地质学报2026，Vol.100Issue(6)：2012-2029,18.DOI:10.19762/j.cnki.dizhixuebao.2025337
北祁连造山带玉石沟蛇绿岩地幔橄榄岩中发现金刚石
Discovery of diamonds in mantle peridotites from the Yushigou ophiolite,North Qilian orogenic belt
摘要
Abstract
Ophiolite-hosted diamonds have been discovered in several ophiolites within the Neo-Tethyan tectonic belt,however,the presence of diamonds in Paleo-Tethyan ophiolites remains unclear.This study focuses on the 550～495 Ma Yushigou ophiolite within the North Qilian orogenic belt.Heavy mineral separation and petrological studies of mantle peridotites were conducted.The results reveal the separation of 25 diamond-grains and other unusual minerals from approximately 510 kg of harzburgite.The diamonds mainly range in size from 50 to 150 μm,exhibiting colorless to pale yellow hues,and display crystal forms including octahedral,broken irregular,and rounded shapes.Raman spectroscopy shows a characteristic peak at 1330.37 cm-1.The host harzburgite consists mainly of olivine(75％～85％),orthopyroxene(14％～24％),and minor chromian spinel(<1％).Olivine has Fo values of 90.9～93.23,classifying it as forsterite,with the highest Fo value(93.23)observed in olivine inclusions within chromian spinel.Orthopyroxene occurs primarily in two types of porphyroclastic and intergranular.Porphyroclastic orthopyroxene has Mg#values of 91.07～92.59,Al2O3 contents of 0.94％～1.92％,and Cr2O3 contents of 0.43％～0.73％.Intergranular orthopyroxene has Mg#values of 91.40～92.31,Al2O3 contents of 1.09％～1.80％,and Cr2O3 contents of 0.46％～0.65％.The variation ranges of Mg#,Al2O3,and Cr2O3 in porphyroclastic orthopyroxene are all slightly larger than those in intergranular orthopyroxene.Chromian spinel has Cr#values of 56.14～70.21,Mg#values of 43.89～58.33,and TiO2 contents below 0.05％.The Mg#-Cr#diagram of spinel indicates that the harzburgite underwent a high degree of partial melting(25％～35％)and experienced metasomatism by melts/fluids in a forearc subduction zone.Ultrahigh-pressure minerals like diamonds suggest formation depths>150 km.This implies that oceanic crust/mantle materials were transported into the deep mantle during subduction.Diamonds and other minerals formed under high-pressure and highly reducing conditions,were encapsulated by mantle peridotite and chromitite,and then were subsequently carried to the surface during the exhumation process.This study confirms the globally significant distribution of ophiolite-hosted diamonds and provides new insights into deep subduction processes and deep mantle material recycling within the North Qilian orogenic belt.关键词
北祁连造山带/玉石沟蛇绿岩/地幔橄榄岩/金刚石/俯冲带弧前环境Key words
North Qilian orogenic belt/Yushigou ophiolite/mantle peridotite/diamond/forearc subduction zone引用本文复制引用
张曼利,刘飞,冯光英,朱昕洋,吴少锋,方子健,许佳鸿,杨经绥..北祁连造山带玉石沟蛇绿岩地幔橄榄岩中发现金刚石[J].地质学报,2026,100(6):2012-2029,18.基金项目
本文为国家自然科学基金项目(编号42472094、42330306),深地国家科技重大专项(2025ZD1006102)和中国地质调查局地质调查项目(编号DD20240204901,DD20242124,DD20240075,DD20221630)联合资助的成果. （编号42472094、42330306）
