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This paper focuses on one orogenic belt that formed during the Rinconada phase on the final stage of the Famatinian orogeny, between 445 and 410 Ma, which is well exposed at Sierra de Ramaditas and neighbouring ranges in western Argentina. The Ramaditas Complex is formed by metasedimentary and meta-ultrabasic rocks and amphibolites. This complex forms the upper nappe of a thrust stack resulting from westward thrusting. Deformation consists of an early high-temperature S1 foliation (stromatic migmatites), coeval with thrusting and metamorphism. Metamorphism attained peak P–T conditions of 6.0–6.9 kbar and 795–810 °C, at c. 440 Ma, i.e. coincident with the Rinconada orogenic phase. The lower unit and intermediate nappes crop out in the nearby sierras of Maz and Espinal and underwent low- to medium-grade Silurian metamorphism, respectively, together with the upper nappe, defining an inverted Barrovian-type metamorphism with T decreasing and P increasing downwards across the thrust stack (i.e. westward). We argue that the Rinconada orogenic phase developed near the continental margin of SW Gondwana, during a magmatic lull following accretion of the Precordillera terrane to the continental margin at c. 470 Ma. The active margin jumped to the west after accretion, and flat-slab subduction resumed in the early Silurian, provoking thrusting and imbrication of nappe stack under the still hot root (800–900 °C) of the older Famatinian magmatic arc. This 'hot-iron' process explains both the inverted Barrovian-type metamorphism and the missing overburden of 21 to 24 km implied by the P estimate. [ABSTRACT FROM AUTHOR]

The analysis of major and trace elements in zoned minerals is useful for deciphering parts of the tectonothermal evolution of polymetamorphic tarrain. We applied this approach to the Maz Metasedimentary Series in Western Sierras Pampeanas of Argentina, where polymetamorphism resulted in the overprinting of a Grenvillian basement (the Maz Complex) during the pervasive Rinconada tectonic phase of the Famatinian orogeny. The older metamorphism (M1) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M2) was Silurian to early Devonian, essentially between 440 and 410 Ma. The latter resulted from oceanward migration of the orogenic front relative to earlier late Cambrian to Ordovician (490–470 Ma) tectonic phases of the Famatinian orogeny. The M1 and M2 metamorphic events have been recognized in a staurolite‐garnet schist from the Maz Metasedimentary Series. Most metamorphic minerals from this rock were formed during the M2 event which was of the Barrovian type (±kyanite). Part of the metamorphic P–T evolution is recorded in the complex compositional zoning of garnet porphyroblasts. Three types of garnet were identified based on texture and chemistry, including trace elements (REEs). Phase equilibrium analysis, compositional isopleth, and multi‐equilibrium thermobarometry were applied in order to establish the P–T history. M1 is represented by preservation of Grt1 ± Kfs ± Sil, with peak P–T condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D1 episode represented by a relict S1 foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M2 followed a clockwise P–T path with three mineral growth stages. The earliest occurred at ~585°C and ~8.7 kbar and is represented by Grt2 ± St1 ± Bt1 + Qz. Grt2 was partially coeval with growth of St1, which was stable at ~625°C and 9.0 kbar. Grt2 + St1 are syn‐kinematic to the main S2 foliation (D2 episode). Subsequently, decompression (D3) started as St2 (+ Bt2 + Ms1 + Qz + Pl) crystallized, and garnet was partially consumed at ~612–620°C and ~7.3–7.7 kbar. St3 + Grt3 crystallized at ~608°C and ~6.8 kbar at the end of D3. Increasing P–T conditions during the earlier M2 growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D2). Peak metamorphic conditions were attained during thrust stacking. The tectonic phase (D2) was responsible for the main S2 foliation, which was penetrative at all scales. The nearly isothermal decompression path is compatible with exhumation, probably resulting from extension along discrete shear zones (tectonic phase D3) that produced a mylonitic foliation S3. [ABSTRACT FROM AUTHOR]

New structural and age data suggest that West Gondwana may have been at lower palaeolatitudes than previously interpreted from Albian sequences in Gondwana marginal suspect terranes. The Palmer Land event, which juxtaposed Mesozoic terranes on the Gondwana margin, deformed granitoids in the southern Antarctic Peninsula. U-Pb SHRIMP dating of zircons from a microgranite dyke yields a crystallization age of 106.9 [+ or -] 1.1 Ma. This result and re-interpretation of the structural position of another granite pluton date the Palmer Land event, and probable terrane collision, as late Early Cretaceous, and not latest Jurassic as formerly interpreted. Keywords: West Antarctica, Gondwana, superplumes, palaeolatitude.

A study was conducted to examine upper Proterozoic or Precambrian rift-related rocks in the Pensacola Mountains of Antarctica. Sedimentalogical and structural findings show that these upper clastic sedimentary rocks formed in an intracontinental rift setting. The rocks are part of the Patuxent Formation whose turbidities belong to a large depositional system generated by a continental source.

The basement of northeastern Patagonia is characterized by Early Paleozoic igneous and metamorphic rocks that do not crop out in the central, western and Andean sectors of the North Patagonian Massif. A review of U-Pb geochronology, geochemistry, and the Nd, Sr, Hf and O isotope signature of the early Cambrian and early Ordovician magmatic rocks supports the hypothesis that the continental crust of northeastern Patagonia was essentially continuous with that of the Eastern Sierras Pampeanas in early Cambrian times. Mesoproterozoic lower crust is also inferred for this sector. New zircon Hf and O analyses of early Cambrian (Pampean) granites in the Sierras Pampeanas are indistinguishable from those of Cambrian granites in NE Patagonia, indicating an important crustal component in the source. The detrital zircon age patterns of the inferred basement are also similar in the two regions, strongly suggesting a southern Kalahari provenance. A modified hypothesis to explain the continuity of NE Patagonia with the Pampean belt of the Sierras Pampeanas during early Cambrian times, as well as their SW Gondwana geological affinity, is to consider this entire belt as an outboard sector of the mid-Cambrian rifting observed along the South America-South Africa-Weddell Sea margin. The detached sector would then have become juxtaposed against the Río de la Plata craton across the right-lateral Córdoba fault in late Cambrian times. [ABSTRACT FROM AUTHOR]

We clarify some statements on our works included by Bahlburg (2021), which we think are confusing and misleading. Clarification is highly necessary to interpreting the evolution of the Devonian proto-Andean margin of Argentina and Chile, and in this work, we show that this clarification is appropriated and should be considered. [ABSTRACT FROM AUTHOR]

The provenance of Neoproterozoic to Early Paleozoic sedimentary rocks in the Sierras Pampeanas has been established using U–Pb SHRIMP age determination of detrital zircons in twelve metasedimentary samples, with supplementary Hf and O isotope analyses of selected samples. The detrital zircon age patterns show that the western and eastern sectors of the Sierras Pampeanas are derived from different sources, and were juxtaposed during the Early Cambrian ‘Pampean’ collision orogeny, thus defining initiation of the supercontinent stage of southwestern Gondwana. The Western Sierras Pampeanas (WSP), which extend northwards to the southern Puna (Antofalla) and the Arequipa Massif (Peru), constitute a single large continental basement of Paleoproterozoic age — the MARA block — that was reworked during the Grenvillian orogeny. The MARA block probably extends eastwards to include the Río Apa block (southern Brazil), but in this case without a Mesoproterozoic overprint. Detrital zircons from the WSP and Antofalla yield age peaks between 1330 and 1030 Ma, remarkably similar to the range of ages in the Grenville province of eastern Laurentia. The WSP Neoproterozoic sedimentary cover to this basement shows the same 1330–1030 component, but also includes important 1430–1380 Ma zircons whose juvenile Hf and O isotopic signatures strongly suggest derivation from the Grenville and the Southern Granite–Rhyolite provinces of eastern Laurentia. In contrast the Eastern Sierras Pampeanas metasedimentary rocks have a typically bimodal detrital zircon pattern with peaks at ca. 1000 and 600 Ma, which respectively indicate sources in the Natal–Namaqua belt and the East African orogen and/or the Dom Feliciano belt of SE Brazil and Uruguay. Sedimentary rocks in the Eastern Sierras Pampeanas and Patagonia deposited during the Late Early Cambrian–Early Ordovician interval, after the Pampean orogeny, have detrital patterns common to many sectors along the Terra Australis orogen, reflecting increasingly dominant input to the Paleozoic basins from the Neoproterozoic to Early Cambrian orogenic belts of the Gondwana margin. [ABSTRACT FROM AUTHOR]

Ocean floor magnetic anomalies show that New Zealand was the last continental fragment to separate from Antarctica during Gondwana break-up, drifting from Marie Byrd Land, West Antarctica, about 84 Ma ago. Prior to continental drift, a voluminous suite of mafic dykes (dated by Ar-Ar laser stepped heating at 107 [+ or -] 5 Ma) and anorogenic silicic rocks, including syenites and peralkaline granitoids (95-102 Ma), were emplaced in Marie Byrd Land during a rifting event. The mafic dyke suite includes both high- and low-Ti basalts. Trace element and Sr and Nd isotope compositions of the mafic dykes may be modelled by mixing between tholeiitic OIB (asthenosphere-derived) and alkaline high- to low-Ti alkaline magmas (lithospheric mantle derived). Pb isotopes indicate that the OIB component had a HIMU composition. We suggest that the rift-related magmatism was generated in the vicinity of a mantle plume. The plume helped to control the position of continental separation within the very wide region of continental extension that developed when the Pacific-Phoenix spreading ridge approached the subduction zone. Separation of New Zealand from Antarctica occurred when the Pacific-Phoenix spreading centre propagated into the Antarctic continent. Sea floor spreading in the region of the mantle plume may have caused an outburst of volcanism along the spreading ridge generating an oceanic plateau, now represented by the 10-15 km thick Hikurangi Plateau situated alongside the Chatham Rise, New Zealand. The plateau consists of tholeiitic OIB-MORB basalt, regarded as Cretaceous in age, and similar in composition to the putative tholeiitic end-member in the Marie Byrd Land dykes. The mantle plume is proposed to now underlie the western Ross Sea, centred beneath Mount Erebus, where it was largely responsible for the very voluminous, intraplate, alkaline McMurdo Volcanic Group. A second mantle plume beneath Marie Byrd Land formed the Cenozoic alkaline volcanic province. Keywords: Antarctica, Gondwana, continental drift, geochemistry, magmatism.

Abstract: We report the first study integrating in situ U–Pb and Hf isotope data from magmatic zircon and whole-rock Sm–Nd isotope data for granitic rocks of the Sierras Pampeanas, Argentina, in order to evaluate the Palaeozoic growth of the proto-Andean margin of Gondwana. Early–Middle Ordovician granitic magmatism is by far the most voluminous of the Sierras Pampeanas and represents the most significant magmatic event. These calc-alkaline granitoids were intruded at an active continental margin. εHft values range from −3.3 to −14.7 and εNdt from −3.3 to −6.3 (t=473Ma), with average TDM Hf and TDM Nd ranging from 1.5 to 2.2Ga and 1.4 to 1.7Ga, respectively. Middle–Late Devonian magmatism occurred in the foreland, away from the orogenic front in the west, and included F-U-REE rich A-type granites. The Achala granite, the largest batholith in the Sierras Pampeanas, has εHft and εNdt values ranging from −3.6 to −5.8 and −4.0 to −6.5, respectively (t=369Ma). Small scattered Early Carboniferous A-type granite plutons were intruded in a dominantly extensional setting and have εHft and εNdt values ranging from −6.7 to +2.2 and −0.5 to −3.6, respectively (t=341Ma). The generation of Ordovician and Devonian magmas dominantly involved crustal reworking and stabilization rather than the formation of new continental crust by juvenile material accretion, whereas Carboniferous magmatism resulted in part from reworking of supracrustal material, but with variable addition of juvenile magmas. [Copyright &y& Elsevier]

Abstract: Metasedimentary high-pressure upper amphibolite facies gneisses (1.2±0.1GPa and 780±45°C) at Las Chacras, Sierra de Valle Fértil, are tectonically juxtaposed to the westernmost parts (outboard) of the Famatinian (Early Ordovician) magmatic arc, which underwent syn-plutonic middle crust high-grade metamorphism at lower pressure. U–Pb SHRIMP zircon data suggest that the gneisses contain Famatinian igneous detritus, so that their sedimentary protoliths were probably deposited in a forearc basin and then rapidly underthrust and accreted to the lower crust of the arc, essentially coevally with arc magmatism at 468±4Ma. Chemically and isotopically juvenile garnetiferous amphibolites within the gneisses are recognised as representing the most primitive magmas so far observed in this belt, which has often been considered to be a continental arc derived from isotopically mature sources. This is consistent with the idea that at least part of the dominant Famatinian magmatism originated in depleted mantle but was heavily contaminated by crustal components. [Copyright &y& Elsevier]

Abstract: The Neoproterozoic to Early Cambrian amalgamation of SW Gondwana through the Brasiliano/Pan-African orogeny is reviewed with emphasis on the role of the Río de la Plata craton of South America in the light of new evidence from a borehole at the eastern end of the Tandilia belt (38°S). U–Pb, Hf and O isotope data on zircon indicate that this un-reworked Palaeoproterozoic craton abuts against a distinct continental terrane to the east (Mar del Plata terrane). The craton is bounded everywhere by transcurrent faults and there is no evidence to relate it to the Neoproterozoic mobile belts now seen on either side. The Punta Mogotes Formation at the bottom of the borehole contains 740–840Ma detrital zircons that are assigned to a widespread Neoproterozoic rifting event. The data suggest that the Mar del Plata terrane rifted away from the southwestern corner of the Angola block at c. 780Ma. Negative εHft values and δ18O >6.5‰ suggest derivation by melting of old crust during a protracted extensional episode. Other continental terranes may have formed in a similar way in Uruguay (Nico Pérez) and southeastern Brazil, where the Schist Belt of the Dom Feliciano orogenic belt is probably a correlative of the Punta Mogotes sequence, implying that the Dom Feliciano belt must extend at least as far as 38°S. A new geodynamic scenario for West Gondwana assembly includes at least two major oblique collisional orogenies: Kaoko–Dom Feliciano (580–680Ma) and Gariep–Saldania (480–580Ma), the latter resulting from oblique impingement of the Rio de la Plata craton against the Kalahari craton. Assembly of this part of South-West Gondwana was accomplished before the Ordovician (to Silurian?) siliciclastic platform sediments of the Balcarce Formation in the Tandilia Belt covered the southern sector of Río de la Plata craton. [Copyright &y& Elsevier]

Abstract: The oceanic southern margin of Gondwana, from southern South America through South Africa, West Antarctica, New Zealand (in its pre break-up position), and Victoria Land to Eastern Australia is one of the longest and longest-lived active continental margins known. It was the site of the 18,000 km Terra Australis orogen, which was initiated in Neoproterozoic times with the break-up of Rodinia, and evolved into the Mesozoic Australides. The Gondwana margin was completed, in Late Cambrian times, by closure of the Adamastor Ocean (between Brazilian and southwest African components) and the Mozambique Ocean (between East and West Gondwana), forming the Brasiliano-Pan-African mobile belts. During the Early Palaeozoic much of the southern margin was dominated by successive episodes of subduction-accretion. Eastern Australia, Northern Victoria Land and the Transantarctic Mountains were affected by one of the first of these events – the Late Cambrian Ross/Delamerian orogeny, remnants of which may be found in the Antarctic Peninsula – but also contain two accreted terranes of unknown age and origin. Similar events are recognized at the South American end of the margin, where the Cambrian Pampean orogeny occurred with dextral strike-slip along the western edge of the Río de la Plata craton, followed by an Ordovician active margin (Famatinian) associated with the collision of the Precordillera terrane. However, the central part of the margin (the Sierra de la Ventana of eastern Argentina, the Cape Fold Belt of South Africa and the Ellsworth Mountains of West Antarctica) seem to represent a passive margin during the Early Palaeozoic, with the accumulation of predominantly reworked continental sedimentary deposits (Du Toit''s ‘Samfrau Geosyncline’). In many of the outer areas, accretion and intense granitic/rhyolitic magmatism continued during the Late Palaeozoic, with collision of several small continental terranes, many of which are nevertheless of Gondwana origin: e.g., southern Patagonia and (possibly) ‘Chilenia’ in the South American–South African sectors, and the Western Province and Median Batholith terranes of New Zealand. The rhyolitic Permo–Triassic LIP of southern South America represents a Permo-Triassic switch to extensional tectonics, which continued into the Early Jurassic, and was followed by the establishment of the Andean subduction margin. Elsewhere at this time the margin largely became passive, with terrane accretion continuing in New Zealand. In the Mesozoic, the Terra Australis Orogen evolved into the accretionary Australides, with episodic orogenesis in the New Zealand, West Antarctic and South American sectors in Late Triassic–Early Jurassic and mid-Cretaceous times, even as Gondwana was breaking up. [Copyright &y& Elsevier]

Abstract: Metamorphism of Grenvillian age (ca. 1.2 Ga; U–Pb zircon dating) is recognized for the first time in the Western Sierras Pampeanas (Sierra de Maz). Conditions reached granulite facies (ca. 780 °C and ca. 780 MPa). Comparing geochronological and petrological characteristics with other outcrops of Mesoproterozoic basement, particularly in the northern and central Arequipa-Antofalla craton, we suggest that these regions were part of a single continental crustal block from Mesoproterozoic times, and thus autochthonous or parautochthonous to Gondwana. [Copyright &y& Elsevier]

The Ellsworth-Whitmore Mountain terrane of central Antarctica was part of the early Paleozoic amalgamation of Gondwana, including a 13,000 m section of Cambrian- Permian sediments in the Ellsworth Mountains deposited on Grenville-age crust. The Jurassic breakup of Gondwana involved a regional, bimodal magmatic event during which the Ellsworth-Whitmore terrane was intruded by intraplate granites before translation of the terrane to its present location in central Antarctica. Five widely separated granitic plutons in the Ellsworth-Whitmore terrane were analyzed for their whole-rock geochemistry (X-ray fluorescence), Sr, Nd, and Pb isotopic compositions, and U-Pb zircon ages to investigate the origins of the terrane magmas and their relationships to mafic magmatism of the 183 Ma Karoo-Ferrar large igneous province (LIP). We report high-precision (±0.1 m.y.) isotope dilution- thermal ionization mass spectrometry (IDTIMS) U-Pb zircon ages from granitic rocks from the Whitmore Mountains (208.0 Ma), Nash Hills (177.4-177.3 Ma), Linck Nunatak (175.3 Ma), Pagano Nunatak (174.8 Ma), and the Pirrit Hills (174.3-173.9 Ma), and U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages from the Whitmore Mountains (200 ± 5 Ma), Linck Nunatak (180 ± 4 Ma), Pagano Nunatak (174 ± 4 Ma), and the Pirrit Hills (168 ± 4 Ma). We then compared these results with existing K-Ar ages and Nd model ages, and used initial Sr, Nd, and Pb isotope ratios, combined with xenocrystic zircon U-Pb inheritance, to infer characteristics of the source(s) of the parent magmas. We conclude that the Jurassic plutons were not derived exclusively from crustal melts, but rather they are hybridized magmas composed of convecting mantle, subcontinental lithospheric mantle, and lower continental crustal contributions. The mantle contributions to the granites share isotopic similarities to the sources of other Jurassic LIP mafic magmas, including radiogenic 87Sr/86Sr (0.706-0.708), unradiogenic 143Nd/144Nd (εNd < -5), and Pb isotopes consistent with a low-μ source (where μ = 238U/204). Isotopes and zircon xenocrysts point toward a crustal end member of predominantly Proterozoic provenance (0.5-1.0 Ga; Grenville crust), extending the trends illustrated by Ferrar mafic intrusive rocks, but contrasting with the inferred Archean crustal and/or lithospheric mantle contributions to some basalts of the Karoo sector of the LIP. The Ellsworth-Whitmore terrane granites are the result of mafic rocks underplating the hydrous crust, causing crustal melting, hybridization, and fractionation to produce granitic magmas that were eventually emplaced as post-Ferrar, within-plate melts at higher crustal levels as the Ellsworth-Whitmore terrane rifted off Gondwana (47°S) before migrating to its current position (82°S) in central Antarctica. [ABSTRACT FROM AUTHOR]

We review a widespread project database for Devonian–Carboniferous magmatism in the Sierras Pampeanas and Frontal Cordillera between 27° and 35°S, including petrological, geochemical, geochronological, and isotope data, with compiled data from the literature and some new results. We distinguish four main magmatic domains: 1) Devonian Arc, 2) Devonian Foreland, 3) Carboniferous Arc, and 4) Carboniferous Retro-Arc. Devonian segmented subduction led to two oceanic slab configurations: 1) flat-slab subduction in the outboard region and resubduction >800 km inland from the trench, including lithosphere delamination of the upper plate and break-off of the subducted oceanic slab, along with asthenospheric mantle upwelling (31°–33° 30′S), and 2) normal subduction (34° - 35°S). In the first configuration the arc magmatism was absent, but voluminous foreland magmatism was developed, including small-scale high silica adakite. The second geodynamic setting took place during the latest Devonian and Carboniferous when the oceanic slab roll-back occurred. Arc and retro-arc magmatism were developed coetaneously between 27° and 31°S, with northwest migration that could be explained by movement relative to hot asthenospheric mantle. The arc is represented by calc-alkaline granitoids, whereas retro-arc magmatism consisted of (a) metaluminous to weakly peraluminous A-type granites, and (b) strongly peraluminous A-type granites, these latter with sometimes incomplete isotopic homogenization of the parental magma. Devonian–Carboniferous magmatic evolution here is explained by segmented tectonic subduction and a switch-off and switch-on geodynamic model. Magmatic activity was mainly continuous from ca. 390 to 320 Ma, although compositional variations occurred through time and space (foreland, arc, and retro-arc). Major involvement of mantle sources in the genesis of the Carboniferous arc granites at 28°–30°S contrast with a dominant continental signature in the granites of the Devonian arc at 34°–35°S. These differences are explained by two different configurations in the subduction system related to advance (28°–30°S) or retreat (34°–35°S) of the subducted ocean slab. The main conclusion of this work is that the complex interaction of oceanic and continental plates can produce different types of magmatism (or its absence): subduction processes do not consist only of an oceanic plate sinking under a continental plate. • Geochemical, isotopic, and geochronological dataset for granitic rocks is reported. • Reported data indicate long-lived subduction during the Devonian and Carboniferous. • Configuration of the subducted oceanic slab produce different magmatism type. • Geodynamic switching model explain Devonian and subsequent Carboniferous magmatism. • Segmented tectonic subduction leads to absence and presence of Devonian magmatism. • Flat subduction yield adakite rocks in the foreland domain. [ABSTRACT FROM AUTHOR]