加里曼丹東南部梅拉圖斯斜長花崗巖的鋯石U-Pb年代學及其地質意義

王逸文, 陳新躍*, 甘成勢

加里曼丹東南部梅拉圖斯斜長花崗巖的鋯石U-Pb年代學及其地質意義

王逸文1, 陳新躍1*, 甘成勢2

(1. 湖南科技大學 地球科學與空間信息工程學院, 湖南 湘潭 410201; 2. 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)

加里曼丹島位于特提斯和太平洋構造域的交匯之處, 是研究兩大構造域演化、延伸及耦合的關鍵地區。梅拉圖斯蛇綠混雜巖呈近S-N向分布于加里曼丹島東南部, 但該蛇綠混雜巖帶的年代學、構造歸屬及其與特提斯和太平洋構造域的親緣性存在爭議。本文針對梅拉圖斯蛇綠混雜巖帶內的斜長花崗巖開展了巖相學、年代學、主量和微量元素、Sr-Nd同位素地球化學分析。LA-ICPMS鋯石U-Pb年代學結果揭示斜長花崗巖的結晶年齡為143.2±0.5 Ma(MSWD=0.4)。斜長花崗巖樣品具較高的Ab含量(74%～91%), 屬于奧長花崗巖, 其SiO2=62.95%～66.92%, Al2O3=17.81%～20.48%, MgO=0.09%～3.02%, Fe2O3<0.92%, Na2O=8.62%～10.61%, K2O=0.06%～0.22%和TiO2<0.05%。樣品A/CNK和A/NK值分別為0.82～1.03和1.11～1.43, 屬于準鋁質?弱過鋁質花崗巖系列。斜長花崗巖富集大離子親石元素和輕稀土元素, 具顯著的Ba、Sr和Eu正異常特征, 具較低的(87Sr/86Sr)i值(0.70493)和較高的Nd()值(+3.6), 為基性巖部分熔融的產物。綜合對比結果顯示, 梅拉圖斯蛇綠混雜巖與爪哇島盧克烏璐蛇綠混雜巖在年代學、巖石組合及地球化學特征上相近, 二者都屬于特提斯洋產物。

斜長花崗巖; 梅拉圖斯蛇綠混雜巖; 加里曼丹; 特提斯構造域

0 引 言

東南亞位于歐亞大陸東南緣, 處于歐亞板塊、菲律賓板塊和印度?澳大利亞板塊的交匯區域(圖1a), 毗鄰特提斯洋和太平洋兩大匯聚帶。由于東南亞及其周緣地區發現與特提斯洋和太平洋演化相關的豐富記錄, 已成為國內外眾多學者關注的熱點地區(Hutchison, 1989; Metcalfe, 1990, 2005, 2013, 2021; Wang et al., 2018, 2021, 2022a)。加里曼丹島(又稱婆羅洲)及其周緣地區位于特提斯和太平洋構造域的接合部位, 在毗鄰加里曼丹島的南西部和北東部均發現與特提斯和太平洋構造域相關的晚中生代地質記錄, 因此成為研究兩大構造域疊加和耦合的關鍵地帶(圖1a、b; Hutchison, 1989, 2005; Hennig et al., 2017)。

加里曼丹島東南部絕大部分地區被新生代沉積巖覆蓋, 以出露近S-N向帶狀展布的梅拉圖斯(Meratus)蛇綠混雜巖為特征。加里曼丹島南部與特提斯的演變有關, 由爪哇島早白堊世盧克烏璐(Luk Ulo)蛇綠混雜巖及其西延的蘇門答臘島沃伊拉(Woyla)晚侏羅世?早白堊世俯沖增生雜巖組成; 其北部與太平洋俯沖作用有關, 由巴拉望島中晚侏羅世混雜堆積巖和菲律賓卡拉棉群島二疊紀?白堊紀俯沖增生雜巖等組成(圖1a; Wakita et al., 1994a, 1994b; Barber, 2000; Kadarusman et al., 2007; Yumul et al., 2009; 周蒂和孫珍, 2017)。因此加里曼丹島東南部的梅拉圖斯蛇綠混雜巖的年代學及其構造屬性是剖析兩大構造域疊合的關鍵要素, 但時至今日, 對該蛇綠混雜巖帶的年代學及其構造歸屬等仍存在諸多爭議(圖1b; Parkinson et al., 1998; Wakita et al., 1998)。斜長花崗巖以富鈉而貧鉀為特征, 通常出現在現代洋殼和代表古老洋殼的蛇綠巖中, 對于限定洋殼和蛇綠巖的形成時代、增生過程及演化具重要意義(Koepke et al., 2004; Tilton et al., 2012; Grimes et al., 2013; Xu et al., 2017; Zhang et al., 2020)。本研究選取梅拉圖斯蛇綠巖中斜長花崗巖開展了巖相學、鋯石U-Pb年代學和元素地球化學研究, 為探討梅拉圖斯蛇綠混雜巖的大地構造歸屬提供了基礎數據。

1 區域地質背景及巖相學特征

加里曼丹島東部與蘇祿海?西里伯斯海?望加錫海峽?西蘇拉威西島相連, 南部及西部與蘇門答臘島?爪哇島?馬來半島相隔, 北接中國南海?菲律賓巴拉望島, 主要由西南加里曼丹、古晉帶、錫布帶、米里帶及東加里曼丹等五部分組成(圖1a、b; Haile, 1974; Hutchison, 1989, 2005; Breitfeld et al., 2019)。西南加里曼丹通常被認為是從岡瓦納大陸裂離而拼貼至巽他陸塊的微陸塊(Haile, 1974; Hall et al., 2009; Metcalfe, 2013, 2021; Davies et al., 2014)。古晉帶是一條重要的E-W向構造巖漿帶, 被認為與古太平洋板塊的俯沖作用有關(Katili, 1971; Breitfeld et al., 2017; Hennig et al., 2017)。錫布帶主要發育一套晚白堊世?古近紀深海?半深海復理石沉積(拉讓江群); 而米里帶則以一套新近紀陸源碎屑巖和碳酸鹽巖沉積為主, 不整合覆蓋于拉讓江群之上(Haile, 1974; Hutchison, 1989, 2005; Galin et al., 2017; Hall and Breitfeld, 2017)。東加里曼丹絕大部分地區被新生代沉積巖所覆蓋, 出露特魯克和梅拉圖斯蛇綠巖組合(Hutchison, 1989, 2005; Wakita et al., 1998; Parkinson et al., 1998)。

圖1 環南海地區地理概圖及加里曼丹簡略地質圖(據Galin et al., 2017修改)

梅拉圖斯地區出露地層主要有白堊系、新生界及蛇綠混雜巖, 白堊系Pitap組不整合上覆于梅拉圖斯蛇綠混雜巖之上(Hamilton, 1979; Sikumbang, 1990; Wakita et al., 1998; Setiawan et al., 2015)。上白堊統Haruyan組以中基性火山熔巖、凝灰巖和凝灰質角礫巖為主, Pitap組主要由礫巖、砂巖、鈣質泥巖及灰巖夾層組成(Wakita et al., 1998)。

蛇綠混雜巖呈帶狀分布于梅拉圖斯山脈和勞特島等地, 主要由變質巖、蛇綠巖、碎屑巖、碳酸鹽巖和硅質巖等巖塊和強烈變形的基質組成(Hamilton, 1979; Wakita et al., 1998; Setiawan et al., 2015)。帶內變質巖主要有綠簾石藍閃石片巖、石英云母片巖、滑石片巖、石英片巖和云母石英片巖, 蛇綠巖主要包括有超基性巖、輝長?輝綠巖、枕狀玄武巖和斜長花崗巖等, 而碎屑巖、碳酸鹽巖和硅質巖主要有硅質巖、硅質頁巖、灰巖和泥灰巖等(Sikumbang, 1990; Wakita et al., 1998; Sikumbang and Heryanto, 2009; Setiawan et al., 2015)。本研究的斜長花崗巖呈不規則脈狀和透鏡狀產出于超基性巖中(圖2a、b)。斜長花崗巖具細粒花崗結構和塊狀構造, 主要礦物有斜長石(60%～80%)和石英(30%～40%), 含少量角閃石(<5%)。其中斜長石呈自形?半自形板狀鑲嵌于石英顆粒之上, 石英呈粒狀充填于斜長石顆粒之間(圖2c、d)。

2 分析方法

選取新鮮的巖石樣品, 運用人工重砂法從中分選出鋯石顆粒, 在雙目顯微鏡下挑選透明、無裂縫和晶形完好的鋯石顆粒, 再用環氧樹脂將它們固定并拋光至鋯石顆粒中心位置。在光學顯微鏡和掃描電子顯微鏡下觀察并記錄鋯石顆粒的形態和內部結構特征。鋯石U-Pb年代學測試在廣東省地球動力作用與地質災害重點實驗室完成, 所用儀器主要包括iCAP RQ型電感耦合等離子體質譜儀(ICP-MS)和Geolas HD型激光剝蝕系統(LA)。詳細的分析方法和實驗過程見Wang et al. (2020)。采用91500和Ple?ovice進行U-Pb同位素的分餾校正, NIST SRM610進行微量元素的校正。樣品的鋯石U-Pb年齡采用GLITTER軟件處理, 加權平均年齡計算及諧和圖采用Isoplot(rev. 2.50)程序繪制(Ludwig et al., 2009)。

礦物代號: Qz. 石英; Pl. 斜長石。

樣品主量、微量元素和Sr-Nd同位素測試均在廣東省地球動力作用與地質災害重點實驗室完成。主量元素測試在ARL-Perform’X4200型熒光光譜儀(XRF)上完成。微量元素和Sr-Nd同位素測試分別在iCAP RQ型ICP-MS和Neptune Plus型多接收電感耦合等離子體質譜儀上完成。詳細的分析方法見Wang et al. (2020)。

3 結 果

3.1 鋯石U-Pb年代學

對斜長花崗巖樣品(18JV-26-5)中22顆鋯石開展了U-Pb定年分析, 分析結果見表1。鋯石呈透明狀, 短柱狀, 長寬比為1∶1～2∶1, 長80～120 μm, CL圖像可見韻律環帶結構, Th/U值變化于0.34～4.39之間, 為典型巖漿成因鋯石。其中第8、15和17號分析點具較大的206Pb/238U表觀年齡, 分別為161 Ma、158 Ma和426 Ma, 屬于捕獲鋯石年齡; 其余鋯石的206Pb/238U表觀年齡變化范圍為142～144 Ma, 加權平均年齡為143.2±0.5 Ma(MSWD=0.4,=19; 圖3), 代表了斜長花崗巖的結晶年齡。

3.2 主量、微量元素和Sr-Nd同位素組成

對梅拉圖斯蛇綠巖中6件斜長花崗巖樣品開展主量、微量元素分析測試(表2)。結果顯示, 斜長花崗巖樣品SiO2含量變化范圍為62.95%～66.92%, K2O+Na2O含量介于8.78%～10.70%之間, 樣品中Al2O3(17.81%～20.48%)和Na2O(8.62%～10.61%)含量高, MgO(0.09%～3.02%)、FeOT(<0.92%)、K2O(0.06%～0.22%)和TiO2(<0.05%)含量低。在TAS圖解中, 樣品點落入石英二長巖范圍內(圖4a); A/CNK值為0.82～1.03(平均值為0.93), A/NK值為1.11～1.43(平均值為1.20), 屬于準鋁質?弱過鋁質花崗巖系列(圖4b)。CIPW標準礦物計算得出其An含量變化于5%～17%之間, Ab和Or含量分別變化于74%～91%和0～1%, 在An-Ab-Or圖解中樣品落入奧長花崗巖范圍(圖5)。在原始地幔標準化微量元素蛛網圖(圖6a)上, 樣品相對富集大離子親石元素, 具顯著的Ba、Sr和Zr-Hf正異常。樣品的稀土元素總量較低, 變化范圍為1.0×10?6～3.0×10?6(表2)。在球粒隕石標準化稀土元素配分模式圖(圖6b)中, 樣品相對富集輕稀土元素和重稀土元素而虧損中稀土元素, (La/Yb)N=6.6～ 97.5, (La/Yb)N=0.4～2.2, 具明顯Eu正異常的特征。Sr-Nd同位素結果(表2)顯示, 梅拉圖斯斜長花崗巖的87Sr/86Sr值為0.704928, (87Sr/86Sr)i為0.70493,Nd()值為+3.6。

表1 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖的LA-ICPMS鋯石U-Pb年代學分析結果

圖3 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖的鋯石U-Pb年齡諧和圖

表2 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖的主量元素(%)、微量元素(×10?6)和Sr-Nd同位素分析結果

續表2:

圖4 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖(K2O+Na2O)-SiO2(a)和A/NK-A/CNK(b)圖解

4 討 論

4.1 梅拉圖斯蛇綠混雜巖的形成年齡

斜長花崗巖常常作為蛇綠混雜巖的組成部分之一, 對于限定蛇綠混雜巖的形成時代具有重要意義(Grimes et al., 2013; Xu et al., 2017; Zhang et al., 2020)。本文首次獲得了蛇綠混雜巖帶內斜長花崗巖的鋯石U-Pb年齡為143.2±0.5 Ma。已有的資料表明, 梅拉圖斯蛇綠混雜巖帶內的硅質巖和硅質頁巖中含大量早白堊世放射蟲化石(Wakita et al., 1998)。該蛇綠巖帶內石榴石?角閃石片巖和綠泥石?綠簾石片巖的Rb-Sr等時線年齡為116～110 Ma, 藍閃石片巖Rb-Sr等時線年齡為113 Ma, 云母石英片巖的K-Ar年齡集中于約119～110 Ma(Wakita et al., 1998; Alfing et al., 2021), 這些變質巖與爪哇島盧克烏璐和蘇拉威西島班迪馬拉蛇綠混雜巖帶內變質巖具相似的形成年齡(Wakita et al., 1994b; B?hnke et al., 2019; Hoffmann et al., 2019; Alfing et al., 2021)。Soesilo (2012)、Soesilo et al. (2014)和Wakita et al. (1998)在Purui Dalam獲得斜長花崗巖全巖K-Ar年齡為155 Ma。Soesilo (2012)也在梅拉圖斯蛇綠混雜巖中獲得了～137 Ma的變質巖鋯石U-Pb年齡。Wang et al. (2022b)獲得了該蛇綠巖帶內玄武巖的鋯石U-Pb年齡為128±2 Ma。帶內硅質巖中火山夾層的鋯石U-Pb年齡變化范圍為140～121 Ma, 峰值集中于127 Ma (Wang et al., 2022b)。另外上覆于梅拉圖斯蛇綠混雜巖之上的Pitap組頁巖和硅質巖含有晚白堊世Aptian晚期?Cenomanian早期(約115～100 Ma)放射蟲和軟體動物化石(Supriatna, 1989; Wakita et al., 1998)。綜合研究表明, 梅拉圖斯蛇綠混雜巖帶很可能形成于約115～145 Ma的早白堊世。

圖5 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖An-Ab-Or圖解

4.2 巖石成因及地質意義

斜長花崗巖的巖石成因模式主要有兩種: ①基性巖漿分離結晶(Lippard et al., 1986; Floyd et al., 1998; Jiang et al., 2008); ②輝長巖或斜長角閃巖部分熔融(Flagler and Spray, 1991; Koepke et al., 2004; Zi et al., 2012; Grimes et al., 2013)。梅拉圖斯蛇綠混雜巖帶內斜長花崗巖具較低的Rb/Sr值(<0.001)、TiO2含量和中等SiO2含量, 顯著Ba、Sr和Eu正異常(圖6), 這些特征不同于由基性巖漿分離結晶而形成的斜長花崗巖(Floyd et al., 1998; Jiang et al., 2008)。相反, 其較低的Zr(15×10?6～36×10?6)、Y(0.21×10?6～ 0.67×10?6)含量及Zr/Y值(29～120), 與Karmoy型斜長花崗巖相似(Pedersen and Malpas, 1984)。此外, 梅拉圖斯斜長花崗巖具較高的Nd()值(+3.6), 接近于帶內基性巖的Nd()值(Wang et al., 2022b)。地球化學特征暗示, 梅拉圖斯斜長花崗巖可能是輝長巖或斜長角閃巖部分熔融的產物。

圖6 梅拉圖斯蛇綠混雜巖帶內斜長花崗巖原始地幔標準化的微量元素蛛網圖(a)和球粒隕石標準化稀土元素配分曲線(b)(原始地幔和球粒隕石值引自Sun and McDonough, 1989)

目前關于梅拉圖斯蛇綠混雜巖帶的構造屬性及其與特提斯和太平洋構造域的關聯依然存在爭議, 一種觀點認為該蛇綠混雜巖帶與爪哇島盧克烏璐和蘇拉威西島班迪馬拉蛇綠混雜巖帶相連, 屬于特提斯構造域范疇(顏佳新, 2005; 魯寶亮等, 2014; 周蒂和孫珍, 2017); 而另一種觀點認為該蛇綠混雜巖帶與特魯克蛇綠巖帶相接, 受太平洋構造域的影響(Hamilton, 1979; Metcalfe, 1990, 2005; Parkinson et al., 1998; Setiawan et al., 2013)。

本次研究表明梅拉圖斯蛇綠混雜巖帶形成于約145～115 Ma的早白堊世, 前人研究顯示, 爪哇島盧克烏璐和蘇拉威西島班迪馬拉蛇綠混雜巖也形成于早白堊世, 三者的峰期變質作用均同步發生在119～110 Ma(表3; Wakita et al., 1994a, 1994b, 1998; Parkinson et al., 1998; Setiawan et al., 2013, 2015; White et al., 2016)。另外, 班迪馬拉混雜巖中石榴石云母片巖的峰期變質溫壓分別為615～678 ℃和2.6～2.7 GPa(Setiawan et al., 2013, 2015), 盧克烏璐混雜巖中榴輝巖峰期變質溫壓分別為473～557℃和2.1～2.3 GPa(Kadarusman et al., 2007; Setiawan, 2013); 梅拉圖斯蛇綠混雜巖中的變質巖峰期變質溫壓為547～690℃和1.1～1.5 GPa(Setiawan et al., 2013, 2015)。由此可知三條混雜巖帶內變質巖具相似的峰期變質溫壓條件和順時針的-軌跡(表3; Setiawan et al., 2013, 2015)。此外, 沉積巖碎屑鋯石U-Pb年齡數據也揭示加里曼丹東南部、南蘇拉威西及爪哇島均具有與澳大利亞地區相似的鋯石年齡譜系, 顯示出澳大利亞親緣性(Hennig et al., 2017; Decker et al., 2017; Hoffmann et al., 2019; Zhang et al., 2021)。相反, 沙巴地區特魯克蛇綠巖帶形成時代明顯年輕, 其變質程度相對微弱(Hamilton, 1979; Metcalfe, 1990, 2021); 且婆羅洲東北部沙巴地區碎屑鋯石年齡譜系明顯不同于岡底斯?澳大利亞的碎屑鋯石年齡譜系, 而與華南大陸相似(Wang et al., 2013)。因此本文更傾向認為梅拉圖斯蛇綠混雜巖帶與爪哇島盧克烏璐和蘇拉威西島班迪馬拉蛇綠混雜巖帶相連, 均受特提斯洋俯沖的影響。

表3 加里曼丹東南部及其周緣地區蛇綠混雜巖帶內變質巖特征匯總

5 結 論

(1) 梅拉圖斯蛇綠混雜巖帶中斜長花崗巖的結晶年齡為143.2±0.5 Ma, 屬早白堊世產物。

(2) 梅拉圖斯蛇綠混雜巖與爪哇島盧克烏璐蛇綠混雜巖具相似的特征, 屬特提斯洋產物。

致謝:感謝中山大學王玉琨和楊雪博士在鋯石U-Pb年代學、主量和微量元素、Sr-Nd同位素測試過程中的幫助。三位匿名審稿專家為論文提出了建設性意見和建議, 在此表示衷心感謝！

魯寶亮, 王璞珺, 梁建設, 孫曉猛, 王萬銀. 2014. 古南海構造屬性及其與特提斯和古太平洋構造域的關系. 吉林大學學報(地球科學版), 44(5): 1441–1450.

顏佳新. 2005. 加里曼丹島和馬來半島中生代巖相古地理特征及其構造意義. 熱帶海洋學報, 24(2): 26–32.

周蒂, 孫珍. 2017. 晚中生代以來太平洋域板塊過程及其對東亞陸緣構造研究的啟示. 熱帶海洋學報, 36(3): 1–19.

Alfing J, Brocker M, Setiawan N I. 2021. Rb-Sr geochronology of metamorphic rocks from the Central Indonesian Accretionary Collision Complex: Additional age constraintsfor the Meratus and Luk Ulo Complexes (South Kalimantan and Central Java)., 388–389, 105971.

Barber A J. 2000. The origin of the Woyla Terranes in Sumatraand the Late Mesozoic evolution of the Sundaland margin., 18(6): 713–738.

B?hnke M, Br?cker M, Maulana A, Klemd R, Berndt J, Baier H. 2019. Geochronology and Zr-in-rutile thermometry of high-pressure/low temperature metamorphic rocks from the Bantimala complex, SW Sulawesi, Indonesia., 324–325: 340–355.

Breitfeld H T, Hall R, Galin T, Forster M A, BouDagher- Fadel M K. 2017. A Triassic to Cretaceous Sundaland- Pacific subduction margin in West Sarawak, Borneo., 694: 35–56.

Breitfeld H T, Macpherson C, Hall R, Thirlwall M, Ottley C J, Hennig-Breitfeld J. 2019. Adakites without a slab: Remelting of hydrous basalt in the crust and shallow mantle of Borneo to produce the Miocene Sintang Suite and Bau Suite magmatism of West Sarawak., 344(1): 100–121.

Davies L, Hall R, Armstrong R. 2014. Cretaceous crust in SW Borneo: Petrological, geochemical and geochronological constraints from the Schwaner Mountains. Jakarta: Proceedings Indonesian Petroleum Association 38thAnnual Convention and Exhibition, IPA14-G-025.

Decker J, Ferdian F, Morton A, Fanning M, White L T. 2017. New geochronology data from eastern Indonesia — An aid to understanding sedimentary provenance in a frontierregion. Jakarta: Proceedings of the Indonesian Petroleum Association, 41thAnnual Convention and Exhibition, IPA17-551-G: 1–18.

Flagler P A, Spray J G. 1991. Generation of plagiogranite by amphibolite anatexis in oceanic shear zones., 19(1): 70–73.

Floyd P A, Yaliniz M K, Goncuoglu M C. 1998. Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey., 42(3–4): 225–241.

Galin T, Breitfeld H T, Hall R, Sevastjanova I. 2017. Provenance of the Cretaceous-Eocene Rajang Group submarine fan, Sarawak, Malaysia from light and heavy mineral analysis and U-Pb zircon geochronology., 51: 209–233.

Grimes C B, Ushikubo T, Kozdon R, Valley J W. 2013. Perspectives on the origin of plagiogranite in ophiolites from oxygen isotopes in zircon., 179: 48–66.

Haile N S. 1974. Borneo // Spencer A M. Mesozoic-Cenozoic Orogenic Belts.,,, 4: 333–347.

Hall R, Breitfeld H T. 2017. Nature and demise of the proto-South China Sea., 63: 61–76.

Hall R, Clements B, Smyth H R. 2009. Sundaland: Basement character, structure and plate tectonic development. Jakarta: Proceedings Indonesian Petroleum Association 33rdAnnual Convention, IPA09-G-134: 1–27.

Hamilton W B. 1979. Tectonics of the Indonesian region. Washington: US Government Printing Office: 1078.

Hennig J, Breitfeld H T, Hall R, Nugraha A M S. 2017. The Mesozoic tectono-magmatic evolution at the Paleo-Pacific subduction zone in West Borneo., 48: 292–310.

Hoffmann J, Br?cker M, Setiawan N I, Klemd R, Berndt J, Maulana A, Baier H. 2019. Age constraints on high-pressure/ low-temperature metamorphism and sedimentation in the Luk Ulo complex (Java, Indonesia)., 324–325: 747–762.

Hutchison C S. 1989. Geological Evolution of South-east Asia. London: Clarendon Press Oxford: 368.

Hutchison C S. 2005. Geology of North-West Borneo. Elsevier: Science limited: 383–397.

Jiang Y H, Liao S Y, Yang W Z, Shen W Z. 2008. An island arc origin of plagiogranites at Oytag, western Kunlun orogen, northwest China: SHRIMP zircon U-Pb chronology, elemental and Sr-Nd-Hf isotopic geochemistry and Palaeozoic tectonic implications., 106(3–4): 323–335.

Kadarusman A, Massonne H J, van Roermund H, Permana H, Munasri. 2007.-evolution of eclogites and blueschists from the Luk Ulo complex of Central Java, Indonesia., 49(4): 329–356.

Katili J A. 1971. A review of the geotectonic theories and tectonic maps of Indonesia., 7(3): 143–163.

Koepke J, Feig S T, Snow J, Freise M. 2004. Petrogenesis of oceanic plagiogranites by partial melting of gabbros: An experimental study., 146: 414–432.

Lippard S J, Shelton A W, Gass I G. 1986. The Ophiolite of Northern Oman. Oxford: Geological Society Memoir, 11, Blackwell Scientific: 178.

Ludwig K. 2009. Sqiud 2: A User’s Manual. Berkeley Geochron Center Special publication, 5: 1–110.

Metcalfe I. 1990. Allochthonous terrane processes in Southeast Asia.,, 331(1620): 625–640.

Metcalfe I. 2005. Asia: South-east., 1: 169–198.

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

Metcalfe I. 2021. Multiple Tethyan ocean basins and orogenic belts in Asia., 100: 87–130.

Parkinson C D, Miyazaki K, Wakita K, Barber A J, Carswell D A. 1998. An overview and tectonic synthesis of the pre-Tertiary very-high-pressure metamorphic and associated rocks of Java, Sulawesi and Kalimantan, Indonesia., 7(1–2): 184–200.

Pedersen R B, Malpas J. 1984. The origin of oceanic plagiogranites from the Karmoy ophiolite, western Norway., 88(1): 36–52.

Setiawan N I, Osanai Y, Nakano N, Adachi T, Asy’ari A. 2015. Metamorphic evolution of garnet-bearing epidote- barroisite schist from the Meratus complex in South Kalimantan, Indonesia., 2(3): 139–156.

Setiawan N I, Osanai Y, Nakano N, Adachi T, Yonemura K, Yoshimoto A, Wahyudiono J, Mamma K. 2013. An overview of metamorphic geology from Central Indonesia: Importance of South Sulawesi, Central Java and South-West Kalimantan metamorphic terranes., 19: 39–55.

Sikumbang N. 1990. Geology and tectonics of Pre-Tertiary rocks in the Meratus Mountains Southeast Kalimantan, Indonesia., 13(2): 1–31.

Sikumbang N, Heryanto R. 2009. Geological map of the Banjarmasin Quadrangle, Kalimantan. Scale 1∶250,000.Geological Research and Development Centre of Indonesia, Bandung.

Soesilo J. 2012. Cretaceous Paired Metamorphic Belts in Southeast Sundaland. Bandung Institute of Technology Indonesia: 180.

Soesilo J, Schenk V, Suparka E, Abdullah C I, Amiruddin A. 2014. The K-Ar and U-Pb SHRIMP Zircon Age Dating of The Batangalai Pluton Central Meratus Complex, Southeast Kalimantan. Jakarta: Prosiding Seminar NasionalGeologi Nuklir Dan Sumber Daya Tambang Tahun: 1–16.

Sun S S, McDonough W F. 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes.,,, 42: 313–345.

Supriatna S. 1989. Data Baru Mengenai geologi Pegunungan meratus Kalimantan Selantan., 13: 30–38.

Tilton G R, Hopson C A, Wright J E. 2012. Uranium-lead isotopic ages of the Samail Ophiolite, Oman, with applications to Tethyan ocean ridge tectonics.:, 86(B4): 2763– 2775.

Wakita K, Miyazaki K, Zulkarnain I, Sopaheluwakan J, Sanyoto P. 1998. Tectonic implications of new age data for the Meratus complex of South Kalimantan, Indonesia., 7(1–2): 202–222.

Wakita K, Bambang W. 1994a. Cretaceous radiolariansfrom the Luk-Ulo melange complex in the Karangsambung area, Central Java, Indonesia., 9(1–2): 29–43.

Wakita K, Sopaheluwakan J, Zulkarnain I, Miyazaki K. 1994b. Early Cretaceous tectonic events implied in the time-lag between the age of radiolarian chert and its metamorphic basement in the Bantimala area, South Sulawesi, Indonesia., 3(2): 90–102.

Wang Y J, Fan W M, Zhang G W, Zhang Y H. 2013. Phanerozoic tectonics of the South China Block: Key observations and controversies., 23(4): 1273–1305.

Wang Y J, Liu Z, Murtadha S, Cawood P A, Qian X, Ghani A, Gan C S, Zhang Y Z, Wang Y, Li S, Zhang P Z. 2022a. Jurassic subduction of the Paleo-Pacific Plate in Southeast Asia: New insights from the igneous and sedimentary rocks in West Borneo., https: //doi.org/10.1016/j.jseaes.2022.105111.

Wang Y J, Qian X, Cawood P A, Ghani A, Gan C S, Wu S N, Zhang Y Z, Wang Y, Zhang P Z. 2022b. Cretaceous Tethyan subduction in SE Borneo: Geochronological andgeochemical constraints from the igneous rocks in the Meratus Complex., 226(3–4), 105084.

Wang Y J, Qian X, Cawood P A, Liu H C, Feng Q L, Zhao G C, Zhang Y Z, He H Y, Zhang P Z. 2018. Closure of the East Paleotethyan Ocean and amalgamation of the Eastern Cimmerian and Southeast Asia continental fragments., 186: 195–230.

Wang Y J, Qian X, Zhang Y Z, Gan C S, Zhang A M, Zhang F F, Feng Q L, Cawood P A, Zhang P Z, 2021. Southern extension of the Paleotethyan zone in SE Asia: Evidence from the Permo-Triassic granitoids in Malaysia and West Indonesia., 398–399, 106336.

Wang Y J, Yang T X, Zhang Y Z, Qian X, Gan C S, Wang Y K, Wang Y, 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(1), 104333.

White L T, Graham I, Tanner D, Hall R, Armstrong R A, Yaxley G, Barron L, Spencer L, van Leeuwen T. 2016. The provenance of Borneo’s enigmatic alluvial diamonds: A case study from Cempaka, SE Kalimantan., 38: 251–272.

Xu Y, Liu C Z, Chen Y, Guo S, Wang J G, Sein K. 2017. Petrogenesis and tectonic implications of gabbro and plagiogranite intrusions in mantle peridotites of the Myitkyina ophiolite, Myanmar., 284–285: 180–193

Yumul G P, Dimalanta C B, Marquez E J, Quea?o K L. 2009. On land signatures of the Palawan microcontinental block and Philippine mobile belt collision and crustal growth process: A review., 34(5): 610–623.

Zhang X, Chung S L, Tang J T, Maulana A, Mawaleda M, Oo T, Tien C Y, Lee H Y. 2021. Tracing Argoland in eastern Tethys and implications for India-Asia convergence., 133(7–8): 1712–1722.

Zhang Y Z, Yang X, Wang Y J, Qian X, Wang Y K, Gou Q Y, Senebouttalath V, Zhang A M. 2020. Rifting and subduction records of the Paleo-Tethys in North Laos: Constraints from Late Paleozoic mafic and plagiogranitic magmatism along the Song Ma tectonic zone., 133(1–2): 212–232.

Zi J W, Cawood P A, Fan W M, Wang Y J, Tohver E. 2012. Contrasting rift and subduction related plagiogranites in the Jinshajiang ophiolitic mélange, southwest China, and implications for the Paleo-Tethys., 31(2), TC2012.

Zircon U-Pb Dating and Tectonic Significance of the Plagiogranite in the Meratus Ophiolitic Mélange of SE Kalimantan

WANG Yiwen1, CHEN Xinyue1*, GAN Chengshi2

(1.School of Earth Sciences and Spatial Information Engineering, Hunan University of Science and Technology, Xiangtan 410201, Hunan, China; 2.Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai 519082, Guangdong, China)

Kalimantan is mainly surrounded by the Tethyan and Pacific tectonic domains, and it is an important place for exploring the tectonic evolution and interaction of the two domains. The N-S trending Meratus ophiolitic mélange is located in SE Kalimantan, but the formation time and tectonic nature of this mélange are poorly constrained. This study firstly presents the zircon U-Pb age and major element contents of the plagiogranite in the Meratus ophiolitic mélange. Our data show that the plagiogranite formed at 143.2±0.5 Ma. The plagiogranite samples are characterized by high Al2O3(17.81%–20.48%) and Na2O (8.62%–10.61%) with SiO2=62.95%–66.92%, MgO=0.09%–3.02%, Fe2O3<0.92%, K2O=0.06%–0.22% and TiO2<0.05%. They are metaluminous to weakly peraluminous with A/CNK=0.82–1.03 and A/NK=1.11–1.43. The plagioclase in the plagiogranite has high Ab (74%–91%), and thus the plagiogranite can be termed as trondhjemite. They are enriched in LILE and LREE with significant Ba, Sr and Eu positive anomalies. They have low initial87Sr/86Sr ratio of 0.704927 and highNd(t) value of +3.6, likely deriving from partial melting of metasomatized gabbro or amphibolites. In combination with other data, the Meratus ophiolitic mélange has geological and geochemical features similar to those of theLuk Ulo and Bantimala ophiolitic mélanges in Central Java and SW Sulawesi, suggestive of the Tethyan subduction initiating at the earliest Cretaceous.

plagiogranite; Meratus ophiolitic mélange; Kalimantan; Tethyan domain

10.16539/j.ddgzyckx.2022.03.015

2021-12-10;

2022-02-25

國家自然科學基金項目(42002236)資助。

王逸文(2000–), 女, 學士, 巖石學專業。E-mail: 2835437696@qq.com

陳新躍(1977–), 男, 教授, 主要從事大地構造和地球化學方面研究。E-mail: xinychen@163.com

P581; P597

A

1001-1552(2022)03-0622-011