Zircon U−Pb dating and geochemistry of basalt in Guaizhangshan Group from the Southern Danghe Mountain in South Qilian and its tectonic setting
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摘要:研究目的
前人在南祁连志留纪巴龙贡噶尔组中解体出新元古代拐杖山岩群,对该群中玄武岩的年龄、成因与成岩构造环境的研究是厘清南祁连地区构造演化的重要手段。
研究方法本文基于 LA−ICP−MS 锆石 U−Pb 年龄和全岩地球化学分析等方法研究拐杖山岩群火山岩的形成年代、地球化学特征及地质意义。
研究结果锆石U−Pb定年结果显示,玄武岩喷发年龄为(786.6±5.8)Ma,表明拐杖山岩群形成于新元古代早期。岩石地球化学分析结果表明,玄武岩SiO2含量在48.09%~50.97%,高TiO2(1.34%~2.55%),低MgO(5.78%~7.11%),显示亚碱性拉斑玄武岩特征。岩石轻、重稀土分异明显((La/Yb)N=3.76~4.51),无明显Eu异常(δEu=0.80~1.05),大离子亲石元素Ba、Th、U相对富集,Pb强富集,亏损Nb、Ta、Ti等高场强元素。
结论岩石地球化学特征暗示拐杖山岩群玄武岩是遭受陆壳物质混染的地幔源区玄武岩,该火山岩形成于大陆裂谷环境,响应了全球新元古代Rodinia超大陆裂解事件。
创新点:采用 LA−ICP−MS 锆石测年和全岩地球化学分析等方法揭示了拐杖山岩群火山岩的形成年代、岩石成因及源区特征。
Abstract:This paper is the result of geological survey engineering.
ObjectiveThe Neoproterozoic Guaizhangshan Group was disintegrated from the Silurian Balonggonggaer Formation. The study of the petrogenesis and tectonic setting of the basalt in Guaizhangshan Group is crucial to clarify the tectonic evolution of South Qilian.
MethodsBased on LA−ICP−MS zircon U−Pb datingand whole−rock geochemistry analysis, the formation age, geochemical characteristics and geological significance of the basalt in Guaizhangshan Group are constrained.
ResultsThe dating results indicate the eruption age of the basalt is (786.6±5.8) Ma, suggesting that the Guaizhangshan Group formed during Early Neoproterozoic. Geochemical analyses of the basalt show that: SiO2=48.09%–50.97%, TiO2=1.34%–2.55%, MgO=5.78%–7.11%, displaying characteristics of subalkaline tholeiite; Significant differentiation between light rare earth element (LREE)and heavy rare earth elements (HREE) ((La/Yb)N=3.76–4.51), and inconspicuous Eu anomalies (δEu=0.80–1.05); Enrichment of Ba, Th, U, Pb, and depletionin Nb, Ta, Ti.
ConclusionsThese geochemical characteristics indicate that the basalts were derived from mantle and contaminated by crustal materials. The basalt was formed in continental rift setting, which may be relevant to the break−up of the Rodinia supercontinent.
Highlights:The formation age, petrogenesis and source characteristics of the basalt in Guaizhangshan Group are revealed by the LA−ICP−MS zircon dating and whole−rock geochemistry analysis.
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1. 引 言
祁连山位于青藏高原东北缘,隶属于秦—祁—昆中央造山带中段,西为阿尔金断裂所截,东延入秦岭造山带,南与柴北缘造山带和柴达木地块相接,北接阿拉善地块,是世界上典型的增生型造山带(Xiao et al., 2009; 樊新祥等, 2020)。祁连造山带经历了新元古代Rodinia超大陆裂解、早古生代北祁连有限洋盆的开启和扩张、大洋俯冲及弧后拉张,直到大洋关闭、弧−陆及陆−陆碰撞的构造演化过程(Yin and Harrison, 2000; Gehrels et al., 2003; Zhang et al., 2007; Tseng et al., 2009; Xiao et al., 2009; Xu et al., 2010; Wu et al., 2011; Song et al., 2013)。许多学者对于北祁连、中祁连陆块及南部柴北缘造山带的地层、火山作用及构造演化等方面进行了大量卓有成效的研究(冯益民等, 1996; 夏林圻等, 2001, 2003, 2016; 杜远生等, 2006; 樊光明等, 2007; 何世平等, 2008; 徐亚军等, 2013; Wang et al., 2017; Li et al., 2019; Zhao et al., 2020),但对于南祁连地区的研究相对薄弱,这也制约了学者对整个祁连造山带的形成与演化的认识。
南祁连地区广泛分布着志留纪巴龙贡噶尔组(图1b)(赵生贵, 1996; 冯益民等, 1996; 罗明非, 2010; 夏林圻等, 2016; Wang et al., 2017),但其形成时代一直存在争议,主要有3种观点:(1)一种观点认为巴龙贡噶尔组形成于晚奥陶世—早志留世
1 2 (牛广智等, 2016);(2)另一种观点则认为该组形成于新元古代中期—中奥陶世(秦宇, 2018; Li et al., 2019);(3)还有一种观点认为原定巴龙贡噶尔组中存在砂岩、片岩与火山岩3个岩性段,其中砂岩段为符合原始定义的志留纪巴龙贡噶尔组,而以强变形、弱变质为特征的片岩段与火山岩段则划为中—新元古代,分别命名为“拐杖山岩群”与“天峻组”(计波等, 2018; 白春东等, 2019; 王军等, 2019; 王磊等, 2019; 潘建等, 2019)。究其原因,一方面是巴龙贡噶尔组片岩段构造变形强烈,原岩难以识别,并且大型劈理褶皱发育,与砂岩段容易混淆;另一方面,该组在多数地区缺少可靠的地质年代证据,制约了对其进一步的划分与研究。因此,巴龙贡噶尔组片岩段中出露的玄武质火山岩是解决该问题的关键因素,也是研究该地区元古宙时期构造演化的重要载体。本文通过详细的野外地质调查,以南祁连西缘党河南山地区拐杖山岩群中的火山岩为研究对象,开展岩石地球化学和锆石U−Pb年代学的分析,厘定该地层的形成时代与构造环境,为完善南祁连地区的构造演化过程提供详实的依据。Figure 1. Structural location and geological sketch map of Qilian block (a) (after Xia Linqi et al., 2016), regional geological map of the Danghe mountain in northwest of South Qilian (b) (modifed from Xu Xueyi et al., 2009)2. 地质背景
研究区位于甘肃省肃北县一带,构造上处于南祁连造山带西北缘,靠近中、南祁连之间的党河南山断裂。酸性侵入岩主要分布在研究区北部与南部,出露大面积早古生代花岗岩,岩性包括花岗岩、花岗闪长岩与石英闪长岩。区内出露地层有奥陶系、志留系、泥盆系、石炭系、侏罗系、古近系和第四系,其中以奥陶系与志留系为主(图1a)。奥陶系由下及上分别为吾力沟组、盐池湾组与多索曲组。早奥陶世吾力沟组主要由双峰式火山岩、凝灰岩、灰岩、中酸性火山岩夹硅质岩等组成,顶部沉积大套的中—厚层状泥晶灰岩,火山岩及火山碎屑岩较为发育;中奥陶世盐池湾组以粉砂岩与泥岩为主,按不同比例重复组合,夹少量碳酸盐岩;晚奥陶世多索曲组整合于盐池湾组之上,主要由火山熔岩与火山碎屑岩为主,地层顶部以灰紫色长石杂砂岩为特征。原志留系巴龙贡噶尔组呈北西向带状展布,其北部与奥陶系多索曲组呈断层接触,南部被第四系覆盖。通过野外地质调查工作发现区内该地层可分为砂岩、火山岩与片岩3个岩性段,分别对应志留系巴龙贡噶尔组、新元古代天峻组与拐杖山岩群(计波等, 2018; 王军等, 2019; 王磊等, 2019)。志留系巴龙贡噶尔组主要为变质砂岩、粉砂岩和板岩,局部夹凝灰岩,细粒沉积物互层明显,显示复理石韵律特征,与下伏新元古代天峻组火山岩呈断层接触关系;新元古代天峻组以中基性变火山熔岩与凝灰岩为主,后期遭受变质变形作用,与片岩段断层接触;拐杖山岩群呈北西向分布与区域构造线基本一致,为一套低绿片岩相变质岩系,主要由石英片岩、绢云石英片岩、黑云斜长石英片岩等组成,劈理与褶皱发育,普遍见绢云母化与绿帘石化,片岩夹层中局部见灰绿色变玄武质火山岩与凝灰岩。最新的1∶5万当金山幅区调查
3 将党河南山哈拉乔克以南的原巴龙贡噶尔组划为拐杖山岩群,研究区内的新元古代地层可能为其向东延伸的部分。3. 采样位置及岩石特征
拐杖山岩群原岩为一套海相细粒碎屑沉积物,以石英片岩为主(图2a),夹少量玄武质火山岩(图2b)。在火山岩中采集了7件玄武岩地球化学样品和1件年代学样品(地理坐标:39°06′27″N, 95°20′02″E),采样位置如图1。样品均采自基岩出露较好的部位,样品呈块状,岩石新鲜。
玄武岩呈灰绿色,块状构造,主要由斜长石、暗色矿物以及隐晶质组成。岩石中斜长石呈他形针状,边界多不清楚,具蚀变与碳酸盐化特征,以局部格架状或流动似定向方式排列分布于隐晶质中。暗色矿物呈半自形晶,杂乱或填隙状分布。隐晶质分布于长石针状晶体之间,含少量方解石与褐铁矿。
4. 测试分析方法
主量元素、微量元素、稀土元素以及LA−ICP−MS锆石微区U−Pb年龄测定均由中国地质调查局西安地质调查中心 自然资源部岩浆作用成矿与找矿重点实验室分析测试。主量元素分析仪器为荷兰帕纳科公司Axios 4.0kw顺序式−X射线荧光光谱仪(XRF),分析精度优于5%。微量和稀土元素分析仪器为美国热电公司SeriesⅡ型电感耦合等离子体质谱仪(ICP−MS)测定,分析精度优于5%~10%。
锆石分选在河北省地质调查研究院完成,样品经常规的粉碎和重选,分选出纯度较高的锆石,然后在双目镜下经人工挑选出纯度在99%以上的锆石样品,用环氧树脂固定,待其充分固化后抛光至锆石露出核部,进行锆石CL显微图像分析。锆石U−Pb同位素测定的激光剥蚀系统为GeoLas Pro,ICP−MS为Agilent 7700x。激光剥蚀过程中采用氦气作载气、氩气为补偿气以调节灵敏度,二者在进入ICP之前通过一个T型接头混合。每个时间分辨分析数据包括大约10 s的空白信号和40 s的样品信号。锆石年龄采用国际标准锆石91500作为外标标准物质,元素含量采用NIST SRM610作为外标,29Si作为内标。对分析数据的离线处理(包括对样品和空白信号的选择、仪器灵敏度漂移校正、元素含量及U−Th−Pb同位素比值和年龄计算)采用软件Glitter 4.4完成,详细仪器参数和测试过程可参考李艳广等(2015)。
5. 分析结果
5.1 锆石分析结果
用于U−Pb定年的锆石均无色,透明,呈长柱状或不规则粒状,自形程度不一,岩浆振荡环带清楚,部分具继承核,测点位置尽量避开锆石内部的裂隙、包裹体和重结晶的部分。晶形相对完整的锆石颗粒长轴以50~160 μm为主,短轴以30~80 μm为主,长宽比为1.5~2.5。锆石U−Pb分析获得有效测点24个,分析结果见表1。阴极发光图像(图3)显示多数锆石显环带结构,少数为无核结构。Th含量变化为21×10−6~496×10−6,U含量变化为27×10−6~738×10−6,Th/U比值0.1~4.2,平均值0.9,绝大多数大于0.4,且Th、U之间具有良好的正相关关系,表明以岩浆成因锆石为主。锆石测点年龄主要分布在779~795 Ma,1112~1191 Ma以及1850~2508 Ma。1112~1191 Ma与1850~2508 Ma区间的测点分别有4个和3个,属于捕获的古老岩浆锆石的年龄信息,其形成与祁连陆块地区发育的元古宙岩浆事件以及古老基底有关(马旭东等, 2006; Mattinson et al., 2006, 2007, 2009; Zhang et al., 2006)。在779~795 Ma区间的测点有17个,在U−Pb谐和图中成群集中分布于谐和线上,206Pb/238U加权平均年龄为(786.6±5.8) Ma(MSWD=0.15)(图4b),Th/U比值范围为0.3~1.7,明显高于变质成因锆石(<0.1),而与岩浆成因的锆石一致(>0.4),表明这些锆石为同期岩浆成因。因此,206Pb/238U加权平均年龄代表了该玄武岩的形成年龄,显示地层形成时代为新元古代早期。
表 1 拐杖山岩群玄武岩锆石LA−ICP−MS U−Pb年龄Table 1. LA−ICP−MS zircon U−Pb ages of basalt in the Guaizhangshan Group测点号 含量/10−6 Th/U 同位素比值 年龄/Ma Pb U Th 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ PMJ−17−01 160 738 78 0.1 0.1652 0.0031 10.8258 0.1964 0.4756 0.0058 2509 31 2508 17 2508 26 PMJ−17−02 46 87 35 0.4 0.0660 0.0028 1.1739 0.0483 0.1291 0.0019 806 86 789 23 783 11 PMJ−17−03 158 230 258 1.1 0.0707 0.0046 1.2754 0.0814 0.1309 0.0026 949 129 835 36 793 15 PMJ−17−04 33 174 106 0.6 0.0639 0.0028 1.1396 0.0480 0.1294 0.0019 738 89 772 23 785 11 PMJ−17−05 406 455 450 1.0 0.0668 0.0013 1.2004 0.0234 0.1304 0.0014 831 41 801 11 790 8 PMJ−17−06 45 63 25 0.4 0.1610 0.0035 10.3782 0.2175 0.4677 0.0061 2466 36 2469 19 2473 27 PMJ−17−07 21 252 302 1.2 0.0680 0.0030 1.2215 0.0518 0.1304 0.0019 867 88 811 24 790 11 PMJ−17−08 159 734 76 0.1 0.0773 0.0019 2.0370 0.0480 0.1912 0.0023 1129 47 1128 16 1128 12 PMJ−17−09 418 460 452 1.0 0.113 0.0018 5.1850 0.0794 0.3321 0.0036 1853 28 1850 13 1849 17 PMJ−17−10 62 119 496 4.2 0.0768 0.0033 1.9918 0.0838 0.1882 0.0028 1115 84 1113 28 1112 15 PMJ−17−11 42 58 21 0.4 0.0727 0.0056 1.3080 0.0977 0.1305 0.0028 1006 148 849 43 791 16 PMJ−17−12 48 94 137 1.5 0.0672 0.0028 1.2144 0.0500 0.1312 0.0019 843 85 807 23 795 11 PMJ−17−13 45 86 85 1.0 0.0659 0.0040 1.1792 0.0704 0.1298 0.0023 805 123 791 33 786 13 PMJ−17−14 116 223 238 1.1 0.0647 0.0066 1.1614 0.1157 0.1302 0.0030 765 200 783 54 789 17 PMJ−17−15 133 316 254 0.8 0.0652 0.0022 1.1623 0.0374 0.1294 0.0016 780 68 783 18 784 9 PMJ−17−16 107 397 145 0.4 0.0651 0.0039 1.1525 0.0675 0.1285 0.0022 777 121 778 32 779 13 PMJ−17−17 52 69 89 1.3 0.0653 0.0043 1.1597 0.0739 0.1289 0.0024 783 131 782 35 782 14 PMJ−17−18 83 104 68 0.7 0.0775 0.0013 2.1672 0.0360 0.2028 0.0022 1135 34 1171 12 1191 12 PMJ−17−19 19 116 62 0.5 0.0652 0.0059 1.1574 0.1026 0.1287 0.0031 782 180 781 48 781 18 PMJ−17−20 385 290 101 0.3 0.0674 0.0043 1.1931 0.0743 0.1285 0.0023 849 127 797 34 779 13 PMJ−17−21 41 80 99 1.2 0.0786 0.0027 2.1432 0.0710 0.1979 0.0027 1162 66 1163 23 1164 14 PMJ−17−22 14 27 45 1.7 0.0655 0.0045 1.1743 0.0791 0.1302 0.0025 789 138 789 37 789 14 PMJ−17−23 56 108 80 0.7 0.0652 0.0063 1.1598 0.1103 0.1290 0.0031 781 192 782 52 782 18 PMJ−17−24 22 223 175 0.8 0.0653 0.0038 1.1693 0.0668 0.1299 0.0022 784 118 786 31 787 13 5.2 主量元素
本文所获得的新元古代火山岩的地球化学数据见表2,从表中可以看出样品火山岩为基性岩,SiO2含量在48.09%~50.97%,TiO2含量为1.34%~2.55%。MgO含量为5.78%~7.11%,Mg#为48.58~54.90,平均值51.77,低于原生岩浆范围(Mg#=68~75; Wilson, 1989),表明岩浆演化过程中发生了明显的分离结晶作用。由于遭受区域变质作用导致烧失量较高,LOI可达3.18%~4.46%,为正确确定岩石类型,采用抗蚀变Nb/Y – SiO2图解进行岩石分类判别(图5a),所有样品均无一例外的落在亚碱性玄武岩区域,并且玄武质熔岩显示拉斑系列特征(图5b)。
表 2 拐杖山岩群玄武岩主量元素(%)和微量、稀土元素(10−6)分析结果Table 2. Major (%), trace and rare earth elements concentrations (10−6) of basalt in the Guaizhangshan Group样号 PMJ−17−1h PMJ−17−2h PMJ−17−3h PMJ−17−4h PMJ−17−5h PMJ−17−6h PMJ−17−7h SiO2 48.53 50.97 48.2 49.11 49.88 49.81 48.09 Al2O3 15.4 13.66 11.92 13.8 14.0 13.51 15.73 Fe2O3 3.24 2.64 3.20 2.85 3.40 2.84 3.29 FeO 8.23 7.49 8.27 7.29 7.04 7.61 7.37 CaO 8.04 8.72 11.46 10.79 10.36 10.54 9.29 MgO 5.95 5.78 7.03 6.05 5.92 6.36 7.11 K2O 0.19 0.15 0.14 0.18 0.17 0.15 0.27 Na2O 4.14 4.46 2.78 3.72 3.64 3.46 3.03 TiO2 1.34 1.56 2.55 1.88 1.98 1.99 1.38 P2O5 0.19 0.18 0.12 0.16 0.13 0.12 0.19 MnO 0.19 0.19 0.22 0.18 0.18 0.20 0.18 LOI 4.46 4.10 3.98 3.90 3.18 3.31 4.02 Total 99.9 99.9 99.87 99.91 99.88 99.9 99.95 Mg# 48.58 50.85 52.67 52.04 50.89 52.47 54.90 Pb 15.3 19.3 27.3 16.9 12.4 19.8 23.5 Zn 80.8 83.8 97.5 91.5 79.9 90.4 104 Cr 95.8 156 184 106 132 167 114 Ni 35.4 25.4 31.5 33.9 27.4 28.4 89.0 Co 37.8 35.0 41.7 42.4 38.0 40.8 52.3 Li 24.8 18.4 15.3 14.0 13.8 15.1 45.6 Rb 6.21 3.23 2.03 2.74 2.96 2.40 25.1 Cs 0.19 0.12 0.12 0.12 0.09 0.11 1.02 Sr 355 287 330 409 416 371 372 Ba 136 94.4 82.0 96.0 93.8 89.5 165 V 284 363 507 405 411 434 231 Sc 32.6 40.9 54.7 26.0 40.1 34.8 29.7 Nb 6.19 7.85 7.43 4.99 5.42 5.59 5.44 Ta 0.38 0.49 0.47 0.30 0.35 0.33 0.39 Zr 240 318 207 170 182 186 99.9 Hf 5.60 8.77 4.87 4.01 4.48 4.30 2.95 Be 0.69 0.98 1.03 0.78 0.70 0.81 0.84 U 0.40 0.50 0.38 0.29 0.30 0.34 0.34 Th 1.86 2.46 1.50 0.90 1.28 1.12 2.70 La 25.8 32.4 21.9 15.1 18.8 16.8 14.2 Ce 57.1 71.0 51.8 36.4 42.9 38.6 36.6 Pr 7.16 9.22 6.85 4.82 5.66 5.30 5.13 Nd 28.3 35.7 28.0 19.2 22.3 20.3 22.1 Sm 6.48 8.69 6.51 4.58 5.10 4.85 5.16 Eu 2.00 2.31 2.01 1.64 1.78 1.69 1.70 Gd 6.56 8.91 6.80 4.92 5.29 5.02 4.95 Tb 1.11 1.49 1.15 0.84 0.91 0.88 0.80 Dy 6.69 9.03 6.88 5.05 5.30 5.20 4.72 Ho 1.37 1.95 1.37 1.00 1.10 1.07 0.99 Er 4.09 5.54 3.91 2.97 3.10 3.00 2.63 Tm 0.58 0.82 0.58 0.45 0.48 0.46 0.40 Yb 4.10 5.36 3.96 2.88 3.26 3.08 2.55 Lu 0.58 0.79 0.57 0.44 0.47 0.44 0.39 Y 39.4 53.0 41.2 26.9 31.4 30.2 27.4 ∑REE 151.92 193.21 142.29 100.29 116.45 106.69 102.32 LREE 126.84 159.32 117.07 81.74 96.54 87.54 84.89 HREE 25.08 33.89 25.22 18.55 19.91 19.15 17.43 (La/Yb)N 4.51 4.34 3.97 3.76 4.14 3.91 3.99 δEu 0.93 0.80 0.92 1.05 1.04 1.04 1.01 注:Mg#=(MgO/40)/(MgO/40+FeOT/72+MnO/71)%。 Figure 5. SiO2 vs. Nb/Y diagram (a) (after Winchester and Floyd, 1977) and FeOT/MgO vs. SiO2 diagram (b) (after Miyashiro, 1975) of basalt in the Guaizhangshan Group5.3 微量元素
玄武岩稀土总量(∑REE)为100.29×10−6~193.21×10−6,平均为130.45×10−6,轻稀土元素(LREE)轻度富集,LREE/HREE范围在4.41~5.06,(La/Yb)N=3.76~4.51,轻重稀土分异明显。δEu=0.80~1.05,平均值0.97,无明显的Eu异常,显示斜长石分离结晶作用不明显。在球粒陨石标准化稀土元素配分图(图6a)中,整体表现为右倾型的配分模式,轻重稀土分异程度介于N−MORB与OIB之间。在原始地幔标准化微量元素蛛网图(图6b)中,样品微量元素具有相似的地球化学特征,大离子亲石元素(LILE)Ba、Th、U相对富集,Pb强富集,高场强元素(HFSE)Nb、Ta和Ti表现为亏损。其中Nb/Ta比值为14.0~16.9,略低于OIB和原始地幔(分别为17.78,17.5±2.0;Sun and McDonough, 1989)。
图 6 拐杖山岩群玄武岩球粒陨石标准化稀土元素配分图(a)和原始地幔标准化微量元素蛛网图(b)Figure 6. Chondrite−normalized REE patterns (a) and primitive mantal−normalized trace element spidergram (b) of basalts in the Guaizhangshan Group(normalization values after Sun and McDonough, 1989; data of Etendeka flood basalts in Namibia after Ewart et al., 1998, 2004)6. 讨 论
6.1 时代意义
前人采用了区域地层对比与碎屑锆石U−Pb测年等手段来限定拐杖山岩群的地层时代。
赵生贵等(1996)对当金山口—后塘南山一带中等变质地层进行调查研究后认为该地层变质变形程度较高,与典型的巴龙贡噶尔组明显不同,因此划归至志留系不妥,建议将其归为元古界;王国华等(2016)在拜兴沟地区原巴龙贡噶尔组中发现一套中浅变质、强变形的岩石地层,以石英片岩与变粒岩为主,与上覆早奥陶世盐池湾组断层接触,命名为“哈尔达乌片岩(Pt2-3Hsch)”,综合区域地质背景分析将其时代划归中—新元古代;秦宇(2018)在钦果嘎吉和塔塔楞地区原巴龙贡噶尔组片岩分布地区中分别获得石英斜长片岩和黑云母斜长石英片岩最年轻年龄峰值为~715 Ma与741 Ma,并在夏拉诺尔西北部识别出被第四系覆盖的辉长岩岩株,成岩年龄为(738±11)Ma;甘肃省地质调查院
3 在当金山地区开展了1∶5万区域地质调查,在测区东南部拐杖山岩群中采集到斜长角闪岩(原岩为碎屑沉积岩)年代学样品,获得重复性较好的最小年龄为~800 Ma,但王军等(2019)认为其中~1663 Ma和~963 Ma两个峰值年龄分别代表岩石地层的初始年龄和沉积结束年龄,时代划归中—新元古代;Li et al.(2019)根据大量的碎屑锆石年代学研究将南祁连原巴龙贡噶尔组划分为时代不同的两个地层单元,下部新元古代地层沉积开始于720 Ma左右,形成于Rodinia超大陆裂谷时期,而上部地层的沉积则要年轻得多(< 560 Ma),是由冈瓦纳超级扇系统在冈瓦纳邻近大陆架上形成的。根据王军等(2019)与Li et al.(2019)在当金山一带测得的年代学结果,该地区原巴龙贡噶尔组的最大沉积时代应在800~720 Ma。本次研究在野外调查的基础上,在拐杖山岩群中采集了玄武岩样品(PMJ-17)并进行了锆石U−Pb测年,获得206Pb/238U加权平均年龄为(786.6±5.8)Ma(MSWD=0.15),可作为玄武岩的喷发年龄。该测年结果与前人的研究结果较为吻合,据此推断党河南山红庙沟一带的拐杖山岩群的形成时代应厘定为新元古代早期。6.2 岩石成因
本次研究样品样品Mg#低于原生岩浆65的参考值(Olsen, 1995),相容元素Cr(96×10−6~184×10−6)和Ni(25×10−6~89×10−6)含量也远低于原生玄武岩浆岩范围(Cr:300×10−6~500×10−6, Ni:300×10−6~400×10−6;Hess, 1992),并且玄武岩锆石U−Pb样品中出现了较多元古宙的捕获锆石,表明在玄武岩的形成过程中可能捕获了陆壳物质,或许受到了地壳不同程度的混染。地壳物质通常具有高La/Nb、高Ba/Nb和低La/Ba值的特点(Wedepohl, 1995),如果幔源玄武岩浆遭受到大陆地壳物质的混染,会增加SiO2、K2O、Rb、Ba、Zr、Th等氧化物或元素的丰度(Baker et al., 1997; McDonald et al., 2001),岩浆中的不相容元素如La或Ba就会相对于Nb明显增高,从而具有低Nb/La、低La/Ba的特点。因此,利用稀土元素和高场强元素讨论同化混染是比较可靠的。非常高的原始地幔标准化Th/Nb值(> > 1)(Saunders et al., 1992)和Nb/La(Kieffer et al., 2004)可以用来判断地壳物质的混染程度。拐杖山岩群玄武岩(Th/Nb)N比值为1.15~4.16,平均值2.31,而(Nb/La)N比值为0.23~0.37,平均值0.30,远小于1,Nb/La比值为0.24~0.38,与没有遭受岩石圈混染的(0.91~5.07)大陆玄武质熔岩(夏林圻等, 2007; Xia, 2014)也明显不同。这些受到地壳混染的岩石具有与非洲东南部纳米比亚大陆溢流玄武岩(受陆壳混染)以及朱龙关群大陆溢流玄武岩(受陆壳混染)(夏林圻等,2016)相似的稀土元素蛛网图与微量元素标准化配分型式图(图6),都具有一致的Nb、Ta亏损和大离子亲石元素Ba、Th、U等相对富集。而其在具有高La/Nb值(2.61~4.17)的同时,也具有较高的La/Ba值(0.09~0.34),可能与成岩后期遭受蚀变导致Ba含量相对较高低有关,这与野外观察到的蚀变特征相符。因此,党河南山地区拐杖山岩群玄武岩是遭受陆壳物质混染的地幔源区玄武岩。
6.3 新元古代构造环境
中国的新元古代中—晚期裂谷火山和岩浆活动可以被划分为2个阶段:第一阶段为877~604 Ma,主要发育于阿拉善、祁连、柴达木、华南及相邻陆块中;第二阶段为773~540 Ma,主要育于塔里木克拉通及相邻陆块中(Xia et al., 2012; 夏林圻等, 2016)。现有研究表明,祁连地块及其周缘地体在经历了新元古代早期Rodinia超大陆的聚合之后,于新元古代中—晚期发生裂解(800~750 Ma)(史仁灯等, 2004; 董国安等, 2007; Song et al., 2010; Tung et al., 2013),形成了一系列新元古代岩浆岩。祁连地块新元古代中—晚期(848~604 Ma)主要发育裂谷火山岩系,包括有分布于祁连陆块西北部的朱龙关群和多若诺尔火山岩系(738~604 Ma),分布于祁连陆块东部的兴龙山群火山岩(824~713 Ma)和祁连陆块南部的全吉群裂谷火山岩(~800 Ma)(Xia et al., 2012; 夏林圻等, 2016)。此外,在南祁连夏拉诺尔与天峻县一带发现了新元古代晚期大陆裂谷背景下形成的火山岩(秦宇, 2018; 白春东等, 2019),党河南山科克巴斯陶一带发现了具有板内洋岛特征的新元古代晚期玄武岩(王磊等, 2019)。
如前所述,拐杖山岩群玄武岩原始地幔标准化微量元素蛛网图中Nb、Ta出现异常是由于受到不同程度的地壳混染作用影响。夏林圻等(2016)在研究祁连山新元古代裂谷玄武质熔岩时发现,朱龙关群基性火山岩中存在受到地壳或/和陆下岩石圈混染的大陆玄武岩,其具有较低的Nb/La比值,明显亏损Nb、Ta、P、Zr、Hf和Ti,并且该类玄武岩在采用Nb、Ta或Ti等作为判别因子的构造环境地球化学判别图解时,会向低Nb、低Ta或Ti的方向迁移,落入岛弧玄武岩成分域。本次研究的玄武岩样品在使用Nb、Ta元素相关的构造判别图解中几乎全部样品落入岛弧拉斑玄武岩的区域之中(图7a、b)。因此,利用稀土元素与高场强元素讨论受到地壳混染的玄武岩构造环境时,尽量使用不含Nb、Ta元素的图解,这样可以避免亏损Nb、Ta带来的不确定性。在Zr−Zr/Y图解中(图7c),玄武质熔岩样品全部落在板内玄武岩区域,进一步利用Ti/1000−V图解(图7d),样品显示了洋中脊玄武岩和大陆溢流玄武岩的特征。同时,高场强元素亏损特征不同于洋岛玄武岩(OIB),说明火山岩应产于大陆板内。研究区拐杖山岩群中片岩原岩以泥岩与细粒杂砂岩为主,属低密度浊流沉积,具有水下扇中扇—外扇的沉积特征,可能为陆内裂谷化早期裂谷盆地快速沉降形成的深水沉积产物(计波等, 2018)。此外,南祁连地块在959~780 Ma时期全吉地块和中祁连地块存在良好的亲缘性,并且在780 Ma之后从扬子板块裂离,作为微陆块碎片向古特提斯洋移动(Yan et al., 2015, 2019;Li et al., 2018;Fu et al., 2019)并对应该时期的Rodinia超大陆裂解事件,南祁连地区的新元古代火山岩是对该事件重要的岩浆事件记录,响应了全球新元古代Rodinia超大陆裂解事件。
7. 结 论
(1)本文在南祁连党河南山地区拐杖山岩群中新发现了玄武岩,LA−ICP−MS锆石U−Pb定年显示其形成时代为(786.6±5.8)Ma,表明该地层形成于新元古代早期。
(2)拐杖山岩群中的火山岩属于亚碱性拉斑火山岩系列,是遭受陆壳物质混染的地幔源区玄武岩。
(3)研究区玄武岩的环境判别指示南祁连地区在新元古代处于大陆裂谷环境,响应了全球新元古代Rodinia超大陆裂解事件。
1 ➊青海省地质局青海第一区测队. 1976. 中华人民共和国1∶20万下环仓幅区域地质调查报告[R]. 西宁: 青海省地质局.2 ➋陕西地矿第一地质队. 2017. 中华人民共和国1∶5万卡克图敖包幅区域地质矿产调查报告[R]. 咸阳: 陕西地矿第一地质队.3 ➌甘肃省地质调查院. 2017. 中华人民共和国1∶5万当金山口幅区域地质调查报告[R]. 兰州: 甘肃省地质调查院. -
图 1 祁连陆块构造位置与地质略图(a)(据夏林圻等, 2016)和南祁连党河南山地区地质简图(b)(据徐学义等, 2009修改)
Figure 1. Structural location and geological sketch map of Qilian block (a) (after Xia Linqi et al., 2016), regional geological map of the Danghe mountain in northwest of South Qilian (b) (modifed from Xu Xueyi et al., 2009)
图 5 拐杖山岩群玄武岩SiO2−Nb/Y图解(a)(据Winchester and Floyd, 1977)和FeOT/MgO−SiO2图解(b)(据Miyashiro, 1975)
Figure 5. SiO2 vs. Nb/Y diagram (a) (after Winchester and Floyd, 1977) and FeOT/MgO vs. SiO2 diagram (b) (after Miyashiro, 1975) of basalt in the Guaizhangshan Group
图 6 拐杖山岩群玄武岩球粒陨石标准化稀土元素配分图(a)和原始地幔标准化微量元素蛛网图(b)
(标准化值据Sun and McDonough, 1989;纳米比亚Etendeka溢流玄武岩引自Ewart et al., 1998, 2004)
Figure 6. Chondrite−normalized REE patterns (a) and primitive mantal−normalized trace element spidergram (b) of basalts in the Guaizhangshan Group
(normalization values after Sun and McDonough, 1989; data of Etendeka flood basalts in Namibia after Ewart et al., 1998, 2004)
表 1 拐杖山岩群玄武岩锆石LA−ICP−MS U−Pb年龄
Table 1 LA−ICP−MS zircon U−Pb ages of basalt in the Guaizhangshan Group
测点号 含量/10−6 Th/U 同位素比值 年龄/Ma Pb U Th 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ PMJ−17−01 160 738 78 0.1 0.1652 0.0031 10.8258 0.1964 0.4756 0.0058 2509 31 2508 17 2508 26 PMJ−17−02 46 87 35 0.4 0.0660 0.0028 1.1739 0.0483 0.1291 0.0019 806 86 789 23 783 11 PMJ−17−03 158 230 258 1.1 0.0707 0.0046 1.2754 0.0814 0.1309 0.0026 949 129 835 36 793 15 PMJ−17−04 33 174 106 0.6 0.0639 0.0028 1.1396 0.0480 0.1294 0.0019 738 89 772 23 785 11 PMJ−17−05 406 455 450 1.0 0.0668 0.0013 1.2004 0.0234 0.1304 0.0014 831 41 801 11 790 8 PMJ−17−06 45 63 25 0.4 0.1610 0.0035 10.3782 0.2175 0.4677 0.0061 2466 36 2469 19 2473 27 PMJ−17−07 21 252 302 1.2 0.0680 0.0030 1.2215 0.0518 0.1304 0.0019 867 88 811 24 790 11 PMJ−17−08 159 734 76 0.1 0.0773 0.0019 2.0370 0.0480 0.1912 0.0023 1129 47 1128 16 1128 12 PMJ−17−09 418 460 452 1.0 0.113 0.0018 5.1850 0.0794 0.3321 0.0036 1853 28 1850 13 1849 17 PMJ−17−10 62 119 496 4.2 0.0768 0.0033 1.9918 0.0838 0.1882 0.0028 1115 84 1113 28 1112 15 PMJ−17−11 42 58 21 0.4 0.0727 0.0056 1.3080 0.0977 0.1305 0.0028 1006 148 849 43 791 16 PMJ−17−12 48 94 137 1.5 0.0672 0.0028 1.2144 0.0500 0.1312 0.0019 843 85 807 23 795 11 PMJ−17−13 45 86 85 1.0 0.0659 0.0040 1.1792 0.0704 0.1298 0.0023 805 123 791 33 786 13 PMJ−17−14 116 223 238 1.1 0.0647 0.0066 1.1614 0.1157 0.1302 0.0030 765 200 783 54 789 17 PMJ−17−15 133 316 254 0.8 0.0652 0.0022 1.1623 0.0374 0.1294 0.0016 780 68 783 18 784 9 PMJ−17−16 107 397 145 0.4 0.0651 0.0039 1.1525 0.0675 0.1285 0.0022 777 121 778 32 779 13 PMJ−17−17 52 69 89 1.3 0.0653 0.0043 1.1597 0.0739 0.1289 0.0024 783 131 782 35 782 14 PMJ−17−18 83 104 68 0.7 0.0775 0.0013 2.1672 0.0360 0.2028 0.0022 1135 34 1171 12 1191 12 PMJ−17−19 19 116 62 0.5 0.0652 0.0059 1.1574 0.1026 0.1287 0.0031 782 180 781 48 781 18 PMJ−17−20 385 290 101 0.3 0.0674 0.0043 1.1931 0.0743 0.1285 0.0023 849 127 797 34 779 13 PMJ−17−21 41 80 99 1.2 0.0786 0.0027 2.1432 0.0710 0.1979 0.0027 1162 66 1163 23 1164 14 PMJ−17−22 14 27 45 1.7 0.0655 0.0045 1.1743 0.0791 0.1302 0.0025 789 138 789 37 789 14 PMJ−17−23 56 108 80 0.7 0.0652 0.0063 1.1598 0.1103 0.1290 0.0031 781 192 782 52 782 18 PMJ−17−24 22 223 175 0.8 0.0653 0.0038 1.1693 0.0668 0.1299 0.0022 784 118 786 31 787 13 表 2 拐杖山岩群玄武岩主量元素(%)和微量、稀土元素(10−6)分析结果
Table 2 Major (%), trace and rare earth elements concentrations (10−6) of basalt in the Guaizhangshan Group
样号 PMJ−17−1h PMJ−17−2h PMJ−17−3h PMJ−17−4h PMJ−17−5h PMJ−17−6h PMJ−17−7h SiO2 48.53 50.97 48.2 49.11 49.88 49.81 48.09 Al2O3 15.4 13.66 11.92 13.8 14.0 13.51 15.73 Fe2O3 3.24 2.64 3.20 2.85 3.40 2.84 3.29 FeO 8.23 7.49 8.27 7.29 7.04 7.61 7.37 CaO 8.04 8.72 11.46 10.79 10.36 10.54 9.29 MgO 5.95 5.78 7.03 6.05 5.92 6.36 7.11 K2O 0.19 0.15 0.14 0.18 0.17 0.15 0.27 Na2O 4.14 4.46 2.78 3.72 3.64 3.46 3.03 TiO2 1.34 1.56 2.55 1.88 1.98 1.99 1.38 P2O5 0.19 0.18 0.12 0.16 0.13 0.12 0.19 MnO 0.19 0.19 0.22 0.18 0.18 0.20 0.18 LOI 4.46 4.10 3.98 3.90 3.18 3.31 4.02 Total 99.9 99.9 99.87 99.91 99.88 99.9 99.95 Mg# 48.58 50.85 52.67 52.04 50.89 52.47 54.90 Pb 15.3 19.3 27.3 16.9 12.4 19.8 23.5 Zn 80.8 83.8 97.5 91.5 79.9 90.4 104 Cr 95.8 156 184 106 132 167 114 Ni 35.4 25.4 31.5 33.9 27.4 28.4 89.0 Co 37.8 35.0 41.7 42.4 38.0 40.8 52.3 Li 24.8 18.4 15.3 14.0 13.8 15.1 45.6 Rb 6.21 3.23 2.03 2.74 2.96 2.40 25.1 Cs 0.19 0.12 0.12 0.12 0.09 0.11 1.02 Sr 355 287 330 409 416 371 372 Ba 136 94.4 82.0 96.0 93.8 89.5 165 V 284 363 507 405 411 434 231 Sc 32.6 40.9 54.7 26.0 40.1 34.8 29.7 Nb 6.19 7.85 7.43 4.99 5.42 5.59 5.44 Ta 0.38 0.49 0.47 0.30 0.35 0.33 0.39 Zr 240 318 207 170 182 186 99.9 Hf 5.60 8.77 4.87 4.01 4.48 4.30 2.95 Be 0.69 0.98 1.03 0.78 0.70 0.81 0.84 U 0.40 0.50 0.38 0.29 0.30 0.34 0.34 Th 1.86 2.46 1.50 0.90 1.28 1.12 2.70 La 25.8 32.4 21.9 15.1 18.8 16.8 14.2 Ce 57.1 71.0 51.8 36.4 42.9 38.6 36.6 Pr 7.16 9.22 6.85 4.82 5.66 5.30 5.13 Nd 28.3 35.7 28.0 19.2 22.3 20.3 22.1 Sm 6.48 8.69 6.51 4.58 5.10 4.85 5.16 Eu 2.00 2.31 2.01 1.64 1.78 1.69 1.70 Gd 6.56 8.91 6.80 4.92 5.29 5.02 4.95 Tb 1.11 1.49 1.15 0.84 0.91 0.88 0.80 Dy 6.69 9.03 6.88 5.05 5.30 5.20 4.72 Ho 1.37 1.95 1.37 1.00 1.10 1.07 0.99 Er 4.09 5.54 3.91 2.97 3.10 3.00 2.63 Tm 0.58 0.82 0.58 0.45 0.48 0.46 0.40 Yb 4.10 5.36 3.96 2.88 3.26 3.08 2.55 Lu 0.58 0.79 0.57 0.44 0.47 0.44 0.39 Y 39.4 53.0 41.2 26.9 31.4 30.2 27.4 ∑REE 151.92 193.21 142.29 100.29 116.45 106.69 102.32 LREE 126.84 159.32 117.07 81.74 96.54 87.54 84.89 HREE 25.08 33.89 25.22 18.55 19.91 19.15 17.43 (La/Yb)N 4.51 4.34 3.97 3.76 4.14 3.91 3.99 δEu 0.93 0.80 0.92 1.05 1.04 1.04 1.01 注:Mg#=(MgO/40)/(MgO/40+FeOT/72+MnO/71)%。 -
[1] Bai Chundong, Zhuan Shaopeng, Mao Zhifang, Chen Yuanyuan, Li Jie. 2019. LA−ICP−MS Zircon U−Pb ages, geochemical characteristics and geotectonic significance of the metamorphosed volcanic rocks in Neoproterozoic Balongonggaer Formation in Tianjun County, Southern Qilian Mountain[J]. Geological Review, 65(3): 755−771 (in Chinese with English abstract).
[2] Baker J A, Menzies M A, Thirlwall M F, Macpherson C G. 1997. Petrogenesis of Quaternary intraplate volcanism, Sana’a, Yemen: Implications for plume–lithosphere interaction and polybaric melt hybridization[J]. Journal of Petrology, 38(10): 1359−1390. doi: 10.1093/petroj/38.10.1359
[3] Dong Guo'an, Yang Huaiyi, Yang Hongyi, Liu Dunyi, Zhang Jianxin, Wan Yusheng, Zeng Jianyuan. 2007. Zircon SHRIMP U–Pb chronology of Precambrian basement in the Qilian block and its geological significance[J]. Chinese Science Bulletin, 52(13): 1572−1585 (in Chinese). doi: 10.1360/csb2007-52-13-1572
[4] Du Yuansheng, Zhu Jie, Gu Songzhu. 2006. Sedimentary geochemistry and tectonic significance of Ordovician cherts in Sunan, North Qilian Mountains[J]. Earth Science——Journal of China University of Geosciences, 31(1): 101−109 (in Chinese with English abstract).
[5] Ewart A, Marsh J S, Milner S C, Duncan A R, Kamber B S, Armstrong R A. 2004. Petrology and geochemistry of Early Cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia. Part 1: Introduction, mafic lavas and re–evaluation of mantal source components[J]. Journal of Petrology, 45(1): 59−105. doi: 10.1093/petrology/egg083
[6] Ewart A, Milner S C, Armstrong R A, Dungan A R. 1998. Etendeka volcanism of the Goboboseb mountains and Messum igneous complex, Namibia. Part Ⅰ: Geochemical evidence of Early Cretaceous Tristan plum melts and the role of crustal contamination in the Parana–Etendeka CFB[J]. Journal of Petrology, 39(2): 191−225. doi: 10.1093/petroj/39.2.191
[7] Fan Guangming, Lei Dongning. 2007. Precise timing and significance of Caledonian structural deformation Chronology in Southeast Qilian[J]. Earth Science— Journal of China University of Geosciences, 32(1): 39−44 (in Chinese with English abstract).
[8] Fan Xinxiang, Kong Weiqiong, Yang Zhenxi, Zhao Jichang, Li Yuxing. 2020. U–Pb chronology, geochemical characteristics and petrogenesis of the Chelugou pluton in the western part of North Qilian orogenic belt[J]. Geology in China, 47(3): 755−766 (in Chinese with English abstract).
[9] Feng Yimin, He Shiping. 1996. Geotectonic and Orogeny in Qilian Mountains[M]. Beijing: Geological Publishing House, 1–135 (in Chinese).
[10] Fu C L, Yan Z, Guo X Q, Niu M L, Cao B, Wu Q, Li X C, Wang Z Q. 2019. Assembly and dispersal history of continental blocks within the Altun–Qilian–North Qaidam mountain belt, NW China[J]. International Geology Review, 61: 424−447. doi: 10.1080/00206814.2018.1428831
[11] Gehrels G E, Yin A, Wang X F. 2003. Detrital–zircon geochronology of the northeastern Tibetan plateau[J]. Geological Society of America Bulletin, 115(7): 881−896. doi: 10.1130/0016-7606(2003)115<0881:DGOTNT>2.0.CO;2
[12] He Shiping, Wang Hongliang, Chen Junlu, Xue Xueyi, Zhang Hongfei, Ren Guangmin, Yu Jiyuan. 2008. LA–ICP–MS U–Pb geochronology of basic dikes within Maxianshan rock group in the central Qilian Mountains and its tectonic implications[J]. Earth Science— Journal of China University of Geosciences, 33(1): 35−45 (in Chinese with English abstract). doi: 10.3799/dqkx.2008.005
[13] Hess P C. 1992. Phase equilibria constraints on the origin of ocean floor basalts[C]//Morgan J P, Blackman D K , Sinton J M (eds. ). Mantle Flow and Melt Generation at Mid–Ocean Ridges. Geophysical Monograph. Washington DC: American Geophysical Union, 67–102.
[14] Ji Bo, Yu Jiyuan, Li Xiangmin, Huang Botao, Wang Lei. 2018. On disintegration of Balonggonggaer Formation and its definition of lithostratigraphic unit from Danghenanshan Area in South Qilian—Evidence from petrology and chronology[J]. Geological Bulletin of China, 37(4): 621−633 (in Chinese with English abstract).
[15] Kieffer B, Arndt N, Lapierre H, Lapierre H, Bastien F, Bosch D, Pecher A, Yirgu G, Ayalew D, Eeis D, Jerram D A, Keller F, Meugniot C. 2004. Flood and shield basalts from Ethiopia: Magmas from the African superwell[J]. Journal of Petrology, 45(4): 793−834. doi: 10.1093/petrology/egg112
[16] Li M, Wang C, Li R S, Joseph G M, Peng Y, Zhang J H. 2019. Identifying late Neoproterozoicearly Paleozoic sediments in the South Qilian Belt, China: A peri–Gondwana connection in the northern Tibetan Plateau[J]. Gondwana Research, 76: 173−184. doi: 10.1016/j.gr.2019.06.010
[17] Li Yanguang, Wang Shuangshuang, Liu Minwu, Meng En, Wei Xiaoyan, Zhao Huibo, Jin Mengqi. 2015. U–Pb dating study of Baddeleyite by LA–ICP–MS: Technique and application[J]. Acta Geologica Sinica, 89(12): 2400−2418 (in Chinese with English abstract).
[18] Li Y L, Tong X, Zhu Y H, Li J W, Zheng J P, Brouwer F M. 2018. Tectonic affinity and evolution of the Precambrian Qilian block: Insights from petrology, geochemistry and geochronology of the Hualong Group in the Qilian Orogen, NW China[J]. Precambrian Research, 315: 179−200. doi: 10.1016/j.precamres.2018.07.025
[19] Luo Mingfei. 2010. Research on Early Paleozoic Tectonic Characters of DHNS, GS[D]. Chengdu: Chengdu University of Technology, 1–60 (in Chinese with English abstract).
[20] Ma Xudong, Chen Danling. 2006. LA–ICP–MS zircon U–Pb dating of quartz–feldspathic gneisses–the country rocks of ultra–high–pressure metamorphic rocks on the northern margin of the Qaidam basin, Northwest China[J]. Geological Bulletin of China, 25(1/2): 99−103 (in Chinese with English abstract).
[21] Mattinson C G, Menold C A, Zhang J X, Bird D K. 2007. High–and ultrahigh–pressure metamorphism in the north Qaidam and south Altyn terranes, western China[J]. International Geology Review, 49(11): 969−995. doi: 10.2747/0020-6814.49.11.969
[22] Mattinson C G, Wooden J L, Liou J G, Bird D K, Wu C L. 2006. Geochronology and tectonic significance of Middle Proterozoic granitic orthogneiss, North Qaidam HP/UHP terrane, Western China[J]. Mineralogy and Petrology, 88: 227−241. doi: 10.1007/s00710-006-0149-1
[23] Mattinson C G, Wooden J L, Zhang J X, Bird D K. 2009. Paragneiss zircon geochronology and trace element geochemistry, North Qaidam HP/UHP terrane, western China[J]. Journal of Asian Earth Science, 35(3): 298−309. doi: 10.1016/j.jseaes.2008.12.007
[24] McDonald R, Rogers N W, Fitton J G, Black S, Smith M. 2001. Plume–lithosphere interactions in the generation of the basalts of the Kenya rift, East Africa[J]. Journal of Petrology, 42: 877−900. doi: 10.1093/petrology/42.5.877
[25] Miyashiro A. 1975. Classification, characteristics and origin of ophiolites[J]. Journal of Geology, 83: 249−281. doi: 10.1086/628085
[26] Niu Guangzhi, Huang Gang, Deng Changsheng, Xu Yan, Chen Tao, Ji Chun, Li Wenjun. 2016. LA–ICP–MS zircon U–Pb ages of metamorphic volcanic rocks in Balonggonggaer Formation of south Qilian Mountain in Qinghai Province and their geological significance[J]. Geological Bulletin of China, 35(9): 1441−1447 (in Chinese with English abstract).
[27] Olsen K H. 1995. Continental Rifts: Evolution, Structure, Tectonics[M]. Amsterdam: Elsevier, 255–260.
[28] Pan Jian, Li Guiyi, Li Guangtie. 2019. Re–division of Balonggonggaer Formation in Qinghai Province and its geological significance[J]. Global Geology, 38(4): 900−909 (in Chinese with English abstract).
[29] Qin Yu. 2018. Neoproterozoic to Early Paleozoic Tectonic Evolution in the South Qilian Orogen[D]. Xi'an: Northwest University, 1–153 (in Chinese with English abstract).
[30] Saunders A D, Storey M, Kent R W, Norry M J. 1992. Consequences of plume–lithosphere interactions[J]. Geological Society, London, Special Publications, 68: 41–60.
[31] Shi Rendeng, Yang Jingsui, Wu Cailai, Wooden J. 2004. First SHRIMP dating for the Formation of the Late Sinian Yushigou ophiolite North Qilian Mountains[J]. Acta Geologica Sinica, 78(5): 649−657 (in Chinese with English abstract).
[32] Song S G, Niu Y L, Su L, Xia X H. 2013. Tectonics of the North Qilian orogen, NW China[J]. Gondwana Research, 23(4): 1378−1401. doi: 10.1016/j.gr.2012.02.004
[33] Song S G, Su L, Li X H, Zhang G B, Niu Y L, Zhang L F. 2010. Tracing the 850 Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt, NW China[J]. Precambrian Research, 183(4): 805−816. doi: 10.1016/j.precamres.2010.09.008
[34] Sun S S, McDonough W F. 1989. Chemical and isotopic systematic of oceanic basalts: Implication for mantle composition and processes[C]//Saunders A D, Norry M J (eds.). Magmatism in Oceanic Basins. Geological Society, Special Publications, London, 42(1): 313–345.
[35] Tseng C Y, Yang H J, Yang H Y, Liu D Y, Wu C L, Cheng C K, Chen C H, Ker C M. 2009. Continuity of the North Qilian and North Qinling orogenic belts, Central Orogenic System of China: Evidence from newly discovered Paleozoic adakitic rocks[J]. Gondwana Research, 16(2): 285−293. doi: 10.1016/j.gr.2009.04.003
[36] Tung K, Yang H Y, Liu D Y, Zhang J X, Yang H J, Shau Y H, Tseng C Y. 2013. The Neoproterozoic granitoids from the Qilian block, NW China: Evidence for a link between the Qilian and South China blocks[J]. Precambrian Research, 235: 163−189. doi: 10.1016/j.precamres.2013.06.016
[37] Wang C, Li R S, Smithies R H, Li M, He S P. 2017. Early Paleozoic felsic magmatic evolution of the western Central Qilian belt, Northwestern China, and constraints on convergent margin processes[J]. Gondwana Research, 41: 301−324. doi: 10.1016/j.gr.2015.12.009
[38] Wang Guohua, Qi Ruirong, Jia Xiangxiang, Bing Mingming. 2016. Tectonic characteristics and age of Haerdawu schist in south Qilian area of Qihang Province[J]. Gansu Geology, 25(3): 48−52 (in Chinese).
[39] Wang Jun, Sun Xinchun, Li Xiaoqiang, Liang Minhong, Wang Yuxi, Ren Xiuwen. 2019. Recognition and tectonic significance of previously named Balonggonggaer Formation in west Qilian Mountain[J]. Geological Bulletin of China, 38(7): 1116−1126 (in Chinese with English abstract).
[40] Wang Lei, Li Xiangmin, Hu Zhaoguo, Yang Chao, Guo Lingfen, Yan Haizhong, Ge Ruichen, Ji Bo. 2019. Zircon U–Pb dating and geochemistry of Kebasitaobasalt from the middle part of southern Danghe mountains in southern Qilian andits geological implication[J]. Geotectonic et Metallogenia, 43(5): 1069−1077 (in Chinese with English abstract).
[41] Wedepohl K H. 1995. The composition of the continental crust[J]. Geochimica et Cosmochimica Acta, 59(7): 1217−1232. doi: 10.1016/0016-7037(95)00038-2
[42] Wilson M. 1989. Igneous Petrogenesis[M]. London: Unwin Hyman, 1–466.
[43] Winchester J A, Floyd P A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements[J]. Chemical Geology, 20: 325−343. doi: 10.1016/0009-2541(77)90057-2
[44] Wu C L, Gao Y Y, Frost B R, Robinson P T, Wooden J L, Wu S P, Chen Q L, Lei M. 2011. An early Paleozoic double–subduction model for the North Qilian oceanic plate: Evidence from zircon SHRIMP dating of granites[J]. International Geology Review, 53(2): 157−181. doi: 10.1080/00206810902965346
[45] Xia L Q. 2014. The geochemical criteria to distinguish continental basalts from arc related ones[J]. Earth Science Review, 139: 195−212. doi: 10.1016/j.earscirev.2014.09.006
[46] Xia L Q, Xia Z C, Xu X Y, Li X M, Ma Z P. 2012. Mid–late–Neoproterozoic rift–related volcanic rocks in China: Geological records of rifting and break–up of Rodinia[J]. Geoscience Frontiers, 3(4): 375−399. doi: 10.1016/j.gsf.2011.10.004
[47] Xia Linqi, Li Xiangmin, Yu Jiyuan, Wang Guoqiang. 2016. Mid–Late Neoproterozoic to Early Paleozoic volcanism and tectonic evolution of the Qilian Mountain[J]. Geology in China, 43(4): 1087−1138 (in Chinese with English abstract).
[48] Xia Linqi, Xia Zuchun, Ren Youxiang, Xu Xueyi, Yang Hequn. 2001. Tectonic–volcano–magma–metallogenic dynamics in North Qilian Mountains[M]. Beijing: China Land Press, 1–296 (in Chinese).
[49] Xia Linqi, Xia Zuchun, Xu Xueyi. 2003. Magmagenesis of Ordovician back–arc basins in the Northern Qilian Mountains[J]. Geology in China, 30(1): 48–60 (in Chinese with English abstract).
[50] Xia Linqi, Xia Zuchun, Xu Xueyi, Li Xiangmin, Ma Zhongping. 2007. The discrimination between continental basalt and island arc basalt based on geochemical method[J]. Acta Petrologica et Mineralogica, 26(1): 77−89 (in Chinese with English abstract).
[51] Xiao W J, Windley B F, Yong Y, Yan Z, Yuan C, Liu C Z, Li J L. 2009. Early Paleozoic to Devonian multiple–accretionary model for the Qilian Shan, NW China[J]. Journal of Asian Earth Sciences, 35(3/4): 323−333. doi: 10.1016/j.jseaes.2008.10.001
[52] Xu Xueyi, Li Xiangmin, Wang Hongliang. 2009. Metallogenic Geological Map And Specification of Qilian Mountains and Adjacent Areas on 1: 1000000[M]. Beijing: Geological Publishing House, 1–48 (in Chinese).
[53] Xu Y J, Du Y S, Cawood P A, Guo H, Huang H, An Z H. 2010. Detrital zircon record of continental collision: Assembly of the Qilian Orogen, China[J]. Sedimentary Geology, 230(1): 35−45.
[54] Xu Yajun, Du Yuansheng, Yang Jianghai. 2013. Tectonic evolution of the North Qilian orogenic belt from the Late Ordovician to Devonian: Evidence from detrital zircon geochronology[J]. Earth Science—Journal of China University of Geosciences, 38(5): 934−946 (in Chinese with English abstract). doi: 10.3799/dqkx.2013.092
[55] Yan Z, Aitchison J, Fu C L, Guo X Q, Niu M N, Xia W J, Li J L. 2015. Hualong Complex, South Qilian terrane: U–Pb and Lu–Hf constraints on Neoproterozoic micro–continental fragments accreted to the northern Proto–Tethyan margin[J]. Precambrian Research, 266: 65−85.
[56] Yan Z, Fu C L, Aitchison J C, Niu M N, Buckman S, Cao B. 2019. Early Cambrian Muli arc–ophiolite complex: A relic of the Proto–Tethys oceanic lithosphere in the Qilian Orogen, NW China[J]. International Journal of Earth Sciences, 108: 1147−1164. doi: 10.1007/s00531-019-01699-6
[57] Yin A, Harrison T M. 2000. Geologic evolution of the Himalayan–Tibetan orogen[J]. Annual Review of Earth & Planetary Sciences, 28(28): 211−280.
[58] Zhang J X, Meng F C, Wan Y S. 2007. A cold Early Paleozoic subduction zone in the North Qilian Mountains, NW China: Petrological and U–Pb geochronological constraints[J]. Journal of Metamorphic Geology, 25(3): 285−304. doi: 10.1111/j.1525-1314.2006.00689.x
[59] Zhang J X, Yang J S, Meng F C, Wan Y S, Li H M, Wu C L. 2006. U–Pb isotopic studies of eclogites and their host gneisses in the Xitieshan area of the North Qaidam mountains, western China: New evidence for an Early Paleozoic HP–UHP metamorphic belt[J]. Journal of Asian Earth Sciences, 28: 143−150. doi: 10.1016/j.jseaes.2005.09.017
[60] Zhao G J, Wang C, Zhu X H., Hao J B, Li H, Meert J G, Gai Y S, Long X P, Ma T. 2020. Intraoceanic back–arc magma diversity: Insights from a relic of the ProtoTethys oceanic lithosphere in the western Qilian Orogen, NW China[J]. Chemical Geology, 550: 119756. doi: 10.1016/j.chemgeo.2020.119756
[61] Zhao Shenggui. 1996. Characteristics and tectonic evolution of Qilian orogenic belt[J]. Acta Geologica Gansu, 5(1): 16−31 (in Chinese).
[62] 白春东, 专少鹏, 毛志芳, 陈圆圆, 李杰. 2019. 南祁连天峻巴龙贡嘎尔组变质火山岩LA–ICP–MS锆石U–Pb年龄、地球化学特征及构造意义[J]. 地质论评, 65(3): 755−771. [63] 董国安, 杨怀仁, 杨宏仪, 刘敦一, 张建新, 万渝生, 曾建元. 2007. 祁连地块前寒武纪基底锆石SHRIMPU–Pb年代学及其地质意义[J]. 科学通报, 52(13): 1572−1585. [64] 杜远生, 朱杰, 顾松竹. 2006. 北祁连肃南一带奥陶纪硅质岩沉积地球化学特征及其多岛洋构造意义[J]. 地球科学(中国地质大学学报), 31(1): 101−109. [65] 樊光明, 雷东宁. 2007. 祁连山东南段加里东造山期构造变形年代的精确限定及其意义[J]. 地球科学(中国地质大学学报), 32(1): 39−44. [66] 樊新祥, 孔维琼, 杨镇熙, 赵吉昌, 李昱星. 2020. 北祁连造山带西段车路沟岩体U–Pb年代学、地球化学特征及岩石成因[J]. 中国地质, 47(3): 755−766. doi: 10.12029/gc20200314 [67] 冯益民, 何世平. 1996. 祁连山大地构造与造山作用[M]. 北京: 地质出版社, 1–135. [68] 何世平, 王洪亮, 陈隽璐, 徐学义, 张宏飞, 任光明, 余吉远. 2008. 中祁连马衔山岩群内基性岩墙群锆石LA–ICP–MS U–Pb年代学及其构造意义[J]. 地球科学(中国地质大学学报), 33(1): 35−45. [69] 计波, 余吉远, 李向民, 黄博涛, 王磊. 2018. 南祁连党河南山地区巴龙贡噶尔组的解体与岩石地层单位厘定—来自岩石学与年代学的证据[J]. 地质通报, 37(4): 621−633. [70] 李艳广, 汪双双, 刘民武, 孟恩, 魏小燕, 赵慧博, 靳梦琪. 2015. 斜锆石LA–ICP–MS U–Pb定年方法及应用[J]. 地质学报, 89(12): 2400−2418. doi: 10.3969/j.issn.0001-5717.2015.12.015 [71] 罗明非. 2010. 甘肃党河南山早古生代大地构造性质研究[D]. 成都: 成都理工大学, 1–60. [72] 马旭东, 陈丹玲. 2006. 柴达木盆地北缘超高压变质岩的围岩长英质片麻岩LA–ICP–MS 锆石U–Pb定年[J]. 地质通报, 25(1/2): 99−103. [73] 牛广智, 黄岗, 邓昌生, 徐岩, 陈涛, 季春, 李文军. 2016. 青海南祁连巴龙贡噶尔组变火山岩LA–ICP–MS锆石U–Pb年龄及其地质意义[J]. 地质通报, 35(9): 1441−1447. doi: 10.3969/j.issn.1671-2552.2016.09.006 [74] 潘建, 李贵义, 李广铁. 2019. 青海省巴龙贡噶尔组的重新划分及地质意义[J]. 世界地质, 38(4): 900−909. doi: 10.3969/j.issn.1004-5589.2019.04.002 [75] 秦宇. 2018. 南祁连造山带新元古代–早古生代构造演化[D]. 西安: 西北大学, 1–153. [76] 史仁灯, 杨经绥, 吴才来, Wooden J. 2004. 北祁连玉石沟蛇绿岩形成于晚震旦世的SHRIMP年龄证据[J]. 地质学报, 78(5): 649−657. doi: 10.3321/j.issn:0001-5717.2004.05.009 [77] 王国华, 齐瑞荣, 贾祥祥, 邴明明. 2016. 青海南祁连哈尔达乌片岩的构造特征及时代讨论[J]. 甘肃地质, 25(3): 48−52. [78] 王军, 孙新春, 李小强, 梁明宏, 王玉玺, 任文秀. 2019. 祁连山西段当金山一带原巴龙贡噶儿组的重新厘定及其构造意义[J]. 地质通报, 38(7): 1116−1126. doi: 10.12097/j.issn.1671-2552.2019.07.005 [79] 王磊, 李向民, 胡兆国, 杨超, 郭令芬, 闫海忠, 葛瑞臣, 计波. 2019. 南祁连党河南山中段科克巴斯陶玄武岩年代学、地球化学特征及其地质意义[J]. 大地构造与成矿学, 43(5): 1069−1077. [80] 夏林圻, 李向民, 余吉远, 王国强. 2016. 祁连山新元古代中—晚期至早古生代火山作用与构造演化[J]. 中国地质, 43(4): 1087−1138. doi: 10.12029/gc20160401 [81] 夏林圻, 夏祖春, 任有祥, 徐学义, 杨合群. 2001. 北祁连山构造–火山岩浆–成矿动力学[M]. 北京: 中国大地出版社, 1–296. [82] 夏林圻, 夏祖春, 徐学义, 李向民, 马中平. 2007. 利用地球化学方法判别大陆玄武岩和岛弧玄武岩[J]. 岩石矿物学杂志, 26(1): 77−89. doi: 10.3969/j.issn.1000-6524.2007.01.011 [83] 夏林圻, 夏祖春, 徐学义. 2003. 北祁连山奥陶纪弧后盆地火山岩浆成因[J]. 中国地质, 30(1): 48−60. doi: 10.3969/j.issn.1000-3657.2003.01.006 [84] 徐学义, 李向民, 王洪亮. 2009. 1: 100万祁连山及邻区成矿地质背景图及说明书[M]. 北京: 地质出版社, 1–48. [85] 徐亚军, 杜远生, 杨江海. 2013. 北祁连造山带晚奥陶世–泥盆纪构造演化: 碎屑锆石年代学证据[J]. 地球科学(中国地质大学学报), 38(5): 934−946. [86] 赵生贵. 1996. 祁连造山带特征及其构造演化[J]. 甘肃地质学报, 5(1): 16−31.