Geochemical Characteristics And Genesis Of The Carbonate Rocks In Hannuoba Area, Zhangbei

Previous studies of carbonate rocks in Zhangbei region were focused on Erdaobian carbonatite cylinder, this time during the field geological survey in Zhangbei Hannuoba, carbonate veins were discovered in Heinaobao, the size is from ten meters to more than one hundred meters, with alkaline basalts and the mantle peridotite xenoliths have a close symbiosis. By use of the result of petrographic, mineralogical, geochemical analysis,this paper will study the regin of carbonate rocks in Zhangbei region.Studies have shown that carbonatite barrel in Zhangbei Erdaobian and carbonate carbonatite dikes in Heinaobao are calcite carbonate, which have higher CaO containing, the mainly minerals are calcite, secondary minerals are magnesium olivine, orthopyroxene, monoclinic pyroxene and chrome spinel. In some places carbonatite veins and mantle xenoliths may have a metasomatism, leading to an increase of MgO content.Carbonate rocks in the study area generally have a columnar crystal structure, showing that the carbonatite have a igneous genesis. Trace REE geochemical characteristics are similar to the Eruption carbonate rock during the Cenozoic in Gansu Lixian. Carbonate, calcite Sr elements and the characteristics of Ta, Zr, Hf element content Characteristics are consistent with the igneous carbonatites. I speculate the carbonate rocks in Zhangbei Hannuoba area are the result of the Fluid unmixing of the silicate liquid which has rich carbonate CO₂, firstly the silicate melt erupt to surface, forming alkaline basalts, which generate a lot of crack when it is affected by the late thermal, then the carbonate melt insert in the alkaline basalts have been consolidated, forming a Heinaobao carbonate veins, as veins interspersed in basalt and mantle peridotite. When the partitioned carbonate melt have a greater pressure, it will break through the overburden to produce blasting eruption, forming blasting carbonatite Road tube in Erdaobian.In the process of the evolution of CO₂-rich silicate magma, of plagioclase crystallized through crystallization differentiation, resulting in a low Eu feature in magma, this featue was inherited by carbonate melt and silicate melt after dissolution, may be it is the reason of the negative Eu of the carbonatite in Zhangbei Hannuoba area. We speculated that the negative of the rare earth element Eu in calcite single mineral is caused by a magma eruption which led to material inhomogeneities.