Inverted metamorphic gradients are recognized in several Proterozoic to Phanerozoic orogens. However, the mechanisms that are responsible for the formation of these gradients are still a matter of discussion. In the southern Brasília Orogen, an inverted metamorphic gradient is recorded in the Passos Nappe, that comprises a sequence of metasedimentary rocks with minor intercalations of tholeiitic metamafic rocks, metamorphosed under greenschist facies (biotite zone) at the bottom and high-pressure granulite facies at the top. This paper presents a detailed investigation of pressure and temperature conditions along the Passos Nappe by integrating conventional geothermobarometry in metamafic rock and single-trace elements geothermometry (Zr-in-rutile and Ti-in-quartz) in quartzite. Nine lithostratigraphic units are identified in the Passos Nappe, which are informally named A to I, from the bottom to top, adding up to a minimum thickness of 4.56 km. In mafic rocks, the increase of metamorphic conditions is indicated by: (1) chemical variation of amphiboles, from actinolite/edenitic hornblende in Unit C, to pargasitic hornblende in Units E and G, and Fe-pargasite in Units H and I; (2) plagioclase composition varying from An1-13 in Unit C, An15-27 in Unit D to andesine at upper units; and (3) occurrence of clinopyroxene from the top of Unit E upwards. Additional petrographic features in quartzite also corroborate these insights, such as: the increase of grain size of both quartz and rutile, from bottom to top; the morphology of rutile crystals; the mechanism of quartz recrystallization (subgrain rotation dominates in lower units while grain boundary migration dominates in upper units) and the occurrence of rutile needles in quartz in the upper units, which suggest a continuous gradient. Combined application of Zr-in-rutile and Ti-in-quartz geothermometers in quartzite provided the following average temperature and pressure values for each unit: 673 °C and 11.7 kbar for Unit E, 690 °C and 9.5 kbar for Unit G, 747 °C and 11.6 kbar for Unit H and 758 °C and 11.3 kbar for Unit I. Our data indicate that the Zr-in-rutile and Ti-in-quartz systems do not re-equilibrate in metamorphic conditions lower than 600 °C. The extrapolation of these results to the low-grade units indicate: 496 °C and 4.8 kbar at Unit A, 504 °C and 4.8 kbar at Unit B, 502 °C and 4.4 kbar at Unit C. The results obtained with the geothermometer hornblende-plagioclase and the geobarometer garnet-rutile-ilmenite-plagioclase-quartz in metamafic rocks yielded the following average values for each unit: 486 °C and 5.0 kbar at Unit C, 568 °C and 6.0 kbar at Unit D, 622 °C and 8.1 kbar at Unit E, 650 °C and 8.4 kbar at Unit G, 743 °C and 9.4 kbar at Unit H and 723 °C and 11.2 kbar at Unit I. Since the two geothermobarometric approaches are based on independent chemical systems, the results obtained represent robust estimates for the temperature and pressure conditions for the inverted metamorphic gradient of the Passos Nappe. Comparing the inverted metamorphic gradient at the Passos Nappe with classical occurrences at the Himalaya Orogen, it is possible to assume that both origins were similar, which probably involved isotherm inversion due to subduction, channel flow process associated with shear heating and transport of higher pressure rocks over low-pressure rocks by reverse ductile shearing.

在几个元古代到显生宙的造山带中发现了倒置的变质梯度。然而，导致这些梯度形成的机制仍有待讨论。在巴西利亚南部的造山带，在 Passos Nappe 记录了一个倒置的变质梯度，包括一系列变质沉积岩，少量夹层拉斑变质岩，在底部的绿片岩相（黑云母带）和高压麻粒岩相下变质。顶端。本文通过将传统的变质岩地热气压法和单微量元素地热法相结合，对 Passos Nappe 沿线的压力和温度条件进行了详细调查（金红石中的锆和石英中的钛）在石英岩中。Passos Nappe 中确定了九个岩石地层单元，从下到上，非正式地命名为 A 到 I，加起来最小厚度为 4.56 公里。在基性岩中，变质条件的增加表现为： (1) 闪石的化学变化，从 C 单元的阳起石 / 伊敦质角闪石到 E 和 G 单元的短闪石角闪石，以及 H 和 I 单元的铁短闪石；(2) 斜长石组成从C单元的An1-13、D单元的An15-27到上部单元的长石长石；(3) 单斜辉石从E单元顶部向上产状。石英岩中的其他岩相特征也证实了这些见解，例如：石英和金红石的粒度增加，从下到上；金红石晶体的形态；石英再结晶机制（下单元以亚晶旋转为主，上单元以晶界迁移为主）和上单元石英中金红石针的出现，表明连续梯度。金红石中锆和石英中钛地温计在石英岩中的组合应用为每个单元提供了以下平均温度和压力值：单元 E 为 673 °C 和 11.7 kbar，单元 G 747 为 690 °C 和 9.5 kbar H 单元为°C 和 11.6 kbar，I 单元为 758°C 和 11.3 kbar。我们的数据表明，金红石中的锆和石英中的钛系统在低于 600°C 的变质条件下不会重新平衡。将这些结果外推到低等级单位表明：单位 A 为 496 °C 和 4.8 kbar，单位 B 为 504 °C 和 4.8 kbar，502 °C 和 4.4 kbar 在 C 单元。在变质岩中使用地热计角闪石-斜长石和地质气压计石榴石-金红石-钛铁矿-斜长石-石英获得的结果为每个单元产生以下平均值：486 °C 和 5.0 kbar 在C 单元，D 单元 568 °C 和 6.0 kbar，E 单元 622 °C 和 8.1 kbar，G 单元 650 °C 和 8.4 kbar，H 单元 743 °C 和 9.4 kbar，723 °C 和 11.2 kbar单元 I。由于这两种地热气压方法基于独立的化学系统，因此获得的结果代表了对 Passos Nappe 倒变质梯度的温度和压力条件的可靠估计。比较 Passos Nappe 的倒变质梯度与喜马拉雅造山带的经典事件，可以假设两个起源相似，