Material Composition And Emplacement Mechanism Of Accretionary Wedge Ophiolite Melange In Karamari,East Junggar

The Kalamaili ophiolite belt is located in the northeastern margin of the Junggar landmass.It is the junction of the Siberian plate and the Kazakhstan-Junggar plate.It is an important unit of the eastern Junggar accretionary orogenic belt.On the basis of field geological investigation and related data collection in Kalamaili area,this paper focuses on the material composition,geochemical characteristics and emplacement mechanism of ophiolitic melanges in this area.The Kalamaili ophiolitic structural melange is tectonically intruded into the early Carboniferous karameric accretive melange belt.Under the action of right-handed ductile-brittle shear,all units in the ophiolitic melange belt are in contact with tectonic emplacement,and the boundary is nearly straight or arc-shaped fracture.The melange in plane is generally lenticular.The gabbro and metamorphic peridotite in the ophiolite melange belt have three different REE distribution patterns,ranging from right-dipping REE distribution curve,positive Eu anomaly to flat REE,slightly enriched LREE and no Eu anomaly.The overall characteristics of the transition are from mid-ocean ridge basalt(MORB)to island arc tholeiite(IAB).The three distribution patterns show the evolution trend from MORB to SSZ,and reveal that the Karamari region has undergone complex oceanic-continental transition.Geochemical characteristics of platinum group elements(PGE)indicate that gabbro and metamorphic peridotite are characterized by obvious enrichment of Ir,obvious depletion of Ru and Rh,and wide variation of Pd.The enrichment and depletion of Pd in this area may be related to the partial melting of oceanic island basalts in the subduction zone of the upper mantle.The LA-ICP-MS zircon U-Pb age of banded gabbro in the Kalamaili ophiolite is 398.5(+1.7 Ma).Geochemical and chronological results show that the oceanic basin in the early Devonian period was open in a back-arc environment,subduction plate fluid,residual oceanic islands and other components.