| 准噶尔盆地东北缘石炭系火山岩形成机制:对准噶尔洋盆闭合时限的新启示 |
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| 引用本文： | 焦小芹,张关龙,牛花朋,王圣柱,于洪洲,熊峥嵘,周健,谷文龙.准噶尔盆地东北缘石炭系火山岩形成机制:对准噶尔洋盆闭合时限的新启示[J].地学前缘,2022,29(4):385-402. |
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| 作者姓名： | 焦小芹 张关龙 牛花朋 王圣柱 于洪洲 熊峥嵘 周健 谷文龙 |
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| 作者单位： | 1.中国石油大学(北京) 油气资源与探测国家重点实验室, 北京 1022492.中国石油大学(北京) 地球科学学院, 北京 1022493.中国石油化工股份有限公司 胜利油田分公司 勘探开发研究院, 山东 东营 257015 |
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| 基金项目： | 国家科技重大专项(2017ZX05063002—006);北京高等学校青年英才计划项目(YETP0669) |
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| 摘 要： | 准噶尔古大洋作为古亚洲洋北部的重要分支及阶段性演化产物,其洋盆的俯冲、闭合时限以及盆地基底属性一直存在分歧。本文选取准噶尔盆地东北缘(乌伦古地区)石炭系火山岩来说明其岩浆来源及成因机制,通过主微量元素、Sr-Nd同位素分析结果,进一步阐明准噶尔洋盆在晚古生代的闭合时限。本次研究包括玄武岩、玄武质安山岩和安山岩三类火山岩,岩体显示低TiO2(0.60%~0.84%)、较高的全碱K2O+Na2O含量(1.18%~8.59%),玄武岩为岛弧拉斑系列,安山岩类的钙碱元素含量高,具有火山弧火山岩特征。中-低87Sr/86Sr(i)(0.703 250~0.704 559)、相对亏损的Nd同位素(+4.8~+6.8)以及tDM2(483~625 Ma)值表明玄武岩、玄武质安山岩和安山岩同为亏损地幔熔融岩浆分异结晶的产物,安山岩为地幔熔融岩浆后期分离结晶形成;微量元素与同位素地球化学示踪暗示玄武岩、玄武质安山岩和安山岩含有洋壳俯冲过程的脱水流体交代上覆地幔楔的消减组分,安山岩在深部岩浆房经历了壳-幔混合作用,受地壳成分的混染程度更大。大离子亲石元素(LILE)Ba、Sr和轻稀土元素、不相容元素(Th、U、K)相对富集,高场强元素(HFSE)Nb、Ta相对亏损,以及Pb、Zr、Hf的富集,说明该区属于与俯冲消减带相关的构造背景;结合本套火山岩高Ba/La(30.14~208.86)值、低TiO2(0.60%~0.84%)值,以及Ce/Nb比(8.71~12.05)、Th/Nb比(0.93~1.74)等,表明准噶尔洋盆于石炭纪沿着大陆板块下部持续俯冲,洋壳板片的俯冲脱水流体交代地幔楔后增生岛弧。该套中-基性火山岩建造佐证了准噶尔洋盆闭合时限为晚石炭世(ca. 305.5±4.4 Ma),结合区域地质资料分析,提出与俯冲带有关的岩浆通过岛弧拼贴增生到大陆地壳上,进一步为准噶尔盆地基底的岛弧拼贴成因提供了新依据。
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| 关 键 词： | 准噶尔盆地 乌伦古 石炭系 火山岩 岛弧 岩石成因 |
| 收稿时间： | 2021-07-29 |
Genesis of Carboniferous volcanic rocks in northeastern Junggar Basin: New insights into the Junggar Ocean closure |
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| JIAO Xiaoqin,ZHANG Guanlong,NIU Huapeng,WANG Shengzhu,YU Hongzhou,XIONG Zhengrong,ZHOU Jian,GU Wenlong.Genesis of Carboniferous volcanic rocks in northeastern Junggar Basin: New insights into the Junggar Ocean closure[J].Earth Science Frontiers,2022,29(4):385-402. |
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| Authors: | JIAO Xiaoqin ZHANG Guanlong NIU Huapeng WANG Shengzhu YU Hongzhou XIONG Zhengrong ZHOU Jian GU Wenlong |
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| Institution: | 1. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China2. College of Geosciences, China University of Petroleum, Beijing 102249, China3. Research Institute of Petroleum Exploration and Development, Sinopec Shengli Oilfield Company, Dongying 257015, China |
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| Abstract: | The Junggar Ocean is an important branch of the northern Paleo-Asian Ocean and part of its stage evolution. However, the subduction and closure time of the Junggar Ocean and the basement property of the Junggar Basin are still unclear. In this study, Carboniferous volcanic rocks including basalts, basaltic andesites, and andesites in the northeastern margin of the Junggar Basin (Wulungu area) were investigated to reveal their magmatic provenance and formation mechanism. Combined with major and trace element and Sr-Nd isotope analysis, the closure time of the Junggar Ocean during the Late Paleozoic was further clarified. Three types of basement volcanic rocks with low TiO2 (0.60%-0.84%) and relatively high alkaline (1.18%-8.59%) contents were identified. The basalts belong to tholeiitic series while andesites to high calc-alkaline series, indicating a volcanic arc association. The low-medium 87Sr/86Sr(i) ratios (0.703250- 0.704559) and relatively depleted εNd(t) (+4.8-+6.8) and tDM2 (483-625 Ma) values suggested all three types formed from fractional crystallization of depleted mantle magmas, with andesites formed later than the others. Trace element and isotope tracing suggested the volcanic rocks originated from mantle wedge metasomatized by slab-derived fluid, with andesites more impacted by crustal contamination. The volcanic rocks were enriched in LILEs (Ba, Sr), Pb, Zr and Hf, and showed strong negative Nb and Ta anomalies. These characteristics are consistent with the tectonic setting of a subduction zone. The rock series showed enrichments of incompatible elements (Th, U, K) and LREE, high Ba/La ratio (30.14-208.86), low TiO2 content (0.60%-0.84%), and low Ce/NB (8.71-12.05) and Th/Nb (0.93-1.74) ratios. These characteristics support the continuing Carboniferous Junggar Ocean subduction along the continental block, which led to island arc accretion, followed by Junggar Ocean closure in the Late Carboniferous (ca. 305.5±4.4 Ma) and subduction-related magma superposition onto the continental crust through island arc. The above results provided new basis for the understanding of basement formation in the Junggar Basin. |
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| Keywords: | Junggar Basin Wulungu Carboniferous volcanic rocks island arc petrogenesis |
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