Unusual micro- and nano-inclusions in diamonds from the Juina Area, Brazil
Unusual micro- and nano-inclusions in diamonds from the Juina Area, Brazil
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DOI：
10.1016/j.epsl.2009.06.043
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发表时间：
2009-08
影响因子：
5.3
通讯作者：
R. Wirth;F. Kaminsky;S. Matsyuk;A. Schreiber
中科院分区：
文献类型：
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作者：
R. Wirth;F. Kaminsky;S. Matsyuk;A. Schreiber
在巴西马托格罗索州里奥索里索砂矿矿床的钻石中发现了一系列罕见的微米和纳米夹杂物。微观夹杂物的尺寸各不相同，从 1 微米到 300 微米不等。通常，它们是多矿物的，主要由碳酸盐、硅酸盐和其他矿物共生形成。碳酸盐主要以白云石为代表，偶尔以方解石为代表。发现的硅酸盐有柯石英、硅灰石-II、尖钙石和蒙硅石。硫化物和钛铁矿也形成微包裹体。纳米夹杂物与微米夹杂物的不同之处不仅在于尺寸（不超过200纳米）；它们通常包含在微观夹杂物中。在纳米夹杂物中，鉴定出卤化物（NaCl、KCl、CaCl2 和 PbCl2）、硬石膏、尖晶石、金云母、PbO2、具有 α-PbO2 结构的 TiO2、天然 Fe 和其他物相。所有这些矿物都属于榴辉岩伴生：它们要么与柯石英伴生，要么包含在具有轻质“有机”碳同位素组成的钻石中（δ13C 范围为 -14 至 -25‰ PDB）。这证实了我们之前的结论，即 Juina 地区的钻石可能是由于地壳物质俯冲到至少下过渡带甚至下地幔的深度而形成的。所研究钻石的压力估计值在 3 至 10 GPa 之间。在一颗研究的钻石中发现了一种有趣的组合，即方解石 + 尖钙石 + 硅灰石 + 蒙硅石 + 流体，该组合被认为是硅灰石 + 流体形成尖钙石 + 蒙硅石的反应产物。矿物包裹体中存在大量的孔隙、空腔和气泡，以及含有挥发物的矿物包裹体的识别，例如卤化物（NaCl、KCl、CaCl2 和 PbCl2）、含氟硅酸盐尖晶石和金云母，这些都强调了挥发物（尤其是氯和氟）在钻石形成中的重要作用。
A series of uncommon micro- and nano-inclusions has been identified in diamonds from the Rio Soriso placer deposit in Mato Grosso State, Brazil. The micro-inclusions are variable in size, from 1 to 300 µm. Usually, they are polymineralic, being formed predominantly by intergrowths of carbonates, silicates and other minerals. Carbonates are represented mostly by dolomite and occasionally by calcite. Silicates found are coesite, wollastonite-II, cuspidine and monticellite. Sulphides and ilmenite form micro-inclusions as well. Nano-inclusions are different from micro-inclusions not only in size (not exceeding 200 nm); they are usually included in micro-inclusions. Among nano-inclusions, halides (NaCl, KCl, CaCl2and PbCl2), anhydrite, spinel, phlogopite, PbO2, TiO2with an α-PbO2structure, native Fe, and other phases are identified. All these minerals are of the eclogitic association: they are either associated with coesite or are included in a diamond with a light, ‘organic’ carbon isotopic composition (with δ13C from −14 to −25‰ PDB). This confirms our earlier conclusion that diamonds from the Juina area may have formed as a result of subduction of the crustal material to depths of at least the lower transition zone or even the lower mantle. The pressure estimates for the investigated diamonds vary in a range from 3 to 10 GPa. An interesting assemblage of calcite + cuspidine + wollastonite + monticellite + fluid identified in one of the studied diamonds is considered as a product of a reaction of wollastonite + fluid forming cuspidine + monticellite. The presence of numerous pores, cavities and bubbles in mineral inclusions, and identification of an association of volatile-containing mineral inclusions, such as halides (NaCl, KCl, CaCl2, and PbCl2), fluorine-containing silicate cuspidine, and phlogopite emphasize the important role of volatiles, particularly chlorine and fluorine in the formation of the diamonds.