Geological and Geochemical Characteristics of Gabbros in the Xiwuqi Ophiolites of Inner Mongolia

摘要

Two ophiolite zones are distributed in the study area, which are, in order, Baiyinbulage ophiolite zone and Naolaiketu ophiolite zone from north to south. Among them, the gabbros are fully formed, which are distributed rootless in block mass on metamorphic peridotites. The gabbro consists of 45.53-46.84% of SiO_2, high A1203 and low TiO_2 and P205, belonging to mafic cumulate of ophiolite. For the gabbro located in this area, ΣREE is 4.65× 10-6~9.54 × 10-6, LaN/YbN is 0.15~0.41, δEu is 1.33~2.06, which indicates positive anomaly. In the primitive mantle-normalized trace element spider diagram, the large-ion lithophile elements (LILE) such as Ba, Ta and Sr, are rich, Rb, Th, U and Nb are relatively depleted, and the Dy-Lu section shows a slight left-leaning flat pattern. In addition, different specimens have similar trace element spider diagram and rare earth element (REE) distribution patterns. Base on the research on the geological and geochemical characteristics of the gabbros in Xiwuqi area, it is concluded that the gabbros in the ophiolites of Xiwuqi are the product of active continental margins or island arc environments and that the formation environment of the ophiolite in this area takes on the SSZ-type.