Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism
Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism
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DOI：
10.1007/s00410-010-0490-6
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发表时间：
2010-10-01
影响因子：
3.5
通讯作者：
Gobbo, Luiz
中科院分区：
文献类型：
--
作者：
Bulanova, Galina P.;Walter, Michael J.;Gobbo, Luiz
我们报告了来自巴西朱伊纳白垩纪Collier 4金伯利岩管的一系列钻石，它们主要是无氮的II型晶体，显示出复杂的内部生长结构。同生矿物包裹体包括具有钙钛矿化学计量的富钙和钛相、富Ca的多晶石榴石、斜辉石、橄榄石、TAPP相、具有CAS和K-霍兰石相化学计量的矿物、SiO2、FeO、自然铁、低Ni硫化物和Ca-Mg-碳酸盐。根据金刚石核带的碳同位素组成（δ C-13），我们将金刚石分为三组。第1组钻石具有重的地幔状δ C-13（千分之5至千分之10），矿物包裹体表明来自镁铁质原岩的过渡带。第2组金刚石具有中等三角洲C-13（千分之-12至-15），内含物成分表明来自上地幔或过渡带深部洋壳的近原生和分异碳酸盐熔体的结晶。CaTiSi钙钛矿包裹体（第2组）的Pb-206/U-238年龄为101 ± 7 Ma，接近金伯利岩侵位时间（93.1 ± 1.5 Ma）。第3组金刚石具有极轻的δ C-13（千分之25），并且宿主包裹体具有类似于高压温度相的成分，预计在俯冲到过渡带深度的远洋沉积物中稳定。总的来说，科利尔4号钻石及其内含物表明了在动态变化的化学环境中的多阶段、多压力生长历史。年轻的包体年龄，无处不在的化学和同位素特征指示俯冲物质，和区域构造历史，提出了一个模型，在该模型中，岩石圈下的金刚石及其包体，和原金伯利岩岩浆的生成，在遗传上，时间和地理上的俯冲岩石圈和白垩纪羽的相互作用。
We report on a suite of diamonds from the Cretaceous Collier 4 kimberlite pipe, Juina, Brazil, that are predominantly nitrogen-free type II crystals showing complex internal growth structures. Syngenetic mineral inclusions comprise calcium- and titanium-rich phases with perovskite stoichiometry, Ca-rich majoritic-garnet, clino-pyroxene, olivine, TAPP phase, minerals with stoichiometries of CAS and K-hollandite phases, SiO2, FeO, native iron, low-Ni sulfides, and Ca-Mg-carbonate. We divide the diamonds into three groups on the basis of the carbon isotope compositions (delta C-13) of diamond core zones. Group 1 diamonds have heavy, mantle-like delta C-13 (-5 to -10 parts per thousand) with mineral inclusions indicating a transition zone origin from mafic protoliths. Group 2 diamonds have intermediate delta C-13 (-12 to -15 parts per thousand), with inclusion compositions indicating crystallization from near-primary and differentiated carbonated melts derived from oceanic crust in the deep upper mantle or transition zone. A Pb-206/U-238 age of 101 +/- 7 Ma on a CaTiSi-perovskite inclusion (Group 2) is close to the kimberlite emplacement time (93.1 +/- 1.5 Ma). Group 3 diamonds have extremely light delta C-13 (-25 parts per thousand), and host inclusions have compositions akin to high-pressure temperature phases expected to be stable in pelagic sediments subducted to transition zone depths. Collectively, the Collier 4 diamonds and their inclusions indicate multi-stage, polybaric growth histories in dynamically changing chemical environments. The young inclusion age, the ubiquitous chemical and isotopic characteristics indicative of subducted materials, and the regional tectonic history, suggest a model in which generation of sublithospheric diamonds and their inclusions, and the proto-kimberlite magmas, are related genetically, temporally and geographically to the interaction of subducted lithosphere and a Cretaceous plume.