Late Neoproterozoic P-T-t paths of syn- and post-collisional metamorphism in the Paranaguá Terrane, Ribeira Belt (Brazil): implications for West Gondwana assembly

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.

相图模拟与独居石U-Pb定年结果揭示了巴西东南部里贝拉造山带（Ribeira Belt）内巴拉瓜阿地体（Paranaguá Terrane）的顺时针压力-温度-时间（P-T-t）变质演化，并识别出了重要的构造事件。将本数据集与多姆费利西亚诺造山带（Dom Feliciano Belt）、卡奥科造山带（Kaoko Belt）的相关数据对比后可知，在西冈瓦纳聚合过程中，南美与非洲地块展现出截然不同的变质演化特征。巴拉瓜阿地体被认为是西冈瓦纳增生过程中形成的弧相关地块，由古元古代基底残块、变沉积岩与新元古代晚期花岗岩组成。泥质变质岩的矿物组合、地球化学特征结合同位素数据表明，该地块存在三期构造-变质作用。第一期变质作用（M1，640~610 Ma）与碰撞作用相关，形成了绿片岩相至低角闪岩相的区域变质环境，变质条件为540~580℃、约6~8千巴（kbar）。变质作用演化遵循约2~4千巴的减压路径，最终达到约725℃、约5千巴的P-T条件（M2，610~580 Ma）。第二期变质作用（M2）与碰撞后构造作用相关，该作用与板片拆沉及深埋藏岩层序列的部分折返有关。泥质变质岩的低温退变质特征代表了晚期第三期变质作用（M3，540~500 Ma）。本研究结果阐明了巴拉瓜阿-多姆费利西亚诺-卡奥科造山系的异同特征。巴拉瓜阿地体与多姆费利西亚诺造山带北部的变质演化呈现出受广泛岩浆活动及碰撞后构造作用调控的地热梯度特征。与之相反，其对应的非洲地块（卡奥科造山带）则展现出巴罗式变质作用的演化趋势。本数据集实现了对西南冈瓦纳上述地块时空演化过程的精细化刻画。