Ion microprobe Pb–Pb dating of carbonado, polycrystalline diamond
Ion microprobe Pb–Pb dating of carbonado, polycrystalline diamond
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黑金刚石、多晶金刚石的离子微探针 Pb-Pb 定年
DOI：
10.1016/s0301-9268(01)00208-x
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发表时间：
2002
影响因子：
3.8
通讯作者：
M. Ozima
中科院分区：
文献类型：
--
作者：
Y. Sano;R. Yokochi;K. Terada;M. Chaves;M. Ozima
本文报道了巴西米纳斯吉拉斯州含金刚石存款中的一个元古代砾岩中的石英、金红石和粘土矿物包裹体以及多晶金刚石的基质部分的原位离子探针Pb-Pb年龄，以及从该存款中提取的锆石的U-Pb年龄。GM 01碳酸盐岩中7个石英颗粒上的34个点测得207 Pb/206 Pb等时线年龄为3247±800 Ma（2σ; MSWD=0.75），3个金红石包裹体上的6个点测得207 Pb/206 Pb等时线年龄为3916±1300 Ma（2σ; MSWD=0.092）。DO 3碳酸盐岩的3个粘土矿物包裹体上有7个点显示出相同的铅成分，基质上有4个点确定了207 Pb/206 Pb等时线年龄，为3811±1800 Ma（2σ; MSWD=0.012）。同一砾岩中70个锆石颗粒上的76个点显示出2151±17 Ma、2692±20 Ma和2931±22 Ma三个主要的U-Pb一致年龄，以及1726±58 Ma和3599±12 Ma两个一致异常值。最年轻的年龄与其他工作者估计的元古代砾岩的形成年龄1750-1700 Ma相一致。3.6Ga锆石是南美洲地台中最古老的记录。它可能是碎屑成因的，反映了太古代克拉通的残余。GM 01碳酸盐岩中石英和金红石包裹体的Pb-Pb年龄分别为3315±720 Ma和3811±1800 Ma。基质年龄与文献报道的中非碳酸盐岩Pb-Pb年龄2.6- 3.8Ga一致，表明巴西碳酸盐岩与非洲碳酸盐岩有密切的成因联系。
We report in situ ion microprobe Pb–Pb dating of quartz, rutile and clay mineral inclusions and matrix part of polycrystalline diamonds, ‘carbonado’ derived from a Proterozoic conglomerate in diamond-bearing deposit of Minas Gerais in Brazil together with U–Pb ages of zircons also extracted from the deposit. Thirty four spots on seven quartz grains located in the cavity of the GM01 carbonado yield207Pb/206Pb isochron age of 3247±800 Ma (2σ; MSWD=0.75) and six spots on three rutile inclusions give the age of 3916±1300 Ma (2σ; MSWD=0.092). Seven spots on three clay mineral inclusions of the DO3 carbonado show common lead compositions while four spots on matrix define207Pb/206Pb isochron age of 3811±1800 Ma (2σ; MSWD=0.012). Seventy six spots on seventy zircon grains derived from the same conglomerate show three major U–Pb concordant ages of 2151±17 Ma, 2692±20 Ma and 2931±22 Ma with two concordant zircon outliers of 1726±58 Ma and 3599±12 Ma. The youngest age is consistent with the formation age of 1750–1700 Ma in the Proterozoic conglomerate estimated by other workers. The 3.6 Ga zircon is the oldest record in the South American platform. It may be detrital in origin and reflect the remnant of an Archean craton. The Pb–Pb age of quartz and rutile inclusions in GM01 carbonado and that of DO3 carbonado matrix are 3315±720 Ma and 3811±1800 Ma. The matrix age is consistent with Pb–Pb age of 2.6–3.8 Ga of Central African carbonados in the literature, suggesting a close genetic relationship between Brazilian and African carbonados.