THE FEATURES OF OPHIOLITES IN THE GENTRAL SECTOR OF INNER MONGOLIA AND ITS CEOLOGICAL SIGNIFICANCE

There occur many ophiolite blocks of varying sizes between the Sino-Korean paleoplate andthe Siberian paleoplate in the central sector of Inner Mongolia. They extend discontinuously in anENE direction. This paper systernatically describes the sequence, rock association, mineral com-position, petrochemical features, formation ages and tectonic environments of ophiolites in thearea. The Solon Mountain-Hegen Mountain ophiolite belt in its north part lies on the south sideof the Siberian paleoplate and extends as far as 600 km. It is unconformably overlain by LowerPermian conglomerate and in limestone and chert there occur Middle Carboniferous fusulinids andMid-Late Devonian radiolarians and corals, which indicates that the ophiolites originated in theLate Paleozoic. The Ondor Sum-Kedan Mountain ophiolite belt in the south is located on thenorth margin of the Sino-Korean paleoplate, extending discontinuously for about 340 km. Inchert thereoccur fossils of radiolarians, Hyolitha and ostracods, and pillow lavas gave a Rb-Srage of 630 Ma, which demonstrates that the ophiolites are of Early Cambrian-Middel Ordovicianage. The above-mentioned large-scale ophiolite belts are the result of paleoplate subduction andprovide important evidence for determining the location and time of oceanic crust-continentalcrust collision （or junction）. Besides, some small ophiolite blocks are the by-product of develop-ment of regional thrusts.