赵思旭,曾志刚. 马里亚纳海槽中部、南部火山岩地球化学特征及源区地幔性质[J]. 海洋地质与第四纪地质,2023,43(5): 73-84. DOI: 10.16562/j.cnki.0256-1492.2022112101
引用本文: 赵思旭,曾志刚. 马里亚纳海槽中部、南部火山岩地球化学特征及源区地幔性质[J]. 海洋地质与第四纪地质,2023,43(5): 73-84. DOI: 10.16562/j.cnki.0256-1492.2022112101
ZHAO Sixu,ZENG Zhigang. Petrogeochemical characteristics of mantle sources of volcanic rocks in the southern and middle Mariana Trough[J]. Marine Geology & Quaternary Geology,2023,43(5):73-84. DOI: 10.16562/j.cnki.0256-1492.2022112101
Citation: ZHAO Sixu,ZENG Zhigang. Petrogeochemical characteristics of mantle sources of volcanic rocks in the southern and middle Mariana Trough[J]. Marine Geology & Quaternary Geology,2023,43(5):73-84. DOI: 10.16562/j.cnki.0256-1492.2022112101

马里亚纳海槽中部、南部火山岩地球化学特征及源区地幔性质

Petrogeochemical characteristics of mantle sources of volcanic rocks in the southern and middle Mariana Trough

  • 摘要: 马里亚纳海槽作为正在活动的典型弧后盆地,是研究俯冲作用对岩浆作用和壳幔动力学影响的理想场所。通过对采自该海槽中南部的样品进行系统的岩石地球化学特征对比与研究,并结合前人已发表的岩石地球化学数据,探讨了马里亚纳海槽中南部的地幔富集(亏损)程度、地幔熔融程度、地幔熔融深度以及俯冲物质的加入程度。结果表明:(1)马里亚纳海槽中南部主要发育一套中低钾钙碱性系列玄武岩、玄武质安山岩;(2)海底岩石富集了大离子亲石元素、轻稀土元素,亏损高场强元素、重稀土元素;(3)将马里亚纳海槽沿扩张中心分为三段,对每段地幔熔融的程度和深度进行计算并且消除地幔不均一性的影响,发现在15°N和18°N附近二者呈现负相关关系,其余地区则呈现正相关关系,证明海槽存在两种地幔熔融模式;(4)微量元素比值显示海槽受多种俯冲组分影响,并且马里亚纳海槽南部的南段可能存在另一个富水熔体端元,可能是导致海槽扩张速率较快的原因。对俯冲物质的加入程度进行计算,发现靠近15°N与18°N俯冲组分的影响变弱,这进一步表明,马里亚纳海槽火山岩的变化可能是由于类似N-MORB的地幔源区与类似岛弧的地幔源区混合造成的;俯冲物质是控制地幔熔融程度的主要因素,并且扩张速率与地幔富集/亏损程度等也发挥了重要作用。

     

    Abstract: The Mariana Trough, as a typical active back-arc basin, is an ideal place to study the effects of subduction on magmatism and crust-mantle dynamics. The petrogeochemical characteristics of the samples from two areas of the trough were revealed based on the published petrogeochemical data, from which the degree of mantle enrichment/depletion, the degree of mantle melting, the depth of mantle melting, and the degree of subduction material incorporation in the southern and middle Mariana Trough were clarified. Results show that a set of medium-low potassium calc-alkaline series basalt and basaltic andesite occur in the southern and middle Mariana Trough. The volcanic rocks are rich in large ionic lithophile elements (LILE) and light rare earth elements (LREE) while deficient in high field strength elements (HFSE) and heavy rare earth elements (HREE). The Mariana Trough could be divided into three sectors along spreading center, and the mantle-melting degree and the depth of each sector were calculated and the effect of mantle heterogeneity eliminated. The correlation between mantle-melting degree and the depth in each sector was found negative near 15°N and 18°N, but positive in the other areas, which proves that there are two mantle-melting modes in the trough. Volcanic rocks in the southern and middle Mariana Trough are influenced by multiple subduction-components and there may be another water-rich melt end-member in the southern part of the trough that may be resulted from the faster spreading rate of the trough. Calculations of the extent of subduction accretion show that the influence of subduction components weakens near 15°N and 18°N. The variation of volcanic rocks in the Mariana Trough may be caused by the mixing of an N-MORB-like mantle source involved with an island arc-like mantle source. Therefore, subduction material is an important factor on mantle-melting degree, and spreading rate and mantle enrichment/depletion degree are also play an essential roles.

     

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