扬子地台西缘钾质煌斑岩岩石化学所反映的古俯冲作用及其与金刚石含矿性的关系

LITHOCHEMISTRY OF POTASSIC LAMPROPHYRES FROM WESTERN BORDER OF THE YANGZI PLATFORM: IMPLICATIONS FOR PALEOSUBDUCTION AND THE OCCURRENCE OF DIAMONDS

为了对沿扬子地台西缘分布的钾质煌斑岩的含金刚石性进行评价。作者进行了较详细的地质学、岩石学和地球化学工作。研究结果表明:研究区钾质煌斑岩在化学成分上具有贫Nb、Ti、富K、Rb、Bs、Sr的特征。这种成分特征是由位于研究区西部的古板块向扬子地台俯冲造成的。由于这种作用的影响,使钾质煌斑岩的源区地幔处于地温梯度高、氧逸度高的不稳定状态。这种状态不利于金刚石的形成和保存。故研究区钾质煌斑岩中含金刚石的可能性很小。

In order to evaluate the diamond-bearing properties of the potassic lamprophyres distributed along the west border of Yangzi Platform, a detailed investigation on the geology, petrology, and geochemistry was conducted. The results show that the lamprophyres from the research area are poor in Ti, Nb and rich in K, Rb, Ba, Sr. This composition occurred when the plate located to the west of research area commenced subduction beneath the Yangzi Plat. form. Under the influence of the subduction, the source mantle of the potassic lamprophyres has a high geothermal gradient and oxygen fugacity. Such conditions are unstable and are not conducive to the formation and preservation of diamonds. Therefore, these findings suggest diamond-bearing potential of the potassic lamprophyres in the research area to be low.