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Title:: Formation Ages and Tectonic Significance of Ophiolites in Wandashan Terrane of the Eastern Heilongjiang

Author(s):: WANG Ji-yao; YANG Yan-chen; HUANG Yong-wei; HOU Yu-shu; TAN Yan; ZHANG Guo-bin; 1. College of Earth Sciences, Jilin University, Changchun 130061, Jilin, China; 2. The First Institute of Geology Exploration of Heilongjiang Province, Mudanjiang 157000, Heilongjiang, China

Keywords:: ophiolite; geochemistry; zircon U-Pbdating; oceanic island; back arc basin; tectonic evolution; Wandashan terrane; Heilongjiang

Abstract:: Rock geochemistry and zircon U-Pb dating are reported for Raohe and Yuejinshan ophiolites in Wandashan orogenic belt in order to understand its origin and age, and reveal their regional tectonic setting. Content of TiO₂ is high, high field strength elements (Nb, Ta, Hf, Zr, etc.) are enriched, large ion lithophile elements (Rb, Sr, Ba, etc.) are relative enriched for Raohe ophiolite; chondritenormalized REE patterns and primitive mantle-normalized trace element spider diagrams of rock are consistent with that of the typical oceanic island basalt (OIB), showing the characteristics of OIB. The characteristics of trace elements of Yuejinshan ophiolite are both mid-ocean ridge tholeiite and island arc tholeiite, large ion lithophile elements (Rb, Ba, K, Sr, etc.) are enriched, high field strength elements (Zr, Hf, Nb, Ta, etc.) are depleted, Eu anomaly is not negative, LREE is enriched lightly, and Yuejinshan ophiolite is formed in back-arc environment. Dating results show the ages of Raohe and Yuejinshan ophiolites are (219.0±2.4)Ma and (311±11)Ma, respectively. Combined with the formation of tectonic environment, the eastern Heilongjiang in Late Paleozoic Late Triassic experiences a series of complicated geodynamic processes in the background of the westward subduction of Paleo-Pacific Plate, including the scaling and combining of oceanic island or seamount and “arc-basin” system evolution.