Amalgamation Of Gondwana Research Articles

Pressure-temperature-time paths from metapelites reveal neoproterozoic continental crust underthrusting related to the West Gondwana amalgamation

In this contribution, we employed a petrochronological approach to investigate the tectonometamorphic evolution of Al-rich garnet-staurolite and garnet-staurolite-kyanite (biotite- and plagioclase-free) metapelites of the southernmost portion of the Neoproterozoic Brasília orogen. We have reconstructed the first prograde to peak pressure-temperature-time (P-T-t) paths reported for metamorphic units of the area, by combining petrographic analyses, quantitative compositional mapping of major elements, phase equilibrium modeling, and EPMA Th–U–Pb monazite chemical dating. The metamorphic reactions involved in the prograde metamorphic evolution are discussed, including the effects of garnet fractionation, exhaustion of reactants, and re-equilibration reactions on the major-element composition of garnet porphyroblasts, and their influence on P-T condition estimates. Raman spectroscopy on carbonaceous material (RSCM) thermometry provided insights into the synkinematic retrograde path. A steep prograde path marked by two stages is recorded by the garnet porphyroblasts of garnet-staurolite-muscovite (±kyanite) schists: (i) 555–585 °C and 0.60–0.90 GPa; (ii) 590–635 °C and 1.0–1.4 GPa. Monazite crystals record the prograde to peak path from ca. 630–625 Ma to ca. 605–595 Ma. Matrix graphite crystals suggest post-peak cooling to 400–500 °C concurrent with the late stages of development of the main foliation. The reconstructed P-T-t paths indicate an intermediate dT/dP metamorphism, and a burial rate of ~0.55 km/Ma, with garnet compositional zoning suggesting that the high-pressure P-T-t path resulted from a single metamorphic event. The corresponding geothermal gradients, and in-situ ages, combined with regional evidence, suggest that peak metamorphic conditions were attained during collisional underthrusting of the continental crust related to the West Gondwana amalgamation.

The geology of the Aracruz pluton (Espírito Santo, Brazil), a Cambrian post-orogenic intrusion in the aftermath of Gondwana amalgamation

ABSTRACT We present the first geological map of the Aracruz pluton (Espírito Santo, Brazil), which belongs to the late Cambrian post-orogenic suite that intruded the Nova Venécia metapelites and Ediacaran syn-orogenic S-type granites of the Araçuaí belt. Our mapping coupled with airbone magnetic and radiometric observations reveals that the pluton is not regularly zoned. It is composed of porphyric alkali feldspar granites, into which charnockite and quartz-diorite bands intruded as several pulses while the granites were a deforming crystal mush, and an undeformed central norite emplaced when most movement of the host magma had ceased. Steep-dipping concentric magmatic foliation, magmatic foliation parallel to tectonic foliation in the country rock, the noritic core, and the irregular charnockite and quartz-diorite band alignment suggest buoyancy-driven diapirism as emplacement mechanism. The Aracruz pluton is a superb example of mantle-derived post-orogenic intrusion attesting for the production of continental crust during the final stages of a Wylson cycle.

Protracted mantle heat conduction after lithospheric foundering beneath the Malagasy orogen

Ultrahigh-temperature metamorphism (UHTM) is important for the evolution and long-term stability of continental crust. The Anosyen domain in southeastern Madagascar is a well-preserved UHTM terrane that formed during the amalgamation of Gondwana. The heat source(s) required to reach peak conditions is(are) a matter of debate. One potential cause of extreme crustal heating is the intrusion of mantle-derived melts into the crust. Foundering of the mantle lithosphere can also lead to increased heat flow. To assess the role of these heating mechanisms, we measured zircon δ18O, εHf(t) compositions, and U-Pb dates for plutonic rocks in the midcrustal UHTM domain. Our results indicate that pluton emplacement predated UHTM by as much as 40 m.y. and that all zircons have crustal O and Hf isotopic compositions. We propose that mantle lithosphere foundering caused melting in the lower crust, producing the magmas responsible for plutonism during the early stages of orogenesis. Prolonged conductive heating of the crust—combined with above-average radiogenic heating—may explain why UHTM occurred ∼40 m.y. after foundering. This suggests that foundering of the mantle lithosphere can swiftly lead to partial melting in the lower crust, as well as protracted heating of the middle crust that culminates tens of millions of years later.

Tectonic setting and Pan-African structural evolution of the western Saldania Belt, South Africa

Abstract The western Saldania Belt records the closure of the Adamastor Ocean and amalgamation of southwest Gondwana in the latest Neoproterozoic and early Phanerozoic, but the geodynamic setting and evolution of the belt remains controversial. Regional mapping and the integration of structural data presented in this paper document the juxtaposition of domains with distinct fabric development and kinematics. Structures record Pan-African strains and a strike-slip dominated sinistral transpression during southeast-directed subduction and convergence at low angles to the continental margin. Two main, structurally overlying domains – an upper and a lower domain – can be distinguished. Rocks of the upper domain record the partitioning of the transpressional strain into (1) broad regions of more or less upright, north to northwesterly-trending folds (F2) that record horizontal, mainly coaxial, east-northeast to west-southwest directed shortening at high angles to the continental margin, and (2) the northwesterly-trending, sinistral strike-slip Colenso Fault Zone that accommodates the margin-parallel, non-coaxial component of deformation between ca. 555 and 520 Ma. The strike-slip partitioning was promoted by strain localisation into synkinematic plutons of the Cape Granite Suite. In contrast, rocks in the pervasively transposed, mélange-like lower domain in the central Swartland region record episodes of vertical, coaxial shortening alternating with non-coaxial top-to-the-west and -northwest thrusting. The coaxial shortening strains relate to the thickening and gravitational loading of the succession in response to thrusting and tectonic underplating. Non-coaxial strains denote episodes of seismic slip during underthrusting. The different fabric domains are interpreted to represent a section through a fore-arc region, from the deeper level accretionary prism (lower domain) to the overlying, folded fore-arc basin succession (upper domain). Regional-scale klippen structures indicate the transfer of lower-domain phyllites into the overlying fore-arc sequence. The proposed fore-arc setting of the Saldania Belt suggests the subduction of the Adamastor Ocean below the leading edge of the Kalahari Craton. This challenges stratigraphic and structural correlations between the Saldania Belt and the Gariep Belt to the immediate north.

Tectonic structures of the Dome Fuji region, East Antarctica, based on new magnetic data

The Oldest Ice Reconnaissance (OIR) airborne geophysical survey in East Antarctica was flown over approximately 170,000 km2 of the Dome Fuji region in 2016/17. The survey’s results support new insights into the subglacial geology and its meaning for the tectonic histories of the supercontinents Rodinia and Gondwana. The new magnetic and radar-derived bed topography data are integrated with previously acquired magnetic and gravity data, allowing the mapping of crustal domains within and beyond the survey’s limits. The magnetic data reveal three distinct domains within the survey region, delineated by N–S oriented boundaries, partly aligned with gravity domains following upward continuation transformations for both datasets. Additionally, four primary sets of magnetic lineaments were identified, exhibiting correlations with topographic and gravity patterns. These correlations indicate the continuation of the Tonian Oceanic Arc Super Terrane (TOAST) southward of its previously known southern limit. Moreover, an E–W-trending magnetic anomaly, the Elbert magnetic anomaly, suggests the suture between the recently-proposed subglacial Valkyrie craton and the TOAST. Furthermore, the analysis reveals a broad scale shear zone, named here the OIR shear zone, which formed as a result of oblique collision of the Ruker and Valkyrie cratons during the amalgamation of Gondwana.

The assembly of Pangaea: geodynamic conundrums revisited

Geodynamic models for Pangaea assembly require knowledge of Paleozoic mantle convection patterns. Application of basic geodynamic principles to Neoproterozoic–Paleozoic plate reconstructions yields Pangaea in the incorrect configuration (predicting that it should have formed by consumption of the exterior palaeo-Pacific Ocean instead of the Iapetus, Rheic and Proto-Tethys oceans). We contend that the mantle legacy of Late Neoproterozoic–Cambrian amalgamation of Gondwana must be factored into models for Pangaea amalgamation. Proxy data suggest that the mantle downwelling driving Pan-African collisions and Gondwana assembly evolved into a mantle upwelling as evidenced by the interplay between subduction-related and plume-related tectonics around the periphery of Gondwana. Orthoversion theory, whereby a supercontinent assembles c . 90° away from the centre of the previous supercontinent, suggests that Gondwana amalgamated above an intense downwelling along a meridional subduction girdle that bisected two antipodal sub-equatorial upwellings. Several processes beneath and around Gondwana reduced the intensity of the original downwelling, as evidenced by plume-related activity along its margins, initiation of subduction zone rollback, and the export of terranes from Gondwana that collided with the margin of Laurentia–Baltica. As upwelling beneath it intensified, Gondwana migrated along the girdle until it collided with Laurentia–Baltica, resulting in the final assembly of Pangaea.

Dynamic evolution of West Gondwana inferred from crustal anisotropy of the South American platform

SUMMARY The amalgamation and breakup of the West Gondwana shaped the South American platform. The dynamics during the processes can be reflected by crust anisotropy of the platform, but there are no specialized crustal anisotropic measurements yet. Splitting analysis of Moho-converted shear waves in P-wave receiver functions (Pms) can reveal crustal-scale anisotropy, which is important for understanding the dynamic evolution of the crust and for the interpretation of mantle anisotropy from splitting analysis of core–mantle refracted shear waves (XKS phases). This study measured crustal anisotropy for the old and stable South American platform by Pms splitting analysis. The splitting times vary mainly in the range of 0–0.5 s, with a regional mean of 0.2 s, slightly lower than that observed in tectonically active regions. The detected crustal anisotropy shows distinct characteristics and spatial zoning, providing insights into tectonic processes. (1) Fast polarization directions at stations close to the Transbrasiliano Lineament (TBL) are oriented NNE–SSW, generally consistent with the strike of the TBL but inconsistent with the maximum horizontal compressive stress, implying that they might be formed by dynamic metamorphism during the formation of the TBL. (2) Crustal anisotropy along the passive continental margin in the east and northeast is weak. Still, the fast polarization directions tend to be oriented along the margin, implying the existence of fossil extensional crustal fabrics formed during the continental rifting of West Gondwana. (3) The Paraná Basin, one of the world's largest Large Igneous Provinces (LIP) covered by continental flood basalts, shows distinctively strong anisotropy, with fast polarization directions highly aligned with mantle anisotropy, implying that synchronous crust–mantle deformation occurred in these regions as a result of magmatism during the breakup of West Gondwana.

Paleomagnetism of the Rio Perdido mafic dike swarm (1110 Ma) and the paleogeography of Amazonia and its role for supercontinents Rodinia and Gondwana

The Rio Apa Terrane (RAT) is situated at the south end of the Amazonian Craton (AC) separated from it by the aulacogen Tucavaca belt. It encompasses basement rocks that evolved mainly during the Paleoproterozoic. Its relationship to the AC during Proterozoic is yet undefined, although geologic, geochronologic and isotopic evidence suggest it was close to the Ventuari-Tapajós and Rio Negro-Juruena Provinces at Paleoproterozoic and linked to southwestern AC at ca. 1320 Ma. Aiming to elucidate the paleogeographic relation of the RAT to the AC during the Proterozoic, we performed a paleomagnetic study of the 1110 Ma Rio Perdido mafic dike swarm that crosscut the RAT. These dikes strike preferentially WNW-ESE and are mostly undeformed and unmetamorphosed. Magnetic experiments (hysteresis curves, isothermal remanent magnetization (IRM) curves, thermomagnetic curves and first order reverse curves-FORCs) revealed pseudo-single domain (PSD) Ti-poor titanomagnetite as the main magnetic carrier in these dikes. Alternating field (AF) and thermal demagnetization were efficient in isolating southwestern and northeastern directions with low inclinations, whose mean direction (Dec = 51.8°, Inc = −0.8°, N = 14, α95 = 13.8°, k = 9.3) yielded the paleomagnetic pole (RP) at 34.8°S/197.3° (A95 = 10.9°). This pole passed a baked contact test and meets 6 out of 7 pole reliability criteria (R = 6). The Rio Perdido pole implies that RAT could be linked to the southwestern AC at 1110 Ma but rotated counterclockwise ∼ 110° related to its present position. The AC linked to RAT probably belonged to the 1100 Ma Umkondia megacontinent which later collided with Laurentia during the formation of Rodinia at ca. 1000–900 Ma. Also, paleomagnetic data suggest that the RAT and the southwestern AC (Paraguá Terrane) were linked to Ventuari-Tapajós and Rio Negro-Juruena provinces at ca. 1780 Ma and had a joint geological evolution during the Paleo- and Mesoproterozoic. Finally, during the amalgamation of West Gondwana, the RAT rotated clockwise to its present position.

From 3.4 Ga TTG generation to 2.9 Ga crustal anatexis: The Archean crustal evolution of Porteirinha Complex (SE, Brazil)

The Porteirinha Block (PB) provides an important record of the origin and evolution of South American crust. The PB records the generation of Paleoarchean TTG, Mesoarchean anatexis, and Paleoproterozoic crustal reworking. It is exposed as a basement inlier in the Araçuaí Orogen as a result of a tectonic involvement of the continental margins of São Francisco Congo Paleocontinent (PSFC) during the collisional processes of Gondwana amalgamation at the Neoproterozoic. The PB basement unit is the Porteirinha Complex (PC), which consists of TTG orthogneisses, migmatites, amphibolites, metaultramafics rocks and Neoarchean granitoids. In this paper, we discuss the evolution of the TTG orthogneisses and migmatites from PC based on field, geochronological and whole-rock geochemistry data. Zircon U–Pb ages (LA-ICP-MS) show a complex and polycyclic evolution of these rocks. Concordant ages were obtained for crystallization of TTG magma at ca. 3.4 Ga and the geochemical signature supports the idea of TTG generation by partial melting of hydrated mafic crust under garnet-amphibolite facies conditions. Zircon U–Pb ages also suggest crustal reworking events at 3.1 Ga. Metatexite and diatexite domains related to partial melting of TTG orthogneisses are individualized. The migmatites record processes of crustal anatexis and melt generation that occurred between 2.8 and 2.9 Ga (LA-ICP-MS, U–Pb in zircon) and are linked to crustal reworking and heat generation events recognized regionally. The new data presented in this work allow us to establish correlations between Archean and Paleoproterozoic units of the PB and those that occur regionally, particularly those related to Gavião block, where a series of stages and events of early crustal evolution are shared.

Speculations on the Paleozoic legacy of Gondwana amalgamation

Using Gondwana as an example, we show how the geological record can be interrogated to detect significant changes in mantle convection patterns at critical junctures in Earth’s evolution. Evidence of major changes in mantle circulation in the aftermath of late Neoproterozoic-early Paleozoic Gondwana assembly is provided by widespread (i) plume-related magmatism around Gondwana’s periphery, (ii) ironstone deposits related to mantle plume-ocean ridge interaction and enhanced hydrothermal activity, and (iii) super-mature clastic deposits that reflect epeirogenic uplift triggered by mantle upwelling beneath Gondwana combined with deep tropical weathering.In our model, Gondwana assembled above a region of mantle downwelling in which subducted slabs between the converging Gondwanan continents descended to the core-mantle boundary. Renewed subduction along Gondwana’s periphery yielded early arc magmas. But as downwelling beneath Gondwana evolved into upwelling as a result of the ponding of subducted slabs at the base of the mantle, mantle plumes rose from the margins of the nascent upwelling to interact with the edges of Gondwana, where they penetrated the peripheral subduction zones via slab windows, tears and transform faults to generate voluminous calc-alkalic crustal melts in hydrated arc regions and A-type magmas in dry back-arc regions. The plumes also underplated oceanic lithosphere and interacted with adjacent ocean ridges, thereby enhancing hydrothermal activity and the flux of bioessential nutrients, leading to the recurrence of marine iron-rich sedimentary rocks in the geological record. At the same time, upwelling beneath a tropical to equatorial Gondwana led to epeirogenic uplift, deep weathering and erosion, resulting in the production of widespread super-mature clastic deposits. We contend that major changes in mantle convection patterns were encoded into the geological record of Gondwana assembly, influenced global-scale mantle convection patterns, and should be incorporated into geodynamic models for the assembly of Pangea.

Tectonic significance of the late-Ediacaran syn-orogenic basin in the easternmost portion of the Paraguay Belt, Tocantins Province, central Brazil

Sedimentary provenance studies using detrital zircon U–Pb ages represent an important tool to investigate the evolution of orogenic basins and to suggest tectonic settings and paleogeography reconstructions when it comes to supercontinent modeling. Syn-orogenic basins worldwide are characterized by a large proportion of zircons with ages close to the maximum depositional period, reflecting the proximity of recently formed magmatic rocks. In this work, we combine field observations, detrital zircon U–Pb ages, whole-rock Sm–Nd and mica Ar–Ar isotopic analyses to constrain the final tectonic evolution of a restricted basin located in a poorly studied region at the easternmost limit of the Paraguay Belt in the Tocantins Province, central Brazil. The investigated area corresponds to the boundary sector of the Paraguay Belt and the Brasília Belt and is also transected by the strike-slip fault system associated with the Transbrasiliano Lineament. This sector was previously mapped as part of the Cuiaba Group, internal zone of the Paraguay Belt. We provide 465 new detrital zircon U–Pb data with ages distributed from the early Cambrian to the Archean, with approximately 60% of the analyzed grains derived from Ediacaran-Cryogenian sources. The maximum depositional age of the basin is defined at ca. 590 Ma, constrained by the youngest age peak and an evident provenance shift in detrital input in the Paraguay Belt was demonstrated. The syn-orogenic character of the basin is inferred based on the main peak of the detrital zircon population age distribution around 600 Ma, which is very close to the maximum depositional period and points to a short time between erosion, deposition, and burial processes. The muscovite 40Ar/39Ar age of ca. 536–546 Ma obtained for muscovite schist metamorphosed under greenschist facies conditions indicates that the regional thermal regime was maintained up to the early-Cambrian in the area. The minimum fast cooling rate of 25 °C/Myr defined in the investigated area is constrained by the 40Ar/39Ar analysis of biotite (549.16 ± 1.30 Ma) from a syn-to late-kinematic granodiorite intrusion. The very rapid magma emplacement occurred into relatively shallow crustal levels through the associated strike-slip faults. The Transbrasiliano Lineament would have facilitated the rapid unroofing of the study area and therefore the syn-orogenic deposition in a foreland domain at the final phase of West Gondwana amalgamation. The studied metasedimentary rocks represent a transition phase from the passive margin sedimentation (Cuiabá Group) to an orogenic phase, constraining an inversion event in the West Gondwana around ca. 590 Ma. The data provide evidence of a late orogenic basin that was formed contemporaneously with the evolution of an active margin between the Amazonian Craton and the eastern blocks/cratons (São Francisco-Congo and Rio de la Plata cratons and Paranapanema Block) close to Cambrian times. Our results support the existence of the younger Clymene Ocean and the subsequent final assembly of West Gondwana in the Cambrian.

Symplectite and kelyphite formation during decompression of mafic granulite from Gjelsvikfjella, central Dronning Maud Land, Antarctica

Abstract. Central Dronning Maud Land (cDML) is part of the late Mesoproterozoic Maud Belt in East Antarctica, which was metamorphosed and deformed during the Ediacaran–Cambrian Gondwana assembly. Here we study high-pressure (HP) mafic rocks in Gjelsvikfjella, cDML, which occur as lenses and pods transposed in highly strained, upper amphibolite-facies gneisses. We present a P–T–t history for the HP rocks based on mineral assemblages, reaction textures and new U–Pb zircon data. Relics that indicate an early HP granulite-facies stage have been identified in anhydrous garnet–clinopyroxene rocks. The peak-pressure assemblage was plagioclase-free and contained garnet, titanite, clinopyroxene and quartz. The HP assemblage has been extensively overprinted by lower-pressure phases and exhibits a variety of symplectite and corona textures that record the post-peak-pressure evolution of the rocks. Decompression and heating in the granulite-facies field resulted in the replacement of titanite by ilmenite–clinopyroxene symplectite, formation of clinopyroxene–plagioclase intergrowths and resorption of garnet by plagioclase–clinopyroxene kelyphite. Formation of late orthopyroxene in symplectites and kelyphites demonstrates that the P–T evolution entered the medium-pressure granulite-facies field. The peak metamorphic stage was followed by retrograde cooling into the amphibolite facies. In situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating of zircons indicate Mesoproterozoic protolith ages (1150–1000 Ma) and Ediacaran–Cambrian metamorphic reworking at ca. 568 and ca. 514 Ma. The HP granulites were formed and exhumed during a clockwise P–T evolution related to continental collision during Gondwana amalgamation, followed by post-collisional extension and orogenic collapse.

Sedimentary record of Variscan unroofing of the Bohemian Massif

The Bohemian Massif in the eastern Variscan Orogen is the host of globally significant ultrahigh-pressure metamorphic rock suites that experienced enigmatic unroofing processes. In the eastern Bohemian Massif, the Moravosilesian Culm Basin (The Czech Republic) with ≤7.5 km thick Lower Carboniferous siliciclastic turbidities has recorded crustal unroofing associated with the late Paleozoic amalgamation of Gondwana and Laurussia. This study presents data from sandstone petrography, heavy mineral assemblages, and detrital zircon U-Pb geochronology from Moravosilesian Culm sediments. Sandstone modal compositions imply continental/recycled orogen affinities. High-grade metamorphic lithic fragments and high garnet contents in upper Culm sediments indicate the exhumation of the middle to lower crustal materials, consistent with those of the Bohemian Massif. Detrital zircon U-Pb data constrain maximum depositional ages of sediments in the Drahany Upland to 335–326 Ma (late Viséan–middle Serpukhovian). Detrital, igneous and metamorphic zircon U-Pb data compiled from surrounding regions support that source regions for lower Culm sediments (Moldanubian Unit and Sudetes) remained the same. Whereas, upper Myslejovice sediments might have derived from exhumation and erosion of the root of the Moldanubian Unit and/or Moravosilesian Nappes. Rapid exhumation of the Moldanubian Unit within the Bohemian Massif during the deposition of upper Culm sediments is inferred.

Heterogeneous sulfide reoxidation buffered oxygen release in the Ediacaran Shuram ocean

Ediacaran (∼635–539 Ma) carbonate rocks record the largest negative carbonate-carbon isotope excursion in Earth history, termed the Shuram Excursion (SE). This event has been attributed to anaerobic oxidation of dissolved organic carbon as a result of enhanced weathering inputs of sulfate to the ocean during the amalgamation of Gondwana. However, the effect of carbon–sulfur cycle interplay on the net redox state of the ocean–atmosphere system remains unclear, impeding our understanding of the co-evolution of life and the environment during the Ediacaran. Here, we generate high-resolution records of paired sulfate sulfur and oxygen isotopes, in addition to phosphorus concentrations, for the SE interval in South Australia (Parachilna Gorge) and South China (Jiulongwan and Xiang’erwan sections, Three Gorges), and we evaluate these data in the context of COPSE biogeochemical model simulations to assess net long-term redox changes. Our results support widespread H2S reoxidation in shelf areas during the SE, which would have buffered the net release of oxygen sourced from the burial of organic carbon and pyrite. Varying degrees of H2S reoxidation on different cratons likely contributed significantly to high spatial heterogeneity in both local oceanic redox state and nutrient availability, which characterized local oxygen-deficient conditions in an overall oxygenated SE shelf ocean, and likely affected the distribution of the Ediacaran Biota. Our study highlights the important role of H2S reoxidation in the coevolution of marine redox conditions and complex life during the critical Ediacaran period.

Expanding Azania at the heart of Gondwana: Terrane correlation from Southern India to Sri Lanka

The reconstruction of megacontinent Gondwana was arguably the first crowning achievement of paleogeography, nonetheless the kinematics of its assembly remains controversial. The now-outmoded concept that Gondwana assembly was simply the amalgamation of East and West Gondwana has been replaced by models involving multiple terrane accretions and continental collisions along different orogenic belts. Although the affinities of large cratons are well established, figuring out the relationships between the multiple “Pan-African” orogenic belts has been hindered by poorly defined smaller intervening terranes. At the center of Gondwana, the polymetamorphic terranes in Sri Lanka have been correlated to various crustal blocks without broad consensus, mainly because of a paucity of high-quality geochronological results. Terrane correlations and figuring out the spatial distributions of “Pan-African” orogenic belts in the central part of Gondwana are, therefore, hampered by the controversies about Sri Lanka. We present new data on the high-grade metamorphic rocks occurring in the Highland Complex of Sri Lanka, which reveal the widespread Paleoproterozoic magmatism with U-Pb ages of ≥ 2465 – 1803 Ma and uniform Archean Hf model ages. Our data confirm the pervasive metamorphic ages of ∼ 610 – 510 Ma, and for the first time, we present multiple episodes of metamorphism at Paleoproterozoic (1854 – 1803 Ma) and Neoproterozoic (∼637 – 635 Ma) which are comparable with those reported from the East African Orogen. Based on a comparison with neighboring crustal blocks, we suggest that these early Precambrian basement components as well as the multiple metamorphism of the Highland Complex in Sri Lanka can be correlated with micro-continent Azania. These new data not only confirm the widespread early Precambrian basement components in Sri Lanka, but also open up new ways for terrane correlations from East Africa through Sri Lanka to East Antarctic.

Tracing a Neoproterozoic subduction to collision magmatism in the eastern Pernambuco–Alagoas domain, northeastern Brazil

The Pernambuco–Alagoas (PEAL) Domain, southern Borborema Province, northeastern Brazil, bears the most voluminous Cryogenian–Ediacaran granitic rocks in this province, which was formed during the convergence of the São Francisco Craton and the Borborem Province, during the western Gondwana amalgamation. New geochemical and isotopic data along those from the literature, for one of the largest intrusions, the Correntes composite batholith, at the southern part of this domain, indicate that the granitic rocks are intermediate to acid, oxidized, metaluminous to peraluminous, magnesian, and are high-K calc alkalic to shoshonitic with I-type signature. They are enriched in large-ion lithophile elements, exhibit lightly negative Eu in rare-earth element patterns and negative Ta–Nb, P, and Ti anomalies in spidergrams. Average initial 87Sr/86Sr is 0.7055 and rocks present values of whole-rock εNd (0.6 Ga) that fall into two groups. The pre-to syn-collisional, 635–628 Ma plutons present εNd (0.6 Ga) values from +1.3 to −2.5, with Nd model ages varying from 1.29 to 0.92 Ga, while the late-to post-collisional, 602–580 Ma, plutons show more negative values (−8.2 to −9.5), and older Nd model ages from 1.95 to 1.81 Ga. This Nd-isotope pattern is also observed in other plutons of the southern PEAL Domain and indicates a change in the lower crust source rock with time, with larger contributions of crustal components in the late-to post-collisional rocks. The chemical and isotopic characteristics of the studied granitic rocks and other granitic batholiths in the southern PEAL Domain are compatible with modern magmatic arcs of continental active margins. We propose that in earlier stages of convergence, melting has further affected the younger (Stenian –Tonian), likely less refractory rocks associated with abundance of volatiles, whose segregation would have differentiated to form the oldest plutons. Slow cooling allowed the accumulation of heat from mantle-derived magma in the pre-collisional period, which, together with radiogenic heat from thickened crust, led to partial melting of older crustal rocks, and the formation of magmas whose segregation and differentiation of the melt would originate the younger plutons in this part of the PEAL Domain. Older plutons formed during a Cryogenian-Ediacaran flare-up event that occurred in the southern PEAL Domain.

The early Ediacaran Brachina sequence, Flinders Ranges, South Australia: its age, formation and plate tectonic setting

Throughout the Flinders Ranges of South Australia, the red bed Brachina sequence comprises the lower of two regressive, coarsening-upward successions that together constitute the Ediacaran-aged Wilpena Group. Detailed examination of the Brachina sequence has identified evidence of ice-rafting, supporting the contention that frigid climatic conditions continued well after cessation of the Marinoan Glaciation, as well as features postulated to be harbingers of the macroscopic metazoans that occur in abundance higher in the local stratigraphy. Although tuffaceous and lying stratigraphically between deposits of the Marinoan Glaciation and the Acraman Impact/Gaskiers Glaciation, no absolute age dates exist for the sequence. However, through correlation to the global carbon isotope profile, the timespan of Brachina sequence deposition can be constrained to between 635 and 586 Ma, when the regression climaxed with terrestrial deposition upon a local disconformity. The tuffaceous input is timed to have begun at 620 Ma, essentially coincident with initial formation of the passive volcanic continental margin of southeastern Australia and initiation of both the Volyn Large Igneous Province and activity within the Central Iapetus Magmatic Province, all components marking the demise of Rodinia and initial amalgamation of Gondwana.

Control of inherited structural fabric on the development and exhumation of passive margins – Insights from the Araçuaí Orogen (Brazil)

The Araçuaí Orogen, in eastern Brazil, was formed during the Neoproterozoic – Cambrian amalgamation of West Gondwana. During the Mesozoic – Cenozoic opening of the South Atlantic Ocean, and the associated divergent tectonics, the orogen developed as basement to the passive margin of South America and was progressively covered by thick offshore sedimentary basins, particularly the Espírito Santo, Mucuri, and Cumuruxatiba basins, in which hydrocarbon systems have been exploited. Our understanding of the Araçuaí Orogen's passive margin evolution, erosion, and sediment transfer to these basins ultimately depends on constraining the onshore exhumation in response to Mesozoic – Cenozoic events. Here, new and previously published data from apatite fission-track (AFT) analyses and inverse thermal history modelling of (Pre)Cambrian basement rocks from the Araçuaí Orogen resolve three discrete basement cooling and associated erosional exhumation episodes. In the Pre-Rift phase, Jurassic – Hauterivian erosion of the Araçuaí Orogen is most likely related to the adjoining intra-continental West Gondwana flexural subsidence, which increased hillslope and river erosion power. In the Rift and Transitional phases, Barremian – Albian accelerated phase of erosion is associated with the uplift of the Atlantic rift shoulders and the establishment of an oceanic base-level. In the Drift phase, reactivations in response to far-field stresses likely triggered a Late Cretaceous – Paleocene rapid erosion event. The rates at which these events unfolded vary spatially and are controlled by inherited structures. The Araçuaí Orogen experienced slower denudation rates in areas closer to the São Francisco Craton, which suggests that the tectonic reactivation and related surface uplift during the Mesozoic–Cenozoic is in first-order controlled by lithospheric rigidity. Furthermore, the structural framework of the Paramirim and Pirapora aulacogens and NE-oriented shear zones in the orogen’s southeast facilitated later reactivations. From the spatial pattern of denudation/exhumation of the Araçuaí Orogen during the Mesozoic – Cenozoic, we draw inferences on the tectonic development of the offshore basins regarding their hydrocarbon potentials.

The provenance of Avalonia and its tectonic implications: a critical reappraisal

Abstract The late Neoproterozoic–Cambrian interval is characterized by global-scale orogenesis, rapid continental growth and profound changes in Earth systems. Orogenic activity involved continental collisions spanning more than 100 myr, culminating in Gondwana amalgamation. Avalonia is an example of arc magmatism and accretionary tectonics as subduction zones re-located to Gondwana's periphery in the aftermath of those collisions, and its evolution provides significant constraints for global reconstructions. Comprising late Neoproterozoic ( c. 650–570 Ma) arc-related magmatic and metasedimentary rocks, Avalonia is defined as a composite terrane by its latest Ediacaran–Ordovician overstep sequence: a distinctive, siliciclastic-dominated cover bearing ‘Acado-Baltic’ fauna. This definition implies that Neoproterozoic Avalonia may consist of several terranes, and so precise palaeomagnetic or provenance determination in one locality need not apply to all. On the basis of detrital zircon and Nd isotopic data, Avalonia and other lithotectonically related terranes, such as Cadomia, have long been thought to have resided along the Amazonian–West African margin of Gondwana between c. 650 and 500 Ma – Avalonia connected to Amazonia, and Cadomia to West Africa. These interpretations have constrained Paleozoic reconstructions, many of which imply that the departure of several peri-Gondwanan terranes led to the Early Paleozoic development of the Rheic Ocean whose subsequent demise in the Late Paleozoic led to Pangaea's amalgamation. Since these ideas were proposed, several new lines of evidence have challenged the Amazonian affinity of Avalonia. First, there is evidence that some Avalonian terranes may have been ‘peri-Baltican’ during the Neoproterozoic. Baltica was originally excluded as a potential source for Avalonia because, unlike Amazonia, arc-related Neoproterozoic rocks were not documented. However, subsequent recognition of Ediacaran arc-related sequences in the Timanides of northeastern Baltica invalidates this assumption. Second, detailed palaeontological and lithostratigraphic studies have been interpreted to reflect an insular Avalonia, well removed from either Gondwana or Baltica during the Ediacaran and early Cambrian. Third, recent palaeomagnetic data have raised the possibility of an ocean (Clymene Ocean) between Amazonia and West Africa in the late Neoproterozoic, thereby challenging conventional reconstructions that show the ‘peri-Gondwanan’ terranes as a contiguous belt straddling the suture zone between these cratons. In this contribution, we critically re-evaluate the provenance of the so-called ‘peri-Gondwanan’ terranes, the contiguity of the so-called ‘Avalonian–Cadomian’ belt and the validity of the various plate tectonic models based on the traditional interpretation of these terranes. In addition, we draw attention to critical uncertainties and the challenges that lie ahead.

Distinct tectono-magmatism on the margins of Rodinia and Gondwana

The orogenic petrological processes associated with the amalgamation of Rodinia (ca. 1 Ga) and Gondwana (ca. 550 Ma) reflect distinct tectonic dynamics that might have contributed to the contrasting geochemical and biological evolution following the orogenies. In this study, we explore these differences using the time sequence analysis of geochemical proxies in the detrital zircons sourced from the margin of East Gondwana. The zircon Eu anomalies are stronger during the formation of Gondwana than Rodinia, indicating a thicker Gondwana crust than Rodinia; the hinterland of Rodinia (∼35 km) is significantly thinner than its core Grenville Province (55–60 km). The Ce to U and Ti ratio, U/Yb, and εHf(t) proxies suggest that the Rodinia assembly was dominated by non-arc intraplate magmatism, consistent with widespread high-temperature magmatism and protracted granulite-facies metamorphism. The thin crust and accordingly, low-elevation terrain, possibly overriding an anomalously hot mantle, limited continental weathering flux, and primary productivity in the Mesoproterozoic oceans. By contrast, the orogenies leading to the assembly of Gondwana may have proceeded in a modern-style plate tectonic manner, resulting in rapid uplift at the Gondwana margin, where voluminous clastic sediments were subsequently recycled and contributed to the post-orogenic magmatism from ca. 500 Ma. This massive crustal reworking is reflected by negative εHf(t) values of zircons that contrast εHf(t)∼0 in the Mesoproterozoic. The emergence of extensive mountains accelerated erosion and delivered key nutrients that might have fueled the rapid diversification of life forms in the late Precambrian and early Paleozoic.