The discovery of manganese nodules in Garze-Litang suture zone

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.