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首页> 外文期刊>Contributions to Mineralogy and Petrology >Tracking flux melting and melt percolation in supra-subduction peridotites (Josephine ophiolite, USA)
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Tracking flux melting and melt percolation in supra-subduction peridotites (Josephine ophiolite, USA)

机译：跟踪超俯冲橄榄岩中的熔剂熔融和熔体渗流（美国约瑟芬蛇绿岩）

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Here, we investigate the scale and nature of melting and melt percolation processes recorded by 17 supra-subduction peridotites collected in a ~70 km~2 area in the northern portion of the Josephine ophiolite (Western USA). We present major and trace element variations in whole rocks; major elements in olivine, orthopyroxene, clinopyroxene and spinel; and trace elements [including rare earth element (REE)] in clinopyroxene and orthopyroxene. In the Josephine peridotites, compositional variability occurs at different scales. On the one hand, large systematic changes from depleted to fertile peridotites occur on large kilometer scales. Field, petrological and geochemi-cal data can be consistently explained if the Josephine mantle experienced variable degrees of hydrous flux melting (10 to >20-23 %), and we argue that small fractions of sub-duction-derived fluids (0.015-0.1 wt%) were pervasive in the -70 km~2 studied area, and continuously supplied during wedge melting. Fluid localization probably led to increased extent of flux melting in the harzburgitic areas. On the other hand, in single outcrops, sharp transitions from dun-ite to harzburgite to lherzolite and olivine websterite can be found on meter to centimeter scales. Thus, some fertile samples may reflect limited degrees of refertilization at the outcrop scale. In addition, clinopyroxene and orthopyroxene in ultra-depleted harzburgites (Spinel Cr# > 58) show variable degrees of LREE enrichment, which reflect percolation of and partial re-equilibration with, small fractions of boninite melt. Because the enriched samples also show the highest spinel Cr#, we argue that these enrichments are local features connected to the presence of dunite channels nearby. Lastly, trace element concentrations of pyroxenes in Josephine harzburgites show that they are one of the most depleted harzburgites among worldwide ophiolitic peridotites, indicating particularly high degrees of melting, potentially past the exhaustion of clinopyroxene.
机译：在这里，我们研究了约瑟芬蛇绿岩（美国西部）北部〜70 km〜2区域中收集的17种超俯冲橄榄岩所记录的熔融和熔融渗流过程的规模和性质。我们介绍了整个岩石中主要和微量元素的变化;橄榄石，邻苯二酚，斜铁基和尖晶石的主要元素; Clinopyroxene和Orthopyroxene中的痕量元素[包括稀土元素（REE）]。在约瑟芬橄榄岩中，成分的变化发生在不同的尺度上。一方面，从贫瘠的橄榄岩到富饶的橄榄岩的大的系统变化发生在大公里的规模上。如果约瑟芬地幔经历了不同程度的含水通量融化（10％至> 20-23％），则可以一致地解释油田，岩石学和地球化学数据，并且我们认为，小部分的俯冲产生的流体（0.015-0.1） wt％）在研究的-70 km〜2区域普遍存在，并在楔形熔化过程中连续供应。流体局部化可能导致在哈茨堡地区熔剂熔化的程度增加。另一方面，在单个露头中，可以发现米色至厘米级从邓尼特到哈尔茨贝格再到锂铁矿和橄榄石韦斯特石的急剧过渡。因此，一些肥沃的样品可能在露头尺度上反映有限的参考程度。此外，超贫化尖晶石（Spinel Cr＃> 58）中的斜辉石和邻苯二酚显示出不同程度的LREE富集，这反映了一部分小量的软陶石的渗滤和部分重新平衡。因为富集的样品还显示出最高的尖晶石Cr＃，所以我们认为这些富集是与附近的榴辉岩通道存在有关的局部特征。最后，约瑟芬·哈兹伯格岩中辉石的痕量元素浓度表明，它们是全世界脂橄榄岩橄榄石中最贫乏的哈兹伯格岩之一，表明熔融程度特别高，有可能超过了金碧辉煌。

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