Abstract Hydrogen as an atomic impurity in mantle minerals is recurrently proposed as a key element impacting significantly on many mantle properties and processes such as melting temperature and mechanical strength. Nevertheless, interpretation based on the natural samples remains weak as we do not have yet a robust world-wild database for hydrogen concentrations in mantle mineral and rocks. Here, we report the first hydrogen concentrations in nominally anhydrous minerals from a rare selection of ultramafic rocks and minerals embedded in Mesoproterozoic Wajrakarur kimberlites (Eastern Dharwar craton, India). Based on key chemical elements, we demonstrate that olivine, diopside and garnet from the Dharwar craton are of mantle origin. We quantify the hydrogen concentrations using Fourier transform infrared spectroscopy (FTIR) and mineral-specific FTIR calibrations. Calculated hydrogen concentrations are, in average, 18 ppm wt H2O in olivine, 70 ppm wt H2O in orthopyroxene and 207 ppm wt H2O in clinopyroxene. Garnet has highly variable hydrogen concentration ranging from 0 to 258 ppm wt H2O, probably influenced by nano-scale inclusions. The average of clean garnet spectra yields 14.5 ppm wt H2O. The reconstructed hydrogen bulk concentrations of Dharwar peridotites yields 40 - 8 + 10 ppm wt H2O. This value is two to five times lower than the estimated hydrogen concentration in the lithospheric mantle, and agree well with the lower range of hydrogen bulk concentration from the current data base for the upper mantle minerals transported by kimberlites from other cratons (e.g., South Africa, Siberia). The low hydrogen concentration in mantle minerals, together with petrological and geochemical evidence of carbonated silicate melt metasomatism in Dharwar cratonic lithospheric mantle, suggest that these xenoliths are possibly related to proto-kimberlite melts with low water activity prior to being transported to the surface by the Mesoproterozoic Wajrakarur kimberlites. These observations, valid to a depth of ∼165-km, suggest that cratonic lithosphere beneath the Dharwar craton may not be particularly indicative of an abnormal hydrogen-rich southern Indian lithosphere in the late Archean and that hydroxylic weakening in olivine would induced a negligible effect on the mantle viscosity of Indian subcontinent.

中文翻译：

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从橄榄岩推断的 Dharwar 克拉通岩石圈中的低氢浓度，Wajrakarur 金伯利岩油田：对地幔粘度和碳酸化硅酸盐熔体交代作用的影响

摘要 氢作为地幔矿物中的一种原子杂质被反复提出作为对许多地幔性质和过程（如熔化温度和机械强度）产生显着影响的关键元素。然而，基于自然样本的解释仍然很弱，因为我们还没有一个强大的世界范围内地幔矿物和岩石中氢浓度的数据库。在这里，我们报告了来自中元古代 Wajrakarur 金伯利岩（东达尔瓦尔克拉通，印度）中嵌入的稀有超镁铁质岩石和矿物中名义上无水矿物中的第一次氢浓度。基于关键化学元素，我们证明了来自 Dharwar 克拉通的橄榄石、透辉石和石榴石来自地幔。我们使用傅里叶变换红外光谱 (FTIR) 和矿物特定的 FTIR 校准来量化氢浓度。计算出的氢浓度在橄榄石中平均为 18 ppm wt H2O，在斜辉石中为 70 ppm wt H2O，在斜辉石中为 207 ppm wt H2O。石榴石的氢浓度变化很大，从 0 到 258 ppm wt H2O，可能受纳米级夹杂物的影响。干净的石榴石光谱的平均值产生 14.5 ppm wt H2O。重建的 Dharwar 橄榄岩的氢体积浓度产生 40 - 8 + 10 ppm wt H2O。该值比岩石圈地幔中估计的氢浓度低 2 到 5 倍，并且与来自其他克拉通的金伯利岩（例如，南非、西伯利亚）。地幔矿物中的低氢浓度，以及达尔瓦克拉通岩石圈地幔中碳酸化硅酸盐熔体交代作用的岩石学和地球化学证据，表明这些捕虏体可能与低水活度的原始金伯利岩熔体有关，然后被输送到地表。中元古代Wajrakarur 金伯利岩。这些观测结果在约 165 公里的深度内有效，表明 Dharwar 克拉通下方的克拉通岩石圈可能并不是太古宙晚期印度南部岩石圈异常富氢的特别指示，橄榄石中的羟基减弱会引起可忽略不计的影响印度次大陆的地幔粘度。结合达尔瓦克拉通岩石圈地幔中碳酸化硅酸盐熔体交代作用的岩石学和地球化学证据，表明这些捕虏体可能与中元古代Wajrakarur金伯利岩输送到地表之前具有低水活度的原金伯利岩熔体有关。这些观测结果在约 165 公里的深度内有效，表明 Dharwar 克拉通下方的克拉通岩石圈可能并不是太古宙晚期印度南部岩石圈异常富氢的特别指示，橄榄石中的羟基减弱会引起可忽略不计的影响印度次大陆的地幔粘度。结合达尔瓦克拉通岩石圈地幔中碳酸化硅酸盐熔体交代作用的岩石学和地球化学证据，表明这些捕虏体可能与中元古代Wajrakarur金伯利岩输送到地表之前具有低水活度的原金伯利岩熔体有关。这些观测结果在约 165 公里的深度内有效，表明 Dharwar 克拉通下方的克拉通岩石圈可能并不是太古宙晚期印度南部岩石圈异常富氢的特别指示，橄榄石中的羟基减弱会引起可忽略不计的影响印度次大陆的地幔粘度。表明这些捕虏体可能与中元古代Wajrakarur 金伯利岩输送到地表之前具有低水活度的原金伯利岩熔体有关。这些观测结果在约 165 公里的深度内有效，表明 Dharwar 克拉通下方的克拉通岩石圈可能并不是太古宙晚期印度南部岩石圈异常富氢的特别指示，橄榄石中的羟基减弱会引起可忽略不计的影响印度次大陆的地幔粘度。表明这些捕虏体可能与中元古代Wajrakarur 金伯利岩输送到地表之前具有低水活度的原金伯利岩熔体有关。这些观测结果在约 165 公里的深度内有效，表明 Dharwar 克拉通下方的克拉通岩石圈可能并不是太古宙晚期印度南部岩石圈异常富氢的特别指示，橄榄石中的羟基减弱会引起可忽略不计的影响印度次大陆的地幔粘度。