The high-pressure followed by high-temperature metamorphism related to the evolution of collisional orogens is the expected Pressure-Temperature-time (P-T-t) path for modern-style plate tectonics. However, these P-T-t paths are rarely preserved even in Phanerozoic orogens. In this matter, the Campo Grande migmatite-gneiss area presents an exhumed Archean crust with heterogeneous retrograde eclogites overprinted by amphibolite-facies in NE Brazil. Retrogressed eclogites in the area core are formed by Mn-rich garnet + clinopyroxene porphyroblasts layer with a minor amphibole + quartz + titanite assemblage, whereas the margins display dismembered lenses of Mg-rich garnet porphyroblasts with plagioclase + amphibole coronae and clinopyroxene + plagioclase + ortopyroxene sympleticte mainly within shear zones. Phase equilibria modelling reveals that these distinct retro-eclogites record similar eclogite conditions (up to 18 kbar and 660 ± 20 °C). Mn-rich eclogites display widespread magmatic zoned zircon grains from Mesoarchean to Paleoproterozoic and recrystallized metamorphic grains of 607.7 ± 5.4 Ma. Zircon from Mg-rich eclogites crystallized at 2.67 Ga and overgrowth rims formed at 2.0 Ga and 590.1 ± 1.8 Ma. REE in zircon lack Eu anomaly, displaying flat HREE patterns in 590.1 ± 1.8 Ma Neoproterozoic grains indicate recrystallization under eclogite-facies conditions. In situ U-Pb titanite dating yielded two younger age sets at 574.7 ± 0.5 and 562.8 ± 2.1 Ma. Lastly, in situ U-Pb dating of rutile inclusions in garnet cores present ages of 606.1 ± 4.0 Ma, whereas rutile included in retrograde coronae and sympleticte yielded concordant ages from 559.0 ± 2.3 to 523.2 ± 1.9 Ma. Thus, combined phase equilibria modelling and U-Pb ages reveal a progressive change in metamorphic conditions from eclogite conditions (at least 607.7 ± 5.4 to 590 ± 1.8 Ma; zircon dating and rutile ages included in eclogite garnet) to nearly isothermal decompression (574.7 ± 0.5 Ma; titanite age) of ancient Archean deep crust, which was followed by suggested final exhumation and metamorphic cooling at shallower crustal levels between 559.0 ± 2.3 and 523.2 ± 1.9 Ma (rutile age in retrogressed assemblage). Therefore, the high-pressure conditions followed by decompression and metamorphic cooling during sin- to post-collisional settings were associated with the final assembly of West Gondwana.

中文翻译：

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巴西东北部新元古代榴辉岩的地壳增厚、挖掘和变质冷却：西冈瓦纳组装的时间尺度


与碰撞造山带演化相关的高压后高温变质作用是现代板块构造的预期压力-温度-时间 （P-T-t） 路径。然而，即使在显生代造山带中，这些 P-T-t 路径也很少保存下来。在这个问题上，Campo Grande 云铁矿片麻岩地区呈现出的太古代地壳，在巴西东北部的角闪岩相上覆盖着非均质逆行榴辉岩。区域核心的倒退榴辉岩由富含 Mn 的石榴石 + 斜辉石卟啉层形成，具有少量的角闪石 + 石英 + 钛矿组合，而边缘显示富含 Mg 的石榴石卟啉幼细胞的肢解透镜体，具有斜长石 + 角闪石冠和斜辉石 + 斜长石 + ortopyroxene 同孔，主要在剪切带内。相平衡模型显示，这些不同的逆榴辉岩记录了相似的榴辉岩条件（高达 18 kbar 和 660 ± 20 °C）。富含 Mon 的榴辉岩显示出从中太古代到古元古代的广泛岩浆分区锆石颗粒和 607.7 ± 5.4 马的再结晶变质颗粒。来自富镁榴辉岩的锆石在 2.67 Ga 处结晶，在 2.0 Ga 和 590.1 ± 1.8 马形成过度生长边缘。锆石中的 REE 缺乏 Eu 异常，在 590.1 ± 1.8 马 中显示出平坦的 HREE 模式新元古代晶粒表明在榴辉岩相条件下发生再结晶。原位 U-Pb 钛矿测年得出两个较年轻的年龄组，分别为 574.7 ± 0.5 和 562.8 ± 2.1 马。最后，石榴石核心中金红石内含物的原位 U-Pb 测年年龄为 606.1 ± 4.0 马，而逆行冠状和同层中包括的金红石得出的一致年龄为 559.0 ± 2.3 至 523.2 ± 1.9 马。 因此，结合相平衡模型和 U-Pb 年龄揭示了变质条件的逐渐变化，从榴辉石条件（至少在 607.7 ± 5.4 到 590 ± 1.8 马 锆石测年和金红石年龄）到古代太古代深地壳的近等温减压（574.7 ± 0.5 马钛矿年龄），然后是建议的最后挖掘和在 559.0 ± 2.3 到 523.2 ± 1.9 马 之间的较浅地壳水平的变质冷却（倒退的金红石年龄）组合）。因此，在正弦到碰撞后设置期间，高压条件随后进行减压和变质冷却与西冈瓦纳的最终组装有关。