Genesis of Kumutashi Fluorite Deposit in the West Altyn-Tagh Orogen, NW China: Constraints from Apatite In-Situ U-Pb Dating, Sr-Nd Isotope and Chemistry
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摘要:
近年来,阿尔金西段取得萤石找矿重大突破,相继发现卡尔恰尔和库木塔什等矿床,但成矿时代和成矿机制研究薄弱。笔者选取库木塔什矿床与萤石密切共生磷灰石为研究对象,开展原位U-Pb定年、Sr-Nd同位素及地球化学分析,以探讨萤石矿成矿时代及矿床成因。磷灰石常呈自形–半自形结构,表面均匀,单偏光下近乎透明,主要与萤石、方解石、带云母、氟碳铈矿等矿物共生。结果显示,磷灰石U-Pb同位素年龄为(448±27 )Ma,成矿作用与碱长花岗岩侵入活动密切相关,均为晚奥陶世构造–岩浆活动产物。磷灰石中F含量为4.20%~5.12%,Cl含量小于0.02%,极低的Cl含量表明出溶的流体Cl含量较低。磷灰石稀土元素含量较高(908×10−6~2164×10−6),稀土配分曲线显示强烈Eu负异常和Ce正异常,且与萤石、方解石、碱长花岗岩有明显的一致性,推测与岩浆-热液阶段大量流体出溶密切相关。磷灰石的87Sr/86Sr值为0.70913~0.71047,143Nd/144Nd值为0.51138~0.51153,εNd(t)值为−13.3~−10.3,表明成矿物质具有壳幔混合特征。综合研究表明,阿尔金西段萤石成矿时代为奥陶纪,与同期碱长花岗岩密切相关,形成于后碰撞伸展阶段,成矿流体来源于碱长花岗岩的熔体–流体演化,为岩浆热液充填型矿床。
Abstract:In recent years, significant breakthroughs in fluorite prospecting have been made in the western Altyn-Tagh Terrane, and Kaerqiaer, Kumutashi and other deposits have been discovered successively, however, the research on metallogenic epoch and ore-forming processes are still unclear. In this paper, the closely symbiotic apatite with fluorite were selected as the research object to carry out the main microanalysis of apatite, U-Pb dating and in situ Sr-Nd isotopic test analysis, so as to explore the metallogenic epoch and the genesis of deposit. The apatite often has a self-semi-automorphic structure with uniform surface and nearly transparent under monopolarized light, mainly symbiotic with fluorite, calcite, tainiolite, bastnaesite and other minerals. The study shows that the U-Pb isotope age of apatite microregion is (448±27) Ma, and the fluorite mineralization is closely related to the invasive activity of alkali feldspar granite, all of which are the products of the late Ordovician tectonic-magmatic activity. The F content of apatite is 4.20% to 5.12%; the Cl content is less than 0.02%, and the very low Cl content indicates a low dissolved fluid Cl content. The content of rare earth elements is high (908×10−6~2164×10−6), and the partition curve of rare earth shows strong Eu negative anomaly and positive Ce negative anomaly. This anomaly is obviously consistent with its associated fluorite, calcite and alkali feldspar granite, which may be closely related to the dissolution of massive fluid in the magma-hydrothermal stage. The ratio of 87Sr/86Sr of apatite is from 0.70913 to 0.71047, the ratio of 143Nd/144Nd is from 0.51138 to 0.51153, and εNd(t) is from −13.27 to −10.26, reflecting that the ore-forming materials have the characteristics of crust-mantle mixing. Comprehensive studies show that the ore-forming age of fluorite in the western Altyn-Tagh Terrane is Ordovician, closely related to the same period alkali feldspar granite, formed in the post-collision extension stage, the ore-forming fluid may be derived from the melt-fluid evolution of alkali feldspar granite, and it is a magmatic hydrothermal filling type deposit.
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中亚造山带(CAOB)地处西伯利亚、华北、塔里木和东欧克拉通之间(图1a),是世界上最大的增生型造山带,为古亚洲洋俯冲闭合形成的产物(Sengör et al., 1993; Badarch et al., 2002; Windley et al., 2007,2020)。北山造山带地处中亚造山带南缘中段,西邻东天山造山带,向东与阿拉善地区隔巴丹吉林沙漠所相邻,作为中亚造山带重要组成部分,由大量小的构造单元、构造块体(微陆块、岛弧、蛇绿岩带、增生杂岩体等)所构成,反映了古亚洲洋中段俯冲闭合演化过程(何世平等,2002;龚全胜等,2002,2003;黄河等,2024;吴妍蓉等,2024;杨高学等,2024)。北山造山带内由北向南分布红石山、芨芨台子–小黄山、红柳河–牛圈子–洗肠井和辉铜山–帐房山4条蛇绿岩带(图1b)。许多学者对这4条蛇绿岩带所代表古洋盆构造属性、古亚洲洋在北山地区的起始俯冲以及闭合时限等问题展开研究(孟庆涛等,2021;王国强等,2021),但由于北山造山带多期次多旋回构造演化特点、蛇绿岩带风化剥蚀强烈以及研究手段各异等,对于上述科学问题至目前仍存在较多的争议。
图 1 中亚造山带大地构造位置简图(a)及北山造山带构造纲要图(b)(据Xiao et al., 2010)1.红石山蛇绿岩带;2.芨芨台子–小黄山蛇绿岩带;3.红柳河–牛圈子–洗肠井蛇绿岩带;4.辉铜山–帐房山蛇绿岩带Figure 1. (a) Sketched tectonic map of the CAOB and (b) simplified geological map of the Beishan orogenic belt芨芨台子–小黄山蛇绿岩带位于北山造山带中北部,向北为明水–旱山微陆块,向南则属于公婆泉单元,(图1b)。芨芨台子蛇绿岩作为芨芨台子–小黄山蛇绿岩带重要组成部分,其出露于芨芨台子–小黄山蛇绿岩带西端,向东间断性延伸至石板井、阿民乌素、小黄山等地(左国朝等,1990a;宋泰忠等,2008;Zheng et al., 2013;孟庆涛等,2021)。由于北山造山带构造运动复杂且漫长,蛇绿岩带风化破碎严重,对该蛇绿岩带的研究相对较少,且缺乏高精度锆石U-Pb定年成果,因此对芨芨台子蛇绿岩形成构造背景及形成时代等问题仍存在争议,目前对其构造属性研究主要有以下两种不同认识:①MOR型蛇绿岩,形成于洋中脊环境,代表了塔里木克拉通和哈萨克斯坦板块的缝合位置(左国朝等,1990b,2003;龚全胜等,2002;Zhang et al., 2012)。②SSZ型蛇绿岩,形成于弧后扩张环境,属于南部红柳河–牛圈子–洗肠井古洋盆北向俯冲所形成的弧后盆地闭合的产物(任秉琛等,2001;何世平等,2002;Song et al., 2015)。笔者以芨芨台子蛇绿岩中辉长岩、玄武岩为研究对象,从岩石学、岩石地球化学展开研究,探讨该蛇绿岩带构造属性和形成背景,为北山造山带大地构造单元划分及构造演化历史提供依据。
1. 地质背景及蛇绿岩带地质特征
芨芨台子蛇绿岩带位于明水–旱山微陆块以南,公婆泉单元以北的北山中部地区(图1b),出露于芨芨台子山南约3 km处,蛇绿岩带地表出露面积较小,东西断续延伸约5~6 km,南北宽约1~2 km(图2a)。
该蛇绿岩带主要由构造岩块和基质组成,构造岩块主要为玄武岩、辉长岩、辉石岩、变质橄榄岩等,基质则主要为前寒武系板岩、大理岩、混合岩等,受构造运动影响,构造岩块与基质混杂堆积,呈断层接触,并表现出一系列由北向南的逆冲推覆构造,断层倾角为52°~68°,构造岩块各组分之间也呈断层接触(图2b),玄武岩、辉长岩、辉石橄榄岩等呈团块状互相混杂堆积,原有接触关系遭到破坏,辉石岩与辉石橄榄岩呈构造岩块与大理岩、板岩等断层接触(图3a),但由于受构造及后期岩浆侵入作用等影响,辉石岩与辉石橄榄岩原有接触关系同样遭到破坏(图2b),致使其关系不清。在构造挤压作用下,蛇绿岩带各组分均发生不同程度的变质变形作用,片理产状与区域构造线方向一致,走向近EW向,同时蛇绿岩带局部受第四系覆盖程度较高。
2. 岩石学特征
本次工作在前人研究基础上,通过实测剖面,重点对芨芨台子蛇绿岩带中辉长岩和玄武岩进行采样分析。
辉长岩风化面呈灰褐色,新鲜面呈灰绿色,受构造挤压作用的影响,发生强烈的劈理化(图3b)。块状构造,辉长结构,岩石主要由斜长石、辉石组成,副矿物有磷灰石、磁铁矿等。斜长石含量约55%,半自形板状-他形粒状,粒度一般为0.2~0.4 mm,发育聚片双晶,杂乱分布;辉石含量约35%,粒度一般为0.2~0.4 mm,呈柱状–他形粒状;角闪石含量约5%,主要呈他形粒状,粒径小于0.2 mm。副矿物为磷灰石、磁铁矿等,含量约5%(图4a)。
玄武岩风化面呈褐色-黄褐色,新鲜面呈暗灰色,多为块状构造,部分具有气孔杏仁构造,斑晶主要为斜长石和辉石,含量约5%,斜长石呈半自形板状,辉石呈粒状;基质为间粒间隐结构,主要由针状或细条状斜长石微晶、辉石及其他不透明矿物组成,含量约95%(图4b)。
3. 分析方法
全岩主微量、稀土元素测试分析在天津上诺勘察技术服务有限公司完成。主量元素分析采用熔融玻璃片法,使用X射线荧光光谱分析(XRF)仪器进行,所用仪器型号为RigakuRIX 2100,分析精度达1%;微量元素采用ICP-MS法,使用仪器型号为Agilent 7500a,分析精度达10%,实验过程中使用标准样品AGV-2、AGV-3、BHVO-2、GSR-1和GSR-3进行检测,具体实验流程见Govindaraju(1994)和Li(1997)。
全岩Sr、Nd同位素在中国科学院广州地球化学研究所同位素地球化学国家重点实验室完成,使用Termo Fisher Scientific公司制造的Neptune-plus多接受等离子体质谱仪(MC-ICP-MS)进行测试。使用标准物质BCR-2和BHVO-2为外标,NBS987对Sr同位素监控,实验精度高于0.004%,Jndi-1对Nd同位素进行监控,实验精度高于0.001%。
4. 分析结果
4.1 主量元素
续表1 样品编号 17JJTZ-
HC-0117JJTZ-
HC-0217JJTZ-
HC-0317JJTZ-
HC-0417JJTZ-
XW-0117JJTZ-
XW-0217JJTZ-
XW-0317JJTZ-
XW-0417JJTZ-
XW-0517JJTZ-
XW-06岩性 辉长岩 辉长岩 辉长岩 辉长岩 玄武岩 玄武岩 玄武岩 玄武安山岩 玄武岩 玄武安山岩 Ce 7.91 8.51 7.74 6.92 22.70 24.20 25.50 15.05 24.80 13.65 Pr 1.15 1.26 1.11 1.09 3.14 3.26 3.43 2.16 3.33 1.90 Nd 5.83 6.85 5.89 5.29 13.90 14.50 14.90 10.20 14.60 9.00 Sm 2.18 2.06 1.74 1.76 3.40 3.61 3.65 2.90 3.53 2.49 Eu 0.80 0.90 0.75 0.67 1.23 1.17 1.19 0.95 1.30 0.93 Gd 2.75 3.07 2.83 2.48 3.78 3.96 3.90 3.75 3.98 3.24 Tb 0.49 0.52 0.49 0.46 0.61 0.64 0.62 0.65 0.65 0.58 Dy 3.40 4.04 3.28 3.27 3.83 4.19 3.96 4.44 4.38 3.89 Ho 0.73 0.80 0.74 0.68 0.79 0.91 0.81 0.99 0.95 0.89 Er 2.23 2.41 2.06 1.97 2.27 2.79 2.30 2.95 2.77 2.70 Tm 0.34 0.36 0.33 0.32 0.32 0.41 0.33 0.44 0.40 0.40 Yb 2.24 2.31 2.21 2.07 2.02 2.73 2.06 2.94 2.73 2.68 Lu 0.39 0.38 0.33 0.30 0.32 0.43 0.31 0.47 0.43 0.43 (La/Yb)N 0.99 1.00 1.10 0.93 3.27 2.57 3.62 1.54 2.73 1.53 (La/Sm)N 0.92 1.01 1.25 0.98 1.75 1.75 1.84 1.40 1.90 1.48 (Gd/Yb)N 1.02 1.10 1.06 0.99 1.55 1.20 1.57 1.06 1.21 1.00 ∑REE 33.52 36.68 32.88 29.95 67.51 72.60 73.36 54.19 74.25 48.48 ∑LREE 20.96 22.80 20.61 18.40 53.57 56.54 59.07 37.56 57.96 33.67 ∑HREE 12.56 13.88 12.27 11.56 13.94 16.06 14.29 16.63 16.29 14.81 LREE/HREE 1.67 1.64 1.68 1.59 3.84 3.52 4.13 2.26 3.56 2.27 δEu 0.99 1.09 1.04 0.98 1.05 0.95 0.96 0.88 1.06 1.00 δCe 1.03 1.04 0.98 0.99 1.04 1.05 1.05 1.00 1.03 1.02 辉长岩SiO2含量介于50.39%~51.66%,平均为51.00%;MgO及Mg#分别为6.04%~6.73%和32.33~37.03,低于原始地幔Mg#,SI固结指数介于27.66~31.55,说明岩浆经历了一定程度的演化;Al2O3介于15.82%~16.79%,平均为16.15%;全碱(Na2O+K2O)介于4.48%~4.90%,Na2O含量高于K2O(Na2O/K2O=9.75~17.15);K2O介于0.27%~0.44%,平均为0.32%;TiO2介于0.77%~0.95%,平均为0.85%;P2O5介于0.07%~0.09%,平均为0.08%(表1)。里特曼指数(σ)介于2.58~2.90,小于3.3,说明该辉长岩属于亚碱性系列,在SiO2-K2O图解(图5b)及SiO2-TFeO/MgO图解(图5c)中,样品落入拉斑系列区域内,并靠近钙碱性系列,同时在AFM图解(图5a)中,辉长岩靠近FM演化线分布,反映出明显的贫碱富镁铁的特征,指示该辉长岩属于低钾拉斑辉长岩。
表 1 芨芨台子蛇绿岩主(%)、微量及稀土元素(10−6)分析结果Table 1. Major element (%) and trace element (10−6) composition of the Jijitaizi ophiolite样品编号 17JJTZ-
HC-0117JJTZ-
HC-0217JJTZ-
HC-0317JJTZ-
HC-0417JJTZ-
XW-0117JJTZ-
XW-0217JJTZ-
XW-0317JJTZ-
XW-0417JJTZ-
XW-0517JJTZ-
XW-06岩性 辉长岩 辉长岩 辉长岩 辉长岩 玄武岩 玄武岩 玄武岩 玄武安山岩 玄武岩 玄武安山岩 SiO2 50.64 51.29 50.39 51.66 47.97 50.97 47.71 52.72 50.88 54.96 Al2O3 16.08 15.94 16.79 15.82 15.38 14.56 15.29 13.77 14.38 13.38 BaO 0.02 0.02 0.02 0.02 0.03 0.02 0.04 0.01 0.02 0.01 CaO 9.38 8.93 10.40 9.25 8.02 6.33 8.51 5.42 6.71 4.82 Cr2O3 0.01 0.01 0.01 0.01 0.09 0.01 0.09 0.01 0.01 0.01 TFe2O3 10.90 10.90 10.24 9.87 9.86 14.25 9.26 14.52 14.27 14.06 K2O 0.28 0.27 0.30 0.44 0.77 0.21 1.32 0.19 0.21 0.19 MgO 6.39 6.04 6.10 6.73 9.66 7.13 9.25 6.58 6.80 6.21 MnO 0.18 0.18 0.17 0.17 0.18 0.20 0.16 0.22 0.22 0.18 Na2O 4.37 4.63 4.18 4.29 2.60 4.41 2.58 4.45 4.47 4.42 P2O5 0.08 0.09 0.08 0.07 0.19 0.27 0.19 0.17 0.25 0.16 LOI 0.95 0.99 1.02 1.30 4.01 1.38 4.33 1.30 1.06 0.65 TiO2 0.86 0.95 0.81 0.77 1.25 0.96 1.23 0.98 0.98 0.93 Total 100.14 100.24 100.51 100.40 100.01 100.70 99.96 100.34 100.26 99.98 Mg# 33.58 32.33 33.93 37.03 45.79 30.14 46.27 28.10 29.12 27.58 Na2O+K2O 4.65 4.90 4.48 4.73 3.37 4.62 3.90 4.64 4.68 4.61 Na2O/K2O 15.61 17.15 13.93 9.75 3.38 21.00 1.95 23.42 21.29 23.26 σ(里特曼指数) 2.83 2.90 2.72 2.58 2.29 2.68 3.23 2.21 2.78 1.78 SI固结指数 29.12 27.66 29.30 31.55 42.20 27.42 41.28 25.56 26.41 24.96 Rb 3.66 4.62 3.64 5.58 13.50 3.00 31.00 2.90 2.80 2.90 Ba 92.60 385.00 98.90 45.30 200.00 40.00 260.00 40.00 40.00 30.00 Th 0.29 0.31 0.32 0.23 1.54 1.84 1.65 0.97 1.77 0.79 Cs 0.10 0.07 0.09 0.13 0.45 0.12 1.40 0.14 0.08 0.07 Cr 61.10 41.20 69.40 62.00 474.00 6.00 464.00 16.00 6.00 16.00 Co 39.50 33.10 36.00 35.20 46.40 47.50 43.50 56.00 50.80 47.90 Ni 33.20 28.40 35.40 46.90 195.00 29.00 178.00 39.50 33.00 35.50 K 6392.14 1743.31 10957.95 1577.28 6392.14 1743.31 10957.95 1577.28 1743.31 1577.28 P 829.20 1178.34 829.20 741.92 829.20 1178.34 829.20 741.92 1091.05 698.27 Nb 2.06 2.26 1.93 1.80 4.40 10.40 4.30 6.40 10.40 4.70 Pb 1.08 0.77 2.03 0.28 8.10 1.10 5.80 1.10 1.00 1.70 Sr 197.00 181.00 158.00 159.00 323.00 191.50 299.00 196.50 219.00 166.50 Ta 0.16 0.16 0.12 0.34 0.29 0.47 0.29 0.30 0.46 0.21 Ti 7491.79 5753.69 7371.92 5873.56 7491.79 5753.69 7371.92 5873.56 5873.56 5573.89 U 0.06 0.10 0.08 0.08 0.50 0.70 0.40 0.50 0.70 0.50 Y 21.20 21.90 19.90 19.10 21.40 25.80 22.50 26.80 25.90 24.60 Zr 30.80 37.80 27.70 27.00 109.00 32.90 108.50 25.60 34.80 23.00 Hf 0.97 1.13 0.80 0.88 2.80 1.10 3.00 0.90 1.30 0.80 La 3.09 3.22 3.38 2.67 9.20 9.80 10.40 6.30 10.40 5.70 图 5 芨芨台子辉长岩、玄武岩AFM图解(a)(据Irvine et al., 1971)、和SiO2-K2O图解(b)(Peccerillo et al., 1976)和SiO2-TFeO/MgO图解(c)(据Miyashiro, 1974)Figure 5. (a) AFM diagram, (b) SiO2-K2O diagram and (c) SiO2-TFeO/MgO diagram of Jijitaizi gabbro and basalt玄武岩SiO2介于47.71%~54.96%,平均50.87%,其中17JJTZ-XW-04及17JJTZ-XW-06的SiO2含量分别为52.72%和54.96%,指示这两个样品属于玄武安山岩;MgO及Mg#分别为6.21%~9.66%和27.58~46.27,低于原始地幔Mg#,SI固结指数24.96~42.20,指示岩浆经历了一定程度的结晶分异作用;Al2O3介于13.38%~15.38%,平均14.46%;TiO2介于0.93%~1.25%,平均为1.06%,低于N-MORB(1.15%)(Schilling et al., 1983);全碱(Na2O+K2O)介于3.37%~4.68%,Na2O高于K2O(Na2O/K2O=1.95~23.26);Na2O介于2.58%~4.47%,平均为3.82%;K2O介于0.19%~1.32%,平均为0.48%;P2O5介于0.16%~0.27%,平均为0.21%。里特曼指数(σ)介于1.78~3.23,小于3.3,指示玄武岩-玄武安山岩属于亚碱性系列岩石,SiO2-TFeO/MgO图解(图5c)中,所有样品均落入拉斑系列区域,而在SiO2-K2O图解(图5b)中,虽多数样品落于拉斑系列中,但17JJTZ-XW-01和17JJIZ-XW-03分别落入钙碱性和高钾钙碱性系列,考虑到这两个样品具有相对较高的烧失量,指示相对其他岩石后期经历了一定程度的蚀变,提高了岩石中K2O含量,从而致使这里两个样品在SiO2-K2O图解(图5b)中落入钙碱性和高钾钙碱性区域内。玄武岩-玄武安山岩具有较低的全碱含量,并且在AFM图解中靠近FM演化线分布,反映出明显的贫碱富镁铁的特征,指示该玄武岩-玄武安山岩属于低钾拉斑系列岩石。
4.2 稀土元素及微量元素
芨芨台子蛇绿岩带稀土元素及微量元素显示(表1),辉长岩低稀土元素总量(29.95×10−6~36.68×10−6),轻稀土元素介于18.40×10−6~22.80×10−6,重稀土元素介于11.56×10−6~13.88×10−6,轻重稀土元素含量接近(LREE/HREE=1.59~1.68),轻稀土、重稀土及轻重稀土元素分馏较弱,(La/Sm)N、(Gd/Yb)N、(La/Yb)N分别为0.92~1.25、0.99~1.10、0.93~1.10,δEu介于0.98~1.09,在稀土元素配分图(图6a)平坦分布,介于N-MORB和E-MORB之间,Eu无明显异常或微弱正异常。
图 6 芨芨台子蛇绿岩带稀土元素球粒陨石标准化配分图(a)和微量元素原始地幔标准化蛛网图(b)(据Sun et al., 1989)Figure 6. (a) Chondrite-normalized REE pattern and (b) primitive mantle-normalized trace element spidergram of Jijitaizi ophiolite玄武岩-玄武安山岩稀土元素总量(∑REE)介于48.48×10−6~74.25×10−6,轻稀土元素介于33.67×10−6~59.07×10−6,重稀土元素介于13.94×10−6~16.63×10−6,轻稀土元素含量高于重稀土元素(LREE/HREE=2.26~4.13),轻重稀土元素分馏明显((La/Yb)N=1.63~3.62),轻稀土及重稀土元素分馏较弱((La/Sm)N为1.40~1.90;(Gd/Yb)N为1.00~1.57),δEu介于0.88~1.06,稀土元素配分图(图6a)右缓倾型,Eu无明显异常。
原始地幔蛛网图(图6b)中,辉长岩相对富集Rb、U、K、Sr、P等LILE,玄武岩-玄武安山岩相对富集U、K、P等LILE和Th;辉长岩及玄武岩-玄武安山岩均相对亏损Nb、Ta、Zr、Hf等HFSE。
4.3 全岩Sr-Nd同位素
芨芨台子蛇绿岩Sr-Nd同位素分析数据显示(表2),样品87Sr/86Sr变化于
0.704067 ~0.705816 ,计算初始值(87Sr/86Sr)i 介于0.703700 ~0.704829 ;143Nd/144Nd变化于0.512699 ~0.513102 ,计算初始值(143Nd/144Nd)i 介于0.512234 ~0.512361 。εNd(t)介于+4.18~+6.66。在(87Sr/86Sr)i-εNd(t)图解(图7)中,所有均落于地幔演化线附近。表 2 芨芨台子蛇绿岩带Sr-Nd同位素组成Table 2. Sr-Nd isotopic compositions of the Jijitaizi ophiolite样品号 Rb (10-6) Sr (10-6) 87Sr/86Sr 87Rb/86Sr ±2σ (87Sr/86Sr)i Sm (10-6) 17JJTZ-HC-01 3.66 197 0.704067 0.053726 0.000006 0.703700 2.18 17JJTZ-XW-01 13.5 323 0.705594 0.120884 0.000007 0.704768 3.4 17JJTZ-XW-02 3 191.5 0.704191 0.045303 0.000003 0.703881 3.61 17JJTZ-XW-03 31 299 0.705816 0.299872 0.000004 0.703767 3.65 样品号 Nd (10-6) 147Sm/144Nd 143Nd/144Nd ±2σ (143Nd/144Nd)i εNd(t) TDM2 (Ma) 17JJTZ-HC-01 5.83 0.225948 0.513071 0.000004 0.512361 6.66 669 17JJTZ-XW-01 13.9 0.147803 0.512699 0.000006 0.512234 4.18 871 17JJTZ-XW-02 14.5 0.150439 0.512733 0.000010 0.512260 4.69 830 17JJTZ-XW-03 14.9 0.148022 0.512714 0.000009 0.512249 4.46 848 5. 讨论
5.1 岩石成因
实验岩石学表明下地壳镁铁质岩石部分熔融形成的岩石具有高SiO2特征(Michael et al., 1994),芨芨台子辉长岩、玄武岩–玄武安山岩具有低SiO2和高MgO的地球化学特征,Lu/Yb值0.16~0.17,介于幔源值(0.14~0.15)与壳源值(0.16~0.18)之间并靠近幔源端元,Ce/Pb值2.80~24.44,介于幔源值(9.15)与壳源值(3.91)之间,整体更靠近与幔源端元(Sun et al., 1989),暗示其幔源岩浆的属性。Ce/Nb介于2.32~5.93,类似于N-MORB(Ce/Nb>2,Condie et al., 1989),Nb、Ta元素变化于1.80~10.40和0.12~0.47,介于N-MORB(2.33;0.132)于IAB(48.00;2.70)之间(Sun et al., 1989),蛇绿岩带εNd(t)介于4.18~6.66,显示出源区亏损特征,(87Sr/86Sr)i-εNd(t)图解(图7)中所有样品位于亏损地幔演化线之上并靠近亏损地幔端元,暗示岩浆来源于亏损地幔端元部分熔融,在Zr-Y图解(图8b)中,除一件玄武岩样品(17JJTZ-XW-03)落于过渡地幔区域,其余样品均落于亏损地幔区域中,并且在Zr/Nb-Y/Nb图解(图8a),除两件玄武岩样品(17JJTZ-XW-01、17JJTZ-XW-03)落入富集地幔端元,其余样品均落入亏损地幔端元,指示其原始岩浆为亏损地幔部分熔融产物。
图 8 芨芨台子辉长岩、玄武岩源区判别图解a. Zr/Nb-Y/Nb判别图解(据董朋生等,2018);b. Zr-Y判别图解(据Condie, 1989); c. Zr/Nb-La/Yb判别图解(据Zhao et al., 2007);d. La/Sm-Sm/Yb判别图解(据Dilek, 2011)Figure 8. Discrimination diagrams of source areas of the gabbro and basalt in Jijitaizi石榴子石二辉橄榄岩地幔部分熔融所残留的石榴子石会使Sm/Yb升高从而区别于尖晶石二辉橄榄岩地幔,并且石榴子石相部分熔融形成的熔体具有高Dy/Yb值(>2.5),尖晶石相所产生的熔体Dy/Yb值较低(<1.5),因此可以通过Dy/Yb值及Sm/Yb变化来判断其地幔组成(McKenzie et al., 1991;Aldanmaz et al., 2000, 2008 ; Duggen et al., 2005)。芨芨台子辉长岩、玄武岩-玄武安山岩Dy/Yb为1.45~1.92,介于石榴子石相与尖晶石相之间并靠近尖晶石相范围,在Zr/Nb-La/Yb图解(图8c)及La/Sm-Sm/Yb图解(图8d)中,样品落于尖晶石相及石榴子石相过渡区域,整体处于尖晶石相部分熔融趋势线附近,说明母岩浆以尖晶石二辉橄榄岩的部分熔融为主,含少量石榴子石二辉橄榄岩的部分熔融。石榴子石相与尖晶石相于70~80 km左右转化(McKenzie et al., 1991;张国震等,2021),因此芨芨台子蛇绿岩带部分熔融深度约为70~80 km。
辉长岩、玄武岩–玄武安山岩稀土元素配分曲线介于N-MORB和E-MORB之间,并且在Zr/Nb-La/Yb图解及La/Sm-Sm/Yb图解中,样品显示出逐渐富集的趋势(图8c、图8d)。基性岩浆的富集受沉积物及流体的影响,在沉积物作用下,Th/Yb变化较大而Sr/Nd则变化较小,但流体作用下Th/Yb变化较小而Sr/Nd变化较大,芨芨台子样品Sr/Nd变化较大而Th/Yb几乎无变化,说明流体交代地幔源区富集趋势(图9a)。在交代地幔源区,金云母和角闪石为主要含LILE矿物,含金云母地幔源区部分熔融形成钾质岩浆并具有高Rb/Sr变化和低Ba/Rb变化,含角闪石地幔源区部分熔融则形成钠质岩浆和低Rb/Sr变化以及Ba/Rb变化特征,辉长岩、玄武岩–玄武安山岩均具有相对高Na低K特征,Ba/Rb变化大于Rb/Sr变化(图9b),说明地幔源区中角闪石的存在。
岩浆在上升过程中会经历不同程度的分离结晶和地壳混染作用。辉长岩及玄武岩-玄武安山岩具有较低Mg#(27.58~46.27)及SI固结指数(24.96~42.20),以及低Cr(6×10−6~474×10−6)和Ni(28.40×10−6~195.00×10−6),指示岩浆经历了一定程度的结晶分异作用,但Eu均无明显异常,Sr元素玄武岩无明显异常,辉长岩具有弱正异常,表明岩浆作用过程中斜长石未发生明显的分离结晶作用有限(刘懿馨等,2018;张国震等,2021),同时在Mg#-SiO2图解(图10b)显示所有辉长岩及玄武岩–玄武安山岩演化趋势主要与单斜辉石和橄榄石分离结晶有关,因此辉长岩及玄武岩–玄武安山岩形成过程中主要经历了单斜辉石和橄榄石的分离结晶作用。芨芨台子蛇绿岩带所有样品均具有亏损Nb、Ta等HFSE和HREE,富集K、Pb等LILE和LREE的地球化学特征,这一特征被认为可由①岩浆上升过程中地壳物质的混染。②地幔岩浆源区受到因俯冲进入地幔的地壳物质组分的影响,即源区富集。辉长岩、玄武岩-玄武安山岩(La/Nb)PM和(Th/Ta)PM分别介于0.98~2.51和0.33~2.74,接近下地壳值((La/Nb)PM>1; (Th/Ta)PM接近1)(Sun et al., 1989;代堰锫等,2021),Nb/La-Nb/Th图解(图10a)中所有样品呈正相关,说明地壳混染的存在,但Lu/Yb、Ce/Pb及Ce/Nb处于幔源和壳源范围之间但靠近幔源范围,La/Sm小于4.5(1.42~2.95)以及 (87Sr/86Sr)i接近原始地幔值(约0.704)指示岩浆上升过程中地壳混染作用较弱(Sun et al., 1989)。而俯冲流体所带入的不相容元素使亏损地幔发生富集(图8c、图8d),提高了岩浆源区中LREE及LILE的丰度,致使被交代的地幔发生部分熔融后形成相较于亏损地幔而言更为富集LREE和LILE的岩浆。因此芨芨台子辉长岩、玄武岩中LREE和LILE的弱富集受俯冲物质交代改造有关,这一点也就佐证了上文中岩浆源区受俯冲流体交代富集这一特征。
图 10 芨芨台子蛇绿岩带地壳混染(a)和结晶分异图解(b)(据张国震等,2021)Figure 10. (a)Crustal contamination and (b) crystallization differentiation diagramof Jijitaizi ophiolite5.2 构造背景及构造意义
芨芨台子蛇绿岩位于芨芨台子–小黄山蛇绿岩带西侧,对于该蛇绿岩带的形成环境长期以来存在有争议,部分研究认为该蛇绿岩带属于早古生代北山洋壳残片,代表了板块缝合带位置,南侧的红柳河–牛圈子–洗肠井蛇绿岩带为芨芨台子–小黄山洋盆南向俯冲形成的弧后盆地俯冲消减的产物(左国朝等,1990a;何国琦等,1993;郑荣国等,2012),但也有研究认为,该蛇绿岩带其实是南侧红柳河-牛圈子-洗肠井洋盆北向俯冲所形成的弧后盆地闭合产物(宋泰忠等,2008;李敏等,2020;孟庆涛等,2021;董洪凯等,2022)。从区域地质特征上来看,芨芨台子–小黄山蛇绿岩带位于明水-旱山单元与公婆泉单元之间(图1),北侧的明水–旱山单元上地层沉积组合和变质程度与中天山具有相似的地层沉积组合和变质程度,同时侵入该地体的中酸性侵入岩表现出强烈富集的εNd(t)和εHf(t)同位素特征,表明存在有前寒武系变质基底,及一套由低绿片岩相-高角闪岩相变质岩系组成的北山岩群(何世平等,2002;王鑫玉,2017;辛后田等,2020;宋博等,2021),而南侧的公婆泉单元部分研究认为其不含前寒武系变质基底,仅由中—上奥陶统中基性火山岩、浊积岩等,以及下志留统勒巴泉群、中—上志留系公婆泉群(Song et al., 2013, 2014, 2015, 2016; 王怀涛,2019),但在对阿民乌素、小黄山等地的研究中发现蛇绿岩带两侧均有北山岩群的出露,同时公婆泉单元和明水–旱山单元具有一致的航磁和重力异常(张正平等,2017;辛后田等,2020),说明公婆泉单元和明水–旱山单元具有统一的基底,芨芨台子–小黄山蛇绿岩带不具有分割指示意义,暗示该蛇绿岩带为弧后盆地闭合产物。
此外,从地球化学特征上来看,芨芨台子蛇绿岩样品稀土元素曲线分布平坦,介于N-MORB与E-MORB之间,总体类似于MORB型,微量元素上富集LILE,亏损Nb、Ta等HFSE,又类似于岛弧岩浆岩地球化学特征,暗示其属于SSZ型蛇绿岩带。Zr、Ta、Nb、Hf、Ti等元素及REE在岩浆作用过程中低活动性(夏林圻等,2003),因此可以使用以上元素及其元素对来判别构造背景,在Ti/
1000 -V图解(图11a)中样品主要分布于MORB区域并靠近IAT区域,而在Zr-Ti图解(图11b)中所有样品则主要分布于岛弧岩浆岩范围内并靠近MORB区域中,结合上文岩浆源区受俯冲流体交代富集这一特征,指示芨芨台子蛇绿岩形成于上俯冲带环境下,属于SSZ型蛇绿岩。SSZ型蛇绿岩的形成环境可分为伸展的初始弧后–弧前环境(BA-FA)、弧前环境(FA)、大陆和大洋的弧后盆地(CBA和OBA)(Hawkins, 1977; Stern et al., 2003; Reagan et al., 2010; Dilek et al., 2010;王国强,2015;杜雪亮,2019)。因此芨芨台子蛇绿岩属于SSZ型蛇绿岩,也就指示其所代表的古洋盆形成于弧后盆地或弧前初始俯冲构造环境中。统计了全球
12332 个弧后盆地玄武岩样品(BABB)并计算出其主微量及Sr-Nd-Pb同位素平均值和中位数,结果表明,BABB中Nb平均为2.38×10−6、Ta平均为0.16×10−6、87Sr/86Sr平均为0.703288 ,芨芨台子蛇绿岩Nb、Ta及87Sr/86Sr接近于上述值,同时辉长岩及玄武岩-玄武安山岩Y含量(19.10×10−6~26.80×10−6)、Th/Yb整体小于0.6,少数样品大于0.6(0.11~0.80)与弧后盆地玄武岩类似(Y>20; Th/Yb<0.6)(宋泰忠等,2008),指示芨芨台子蛇绿岩形成于弧后盆地构造环境中。北山造山带内蛇绿岩带分布广泛,但由于不同学者研究手段、研究对象的差异导致对于这些蛇绿岩带认识出入较大,从而对北山造山带古生代构造演化过程产生很多不同的模型,目前总的来说可分为以下3种:1.两陆夹一洋模式(Zuo et al., 1991)2.统一陆块-俯冲增生模式(刘雪亚等,1995;He et al., 2018)3.岛弧拼贴模式(Xiao et al., 2010, 2018; Song et al., 2016)。对于分布于北山造山带的四条蛇绿岩带,红石山蛇绿岩带和辉铜山-帐房山蛇绿岩带通过其蛇绿岩地球化学特征、蛇绿岩带两侧构造单元区域地质特征等,被认为于晚古生代形成于弧后扩张环境中(左国朝等,1990a;王国强等,2014;Shi et al., 2017;牛文超等,2019;王怀涛,2019,2021;张正平等,2020);红柳河–牛圈子–洗肠井蛇绿岩带南侧断续分布的前寒武纪沉积地层为塔里木板块标志性稳定沉积盖层(胡新茁等,2015),北侧公婆泉单元基底为北山岩群,并且主体由奥陶系—志留系组成(丁嘉鑫等,2015;王鑫玉,2017; Wang et al., 2018),蛇绿岩带两侧沉积地层不同,表明红柳河–牛圈子–洗肠井蛇绿岩带具有缝合带意义。此外,红柳河–牛圈子–洗肠井蛇绿岩带所代表古洋盆具有双向俯冲闭合特征,公婆泉单元内岩浆岩地球化学特征与构造变形特征,指示属于红柳河–牛圈子–洗肠井洋盆北向俯冲所形成的陆缘弧,并被认为最早形成于晚寒武世—早奥陶世(Song et al., 2015;Ao et al., 2016;宋东方等,2018;王鑫玉等,2018;王怀涛,2019;李敏等,2020;辛后田等,2020),该时代晚于红柳河–牛圈子–洗肠井蛇绿岩形成时代,并早于芨芨台子–小黄山蛇绿岩形成年龄(左国朝等,1996;宋泰忠等,2008;张元元等,2008;Wu et al., 2011;李向民等,2012;王国强,2015;孟庆涛等,2021),结合上文,笔者可以认为芨芨台子–小黄山蛇绿岩形成于弧后盆地构造环境,所代表古洋盆不具有板块分割意义,而南侧红柳河–牛圈子–洗肠井蛇绿岩带具有分割指示意义,塔里木板块和哈萨克斯坦板块所夹的古洋盆应指红柳河–牛圈子–洗肠井古洋盆,北山造山带古生代构造演化模型应该为“两陆夹一洋”模式。综上所述,于早寒武世开始发生南向俯冲的红柳河–牛圈子–洗肠井洋盆在最晚早奥陶世时发生北向俯冲,形成公婆泉岩浆弧,并在公婆泉岩浆弧后发生裂解形成芨芨台子–小黄山弧后盆地,红柳河–牛圈子–洗肠井洋盆、公婆泉岩浆弧和芨芨台子–小黄山弧后盆地构成沟–弧–盆体系(图12)。
6. 结论
(1)芨芨台子蛇绿岩位于明水-旱山微陆块以南,公婆泉单元以北,地球化学表现出SSZ型(上俯冲带型)蛇绿岩特征。
(2)岩浆起源于亏损地幔含角闪石的尖晶石相二辉橄榄岩和少量石榴子石相二辉橄榄岩的部分熔融,并且岩浆源区受南部红柳河–牛圈子–洗肠井洋盆北向俯冲所带入俯冲流体交代发生一定程度富集,岩浆上升过程中经历了一定程度的结晶分异和地壳混染作用。
(3)芨芨台子–小黄山蛇绿岩带所代表古洋盆为早古生代红柳河–牛圈子–洗肠井洋盆北向俯冲引起弧后扩张产物,属于弧后盆地。
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图 1 阿尔金西段卡尔恰尔-库木塔什超大型萤石矿带地质矿产图
①. 年代学数据来源于张若愚等(2016);②. 年代学数据来源于赵辛敏等(2023);③. 年代学数据来源于高永宝等(2023);④. 本文数据
Figure 1. Geological map of the super-large Kaerqiaer-Kumutashi fluorite mineralization belt in the West Altyn-Tagh Orogen
图 3 库木塔什萤石矿区磷灰石野外及镜下特征
a. 萤石方解石脉;b. 方解石萤石矿石(共生磷灰石);c. 磷灰石单矿物;d. 自形柱状磷灰石被包含于带云母、萤石中(单偏光);e. 萤石交代磷灰石(单偏光);f. 萤石交代方解石、磷灰石(单偏光);g. 磷灰石阴极发光(CL)图像;h. 磷灰石与萤石、方解石共生(背散射);i. 氟碳铈矿与萤石、方解石共生(背散射);Ap. 磷灰石;Bsn. 氟碳铈矿;Tai. 带云母;Cal. 方解石;Fl. 萤石;Pst. 氟碳钙铈矿
Figure 3. Characteristics of apatite from the Kumutashi fluorite deposit
图 5 库木塔什萤石矿区磷灰石SiO2-MnO图解(据Zhao et al., 2020)
Figure 5. SiO2-MnO diagram of apatite from the Kumutashi fluorite deposit
表 1 库木塔什萤石矿区磷灰石主量元素含量(%)
Table 1 Major elements composition (%) of apatite from the Kumutashi fluorite deposit
样号 F SiO2 P2O5 Na2O SrO FeO MnO CaO Cl BaO Total F/Cl 01 4.47 0.15 40.7 0.25 0.12 / 0.06 55.7 0.01 0.16 99.7 745 02 4.39 0.07 41.3 0.23 0.13 0.05 0.04 55.7 0.01 0.10 100 399 03 4.48 0.14 40.4 0.25 0.08 0.03 0.04 56.1 0.02 0.05 99.7 213 04 4.86 0.14 40.6 0.23 0.19 / 0.02 55.7 0.01 0.10 99.8 374 05 4.60 / 41.3 0.45 0.08 0.02 0.01 55.5 0.01 0.01 100 418 06 5.12 0.15 40.6 0.29 0.13 0.04 / 55.5 0.01 / 99.7 639 07 4.59 0.27 40.3 0.22 0.06 0.06 / 55.9 0.01 0.08 99.5 656 08 4.66 0.15 41.1 0.17 0.14 0.03 / 55.5 0.02 / 99.8 194 09 5.04 0.22 41.2 0.27 0.07 / 0.04 55.6 0.01 / 100 630 10 4.20 0.26 41.2 0.21 0.10 0.07 0.09 56.2 0.02 / 101 200 11 4.30 0.22 40.5 0.22 0.09 0.05 0.03 56.0 0.01 0.04 99.6 330 注:“/”表示含量低于检测限。 表 2 库木塔什萤石矿区磷灰石、方解石微量元素与稀土元素表(10−6)
Table 2 Trace element and rare earth element compositions (10−6) of apatite and calcite from the Kumutashi fluorite deposit
样品号 Ap-01 Ap-02 Ap-03 Ap-04 Ap-05 Ap-06 Ap-07 Ap-08 Ap-09 Cal-01 Cal-02 Cal-03 Cal-04 矿物 磷灰石 磷灰石 磷灰石 磷灰石 磷灰石 磷灰石 磷灰石 磷灰石 磷灰石 方解石 方解石 方解石 方解石 Sc 0.26 0.16 0.2 0.22 0.15 0.17 0.2 0.14 0.12 0.36 0.37 0.42 0.28 V 65.3 65.9 68.9 92.5 103 95.1 97 93.1 94.7 0.07 0.13 0.16 0.10 Mn 130 118 287 126 135 111 104 104 111 1158 1187 1187 1182 Fe 248 216 232 203 198 181 182 178 172 1535 1530 1541 1537 Co 0.06 0.03 0.27 0.03 0.02 0.02 0.03 0.02 0.02 0.07 0.08 0.09 0.09 Ga 0.29 0.22 1 0.17 0.13 0.16 0.1 0.13 0.11 0.42 0.34 0.23 0.22 Rb 0 0.01 0 0.03 0 0.04 0.03 0 0.02 0.00 0.00 0.01 0.46 Sr 834 888 891 810 708 713 715 699 676 1218 1228 1235 1221 Y 103 124 118 85 58.1 74.4 78.1 75.4 57.4 36.6 36.8 36.2 35.0 Sn 0.25 0.17 0.22 0.2 0.13 0.12 0.23 0.15 0.13 0.06 0.09 0.02 0.08 Cs 0 0.03 0.01 0.02 0.01 0.01 0 0.01 0 0.00 0.01 0.10 0.08 Ba 3.51 4 32.3 3.6 2.53 3.33 2.99 2.77 2.47 12.8 7.66 6.25 5.70 La 309 366 343 223 159 194 209 205 150 34.3 41.1 14.1 9.87 Ce 892 1016 949 625 453 540 570 561 428 102 113 57.4 46.5 Pr 110 125 119 77.7 57.3 68.2 70.6 70 52.8 13.5 13.4 8.95 7.4 Nd 394 450 434 270 205 241 250 243 189 50 50.2 37.7 33.5 Sm 68.7 78.7 75.3 48.2 35 42.3 43.6 41.7 32.9 10.1 10.5 9 8.75 Eu 6.63 7.72 7.44 5.01 4.07 4.29 4.56 4.43 3.54 1.05 1.07 1 1.02 Gd 45.4 53.2 52.3 32.3 23.7 28 29.4 28 22.6 7.65 7.99 8.23 7.19 Tb 5.55 6.39 6.19 3.99 2.94 3.59 3.6 3.53 2.91 1.13 1.17 1.09 1.1 Dy 27.7 32.5 30.8 21.5 14.9 18.4 18.7 18.1 14.1 6.95 6.78 6.93 6.56 Ho 4.35 5.22 4.98 3.49 2.48 2.91 3.02 2.94 2.45 1.4 1.42 1.35 1.32 Er 11 12.8 12.2 8.34 6.21 7.66 7.81 7.49 5.93 4.08 4.19 4.07 4.17 Tm 1.23 1.56 1.43 1.04 0.75 0.92 0.94 0.96 0.69 0.62 0.59 0.6 0.58 Yb 6.88 8.32 7.32 5.59 3.96 4.62 4.84 4.95 3.74 4.33 4.27 4.31 4.2 Lu 0.77 0.96 0.94 0.68 0.52 0.65 0.58 0.6 0.42 0.69 0.6 0.67 0.66 W 0.05 0.06 0.33 0.06 0.03 0.05 0.02 0.04 0.02 0.00 0.00 0.01 0.01 Bi 5.19 5.08 5.65 4.56 3.5 3.76 3.4 3.56 2.95 0.05 0.16 0.05 0.07 Th 184 184 213 327 260 281 243 243 221 0.00 0.00 0.00 0.00 U 25.7 24.3 27.5 31.7 18.4 22.4 17.1 17.2 15.2 0.00 0.00 0.00 0.00 ΣREE 1883 2165 2043 1325 968 1157 1217 1191 908 238 256 155 133 LREE 1780 2044 1927 1249 913 1090 1148 1124 856 211 229 128 107 HREE 103 121 116 76.9 55.5 66.7 68.9 66.5 52.8 26.8 27 27.2 25.8 LREE/HREE 17.3 16.9 16.6 16.2 16.5 16.3 16.7 16.9 16.2 7.87 8.48 4.7 4.16 (La/Y)N 32.2 31.6 33.6 28.7 28.8 30.2 31 29.7 28.7 5.67 6.91 2.35 1.69 δEu 0.34 0.34 0.34 0.37 0.41 0.36 0.37 0.37 0.38 0.35 0.34 0.35 0.38 δCe 1.18 1.16 1.15 1.16 1.16 1.15 1.15 1.14 1.18 1.17 1.17 1.22 1.27 样品号 Cal-05 Cal-06 Cal-07 Cal-08 Cal-09 Cal-10 Cal-11 Cal-12 Cal-13 Cal-14 Cal-15 Cal-16 Cal-17 矿物 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 方解石 Sc 0.47 0.36 0.37 0.44 0.34 0.45 0.32 0.56 0.19 0.47 0.59 0.50 0.70 V 0.07 0.14 0.06 0.03 0.03 0.20 0.06 0.00 0.01 0.13 1.79 0.18 0.20 Mn 1176 1192 1372 1469 1423 1493 1389 1376 1058 1775 1800 2497 3858 Fe 1556 1549 2695 3668 2559 4443 2475 2466 1169 1885 2636 2506 3710 Co 0.01 0.12 0.11 0.12 0.12 0.08 0.09 0.12 0.07 0.09 0.21 0.09 0.14 Ga 0.28 0.38 0.25 0.24 0.33 0.14 0.21 1.17 0.44 0.52 0.15 0.93 1.42 Rb 0.39 0.10 0.22 0.04 0.04 0.23 0.13 0.12 0.04 0.02 0.42 0.14 0.25 Sr 1187 1211 1110 1117 1125 1028 1146 1165 1047 1423 1049 2015 3011 Y 36.0 35.2 40.3 38.4 40.0 50.6 43.0 42.4 30.4 40.0 47.0 61.9 99.8 Sn 0.06 0.05 0.05 0.05 0.07 0.06 0.06 0.03 0.06 0.10 0.21 0.09 0.26 Cs 0.14 0.02 0.08 0.02 0.04 0.10 0.06 0.03 0.01 0.02 0.10 0.07 0.08 Ba 4.58 7.62 4.55 6.28 6.90 4.92 6.75 24.0 12.7 15.3 9.05 24.3 40.9 La 13.4 30.6 28.5 29.3 43 12.9 99.4 94.6 44.5 29.4 29.9 83.8 259 Ce 46.7 104 75.7 87.5 97.8 44.7 255 254 104 93.9 71.2 198 539 Pr 6.74 12.9 9.65 11.3 11.7 7.29 29.2 29.2 12.2 12.6 11.3 23.8 57.7 Nd 29.2 49.8 41.8 43.9 43.4 33.6 103 100 42.7 48.2 45.3 85 192 Sm 8.66 9.87 9.49 9.21 9.56 10.2 16.3 14.8 8.75 10.7 10.4 17 29.7 Eu 0.98 1.09 1.13 1.13 1.05 1.18 1.42 1.39 0.86 1.25 1.11 1.68 3.29 Gd 6.6 8.04 8.38 8.47 8.45 9.8 10.2 10.1 6.49 8.26 8.62 13 21.1 Tb 1.14 1.08 1.28 1.24 1.25 1.5 1.39 1.24 0.92 1.25 1.24 1.77 3.03 Dy 6.63 6.53 7.72 7.68 7.84 9.91 8.18 8.16 5.28 7.3 7.96 11.7 17.4 Ho 1.35 1.34 1.58 1.46 1.52 1.92 1.65 1.62 1.14 1.34 1.62 2.18 3.73 Er 4.17 4.02 4.83 4.83 4.84 5.62 5.23 4.93 3.42 4.61 5 6.71 10.9 Tm 0.61 0.62 0.75 0.68 0.69 0.79 0.75 0.71 0.47 0.66 0.85 0.99 1.49 Yb 4.05 4.23 5.09 4.81 5 5.66 5.24 5.19 3.25 4.73 5.51 6.63 11.8 Lu 0.67 0.63 0.79 0.74 0.82 0.78 0.91 0.82 0.51 0.75 0.9 1.09 1.67 W 0.03 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.39 0.00 0.01 Bi 0.04 0.04 0.02 0.02 0.03 0.02 0.01 0.00 0.11 0.18 0.40 0.29 0.38 Th 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.31 0.14 0.11 0.35 0.70 U 0.01 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.02 0.04 0.37 0.02 0.60 ΣREE 131 235 197 212 237 146 538 527 235 225 201 453 1152 LREE 106 209 166 182 207 110 504 494 213 196 169 409 1081 HREE 25.2 26.5 30.4 29.9 30.4 36 33.5 32.8 21.5 28.9 31.7 44 71.1 LREE/HREE 4.19 7.87 5.47 6.1 6.79 3.05 15.1 15.1 9.93 6.78 5.33 9.29 15.2 (La/Yb)N 2.37 5.19 4.01 4.37 6.16 1.63 13.6 13.1 9.83 4.45 3.88 9.06 15.7 δEu 0.38 0.36 0.38 0.38 0.35 0.36 0.31 0.33 0.34 0.39 0.35 0.33 0.38 δCe 1.2 1.29 1.12 1.18 1.05 1.11 1.15 1.18 1.08 1.2 0.95 1.07 1.04 注:δEu=EuN/(SmN×GdN)1/2; δCe=CeN/(LaN×PrN)1/2。 表 3 库木塔什矿区磷灰石LA-ICP-MS U-Pb分析结果
Table 3 LA-ICP-MS apatite U-Pb isotopic data from the Kumutashi fluorite deposit
测点号 元素含量(10−6) U/Th 同位素比值 U Th n(238U)/
n(206Pb)2σ n(207Pb)/
n(206Pb)2σ n(207Pb)/
n(235U)2σ n(206Pb)/
n(238U)2σ n(208Pb)/
n(232Th)2σ 01 31.2 220 0.32 3.89 0.0530 0.4044 0.0069 14.16 0.1996 0.2572 0.0035 0.3304 0.0094 02 36.7 258 0.31 4.47 0.0524 0.3835 0.0037 11.57 0.2336 0.2239 0.0026 0.2735 0.0064 03 44.3 284 0.34 4.89 0.0572 0.3817 0.0042 10.53 0.1982 0.2045 0.0024 0.2740 0.0064 04 47.3 300 0.31 5.11 0.0821 0.3622 0.0047 9.54 0.1923 0.1957 0.0031 0.2443 0.0051 05 29.7 202 0.16 3.70 0.0656 0.4060 0.0065 15.23 0.2960 0.2702 0.0048 0.3171 0.0083 06 29.9 212 0.16 3.44 0.0463 0.4171 0.0047 16.10 0.2191 0.2907 0.0039 0.3269 0.0085 07 29.1 198 0.16 3.47 0.0453 0.4134 0.0054 15.83 0.2357 0.2883 0.0038 0.3328 0.0069 08 30.8 214 0.16 3.65 0.0493 0.4119 0.0051 15.01 0.2139 0.2743 0.0037 0.3207 0.0083 09 32.0 225 0.15 3.69 0.0430 0.4134 0.0050 15.01 0.2086 0.2709 0.0032 0.3131 0.0096 10 31.8 217 0.16 3.69 0.0549 0.4207 0.0055 15.25 0.2204 0.2711 0.0040 0.3245 0.0073 11 36.7 255 0.16 4.06 0.0766 0.4008 0.0061 13.24 0.1785 0.2460 0.0046 0.2912 0.0077 12 35.8 247 0.16 4.03 0.0700 0.4063 0.0062 13.56 0.2164 0.2480 0.0043 0.2894 0.0084 13 35.1 240 0.16 4.03 0.0569 0.4098 0.0068 13.71 0.1863 0.2482 0.0035 0.2950 0.0087 14 36.3 250 0.16 4.05 0.0725 0.4123 0.0064 13.68 0.2371 0.2468 0.0044 0.2880 0.0083 15 54.4 331 0.26 5.83 0.1343 0.3344 0.0050 7.48 0.2133 0.1715 0.0040 0.2344 0.0060 16 57.3 345 0.25 5.72 0.0905 0.3442 0.0060 7.77 0.1164 0.1748 0.0028 0.2417 0.0063 17 51.6 323 0.35 6.29 0.1334 0.2775 0.0040 5.95 0.1339 0.1591 0.0034 0.2336 0.0068 18 52.4 322 0.34 6.20 0.1610 0.2811 0.0058 6.09 0.1674 0.1612 0.0042 0.2320 0.0078 19 53.0 329 0.29 5.92 0.1796 0.3070 0.0050 6.76 0.2174 0.1688 0.0051 0.2353 0.0081 20 55.3 339 0.23 5.43 0.0730 0.3645 0.0049 8.58 0.1444 0.1842 0.0025 0.2484 0.0073 21 53.7 328 0.27 5.78 0.1402 0.3228 0.0057 7.21 0.1931 0.1731 0.0042 0.2433 0.0083 22 48.8 309 0.39 6.32 0.1086 0.2587 0.0038 5.61 0.1081 0.1582 0.0027 0.2325 0.0071 23 50.6 319 0.37 6.24 0.1206 0.2646 0.0040 5.80 0.1216 0.1604 0.0031 0.2315 0.0064 24 56.2 347 0.21 5.19 0.1003 0.3873 0.0058 9.57 0.1592 0.1928 0.0037 0.2533 0.0056 25 42.9 308 0.27 4.16 0.0680 0.5004 0.0070 16.28 0.2830 0.2404 0.0039 0.2926 0.0072 26 50.1 358 0.23 5.07 0.0826 0.3905 0.0054 10.31 0.1208 0.1974 0.0032 0.2444 0.0056 27 36.4 289 0.27 4.08 0.0488 0.4882 0.0049 15.99 0.2317 0.2448 0.0029 0.2952 0.0062 28 37.1 362 0.27 6.03 0.0983 0.2567 0.0044 5.95 0.1040 0.1658 0.0027 0.1837 0.0058 29 29.9 235 0.26 3.70 0.0550 0.5267 0.0075 18.96 0.3393 0.2702 0.0040 0.3157 0.0072 30 43.8 457 0.17 4.80 0.0598 0.3948 0.0054 10.93 0.1380 0.2084 0.0026 0.2053 0.0047 31 43.5 256 0.41 5.34 0.0705 0.2731 0.0034 6.79 0.0948 0.1873 0.0025 0.2880 0.0066 32 59.1 332 0.44 7.78 0.1007 0.2113 0.0026 3.62 0.0450 0.1286 0.0017 0.2061 0.0059 33 74.5 493 0.34 8.32 0.0930 0.1960 0.0025 3.36 0.0691 0.1201 0.0013 0.1669 0.0038 34 47.2 280 0.28 5.83 0.0945 0.2570 0.0036 6.07 0.0985 0.1716 0.0028 0.2374 0.0075 35 48.6 285 0.42 6.75 0.0910 0.2251 0.0034 4.42 0.0579 0.1482 0.0020 0.2208 0.0048 36 65.1 384 0.34 7.11 0.0759 0.2165 0.0025 4.31 0.0591 0.1407 0.0015 0.2062 0.0044 37 39.3 340 0.22 6.55 0.0959 0.2264 0.0033 4.90 0.0826 0.1527 0.0022 0.1736 0.0037 38 63.5 328 0.49 8.18 0.0948 0.1847 0.0027 3.09 0.0409 0.1223 0.0014 0.2061 0.0052 39 52.4 336 0.39 7.99 0.1200 0.1875 0.0023 3.23 0.0408 0.1251 0.0019 0.1921 0.0042 40 51.6 340 0.38 7.97 0.1127 0.1804 0.0025 3.13 0.0404 0.1255 0.0018 0.1867 0.0051 表 4 库木塔什磷灰石原位Sr-Nd同位素分析结果
Table 4 Sr and Nd isotopic results from the Kumutashi fluorite deposit
样号 87Rb/86Sr 87Sr/86Sr 147Sm/144Nd 143Nd/144Nd εNd(t) 01 0.000058 0.70933 0.10390 0.51149 −11.1 02 0.000004 0.70973 0.10454 0.51151 −10.6 03 0.000058 0.70943 0.10273 0.51151 −10.7 04 0.000058 0.70947 0.09928 0.51141 −12.7 05 0.000058 0.70960 0.10504 0.51143 −12.1 06 0.000058 0.70948 0.10259 0.51140 −12.8 07 0.000058 0.71047 0.10482 0.51149 −11.1 08 0.000058 0.70938 0.10411 0.51151 −10.7 09 0.000040 0.70949 0.10202 0.51153 −10.3 10 0.000014 0.70965 0.10394 0.51152 −10.4 11 0.000111 0.70916 0.10724 0.51145 −11.8 12 0.000014 0.70928 0.10426 0.51138 −13.3 13 0.000144 0.70913 0.10444 0.51145 −11.9 14 0.000140 0.70921 0.10245 0.51138 −13.2 15 0.000015 0.70915 0.10371 0.51149 −11.0 -
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