Komatiitic magmatism is a characteristic feature of Archean cratons, diagnostic of the addition of juvenile crust, and a clue to the thermal evolution of early Earth lithosphere. The Slave craton in northwest Canada contains >20 greenstone belts but no identified komatiite. The reason for this dearth of komatiite, when compared to other Archean cratons, remains enigmatic. The Central Slave Cover Group (ca. 2.85 Ga) includes fuchsitic quartzite with relict detrital chromite grains in heavy-mineral laminations. Major and platinum group element systematics indicate that the chromites were derived from Al-undepleted komatiitic dunites. The chromites have low 187Os/188Os ratios relative to chondrite with a narrow range of rhenium depletion ages at 3.19 ± 0.12 Ga. While these ages overlap a documented crust formation event, they identify an unrecognized addition of juvenile crust that is not preserved in the bedrock exposures or the zircon isotopic data. The documentation of komatiitic magmatism via detrital chromites indicates a region of thin lithospheric mantle at ca. 3.2 Ga, either within or at the edge of the protocratonic nucleus. This study demonstrates the applicability of detrital chromites in provenance studies, augmenting the record supplied by detrital zircons.

中文翻译：

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碎屑铬铁矿揭示奴隶克拉通失踪的科马提岩

科马提质岩浆活动是太古代克拉通的一个特征，诊断了新生地壳的加入，也是早期地球岩石圈热演化的线索。加拿大西北部的奴隶克拉通包含超过 20 个绿岩带，但没有确定的科马提岩。与其他太古代克拉通相比，科马提岩缺乏的原因仍然是个谜。Central Slave Cover Group (ca. 2.85 Ga) 包括在重矿物叠层中带有残余碎屑铬铁矿颗粒的紫红色石英岩。主要和铂族元素系统学表明铬铁矿来源于未贫铝的科马提质单质岩。铬铁矿相对于球粒陨石具有较低的 187Os/188Os 比率，铼耗尽年龄范围很窄，为 3.19 ± 0.12 Ga。虽然这些年龄与已记录的地壳形成事件重叠，他们确定了未在基岩暴露或锆石同位素数据中保存的未识别的幼年地壳添加物。通过碎屑铬铁矿对科马提质岩浆作用的记录表明大约在 3.2 Ga，在原克拉通核内或边缘。这项研究证明了碎屑铬铁矿在来源研究中的适用性，扩大了碎屑锆石提供的记录。