The Kalamaili ophiolite belt controlled by regional deepfracture zone consists of ultramafic rock bodies，mafic dikes and volcanics. The ultramafic rocks are composed of mantle harzburgites with dunite pods and chromitite ores and characterized by low SiO2， high MgO， LREEenriched Vshaped and LREEslightly enriched patterns. They represent a typical mantle section of the suprasubduction zone (SSZ) setting. The lowTi basalts and their crystallized accumulative dikes comprising gabbro and gabbrodiorite display a lowTi affinity of the island arc tholeiite (IAT) ophiolitic series from the SSZ setting， having， as most distinctive chemical features， low Al2O3， TiO2，K2O+Na2O and K2O<50)， low MgO (1.84%～2.81%， 2.60% on average)， enrichment of incompatible elements and high abundance of REE with LREEenriched REE patterns. They probably are remnants of ocean island，representing the ocean hotspot at the early development stage of the ocean， and might have constituted the hotspot that resulted in the initial extension environment in this region. It can be concluded that the Kalamaili ophiolite belt represents the Devonian oceanic lithosphere relics of the ocean basin that separated the KazkhstanJunggar united continental block from Siberian plate, suggesting that the ocean basin experienced the process from the early intraocean hotspot to the late intraocean plate subduction.