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    甘孜—理塘结合带锰结核的发现及其地质意义

    The discovery of manganese nodules in Garze-Litang suture zone

    • 摘要: 提要:在甘孜—理塘结合带内理塘县中木拉乡附近发现锰结核。通过地质填图和综合研究,该锰结核产于结合带内瓦能蛇绿混杂岩组中的黑色粉砂质板岩中。其沉积层序为玄武岩→硅质岩→含锰结核粉砂质板岩。锰结核主量元素具有高Mn、低Fe、Si、Ca的特点,其中Mn含量为42. 19%,高出大洋锰结核平均值1.83倍,Mn/Fe值较高,达8.1。锰结核中除Cr高于大洋锰结核平均值2~7倍外,多数微量元素低于大洋锰结核平均值。稀土元素具有较明显的Ce正异常,稀土总量、轻重稀土分异程度、Eu异常特征与混杂岩中的砂岩、硅质岩近似,而与玄武岩差别较大。该锰结核产出于大陆边缘构造环境,火山活动微弱,代表甘孜—理塘洋扩张到最大程度时的沉积。其时甘孜—理塘洋规模仍是有限的。

       

      Abstract: Abstract:Manganese nodules were found for the first time near Zhongmula Village of Litang County in Sichuan Province, along the Garze-Litang suture zone. Based on geological mapping and integrated investigation,it is found that the manganese nodules are distributed in the black silt slate of Waneng Mélange belonging to the suture zone,and its sedmentary sequence is basalt→silicite→black manganese nodules-bearing silt slate. The major chemical compositions of the manganese nodules are characterized by high Mn and low Fe, Si, Ca. The Mn content is 42. 19% which is 1.83 times higher than average Mn content of oceanic nodules; Mn/Fe ratios are relatively high, reaching 8.1. The content of most of the trace elements in the manganese nodules is lower than that of ocean nodules except for Cr whose content is 2~7 times higher than that of ocean ones. Rare elements have distinct Ce positive anomalies, and ΣREE,LREE/HREE,δEu are similar to things of sandstone and siliceous rocks but are very different from things of the basalt. The tectonic environment of the manganese nodules is a continental margin with weak volcanic activity,indicating that sedimentation occurred in an environment of the most strong expansion of the Ganze-Litang Ocean, during which the width of ocean was still limited in comparison with modern oceans.

       

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