Granulite facies metamorphism of the lower crust has decreased in scale since the Late Archean, but many of its definitive features have persisted: (1) Punctuated, sometimes relatively short-lived, episodes of high-grade metamorphism. These are recorded, in favorably simple cases, by discrete growth rims on zircons. (2) A consistent age gap of a few to several tens of millions of years between juvenile magmatism (crustal accretion) and high-temperature metamorphism. The secondary thermal pulse is an event distinct from primary crustal accretion. (3) Involvement of mineralizing pore fluids of lowered H2O activity, that is, with high CO2 and saline concentrations. Very high oxidation states of some granulites implicate sulfur as an important fluid component. (4) Transcurrent faulting as a conspicuous feature of synmetamorphic deformation. This gives rise to characteristic transposed foliation and lineation. (5) Emplacement of coeval postorogenic K-rich granites at midcrust levels. These features can be rationalized by concepts of modern plate tectonics. High-angle plate collision is succeeded by orogen-parallel transport. This change of plate motion necessarily detaches the underthrust portion of the lithosphere, liberating asthenospheric melts and/or fluids in a postorogenic resurgence. A generation of volatile-rich mafic magmas invades the continental margin; high CO2 and halogen contents cause outgassing and freezing of the magmas at depth. Liberated volatiles effect granulite facies metamorphism by leaching H2O and lithophile elements, importantly K, and transporting these components and heat upward. Extensive melting of the lower crust is inhibited by the low H2O activity of saline-carbonic pore fluids at high pressure. Melting of orthogneiss and supracrustal rocks occurs at midcrust levels by increase of H2O activity as pressure on alkali chloride solutions falls below 0.6–0.5 GPa. The foregoing hypothesis is an alternative to the classical view that granite results from fluid-absent partial melting of, and extraction from, the lower crust, leaving granulites.

中文翻译：

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新老颗粒：不稳定的联系

自晚太古代以来，下地壳的粒状岩相变质作用的规模有所减小，但其许多确定性特征仍然存在：（1）间断的、有时相对短暂的高级变质作用事件。在比较简单的情况下，这些是通过锆石上离散的生长边缘记录的。(2) 幼年岩浆作用（地壳增生）与高温变质作用之间存在数百万年至数千万年的一致年龄差距。二次热脉冲是不同于一次地壳吸积的事件。(3) H2O 活性降低的矿化孔隙流体的参与，即高 CO2 和盐水浓度。一些麻粒岩的非常高的氧化态表明硫是一种重要的流体成分。(4) 横流断层是同变质变形的显着特征。这产生了特征性的转置叶理和划线。(5) 在中地壳水平上同时期的产后富钾花岗岩的就位。这些特征可以通过现代板块构造的概念来合理化。造山带平行输运成功了大角度板块碰撞。板块运动的这种变化必然会使岩石圈的下冲断层部分脱离，从而在造山后回潮中释放软流圈熔体和/或流体。一代富含挥发分的基性岩浆侵入大陆边缘；高 CO2 和卤素含量会导致岩浆在深处脱气和冻结。释放出的挥发物通过浸出 H2O 和亲石元素（重要的是 K）并输送这些成分并向上传递热量来影响麻粒岩相变质作用。高压下咸碳孔隙流体的低 H2O 活性抑制了下地壳的广泛熔化。当碱金属氯化物溶液的压力低于 0.6-0.5 GPa 时，由于 H2O 活性增加，正方麻岩和上地壳岩石发生熔化。上述假设是经典观点的替代，即花岗岩是由下地壳的无流体部分熔化和提取，留下麻粒岩产生的。