印尼北蘇拉威西中部～10Ma閃長巖的巖石成因及對西里伯斯海向南俯沖的啟示

盧向紅, 錢 鑫, 2*, 甘成勢, 2, 張玉芝, 2, 吳賽男, 王岳軍, 2

印尼北蘇拉威西中部～10Ma閃長巖的巖石成因及對西里伯斯海向南俯沖的啟示

盧向紅1, 錢 鑫1, 2*, 甘成勢1, 2, 張玉芝1, 2, 吳賽男1, 王岳軍1, 2

(1. 中山大學 地球科學與工程學院, 廣東省地球動力作用與地質災害重點實驗室, 廣東 珠海 519082; 2. 南方海洋科學與工程廣東省實驗室(珠海), 廣東 珠海 519082)

蘇拉威西島位于歐亞、太平洋和印度?澳大利亞板塊的交匯處, 經歷了復雜的構造演化歷史, 保存了大量中?新生代巖漿記錄。本研究對北蘇拉威西中部閃長巖開展了鋯石U-Pb年代學和Lu-Hf同位素、全巖元素?同位素地球化學研究。研究顯示, 閃長巖鋯石U-Pb年齡為10.32±0.44 Ma和9.87±0.11 Ma, 形成于晚中新世。樣品SiO2含量為53.81%～59.90%, MgO為3.27%～4.27%, K2O為0.48%～1.22%, A/CNK=0.86～0.92, Mg#為47～49, 屬高鎂中鉀鈣堿性閃長巖。該閃長巖以富集大離子親石元素和輕稀土元素、虧損高場強元素為特征, 具明顯Nb-Ta和Ti負異常, 輕微Eu負異常(Eu/Eu*=0.78～0.96)。閃長巖(87Sr/86Sr)i值變化于0.70498～0.70509之間,Nd()值變化于+5.6～+5.7之間, 鋯石原位Hf()值為+11.2～+16.9。地球化學特征顯示印尼北蘇拉威西中部閃長巖源區受到了俯沖組分的交代改造, 可能是虧損地幔源區輝石巖的部分熔融產物。結合區域地質研究, 認為北蘇拉威西晚中新世閃長巖形成于島弧背景, 受控于晚中新世西里伯斯海的向南俯沖。

鋯石U-Pb年代學; 晚中新世; 高鎂閃長巖; 西里伯斯海俯沖; 北蘇拉威西

0 引 言

東南亞地區分布有一系列邊緣海盆地(如蘇祿海、西里伯斯海、馬魯古海、班達海和爪哇海等)和島鏈(如菲律賓、巴拉望、北蘇拉威西和爪哇等), 它們的形成大多與新生代印度?澳大利亞板塊與歐亞板塊的匯聚、太平洋板塊的俯沖和南海的擴張消亡等構造過程密切相關(圖1a; Hall, 2002, 2012; Advokaat et al., 2018)。蘇拉威西島呈K字型展布于印尼東部, 由多個地質單元構成(圖1b; Katili, 1978; Hamilton 1979; Polvé et al., 1997; White et al., 2014, 2017)。自中生代以來, 該地區經歷了陸塊裂離、板片俯沖和增生碰撞等復雜演化歷史, 已成為研究俯沖帶巖漿作用的天然實驗室(Priadi et al., 1994; Polvé et al., 1997; Hall, 2012; Hennig et al., 2016; Van Leeuwen et al., 2016; Maunala et al., 2016, 2019; Zhang et al., 2020)。

北蘇拉威西主要發育有新生代島弧巖漿巖和相應沉積作用(圖1c), 該區已發表的巖漿巖年代學資料多為K-Ar年齡數據, 主要分布于22～0.9 Ma, 被認為是多期巖漿活動的產物(Kavalieris et al., 1992; Surmont et al., 1994; Polvé et al., 1997; Elburg and Foden, 1998; Hanyu et al., 2012)。但時至今日, 對北蘇拉威西巖漿巖的精細年代學限定還相對薄弱, 對它們的地球化學特征及其巖石成因缺乏深入認知(圖1a; Kopp et al., 1999; Hanyu et al., 2012; Leo et al., 2013)?，F有資料表明, 西里伯斯海形成于始新世, 發育多期俯沖巖漿作用(Silver et al., 1983a; Hutchison, 1989), 而馬魯古海俯沖作用以發育大量晚中新世?上新世弧巖漿巖為特征(Hanyu et al., 2012)。目前北蘇拉威西地區的巖漿作用與其西北側西里伯斯海或東南側馬魯古海的俯沖之間存在何種關聯仍不清晰。值得關注的是, 西里伯斯海海盆具與南海和蘇祿海近于平行展布的磁異常條帶特征(Silver et al., 1983b), 因此, 在位于南海以南、西里伯斯海南緣的北蘇拉威西地區開展詳細的巖漿作用研究, 可以更好地理解西里伯斯海的形成演化, 乃至了解南海的擴張與俯沖消減提供重要啟示(Silver and Rangin, 1991; Spadea et al., 1996; 李家彪等, 2011; 王鵬程等, 2017)。

GF. 哥倫打洛斷層; PKF. 帕魯?科羅斷層; WF. 瓦倫奈斷層; MF. 馬塔諾斷層; LF. 勞諾波斷層; KF. 科拉卡斷層。

1 地質背景及巖相學特征

蘇拉威西島發育的主要斷裂包括哥倫打洛斷裂、帕魯?科羅斷裂、馬塔諾斷裂、勞諾波斷裂、科拉卡斷裂和瓦倫奈斷裂等(圖1b)。根據時代和演化的不同, 蘇拉威西島又分為西蘇拉威西、北蘇拉威西、中蘇拉威西、東蘇拉威西、邦蓋?蘇拉微陸塊和布頓?圖康伯西微陸塊(圖1b)。其中西蘇拉威西除零星出露具岡瓦納大陸親緣性的Malino、Palu、Latimojong、Bantimala和Barru等變質雜巖體以外, 其余地區均被新生代火山?沉積地層所覆蓋(Hutchison, 1989; Metcalfe, 1990; Maunala et al., 2013, 2016)。中蘇拉威西大規模分布的變質帶主要由變沉積巖和蛇綠巖組成, 其變質作用主要發生在早白堊世或漸新世?中新世(Parkinson, 1991; Monnier et al., 1994, 1995; Cornée et al., 1995; Kadarusman et al., 2004)。東蘇拉威西主體由白堊紀或始新世蛇綠混雜巖及上覆新生代沉積巖構成, 有人認為其具澳大利亞親緣性, 也有學者認為其起源于西里伯斯海(Simandjuntak, 1986; Monnier et al., 1994; Mubroto et al., 1994; Hall, 1996; Sidimantjuk and Barber, 1996; Elburg and Foden, 1999)。邦蓋?蘇拉微陸塊發育有島內最古老的古生代?中生代花崗質巖石, 其主體被新生代被動大陸邊緣型沉積所覆蓋(Kundig, 1956; Simandjuntak, 1986; Rangin et al., 1990; Villeneuve et al., 1992; Cornée et al., 1995)。布頓?圖康伯西微陸塊由布頓島、穆納島和周圍島嶼組成, 具中生代基底巖石, 上覆白堊紀?漸新世沉積地層(Davidson, 1991; Smith and Silver, 1991; Hall and Wilson, 2000)。

一般認為, 北蘇拉威西不具古老大陸基底, 以洋內弧屬性為特征, 主體被新生代火山?沉積地層所覆蓋(Silver et al., 1983b; Kavalieris et al., 1992; Polvé et al., 1997; Hanyu et al., 2012)。古近紀巖漿巖主要分布在北蘇拉威西的西部和中部, 而新近紀以來的巖漿巖則廣布于整個北蘇拉威西(圖1c; Kavalieris et al., 1992; Polvé et al., 1997; Elburg and Foden, 1998; Elburg et al., 2003; Maunala et al., 2016)。在北蘇拉威西馬里薩、博羅科和哥倫打洛等地區發育有大量中性?長英質侵入體(圖1c; 高小衛等, 2015)。本文研究的對象為北蘇拉威西中部哥倫打洛地區的閃長巖巖體, 該巖體侵位于古近紀火山?沉積序列中, 并被晚中新世?上新世火山?沉積單元所覆蓋(圖1c, 2a、b)。文中采集的8件閃長巖樣品均具相似礦物組合, 主要由斜長石(50%～60%)、角閃石(15%～20%)、石英(5%～10%)、斜方輝石(8%～12%)、黑云母(3%～5%)和不透明金屬礦物(2%～3%)組成, 可見少量鋯石和磷灰石等副礦物(圖2c～f)。斜長石呈板條狀, 自形程度較好, 部分具有聚片雙晶、環帶結構; 磷灰石呈針狀分布于斜長石和石英等礦物中(圖2c～f)。

2 分析方法

本次研究對8件閃長巖樣品開展了元素?同位素地球化學分析, 并對其中19SU-32-1和19SU-46-1兩件樣品開展了鋯石U-Pb年代學及Lu-Hf同位素分析。上述分析均在中山大學地球科學與工程學院和廣東省地球動力作用與地質災害重點實驗室完成。

通過人工重砂法和電磁選技術從閃長巖樣品中分選出足量鋯石, 制靶后用 Carl Zeiss ∑igmaTM場發射掃描電子顯微鏡拍攝陰極發光圖像。用激光剝蝕系統和iCAP RQ型電感耦合等離子體質譜儀(ICP-MS)聯用開展鋯石U-Pb年代學測試, 詳細的儀器介紹和測試方法參考Wang et al. (2020)。實驗監測和分餾校正的鋯石標樣為91500和Ple?ovice, 用GLITTER軟件(Griffin et al., 2008)和ISOPLOT軟件(Ludwig, 2003)對原始數據和加權平均年齡等進行處理。鋯石原位Lu-Hf同位素分析中采用Geolas HD 193 nm ArF準分子激光剝蝕系統和Neptune Plus多接收器電感耦合等離子體質譜儀(MC-ICP-MS), 詳細的儀器參數和操作程序見Hu et al. (2012)。將新鮮巖石樣品碎至小于200目的粉末后開展主量、微量元素和同位素組成測試。主量元素分析采用熔片法制備待測樣品, 通過ARL-Perform’X4200型X射線熒光光譜分析儀(XRF)測試完成。微量元素分析前用硝酸和氫氟酸對樣品進行初步溶解后, 經高溫溶解和冷卻, 加入稀硝酸和內標溶液制備為待測溶液, 分析測試通過iCAP RQ型ICP-MS儀器完成。Sr和Nd同位素測試通過Neptune Plus型MC-ICP-MS進行,86Sr/88Sr=0.1194和146Nd/144Nd=0.7219用于質量分餾校正, 詳細測試過程及參數設置參考Wang et al. (2020)。

3 結 果

3.1 鋯石U-Pb年代學和原位Lu-Hf同位素

北蘇拉威西中部閃長巖的鋯石U-Pb年代學和Lu-Hf同位素測試結果分別見表1和表2。樣品19SU-32-1和19SU-46-1的鋯石粒徑約150～500 μm, 自形?半自形, 大多呈粒狀或長柱狀, 長寬比介于1︰1與4︰1之間, 發育振蕩環帶, Th/U值變化于0.51～1.49之間, 為典型的巖漿成因鋯石(圖3a、b)。樣品19SU-32-1的14顆鋯石的206Pb/238U加權平均年齡為10.32±0.44 Ma(MSWD=0.03)(圖3a), 對應的鋯石176Hf/177Hf值變化于0.283128～0.283243之間(圖3c),Hf()=+12.8～+16.9, 一階段模式年齡DM1為10～173 Ma。樣品19SU-46-1中的29顆鋯石給出206Pb/238U加權平均年齡為9.87±0.11 Ma(MSWD=0.47)(圖3b), 對應的鋯石176Hf/177Hf值變化于0.283082～0.283193之間,Hf()=+11.2～+15.1,DM1=84～241 Ma(圖3c)。兩件樣品具相似的加權平均年齡, 代表了該閃長巖體的結晶年齡為～10 Ma, 形成于晚中新世。

礦物代號: Pl. 斜長石; Amp. 角閃石; Opx. 斜方輝石; Qtz. 石英; Bi. 黑云母; Zrn. 鋯石; Ap. 磷灰石。

表1 北蘇拉威西中部閃長巖LA-ICP-MS鋯石U-Pb定年結果

續表1:

表2 北蘇拉威西中部閃長巖鋯石原位Lu-Hf同位素分析結果

3.2 全巖主量、微量元素地球化學及Sr-Nd同位素特征

北蘇拉威西中部閃長巖全巖元素和Sr-Nd同位素分析結果見表3。所分析的8件樣品燒失量LOI變化范圍為0.05%～0.47%, 無水標準化后樣品的SiO2變化于53.66%～60.15%, Fe2O3T變化于6.70%～ 8.01%, CaO含量為6.72%～8.48%, Al2O3含量為17.08%～19.18%, TiO2含量為0.75%～0.88%, 具有較高的Na2O含量(3.16%～3.84%)和較低K2O含量(0.48%～1.22%), (K2O+Na2O)為4.13%～4.57%。在TAS圖解中, 閃長巖樣品點落入輝長閃長巖?閃長巖區域(圖4a)。在K2O-SiO2圖解中, 樣品落入(低鉀)拉斑?中鉀鈣堿性系列區域(圖4b)。與正常島弧火山巖相比, 本研究中的閃長巖具有更高MgO含量(3.28%～4.26%)和Mg#值(47～49), 類似加里曼丹島東北部沙巴地區中新世安山巖, 均落在高鎂安山巖/閃長巖區域(圖4c; Bergman et al., 2000; Baharuddin, 2011)。

閃長巖樣品稀土元素總量(ΣREE)為64.2×10?6～ 79.8×10?6, 球粒隕石標準化稀土元素配分曲線呈富集輕稀土元素、虧損重稀土元素的右傾型(圖5a), (La/Yb)N、(La/Sm)N、(Gd/Yb)N值分別為2.67～3.42, 1.59～1.95和1.14～1.42, Eu負異常不明顯(Eu/Eu*=0.78～0.96)。在原始地幔標準化微量元素蛛網圖中(圖5b)中, 樣品以富集大離子親石元素、虧損高場強元素為特征, 具較低的Cr(12.7×10?6～38.8×10?6)、Ni(11.2×10?6～ 17.7×10?6)含量, 具有明顯的Nb-Ta和Ti負異常, 其特征類似沙巴地區中新世安山巖(圖5; Bergman et al., 2000; Baharuddin, 2011)。

沙巴基性巖數據來自Tsikouras et al. (2021)。

表3 北蘇拉威西中部閃長巖全巖主量(%)、微量(×10–6)和Sr-Nd同位素分析結果

續表3:

沙巴中新世安山巖數據來自Bergman et al. (2000)和Baharuddin (2011)。

標準化值數據Sun and McDonough (1989); 沙巴中新世安山巖數據來自Bergman et al. (2000)和Baharuddin (2011)。

數據來源: 南海新生代玄武巖、DMM、OIB和I-MORB數據引自Lai et al. (2021); 西里伯斯?；仔鋷r數據引自Elburg and Foden (1998), 哥倫打洛花崗巖數據引自Maunala et al. (2016)。

閃長巖樣品的Sr-Nd同位素分析表明,87Sr/86Sr值為0.705014～0.705148,143Nd/144Nd值為0.512922～ 0.512929, 回算得到 (87Sr/86Sr)i變化于0.704981～ 0.705094之間,Nd()值為+5.60～+5.74, 其同位素組成與南海玄武巖和哥倫打洛晚中新世?上新世花崗巖相似(圖6; Maunala et al., 2016; Lai et al., 2021)。

4 討 論

4.1 巖石成因

北蘇拉威西中部閃長巖樣品新鮮且燒失量較低(LOI=0.05%～0.47%), 鏡下未發現蝕變礦物, 表明樣品未遭受明顯的后期蝕變影響。盡管閃長巖樣品SiO2含量變化較大但樣品19SU-46-4的SiO2含量最低為53.66%, 說明閃長巖不可能是地殼巖石直接部分熔融的產物。一般遭受顯著地殼混染的巖石具較高的(La/Sm)N值(>4.5)(張永明等, 2019), 而本次研究的閃長巖樣品具較低的(La/Sm)N值(1.59～1.95)。此外, 閃長巖樣品SiO2含量與Nb/La值未見明顯負相關關系。同時, 這些樣品結晶年齡一致、Mg#值(47～49)變化范圍較窄、具有高的正Nd()值(+5.6～ +5.7)和鋯石Hf()值(+11.2～+16.9), 表明閃長巖樣品在侵位過程中沒有遭受明顯的地殼混染。相對于正常島弧火山巖,北蘇拉威西中部閃長巖樣品具更高的MgO、Na2O含量及更低的K2O含量, 為高鎂中鉀鈣堿性閃長巖(圖4a～c), 其可能的成因包括:①拆沉榴輝巖質下地殼部分熔融(Rapp et al., 1991, 1999; Kelemen et al., 1998; Xu et al., 2002); ②殼源和幔源熔體混合(Kawabata and Shuto, 2005; Guo et al., 2007; Streck et al., 2007); ③年輕俯沖板片部分熔融(Rapp et al., 1991, 1999; Sen and Dunn, 1994); ④俯沖板片熔體/流體交代的地幔楔部分熔融(Tatsumi, 1981; Kelemen, 1995; Qian et al., 2017)。

拆沉榴輝巖質下地殼部分熔融形成的高鎂巖石常具較低重稀土元素含量與較高SiO2、Cr、Ni、Sr含量和La/Yb、Sr/Y值(Kelemen et al., 1998)。本研究中, 閃長巖樣品鏡下未見金紅石, 其地球化學特征也明顯有別于上述特征。研究區地質背景為初始未成熟島弧環境(Silver et al., 1983b; Rangin et al., 1997),難以發育地殼加厚拆沉事件, 故區域上也不具備形成榴輝質下地殼拆沉的條件。閃長巖樣品的La/Yb值隨著Yb含量增加變化微弱, 表現出以分離結晶作用為主的演化趨勢(圖7a)。相似的礦物組成, 相對均一的全巖Sr-Nd、鋯石Lu-Hf同位素組成, 以及相似的微量和稀土元素配分模式(圖2、3c、5、6)表明閃長巖樣品不是殼幔熔體混合產物。年輕俯沖板片部分熔融與地幔橄欖巖反應可產生高鎂巖石但此條件下形成的巖石常具有較高SiO2、Sr(>400×10?6)含量和Sr/Y(>20)值, 低Y(<18×10?6)和Yb(<1.9×10?6)含量, 表現出埃達克質巖石的地球化學特征(Defant and Drummond, 1990)。而本研究中, 閃長巖樣品表現出較低的SiO2含量, Y>20.5×10?6, Sr<381×10?6, Sr/Y值為10.3～18.6, 明顯不同于埃達克質巖的特征(Kay, 1978)。

北蘇拉威西中部閃長巖顯示出強烈富集大離子親石元素, 虧損高場強元素的特征和顯著的Nb、Ta、Ti負異常(圖5), 類似于島弧巖漿巖。低Nb/La (0.30～0.39)、Nb/U(3.42～9.44)和Ce/Pb(0.22～3.34)值反映閃長巖樣品源自受俯沖熔體/流體交代的地幔楔源區(Tatsumi et al., 1986)。在Rb/Y-Nb/Y和Nb/Y-Ba圖解上(圖7b、c), 樣品表現出顯著的以俯沖流體交代為主的特征(Zhang et al., 2012; Qian et al., 2017)。通常洋殼來源的熔體/流體常具較低Al2O3和Th含量, 其全巖Sr-Nd同位素與鋯石Hf同位素組成類似大洋板片(Wang et al., 2013; Gou et al., 2014)。而俯沖沉積物來源的熔體/流體可具較高Al2O3、Th和LREEs含量及更富集的Sr-Nd同位素組成(Gan et al., 2020)。已有研究表明, 俯沖沉積物流體在交代過程中, 因為Nd相對Hf更具活動性, 可使地幔楔熔體中沉積物Nd-Hf同位素組成發生解耦(You et al., 1996; Gou et al., 2014)。北蘇拉威西中部閃長巖具有較高的Al2O3含量、相對虧損地幔富集的Sr-Nd同位素組成, 但鋯石Hf()值很高, 類似虧損地幔, 表明源區可能存在俯沖沉積物的交代改造, 且源區在交代過程中可能發生了Nd-Hf同位素的輕度解耦。北蘇拉威西中新世(22～14 Ma)鈣堿性火成巖研究也表明其源區經歷了俯沖流體交代作用(Polvé et al., 1997)。

北蘇拉威西中部閃長巖以斜長石、斜方輝石和角閃石作為其主要礦物, 鏡下未觀察到單斜輝石。通常斜方輝石作為巖漿早期結晶礦物, 表明初始巖漿為硅飽和或過飽和熔體。同時閃長巖樣品的高鎂(Mg#=47～49), 低Cr (12.7×10?6～38.8×10?6)、Ni(11.2× 10?6～17.7×10?6)和Co(18.7×10?6～23.7×10?6)含量特征, 反映了北蘇拉威西中部閃長巖的源區可能以輝石巖為主。因此, 北蘇拉威西中部閃長巖是受俯沖沉積物流體交代的地幔楔源區輝石巖部分熔融產物。

4.2 構造意義

北蘇拉威西廣泛出露新生代巖漿巖, 根據已發表的一些K-Ar和極少量Ar-Ar年齡數據, 有學者提出北蘇拉威西中新世巖漿活動以22～13 Ma和<9.5 Ma的活躍期、及晚中新世(～10 Ma)的寧靜期為主要特征(Bellon and Rangin, 1991; Kavalieris et al., 1992; Priadi, 1993; Polvé et al., 2001; Elburg et al., 2003; Van Leeuwen et al., 2007; Hanyu et al., 2012)。但Polvé et al. (1997)和Maunala et al. (2016)報道了11～8.3 Ma的北蘇拉威西火山巖, 認為巖漿活動自始新世中期一直持續到上新世。結合本研究年代學結果, 北蘇拉威西中部閃長巖形成于～10 Ma, 證實晚中新世(～10 Ma)該地區存在巖漿活動, 并不是一個明顯的寧靜期。

圖7 北蘇拉威西中部閃長巖La/Yb-Yb(a; 據Wang et al., 2017)、Rb/Y-Nb/Y(b; 據Kepezhinskas et al., 1997)和Nb/Y-Ba (c; 據Zhang et al., 2012)圖解

西里伯斯海盆地的擴張大致始于始新世, 發生了多期俯沖事件(Spadea et al., 1996)。北蘇拉威西和東北婆羅洲沙巴地區作為西里伯斯海南北兩側新生代巖漿巖的典型出露地區, 記錄了西里伯斯海的形成與演化(Spadea et al., 1996; Rangin et al., 1997; Kopp et al., 1999; Hanyu et al., 2012)。在沙巴地區仙本那半島和丹特半島發育與西里伯斯海俯沖有關的中新世島弧成因安山巖(Hutchison, 1992; Bergman et al., 2000; Baharuddin, 2011)。Maunala et al. (2016)提出北蘇拉威西哥倫打洛地區花崗巖的形成是西里伯斯海俯沖的結果。另外, 西里伯斯海呈現出不對稱磁異常條帶分布特征, 蘇祿弧方向的北側磁異常條帶保存相對完整, 而南側面向北蘇拉威西方向磁條帶保存較少, 這可能是由于中新世以來印度?澳大利亞板塊向北擠壓、西里伯斯海洋殼向南俯沖消減于北蘇拉威西之下的結果(Silver et al., 1983b; Rangin et al., 1997, 1999)。如前所述, 北蘇拉威西中部晚中新世閃長巖主量、微量元素地球化學特征、鋯石Lu-Hf同位素組成與沙巴地區中新世安山巖類似(圖4、5; Bergman et al., 2000; Baharuddin, 2011), 并具有與南海新生代玄武巖及西里伯斯?；仔鋷r相似的Sr-Nd同位素組成, 是受俯沖沉積物流體交代的地幔楔源區輝石巖部分熔融產物。在Th/Yb-Nb/Yb和Hf/3-Th-Ta構造判別圖解中, 北蘇拉威西閃長巖樣品落入島弧巖漿巖區域(圖8)。因此, 中?晚中新世北蘇拉威西屬俯沖島弧背景。

南海作為東南亞最大的邊緣海, 位于三大板塊的交匯部位(Metcalfe, 2009, 2013; Hall, 2012; Maunala et al., 2016, 2019), 其擴張作用開始于～33 Ma,終止于～15 Ma(Tapponnier et al., 1982; Xu et al., 2012;孫衛東等, 2018)。西里伯斯海、蘇祿海和南海近平行展布的大洋磁條帶表明, 三者的形成演化具有密切聯系(Silver et al., 1983b), 西里伯斯海與蘇祿海自漸新世–中新世以來可能作為南海俯沖的弧后盆地或邊緣海盆持續演化(Tapponnier et al., 1982; Rangin and Silver, 1991; Xu et al., 2012; 孫衛東等, 2018)。因此, 蘇祿海和西里伯斯海周緣約22～14 Ma廣泛的巖漿作用可能代表了其弧后擴張的產物(Shyu et al., 1991; Spadea et al., 1996)。以往的研究認為, ～7.5 Ma以來大規模島弧巖漿活動暗示了南海邊緣海盆俯沖作用的再次啟動(Bellon and Rangin, 1991; Polvé et al., 1997)。而本研究的綜合對比表明, 西里伯斯海、蘇祿海和南海南部的俯沖消減的啟動或再次啟動很可能發生在10 Ma之前, 而不是7.5 Ma或之后(Polvé et al., 2001; Lai et al., 2021), 晚中新世～10 Ma北蘇拉威西或已處于西里伯斯海向南俯沖的構造背景, 俯沖沉積物派生流體交代上覆地幔, 從而形成了北蘇拉威西中部閃長巖的源區。

圖8 北蘇拉威西中部閃長巖Th/Yb-Nb/Yb(a; 據Pearce and Peate, 1995)和Hf/3-Th-Ta(b; 據Wood et al., 1980)圖解

5 主要結論

(1) 印尼北蘇拉威西中部閃長巖的 LA-ICP-MS 鋯石U-Pb 年齡為～10 Ma, 形成于晚中新世。

(2) 北蘇拉威西中部閃長巖主要屬高鎂中鉀鈣堿性系列, 具有島弧微量元素的地球化學特征和虧損的全巖Sr-Nd和鋯石Hf同位素組成。

(3) 北蘇拉威西中部閃長巖源自受俯沖派生流體交代改造的地幔輝石巖源區, 其形成受控于晚中新世西里伯斯海的南向俯沖。

致謝:本研究樣品野外采集和實驗分析得到了印尼Jony, 中山大學余小清、王玉琨、楊雪和徐暢博士等的幫助, 兩位匿名審稿專家提出了建設性意見, 在此一并表示衷心的感謝。

高小衛, 吳秀榮, 楊振強. 2015. 巽他古陸核東南邊緣新生代埃達克質巖的成因和源區: 回顧. 華南地質與礦產, 31(3): 225–235.

李家彪, 丁巍偉, 高金耀, 吳自銀, 張潔. 2011. 南海新生代海底擴張的構造演化模式: 來自高分辨率地球物理數據的新認識. 地球物理學報, 54(12): 3004–3015.

孫衛東, 林秋婷, 張麗鵬, 廖仁強, 李聰穎. 2018. 跳出南?？茨虾！绿靥崴寡箝]合與南海的形成演化. 巖石學報, 34(12): 3467–3478.

王鵬程, 李三忠, 郭玲莉, 趙淑娟, 李璽瑤, 王永明, 惠格格, 王倩. 2017. 南海打開模式: 右行走滑拉分與古南海俯沖拖曳. 地學前緣, 24(4): 294–319.

張永明, 裴先治, 李佐臣, 李瑞保, 劉成軍, 裴磊, 陳有炘, 王盟. 2019. 青海南山構造帶印支早期基性雜巖體年代學、地球化學特征及地質意義. 地球科學, 44(7): 2461–2481.

Advokaat E L, Bongers M L M, Rudyawan A, BouDagher- Fadel M K, Langereis C G, Van Hinsbergen D J J. 2018. Early Cretaceous origin of the Woyla Arc (Sumatra, Indonesia) on the Australian plate., 498: 348–361.

Baharuddin B. 2011. Petrologi dan geokimia batuan gunungapiTersier Jelai di daerah malinau kalimantan timur., 21(4): 203–211.

Bellon H, Rangin C. 1991. Geochemistry and isotopic dating of Cenozoic volcanic arc sequences around the Celebes and Sulu Seas.,, 124: 321–338.

Bergman S, Hutchison C, Swauger D, Graves J. 2000. K-Ar ages and geochemistry of the Sabah Cenozoic volcanic rocks., 44: 165–171.

Cornée J, Tronchetti G, Villeneuve M, Lathuilière B, SamodraH. 1995. Cretaceous of eastern and southeastern Sulawesi (Indonesia): New micropaleontological and biostrati-gra-phical data., 12(1): 41–52.

Davidson J W. 1991. The geology and prospectively of Buton Island, SE. Sulawesi, Indonesia. Jakarta: Proceedings Indonesian Petroleum Association, 20thAnnual Convention: 209–233.

Defant M J, Drummond M S. 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere., 347(6294): 662–665.

Elburg M A, Foden J. 1998. Temporal changes in arc magma geochemistry, Northern Sulawesi, Indonesia., 163(1): 381–398.

Elburg M A, Foden J. 1999. Geochemical response to varying tectonic settings: An example from southern Sulawesi (Indonesia)., 63(7–8): 1155–1172.

Elburg M A, Van Leeuwen T, Foden J, Muhardjo. 2003. Spatial and temporal isotopic domains of contrasting igneous suites in Western and Northern Sulawesi, Indonesia., 199(3–4): 243–276.

Gan C S, Wang Y J, Barry T B, Zhang Y Z, Qian X. 2020. Late Jurassic high-Mg andesites in the Youjiang Basin and their significance for the southward continuation of the Jiangnan Orogen, South China., 77: 260–273.

Griffin W L, Powell W J, Pearson N J, Reilly S Y. 2008. GLITTER: Data reduction software for laser ablation ICP-MS., 40: 204–207.

Guo F, Fan W M, Li C W, Wang C Y, Li H X, Zhao L, Li J Y. 2014. Hf-Nd-O isotopic evidence for melting of recycledsediments beneath the Sulu Orogen, North China., 381: 243–258.

Guo F, Nakamuru E, Fan W M, Kobayoshi K, Li C W. 2007. Generation of Paleocene adakitic andesites by magma mixing; Yanji Area, NE China., 48: 661–692.

Hall R. 1996. Reconstructing Cenozoic SE Asia // Hall R, Blundell D J. Tectonic Evolution of Southeast Asia.,,: 153–184.

Hall R. 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: Computer-based recon-stru-ctions, model and animations., 20(4): 353–431.

Hall R. 2012. Late Jurassic-Cenozoic reconstructions of the Indonesian region and the Indian Ocean., 570: 1–41.

Hall R, Wilson M E J. 2000. Neogene sutures in eastern Indonesia., 18: 781–808.

Hamilton W B. 1979. Tectonics of the Indonesian region., 6: 3–10

Hanyu T, Gill J, Tatsumi Y, Kimura J I, Sato K, Chang Q, Senda R, Miyazaki T, Hirahara Y, Takahashi T, Zulkarnain I. 2012. Across- and along-arc geochemical variations of lava chemistry in the Sangihe arc: Various fluid and meltslab fluxes in response to slab temperature.,,, 13(10), 10021.

Hennig J, Hall R, Armstrong R A. 2016. U-Pb zircon geochronology of rocks from west Central Sulawesi, Indonesia: Extension-related metamorphism and magmatismduring the early stages of mountain building., 32: 41–63.

Hu Z C, Liu Y S, Gao S, Liu W G, Zhang W, Tong X R, Lin L, Zong K Q, Li M, Chen H H. 2012. ImprovedHf isotope ratio analysis of zircon using newly designed X skimmer cone and jet sample cone in combination with the addition of nitrogen by laser ablation multiple collector ICP-MS., 27(9): 1391–1399.

Hutchison C S. 1989. Geological Evolution of South-East Asia. Oxford Monographs on Geology and Geophysics, Clarendon Press: 376.

Hutchison C S. 1992. The southeast Sulu Sea, a Neogene marginal basin with outcropping extensions in Sabah., 32: 89–108.

Kadarusman A, Miyashita S, Maruyama S, Parkinson C D, Ishikawa A. 2004. Petrology, geochemistry and paleo-geo-graphic reconstruction of the East Sulawesi Ophiolite, Indonesia., 392(1–4): 55–83.

Katili J A. 1978. Past and present geotectonic position of Sulawesi, Indonesia., 45: 289–322.

Kavalieris I, Leeuwen T M V, Wilson M. 1992. Geological setting and styles of mineralization, North Arm of Sulawesi, Indonesia., 7(2–3): 113–129.

Kawabata H, Shuto K. 2005. Magma mixing recorded in intermediate rocks associated with high-Mg andesites from the Setouchi volcanic belt, Japan: Implications for Archean TTG formation., 140(4): 241–271

Kay R W. 1978. Aleutian magnesian andesites: Melts from subducted Pacific oceanic crust., 4: 117–132.

Kelemen P B. 1995. Genesis of high-Mg andesites and the continental crust., 120: 1–19.

Kelemen P B, Hart S R, Bernstein S. 1998. Silica enrichment in the continental upper mantle via melt/rock reaction., 164(1–2): 387–406.

Kepezhinskas P, McDermott F, Defant M J, Hochstaedter A, Drummond M S, Hawkesworth C J, Koloskov A, MauryR C, Bellon H. 1997. Trace element and Sr-Nd-Pb isotopic constraints on a three-component model of Kamchatka arc petrogenesis., 61(3): 577–600.

Kopp C, Flueh E R, Neben S. 1999. Rupture and accretion of the Celebes sea crust related to the North-Sulawesi subduction: Combined interpretation of reflection and refraction seismic measurements., 27: 309–325.

Kundig E. 1956. Geology and ophiolite problems of East Celebes., 16: 210–235.

Lai C K, Xia X P, Hall R, Meffre S, Tsikouras B, Tarriela M I, Idrus A, Ifandi E, Norazme N. 2021. Cenozoic evolutionof the Sulu Sea arc-basin system: An overview., 40, e2020TC006630. https: //doi org/10 1029/2020TC006630.

Leo J F D, Wookey J, Hammond J O S, Kendall J M, Kaneshima S, Inoue H, Yamashina T, Harjadi P. 2013. Mantle flow in regions of complex tectonics: Insights from Indonesia.,,, 13(12), Q12008.

Liu H Q, Yumul Jr G P, Dimalanta C B, Quea?o K, Xia X P, Peng T P, Lan J B, Xu Y G, YanY, Guotana J M R, Olfindo V S. 2020. Western Northern Luzon isotopic evidence of transition from Pro-to-South China Sea to South China Sea fossil ridge subduction., 39(2), e05639.

Ludwig K R. 2003. User’s manual for a geochronological toolkit for Microsoft Excel (Isoplot/Ex version 3.0). Berkeley Geochronology Center, Special Publication, 4: 1–71.

Maulana A, Christy A G, Ellis D J, Br?cker M. 2019. The distinctive tectonic and metamorphic history of the Barru Block, South Sulawesi, Indonesia: Petrological, geochemical and geochronological evidence., 172: 170–189.

Maulana A, Imai A, Van Leeuwen T, Watanabe K, Yonezu K, Nakano T, Boyce A, Page L, Schersten A. 2016. Origin and geodynamic setting of Late Cenozoic granitoids in Sulawesi, Indonesia., 124: 102–125.

Maulana A, Watanabe K, Imai A, Yonezu K. 2013. Origin of magnetite- and ilmenite-series granitic rocks in Sulawesi, Indonesia: Magma genesis and regional metallogenic constraint., 6: 50–57.

Metcalfe I. 1990. Allochthonous terrane processes in Southeast Asia., 331: 625–640.

Metcalfe I. 2013. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys., 66: 1–33.

Monnier C, Bellon H, Girardeau J. 1994.40K-40Ar dating of the Sulawesi ophiolite, Indonesia., 319: 349–356.

Monnier C, Girardeau J, Maury R C, Cotten J. 1995. Back-arc basin origin for the East Sulawesi ophiolite (eastern Indonesia)., 23(9): 851–854.

Mubroto B, Briden J C, McClelland E, Hall R. 1994. Paleomagnetism of the Balantak ophiolite., 125: 193–209.

Parkinson C. 1991. Tectonic implication of subophiolite metamorphism in Central Sulawesi.: 42.

Pearce J A, Peate D W. 1995. Tectonic implications of the composition of volcanic arc lavas., 23: 251–285

Polvé M, Maury R C, Bellon H, Rangin C, Priadi B, Yuwono S, Joron J L.1997. Magmatic evolution of Sulawesi (Indonesia): Constraints on the Cenozoic geodynamic history of the Sundaland active margin., 272(1): 69–92.

Polvé M, Maury R C, Vidal P, Priadi B, Bellon H, Soeria- Atmadja R, Joron J L, Cotton J. 2001. Melting of lower continental crust in a young post-collision setting: A geochemical study of Plio-Quaternary acidic magmatismfrom Central Sulawesi (Indonesia)., 172: 333–342.

Priadi B. 1993. Géochimie du magmatisme de l’Ouest et du Nord de Sulawesi, Indonésie: Tra?age des sources et implications géodynamiques. Université fédérale de Toulouse-Midi-Pyrénées, Doctoral Dissertation: 293.

Priadi B, Polvé M, Maury R C, Bellon H, Soeria-Atmadja R, Joron J L, Cotten J. 1994. Tertiary and Quaternary magmatism in Central Sulawesi: Chronological and petrological constraints., 9(1–2): 81–93.

Qian X, Wang Y J, Srithai B, Feng Q L, Zhang Y Z, Zi J W, He H Y. 2017. Geochronological and geochemical constraints on the intermediate-acid volcanic rocks along the Chiang Khong-Lampang-Tak igneous zone in NW Thailand and their tectonic implications., 45: 87–99.

Rangin C, Bellon H, Benard F, Letouzey J, Muller C, Sanudin T. 1990. Neogene arc-continent collision in Sabah, Northern Borneo (Malaysia)., 183(1): 305–319.

Rangin C, Maury R C, Polvé M. 1997. Eocene to Miocene back-arc basin basalts and associated island arc tholeiites from northern Sulawesi (Indonesia): Implications for the geodynamic evolution of the Celebes basin., 168(5): 627–635.

Rangin C, Silver E. 1991. Neogene tectonic evolution of the Celebes-Sulu basins: New insights from Leg 124 drilling.,, 124: 51–63.

Rangin C, Spakman W, Pubellier M, Bijwaard H. 1999. Tomographic and geological constraints on subduction along the eastern Sundaland continental margin (South-East Asia)., 170(6): 775–788.

Rapp R P, Shimizu N, Norman M D, Applegate G S. 1999. Reaction between slab-derived melts and peridotite in the mantle wedge: Experimental constraints at 3.8 GPa., 160: 335–356.

Rapp R P, Watson E B, Miller C F. 1991. Partial melting of amphibole, eclogite and the origin of Archaean trondhjemites and tonalites., 51: 1–25.

Ringwood A E. 1975. Composition and Petrology of the Earth’s Mantle. New York: McGraw-Hill: 618.

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., 117: 394–409.

Shyu J P, Merrill D, Hsu V, Kaminski M A, Müller C M, Nederbragt A J, Scherer R P, Shibuya H. 1991. Biostratigraphic and magnetostratigraphic synthesis of the Celebes and Sulu Seas, Leg 124.:, 124: 11–38.

Sidimantjuk T O, Barber A J. 1996. Contrasting tectonic styles in the Neogene orogenic belts of Indonesia.,,, 106(1): 185– 201.

Silver E A, Mccaffrey R, Joyodiwiryo Y, Stevens S. 1983a. Ophiolite emplacement by collision between the Sula Platform and the Sulawesi Island Arc, Indonesia.:, 88(B11): 9419–9435.

Silver E A, Mccaffrey R, Smith R B. 1983b. Collision, rotation, and the initiation of subduction in the evolution of Sulawesi, Indonesia.:, 88(B11): 9407–9418.

Silver E A, Rangin C. 1991. Development of the Celebes Basin in the context of western Pacific marginal basin history., 124: 39–49.

Simandjuntak T O. 1986. Sedimentology and tectonics of the collision complex in the east arm of Sulawesi, Indonesia. University of London, Royal Holloway and Bedford New College (United Kingdom).

Smith R B, Silver E A. 1991. Geology of a Miocene collision complex, Buton, Eastern Indonesia., 103: 660–678.

Spadea P D, Antonio M, Thirlwall M F. 1996. Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): Chemical and isotopic evidence., 123(2): 159–176.

Streck M J, Leeman W P, Chesley J. 2007. High-magnesian andesite from Mount Shasta: A product of magma mixingand contamination, not a primitive mantle melt., 35: 351–354.

Sun S S, McDonough W F. 1989. Chemical and isotopic systematics of oceanic basalt: Implications for mantle composition and processes // Saunders A D, Norry M J. Magmatism in the Ocean Basins, Magmatism in the Ocean Basins.,,, 42: 313–345.

Surmont J, Laj C, Kissel C, Rangin C, Bellon H, Priadi B. 1994. New paleomagnetic constraints on the Cenozoic tectonic evolution of the North Arm of Sulawesi, Indonesia., 121: 629–638.

Tapponnier P, Peltzer G, Dain A, Armijo R, Cobbold P. 1982. Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine., 10(12), 611.

Tatsumi Y. 1981. Melting experiments on a high magnesian andesite., 54: 357–365.

Tatsumi Y, Hamilton D L, Nesbitt R W. 1986. Chemical characteristics of fluid phase released from a subducted lithosphere and origin of arc magmas: Evidence from high-pressure experiments and natural rocks., 29: 293–309.

Tsikouras B, Lai C K, Ifandi E, Norazme N A, Teo C H, Xia X P. 2021. New zircon radiometric U/Pb ages and Lu-Hf isotopic data from the ultramafic-mafic sequences of Ranau and Telupid (Sabah, east Malaysia): Time to reconsider the geological evolution of SE Asia?, 49(11), e542.

Van Leeuwen T, Allen C M, Elburg M, Massonne H J, Palin J M, Hennig J. 2016. The Palu Metamorphic Complex, NW Sulawesi, Indonesia: Origin and evolution of a young metamorphic terrane with links to Gondwana and Sundaland., 115: 133–152.

Van Leeuwen T, Allen C M, Kadarusman A, Elburg M, Palin J M, Muhardjo, Suwijanto. 2007. Petrologic, isotopic, and radiometric age constraints on the origin and tectonichistory of the Malino metamorphic complex, NW Sulawesi, Indonesia., 29(5–6): 751–777.

Villeneuve M, Cornée J J, Girardeau G, Clermonté J, Butterlin J, Blondeau D, Camoin G, Gla?on G, Gunawan W, Martini R, Samodra H, Sarmili L, Sutrisno, Tronchetti G, Zaninetti L. 1992. Stratigraphy and tectonics of the eastern part of Sulawesi Island (Indonesia). Kyoto, Japan: 29thInternational Geological Congress: 1511.

Wang Y J, Gan C S, Tan Q L, Zhang Y Z, He H Y, Qian X, Zhang Y H. 2018. Early Neoproterozoic (～840 Ma) slab window in South China: Key magmatic records in the Chencai Complex., 314: 434–451.

Wang Y J, He H Y, Zhang Y Z, Srithai B, Feng Q L, Cawood P A, Fan W M. 2017. Origin of Permian OIB-like basalts in NW Thailand and implication on the Paleotethyan Ocean., 274: 93–105.

Wang Y J, Yang T X, Zhang Y Z, Qian X, Senebouttalath V. 2020. Late Paleozoic back-arc basin in the Indochina block: Constraints from the mafic rocks in the Nan and Luang Prabang tectonic zones, Southeast Asia., 195: 104333.

White L T, Hall R, Armstrong R A, Barber A J, Fadel B D, Baxter A, Wakita K, Manning C, Soesilo J. 2017. The geological history of the Latimojong region of western Sulawesi, Indonesia., 138: 72–91.

White L T, Hall R, Armstrong R A. 2014. The age of undeformeddacite intrusions within the Kolaka fault zone, SE Sulawesi, Indonesia., 94: 105–112.

Wood D A. 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province., 50: 11–30.

Xu J F, Shinjo R, Defant M J, Wang Q, Rapp R P. 2002. Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust?, 30: 1111–1114.

Xu Y G, Zhang H H, Qiu H N, Ge W C, Wu F Y. 2012. Oceanic crust components in continental basalts from Shuangliao, Northeast China: Derived from the mantle transition zone?, 328(11): 168–184.

You C F, Castillo P R, Gieskes J M, Chan L H, Spivackm A J. 1996. Trace element behavior in hydrothermal experiments: Implications for fluid processes at shallow depths in subduction zones., 140: 41–52.

Zhang X R, Tien C Y, Chung S L, Maulana A, Lee H Y. 2020. A Late Miocene magmatic flare-up in West Sulawesi triggered by Banda slab rollback., 132(11–12): 2517–2528.

Zhang Y Z, Wang Y J, Fan W M, Zhang A M, Ma L Y. 2012. Geochronological and geochemical constraints on the metasomatised source for the Neoproterozoic (～825 Ma) high-Mg volcanic rocks from the Cangshuipu area (Hunan Province) along the Jiangnan domain and their tectonic implications., 220–221: 139–157.

Petrogenesis of ～10 Ma Diorites from Central North Sulawesi, Indonesia: Implications for the Subduction of the Celebes Sea

LU Xianghong1, QIAN Xin1, 2*, GAN Chengshi1, 2, ZHANG Yuzhi1, 2,WU Sainan1, WANG Yuejun1, 2

(1. Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai 519082, Guangdong, China; 2. Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, Guangdong, China)

The Sulawesi Island, located at the junction region of Eurasia, Pacific, and Indo-Australian plates, has undergone complex tectonic evolution andpreserved abundant Meso-Cenozoic igneous rocks. This paper presents zircon U-Pb geochronological, Lu-Hf isotopic, and whole-rock geochemical results for a dioritic pluton at Central North Sulawesi. The pluton consists of gabbro and diorite. Two representative diorite samples yield zircon U-Pb ages of 10.32±0.44 Ma and 9.87±0.11 Ma respectively.Eight diorite samples have SiO2, MgO, and K2O contents in ranges 53.81% to 59.90%, 3.27% to 4.27% and 0.48% to 1.22%, with Mg#=47–49and A/CNK=0.86–0.92, respectively. Classified as high-Mg and medium-K calc-alkaline series, they are enriched in LILEs and LREEs, and depleted in HFSEs, showing obvious Nb, Ta, and Ti negative anomaliesand slightly Eu negative anomalies (Eu/Eu*=0.78–0.96). They have low (87Sr/86Sr)ivalues of 0.704981–0.705094 and positiveNd() values of +5.6–+5.7. Their in-situ zirconHf() values are in range of +11.2 to +16.9. These geochemical characteristics indicate that the diorites were derived from a depleted mantle that metasomatized by sediment-released fluids. In combination with the available observations, it is concluded that the late Miocene diorites in North Sulawesi were formed in an arc setting in response to the southward subduction of the Celebes Sea.

zircon U-Pb dating; Late Miocene; diorite; Celebes Sea slab subduction; North Sulawesi

10.16539/j.ddgzyckx.2022.03.011

2021-12-10;

2022-02-25

國家自然科學基金項目(U1701641、41830211、42072256)和廣東省基礎與應用基礎研究基金項目(2018B030312007)聯合資助。

盧向紅(1997–), 女, 博士研究生, 地球化學專業。E-mail: luxh9@mail2.sysu.edu.cn

錢鑫(1988–), 男, 副教授, 從事東南亞大地構造及巖石地球化學研究。E-mail: qianx3@mail.sysu.edu.cn

P581; P597; P595

A

1001-1552(2022)03-0569-016