Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

Dispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

Decratonization by Rifting followed by Orogeny and Transcurrent Dispersal of Old Terranes in NE Brazil: A Common Feature of Gondwana Amalgamation?

Dispersion and deformation of cratonic fragments within orogens in the periphery of cratons require weakening of the craton margins in a process of decratonization. The Borborema orogenic province, in NE Brazil, is one of several Brasiliano/Panafrican late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an extension event lasting between 1 Ga and 0.65 Ma. This was followed by inversion and a transpressional orogeny from c. 0.60 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U-Pb and Nd-isotopic model ages to show that the BP consists of up to 65% of strongly sheared ancient rocks affiliated with the Sao Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ~ 15 % addition of juvenile material during the orogeny. This evolution is repeated across a number of Brasiliano/Panafrican orogens, with significant local variations, and indicate that extension weakened entire cratonic regions in a process of decratonization that prepared them for involvement in the orogenies that led to the amalgamation of Gondwana.

Vegetative rescue potential of Brazil nut through epicormic shoots on detached branches

ABSTRACT Obtaining juvenile material may favor the clonal propagation of Brazil nut, Bertholletia excelsa. We aimed to assess the emission of epicormic shoots on detached branches of Brazil nut trees as a function of the mother tree and branch diameter, in order to provide juvenile material for use in clonal multiplication. The experimental design was completely randomized in a 6 (mother trees) x 3 (stem diameter: < 20 20-40 and 40-80 mm) factorial design, with four replicates. Every five days the number of shoots emitted was counted and the sprouting speed index and average sprouting time were calculated. The number of epicormic shoots and the sprouting speed index were dependent on the interaction between mother tree and branch diameter. Branches with larger diameter (20-40 and 40-80 mm) showed higher potential for obtaining propagules for use in Brazil nut clonal multiplication (cutting, grafting and in vitro cultivation).

Petrogenesis of Early Cambrian granitoids in the western Kunlun orogenic belt, Northwest Tibet: Insight into early stage subduction of the Proto-Tethys Ocean

The west Kunlun orogenic belt, located on the northwest margin of the Tibetan Plateau, represents a crucial tectonic junction between the central Asia and Tethys domains. Its evolution was closely related to the Paleozoic subduction and closure of the Proto-Tethys Ocean, which was formed by the breakup of the Rodinia supercontinent following the Neoproterozoic. However, the early evolution of Proto-Tethys oceanic subduction (e.g., subduction initiation timing, polarity, and process) remains controversial. The source of the Early Cambrian granitoids is also unclear. To explore these questions, four Cambrian plutons (i.e., two Tianshuihai monzogranites and south Kunlun diorite and monzogranite) were chosen for geochronological and geochemical studies. Zircon U-Pb dating reveals that these plutons formed at ca. 533–513 Ma and thus represent the oldest arc-related magmatism in the west Kunlun orogenic belt. The Tianshuihai monzogranites have positive εNd(t) values (+0.76 to +1.34) and zircon εHf(t) values of +0.25 to +6.42, with low δ18Ozrn values of +5.11‰ to +7.38‰, suggesting that their source includes juvenile material. These rocks are weakly peraluminous and have relatively old Hf model ages of 1.09–1.48 Ga. Mass balance calculations show that the Tianshuihai monzogranites were derived from partial melting of Mesoproterozoic meta-igneous rocks with the addition of 22% of juvenile material. The south Kunlun monzogranites in this study are weakly peraluminous, and their lowest εNd(t) values are –9.24 to –9.27 and zircon εHf(t) values are –7.80 to –11.2. The oldest Hf model ages are 1.97–2.18 Ga, and the highest zircon δ18Ozrn values are +8.11 to +9.73‰. Their isotopic compositions are different from those of the magmas derived from partial melting of just Paleoproterozoic and Mesoproterozoic basement rocks but can be produced by a mixing source of 32% meta-igneous rock and 68% meta-sedimentary rock. The south Kunlun diorites are characterized by high Sr contents and relatively high Sr/Y (52–63) ratios but low Y, Yb, Cr, and Ni contents, like those of the thickened continental crust-derived adakites. Their Sr-Nd–Hf-O isotopic compositions indicate that their parental magma was derived from a Mesoproterozoic metaigneous basement in the garnet stability field. Based on the newly identified, oldest island arc magmatic records in the west Kunlun orogenic belt, the subduction initiation of the Proto-Tethys oceanic slab must have occurred prior to the Early Cambrian (&gt;533 Ma). Our results, with previously published data, show that the west Kunlun orogenic belt was in an extensional setting during the Early Cambrian and that the magmatism migrated northeastward along the axis of the south Kunlun terrane between 533 Ma and 513 Ma. Therefore, considering the spatial and temporal distribution and petrogenesis of the Early–Middle Cambrian plutons in the west Kunlun orogenic belt, we propose that the Early Cambrian magmatism was most plausibly triggered by asthenospheric upwelling in response to the rollback of southward-subducted Proto-Tethys oceanic slab.

The millipede genus Stemmiulus Gervais, 1844 in Cameroon, with descriptions of three new species (Diplopoda, Stemmiulida, Stemmiulidae)

The large pantropical millipede genus Stemmiulus, which currently encompasses more than 150 species, i.e. the bulk of the species diversity of the family Stemmiulidae and entire order Stemmiulida, is shown to comprise seven species in Cameroon, including three new ones: S.ongot Nzoko Fiemapong &amp; VandenSpiegel, sp. n., S.uncus Nzoko Fiemapong &amp; VandenSpiegel, sp. n., and S.mbalmayoensis Nzoko Fiemapong &amp; VandenSpiegel, sp. n. In addition, S.beroni Mauriès, 1989, previously known only from the type locality in Nigeria, is recorded from Cameroon for the first time, also being redescribed based on new samples. A key is given to all species of the genus encountered in the country, based on male gonopodal conformation, except for S.camerunensis (Silvestri, 1916), which was described only from female and juvenile material.

Extensional Carboniferous magmatism at the western margin of Gondwana: Las Lozas valley, Catamarca, Argentina

The Las Lozas volcanic sequence, which crops out at northwestern border of the Famatina belt-southeastern Puna, NW Argentina, is constituted mainly by rhyolites and a lesser volume of basalts and trachytes, and volcanoclastic deposits. These rocks, previously considered of Early Paleozoic age, are now assigned to the Lower Pennsylvanian (320 Ma U-Pb age). They represent a bimodal volcanic succession that plot in the subalkaline/tholeiitic (rhyolites), alkaline basalts (basalts) and alkaline (trachytes) fields on the total alkali-silica diagram. The basalts display features comparable to transitional MORB and within-plate tholeiites, with contributions from a mantle source affected by crustal contamination. The acid members also show geochemical affinities to within-plate magmas, and their composition suggest a derivation from continental crustal material with mantle source interaction or a juvenile essentially mantle derived crust. The 320 Ma age from the Las Lozas volcanic succession as well as the 342 and 348 Ma U-Pb ages, from rocks in the nearby Cazadero Grande section, to the south, and the U-Pb ages from Sierra Pampeanas granites (332-357 Ma) highlight the importance achieved by Carboniferous magmatic activity in that region, framed between 320 and 350 Ma. Low strontium initial ratios from the Las Lozas (0.70479-0.70164) indicate a predominant contribution by a juvenile component, while the ratios in the nearby Cazadero Grande (0.71433-0.71233) and Sierras Pampeanas granites (0.717 to 0.7124) point to an input by enriched sources with restricted contribution of a mantle component. Nd isotopes from a basalt from the Las Lozas section (εNd(320) with +3.11, TDM with 774.6 Ma) indicates a possible asthenospheric source, with evidence for some mixture between juvenile and reworked crustal material. In contrast Sr-Nd isotopes in a rhyolite from Cazadero Grande (εNd(t) of -2.91 and -0.3, TDM of 1.09 and 1.1 Ga) and of Sierra Pampeanas granites (εNd(t) of -0.6, TDM of 1.19 and 1.1 Ga) suggest a crustal source with minor juvenile input. Taking in account the age difference in the region between Mississippian and the Lower Pennsylvanian magmatism, this would indicate a change in the magma source consistent with a more pronounced extensional tectonic regime for the Lower Pennsylvanian. This assumption need to be considered together with observations along a transect at 27º30’S, where the Carboniferous Eastern Sierras Pampeanas granitic rocks show, regardless of age, a greater contribution of juvenile material of mantle character to the west. Among these rocks, with a major juvenile component, are those of the Las Lozas succession as well the Cerro Gloria Granite, the eastern manifestations of the Carboniferous Eastern Sierras Pampeanas magmatism. From the foregoing emerges that the contribution of juvenile material could be continuously varied in the region through the Carboniferous, due to varying lithospheric extension. An example of this arise from the presented data of the Lozas succession, which indicate that this rocks resulted from reworking of supra-crustal material with input of juvenile magmas, linked to the change in the lithospheric extension

Geochemistry and Nd isotope signature of the Collserola Range Palaeozoic succesion (NE Iberia): Gondwana heritage and pre-Mesozoic geodynamic evolution

The Collserola Range includes a representative stratigraphic succession of the Palaeozoic of the central part of the Catalan Coastal Ranges, ranging from Cambro-Ordovician to Carboniferous times. In this paper we present an up-to-date review of the stratigraphy and structure of the Palaeozoic of the Collserola Range, and provide geochemical and Sm–Nd isotope data to constrain the pre-Mesozoic crustal evolution of this sector of the Variscan Belt. Geochemical compositions indicate that the Palaeozoic siliciclastic rocks of the Collserola Range were fed by a relatively mature heterogeneous source of sediment, comprising quartz-rich sediments to intermediate igneous rocks. The siliciclastic rocks of the Collserola Range show great geochemical affinity with the turbidites of passive margins. The Sm–Nd signature of the siliciclastic rocks is compatible with those of the Palaeozoic and late Proterozoic fine-grained siliciclastic rocks of the neighbouring terrains of SW Europe. There is a small decrease of the εNdT with decreasing age of sedimentation from the Cambro-Ordovician to the Carboniferous, suggesting an increase of the amount of more ‘juvenile’ material. The presence of small volumes of alkaline basaltic rocks provides evidence for the input of juvenile material in the early Palaeozoic basin and suggests that an extensional tectonic regime prevailed during the Cambro-Ordovician sedimentation. From a geodynamic point of view, the overall analysis of the data implies that the Palaeozoic rocks of the Catalan Coastal Ranges were part of the Northern Gondwana passive margin before the closure of the Rheic Ocean and the subsequent Variscan Orogeny.

The 1944 eruption of Vesuvius, Italy: combining contemporary accounts and field studies for a new volcanological reconstruction

We integrate the different contemporary sources together with new field data on the pyroclastic deposits to make a new volcanological reconstruction of the explosive phases of the 1944 Vesuvius eruption. We adopt the four successive phases of the eruption first defined by Imbò (1945), who made the most detailed contemporary description of the eruption: Phase 1 – effusive, Phase 2 – lava fountains, Phase 3 – mixed explosions and Phase 4 – seismic-explosive. Phase 1 consisted of four days of effusive activity. Phase 2 generated eight successive lava fountains which formed agglutinated spatter in a restricted area around the crater. At distances of > 1 km from the crater, reverse graded, well-sorted, scoria lapilli with up to 94 wt % juvenile material and calculations indicate a volume of 8.2 × 106 m3 DRE (Dense Rock Equivalent) for Phase 2. A short pause in scoria fallout was observed that coincides with the transition between Phases 2 and 3 of the eruption. On the crater rim there is clear evidence for the different phases, owing to the stratification of the deposits; however, away from the crater, stratigraphic breaks suggesting any discontinuity in the eruptive activity are absent. The beginning of Phase 3 is marked by the appearance of abundant dense scoria fragments, coincident with the coarsest part of the lapilli. High-density scoria forms 10 wt % of juvenile material in Phase 2, increasing to 45% in the upper part of Phase 3. Isopach maps derived from field measurements indicate a mean volume of 40.2 × 106 m3 DRE for Phase 3. Distal ash, mainly formed during Phase 3, was dispersed to the SE as far as Albania, and calculations yield a volume of 102 × 106 m3 DRE. Intermittent activity associated with Phase 4 generated ash-rich plumes dispersed towards the SW and contemporary thickness descriptions yield a bulk volume of 4.2 × 106 m3 (2.5 × 106 m3 DRE). Small pyroclastic density currents (PDCs) were observed during Phases 3 and 4. The deposits (200 m from the crater rim) of these currents have been identified on the flanks of the cone. Thin, massive and poorly sorted ash layers, that occur up to 2.5 km from the crater rim, are interpreted to represent the distal facies of these PDCs. Mass discharge rate (MDR) estimates for the paroxysmal phase (end of Phase 2 and start of Phase 3) of this event are around 3.5 × 106 kg/s, however, this increases to > 107 kg/s if the mass of distal ash is taken into account. Column height estimates from fallout isopleths associated with the eruption's paroxysmal phase are > 10 km. Based on the contemporaneous chronicles, we were able to define the type and extent of damage associated with the different styles (or temporal phases) of the eruption. Our calculations demonstrate that the present-day population at risk has doubled compared to 1944. The contemporaneous (and also subsequent) scientific literature underestimated the magnitude and intensity of this eruption and very little attention has been dedicated to the damage that occurred. We suggest that this is at least partly related to the extensive destruction of Neapolitan area and the deaths of tens of thousands of civilians related to the Second World War.

Rajeunissement de clones matures d'Hevea brasiliensis (Müll. Arg.) par microgreffage in vitro

In vitro micrografting of apices of two mature genotypes of Hevea brasiliensis (Müll. Arg.), IRCA 18 and PB 235, on 3-wk-old seedlings grown in vitro permitted successfull in vitro micro-cutting of these two genotypes. Microcutting of micrografted material was impossible from nodal explants or shoot tips of scions developed in vitro on rootstocks. Such explants were incapable of caulogenesis activity after their isolation. This problem was resolved using mixed explants, each consisting of a part of the rootstock in contact with the culture medium, and of the clonal scion from which axillary shoots are developed regularly along the subcultures. Budding and shoot elongation abilities along the subcultures have been compared between mixed explants from micrografts, nodal explants from juvenile material and nodal explants from non-micrografted mature genotypes. The results show a very positive effect of micrografting on the in vitro caulogenesis ability in both genotypes. Moreover, shoots produced by mixed explants from micrografts exhibit the same rooting ability as shoots produced by explants collected on juvenile material. Key words: Rejuvenation, Hevea brasiliensis, in vitro micrografting, micropropagation, in vitro microcutting