南山及天峻南山花崗巖為代表的島弧地體, 晚三疊世洋殼閉合進入陸內碰撞造山期(郭安林等, 2009; 彭淵等, 2016)。

5 結論

(1)柴北緣東段烏蘭地區早期的哈德森溝花崗巖鋯石SHRIMP U-Pb年齡為(413±3) Ma, 烏蘭晚期的許給溝巖體的年齡為(254±3) Ma、椅落山巖體為(251±1) Ma、察汗諾巖體為(249±1) Ma、(248±2) Ma,曬勒克郭來巖體為(250±1) Ma、(244±3) Ma, 察汗河巖體為(240±2) Ma。

(2)烏蘭地區早期花崗巖類(413 Ma)巖石不僅富集大離子親石元素, 而且還富集部分高場強元素(Zr、Y、Nb等), 稀土元素配分曲線以明顯的負Eu異常為特征, 同時, 巖石具有較高的10 000×Ga/Al比值和較低的MgO、Ba和Sr的含量, 屬A型花崗巖。晚期花崗巖類以富集大離子親石元素, 虧損高場強元素為特征, 稀土元素以富集輕稀土、且輕稀土分異明顯重稀土分異不明顯、不具有或具有弱的負Eu異常為特征, 屬島弧I型花崗巖。

(3)同位素研究表明, 烏蘭早期A型花崗巖類起源于古元古代陸殼物質的部分熔融, 與祁連巖石圈拆沉導致歐龍布魯克陸塊北緣減薄、拉伸有關, 它的產出標志著歐龍布魯克北緣裂陷的開始; 而晚期具有大陸活動邊緣I型花崗巖類起源于中元古代陸殼物質的部分熔融, 并可能有幔源物質的加入, 其成因與宗霧隆洋殼俯沖于歐龍布魯克陸塊之下有關。

Acknowledgements:

This study was supported by China Geological Survey (Nos. 121201102000150005-06, 12120115027001 and 12120114079901), National Natural Science Foundation of China (Nos. 41472063, 40921001, 40472034 and 40672049), and the Science and Technology Project (No. Sino Probe 05-05).

陳丹玲, 孫勇, 劉良, 張安達, 羅金海, 王焰. 2005. 柴北緣魚卡河榴輝巖的變質演化—石榴石成分環帶及礦物反應結構的證據[J]. 巖石學報, 21: 1039-1048.

陳能松, 王勤燕, 陳強, 李曉彥. 2007a. 柴達木和歐龍布魯克陸塊基底的組成和變質作用及中國中西部古大陸演化關系初探[J]. 地學前緣, 14(1): 43-55.

陳能松, 王新宇, 張宏飛, 孫敏, 李曉彥, 陳強. 2007b. 柴—歐微地塊花崗巖地球化學和Nd-Sr-Pb同位素組成, 基底性質和構造屬性啟示[J]. 地球科學—中國地質大學學報, 32(1): 7-21.

郭安林, 張國偉, 強娟, 孫延貴, 李廣, 姚安平. 2009. 青藏高原東北緣印支期宗務隆造山帶[J]. 巖石學報, 25(01): 1-12.

郭安林, 張國偉, 孫延貴, 程順有, 姚安平. 2007. 共和盆地周緣晚古生代鎂鐵質火山巖地球化學及空間分布: 瑪積雪山三聯點以及東古特提斯多島洋啟示[J]. 中國科學D輯: 地球科學, 37(增刊1): 249-261.

李永祥, 李善平, 王樹林, 王磊, 商健, 張志青, 趙海霞. 2011.青海鄂拉山地區陸相火山巖地球化學特征及構造環境[J].西北地質, 44(4): 23-32.

李玉曄. 2008. 西秦嶺-東昆侖蛇綠巖及島弧型巖漿巖的年代學和地球化學研究——對特提斯洋演化的制約[D]. 合肥: 中國科學技術大學.

林慈鑾, 孫勇, 陳丹玲, 第五春榮. 2006. 柴北緣魚卡河花崗質片麻巖的地球化學特征和鋯石LA-ICPMS定年[J]. 地球化學, 35(5): 489-505.

盧欣祥, 孫延貴, 張雪亭, 肖慶輝, 王曉霞, 尉向東, 谷德敏. 2007. 柴達木盆地北緣塔塔楞環斑花崗巖的SHRIMP年齡[J]. 地質學報, 81(5): 626-634.

陸松年, 陳志宏, 李懷坤, 郝國杰, 周紅英, 相振群. 2004. 秦嶺造山帶中-新元古代(早期)地質演化[J]. 地質通報, 23(2): 107-112.

陸松年, 王惠初, 李懷坤, 袁桂邦, 辛后田, 鄭健康. 2002. 柴達木盆地北緣“達肯大坂群”的再厘定[J]. 地質通報, 21(1): 19-23.

孟繁聰, 張建新, 楊經綏. 2005. 柴北緣錫鐵山早古生代HP/UHP變質作用后的構造熱事件——花崗巖和片麻巖的同位素與巖石地球化學證據[J]. 巖石學報, 21(1): 45-56.

彭淵, 馬寅生, 劉成林, 李宗星, 孫嬌鵬, 邵鵬程. 2016. 柴北緣宗務隆構造帶印支期花崗閃長巖地質特征及其構造意義[J].地學前緣, 23(2): 206-221.

青海省地質礦產局. 1991. 青海區域地質志[M]. 北京: 地質出版社.

宋述光, 牛耀齡, 張立飛, 張貴賓. 2009. 大陸造山運動: 從大洋俯沖到大陸俯沖、碰撞、折返的時限——以北祁連山、柴北緣為例[J]. 巖石學報, 25(9): 2067-2077.

宋述光, 楊經綏. 2001. 柴達木盆地北緣都蘭地區榴輝巖中透長石+石英包裹體: 超高壓變質作用的證據[J]. 地質學報, 75(2): 179-185.

宋述光, 張貴賓, 張聰, 張立飛, 魏春景. 2013. 大洋俯沖和大陸碰撞的動力學過程: 北祁連-柴北緣高壓-超高壓變質帶的巖石學制約[J]. 科學通報, 58(23): 2240-2245.

宋述光, 張立飛, 牛耀齡, 張貴賓. 2007. 大陸碰撞造山帶的兩類橄欖巖——以柴北緣超高壓變質帶為例[J]. 地學前緣, 14(2): 129-138.

孫延貴, 田琪, 王青海. 2001. 西秦嶺與東昆侖的側向碰撞與造山[J]. 青海地質, 18(2): 18-25.

孫延貴. 2004. 西秦嶺-東昆侖造山帶的銜接轉換與共和坳拉谷[D]. 西安: 西北大學.

王惠初, 李懷坤, 陸松年, 袁桂邦, 辛后田. 2006. 柴北緣魚卡地區達肯大坂巖群的地質特征與構造環境[J]. 地質調查與研究, 29(4): 253-262.

王毅智, 拜永山, 陸海蓮. 2001. 青海天峻南山蛇綠巖的地質特征及其形成環境[J]. 青海地質, 21(1): 29-35.

吳才來, 郜源紅, 李兆麗, 雷敏, 秦海鵬, 李名則, 劉春花, FROST B, ROBINSON P T, WOODEN J L. 2014. 都蘭花崗巖鋯石SHRIMP定年及柴北緣超高壓帶花崗巖年代學格架[J]. 中國科學D輯: 地球科學, 44(10): 2142-2159.

吳才來, 郜源紅, 吳鎖平, 陳其龍, WOODEN J L, MAZADAB F K, MATTINSON C. 2007. 柴北緣大柴旦地區古生代花崗巖鋯石SHRIMP定年[J]. 巖石學報, 23(08): 1861-1875.

吳才來, 郜源紅, 吳鎖平, 陳其龍, WOODEN J L, MAZADAB F K, MATTINSON C. 2008. 柴北緣西段花崗巖鋯石SHRIMP U-Pb定年及其巖石地球化學特征[J]. 中國科學D輯: 地球科學, 38(8): 930-949.

吳才來, 徐學義, 高前明, 李向民, 雷敏, 郜源紅, FROST R B, WOODEN J L. 2010. 北祁連早古生代花崗質巖漿作用及構造演化[J]. 巖石學報, 26(4): 1027-1044.

吳才來, 楊經綏, IRELAND T, WOODEN J, 李海兵, 萬渝生,史仁燈. 2001. 祁連南緣嗷嘮山花崗巖SHRIMP鋯石年齡及其地質意義[J]. 巖石學報, 17(02): 215-221.

吳才來, 楊經綏, WOODEN J L, 史仁燈, 陳松永, MEIBOM A, MATTINSON C. 2004. 柴達木北緣都蘭野馬灘花崗巖鋯石SHRIMP定年[J]. 科學通報, 49(16): 1667-1672.

辛后田, 郝國杰, 王惠初, 陳能松, 韓英善, 祁生勝. 2002. 柴北緣前震旦紀地層系統的新認識[J]. 前寒武紀研究進展, 25(2): 113-119.

楊經綏, 宋述光, 許志琴, 吳才來, 史仁燈, 張建新, 李海兵,萬渝生, 劉焰, 邱海峻, 劉福來, MARUYAMA S. 2001. 柴達木盆地北緣早古生代高壓―超高壓變質帶中發現典型的超高壓礦物—柯石英[J]. 地質學報, 75(2): 175-179.

楊經綏, 許志琴, 宋述光, 吳才來, 史仁燈, 張建新, 萬渝生,李海兵, 金小赤, JOLIVET M. 2000. 青海都蘭榴輝巖的發現及對中國中央造山帶內高壓―超高壓變質帶研究的意義[J]. 地質學報, 74(2): 156-168.

袁桂邦, 王惠初, 李惠民, 郝國杰, 辛后田, 張寶華, 王青海,田琪. 2002. 柴北緣綠梁山地區輝長巖的鋯石U-Pb年齡及意義[J]. 前寒武紀研究進展, 25(1): 36-40.

張建新, 孟繁聰, 戚學祥. 2002. 柴達木盆地北緣大柴旦和錫鐵山榴輝巖中石榴子石環帶對比及地質意義[J]. 地質通報, 21(3): 123-129.

張旗, 金惟俊, 李承東, 王元龍. 2010. 再論花崗巖按照Sr-Yb的分類: 標志[J]. 巖石學報, 26(4): 985-1015.

張森琦, 王瑾, 王秉章, 莊永成. 2000. 昆秦結合部鄂拉山陸內斜沖斷裂-巖漿造山帶造山機制研究[J]. “九五”全國地質科技重要成果論文集: 80-85.

張智勇, 殷鴻福, 王秉璋, 王瑾, 張克信. 2004. 昆秦接合部海西期苦海-賽什塘分支洋的存在及其證據[J]. 地球科學——中國地質大學學報, 29(6): 691-696.

References:

BOYNTON W V. 1984. Cosmochemistry of the rare earth elements: Meteorite studies[C]//HENDERSON P (Eds), Rare Earth Element Geochemistry, Developments in Geochemistry 2. Amsterdam: Elsevier: 63-114.

Bureau of Geology and Mineral Resources of Qinghai Province. 1991. Regional geology of Qinghai Province[M]. Beijing: Geology Publishing House(in Chinese).

CHEN D L, LIU L, SUN Y, LIOU J G. 2009. Geochemistry and zircon U-Pb dating and its implications of the Yukahe HP/UHP terrane, the North Qaidam, NW China[J]. Journal of Asian Earth Sciences, 35(3): 232-244.

CHEN Dan-ling, SUN Yong, LIU Liang, ZHANG An-da, LUO Jin-hai, WANG Yan. 2005. Metamorphic evolution of the yuka eclogite in the North Qaidam, NW China: evidences from the compositional zonation of garnet and reaction texturein the rock[J]. Acta Petrological Sinica, 24(4): 1039-1048(in Chinese with English abstract).

CHEN Neng-song, WANG Qin-yan, CHEN Qiang, LI Xiao-yan. 2007a. Components and metamorphism of the basements of the Qaidam and Oulong-buluke micro-continental blocks, and a tentative interpretation of paleocontinental evolution in NW-Central China[J]. Earth Science Frontiers (China University of Geosciences, Beijing; Peking University), 14(1): 43-55(in Chinese with English abstract).

CHEN Neng-song, WANG Xin-yu, ZHANG Hong-fei, SUN Min, LI Xiao-yan, CHEN Qiang. 2007b. Geochemistry and Nd-Sr-Pb Isotopic Compositions of Granitoids from Qaidam and Oulongbuluke Micro-Blocks, NW China: Constraints on Basement Nature and Tectonic Affinity[J]. Earth Science—Journal of China University of Geosciences, 32(1): 7-21(in Chinese with English abstract).

CHERNIAK D J, WATSON E B. 2000. Pb diffusion in zircon[J]. Chemical Geology, 172: 5-24.

CLEMENS J D, HOLLOWAY J R, WHITE A J R. 1986. Origin of an A-type granite: experimental constraints[J]. American Mineralogist, 71(3): 317-324.

CONDIE K C. 1989. Geochemical changes in basalts and andesites across the Archean-Proterozoic boundary: identification and significance[J]. Lithos, 23(1): 1-18.

CORFU F, HANCHAR J M, HOSKIN P W O, KINNY P. 2003. Atlas of zircon textures[J]. Reviews in Mineralogy and Geochemistry, 53(1): 469-495.

FROST B R, BARNES C G, COLLINS W J, ARCULUS R J, ELLIS D J, FROST C D. 2001. A geochemical classification for granitic rocks[J]. Journal of Petrology, 42(11): 2033-2048.

FROST B R, FROST C D. 2008. A geochemical classification for feldspathic igneous rocks[J]. Journal of Petrology, 49(11): 1955-1969.

GORTON M P, SCHANDL E S. 2000. From continents to island arcs: a geochemical index of tectonic setting for arc-related and within-plate felsic to intermediate volcanic rocks[J]. The Canadian Mineralogist, 38(5): 1065-1073.

GUO An-lin, ZHANG Guo-wei, QIANG Juan, SUN Yan-gui, LI Guang, YAO An-ping. 2009. Indosinian zongwuling orogenic belt on the northeastern margin of the Qinghai-Tibet plateau[J]. Acta Petrologica Sinica, 25(01): 1-12(in Chinese with English abstract).

GUO An-lin, ZHANG Guo-wei, SUN Yan-gui, CHENG Shun-you, YAO An-ping. 2007. Geochemistry and spatial distribution of Late Paleozoic mafic volcanic rocks on the periphery of Gonghe Basin: Enlightenment about Triple junction of Maji Snow Mountain and archipelagic ocean of Eastern paleotethys[J]. Science China: Earth Sciences, 37(s1): 249-261(in Chinese).

HOSKIN P W O, SCHALTEGGER U. 2003. The Composition of Zircon and Igneous and Metamorphic Petrogenesis[J]. Reviews in Mineralogy and Geochemistry, 53: 27-62.

IRVINE T N, BARAGAR W R A. 1971. A guide to the chemical classification of the common volcanic rocks[J]. Canadian Journal of Earth Sciences, 8(5): 523-548.

JOGVAN O, MUNTENER O, BURG J P, ULMER P, JAGOUTZ E. 2006. Lower continental crust formation through focused flow in km-scale melt conduits: the zoned ultramafic bodies of the Chilas complex in the Kohistan island arc (NW Pakistan)[J]. Earth and Planetary Science Letters, 242(3-4): 320-342.

KEAY S, COLLINS W J, MCCULLOCH M T. 1997. A three component Sr-Nd isotopic mixing model for granitoid genesis, Lachlan fold belt, eastern Australia[J]. Geology, 25: 307-310.

KING P L, WHITE A J R, CHAPPELL B W, ALLEN C M. 1997. Characterization and origin of aluminous A-type granites from the Lachlan Fold Belt, southeastern Australia[J]. Journal of Petrology, 38(3): 371-391.

LI Yong-xiang, LI Shan-ping, WANG Shu-lin, WANG Lei, SHANG Jian, ZHANG Zhi-qing, ZHAO Hai-xia. 2011. Geochemical Characteristics and Tectonic Environment of the Continental Facies Volcanic Rocks in Elashan Area, Qinghai Province[J]. Northwestern Geology, 44(4): 23-32(in Chinese with English abstract).

LI Yu-ye. 2008. Geochronology and Geochemistry of the Ophiolites and Island-arc-type Igneous Rocks in the Western Qinling Organ and the Eastern Kunlun Orogen: Implication for the Evolution of the Tethyan Ocean[D]. Hefei: University of Science and Technology of China(in Chinese with English abstract).

LIN Ci-luan, SUN Yong, CHEN Dan-ling, DIWU Chun-rong. 2006. Geochemistry and zircon LA-ICPMS dating of Iqe River granitic gneiss, northern margin of Qaidam Basin[J]. Geochimica, 35(5): 489-505(in Chinese with English abstract).

LIU L, CHE Z C, LUO J H. 1996. Recognizing of eclogite from the west segment of Altun[J]. Chinese Science Bulletin, 41(14): 1485-1488.

LIU L, SUN Y, XIAO P X, CHE Z C, LUO J H, CHEN D L, WANG Y, ZHANG A D, CHEN L. 2002. Discovery of ultrahigh pressure magnesite- bearing garnet lherzolite ( ＞3.8 GPa) in the Altyn Tagh, Northwest China[J]. Chinese Science Bulletin, 47(11): 881-886.

LU Song-nian, CHEN Zhi-hong, LI Huai-kun, HAO Guo-jie, ZHOU Hong-ying, XIANG Zhen-qun. 2004. Late Mesoproterozoic—early Neoproterozic evolution of the Qinling orogen[J]. Geological Bulletin of China, 23(2): 107-112(in Chinese with English abstract).

LU Song-nian, WANG Hui-chu, LI Huai-kun, YUAN Gui-bang, XIN Hou-tian, ZHENG Jian-kang. 2002. Redefinition of the“Dakendaban Group” on the northern margin of the Qaidam basin[J]. Geological Bulletin of China, 21(1): 19-23(in Chinese with English abstract).

LU Xin-xiang, SUN Yan-gui, ZHANG Xue-ting, XIAO Qing-hui, WANG Xiao-xia, WEI Xiang-dong, GU De-min. 2007. TheSHRIMP Age of Tatalin Rapakivi Granite at the North Margin of Qaidam Basin[J]. Acta Geologica Sinica, 81(5): 626-634(in Chinese with English abstract).

MANIAR P D, PICCOLI P M. 1989. Tectonic discrimination of granitoids[J]. Geological Society of America Bulletin, 101(5): 635-643.

MATTINSON C G, WOODEN J L, LIOU J G, BIRD D K, WU C L. 2006. Age and duration of eclogite-facies metamorphism, North Qaidam HP/UHP terrane, Western China[J]. American Journal of Science, 306: 683-711.

MCDONOUGH W F, SUN S S. 1985. Isotopic and geochemical systematics in Tertiary-Recent basalts from southeastern Australia and implication for the sub-continental lithosphere[J]. Geochimica et Cosmochimica Acta, 49(10): 2051-2067.

MENG Fan-cong, ZHANG Jian-xin, YANG Jing-sui. 2005. Tectono-thermal event of post-HP/UHP metamorphism in the Xitieshan area of the North Qaidam Mountains, western China: isotopic and geochemical evidence of granite and gneiss[J]. Acta Petrologica Sinica, 21(1): 45-56(in Chinese with English abstract).

MIDDLEMOST E A K. 1994. Naming materials in magma/igneous rock system[J]. Earth Science Review, 37(3-4): 215-224.

MULLER D, GROVES D I. 1994. Potasic igneus rocks and associated gold–copper mineralization[J]. Lithos, 56(2): 265-266.

OSTENDORF J, JUNG S, BERND J, HAUFF F. 2014. Syn-orogenic high-temperature crustal melting: Geochronological and Nd-Sr-Pb isotope constraints from basement-derived granites (Central Damara Orogen, Namibia)[J]. Lithos, 192-195: 21-38.

PATINO DOUCE A E, BEARD J S. 1996. Effects of P, f(o2) and Mg/Fe ratio on dehydration melting of model metagreywackes[J]. Journal of Petrology, 37(5): 999-1024.

PATINO DOUCE A E, MCCARTHY T C. 1998. Melting of crustal rocks during continental collision and subduction[C]//HACKER B R, LIOU J G. (Eds), When Continents collide: Geodynamics and Geochemistry of Ultrahigh-Pressure Rocks. Petrology and Structural Geology, Kluwer Academic Publishers, Dordrecht, 10: 27-55.

PECCERILLO A, TAYLOR S R. 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey[J]. Contributions to Mineralogy and Petrology, 58(1): 63-81.

PENG Yuan, MA Yin-sheng, LIU Cheng-lin, LI Zong-xing, SUN Jiao-peng, SHAO Peng-cheng. 2016. Geological Chatacteristics and Techonic Sifnificance of the Indosinian Granodiorites from the Zongwulong Tectonic Belt in North Qaidam[J]. Earth Science Frontiers, 23(2): 206-221(in Chinese with English abstract).

PIDGEON R T, NEMCHIN A A, HITCHEN G J. 1998. Internal structures of zircons from Archaean granites from the Darling Range batholith: implications for zircon stability and the interpretation of zircon U-Pb ages[J]. Contributions to Mineralogy and Petrology, 132(3): 288-299.

RAPP R P, WATSON E B, MILLER C F. 1991. Partial melting of amphibolite/eclogite and the origin of Archean trondhjemites and tonalities[J]. Precambria Research, 51(1-4): 1-25.

RAPP R P, WATSON E B. 1995. Dehydration melting of metabasalt at 8-32 kbar: implications for continental growth and crust-mantle recycling[J]. Jpurnal of Petrology, 36(4): 891-931.

SEN C, DUNN T. 1994. Dehydration melting of a basaltic composition amphibolite at 1.5 and 2.0 GPa: implications for the origin of adakites[J]. Contributions to Mineralogy and Petrology, 117(4): 394-409.

SERHAT K, GONCUOGLU M C. 2007. Sr and Nd isotopic characteristics of some S-, I- and A-type granitoids from Central Anatolia[J]. Turkish Journal of Earth Sciences, 17: 111-127.

SKJERLIE K P, PATI?O DOUCE A E. 2002. The fluid-absent partial melting of a zoisite-bearing quartz eclogite from 1.0 to 3.2 GPa; implications for melting in thickened continental crust and for subduction-zone processes[J]. Journal of Petrology, 43(2): 291-314.

SONG S G, NIU Y L, SU L, WEI C J, ZHANG L F. 2014a. Adakitic (tonalitic–trondhjemitic) magmas resulting from eclogite decompression and dehydration melting during exhumation in response to continental collision[J]. Geochimica et Cosmochimica Acta, 130(4): 42-62.

SONG S G, NIU Y L, SU L, ZHANG C, ZHANG L F. 2014b. Continental orogenesis fromocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: The example of the North Qaidam UHPM belt, NWChina[J]. Earth-Science Reviews, 129(1): 59-84.

SONG S G, NIU Y L, ZHANG L F, WEI C J, LIOU J G, SU L. 2009. Tectonic evolution of Early Paleozoic HP metamorphic rocks in the North Qilian Mountains, NW China: new perspectives[J]. Journal of Asian Earth Sciences, 35(3-4): 334-353.

SONG S G, YANG J S, LIOU J G, WU C L, SHI R D, XU Z Q. 2003a. Petrology, geochemistry and isotopic ages of eclogites from the Dulan UHPM terrane, the North Qaidam, NW China[J]. Lithos, 70(3-4): 195-211.

SONG S G, YANG J S, XU Z Q, LIOU J G, SHI R D. 2003b. Metamorphic evolution of the coesite-bearing ultrahigh-pressure terrane in the North Qaidam, northern Tibet, NW China[J]. Journal of Metamorphic Geology, 21(6): 631-644.

SONG S G, ZHANG C, LI X H, ZHANG L F. 2011. HP/UHP metamorphic time of eclogite in the Xitieshan terrane, North Qaidam UHPM belt, NW China[J]. Acta Petrologica Sinica, 27: 1191-1197.

SONG S G, ZHANG L F, NIU Y L, SU L, JIAN P, LIU D. 2005. Geochronology of diamond-bearing zircons from garnet peridotite in the North Qaidam UHPM belt, Northern Tibetan Plateau: A record of complex histories from oceanic lithosphere subduction to continental collision[J]. Earth and Planetary Science Letters, 234(1-2): 99-118.

SONG S G, ZHANG L F, NIU Y L, SU L, SONG B, LIU D Y. 2006. Evolution from Oceanic Subduction to Continental Collision: A Case Study of the Northern Tibetan Plateau inferred from geochemical and geochronological data[J]. Journal of Petrology, 47(3): 435-455.

SONG Shu-guang, NIU Yao-ling, ZHANG Li-fei, ZHANG Gui-bin. 2009. Time constraints on orogenesis from oceanic subduction to continental subduction, collision, and exhumation: An example from North Qinlian and North Qaidam HP-UHP belts[J]. Acta Petrologica Sinica, 25(9): 2067-2077(in Chinese with English abstract).

SONG Shu-guang, YANG Jing-sui. 2001. Sanidine+Quartz Inclusions in Dulan Eclogites: Evidence for UHP Metamorphism on the North Margin of the Qaidam Basin, Nw China[J]. Acta Geologica Sinica, 75(2): 179-185(in Chinese with English abstract).

SONG Shu-guang, ZHANG Gui-bin, ZHANG Cong, ZHANG Li-fei, WEI Chun-jing. 2013. Dynamic process of oceanic subduction and continental collision: petrological constraints of HP-UHP belts in Qilian-Qaidam, the northern Tibetan Plateau[J]. Chin Sci Bull, 58(23): 2240-2245(in Chinese).

SONG Shu-guang, ZHANG Li-fei, NIU Yao-ling, ZHANG Gui-bin. 2007. Two types of peridotite in continental orogenic belts—acase study fromthe North Qaidam UHP metamorphic belt[J]. Earth Science Frontiers, 14(2): 129-138(in Chinese with English abstract).

SUN Yan-gui, TIAN Qi, WANG Qing-hai. 2001. Lateral collision and orogeny of west Qinling and east Kunlun[J]. Geology of Qinghai, 18(2): 18-25(in Chinese with English abstract).

SUN Yan-gui. 2004. Gonghe aulacogen and conjugate and transfer between the west Qinling and east Kunlun orogens[J]. Xi’an: Northwest University(in Chinese with English abstract).

WANG Hui-chu, LI Huai- kun, LU Song- nian, YUAN Gui-bang, XIN Hou-tian. 2006. Geological Characteristics and Tectonic Setting of the Dakendaba Group in Iqe Area, Northern Margin of Qaidam Basin[J]. Geological Survey and Research, 29(4): 253-262(in Chinese with English abstract).

WANG Yi-zhi, BAI Yong-shan, LU Hai-lian. 2001. Geological Characteristics of Tianjunnanshan ophiolite in Qinghai and its forming environment[J]. Geology of Qinghai, 21(1): 29-35(in Chinese with English abstract).

WHALEN J B, CURRIE K L, CHAPPELL B W. 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis[J]. Contributions to Mineralogy and Petrology, 95(4): 407-419.

WINTHER K T. 1996. An experimentally based model for the origin of tonalitic and trondhjemitic melts[J]. Chemical Geology, 127(1-3): 43-59.

WOLF M B, WYLLIE J P. 1994. Dehydration-melting of amphibolite at 10 kbar: the effects of temperature and time[J]. Contribution to Mineralogy and Petrology, 115(4): 369-383.

WU Cai-lai, GAO Yuan-hong, LI Zhao-li, LEI Min, QIN Hai-peng, LI Ming-ze, LIU Chun-hua, FROST B, ROBINSON P T, WOODEN J L. 2014. Zircon SHRIMP U-Pb dating of granites from Dulan and the chronological framework of the North Qaidam UHP belt, NW China[J]. Science China: Earth Sciences, 49(16): 1667-1672(in Chinese).

WU Cai-lai, GAO Yuan-hong, WU Suo-ping, CHEN Qi-long, WOODEN J L, MAZADAB F K, MATTINSON C. 2007. Zircon SHRIMP U-Pb dating of granites from the Da Qaidam area in the north margin of Qaidan basin, NW China[J]. Acta Petrologica Sinica, 23(08): 1861-1875(in Chinese with English abstract).

WU Cai-lai, GAO Yuan-hong, WU Suo-ping, CHEN Qi-long, WOODEN J L, MAZADAB F K, MATTINSON C. 2008. Zircon SHRIMP Dating of Granites and lithogeochemical on the west section of northern margin of the Qaidam basin[J]. Science China: Earth Sciences, 38(8): 930-949(in Chinese).

WU Cai-lai, XU Xue-yi, GAO Qian-ming, LI Xiang-min, LEI Min, GAO Yuan-hong, FROST R B, WOODEN J L. 2010. Early Palaeozoic granitiod magmatism and tectonic evolution in North Qilian, NW China[J]. Acta Petrologica Sinica, 26(4): 1027-1044(in Chinese with English abstract).

WU Cai-lai, YANG Jing-sui, IRELAND T, WOODEN J, LI Hai-bing, WAN Yu-sheng, SHI Ren-deng. 2001. Zircon SHRIMP ages of Aolaoshan granite from the south margin of Qilianshan and its geological significance[J]. Acta Petrologica Sinica, 17(02): 215-221(in Chinese with English abstract).

WU Cai-lai, YANG Jing-sui, WOODEN J L, SHI Ren-deng, CHEN Song-yong, MEIBOM A, MATTINSON C. 2004. Zircon SHRIMP Dating of Granites in Yematan of Dulan in the Northern Margin of Qaidam Massif[J]. Chinese Science Bulletin, 49(16): 1667-1672(in Chinese with English abstract).

WU F Y, JAHN B M, WILDE S A, LO CH, YUI T F, LIN Q. 2003. Highly fractionated I-type granites in NE China (II): isotopic geochemistry and implications for crustal growth in the Phanerozoic[J]. Lithos, 67(3-4): 191-204.

XIAO Q H, LU X X, WANG F, SUN Y G, WEI X D, XING Z Y. 2004. Age of Yingfeng rapakivi granite pluton on the north flank of Qaidam and its geological significance[J]. Science in China, 47(3): 357-365.

XIN Hou-tian, HAO Guo-jie, WANG Hui-chu, CHEN Neng-song, HAN ying-shan, QI Sheng-sheng. 2002. New Idea on Presinian Strata in the Northern Margin of Qaidam Massif[J]. Progress in Precambrian Research, 25(2): 113-119(in Chinese with English abstract).

YANG J S, LIU F L, WU C L, WAN Y, ZHANG J, SHI R. 2005. Two Ultrahigh-Pressure Metamorphic Events Recognized in the Central Orogenic Belt of China: Evidence from the U-Pb Dating of Coesite-Bearing Zircons[J]. International Geology Review, 47(4): 327-343.

YANG J S, XU Z Q, LI H B, WU C L, CUI J E, ZHANG J X, CHEN W. 1998. Discovery of eclogite at the northern marginof Qaidam Basin, NW China[J]. Chinese Science Bulletin, 43(20): 1755-1760.

YANG Jing-sui, SONG Shu-guang, XU Zhi-qin, WU Cai-lai, SHI Ren-deng, ZHANG Jian-xin, LI Hai-bing, WAN Yu-sheng, LIU Yan, QIU Hai-jun, LIU Fu-lai, MARUYAMA S. 2001. Discovery of Coesite in the North Qaidam Early Paleozoic Ultrahigh-high Pressure (UHP-HP) Metamorphic Belt, NW China[J]. Acta Geologica Sinica, 75(2): 175-179(in Chinese with English abstract).

YANG Jing-sui, XU Zhi-qin, SONG Shu-guang, WU Cai-lai, SHI Ren-deng, ZHANG Jin-xin, WAN Yu-sheng, LI Hai-bing, JIN Xiao-chi, JOLIVET M. 2000. Discovery of Eclogite in Dulan, Qinghai province and Its significance for studying the HP—UHP Metamorphic Belt along the Central Orogenic Belt of China[J]. Acta Geologica Sinica, 74(2): 156-168(in Chinese with English abstract).

YU S Y, ZHANG J X, DEL REAL P G. 2012. Geochemistry and zircon U–Pb ages of adakitic rocks from the Dulan area of the North Qaidam UHP terrane, north Tibet: constraints on the timing and nature of regional tectonothermal events associated with collisional orogeny[J]. Gondwana Research, 21(1): 167-179.

YU Sheng-yao, ZHANG Jian-xin, MATTINSON C G, DEL REAL P G, LI Yun-shuai, GONG Jiang-hua. 2014. Paleozoic HP granulite-facies metamorphism and anatexis in the Dulan area of the North Qaidam UHP terrane, western China: Constraints from petrology, zircon U–Pb and amphibole Ar–Ar geochronology[J]. Lithos, 198-199: 58-76.

YUAN Gui-bang, WANG Hui-chu, LI Hui-ming, HAO Guo-jie, XIN Hou-tian, ZHANG Bao-hua, WANG Qing-hai, TIAN Qi. 2002. Zircon U-Pb age of the Gabbros in Luliangshan Area on the Northern Margin of Qaidam Basin and its Geological Implication[J]. Progress in Precambrian Research, 25(1): 37-40(in Chinese with English abstract).

ZHANG G B, ZHANG L F, SONG S G, NIU Y L. 2009. UHP metamorphic evolution and SHRIMP geochronology of a coesite-bearing meta-ophiolitic gabbro in the North Qaidam, NW China[J]. Journal of Asian Earth Sciences, 35: 310-322. ZHANG Gui-bin, ZHANG Li-fei, CHRISTY A G, SONG Shu-guang, LI Qiu-li. 2014. Differential exhumation and cooling history of North Qaidam UHP metamorphic rocks, NW China: Constraints from zircon and rutile thermometry and U–Pb geochronology[J]. Lithos, 205: 15-27.

ZHANG J X, MATTINSON C G, MENG F C, WAN Y S, TUNG K. 2008. Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: evidence from zircon U-Pb geochronology[J]. Geological Society of America Bulletin, 120(5-6): 732-749.

ZHANG J X, MATTINSON C. G, YU S Y, LI J P, MENG F C. 2010. U-Pb zircon geochronology of coesite-bearing eclogites from the southern Dulan area of the North Qaidam UHP terrane, northwestern China: spatially and temporally extensive UHP metamorphism during continental subduction[J]. Journal of Metamorphic Geology, 28(9): 955-978.

ZHANG J X, YANG J S, MATTINSON C G, XU Z Q, MENG F C, SHI R D. 2005. Two ontrasting eclogite cooling histories, North QaidamHP/UHP terrane, western China: petrological and isotopic constraints[J]. Lithos, 84(1):51-76.

ZHANG Jian-xin, MENG Fan-cong, QI Xue-xiang. 2002. comparison of garnet zoning between eclogites in Da Daidam and Xitieshan on the northern margin of the Qaidam basin[J]. Geologial Bulletin of China, 21(3): 123-129(in Chinese with English abstract).

ZHANG Qi, JIN Wei-jun, LI Cheng-dong, WANG Yuan-long. 2010. Revisiting the new classification of granitic rocks based on whole-rock Sr and Yb contents: Index[J]. Acta Petrologica Sinica, 26(4): 985-1015(in Chinese with English abstract).

ZHANG Sen-qi, WANG Jin, WANG Bing-zhang, ZHUANG Yong-cheng. 2000. Orogenic mechanism research of Elashan intracontinental oblique thrusting fault-magma orogenic belt in Copulae between Kunlun-Qinling Mountains[J]. The Proceedings of National Important Geological Achievements of Science and Technology in the Ninth Five-Year Plan(in Chinese).

ZHANG Zhi-yong, YIN Hong-fu, WANG Bing-zhang, WANG Jin, ZHANG Ke-xin. 2004. Presence and Evidence of Kuhai-Saishitang Branching Ocean in Copulae between Kunlun-Qinling Mountains[J]. Earth Science — Journal of China University of Geosciences, 29(6): 691-696(in Chinese with English abstract).

Zircon SHRIMP Dating and Genesis of Granites in Wulan Area of Northern Qaidam

WU Cai-lai1), LEI Min1), WU Di2), LI Tian-xiao2)
1) Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037; 2) China University of Geosciences (Beijing), Beijing 100083

Zircon SHRIMP U-Pb dating of granites in Wulan area of northern Qaidam indicates that Hadesengou rock mass was formed at (413±3) Ma, Xugeigou rock mass at (254±3) Ma, Yiluoshan rock mass at (251±1) Ma, hornblende diorite and granite of Chahanruo rock mass at (249±1) Ma and (248±2) Ma, Chahanhe rock mass at (240±2) Ma, granodiorite and granite of Shailekeguo rock mass at (250±1) Ma and (244±3) Ma respectively. These granites have two formation periods: 1) the early period belongs to Early Devonian (413 Ma) with the rock association being adamellite+alkali-feldspar granite; 2) the late period belongs to Late Permian–Early Triassic (254～240 Ma) which can be further divided into three emplacements (254～251 Ma, 250～248 Ma and 244～240 Ma) with the rock association being diorite+granodiorite+granite. Geochemical study indicates that the early granitoids are not only enriched in large ion lithophile elements but also enriched in some high field-strength elements (Zr, Y, Nb etc.), thus belonging to A-type granite; the late granitoids are enriched in large ion lithophile elements and depleted in high field-strength elements, thus belonging to I-type granite.87Sr/86Sr ratio (0.710 8) and Nd model age (T2DM=2.10 Ga) of the early granite are both higher than those of the late granite(0.707 6～0.710 7, T2DM=1.41～1.58 Ga). Nevertheless, εNd(t) of the late granite (?11.6) is lower than that of the early granite (?4.8 ～ ?6.8). These data show that the early A-type granite might have originated from Paleoproterozoic continental crust, whereas the late I-type granite originated from Mesoproterozoic crust. Combined with regional geological structural characteristics, the authors consider that the formation of early A-type granite was related to the thinning and stretching of north Oulongbuluke block caused by Qilian lithosphere delamination which also marked the beginning of Zongwulong rift, while the formation of late I-type granite was related to the southward subduction of Zongwulong oceanic crust beneath Oulongbuluke block.

granite; zircon SHRIMP dating; Oulongbuluke block; Zongwulong tectonic zone; Wulan

P588.121; P597.1

A

10.3975/cagsb.2016.04.11

本文由中國地質調查局項目(編號: 121201102000150005-06; 12120115027001; 12120114079901)、國家自然科學基金項目(編號: 41472063; 40921001; 40472034; 40672049)和國家專項(編號: Sino Probe 05-05)聯合資助。

2016-05-06; 改回日期: 2016-06-26。責任編輯: 閆立娟。

吳才來, 男, 1960年生。博士, 研究員, 博士生導師。主要從事火成巖巖石學及其成礦研究。E-mail: wucailai@126.com。