-
中亚造山带是古亚洲洋消减闭合并经历造山作用的产物（Sengör et al.，1993; Jahn et al.，2000; Windley et al.，2007; Xiao Wenjiao et al.，2008，2009，2015，2019）。中国境内的新疆—甘肃北部—内蒙大部—黑龙江北部一带，是寻找古亚洲洋最终闭合、消亡的区域（图1a）。经历了长期、多样和复杂演化及中部（甘肃北部—内蒙西部）的中新生代盆地覆盖，中亚造山带在中国境内被分割成东、西两段（图1b）。西准噶尔构造带南缘是古亚洲洋分支大洋准噶尔洋演化的产物，区内因造山作用的强烈改造和中新生代陆相盆地覆盖，洋-陆转换的地质记录消失殆尽。所以洋盆最晚何时于何地关闭？何种构造样式关闭等重大科学问题至今未解。
-
目前，有关洋盆在西准噶尔构造带关闭的时限仍存在争议：有泥盆纪末（Xia Linqi et al.，2004，2008）、早石炭世（Wang Zhihong et al.，2003; 赵泽辉等，2006; Zhou Taofa et al.，2008; 陈博等，2011; Yang Gaoxue et al.，2012a，2012b; Gao Rui et al.，2014; 徐学义等，2014; 贺新星等，2015）、晚石炭世（龙晓平等，2006; Zhang Zhaochong et al.，2009; Han Baofu et al.，2011; Ma Chong et al.，2012; 毛翔等，2012; Tao Huifei et al.，2013，2014; 杨维等，2015）、早二叠世（Tang Gongjian et al.，2009，2012; Yin Jiyuan et al.，2010，2011，2015; Li Di et al.，2015; Liu Qian et al.，2019）等4种不同的认识。
-
聚焦包古图地区的洋盆闭合与构造演化，也有两种截然不同的认识：一种认识是晚石炭世属弧-盆体系，并持续到早二叠世（Geng Hongyan et al.，2009; Tang Gongjian et al.，2010，2012; Yin Jiyuan et al.，2010，2015; Ma Chong et al.，2012）；第二种认识是晚石炭世为一残余洋盆体系（陈石等，2010; Chen Shi et al.，2013; Xu Qinqin et al.，2013），而到早二叠世时残余洋盆闭合消亡，进入陆内伸展演化阶段（韩宝福等，2006; Zhou Taofa et al.，2008; Chen Jiafu et al.，2010）。
-
图1 欧亚板块大地构造分区图（a）、中亚造山带大地构造单元划分图（b）、西准噶尔构造带地质图（c）、白杨河组火山岩地质简图（d）、白杨河组与佳木河组不整合接触关系（e、f）及素描图（g）、乌尔禾哈山地区古火山机构典型照片（h）及复原图（i）
-
Fig.1 Schematic tectonic division of Eurasian plate (a) , subdivision of tectonic units of CAOB (b) , geological map of western Junggar tectonic belt (c) , geological map of the study area (d) , angular unconformity between Baiyanghe basalts and Jiamuhe Formation (e, f) and sketch picture (g) , reconstruction of Urho-Hashan area volcanic macroscopic (h) and apparatus (i)
-
1—第四系; 2—砾岩; 3—集块岩; 4—角砾岩; 5—玄武岩; 6—安山岩; 7—杏仁状安山岩; 8—英安岩; 9—凝灰岩; 10—辉绿岩; 11—霏细斑岩; 12—白垩系; 13—白杨河组; 14—佳木河组; 15—阿腊德依克赛组; 16—哈拉阿拉特组; 17—希贝库拉斯组; 18—中基性岩墙群; 19—地质界线; 20—不整合界线; 21—断层
-
1—Quaternary; 2—conglomerate; 3—agglomerate; 4—breccia; 5—basalt; 6—andesite; 7—amygdaloidal basalt; 8—dacite; 9—tuff; 10—diabase; 11—felsite; 12—Cretaceous; 13—Baiyanghe Formation; 14—Jiamuhe Formation; 15—Aladeyikesai Formation; 16—Halaalate Formation; 17—Xibeikulasi Formation; 18—intermediate-basic dykes; 19—geological boundary; 20—unconformity; 21—fault
-
新近发现西准噶尔构造带早二叠世可能存在“滞后弧型”岩浆事件（晁文迪等，2015; 李永军等，2016，2021），其“滞后弧”特征总体与Mo Xuanxue（1993，2000）定义，李伍平等（1999）、廖忠礼等（2001）介绍的“滞后弧火山岩”相似。即：洋盆闭合后地表已进入陆内演化，但深部仍有残余火山岩浆作用，所形成的滞后火山岩在成分、成因上仍继承了弧-盆火山岩的地球化学特征，滞后火山岩与早先的弧-盆体系火山岩二者喷发间隙时间较短，产出空间上保持一致性。白杨河组火山岩是一代表。本文就该火山岩的产出与分布、岩石学、岩石地球化学特征、源区性质及成因加以讨论，佐证本区洋-陆转换过程中的岩浆作用，追索古亚洲洋在中国境内西段的缝合边界位置，约束洋-陆转换的时限。
-
1 区域地质特征
-
西准噶尔构造带位于中亚造山带的核心部位，发育达尔布特等多条泥盆纪蛇绿岩带、石炭纪弧-盆建造、晚石炭世赞岐岩带，并受到二叠纪以来左行走滑断裂和中生代以来右行走滑断裂的改造。期间，发生了从石炭纪弧-盆构造体系向二叠纪陆内构造演化的洋-陆转换过程，形成了石炭系海相陆源碎屑岩-火山岩沉积组合向二叠系陆相磨拉石-滞后弧火山岩转变的记录。
-
哈拉阿拉特山（简称哈山）—乌尔禾一带位处中亚造山带巴尔喀什-西准噶尔增生造山带南缘的包古图构造带，南邻准噶尔中新生代盆地。以克拉玛依蛇绿构造混杂岩带为代表的NNE向构造带及其次级平行断裂带，控制着区内主要地质体的展布（图1c、d）。
-
区内地层以上古生界为主，由下到上依次为下石炭统包古图组→希贝库拉斯组，上石炭统成吉思汗山组→哈拉阿拉特组→阿腊德依克赛组，以及下二叠统佳木河组→白杨河组。下石炭统包古图组以半深海—浅海相细碎屑岩沉积为主（Zong Ruiwen et al.，2015），玄武岩、安山岩呈夹层产出（安山岩LA-ICP-MS锆石U-Pb年龄为347~328 Ma; 李永军等，2010）；希贝库拉斯组为陆棚相粗碎屑岩沉积，火山岩不发育，砂岩碎屑锆石最新优势年龄为328~323 Ma（孙羽等，2014）；上石炭统成吉思汗山组以灰岩层厚度较大而有别于包古图组、希贝库拉斯组，火山岩相对发育，玄武岩LA-ICP-MS锆石U-Pb年龄为313 Ma（郭丽爽等，2010）；哈拉阿拉特组层序特征为下熔岩上火山碎屑岩，玄武岩LA-ICP-MS锆石U-Pb年龄为310~303 Ma（李甘雨等，2016），阿腊德依克赛组层序特征为下陆源碎屑岩上火山岩，玄武岩LA-ICP-MS锆石U-Pb年龄为303~299 Ma（向坤鹏等，2015; 李永军等，2021）。下二叠统佳木河组陆相磨拉石建造（产Paracalamites stenocostatus，Lepidodendrales sp. 等植物化石; 李永军等，2016，2021）角度不整合超覆于石炭系之上，并发生了强烈的纵弯褶皱和复杂变形。白杨河组火山岩具独立的陆相火山机构，其喷发相岩石角度不整合覆于佳木河组及石炭系之上（图1e~i; 晁文迪等，2015; 李永军等，2016），玄武岩LA-ICP-MS锆石U-Pb年龄为283 Ma（李永军等，2016）。包古图构造带南邻准噶尔盆地，出露三叠系及中新生代河湖相沉积。
-
白杨河组在火山通道相主要为一套火山集块岩、角砾岩组合，而喷出相为玄武岩、安山玄武岩及凝灰岩（图1d），共生有辉绿岩岩枝、岩脉等次火山岩类（晁文迪等，2015; 图1d）。火山机构似有对称性（图1i）。
-
2 白杨河组火山岩岩石学特征
-
岩性主要为多斑玄武岩、玄武岩、橄榄玄武岩，偶见安山玄武岩。多斑玄武岩呈灰褐色，斑状结构，基质间粒结构，块状构造（图2a）。斑晶含量约30%，以斜长石为主，有少量橄榄石。斜长石呈半自形板状，粒径0.3 mm×0.1 mm~1.7 mm×0.5 mm，环带、聚片双晶发育；橄榄石多已绿泥石化，粒径0.2~0.5 mm。基质含量约70%，其中斜长石约38%，呈半自形板条状，粒径0.2~0.03 mm，聚片双晶发育，长轴平行定向排列；普通辉石约30%，分布于斜长石之间，柱状、粒状，粒径＜0.1 mm，淡绿色，具辉石式解理。此外磁铁矿、橄榄石、杏仁石等不规则分布其间。
-
玄武岩呈灰色（图2b），具斑状结构，基质交织结构。斑晶含量约20%，以拉长石为主，呈半自形板粒状，粒径0.65 mm×1.7 mm~3.8 mm×1.7 mm，环带、聚片双晶发育；辉石（多已绿泥石化）含量5%，粒径0.5~1.3 mm。基质含量约80%，多为细板条状拉长石，粒径0.03 mm×0.1 mm~0.4 mm×0.1 mm，环带、聚片双晶发育，平行定向分布，间隙内分布约20%的辉石微粒（粒径＜0.13 mm），1%的磁铁矿（粒径＜0.15 mm）。
-
橄榄玄武岩呈深灰色，斑状结构、基质间粒结构，块状构造。斑晶含量约为35%，其中斜长石含量25%，呈半自形板状，粒径0.2 mm×0.1 mm~1.9 mm×0.5 mm，聚片双晶发育；普通辉石5%，呈柱状、粒状，粒径0.2~1.0 mm，淡绿色，具辉石式解理。橄榄石含量5%，粒径0.2~1.0 mm。基质含量约65%，其中斜长石约30%，呈半自形板条状，粒径0.1~0.03 mm，聚片双晶发育；普通辉石含量30%，呈柱状、粒状，粒径＜0.1 mm，淡绿色，具辉石式解理。少量磁铁矿、橄榄石等不规则分布其间。
-
图2 白杨河组多斑玄武岩正交偏光显微照片（a）和玄武岩正交偏光显微照片（b）
-
Fig.2 Microphotographs of basalt with plenty phenocrysts (a) and basalt (b) in Baiyanghe Formation, crossed polars
-
Pl—斜长石; Ol—橄榄石; Cpx—单斜辉石
-
Pl—plagioclase; Ol—olivine; Cpx—clinopyroxene
-
3 样品采集及分析方法
-
采样时避开了接触带、蚀变带和断裂破碎带等，样品较为新鲜。选取了14件样品进行主量元素和微量元素分析，其中4件进行Sr-Nd-Pb同位素分析。主、微量元素在长安大学成矿作用及其动力学实验室完成。主量元素分析测试仪器为日本岛津XRF-1800型波长色散X射线荧光光谱仪。在Shimadzu XRF-1700/1500上采用外标法测定氧化物含量。分析采用国家一级岩石标样GBW07101-07114为基体效应校正。利用标准曲线法校正，分析误差优于5%。微量元素分析采用X系列ICP-MS及Thermo-X7电感耦合等离子体质谱仪进行样品测定，多数微量元素的分析精度优于5%。Sr-Nd和Pb同位素测试分析工作在核工业北京地质研究所分析测试研究中心完成。主要测试仪器为热电离质谱仪，Sr-Nd同位素测试分析仪器型号为Phoenix。87Sr/86Sr比值用86Sr/88Sr=0.1194校正，143Nd/144Nd比值用146Nd/144Nd=0.7219校正。Pb同位素测试分析仪器型号为ISOPROBE-T，样品测试经国际标样NBS987和实验室标样SHINESTU进行监控实验过程中，标样NBS981未校正结果如下：206Pb/204Pb=16.895±0.026（2σ），207Pb/204Pb=15.437±0.029，208Pb/204Pb=36.537±0.121。全流程空白值0.1 ng（李大鹏等，2010）。
-
4 白杨河组火山岩地球化学特征
-
4.1 主量元素
-
白杨河组玄武岩、安山玄武岩的主、微量元素分析结果见表1。玄武岩12个样品的SiO2含量为47.51%~50.74%，平均值为49.39%（仅有2个样品SiO2含量稍高，分别为53.24%、54.34%）。Al2O3含量较高（14.75%~21.19%，仅有1个样品Al2O3含量稍低），平均值为18.22%。TiO2含量（0.74%~1.53%）相对较低，平均值1.11%。样品整体上富钠贫钾（K2O/Na2O值为0.05~0.25），全碱（Na2O+K2O）含量为3.04%~5.00%，平均值为4.11%。所有样品的σ值（1.32~3.29，平均值2.06）均小于3.3，属于钙碱性系列。MgO含量为3.46%~6.97%，镁指数值（Mg#）为40.03~57.97，平均值为47.94，低于原生岩浆（Mg#=73~81; Litvak and Poma，2010），表明岩石经历了一定程度的分离结晶作用。在不活动的高场强元素分类Zr/（TiO2×0.0001）-Nb/Y判别图（图3a）中，样品落入亚碱性玄武岩区及安山/玄武岩区。在SiO2-K2O图解（图3d）中样品显示中—低钾特征。因薄片中见绿泥石化等轻微蚀变，且主量元素分析中1个样品烧失量较高（可能与后期蚀变有关），故选择相对惰性元素Zr、Nb相关图解（图3a），验证结果与（K2O+Na2O）-SiO2判别图（图3b）总体一致，暗示研究区蚀变作用对火山岩主量成分影响较小。
-
续表1
-
注：TFe2O3表示全铁; σ=（K2O+Na2O）2/（SiO2-43）; Mg#=MgO/（MgO+FeO）；稀土元素标准化值引自Henderson，1984。
-
图3 白杨河组玄武岩Zr/（TiO2×0.0001）-Nb/Y判别图（a）（底图据Winchester and Floyd，1977）、（K2O+Na2O）-SiO2判别图（b）（底图据MacDonald，1968）、TFeO-（K2O+Na2O）-MgO图解（c）（底图据Irvine and Baragar，1971）、SiO2-K2O图解（d）（底图据Peccerillo and Taylor，1976）
-
Fig.3 Zr/ (TiO2×0.0001) -Nb/Y diagram (a) (after Winchester and Floyd, 1977) , K2O+Na2O-SiO2 diagram (b) (after MacDonald, 1968) , AFM diagram (c) (after Irvine and Baragar, 1971) and SiO2-K2O diagram (d) (after Peccerillo and Taylor, 1976) of Baiyanghe Formation basalts
-
早二叠世次火山岩数据引自晁文迪等，2015; 晚石炭世火山岩数据引自Li Ganyu et al.，2017; 下同
-
Early Permian subvolcanic rocks date after Chao Wendi et al., 2015; Upper Carboniferous volcanic data after Li Ganyu et al., 2017; the same below
-
4.2 稀土元素
-
稀土元素总量（ΣREE）为20.94~73.86 μg/g，平均值为42.35 μg/g。（La/Yb）N为1.35~4.25，（La/Sm）N为0.85~1.81，（Gd/Yb）N为1.39~1.98，ΣLREE/ΣHREE为2.31~4.55，显示轻、重稀土间分馏程度较高。样品弱的Eu异常（δEu=0.72~1.26）和铈异常（δCe=1~1.08），表示斜长石的分离结晶作用不明显。球粒陨石标准化的REE配分曲线图（图4a）中具轻稀土富集型的特征，与（La/Yb）N值相印证。白杨河组玄武岩及其共生的次火山岩总体与晚石炭世火山岩有相似的稀土配分模式（图4a），仅LREE配分稍显不同，表明二者在部分熔融程度上略有差异（Piccardo et al.，2007）。
-
图4 白杨河组玄武岩球粒陨石标准化曲线图（a）（标准化值据Henderson，1984）、微量元素蛛网图（b）（标准化值据Sun and McDonough，1989）
-
Fig.4 Chondrite-normalized REE patterns (a) (normalization values after Henderson, 1984) and primitive mantle-normalized trace element diagram (b) (normalization values after Sun and McDonough, 1989) of Baiyanghe Formation basalts
-
4.3 微量元素
-
微量元素原始地幔标准化蛛网图（图4b）中显示，大离子亲石元素（LILE）Ba、K、Sr相对富集，其中Sr（含量481.67~761.32 μg/g）呈明显峰值。高场强元素（HFSE）Nb（含量0.59~4.42 μg/g）、Ta（含量0.03~0.26 μg/g）强烈亏损，Zr、Hf相对亏损，指示岩浆受消减带上升流体影响。蛛网图中显著的“TNT”负异常表明岩浆作用中存在俯冲作用改造下岩石圈地幔的参与。
-
4.4 同位素
-
Sr-Nd同位素分析结果如表2所示，样品（87Sr/86Sr）i值为0.703974~0.704299，（143Nd/144Nd）i值为0.512577~0.512620，εNd（t）值为+5.93~+6.76。在Sr-Nd初始值图解（图5a）上，样品落入地幔演化序列范围。相对低的（87Sr/86Sr）i值和高正的εNd（t）值，表明白杨河组玄武岩源于亏损地幔。
-
注：比值中的下标n表示测定值；下标i表示初始值；玄武岩的锆石U-Pb年龄为283.3 Ma；故采用t=283.3 Ma。
-
图5 白杨河组玄武岩εNd（t）-（87Sr/86Sr）i图解（a）（底图据赖绍聪等，2010; 西准噶尔构造带早石炭世岛弧火山岩数据引自 Geng Hongyan et al.，2011）、207Pb/204Pb-206Pb/204Pb图解（b）、208Pb/204Pb-206Pb/204Pb图解（c）（底图据Zindler and Hart，1986）
-
Fig.5 εNd (t) - (87Sr/86Sr) i diagram (a) (after Lai Shaocong et al., 2010; early Carboniferous volcanic rocks data from West Junggar tectonic belt after Geng Hongyan et al., 2011) , 207Pb/204Pb-206Pb/204Pb diagram (b) and 208Pb/204Pb-206Pb/204Pb diagram (c) (after Zindler and Hart, 1986) of Baiyanghe Formation basalts
-
DM—亏损地幔; MORB—大洋中脊玄武岩; BSE—原始未分异地幔; PREMA—最常见地幔端元; EMⅠ和EMⅡ—富集地幔端元
-
DM—depleted mantle; MORB—mid-ocean ridge basalts; BSE—bulk silicate Earth; PREMA—prevalent mantle; EMⅠ—enriched mantle Ⅰ; EMⅡ—enriched mantle Ⅱ
-
4件Pb同位素样品分析结果如表3所示，（206Pb/204Pb）i=17.924~18.000，（207Pb/204Pb）i=15.469~15.509，（208Pb/204Pb）i=37.737~37.879。在207Pb/204Pb-206Pb/204Pb图和208Pb/204Pb-206Pb/204Pb图（图5b、c）中，Pb同位素组成均位于地球演化线的右侧，属于富放射成因铅的异常铅（姜常义等，2009），数据点落于MORB范围内及其附近，表明白杨河组玄武岩的Pb同位素组成类似于MORB。
-
5 讨论
-
5.1 源区及成因
-
幔源岩浆在向地表运移过程中往往会发生同化混染作用和分离结晶作用。白杨河组玄武岩、安山玄武岩样品的Nb/Ta比值（7.90~18.56，平均值为15.24，仅有1个样品特征比值较低，可能与Nb、Ta贮存于黑云母等富Ti矿物，发生部分熔融时Ta优先于Nb进入熔体有关）和Zr/Hf比值（33.26~43.02，平均值为36.64）接近原始地幔值（Nb/Ta=17.5±0.5，Zr/Hf=36.27; Hofmann，1988），表明岩浆在上升过程中受到地壳物质混染的程度很低。在Nb-Nb/La图解（图6a）中，样品也未落入陆壳区域内；样品的Rb/Sr比值（0.0015~0.0192）远低于陆壳相应值（下地壳0.023，上地壳0.32）；岩石的初始Sr同位素比值与SiO2间基本无相关性（图6b）；样品的La/Sm比值均小于5，这些特征均可表明成岩过程中受地壳物质混染影响较小（Lassiter and Depaolo，1997; 张招崇等，2004; Kaygusuz et al.，2014）。玄武岩的Mg#为40.03~57.97，指示在岩浆演化中经历了一定程度的分离结晶作用。样品的Cr、Ni随MgO的减小而降低（图6c、d），表明岩浆在上升过程中经历了一定程度的单斜辉石和橄榄石分离结晶作用。Sr含量及无负Eu异常均说明斜长石的分离结晶不明显。综上，白杨河组火山岩在岩浆演化过程中发生了部分熔融和分离结晶双重作用。此外，在La/Sm与La图解（图6e）中，下二叠统白杨河组玄武岩与晚石炭世弧火山岩样品投点均呈明显的正相关性，暗示两期火山岩为同一源区并经历不同程度的部分熔融作用形成（Allègre and Minster，1978; Bottinga et al.，1978）。
-
注：比值中下标i表示初始值；玄武岩的锆石U-Pb年龄为283.3 Ma；故采用t=283.3 Ma。
-
图6 白杨河玄武岩Nb-Nb/La图解（a）（底图据Rudnick et al.，2000）、 SiO2-（87Sr/86Sr）i图解（b）（底图据Kaygusuz et al.，2014修改）、 MgO-Cr图解（c）、 MgO-Ni图解（d）、 La-La/Sm图解（e）
-
Fig.6 Nb-Nb/La diagram (a) (after Rudnick et al., 2000) , SiO2- (87Sr/86Sr) i diagram (b) (after Kaygusuz et al., 2014) , MgO-Cr diagram (c) , MgO-Ni diagram (d) , La-La/Sm diagram (e) of Baiyanghe Formation basalts
-
由前人研究成果（Li Ganyu et al.，2017）及εNd（t）-（87Sr/86Sr）i图解（图5a）、微量元素蛛网图、稀土元素配分图（图4a、b）等看出，白杨河组玄武岩与晚石炭世弧火山岩在同位素、主微量成分上均体现了高度相似性，且二者在空间分布上具有高度重叠性，暗示白杨河组玄武岩、安山玄武岩可能与区内早先（晚石炭世）发生的火山作用具有同源性，二者喷发间隙时间较短，产出空间上保持一致性，故具有继承性，与尹继元等（2013）提出的二者在演化上具有很好的继承性这一认识相吻合。本组样品相对低的（87Sr/86Sr）i值和高正的εNd（t）值，表明俯冲板片上覆的亏损楔型地幔可能是白杨河组玄武岩、安山玄武岩的源区，符合亏损的楔形地幔是弧玄武岩源区之组成端元这一推论（Davidson，1983; 李曙光，1994）。
-
由于在俯冲过程中，大离子亲石元素往往在俯冲流体中迁移，而Th、Nb以及轻稀土元素通常只在熔体中移动，故特征元素及其比值可以示踪俯冲物质循环，判别俯冲组分。俯冲带沉积物往往富集Th，而Ce在热液体系中容易发生迁移，因此，如果有俯冲沉积物的加入，Th/Ce比值就会升高（尹继元等，2013）。白杨河组玄武岩、安山玄武岩的Th/Ce比值为0.03~0.06，远高于MORB的Th/Ce值（0.016），部分接近OIB（0.05）的Th/Ce比值，表明俯冲沉积物对源区组分有所贡献，并与Ce/Nb-Th/Nb图解（图7a）结果相印证。较低的Th/Yb值（0.17~0.74）和较高的Ba/La值（18.20~127.67）则表明俯冲板片流体的加入程度较高，Ba/La-Ba/Nb图解（图7b）揭示岩浆作用中流体的贡献。白杨河组火山岩大离子亲石元素、HFSE明显亏损，结合前述地球化学特征，表明来自消减板块的流体作为主要端元组分参与了成岩过程，流体交代了上覆地幔楔，导致了地幔橄榄岩发生部分熔融成就了该岩浆作用。
-
由于受地壳或者岩石圈地幔组分混染的大陆玄武岩经常会被误判成弧玄武岩（Ernst et al.，2005），其具有高La/Nb比值、原始地幔标准化Th/Nb比值略大于1、中—低εNd（t）值（＜+2）、中等87Sr/86Sr比值（0.704~0.707）等特征。而没有受到混染的大陆玄武岩通常具有较为平坦的REE分配模式或者LREE富集的分配模式这一特征。对比白杨河组玄武岩、安山玄武岩La/Nb=2.40~4.96，（Th/Nb）N=2~5.05，高正的εNd（t）值（+5.93~+6.76）和较低的（87Sr/86Sr）i值（0.703974~0.704299），轻、重稀土内部分馏程度较低且显示较平坦的分配模式，以及轻稀土相对富集（图4a、b）等特征，表明白杨河组火山岩为弧火山岩，而非受地壳或岩石圈地幔混染的大陆板内玄武岩。
-
5.2 构造环境
-
白杨河组玄武岩、安山玄武岩较高的Al2O3，较低的TiO2（平均值1.11%），轻稀土元素富集，大离子亲石元素（Ba、K、Sr等）相对富集，高场强元素（HFSE）Nb、Ta、Zr、Hf相对亏损。微量元素蛛网图中显著的“TNT”负异常等均体现消减带岩浆的特征。在不同类型玄武岩微量元素蛛网图中，白杨河组玄武岩样品介于IAB和IOAB之间，与弧火山岩的趋势一致（图8）。
-
图7 白杨河组玄武岩Ce/Nb-Th/Nb图解（a）（底图据Song Xieyan et al.，2004）; 白杨河组玄武岩Ba/La-Ba/Nb图解（b）（底图据Geng Hongyan et al.，2011）
-
Fig.7 Ce/Nb-Th/Nb diagram (a) (after Song Xieyan et al., 2004) and Ba/La-Ba/Nb diagram (b) (after Geng Hongyan et al., 2011) of Baiyanghe Formation basalts
-
DM—亏损地幔; N-MORB—正常型洋中脊玄武岩; E-MORB—富集型洋中脊玄武岩; PM—原始地幔; OIB—洋岛玄武岩; ECFB—峨眉山大陆溢流玄武岩
-
DM—depleted mantle; N-MORB—normal mid-ocean ridge basalts; E-MORB—enrich mid-ocean ridge basalts; PM—primitive mantle; OIB—ocean island basalts; ECFB—emeishan continental floor basalts
-
图8 白杨河组玄武岩与不同类型玄武岩微量元素蛛网图（据Li Chusi et al.，2015及相关文献）
-
Fig.8 Primitive mantle-normalized trace element diagram between different types of basalts and Baiyanghe basalts (after Li Chusi et al., 2015 and references therein)
-
OIB—洋岛玄武岩; IAB—岛弧玄武岩; CFB—大陆溢流玄武岩; MORB—洋中脊玄武岩; OPB—大洋高原玄武岩; BABB—弧后盆地玄武岩; CAB—大陆弧玄武岩; IOAB—大洋内弧玄武岩
-
OIB—ocean island basalts; IAB—island arc basalts; CFB—continental floor basalts; MORB—mid-ocean ridge basalts; OPB—ocean plateau basalts; BABB—back-arc basin basalts; CAB—continental arc basalts; IOAB—intra-oceanic arc basalts
-
Th/Ta比值均大于1.6（2.78~9.53），Th/Nb比值均大于0.11（0.24~0.60），La/Nb比值均大于2（2.40~4.97），12个样品Ta/Hf比值小于0.1（仅有2个为0.116和0.124），11个样品Nb/Zr比值小于0.04（有3个分别为0.045、0.0564、0.0846），这些元素比值总体表明其形成于板块汇聚边缘的构造环境中（李永军等，2015）；Zr的含量较低（22.00~116.69 μg/g），均小于130 μg/g，符合弧玄武岩特征（夏林圻等，2007）；在经典构造判别图解Hf/3-Th-Ta（图9）中，样品落入消减性板缘玄武岩区；这些都表明白杨河组火山岩形成于弧构造环境。
-
5.3 对西准噶尔洋盆闭合时间的约束
-
佳木河组磨拉石建造是区内洋盆闭合进入陆内演化阶段的重要标志。区内下石炭统为弧后盆地碎屑岩建造，而上石炭统下部为弧后碎屑岩-火山岩组合，上石炭统顶部为弧火山岩建造间夹火山喷发间隙期的海相碎屑岩夹层。与之形成鲜明对照和悬殊差异的是下二叠统佳木河组为陆相磨拉石建造，其角度不整合超覆于石炭系之上，三叠系及其之上均为河湖相建造，故磨拉石建造是海-陆这一重大转换的关键记录。佳木河组及其下伏地层均经历了强烈的褶皱和复杂的形变，而三叠系及其上覆地层均基本未变形，且火山作用罕见（仅有侏罗纪发现较小规模的板内碱性玄武岩（陈双双等，2013; Wang Jian et al.，2019; Xie Qiuhong et al.，2023），无侵入岩产出，故磨拉石建造是区内俯冲造山与伸展盆地的转折记录。简而言之，海-陆相转变是洋-陆构造体制转换的标志。
-
图9 Hf/3-Th-Ta构造判别图解（据Wood，1980）
-
Fig.9 Hf/3-Th-Ta diagram of Baiyanghe Formation basalts (after Wood, 1980)
-
由前述看出，白杨河组火山岩及其共生的次火山岩极好地继承了晚石炭世海相弧火山岩的地球化学特征，它们在空间上紧密共生，时间上前后紧随，具有同源、同成因、同构造背景特色。暗示区内尽管洋盆已完全消亡闭合并被陆相磨拉石覆盖，但深部具有俯冲性质的岩浆作用活动仍未完全平息，持续到白杨河组火山岩和次火山岩形成之后才完全结束了深部的俯冲作用，即在白杨河组火山岩形成之后，区内才进入真正意义上的陆内伸展演化阶段，这一持续的岩浆作用过程恰好是西准噶尔构造带由洋盆闭合转换成陆的关键演化阶段。因此，本文认为白杨河组火山岩及其共生的次火山岩是区内洋-陆转换的重要记录，也是迄今发现的可追索古亚洲洋缝合边界位置，约束构造演化时限的稀有证据。
-
白杨河组火山岩形成于陆相磨拉石建造之后，却又携带清晰的与岛弧俯冲作用有关的地球化学信息，即地表已进入陆内造山却明显地带有与俯冲相关的地球化学信息，与国内外已报道的“滞后弧”火山岩相似（Hooper et al.，1995; 刘燊等，2003; 陈廷方，2003; 汤超等，2015）。与正常的弧-盆体系相比，“滞后弧”火山岩的区别在于俯冲造山之后海相消失，地表被磨拉石建造覆盖，但深部仍残存俯冲，并且这种俯冲应力场导致了地表二叠系的纵弯褶皱，属汇聚体制构造变形。该滞后弧火山岩的确认，表明西准噶尔构造带俯冲作用至少持续到白杨河组火山岩形成之后，深部的俯冲作用才完全结束，约束区内最终俯冲时限为早二叠世。这一认识也有别于前人对包古图地区洋盆闭合与构造演化的两种认识。区域上，滞后弧火山岩已在东准噶尔构造带三塘湖盆地、陆东—五彩湾地区、陆梁隆起以及卡拉麦里地区陆续有报导（王方正等，2002; 郝建荣等，2006; 周鼎武等，2006; 赵霞等，2008; 吴小奇等，2009; 杨高学等，2010a，2010b），有趣的是，本文作者们连接这些已报导的火山岩产出位置，发现在区域性上呈一线性分布特点，推测该连线位置可能是古亚洲洋在中国境内西段洋盆闭合，造山终成中亚巨型造山带的结合部位（李永军等，2016），因而，有进一步研究的意义。
-
6 结论
-
（1）下二叠统白杨河组火山岩及其共生次火山岩类发育完整的陆相火山机构，喷发不整合覆于下二叠统佳木河组陆相磨拉石建造之上。火山岩类为钙碱性中低钾玄武岩系列，有明显“TNT”负异常，显示与俯冲作用相关的弧火山岩地球化学信息。
-
（2）白杨河组火山岩（206Pb/204Pb）i=17.924~18.000，（207Pb/204Pb）i=15.469~15.509，（208Pb/204Pb）i=37.737~37.879，类似于MORB的Pb同位素组成。另外，样品具有相对低的（87Sr/86Sr）i值和高正的εNd（t）值，表明源区为俯冲板片脱水产生的流体交代的亏损地幔。
-
（3）白杨河组火山岩类继承了晚石炭世海相弧火山岩的地球化学特征，空间上紧密共生，时间上前后紧随，具有同源、同成因、同构造背景等特色，具有“滞后（弧）型”地球化学特色。本组火山岩类清晰记录了区内在地表洋盆闭合之后，深部俯冲活动仍在持续和“挣扎”的过程，表明西准噶尔构造带俯冲造山作用结束的最终时限为早二叠世，其洋-陆转换过程中经历了“滞后弧”这一独特的构造演化历史。连接白杨河组“滞后（弧）型”火山岩与区域上同类型火山岩产出位置，呈一线性分布特点，推测此连线可能是古亚洲洋在中国境内西段洋盆闭合，造山终成中亚巨型造山带的结合部位。
-
致谢：本文在前期工作和成文过程中，就“滞后弧”等相关问题多次请教莫宣学院士；匿名审稿专家指出了许多宝贵的修改意见；张招崇、马昌前、陈立辉、刘永顺等教授为修改、完善本文提出了很多建议，在此一并表示诚挚的谢意。
-
参考文献
-
Allègre C J, Minster J F. 1978. Quantitative models of trace element behavior in magmatic processes. Earth and Planetary Science Letters, 38(1): 1~25.
-
Bottinga Y, Allegre C J, Thompson R N. 1978. Partial melting under spreading ridges. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 288(1355): 501~525.
-
Chao Wendi, Li Yongjun, Wang Ran, Yang Gaoxue, Xiang Kunpeng, Liu Jia, Xu Qian. 2015. Lagged arc magmatism in Western Junggar: Evidence from Early Permian intermediate to mafic dyke swarms in Urho area, east of Western Junggar. Acta Petrologica et Mineralogica, 34(2): 171~183(in Chinese with English abstract).
-
Chen Bo, Zhu Yongfeng. 2011. Petrology, geochemistry and zircon U-Pb chronology of gabbro in Darbut ophiolitic melange, Xinjiang. Acta Petrologica Sinica, 27(6): 1746~1758(in Chinese with English abstract).
-
Chen Jiafu, Han Baofu, Zhang Lei. 2010. Sr-Nd isotopes and tectonic implications of two generations of Late Paleozoic plutons in northern West Junggar, Northwest China. Acta Petrologica Sinica, Geochemistry, 26(8): 2317~2335(in Chinese with English abstract).
-
Chen Shi, Guo Zhaojie. 2010. Time constraints, tectonic setting of Dalabute ophiolitic complex and its significance for Late Paleozoic tectonic evolution in West Junggar. Acta Petrologica Sinica, 26(8): 2336~2344(in Chinese with English abstract).
-
Chen Shi, Guo Zhaojie, Pe-Piper, Zhu Beibei. 2013. Late Paleozoic peperites in West Junggar, China, and how they constrain regional tectonic and palaeoenvironmental setting. Gondwana Research, 23(2): 666~681.
-
Chen Shuangshuang, Su Yuping, Zheng Jianping, Wei Ying. 2013. Geochemical characteristics of Karamay Jurassic basalts and implication on crust-mantle interaction. Geochimica, 42(1): 29~45(in Chinese with English abstract).
-
Chen Tingfang. 2003. The petrology of the volcanic rocks in Tengchong, Yunnan. Sedimentary Geology and Tethyan Geology, 23(4): 56~61(in Chinese with English abstract).
-
Davidson J P. 1983. Lesser Antilles isotopic evidence of the role of subducted sediment in island arc magma genesis. Nature, 306: 253~256.
-
Ernst R E, Buchan K L, Campbell I H. 2005. Frontiers in large igneous province research. Lithos, 79(3-4): 271~297.
-
Gao Rui, Xiao Long, Pirajno Franco, Wang Guocan, He Xinxing, Yang Gang, Yan Shengwu. 2014. Carboniferous-Permian extensive magmatism in the West Junggar, Xinjiang, Northwestern China: Its geochemistry, geochronology, and petrogenesis. Lithos, 204: 125~143.
-
Geng Hongyan, Sun Min, Yuan Chao, Xiao Wenjiao, Xian Weisheng, Zhao Guochun, Zhang Lifei, Wong Kenny, Wu Fuyuan. 2009. Geochemical, Sr-Nd and zircon U-Pb-Hf isotopic studies of Late Carboniferous magmatism in the West Junggar, Xinjiang: Implications for ridge subduction? Chemical Geology, 266(3-4): 364~389.
-
Geng Hongyan, Sun Min, Yuan Chao, Zhao Guochun, Xiao Wenjiao. 2011. Geochemical and geochronological study of early Carboniferous volcanic rocks from the West Junggar: Petrogenesis and tectonic implications. Journal of Asian Earth Sciences, 42(5): 854~866.
-
Guo Lishuang, Liu Yulin, Wang Zhenghua, Song Da, Xu Junfa, Su Li. 2010. The zircon U-Pb LA-ICP-MS geochronology of volcanic rocks in Baogutu areas, Western Junggar. Acta Petrologica Sinica, 26(2): 471~477(in Chinese with English abstract).
-
Han Baofu, Ji Jianqing, Song Biao, Chen Lihui, Zhang Lei. 2006. Late Paleozoic vertical growth of continental crust around the Junggar basin, Xinjiang, China(Part I): Timing of post-collisionai plutonism. Acta Petrologica Sinica, 22(5): 1077~1086(in Chinese with English abstract).
-
Han Baofu, He Guoqi, Wang Xuechao, Guo Zhaojie. 2011. Late Carboniferous collision between the Tarim and Kazakhstan- Yili terranes in the western segment of the South Tian Shan Orogen, Central Asia, and implications for the Northern Xinjiang, Western China. Earth-Science Reviews, 109: 74~93.
-
Hao Jianrong, Zhou Dingwu, Liu Yiqun, Xing Xiujuan. 2006. Geochemistry and tectonic settings of Permian volcanic rocks in Santanghu basin, Xinjiang. Acta Petrologica Sinica, 22(1): 189~198(in Chinese with English abstract).
-
He Xinxing, Xiao Long, Wang Guocan, Gao Rui, Yang Gang, Yan Shengwu. 2015. Petrogenesis and geological implications of Late Paleozoic intermediate-basic dyke swarms in Western Junggar. Earth Science, 40(5): 777~796(in Chinese with English abstract).
-
Henderson P. 1984. General geochemical properties and abundances of the rare earth element. Developments in Geochemistry, 2: 1~32.
-
Hofmann A W. 1988. Chemical differentiation of the Earth: The relationship between mantle, continental crust and oceanic crust. Earth Planet Science Letter, 90: 297~314.
-
Hooper P R, Bailey D G, Holder G A M. 1995. Tertiary calc-alkaline magmatism associated with lithospheric extension in the Pacific Northwest. Geophysical Research, 100(B7): 10303~10319.
-
Irvine T N, Baragar W R. 1971. A guide to the chemical classification of the common volcanic rocks. Canadian Journal of Earth Sciences, 8(5): 523~548.
-
Jahn B M, Wu Fuyuan, Chen Bin. 2000. Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 91: 181~193.
-
Jiang Changyi, Xia Mingzhe, Qian Zhuangzhi, Yu Xu, Lu Ronghui, Guo Fangfang. 2009. Petrogenesis of Kalatongke mafic rock intrusions, Xinjiang. Acta Petrologica Sinica, 25(4): 749~764(in Chinese with English abstract).
-
Kaygusuz A, Arslan M, Siebel W, Sipahi F, I·lbeyli N, I·rfan T. 2014. LA-ICP-MS zircon dating, whole-rock and Sr-Nd-Pb-O isotope geochemistry of the Camiboğazi pluton, eastern Pontides, NE Turkey: Implications for lithospheric mantle and lower crustal sources in arc-related I-type magmatism. Lithos, 192: 271~290.
-
Lassiter J C, DePaolo D J. 1997. Plume/lithosphere interaction in the generation of continental and oceanic flood basalts: Chemical and isotopic constraints. Geophysical Monograph- American Geophysical Union, 335~356.
-
Lai Shaocong, Qin Jiangfeng, Li Xuejun, Zang Wenjuan. 2010. Geochemistry and Sr-Nd-Pb istopic features of the Ganlongtang-Nongba ophiolite from the Changning-Menglian suture zone. Acta Petrologica Sinica, 26(11): 3195~3205(in Chinese with English abstract).
-
Li Chusi, Arndt N T, Tang Qingyan, Riple E M. 2015. Trace element indiscrimination diagrams. Lithos, 232: 76~83.
-
Li Dapeng, Chen Yuelong, Wang Zhong, Liu Changzheng. 2010. Nd-Pb isotopic composition characteristics and geological significances of granitoids with different ages in Inner Mongolia. Geoscience, 24(5): 821~831(in Chinese with English abstract).
-
Li Di, He Dengfa, Santosh M, Ma Delong. 2015. Tectonic framework of the northern Junggar basin part II: The island arc basin system of the western Luliang uplift and its link with the West Junggar terrane. Gondwana Research, 27: 1110~1130.
-
Li Ganyu, Li Yongjun, Xiang Kunpeng, Wang Ran, Liu Jia, Li Zhao, Yang Gaoxue. 2016. Revision and regional correlation of the Hala'alate Formation in western Junggar basin. Journal of Stratigraphy, 40(1): 76~84(in Chinese with English abstract).
-
Li Ganyu, Li Yongjun, Wang Ran, Yang Gaoxue, Xiang Kunpeng, Liu Jia, Tong Lili. 2017. The discovery and significance of Late Carboniferous sanukitoids in Hala' alate Mountain, West Junggar. Acta Petrologica Sinica, 33(1): 16~30(in Chinese with English abstract).
-
Li Ganyu, Li Yongjun, Wang Xuance, Yang Gaoxue, Wang Ran, Xiang Kunpeng, Liu Jia, Tong Lili. 2017. Identifying late Carboniferous sanukitoids in Hala'alate Mountain, Northwest China: New constraint on the closing time of remnant ocean basin in West Junggar. International Geology Review, 59(9): 1116~1130.
-
Li Shuguang. 1994. Implications of εNd-La/Nb, Ba/Nb, Nb/Th diagrams to mantle heterogeneity-classification of island arc basalts and decomposition of EMII component. Geochimica, (2): 105~114(in Chinese with English abstract).
-
Li Wuping, Lu Fengxiang. 1999. New progress of the study of geologic setting for cala alkline volcanic rocks. Bulletin of Geological Science and Technology, 18(2): 15~18(in Chinese with English abstract).
-
Li Yongjun, Tong Lili, Zhang Bing, Liu Jing, Zhang Tianji, Wang Junnian. 2010. On the old and new relationship between Xibeikulasi Formation and Baogutu Formation of the Carboniferous system, West Juggar. Xinjiang Geology, 28(2): 130~136(in Chinese with English abstract).
-
Li Yongjun, Li Ganyu, Tong Lili, Yang Gaoxue, Wang Ran. 2015. Discrimination of ratios of Ta, Hf, Th, La, Zr and Nb for tectonic settings in basalts. Journal of Earth Sciences and Environment, 37(2): 14~21(in Chinese with English abstract).
-
Li Yongjun, Xu Qian, Yang Gaoxue, Chao Wendi, Liu Jia. 2016. Intracontinental "lagged arc volcanic rocks" and its geological significance: Evidence from Early Permian lagged arc magmatism in northern Urho area of Western Junggar. Earth Science Frontiers, 23(4): 190~199(in Chinese with English abstract).
-
Li Yongjun, Li hai, Ning Wentao, Xu Qian, Ren Pengfei, Tao Xiaoyang. 2021. Redefining the Heishantou Formation and defining the Aketamu Formation in West Junggar, Xinjiang. Earth Science Frontiers, 28(2): 348~361 (in Chinese with English abstract).
-
Liao Zhongli, Mo Xuanxue, Yu Xuehui, Zhao Zhidan, Su Shangguo, Dong Guochen. 2001. Development trend of igneous petrology based on the 31st International Geological Congress. Acta Petrologica et Mineralogica, 20(3): 360~366(in Chinese with English abstract).
-
Litvak V D, Poma S. 2010. Geochemistry of mafic Paleocene volcanic rocks in the Valle del Cura region: Implications for the petrogenesis of primary mantle-derived melts over the Pampean flat-slab. Journal of South American Earth Sciences, 29(3): 705~716.
-
Liu Qian, Zhao Guochun, Han Yigui, Zhu Yanlin, Wang Bo, Eizenhöfer P R, Zhang Xiaoran. 2019. Detrital zircon provenance constraints on the final closure of the middle segment of the Paleo-Asian Ocean. Gondwana Research, 69: 73~88.
-
Liu Sheng, Hu Ruizhong, Zhao Junhong, Feng Caixia. 2003. Tectonic background and genesis of volcanic rocks in the Qingshan Formation of Luxi: Evidence of main elements and trace elements. Geochimica, 32(4): 306~316(in Chinese with English abstract).
-
Long Xiaoping, Sun Min, Yuan Chao, Xiao Wenjiao, Chen Hanlin, Zhao Yongjiu, Cai Keda, Li Jiliang. 2006. Genesis of Carboniferous volcanic rocks in the Eastern Junggar: Constraints on the closure of the Junggar Ocean. Acta Petrologica Sinica, (1): 31~40(in Chinese with English abstract).
-
Ma Chong, Xiao Wenjiao, Windley B F, Zhao Guiping, Han Chunming, Zhang Jien, Luo Jun, Li Chao. 2012. Tracing a subducted ridge-transform system in a late Carboniferous accretionary prism of the southern Altaids: Orthogonal sanukitoid dyke swarms in Western Junggar, NW China. Lithos, 140(3): 152~165.
-
MacDonald G A. 1968. Composition and origin of Hawaiian lavas. Geological Society of America Memoirs, 116: 477~52.
-
Mao Xiang, Li Jianghai, Zhang Huatian, Wang Luo. 2012. Study on the distribution and developmental environment of the Late Paleozoic volcanoes in Junggar basin and its adjacent areas. Acta Petrologica Sinica, 28(8): 2381~2391(in Chinese with English abstract).
-
Mo Xuanxue. 2000. Lagged arc volcanic rocks and their geodynamic implications. Abstracts 31st International Geological Congress, 6~8.
-
Mo Xuanxue, Lu Fengxiang, Shen Shangyue, Zhu Qinwen, Hou Zengqian. 1993. Volcanism and Mineralization of Sanjiang Tethys Orogenic Belt. Beijing: Geology Press (in Chinese).
-
Peccerillo R, Taylor S R. 1976. Geochemistry of Eocene calcalkaline colcanic rocks from the Kastamonu area, northem Turkey. Contributions to Mineralogy and Petrology, 58(1): 63~81.
-
Piccardo G B, Zanetti A, Mintener O. 2007. Melt peridotite interaction in the southern Lanzo peridotite: Field, textural and geochemical evidence. Lithos, 94(1-4): 181~209.
-
Rudnick R L, Barth M, Horn I I, Mcdonough W F. 2000. Rutile-bearing refractory eciogites: Missing link beteeen continents and depletea mantle. Science, 287(5451): 278~281.
-
Sengör A M C, Natal'in B A, Burtman U S. 1993. Evolution of the Altaid tectonic collage and Paleozoic crustal growth in Eurasia. Nature, 364: 209~304.
-
Song Xieyan, Zhou Meifu, Cao Zhimin, Robinson P T. 2004. Late Permian rifting of the South China craton caused by the Emeishan mantle plume? Journal of the Geological Society, 161: 773~781.
-
Sun S S, McDonough W F. 1989. Chemical and isotopic systematic of oceanic basalts: Implications for mantle composition and processes. Geological Society, 42 (1): 313~345.
-
Sun Yu, Zhao Chunhuan, Li Yongjun, Tong Lili, Yang Gaoxue, Yan Jing, Jiao Guanglei, Yi Shanxin. 2014. Detrital zircon LA-ICP-MS U-Pb dating of the Carboniferous Xibeikulasi Formation sandstone in the Baogutu area, Western Junggar, and its geological significance. Journal of Stratigraphy, 38(1): 42~50(in Chinese with English abstract).
-
Tang Chao, Li Zhidan, Chen Junqiang, Liu Xiaoxue. 2015. Geochemical characteristics and tectontic setting of tonalite rocks in the Alageobo region, Damaoqi, Inner Mongolia. Mineralogy and Petrology, 35(2): 51~59(in Chinese with English abstract).
-
Tang Gongjian, Wang Qiang, Zhao Zhenhua, Derek A Wyman, Chen Haihong, Jia Xiaohui, Jiang Ziqi. 2009. Geochronology and geochemistry of the Ore-Bearing porphyries in the Baogutu area, western Junggar: Petrogenesis and their implications for tectonics and Cu-Au mineralization. Earth Science, 34(1): 56~74(in Chinese with English abstract).
-
Tang Gongjian, Wang Qiang, Wyman D A, Li Zhengxiang, Zhao Zhenhua, Jia Xiaohui. 2010. Ridge subduction and crustal growth in the Central Asian Orogenic Belt: Evidence from Late Carboniferous adakites and high-Mg diorites in the Western Junggar region, Northern Xinjiang (West China). Chemical Geology, 277(3-4): 281~300.
-
Tang Gongjian, Wang Qiang, Wyman D A, Li Zhenxiang, Zhao Zhenhua, Yang Yueheng. 2012. Late Carboniferous high εNd(t)-εHf(t) granitoids, enclaves and dikes in western Junggar, NW China: Ridge-subduction- related magmatism and crustal growth. Lithos, 140(5): 86~102.
-
Tao Huifei, Wang Qingchen, Yang Xiaofa, Jiang Lin. 2013. Provenance and tectonic setting of Late Carboniferous clastic rocks in West Junggar, Xinjiang, China: A case from the Ala-alat Mountains. Journal of Asian Earth Sciences, 64: 210~222.
-
Tao Huifei, Sun Shu, Wang Qingchen, Yang Xiaofa, Jiang Lin. 2014. Petrography and geochemistry of Lower Carboniferous greywacke and mudstones in Northeast Junggar, China: Implications for provenance, source weathering, and tectonic setting. Journal of Asian Earth Sciences, 87: 11~25.
-
Wang Fangzheng, Yang Meizhen, Zheng Jianping. 2002. Geochemistry and tectonic settings of basement volcanic rocks in the Luliang area of the Junggar basin. Acta Petrologica Sinica, 18(1): 9~16(in Chinese with English abstract).
-
Wang Jian, Su Yuping, Zheng Jianping, Gao Shanlin, Dai Hongkun, Ping Xianquan, Xiong Qing. Niyaz K. 2019. Geochronology and petrogenesis of Jurassic intraplate alkali basalts in the Junggar terrane, NW China: Implication for low-volume basaltic volcanism. Lithos, 324: 202~215.
-
Wang Zhihong, Sun Shu, Li Jiliang, Hou Quanlin, Qin Kezhang, Xiao Wenjiao, Hao Jie. 2003. Paleozoic tectonic evolution of the northern Xinjiang, China: Geochemical and geochronological constraints from the ophiolites. Tectonics, 22(2): 1014~1029.
-
Winchester J A, Floyd P A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 20: 325~343.
-
Windley B F, Alexeiev D, Xiao Wenjiao, Kröner A, Badarch G. 2007. Tectonic models for accretion of the Central Asian Orogenic Belt. Journal of the Geological Society, 164: 31~47.
-
Wood D A. 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth and Planetary Science Letters, 50(1): 11~30.
-
Wu Xiaoqi, Liu Deliang, Li Zhensheng. 2009. Post-collisional volcanism of Kalamaili suture zone. Earth Science Frontiers, 16(3): 220~230(in Chinese with English abstract).
-
Xia Linqi, Xu Xueyi, Xia Zuchun, Li Xiangmin, Ma Zhongpin, Wang Lishe. 2004. Petrogenesis of Carboniferous rift-related volcanic rocks in the Tianshan Mountains, Northwestern China. Geological Society of America Bulletin, 116(3): 419~433.
-
Xia Linqi, Xia Zuchun, Xu Xueyi, Li Xiangmin, Ma Zhongping. 2007. The discrimination between continental basalt and island arc basalt based on geochemical method. Acta Petrologica et Mineralogica, 26(1): 77~89(in Chinese with English abstract).
-
Xia Linqi, Xia Zuchun, Xu Xueyi, Li Xiangmin, Ma Zhongpin. 2008. Relative contributions of crust and mantle to the generation of the Tianshan Carboniferous rift-related basic lavas, Northwestern China. Journal of Asian Earth Sciences, 31(4-6): 357~378.
-
Xiang Kunpeng, Li Yongjun, Li Zhao, Wang Ran, Yang Gaoxue, Duan Fenghao, Li Ganyu. 2015. LA-ICP-MS zircon age and geochemistry of the Aladeyikesai Formation volcanic rocks in the Halaalate Mountain of West Junggar, Xinjiang, and their tectonic significance. Acta Geologica Sinica, 89(5): 843~855(in Chinese with English abstract).
-
Xiao Wenjiao, Han Chunming, Yuan Chao, Sun Min, Lin Shoufa, Chen Hanlin, Li Zilong, Li Jiliang, Sun Shu. 2008. Middle Cambrian to Permian subduction-related accretionary orogenesis of North Xinjiang, NW China: Implications for the tectonic evolution of Central Asia. Journal of Asian Earth Sciences, 32: 102~117.
-
Xiao Wenjiao, Windley B F, Yuan Chao, Sun Min, Han Chunming, Lin Shoufa, Chen Hui, Yan Quanren, Liu Dunyi, Qin Kezhang, Li Jiliang, Sun Shilu. 2009. Paleozoic multiple subduction-accretion processes of the southern Altaids. American Journal of Science, 309: 221~270.
-
Xiao Wenjiao, Windley B F, Sun Shu, Li Jiliang, Huang Baochun, Han Chunming, Yuan Chao, Sun Ming, Chen Hanlin. 2015. A tale of amalgamation of three Permo-Triassic collage systems in Central Asia: Oroclines, sutures, and terminal accretion. Annual Review of Earth and Planetary Sciences, 43: 16. 1~16. 31.
-
Xiao Wenjiao, Song Dongfang, Windley B F, Li Jiliang, Han Chunming, Wan Bo, Zhang Jien, Ao Songjian, Zhang Zhiyong. 2019. Research progress on accretionary and mineralization of Central Asia. Scientia Sinica (Terrae), 49(10): 1512~1545(in Chinese).
-
Xie Qiuhong, Zhang Zhaochong, Foley S F, Chen Chunfei, Cheng Zhiguo, Wang Yu, Kong Weiliang, Lv Yiwen, Santosh M, Jin Qizhen, Krmicek Lukas, Zhu Xiangkun. 2023. Transition from tholeiitic to alkali basalts via interaction between decarbonated eclogite-derived melts and peridotite. Chemical Geology, 621: 121354.
-
Xu Qinqin, Ji Jianqing, Zhao Lei, Gong Junfeng, Zhou Jing, He Guoqi, Zhong Dalai, Wang Jinduo, Lee G. 2013. Tectonic evolution and continental crust growth of Northern Xinjiang in Northwestern China: Remnant ocean model. Earth-Science Reviews, 126(11): 178~205.
-
Xu Xueyi, Li Rongshe, Chen Junlu, Ma Zhongping, Li Zhipei, Wang Hongliang, Bai Jianke, Tang Zhuo. 2014. New constrains on the Paleozoic tectonic evolution of the Northern Xinjiang area. Acta Petrologica Sinica, 30(6): 1521~1534(in Chinese with English abstract).
-
Yang Gaoxue, Li Yongjun, Si Guohui, Wu Hongen, Jin Zhao, Zhang Yongzhi. 2010a. LA-ICP-MS U-Pb zircon dating of the Beilekuduke granite in Kalamaili area, East Junggar, Xinjiang, China and its geological implication. Geotectonica et Metallogenia, 34(1): 133~138(in Chinese with English abstract).
-
Yang Gaoxue, Li Yongjun, Li Zhucang, Liu Xiaoyu, Yang Baokai, Wu Hongen. 2010b. Genesis and tectonic environment of post-collision volcanic rocks in the northeast margin of East Junggar. Earth Science Frontiers, 17(1): 49~60(in Chinese with English abstract).
-
Yang Gaoxue, Li Yongjun, Gu Pingyang, Yang Baokai, Tong Lili, Zhang Hongwei. 2012a. Geochronological and geochemical study of the Darbut ophiolitic complex in the West Junggar (NW China): Implications for petrogenesis and tectonic evolution. Gondwana Research, 21(4): 1037~1049.
-
Yang Gaoxue, Li Yongjun, Santosh M, Gu Pingyang, Yang Baokai, Zhang Bing, Wang Haibo, Zhong Xing, Tong Lili. 2012b. A Neoproterozoic seamount in the Paleoasian Ocean: Evidence from zircon U-Pb geochronology and geochemistry of the Mayile ophiolitic mélange in West Junggar, NW China. Lithos, 140: 53~65.
-
Yang Wei, Wang Guocan, Zong Ruiwen, Xiao Long, Li Li, Yang Gang. 2015. Determination of Silurian-Devonian arc-basin pattern in Western Junggar and its regional tectonic significance. Earth Science, 40(3): 448~460(in Chinese with English abstract).
-
Yin Jiyuan, Yuan Chao, Sun Min, Long Xiaoping, Zhao Guochun, Wong Kenng Powan, Geng Hongyan, Cai Keda. 2010. Late Carboniferous high-Mg dioritic dikes in Western Junggar, NW China: Geochemical features, petrogenesis and tectonic implications. Gondwana Research, 17(1): 145~152.
-
Yin Jiyuan, Yuan Chao, Wang Yujing, Long Xiaoping, Guan Yili. 2011. Magmatic records on the Late Paleozoic tectonic evolution of Western Junggar, Xinjiang. Geotectonica et Metallogenia, 32(2): 278~291(in Chinese with English abstract).
-
Yin Jiyuan, Chen Wen, Long Xiaoping, Yuan Chao, Zhang Yunying, Wang Yujing, Guan Yili. 2013. Age and geochemical characteristics of Early Permian diorite in the Baiyanghe region, West Junggar: Petrogenesis and tectonic implication. Geochimica, 42(4): 361~372(in Chinese with English abstract).
-
Yin Jiyuan, Chen Wen, Yuan Chao, Yu Shun, Xiao Wenjiao, Long Xiaoping, Li Jie, Sun Jingbo. 2015. Petrogenesis of Early Carboniferous adakitic dikes, Sawur region, Northern West Junggar, NW China: Implications for geodynamic evolution. Gondwana Research, 27(4): 1630~1645.
-
Zhang Zhaochong, Wang Fusheng, Hao Yanli, JohnJ. Mahoney. 2004. Geochemistry of the picrites and associated basalts from the Emeishan large lgneous basalt province and constraints on their source region. Acta Geologica Sinica, (2): 171~180(in Chinese with English abstract).
-
Zhang Zhaochong, Zhou Gang, Kusky Timothy M, Yan Shenghao, Chen Bailin and Zhao Li. 2009. Late Paleozoic volcanic record of the Northern Junggar terrane, Xinjiang, Northwestern China: Major and trace element characteristics, Sr-Nd isotopic systematics and implications for tectonic evolution. Gondwana Research, 16(2): 201~215.
-
Zhao Xia, Jia Chengzao, Zhang Guangya, Wei Yanzhao, Lai Shaocong, Fang Xiang, Zhang Lijun. 2008. Geochemistry and tectonic settings of Carboniferous intermediate-basic volcanic rocks in Ludong-Wucaiwan, Junggar basin. Earth Science Frontiers, 15(2): 272~279(in Chinese with English abstract).
-
Zhao Zehui, Guo Zhaojie, Han Baofu, Wang Yi. 2006. The geochemical characteristics and tectonic-magmatic implications of the latest Paleozoic volcanic rocks from Santanghu basin, Eastern Xinjiang, Northwest China. Acta Petrologica Sinica, (1): 199~214(in Chinese with English abstract).
-
Zhou Dingwu, Liu Yiqun, Xing Xiujuan, Hao Jianrong, Dong Yunpeng, Ouyang Zhengjian. 2006. Paleotectonic environment restoration and regional tectonic background tracing from Permian basalt formation in Tu-Ha and Santanghu basins of Xinjiang. Scientia Sinica(Terrae), 36(2): 143~153(in Chinese with English abstract).
-
Zhou Taofa, Yuan Feng, Fan Yu, Zhang Dayu, Cooke D, Zhao Guochun. 2008. Granites in the Sawuer region of the West Junggar, Xinjiang Province, China: Geochronological and geochemical characteristics and their geodynamic significance. Lithos, 106(3-4): 191~206.
-
Zindler A, Hart S. 1986. Chemical geodynamics. Annual Review of Earth and Planetary Sciences, 14: 493~571.
-
Zong Ruiwen, Fan Ruoying, Gong Yiming. 2015. Advances in the research on Carboniferous deep-water marine deposits in Western Junggar, Northwestern China. Geological Journal, 50(2): 111~121.
-
晁文迪, 李永军, 王冉, 杨高学, 向坤鹏, 刘佳, 徐倩. 2015. 西准噶尔“滞后型”弧岩浆作用: 来自西准噶尔东部乌尔禾早二叠世中基性岩墙群的证据. 岩石矿物学杂志, 34(2): 171~183.
-
陈博, 朱永峰. 2011. 新疆达拉布特蛇绿混杂岩中辉长岩岩石学、微量元素地球化学和锆石U-Pb年代学研究. 岩石学报, 27(6): 1746~1758.
-
陈石, 郭召杰. 2010. 达拉布特蛇绿岩带的时限和属性以及对西准噶尔晚古生代构造演化的讨论. 岩石学报, 26(8): 2336~2344.
-
陈双双, 苏玉平, 郑建平, 魏颖. 2013. 克拉玛依侏罗纪玄武岩地球化学特征及其壳幔作用过程研究. 地球化学, 42(1): 29~45.
-
陈廷方. 2003. 云南腾冲火山岩岩石学特征. 沉积与特提斯地质, 23(4): 56~61.
-
郭丽爽, 刘玉琳, 王政华, 宋达, 许发军, 苏犁. 2010. 西准噶尔包古图地区地层火山岩锆石LA-ICP-MSU-Pb年代学研究. 岩石学报, 26(2): 471~477.
-
韩宝福, 季建清, 宋彪, 陈立辉, 张磊. 2006. 新疆准噶尔晚古生代陆壳垂向生长(Ⅰ)——后碰撞深成岩浆活动的时限. 岩石学报, 22(5): 1077~1086.
-
郝建荣, 周鼎武, 柳益群, 邢秀娟. 2006. 新疆三塘湖盆地二叠纪火山岩岩石地球化学及其构造环境分析. 岩石学报, 22(1): 189~198.
-
贺新星, 肖龙, 王国灿, 高睿, 杨钢, 鄢圣武. 2015. 西准噶尔晚古生代中基性岩墙群岩石学成因及地质意义. 地球科学, 40(5): 777~796.
-
姜常义, 夏明哲, 钱壮志, 余旭, 卢荣辉, 郭芳放. 2009. 新疆喀拉通克镁铁质岩体群的岩石成因研究. 岩石学报, 25(4): 749~764.
-
赖绍聪, 秦江锋, 李学军, 臧文娟. 2010. 昌宁-孟连缝合带干龙塘-弄巴蛇绿岩地球化学及Sr-Nd-Pb同位素组成研究. 岩石学报, 26(11): 3195~3205.
-
李大鹏, 陈岳龙, 王忠, 刘长征. 2010. 内蒙古不同时代花岗岩类Nd、Pb同位素特征及其地质意义. 现代地质, 24(5): 821~831.
-
李甘雨, 李永军, 向坤鹏, 王冉, 刘佳, 李钊, 杨高学. 2016. 西准噶尔哈拉阿拉特组的重新厘定及区域对比. 地层学杂志, 40(1): 76~84.
-
李曙光. 1994. εNd-La/Nb、Ba/Nb、Nb/Th图对地幔不均一性研究的意义—岛弧火山岩分类及EMII端元的分解. 地球化学, (2): 105~114.
-
李伍平, 路凤香. 1999. 钙碱性火山岩构造背景的研究进展. 地质科技情报, 18(2): 15~18.
-
李永军, 佟丽莉, 张兵, 刘静, 张天继, 王军年. 2010. 论西准噶尔石炭系希贝库拉斯组与包古图组的新老关系. 新疆地质, 28(2): 130~136.
-
李永军, 李甘雨, 佟丽莉, 杨高学, 王冉. 2015. 玄武岩类形成的大地构造环境的Ta、Hf、Th、La、Zr、Nb比值对比判别. 地球科学与环境学报, 37(2): 14~21.
-
李永军, 徐倩, 杨高学, 晁文迪, 刘佳. 2016. 陆内“滞后”弧岩浆岩特征及其地质意义: 来自西准噶尔乌尔禾北早二叠世岩浆作用的证据. 地学前缘, 23(4): 190~199.
-
李永军, 李海, 宁文涛, 徐倩, 任朋飞, 陶晓杨. 2021. 新疆准噶尔地层区黑山头组的重新厘定及阿克塔木组新建. 地学前缘, 28(2): 348~361.
-
廖忠礼, 莫宣学, 喻学惠, 赵志丹, 苏尚国, 董国臣. 2001. 从31届地质大会看火成岩石学的研究动向. 岩石矿物学杂志, 20(3): 360~366.
-
刘燊, 胡瑞忠, 赵军红, 冯彩霞. 2003. 鲁西青山组火山岩形成的构造背景及其成因探讨： 主元素和微量元素证据. 地球化学, 32(4): 306~316.
-
龙晓平, 孙敏, 袁超, 肖文交, 陈汉林, 赵永久, 蔡克大, 李继亮. 2006. 东准噶尔石炭系火山岩的形成机制及其对准噶尔洋盆闭合时限的制约. 岩石学报, (1): 31~40.
-
毛翔, 李江海, 张华添, 王洛. 2012. 准噶尔盆地及其周缘地区晚古生代火山机构分布与发育环境分析. 岩石学报, 28(8): 2381~2391.
-
莫宣学, 路凤香, 沈上越, 朱勤文, 侯增谦. 1993. 三江特提斯火山作用与成矿. 北京： 地质出版社.
-
孙羽, 赵春环, 李永军, 佟丽莉, 杨高学, 严境, 焦光磊, 易善鑫. 2014. 西准噶尔包古图地区石炭系希贝库拉斯组碎屑锆石LA-ICP-MS U-Pb年代学及其地质意义. 地层学杂志, 38(1): 42~50.
-
汤超, 李志丹, 陈军强, 刘晓雪. 2015. 内蒙古达茂旗阿拉格敖包地区英云闪长岩地球化学特征及构造背景. 矿物岩石, 35(2): 51~59.
-
唐功建, 王强, 赵振华, Derek A W, 陈海红, 贾小辉, 姜子琦. 2009. 西准噶尔包古图成矿斑岩年代学与地球化学: 岩石成因与构造、铜金成矿意义. 地球科学: 中国地质大学学报, 34(1): 56~74.
-
王方正, 杨梅珍, 郑建平. 2002. 准噶尔盆地陆梁地区基底火山岩的岩石地球化学及其构造环境. 岩石学报, 18(1): 9~16.
-
吴小奇, 刘德良, 李振生. 2009. 卡拉麦里缝合带后碰撞期火山活动. 地学前缘, 16(3): 220~230.
-
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. 岩石矿物学杂志, 26(1): 77~89.
-
向坤鹏, 李永军, 李钊, 王冉, 杨高学, 段丰浩, 李甘雨. 2015. 新疆西准噶尔哈拉阿拉特山火山岩LA-ICP- MS锆石U-Pb年龄、地球化学特征及意义. 地质学报, 89(5): 843~855.
-
肖文交, 宋东方, Windley B F, 李继亮, 韩春明, 万博, 张继恩, 敖松坚, 张志勇. 2019. 中亚增生造山过程与成矿作用研究进展. 中国科学: 地球科学, 49(10): 1512~1545.
-
徐学义, 李荣社, 陈隽璐, 马中平, 李智佩, 王洪亮, 白建科, 唐卓. 2014. 新疆北部古生代构造演化的几点认识. 岩石学报, 30(6): 1521~1534.
-
杨高学, 李永军, 司国辉, 吴宏恩, 金朝, 张永智. 2010a. 东准卡拉麦里地区贝勒库都克岩体锆石LA-ICPMS U-Pb测年及地质意义. 大地构造与成矿学, 34(1): 133~138.
-
杨高学, 李永军, 李注苍, 刘晓宇, 杨宝凯, 吴宏恩. 2010b. 东准噶尔东北缘后碰撞火山岩成因与构造环境. 地学前缘, 17(1): 49~60.
-
杨维, 王国灿, 纵瑞文, 肖龙, 李理, 杨钢. 2015. 西准噶尔志留纪—泥盆纪弧盆格局的确定及其区域构造演化意义. 地球科学(中国地质大学学报), 40(3): 448~460.
-
尹继元, 陈文, 龙晓平, 袁超, 张运迎, 王毓婧, 关义立. 2013. 西准噶尔白杨河地区早二叠世闪长岩的年代学和地球化学: 岩石成因和构造意义. 地球化学, 42(4): 361~372.
-
张招崇, 王福生, 郝艳丽, Mahoney J J. 2004. 峨眉山大火成岩省中苦橄岩与其共生岩石的地球化学特征及其对源区的约束. 地质学报, (2): 171~180.
-
赵霞, 贾承造, 张光亚, 卫延召, 赖绍聪, 方向, 张丽君. 2008. 准噶尔盆地陆东-五彩湾地区石炭系中、基性火山岩地球化学及其形成环境. 地学前缘, 15(2): 272~279.
-
赵泽辉, 郭召杰, 韩宝福, 王毅. 2006. 新疆三塘湖盆地古生代晚期火山岩地球化学特征及其构造-岩浆演化意义. 岩石学报, (1): 199~214.
-
周鼎武, 柳益群, 邢秀娟, 郝建荣, 董云鹏, 欧阳征健. 2006. 新疆吐-哈、三塘湖盆地二叠纪玄武岩形成古构造环境恢复及区域构造背景示踪. 中国科学(D辑): 地球科学, 36(2): 143~153.
-
摘要
西准噶尔构造带位于中亚造山带西南缘，是研究古亚洲洋演化的关键地区。该带在晚石炭世构造属性与演化认识久存争议。最新发现的西准噶尔构造带下二叠统白杨河组火山岩为解决这一争议提供了可能。白杨河组火山岩主要为玄武岩及其共生的次火山岩，发育完整的陆相火山机构，不整合于下二叠统佳木河组陆相磨拉石建造之上。火山岩高Al2O3、低TiO2，属钙碱性中低钾系列。ΣLREE/ΣHREE为2.31~5.00，富集LREE，δEu为0.99~1.29。富集大离子亲石元素Ba、K、Sr，亏损高场强元素Nb、Ta、Zr、Hf，具有明显“TNT”负异常。(206Pb/204Pb)i=17.924~18.000，(207Pb/204Pb)i=15.469~15.509，(208Pb/204Pb)i=37.737~37.879。正的εNd(t)(+5.93~+6.76)值和相对低的初始87Sr/86Sr比值(0.703974~0.704299)，表明源区可能为俯冲板片脱水产生的流体交代的亏损地幔。这些特征与晚石炭世海相弧火山岩地球化学特征总体一致，时空上密切相关，具有同源、同成因、同构造背景特色，显示了较好的继承性。白杨河组晚于佳木河组陆相磨拉石，明显滞后于洋盆闭合时限，属“滞后弧型”建造。结合前人研究和区域地质背景，本文认为西准噶尔构造带洋盆在晚石炭世关闭后，深部的俯冲作用持续到下二叠统白杨河组形成后，其洋-陆转换过程中经历了“滞后弧”这一独特的构造演化过程。“滞后弧型”火山岩为追索古亚洲洋在本区闭合位置和约束构造演化过程提供新的制约。
Abstract
West Junggar structural zone is located in the southwestern part of the Central Asian Orogenic Belt and is considered a key area for studying the evolution of the Paleo-Asian Ocean. However, there are currently controversies regarding the tectonic evolution of the West Junggar tectonic zone during the late Carboniferous period. The recently discovered volcanic rocks from the Lower Permian Baiyanghe Formation have the potential to address these controversies. These volcanic rocks mainly consist of basalts and associated subvolcanic rocks. They display an angular unconformity relationship with the Lower Permian Jiamuhe Formation, which represents a continental molasse sequence. Geochemically, the basalts exhibit relatively high concentrations of Al2O3 and low concentrations of TiO2, placing them within the middle-low K calc-alkaline series. The ratio of ΣLREE/ΣHREE ranges from 2.31 to 5.00. All the basalts from the Baiyanghe Formation are enriched in LREE without obvious Eu anomaly (δEu=0.99~1.29). Furthermore, they are enriched in light LILE, such as Ba, K, and Sr. In addition, they are depleted in HFSE such as Nb, Ta, Zr, and Hf, exhibiting a negative “TNT” anomaly. Isotopic composition shows (206Pb/204Pb)i =17.924~18.000, (207Pb/204Pb)i =15.469~15.509, (208Pb/204Pb)i =37.737~37.879. The εNd(t) values range from +5.93 to +6.76, and the 87Sr/86Sr ratios range from 0.703974 to 0.704299. These characteristics suggest that the source of these basalts is probably the dehydration of a subducted plate to produce the fluid that results in a metasomatically depleted mantle. These geochemical characteristics are consistent with those of Late Carboniferous marine island arc basalts, indicating temporal and spatial correlation and suggesting excellent inheritance. The Baiyanghe Formation is later in age than the Jiamuhe Formation molasse, which confirms that the Baiyanghe Formation basalts were erupted after the closure of the ocean basin, so it belongs to the “lagged arc” formation. Considering previous research and the regional geological background, it can be inferred that the ocean basin closed in the Late Carboniferous while deep subduction continued, eventually leading to the formation of the Baiyanghe Formation. This unique tectonic evolution process of the “lagged arc” occurred during the ocean-continent transition. The volcanic rocks associated with the “lagged arc” formation provide crucial constraints for determining the suture location of the Paleo-Asian Ocean and understanding the tectonic evolution process in West Junggar tectonic zone.
Keywords
Baiyanghe Formation ； “lagged arc” basalts ； geochemistry ； Early Permian ； Urho-Hashan ； Xinjiang
