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The Dom Feliciano Belt is the South American part of an extensive Neoproterozoic orogenic system that developed during the late Cryogenian–early Cambrian close to the margin of southwest Gondwana. The link of its evolution with the tectonic processes in its African counterpart is still not well understood. P–T estimates, Lu–Hf garnet–whole-rock ages, U–Pb monazite SIMS ages and REE garnet and monazite data from samples of the Porongos and Passo Feio complexes indicate diachronous tectonic evolution of the central Dom Feliciano Belt foreland. Metasedimentary rocks of the eastern Porongos Complex reached previously estimated metamorphic peak conditions of ~ 560–580 °C and 5.8–6.3 kbar at 654 ± 2 Ma, based on Lu–Hf isochron garnet–whole-rock age data. This episode represents an early orogenic thickening in the foreland as a response to the beginning of the transpressive convergent evolution of the belt. The monazite age of 614 ± 6 Ma (U–Pb SIMS) is interpreted as associated with post-exhumation magmatic activity in the foreland and suggests that the eastern Porongos Complex was exhumed sometime between ca. 660 and 615 Ma. The main metamorphic and deformation event in the Porongos Complex's western region occurred at ~ 545–565 °C and 4.3–5.3 kbar at 563 ± 1 Ma (garnet–whole-rock Lu–Hf isochron age). The exhumation of this part of the foreland is dated using monazite crystallising during garnet breakdown and suggests retrograde metamorphism at 541 ± 7 Ma (U–Pb SIMS). The main metamorphic fabric in the Passo Feio Complex further to the west developed at 571 ± 2 Ma (garnet–whole-rock Lu–Hf isochron age) at 560–580 °C and 4.7–6.4 kbar. The western part of the Porongos Complex and the Passo Feio Complex have deformed at similar P–T conditions and apparent geothermal gradients at ca. 570–565 Ma. These regions record a second crustal thickening event in the Dom Feliciano Belt foreland and the orogenic front migration towards the west as a response to the onset of crustal thickening on the African side of this long-lived transpressive orogenic system. [ABSTRACT FROM AUTHOR]

Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550 Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear-dominated deformation associated with development of N-S trending S2 cleavage preserved in the central profile, followed by sinistral simple shear-dominated deformation on newly developed NW-SE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550 Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling. [ABSTRACT FROM AUTHOR]

Existing models of tectonic evolution of the Neoproterozoic orogenic system rimming the shores of the South Atlantic Ocean (the Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep belts) interpret the belts as subduction-related orogens and emphasize the role of the "Adamastor Ocean" in their pre-collisional evolution. A critical problem in such an interpretation is the confined nature of the northern termination of the orogenic system, as well as a very short time span between the end of rifting and onset of convergence recognized in its southern part. In this contribution, we review the data for the pre- and synorogenic evolution of this system of orogens (here collectively called the South Atlantic Neoproterozoic Orogenic System) and show that the data speak against the presence of a large oceanic domain before the onset of its orogenic evolution. We propose a new and simple intracontinental model, suggesting that Neoproterozoic oceanic crust played only a minor role in the development of the South Atlantic Neoproterozoic Orogenic System and that its overall architecture and thermal evolution is the result of inversion of large-scale rift structures with a protracted, and probably episodic, extensional history. True oceanic crust probably developed only in the southern part of the rift system, but it must have been narrow, akin to the Red Sea–Gulf of Aden stage of the "Adamastor Rift" evolution just before the onset of convergent thickening. Unlabelled Image • Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep orogens are largely intracontinental. • Subduction-related models for their origin pose severe space problems. • Inversion of Adamastor Rift is proposed as a tectonic model for these belts. [ABSTRACT FROM AUTHOR]

Existing models of tectonic evolution of the Neoproterozoic orogenic system rimming the shores of the southern Atlantic Ocean (the Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep belts) interpret the belts as subduction-related orogens and stress out the role of the "Adamastor Ocean" in their pre-collisional evolution. A critical problem in such interpretation is the confined nature of the northern termination of the orogenic system, as well as a very short time span between the end of rifting and onset of convergence recognized in its southern part. Moreover, the existing subduction-related models for various parts of the orogenic system are often contradictory and incompatible with existing data. In this contribution, we summarize the data that speak against the presence of a large oceanic domain before the onset of thickening and test a new and simple intracontinental model for the Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep belts. In the northernmost part of the orogenic system, the Araçuaí–Congo Belt terminates into an embayment within the São Francisco–Congo Craton. The data suggest crustal thickening to ca. 60–65 km in the hot anatectic centre of the belt, which can only be achieved by ca. 500 km of orogenic shortening. In order to allow such amount of convergence, but maintain the São Francisco–Congo cratonic connection, the pre-convergence configuration must have involved smaller-scale rift domains in the northern part of the São Francisco–Congo basement that allowed for its shortening during the Neoproterozoic. The area of the Araçuaí–Congo Belt is interpreted as an intracontinental hot orogen with thermomechanical evolution similar to the Himalaya–Tibet system that developed through inversion of a ca. 750 km wide rift basin (without the presence of a significant oceanic domain), which was shortened to ca. 250 km.Data from the Kaoko–Dom Feliciano–Gariep orogenic system suggest that the early Neoproterozoic rifting preceding the formation of this belt started at ca. 820–800 Ma and continued up to ca. 660 Ma. However, early convergence and related metamorphism on the South American side, as well as flysch sedimentation on the African side of the orogenic system at ca. 650–645 Ma suggest a very short lifetime for the presumed oceanic domain. The only remnants of oceanic-like crust are present in the Gariep Belt, where it was obducted on top of the Neoproterozoic rift-related sediments at the edge of the Kalahari Craton. We suggest that Neoproterozoic oceanic crust played minor role in the development of the Araçuaí–Ribeira–Congo and Dom Feliciano–Kaoko–Gariep belts and that their overall architecture and thermal evolution is the result of inversion of large-scale rift structures with more than 160 my of extensional history. A true oceanic environment probably developed only in the southern part of the rift system, but it must have been narrow, suggesting the Red Sea stage of the development of the "Adamastor Rift" just before the onset of thickening.JK appreciates financial support of the Czech Science Foundation (GACR 18-24281S). [ABSTRACT FROM AUTHOR]

The Encruzilhada Block lies between the eastern hinterland and western foreland of the Dom Feliciano Belt (southern Brazil) and its tectonic meaning in the orogenic evolution of the belt is still poorly understood. Its low magnetic signal is similar to that of the foreland supracrustal sequences, whereas the high gammaspectrometric signal appears due to the hinterland post-collisional granitoids. Satellite image lineament analysis points to tectonic similarities between the Encruzilhada Block and the foreland, as the structures in both domains show predominantly NNW and NNE trends, while the hinterland mostly presents NE-trending structures. The pre-orogenic connection between the Encruzilhada Block and the foreland is indicated by the correlation between the Várzea do Capivarita and Cerro da Árvore complexes. Both contain 800 – 780 Ma metaigneous rocks with arc-like geochemistry, and parametamorphic rocks with similar sedimentary provenance. Common syn-orogenic deformation history of both complexes is suggested by progressive to P-T o-th E-W transpressive deformation and similar peak metamorphic age (660 – 640 Ma). PT-paths suggest exhumation of the hinterland Várzea do Capivarita Complex from high-T/low-P conditions of 790–820 °C/4.4–4.8 kbar to 660–720 °C/2.5–3.4 kbar at ca. 630 Ma. On the other hand, the foreland Cerro da Árvore Complex was subject to progressive metamorphism from 555 to 565 °C/5.4–5.7 kbar to 560–580 °C/5.8–6.3 kbar, which is interpreted as a result of orogenic thickening. Evidence suggests that both complexes have originated in a similar, if not a single, basin on an attenuated lithosphere with high geothermal gradient, possibly a (back-arc?) rift. Oblique collision has caused basin inversion and thrusting of the lower crust over the rift margin, which may have been accompanied by lithosphere delamination. Progressive transpressional deformation and voluminous post-collisional magmatism (640 – 578 Ma) controlled by major lineaments have blurred the original tectonic contact and finally caused thermal metamorphism in both complexes at ca. 3 kbar, when the autochthonous Encruzilhada Block was stabilized in its present geological configuration. The intracontinental character of major shear zones limiting hinterland and foreland requires a review of the existing evolutionary model for the Dom Feliciano Belt in the context of Western Gondwana amalgamation. [ABSTRACT FROM AUTHOR]

• The Neoproterozoic Araçuaí orogen fits an intracontinental model of mountain building. • The tectonic setting of the Rio Doce "arc" magmatism should be reconsidered. • 50 m.y. of oceanic subduction is incompatible with a confined orogenic setting. • Amphibolite of the Ribeirão da Folha Fm. is not evidence for a wide Adamastor ocean. The Neoproterozoic Araçuaí-West Congo orogen in Brazil and Congo represents a branch of the Brasiliano/Pan-African orogenic system that is considered to terminate northward into a confined cratonic environment defined by the horseshoe-shaped pre-Atlantic São Francisco-Congo craton. The prevailing interpretation is that this orogen formed as a result of 50 m.y. of subduction leading to a classical continent–continent collision. This subduction-collision model hinges on interpretation of 630–580 Ma granitoids in the core of the orogen as being arc-related, and of locally exposed mafic and ultramafic metamorphic rocks as being ophiolitic. We show that when tested beyond geochemical signature, the model has fundamental problems that cannot be accounted for. In particular, there is an insurmountable oceanic space problem in this confined setting that is overlooked in most of the current literature. There are also problems with subduction initiation, lack of unambiguous evidence for oceanic crust, no trace of any high-P metamorphism and the abrupt termination of an ocean with no realistic way to transfer the large amount of oceanic opening displacement and subsequent convergence required by the model. We conclude that the prevailing subduction-collision model cannot possibly work and argue that the existing data are more consistent with hot intracontinental orogeny. We stress the importance of building tectonic models on more than one type of data, making realistic restorations and palinspastic reconstructions, and taking into account modern geotectonic knowledge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Várzea do Capivarita Complex orthogneisses demonstrate Tonian protolith ages. • Várzea do Capivarita and Porongos complexes shared an igneous history at ca. 790 Ma. • Várzea do Capivarita Complex has a syn-volcanic–sedimentary origin at ca. 790 Ma. • Dom Feliciano Belt ca. 790 Ma zircon crystallized in the more evolved magmas. This work investigates the pre-collisional (before ca. 650 Ma) history of the Dom Feliciano Belt in southernmost Brazil through geochronological and zircon oxygen isotope study. U–Pb SHRIMP dating of two orthogneiss samples from the Várzea do Capivarita Complex and one metarhyolite sample from the Porongos Complex yielded crystallisation ages of 786 ± 5 Ma, 780 ± 10 Ma and 787 ± 5 Ma, respectively. The mean oxygen isotope values calculated for the ca. 790 Ma zircon cores from the orthogneisses are 8.41 ± 0.13‰ and 8.68 ± 0.14‰, and 8.75 ± 0.72‰ for the metarhyolite. Such values suggest that zircon crystallised in the more evolved magmas, either from the melting of host rocks and sediments or assimilation of crustal material by mantle-derived magmas. The detrital zircon population was analysed in one additional paragneiss sample from the Várzea do Capivarita Complex, and most of the values cluster at 790–750 Ma. The data spread is centred at ca. 790 Ma, which is the crystallisation age of the interleaved orthogneisses. In our interpretation, such dataset suggests a syn-volcanic origin of the paragneiss protolith and, therefore, a volcano-sedimentary origin of the Várzea do Capivarita Complex. The correspondence of geochronological data and zircon oxygen isotope values for the studied meta-igneous samples suggests that the Várzea do Capivarita and Porongos complexes have shared the same igneous history. Therefore, the samples probably represent one magmatic event at different levels of a single basin at ca. 800–770 Ma. Such results bring first-order information about the meaning of tectonic limits in this Gondwana-related belt and implications for reconstructing the pre-collisional history of the orogen. [ABSTRACT FROM AUTHOR]

Metamorphic–deformation paths and interpretations of regional structures are essential for the understanding of how orogens evolve. While in active orogens, structures can be easily mapped for hundreds of kilometres, regional structures in ancient mountain belts may appear only as subsurface geophysical data. In this paper, we constrain the metamorphic–deformation history of the southeastern part of the Passo Feio Complex located in the Neoproterozoic Dom Feliciano Belt in southernmost Brazil. The complex is crosscut by a block-limiting structure defined by magnetometric data, the Caçapava Lineament. Our petrographic interpretations and thermodynamic modelling of pelitic schists of the Passo Feio Complex indicate the beginning of garnet growth at ca. 530–550 °C and 3–4.3 kbar during D 1 , and metamorphic peak at ca. 560–570 °C and 5–5.5 kbar (M 1), during progression to D 2. After M 1 (~17–19 km depth), the complex was exhumed to at least 14 km (~4 kbar) depth, as the contact metamorphism by the Caçapava Granite (ca. 562 Ma) produced andalusite. The correlation of D 3 structures of the Passo Feio Complex (S 3 and L 3), magmatic structures in the Caçapava Granite, orientation of geophysical anomalies in the region and kinematics of S 3 corroborate the interpretation of the Caçapava Lineament as a dextral shear zone. Due to the location of anomalies and previous three-dimensional modelling of the granitic body, we interpret that a curved ENE to NS branch of the NE-striking Caçapava Shear Zone is responsible for the accommodation of the Caçapava Granite. Lastly, we discuss the regional implications of such interpretation, which brings up the question of block-limiting character of the Caçapava Shear Zone and the geotectonic position of the Passo Feio Complex. • Onset of Garnet growth from 490 to 550 °C, 2.5–4.3 kbar. • M 1 peak metamorphic conditions of 500–510 °C, 5–6.4 kbar in a Gt phyllite. • M1 peak metamorphic conditions of 560–570 °C/5–5.5 kbar in a Gt–St schist. • Regional metamorphism not compatible with low-P conditions; Andalusite related to contact. • Caçapava Lineament origin as a dextral transcurrent shear zone. [ABSTRACT FROM AUTHOR]