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首页> 外文期刊>Contributions to Mineralogy and Petrology >Vanished diamondiferous cratonic root beneath the Southern Superior province: evidence from diamond inclusions in the Wawa metaconglomerate
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Vanished diamondiferous cratonic root beneath the Southern Superior province: evidence from diamond inclusions in the Wawa metaconglomerate

机译：南部优越省以下的消失的钻石状克拉通根：Wawa巨集集团中的钻石包裹体证据

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We studied diamonds from a 2.697–2.700 Ga Wawa metaconglomerate (Southern Superior craton) and identified mineral inclusions of high-Cr, low-Ca pyrope garnet, low-Ti Mg-chromite, olivine (Fo93), and orthopyroxene (En94). The diamonds have δ13C of −2.5 to −4.0 ‰ and derive from the spinel-garnet and garnet facia of harzburgite. Geothermobarometry on non-touching, coexisting garnet-olivine and garnet-orthopyroxene pairs constrains the maximum geothermal gradient of 41 mW/m2 for the Neoarchean and a minimum lithosphere thickness of 190 km. The depleted harzburgitic paragenesis equilibrated at a relatively cold geotherm suggests the presence of a pre-2.7 Ga diamondiferous cratonic root beneath the northern Wawa terrane or the Opatica terrane of the Southern Superior craton, i.e., beneath terranes identified as sources for the metaconglomerate diamonds. Geophysical surveys, geothermal data, and petrology of mantle xenoliths emplaced in the Proterozoic-Mesozoic trace evolution of the mantle thermal regime and composition from the Archean to present. The root was thinned down to 150 km by the Jurassic, when the mantle was heated to 41–42 mW/m2. The diamondiferous root destruction was accompanied by more significant heating and was complete by 1.1 Ga in areas adjacent to the Midcontinent Rift. The geometry of the current high-velocity root and spatial correlations with boundaries of crustal terranes that docked to the nuclei of the Superior protocraton in the Neoarchean suggest that the root destruction in the Southern Superior may have been associated with tectonic erosion, craton amalgamation, and ensuing ingress of asthenospheric fluids.
机译：我们研究了2.697–2.700 Ga Wawa巨砾岩（南部上等克拉通）中的钻石，并确定了高铬，低钙吡啶鎓石榴石，低钛镁铬铁矿，橄榄石（Fo 93 ）的矿物包裹体以及邻苯二酚（En 94 ）。钻石的δ 13 C为-2.5至-4.0‰，且源自尖晶石-石榴石和石榴石的辉石。非接触，共存的石榴石-橄榄石和石榴石-邻二甲苯对的地热大气法限制了新古生界的最大地热梯度为41 mW / m 2 和最小的岩石圈厚度为190 km。在相对较冷的地热下平衡的枯竭的哈茨堡系共生现象表明，北部Wawa地层或南部上克拉通的Opatica地层以下，即被确定为超聚结钻石来源的地底下，存在一个Ga 2.7以前的克拉通克拉通根。地球物理调查，地热数据和地幔异种岩的岩石学，都存在于从太古宙到现在的地幔热力状态和组成的元古代—中生代遗迹。当地幔加热到41–42 mW / m 2 时，侏罗纪将根部细化到150 km。含钻石的根部破坏伴随着更明显的加热，并且在中大陆裂谷附近的区域中被1.1 Ga完全破坏。当前高速根的几何形状以及与地壳的边界相关的空间相关性，这些地壳的边界对接于新archarean的上层原生层的核，这表明南部上层的根部破坏可能与构造侵蚀，克拉通合并以及从而导致软流圈流体的进入。

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