Partial melting of crustal rocks, also known as anatexis, is the major mechanism of the fractionation of the continental crust and generation of felsic melts. The segregation of melts leaves residual melt-depleted rocks called restites, which are major constituents of migmatite and granulite metamorphic complexes. Restites from over 20 complexes summarized in this work, formed over a wide range of P-T conditions from low-pressure to ultra-high temperature (UHT) and ultra-high pressure (UHP) conditions. Due to protolith heterogeneity and variable melt loss, restite and protolith compositions commonly overlap, however distinctive trends are apparent. Regardless of melting conditions metasedimentary restitic rocks tend to show loss of SiO, KO, NaO, and enrichment in ferromagnesian elements, often AlO, and TiO. These trends can be explained readily by the extraction of significant amount of granitic melt. The trace element features of restites show systematic changes with melting temperature, pressure and fluid regime. The restites after lower crustal melting show depletion in P, B, Rb, Cs, Pb and U, and subtler features, such as Nb/Ta fractionation, which all correspond to enrichment patterns of S-type and, ultimately, rare metal granites. Lithium and Be are undepleted in the relatively shallow, low-pressure cordierite-bearing restites, and depleted from deeper lower crustal restites containing garnet. The fractionation of trace elements during anatexis contributes to the development of features of the upper continental crust such as elevated content of LILE and heat producing elements (K, Th, U), reduced Nb/Ta and overall felsic composition. The pre-dehydrated UHT terranes display characteristics consistent with minor melt loss and depletion. The compositional effect of anatexis at UHT conditions, is sensitive to dehydration history of rocks, and melting of undehydrated sediments results in depletion in LREE, Th, Ga, ±Zr, ±Nb, which is complementary to A-type granitoids enrichment patterns. It is noted that anatexis produces melts with rather limited degrees of enrichment and high-degree fractional crystallisation of granitic magmas is a prerequisite for formation of ore-grade granitic intrusions. While restite geochemistry shows multiple consistent patterns, many remain unexplained and for certain elements the data are scarce, suggesting targets for fruitful research.

中文翻译：

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变沉积回生岩的地球化学及其对地壳长英质岩浆熔化条件和金属潜力的影响


地壳岩石的部分熔融，又称深熔作用，是大陆地壳分异和长英质熔体生成的主要机制。熔体的偏析留下残留的熔体贫化岩石，称为残余岩，它们是混合岩和麻粒岩变质杂岩的主要成分。这项工作中总结的来自 20 多种配合物的 Restite，在从低压到超高温 (UHT) 和超高压 (UHP) 条件的各种 P-T 条件下形成。由于原岩的异质性和可变的熔损，复位岩和原岩的成分通常重叠，但明显的趋势是明显的。无论熔化条件如何，变沉积回生岩往往会表现出 SiO、KO、Na2O 的损失，以及铁镁元素（通常是 Al2O 和 TiO）的富集。这些趋势可以很容易地通过提取大量花岗岩熔体来解释。复位点的微量元素特征显示出随熔化温度、压力和流体状态的系统变化。下地壳熔融后的复位辉石显示出 P、B、Rb、Cs、Pb 和 U 的贫化，以及 Nb/Ta 分馏等更微妙的特征，这些特征都对应于 S 型以及最终的稀有金属花岗岩的富集模式。锂和铍在相对较浅、低压的含堇青石休憩岩中未被耗尽，而在更深的含有石榴石的下地壳休憩站点中则被耗尽。深熔过程中微量元素的分馏有助于上大陆地壳特征的发展，例如 LILE 和产热元素（K、Th、U）含量升高、Nb/Ta 和整体长英质成分减少。预脱水的超高温处理地体表现出与较小的熔损和损耗一致的特征。 超高温条件下深熔作用的成分效应对岩石的脱水历史敏感，未脱水沉积物的熔融会导致轻稀土元素、Th、Ga、±Zr、±Nb 的损耗，这与 A 型花岗岩富集模式是互补的。值得注意的是，深熔作用产生的熔体富集程度相当有限，并且花岗质岩浆的高度分异结晶是形成矿石级花岗质侵入体的先决条件。虽然复位地球化学显示出多种一致的模式，但许多模式仍然无法解释，并且某些元素的数据很少，这表明了富有成效的研究目标。