地学前缘 ›› 2015, Vol. 22 ›› Issue (1): 238-250.DOI: 10.13745/j.esf.2015.01.020

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觉罗塔格南缘石炭系火山岩地球化学特征及其对古亚洲洋南缘构造演化的指示意义

 木合塔尔·扎日, 尼加提·阿布都逊, 吴兆宁   

  1. 1. 新疆大学 地质与矿业工程学院, 新疆 乌鲁木齐 830046
    2. 新疆中亚造山带大陆动力学与成矿预测自治区重点实验室, 新疆 乌鲁木齐 830046
  • 收稿日期:2013-12-12 修回日期:2014-05-22 出版日期:2015-01-15 发布日期:2015-01-15
  • 作者简介:木合塔尔·扎日(1960—)，男，博士，教授，硕士生导师，从事区域大地构造学的教学与科研工作。E-mail:mhtrz_xju@sina.com.cn
  • 基金资助:

    国家自然科学基金项目(41162006，40862006)；新疆中亚造山带大陆动力学与成矿预测实验室开放基金项目(XJDX1102-2013-01)

Geochemical characteristics of the volcanics from the Southern Jueluotage Area and their constraints on the tectonic evolution of Paleo-Asian Ocean

  • Received:2013-12-12 Revised:2014-05-22 Online:2015-01-15 Published:2015-01-15

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摘要：

研究了觉罗塔格南缘石炭系雅满苏组与土古土布拉克组火山岩的主量元素、微量元素和Sr-Nd同位素特征。结果显示，雅满苏组(中)酸性熔岩属贫钾钙碱性岩浆系列，Mg#值介于0.49~0.51，ISr介于0.706 42~0.707 68、εNd(t) 为3.28~5.49，富集轻稀土与大离子亲石元素、相对亏损重稀土与高场强元素，具中等负Eu异常(δEu=0.62~0.65)，其形成可能与幔源基性岩浆结晶分异有关。土古土布拉克组中(酸)性火山岩属钙碱性高钾钙碱性系列，Mg#值介于0.53~0.57，轻稀土相对富集，重稀土相对亏损，略具负铕异常(δEu=0.63~0.84)，富集大离子亲石元素，相对亏损高场强元素，ISr介于0.703 71~0.708 47、εNd(t)为6.48~6.83，表明其母岩浆来源于受交代的富集岩石圈地幔楔。结合区域地质背景研究成果，认为它们形成于古亚洲洋壳向南俯冲的岛弧环境，并且早石炭世的雅满苏组火山岩代表不成熟的洋内岛弧的产物，而晚石炭世的土古土布拉克组火山岩是岛弧演化到相对成熟阶段的产物。这种物质成分和时空分布特征揭示的石炭纪该区壳幔岩石圈由北向南、由老到新明显增厚现象，为古亚洲洋南缘吐哈古洋壳当时在该处具有向南俯冲的极性提供了有力证据。

关键词: 觉罗塔格, 雅满苏组, 土古土布拉克组, 岛弧, 古亚洲洋, 构造演化

Abstract:

This paper deals with the geochemical data including major and trace elements and Sr-Nd isotopes of the volcanics from Yamansu Formation and Tugut Bulak Formation, occurring along the southern Juoluotage tectonic belt. Yamansu felsic lava is mainly of lowK tholeiite series, Mg# changes from 49 to 51. The values of ISr range from 0.70642 to 0.70768 and εNd(t) from 3.28 to 5.49. It is relatively enriched in LREEs and LILEs, and depleted in HREE and HFSE with moderate Eu anomalies(δEu=0.620.65). All these geochemical characteristics suggest that the formation of the Yamansu felsic lava is probably related to differentiation process of mantlederived mafic magma. The andesites from the Tugut Bulak Formation are mainly of calc-alkaline and high K calcalkaline series, Mg# changes from 53 to 57. Geochemical studies on trace elements demonstrate the total LREE enrichment and relative HREE depletion with slight negative Eu anomalies(δEu=0.630.84). The primordial mantlenormalized trace element patterns are characterized by LILE enrichment and HFSE depletion. SrNd isotopic data show that the ISr values range from 0.70371 to 0.70498, while εNd(t) changes from 6.48 to 6.83, indicating that the parent magma is originated from a juvenile lithospheric mantle wedge that was previously metasomatized by subduction zone fluids. Combining with previous studies, we suggest volcanics from the southern Juoluotage area were formed in island arc setting which was related to southward subduction of Paleo-Asian Oceanic lithosphere. Early Carboniferous volcanics from Yamansu Formation represent juvenile intra-oceanic arc, while Late Carboniferous volcanics from Tugut Bulak formation indicate that the previous juvenile arc had evolved to a relatively mature stage. The composition and temporalspatial distribution of the volcanics in the study area reveals the southward thickening of lithosphere during Carboniferous, which provides strong evidence for the southward subduction of the southern margin of Tuha oceanic crust.

Key words: Juoluotage, Yamansu Formation, Tugut Bulak Formation, volcanic arc, Paleo-Asian Ocean, tectonic evolution

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