Sulphide survival and diamond genesis during formation and evolution of Archaean subcontinental lithosphere: A comparison between the Slave and Kaapvaal cratons
Sulphide survival and diamond genesis during formation and evolution of Archaean subcontinental lithosphere: A comparison between the Slave and Kaapvaal cratons
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DOI：
10.1016/j.lithos.2009.03.048
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发表时间：
2009-11-01
期刊：
影响因子：
3.5
通讯作者：
Harris, Jeff W.
中科院分区：
文献类型：
--
作者：
Aulbach, Sonja;Stachel, Thomas;Harris, Jeff W.
对来自 Slave 克拉通中部 Diavik 金伯利岩的 35 颗榴辉岩钻石和 7 颗橄榄岩钻石的硫化物包裹体进行了表征，以解决钻石年龄和克拉通形成的问题。榴辉状硫化物包裹体出现在具有类地幔 Delta C-13 (-4.94 +/- 0.72 1 sigma) 和低 N 聚集状态（%N as B=8.2 +/- 10.0，平均 N 含量为 720 ppm）的钻石中，表明地幔停留温度相对较低。榴辉岩硫化物的 1.86 +/- 0.19 Ga Re-Os 年龄阵列与软骨晶上初始 Os-187/Os-188 为 0.13 (+/- 0.10) 表明榴辉岩金刚石形成、榴辉岩侵位和影响从属克拉通的碰撞事件之间存在密切的时间联系。橄榄岩钻石中的硫化物积聚较老。先前建立的 3.3 和 3.5 Ga 等时线，与较高的平均 N 聚集状态（类似于 20%）一致，尽管与榴辉岩钻石相比，其宿主钻石的 N 含量较低（类似于 230 ppm）。通过比较 Slave 和 Kaapvaal 之间的钻石数量和形成年龄，得出两个有趣的观察结果，分别表明根本不同和常见的钻石形成机制：（1）尽管橄榄岩普遍丰富硅酸盐包裹体、橄榄岩硫化物包裹体在 Kaapvaal 中很少见，出现在相对年轻的钻石中，而在 Slave 中部则有相当多的太古宙种群。 (2) 与钻石中硅酸盐包裹体的分布相比，两个克拉通的榴辉岩相对于橄榄岩硫化物包裹体都过多。在Kaapvaal岩石圈地幔形成期间，从钻石中极度贫化的硅酸盐包裹体来看，大的熔融间隔导致了残余物中硫化物的耗尽。含橄榄岩硫化物包裹体的钻石的形成仅发生在相当晚的时间，即伴随着交代作用的再硫化之后。相比之下。 Slave 克拉通中央下方贫化程度较低的深部岩石圈地幔可能是在地幔柱潜分泌过程中形成的，由于存在预先存在的岩石圈地幔盖，导致熔化间隔更小，从而允许同时沉积含硫化物包裹体的钻石。大量榴辉岩含硫化物包裹体钻石可能与 Slave 和 Kaapvaal 克拉通边缘的增生过程有关，这表明硫化物饱和的榴辉岩是钻石形成的丰富来源。底层海水蚀变橄榄岩脱水产生的液体减少，可能与上覆洋壳发生反应，沉淀出榴辉岩含硫化物钻石，与变质作用和榴辉岩就位到克拉通下岩石圈的构造同时发生。 (C) 2009 年，Elsevier B.V. 出版
Sulphide inclusions from 35 eclogitic and 7 peridotitic diamonds from the Diavik kimberlites in the central Slave craton have been characterized to address questions of diamond age and craton formation. Eclogitic sulphide inclusions occur in diamonds with mantle-like delta C-13 (-4.94 +/- 0.72 1 sigma) and low N aggregation states (%N as B=8.2 +/- 10.0, average N contents of 720 ppm) indicative of relatively low mantle residence temperatures. A 1.86 +/- 0.19 Ga Re-Os age array for eclogitic sulphides with suprachondritic initial Os-187/Os-188 of 0.13 (+/- 0.10) indicates a close temporal link between eclogitic diamond formation, eclogite emplacement and collisional events affecting the Slave craton. Sulphides in peridotitic diamonds plot on older. previously established 3.3 and 3.5 Ga isochrons, consistent with higher average N aggregation states (similar to 20%) despite lower N contents (similar to 230 ppm) for their host diamonds compared to eclogitic diamonds.Two intriguing observations emerge from a comparison of diamond populations and formation ages between the Slave and Kaapvaal that indicate fundamentally different and common diamond formation mechanisms, respectively: (1) Despite the general abundance of peridotitic silicate inclusions, peridotitic sulphide inclusions are rare in the Kaapvaal and occur in relatively young diamonds whereas in the central Slave there is a sizable Archaean population. (2) Compared to the distribution of silicate inclusions in diamonds, both cratons have an overabundance of eclogitic relative to peridotitic sulphide inclusions.During Kaapvaal lithospheric mantle formation, large melting intervals, as gauged by extremely depleted silicate inclusions in diamonds, led to exhaustion of sulphide in the residue. Formation of peridotitic sulphide inclusion-bearing diamonds occurred only significantly later, after re-sulphidation accompanying metasomatism. By contrast. the less depleted deep lithospheric mantle beneath the central Slave craton may have formed during plume subcretion, leading to smaller melting intervals due to the presence of a pre-existing lithospheric mantle lid, thereby allowing for coeval precipitation of sulphide inclusion-bearing diamonds.Abundant eclogitic sulphide inclusion-bearing diamonds that can be related to accretionary processes along the edges of the Slave and Kaapvaal craton indicate that sulphide-saturated eclogite is a fertile source for diamond formation. Reduced fluids from dehydration of underlying seawater-altered peridotite may react with the overlying oceanic crust to precipitate eclogitic sulphide-bearing diamonds penecontemporaneously with metamorphism and tectonic emplacement of eclogite into the subcratonic lithosphere. (C) 2009 Published by Elsevier B.V.