塔里木东南缘安南坝地区约2.5Ga花岗闪长质片麻岩的发现及岩石成因
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摘要
塔里木东南缘安南坝地区新发现的花岗闪长质片麻岩主要由斜长石、碱性长石、石英、角闪石、黑云母等组成。岩石SiO_2(>70%)、Al_2O_3(>15%)、Na_2O(3.56%～4.15%)含量较高;MgO(0.39%～0.59%)、Fe_2O_3(0.23%～0.36%)、FeO(0.76%～1.11%)含量、K_2O/Na_2O值(0.64～0.81)及Mg#值(19～27)均较低。花岗闪长质片麻岩稀土元素总量低(∑REE=28.81×10~(-6)～68.51×10~(-6)),(La/Yb)N=(46.27～98.27),轻、重稀土元素分异明显,球粒陨石标准化稀土元素配分曲线表现为右倾型,Eu(δEu=1.57～2.00)呈明显的正异常。岩石Rb、Ba、Sr等大离子亲石元素含量较高,Nb、Ta等高场强元素及Cr、Ni等相容元素含量较低。地球化学特征显示,该花岗闪长质片麻岩具有高铝型TTG和低重稀土元素系列TTG的地球化学特征。研究表明,阿克塞县安南坝地区花岗闪长质片麻岩可能是在榴辉岩相压力条件下,由加厚的玄武质下地壳部分熔融形成,源区残留相主要为石榴子石、金红石(少量)及角闪石。LA-ICP-MS锆石U-Pb上交点年龄为2555±11Ma,代表了花岗闪长质片麻岩的成岩时代,说明新太古代晚期是塔里木东南缘重要的陆壳增生期。此外,岩石中还获得了约2.44Ga、约1.96Ga的变质年龄,表明塔里木东南缘基底岩石在古元古代经历了2期构造-热事件的叠加改造。
The newly-discovered granodioritic gneiss is mainly composed of plagioclase,alkali feldspar,quartz,amphibolite and biotite in Ananab area,southeastern Tarim, characterized by high SiO_2(>70%), Al_2O_3(>15%)and Na_2O(3.56%～4.15%), and low MgO(0.39% ～0.59%), Fe_2O_3(0.23% ～0.36%), FeO(0.76% ～1.11%), K_2O/Na_2O(0.64～0.81)and Mg~#(19～27). Meanwhile,the granodioritic gneiss has lower content of ∑ REE,with strong fractionation of LREE/HREE((La/Yb)N=46.27～98.27); the chondrite-normalized REE patterns show right-inclined patterns with obvious positive Eu(δEu=1.57～2.00)anomalies. The rocks are enriched in LILE(such as Rb, Ba and Sr)and depleted in HFSE(such as Nb and Ta); in addition, the values of compatible elements(Cr, Ni)are relatively low. On the basis of the above data, the geochemical analyses indicate that granodioritic gneiss is characteristic of high-Al TTG series and low-HREE TTG. It is therefore held that the rocks might have been formed by partial melting of thickened mafic lower crust under the pressure condition of eclogite facies, with garnet, rutile and amphibole left in the residual magmas. LA-ICP-MS zircon U-Pb dating of granodioritic gneiss from Annanba area of Aksai yielded the formation time of 2555±11 Ma, basically consistent with the age of magmatism of southeastern Tarim(2.5～2.6 Ga), showing the significant continental crust accretion in late Neoarchean. In addition, the metamorphic ages of ca.2.44 Ga and ca.1.96 Ga were obtained for granodioritic gneiss, which implies that the basement rocks from southeastern Tarim were superimposed upon and reconstructed by two episodes of tectonic thermal events in Palaeoproterozoic.
The newly-discovered granodioritic gneiss is mainly composed of plagioclase,alkali feldspar,quartz,amphibolite and biotite in Ananab area,southeastern Tarim, characterized by high SiO_2(>70%), Al_2O_3(>15%)and Na_2O(3.56%～4.15%), and low MgO(0.39% ～0.59%), Fe_2O_3(0.23% ～0.36%), FeO(0.76% ～1.11%), K_2O/Na_2O(0.64～0.81)and Mg~#(19～27). Meanwhile,the granodioritic gneiss has lower content of ∑ REE,with strong fractionation of LREE/HREE((La/Yb)N=46.27～98.27); the chondrite-normalized REE patterns show right-inclined patterns with obvious positive Eu(δEu=1.57～2.00)anomalies. The rocks are enriched in LILE(such as Rb, Ba and Sr)and depleted in HFSE(such as Nb and Ta); in addition, the values of compatible elements(Cr, Ni)are relatively low. On the basis of the above data, the geochemical analyses indicate that granodioritic gneiss is characteristic of high-Al TTG series and low-HREE TTG. It is therefore held that the rocks might have been formed by partial melting of thickened mafic lower crust under the pressure condition of eclogite facies, with garnet, rutile and amphibole left in the residual magmas. LA-ICP-MS zircon U-Pb dating of granodioritic gneiss from Annanba area of Aksai yielded the formation time of 2555±11 Ma, basically consistent with the age of magmatism of southeastern Tarim(2.5～2.6 Ga), showing the significant continental crust accretion in late Neoarchean. In addition, the metamorphic ages of ca.2.44 Ga and ca.1.96 Ga were obtained for granodioritic gneiss, which implies that the basement rocks from southeastern Tarim were superimposed upon and reconstructed by two episodes of tectonic thermal events in Palaeoproterozoic.
引文
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(1)辜平阳,董增产,陈锐明,等.青海阿尔金1∶5万打柴沟等6幅区域地质调查报告.2015.
[2]Moyen J F,Martin H.Forty years of TTG research[J].Lithos,2012,148:312-336.
[3]张旗,翟明国.太古宙TTG岩石是什么含义?[J].岩石学报,2012,28(11):3446-3456.
[4]万渝生,董春艳,任鹏,等.华北克拉通太古宙TTG岩石的时空分布、组成特征及形成演化:综述[J].岩石学报,2017,33(5):1405-1419.
[5]何登发,李德生.塔里木盆地构造演化与油气聚集[M].北京:地质出版社,1996:1-6.
[6]贾承造.中国塔里木盆地构造特征与油气[M].北京:地质出版社,1997:29-92.
[7]张建新,李怀坤,孟繁聪,等.塔里木盆地东南缘(阿尔金山)“变质基底”记录的多期构造热事件:锆石U-Pb年代学的制约[J].岩石学报,2011,27(1):23-46.
[8]刘永顺,于海峰,辛后田,等.阿尔金山地区构造单元划分和前寒武纪重要地质事件[J].地质通报,2009,28(10):1430-1438.
[9]辛后田,赵凤清,罗照华,等.塔里木盆地东南缘阿克塔什塔格地区古元古代精细年代格架的建立及其地质意义[J].地质学报,2011,85(12):1977-1993.
[10]辛后田,刘永顺,罗照华,等.塔里木盆地东南缘阿克塔什塔格地区新太古代陆壳增生:米兰岩群和TTG片麻岩的地球化学及年代学约束[J].地学前缘,2013,20(1):240-259.
[11]陆松年,袁桂邦.阿尔金山阿克塔什塔格早前寒武纪岩浆活动的年代学证据[J].地质学报,2003,77(1):61-68.
[12]刘永顺,辛后田,周世军,等.阿尔金山东段拉配泉地区前寒武纪及古生代构造构造演化[M].北京:地质出版社,2010:84-87.
[13]Lu S N,Li H K,Zhang C L,et al.Geological and geochronological evidence for the Precambrian evolution of the Tarim Craton and surrounding continental fragments[J].Precambrian Research,2008,160(1/2):94-107.
[14]校培喜,高晓峰,胡云绪,等.阿尔金-东昆仑西段成矿带地质背景研究[M].北京:地质出版社,2014:48-51.
[15]Gao S,Liu Xiaoming,Yuan Honglin,et al.Analysis of forty-two major and trace elements of USGS and NIST SRM Glasses by LA-ICPMS[J].Geostand Newsl,2002,22:181-195.
[16]Anderson T.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,2002,192:59-79.
[17]Ludwig K R.3.0-A geochronologycal toolkit for Micro-soft Excel[J].Berkeley Geo chronology Certer,Special Publication,2003,(4):1-70.
[18]Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and process[C]//Sauders A D,Norry M J.Magmatism in the Ocean Basins.Geological Society Special Publication,1989,42:3l3-345.
[19]万渝生,刘敦一,董春艳,等.高级变质作用对锆石U-Pb同位素体系的影响:胶东栖霞地区变质闪长岩锆石定年[J].地学前缘,2011,18(2):17-25.
[20]朱文斌,葛荣峰,吴海林.北阿尔金地区古元古代ca.2.0Ga岩浆-变质事件[J].岩石学报,2018,34(4):1175-1190.
[21]Ma M Z,Wan Y S,Santosh M,et al.Decoding multiple tectonothermal events in zircons from single rock samples:SHRIMP zircon U-Pb data from the Late Neoarchean rocks of Daqingshan,North China Craton[J].Gondwana Research,2012,22(3/4):810-827.
[22]胡霭琴,韦刚健.塔里木盆地北缘新太古代辛格尔灰色片麻岩形成时代问题[J].地质学报,2006,80(1):126-134.
[23]邓兴梁,舒良树,朱文斌,等.新疆兴地断裂带前寒武纪构造-岩浆-变形作用特征及其年龄[J].岩石学报,2008,24(12):2800-2808.
[24]Long X P,Yuan C,Sun M,et al.Archean crustal evolution of the northern Tarim Craton,NW China:zircon U-Pb and Hf isotopic constrains[J].Precambrian Research,2010,180(3/4):272-284.
[25]Zhang C L,Li H K,Santosh M,et al.Precambrian evolution and cratonization of the Tarim Block,NW China:Petrology,geochemistry,Nd-isotopes and U-Pb zircon geochronology from Archaean gabbro-TTG-potassic granite suite and Paleoproterozoic metamorphic belt[J].Journal of Asian Earth Sciences,2012,47:5-20.
[26]Zhang J X,Gong J H,Yu S Y,et al.Neoarchean-Paleoproterozoic multiple tectonothermal events in the western Alxa block,North China Craton and their geological implication:Evidence from zircom U-Pb ages and Hf isotopic composition[J].Precambrian Research,2013,235:36-45.
[27]赵燕,第五春荣,孙勇,等.甘肃敦煌水峡口地区前寒武纪岩石的锆石U-Pb年龄、Hf同位素组成及其地质意义[J].岩石学报,2013,29(5):1698-1712.
[28]Shu L S,Deng X L,Zhu W B,et al.Precambrian tectonic evolution of the Tarim Block,NW China:New geochronological insights from the Quruqtagh domain[J].Journal of Asian Earth Sciences,2011,42(5):774-790.
[29]郭召杰,张志诚,刘树文,等.塔里木克拉通早前寒武纪基底层序与组合:颗粒锆石U-Pb年龄新证据[J].岩石学报,2003,5(3):537-542.
[30]董昕,张泽明,唐伟.塔里木克拉通北缘的前寒武纪构造热事件--新疆库尔勒铁门关高级变质岩的锆石U-Pb年代学限定[J].岩石学报,2011,27(1):47-58.
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