北祁连造山带玉石沟蛇绿岩地幔橄榄岩中发现金刚石OA
Discovery of diamonds in mantle peridotites from the Yushigou ophiolite,North Qilian orogenic belt
蛇绿岩型金刚石在新特提斯构造带的多个蛇绿岩中被发现,然而原特提斯蛇绿岩中是否存在金刚石还不清楚.本文选择北祁连造山带550～495 Ma玉石沟蛇绿岩为研究对象,开展矿物重砂分选和地幔橄榄岩的岩石学研究.结果显示,在约510 kg方辉橄榄岩中分选出25粒金刚石等异常矿物.金刚石粒径约50～150 μm,呈无色、浅黄色,具有八面体、破碎不规则状和浑圆状等晶型,拉曼光谱显示1330.37 cm-1 特征峰.金刚石围岩方辉橄榄岩主要由橄榄石(75％～85％)、斜方辉石(14％～24％)及少量铬尖晶石(<1％)组成.橄榄石Fo值为90.9～93.23,属于镁橄榄石,其中包裹于铬尖晶石内的橄榄石Fo值最高(93.23).斜方辉石主要呈碎斑状与粒间状两种类型:碎斑状斜方辉石 Mg#值为91.07～92.59,Al2O3 含量0.94％～1.92％,Cr2O3 含量0.43％～0.73％;粒间状斜方辉石 Mg#值为91.40～92.31,Al2O3 含量1.09％～1.80％,Cr2O3 含量0.46％～0.65％,由此可以看出碎斑状斜方辉石的 Mg#值和 Al2O3、Cr2O3 的变化范围都略大于粒间状斜方辉石.铬尖晶石 Cr#值为56.14～70.21,Mg#值为43.89～58.33,TiO2 含量低于0.05％.根据尖晶石的 Mg#-Cr#图解显示方辉橄榄岩经历了25％～35％的高程度部分熔融,并受到弧前俯冲带熔/流体交代作用.金刚石等超高压矿物指示其形成于>150 km,指示洋壳/地幔物质在俯冲过程中被带入深部地幔,在高压强还原环境下形成金刚石等矿物后,被地幔橄榄岩-铬铁矿包裹,在回返过程中携带至地表.本研究验证了蛇绿岩型金刚石全球分布的重要意义,为揭示北祁连造山带深俯冲过程和地幔深部物质循环提供了新的视角.
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.
张曼利;刘飞;冯光英;朱昕洋;吴少锋;方子健;许佳鸿;杨经绥
深地探测与矿产勘查全国重点实验室,中国地质科学院地质研究所,北京,100037深地探测与矿产勘查全国重点实验室,中国地质科学院地质研究所,北京,100037深地探测与矿产勘查全国重点实验室,中国地质科学院地质研究所,北京,100037中国地质大学(武汉)地球科学学院,湖北 武汉,430074青海省第四地质勘查院,青海 西宁,810029中国地质大学(武汉)地球科学学院,湖北 武汉,430074中国地质大学(北京)珠宝学院,北京,100083深地探测与矿产勘查全国重点实验室,中国地质科学院地质研究所,北京,100037
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
North Qilian orogenic beltYushigou ophiolitemantle peridotitediamondforearc subduction zone
《地质学报》 2026 (6)
2012-2029,18
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.
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