Abstract The olivine melilitites from the southern part of the 6.8 Ma-old Takarindiona volcanic field (Eastern Madagascar) are olivine ± chromite -phyric lavas, with zoned titanaugite, perovskite, melilite, nepheline, monticellite, Ba–Ti-mica and Fe–Ti oxides as microphenocrysts and groundmass phases. The rocks are very primitive, rich in incompatible trace elements (e.g., Ba = 1049 ± 153 ppm, Sr = 1050 ± 167 ppm, Nb = 98 ± 13 ppm; La/Ybn = 41 ± 5; La/Nb = 0.88 ± 0.05), and have restricted ranges of initial 87Sr/86Sr (0.70391–0.70410) and 143Nd/144Nd (0.51272–0.51282). The rocks follow a differentiation trend controlled by ab. 20% removal/addition of phenocryst olivine ± chromite. The olivine melilititic magmas are the product of small degrees of partial melting (1–3%) of a peridotitic source, enriched in highly incompatible trace elements by CO2-, F-, and H2O-rich melts, located within the garnet stability field (3–3.5 GPa and ∼100 km depth) of sub-continental lithospheric mantle, where carbonates (dolomite) and possibly phlogopite were stable phases. Mantle xenoliths within the volcanics are mostly spinel harzburgites having mineral modes and chemical compositions suggesting variable degrees of “basalt” melt extraction. Based on textural and chemical evidence, and quantitative thermobarometric estimates, the xenoliths were incorporated at a pressure of ∼1.1 GPa (∼35–40 km depth), far shallower than the source of the melilititic magmas, and along a predictably cool geotherm beneath Archean continental lithosphere. Highly resorbed orthopyroxene xenocrysts mantled by augite indicate that the melilitites may have also entrained lower crustal materials or underplated subalkaline rocks. The mantle sources of the lavas and mantle xenoliths of the Takarindiona district indicate stratification of the lithospheric mantle, and help constraining the lithospheric features and the magmatic history of the Eastern Madagascar craton.

中文翻译：

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takarindiona 地区的橄榄石黄长石、地幔包体和包体：马达加斯加中东部的岩石成因、岩浆演化和次大陆岩石圈地幔

摘要 产自 6.8 Ma 龄 Takarindiona 火山区南部（马达加斯加东部）的橄榄石黄长石为橄榄石±铬铁矿岩浆，分带钛辉石、钙钛矿、黄长石、霞石、蒙脱石、Ba-Ti-mica 和 Fe-Ti氧化物作为微斑晶和基体相。岩石非常原始，富含不相容的微量元素（例如，Ba = 1049 ± 153 ppm，Sr = 1050 ± 167 ppm，Nb = 98 ± 13 ppm；La/Ybn = 41 ± 5；La/Nb = 0.88 ± 0.05 )，并且具有初始 87Sr/86Sr (0.70391–0.70410) 和 143Nd/144Nd (0.51272–0.51282) 的限制范围。岩石遵循 ab 控制的分化趋势。去除/添加 20% 的斑晶橄榄石 ± 铬铁矿。橄榄石黄长石岩浆是橄榄岩源的小程度部分熔融 (1-3%) 的产物，通过 CO2-富含高度不相容的微量元素，富含 F 和 H2O 的熔体，位于次大陆岩石圈地幔的石榴石稳定场（3-3.5 GPa 和约 100 公里深度）内，其中碳酸盐（白云岩）和可能的金云母是稳定相。火山岩中的地幔捕虏体主要是尖晶石斜方辉石，其矿物模式和化学成分表明不同程度的“玄武岩”熔体提取。根据质地和化学证据，以及定量热气压估计，捕虏体在约 1.1 GPa（约 35-40 公里深度）的压力下被合并，远比黄长石岩浆的来源浅，并且沿着太古代下方可预测的凉爽地温大陆岩石圈。被辉石覆盖的高度再吸收的斜方辉石异晶表明黄长石也可能夹带了下地壳物质或未镀层的亚碱性岩石。