ABSTRACT

Phase diagram modelling and U-Pb monazite ages reveal a clockwise Pressure-Temperature-time metamorphic evolution in the Paranaguá Terrane (Ribeira Belt – SE Brazil) and characterized important tectonic events. Comparisons of our dataset with the Dom Feliciano and Kaoko belts indicate a contrasting metamorphic evolution of South American and African units during West Gondwana assembly. The Paranaguá Terrane is considered an arc-related unit formed during the western Gondwana accretion, comprising Paleoproterozoic basement inliers, metasedimentary rocks and late Neoproterozoic granites. Metapelites mineral assemblages and chemistry combined with isotopic data indicate three tectonometamorphic stages for the terrane. M1 (640–610 Ma) is associated with collisional processes that resulted in a greenschist to lower amphibolite facies regional metamorphism (540–580°C and ~6-8 kbar). The progression of the metamorphism followed a decompression path of c. 2–4 kbars and reached P-T conditions of ~725°C at ~5 kbars (M2 – 610-580 Ma). M2 is associated with post-collisional processes related to slab-break off and partial exhumation of deeply buried sequences. Metapelites low-temperature retrograde conditions define a late M3 (540–500 Ma) metamorphic event. Our results demonstrate the similarities and differences of the Paranaguá-Dom Feliciano-Kaoko orogenic system. The metamorphic evolution of the Paranaguá Terrane and Northern Dom Feliciano Belt exhibits a geothermal gradient controlled by broad magmatic activity and post-collisional processes. In contrast, their suggested African counterpart (Kaoko Belt) shows a Barrovian metamorphic trend. This dataset permitted a refined time-space evolution of these southwest Gondwana units.

摘要

相图模型和 U-Pb 独居石年龄揭示了巴拉那瓜地体（里贝拉带 - 巴西东南部）的顺时针压力-温度-时间变质演化，并表征了重要的构造事件。我们的数据集与 Dom Feliciano 和 Kaoko 带的比较表明，在西冈瓦纳大陆组装期间，南美和非洲单位的变质演化形成鲜明对比。巴拉那瓜地体被认为是冈瓦纳西部增生形成的一个弧相关单元，包括古元古代基底内层、变沉积岩和晚新元古代花岗岩。Metapelites 矿物组合和化学结合同位素数据表明地体的三个构造变质阶段。M1 (640–610 Ma) 与碰撞过程有关，导致绿片岩降低角闪岩相区域变质作用（540–580°C 和 ~6-8 kbar）。变质作用的进展遵循 c 的减压路径。2–4 kbars 并在 ~5 kbars (M2 – 610-580 Ma) 下达到 ~725°C 的 PT 条件。M2 与与深埋层序的板块断裂和部分折返有关的碰撞后过程有关。变质岩低温逆行条件定义了 M3 晚期（540-500 Ma）变质事件。我们的结果证明了巴拉那瓜-Dom Feliciano-Kaoko 造山系统的异同。Paranaguá Terrane 和北 Dom Feliciano 带的变质演化表现出由广泛的岩浆活动和碰撞后过程控制的地温梯度。相比之下，他们建议的非洲对应物（Kaoko Belt）显示出巴罗维亚变质趋势。该数据集允许对这些西南冈瓦纳单元进行精细的时空演化。