黔东施秉下翁哨地区金刚石指示矿物地球化学特征及其地质意义

Geochemical characteristics and geological significance of diamond indicator minerals in Xiawengshao area,Shibing County,eastern Guizhou Province

对黔东施秉下翁哨地区金刚石指示矿物镁铝榴石、铬尖晶石分别进行了电子探针(EMPA)主量元素和LA-ICP-MS微区原位微量元素测试,结果表明:镁铝榴石主要属于G9型(约占87%),次为G12型(约占11%)和G3型(约占2%),源区为二辉橄榄岩和异剥橄榄岩,当其与橄榄石共生,获得平衡温度(tNi)为686~1225℃,压力(PCr)为1.9~4.0 GPa,少数落在形成金刚石的主要温压范围内(压力约4.0~6.5 GPa,温度约950~1300℃);铬尖晶石主要来源于橄榄岩尖晶石捕虏晶(Xen)(约占90%),少量为铬铁矿(Chr)(约占10%),个别落在全球原生金刚石中铬铁矿包裹体的范围内。研究认为,恢复区域加里东期造山运动以来的古地貌,寻找金刚石指示矿物的母岩体/新岩体及开展其矿物间的对比研究工作,特别是对加里东期以来区域的地幔物质组成、岩石圈厚度和热状态等进行深入研究,将对扬子克拉通的演化、深部地幔结构剖析和金刚石成矿事件等具有重要的科学研究意义。

Diamond indicator minerals pyropes and Cr-spinels from Xiawengshao area of Shibing County,East Guizhou,were subjected to electron microprobe(EMPA)major elements analysis and LA-ICP-MS micro-area in-situ trace element stesting.The results indicate that these pyropes mainly belongs to G9 type(ca.87%),followed by G12 type(ca.11%)and G3 type(ca.2%),with the source rock being lherzolite and wehrlite.When coexisting with olivine,equilibrium temperatures(tNi)range from 686 to 1225°C and pressures(PCr)range from 1.9 to 4.0 GPa,with a few falling within the main pressure—temperature range for diamond formation(pressure ca.4.0~6.5 GPa,temperature ca.950~1300°C).Cr-spinel mainly originates from xenocrysts captured by peridotite(Xen)(ca.90%),with a small portion being chromite(Chr)(ca.10%),and a few falling within the range of chromite inclusions in primary diamonds worldwide.The study suggests that reconstructing the paleogeography since the Caledonian orogeny,identifying the source rock/new rock of diamond indicator minerals,and conducting comparative studies on minerals are crucial.Particularly,in-depth investigations into the composition of mantle materials,lithospheric thickness,and thermal state since the Caledonian orogeny in the region will have significant scientific implications for the evolution of the South China Continent,analysis of deep mantle structure,and diamond mineralization events.