Search

Submitted by CV Deposit (cvuser@cienciavitae.pt) on 2020-12-07T10:27:20Z No. of bitstreams: 2 Pereira_et_al.,_2019_reply_to_Pereira_F_et_al.pdf: 1256923 bytes, checksum: bdf7f3fa1bd9f4ded666862010280701 (MD5) package.zip: 1140324 bytes, checksum: e21f8c9e9cc52e3e4ba9974e490a9d6f (MD5) Approved for entry into archive by Paula Candeias (paula.candeias@lneg.pt) on 2020-12-15T14:39:13Z (GMT) No. of bitstreams: 2 package.zip: 1140324 bytes, checksum: e21f8c9e9cc52e3e4ba9974e490a9d6f (MD5) Pereira_et_al.,_2019_reply_to_Pereira_F_et_al.pdf: 1256923 bytes, checksum: bdf7f3fa1bd9f4ded666862010280701 (MD5) Made available in DSpace on 2020-12-15T14:39:13Z (GMT). No. of bitstreams: 2 package.zip: 1140324 bytes, checksum: e21f8c9e9cc52e3e4ba9974e490a9d6f (MD5) Pereira_et_al.,_2019_reply_to_Pereira_F_et_al.pdf: 1256923 bytes, checksum: bdf7f3fa1bd9f4ded666862010280701 (MD5) Previous issue date: 2019 info:eu-repo/semantics/publishedVersion

A multidisciplinary study involving lithofacies analysis, palynofacies, and palynology is presented for the Muaradzi Sub-basin. This sub-basin is part of the Moatize-Minjova Basin (MMB), an important Karoo aged coalfield in Mozambique. A total of 99 core samples from 3 coal exploration boreholes (DW11, DW21, and DW141) were analysed and all the successions were assigned a Lopingian age based on palynology. According to the data, in the Muar ' adzi Sub-basin, a vast lowland fluvial setting existed with floodplains and wetlands, in an area controlled by tectonic movements associated with a continental rifting phase. Typical vegetation of the Glossopteris Province is recorded in the palynological assemblages of this sub-basin, which allowed for the characterization of a flora dominated by glossopterids (Protohaploxypinus and Striatopodocarpites) and gymnosperm pollen (Alisporites). Other palynomorphs revealed the presence of gingkoales, ferns (Filicopsida), sphenopsids, and lycopsids in the area, indicating a typical lowland setting. Humid and warm climates, associated with higher CO2 atmospheric levels, promoted the growth of widespread vegetation that led to the development of the thick coal beds in anoxic to dysoxic depositional environments. Fundacao para a Ciencia e Tecnologia, PortugalPortuguese Foundation for Science and Technology [PTDC/CTA-GEO/30082/2017]; Fundacao para a Ciencia e TecnologiaPortuguese Foundation for Science and TechnologyEuropean Commission [UIDP/00350/2020] info:eu-repo/semantics/publishedVersion

The Muarádzi Sub-basin is part of the Moatize-Minjova Basin (MMB), an important Karoo aged coalfield in Tete Province, Mozambique. It is a WNW-ESE trending, elongated sedimentary basin located in the eastern part of the MMB, whilst during the late Permian was situated in the southern-central part of Gondwana. In this study, we undertook a multidisciplinary approach involving the lithological, palynofacies, and palynological analysis of samples collected from 3 coal exploration boreholes (DW11, DW21, and DW141) collected from this sub-basin. A total of 99 core samples were collected and studied, allowing for the characterisation of depositional environments and existing palaeofloras for this sub-basin.The palynological data indicates that all the successions have a Lopingian age, and a vast lowland fluvial setting existed in an area controlled by tectonic movements associated with a continental rifting phase. Correlation between the three sections enabled the recognition of an initial meandering fluvial system affected by repeated flooding events that changed to a braided river. The palynofacies corroborate the interpreted fluvial model and the palynological record obtained.The existence of a humid and warm climate during the Lopingian led to the development of vast floodplains and diversified wetland types, typical of lowland settings recorded in the analysed samples. The palynofacies analysis also indicate that the thick coal beds’ development is associated with deposition in anoxic to dysoxic environments. Furthermore, the Glossopteris Province vegetation, responsible for the coal development in the Muarádzi Sub-basin, is documented in the palynological assemblages, allowing for the characterization of a flora dominated by glossopterids (Protohaploxypinus and Striatopodocarpites) and gymnosperm pollen (Alisporites). The palaeofloral analysis based on palynological data also shows that associated ferns (e.g., Osmundidacites senectus, Thymospora pseudothiessenii), sphenophytes (e.g., Calamospora) and lycophytes (e.g., Lundbladispora, Kraeuselisporites) were common in this area. Additionally, upland vegetation indicators in the palynological assemblages, as monosaccate pollen grains, are rare, indicating that upland regions were distant from the studied sections. AcknowledgementsThis research was fully supported by the project PALEOCLIMOZ (PTDC/CTA-GEO/30082/2017), funded by Fundação para a Ciência e Tecnologia, Portugal. The authors would also like to acknowledge the financial support of the Portuguese Foundation of Science and Technology (FCT) to CIMA through UIDP/00350/2020.

We present palynological results from the northern sector of the Pulo do Lobo Domain, combining sections studied in Portugal and Spain. A total of 139 samples were studied, of which 56 are positive for palynology. The first age determination for the Pulo do Lobo Formation was achieved, indicating a mid-Frasnian age (Verrucosisporites bulliferus and Pustulatisporites rugulatus). The sediments of Peramora Melange (Spain) yielded the same palyno-assemblage as that of the Pulo do Lobo Fm. and are interpreted as a part of this formation. The Ribeira de Limas Fm. also yielded mid-Frasnian miospore assemblages, indicating the same age as the Pulo do Lobo Fm. The Santa Iria and Horta da Torre formations present spore assemblages assigned to the late Famennian in both Portugal and Spain. The phyllites interbedded with the quartzites of the Alajar Melange yielded a palyno-assemblage late Famennian in age that can be correlated to the Horta da Torre Fm. Therefore, the Alajar quartzites are interpreted as a lateral equivalent of the Horta da Torre Fm. in Spain. The palynological results obtained for the units of the northern sector of the Pulo do Lobo Domain are highly consistent and in agreement with stratigraphic mapping and structural interpretations. A detailed discussion of the palynological versus geochronological ages based on detrital zircons is included in this study. The palynological results and their comparison with the worldwide Upper Devonian palynological record suggest a close affinity with NW European palynofloras, placing the Pulo do Lobo Domain within the Avalonian paleobiogeographical province.

Detrital zircon U-Pb geochronology data from late Carboniferous to Triassic clastic sedimentary rocks in SW Iberia were used to investigate the regional paleogeography during the transition from Pangea amalgamation to breakup. The major U-Pb zircon age peaks are middle Devonian to Carboniferous (similar to 390-300 Ma), Cambrian Ordovician (similar to 530-440 Ma), Cryogenian-Ediacaran (similar to 750-540 Ma), Stenian-Tonian (similar to 1.2-0.9 Ga) and Paleoproterozoic (similar to 2.3-1.8 Ga). Rapid exhumation of Variscan crystalline rocks at the contact between the South Portuguese zone and Ossa Morena Zone, explains the abundance of late Paleozoic ages in the upper Carboniferous-lower Permian continental successions. The U-Pb zircon data constrain the maximum depositional age of the Santa Susana Basin to c. 304 Ma and the Viar Basin to c. 297 Ma. The Triassic sequences, despite being c. 100 Ma younger than the Variscan tectonothermal events, contain low proportions of late Paleozoic zircon. The major peaks in all zircon spectra closely resemble those found in the adjacent basement rocks, indicating small source areas, mainly located near the rift shoulders. Longer travelled fluvial systems are postulated for the eastern portions of the Algarve Basin, which was closer to the westward advancing Tethys Ocean than the rift basins of West Iberia. Sequences that contain significant proportions of similar to 1.2-0.9 Ga zircon are probably recycled from post-collisional Carboniferous-Permian continental deposits that were more extensive than those found today. (C) 2017 Elsevier B.V. All rights reserved. Portuguese Foundation for Science and Technology (FCT) [SFRH/BSAB/1233/2011]; Iberoamerican Santander (Banco Santander) grant; Science Foundation Ireland [12/IP/1663]

The geology of SW Iberia records a sequence of geologic events from the Cambrian-Early Ordovician rifting and subsequent passive margin development along the southern flank of the Rheic Ocean, to onset of oblique (sinistral) subduction in the Devonian, followed by oblique terrane accretion, ocean closure/continental collision and orogenic collapse. As a result, SW Iberia contains the southernmost exposure of the Pangean suture in the European Variscides. This suture zone is characterized by a belt of dismembered oceanic-related rocks and HP metamorphic complexes which are tectonically juxtaposed with the Gondwanan passive margin to the north (OMZ) and with the exotic South Portuguese Terrane to the south, which is thought to be either a remnant of Avalonia or Meguma.

The Moatize-Minjova Basin is a Karoo-aged rift basin located in the Tete Province of central Mozambique along the present-day Zambezi River valley. In this basin the Permian Moatize and Matinde formations consist of interbedded carbonaceous mudstones and sandstones with coal seams. The thermal history has been determined using rock samples from two coal exploration boreholes ( ca. 500 m depth) to constrain the burial and exhumation history of the basin. Organic maturation levels were determined using vitrinite reflectance and spore fluorescence/colour. Ages and rates of tectonic uplift and denudation have been assessed by apatite fission track analysis. The thermal history was modelled by inverse modelling of the fission track and vitrinite reflectance data. The Moatize Formation attained a coal rank of bituminous coals with low to medium volatiles (1.3–1.7% Rr ). Organic maturation levels increase in a linear fashion downhole in the two boreholes, indicating that burial was the main process controlling peak temperature maturation. Calculated palaeogeothermal gradients range from 59 °C/km to 40 °C/km. According to the models, peak burial temperatures were attained shortly (3–10 Ma) after deposition. Apatite fission track ages [146 to 84 Ma (Cretaceous)] are younger than the stratigraphic age. Thermal modelling indicates two episodes of cooling and exhumation: a first period of rapid cooling between 240 and 230 Ma (Middle – Upper Triassic boundary) implying 2500–3000 m of denudation; and a second period, also of rapid cooling, from 6 Ma (late Miocene) onwards implying 1000–1500 m of denudation. The first episode is related to the main compressional deformation event within the Cape Fold Belt in South Africa, which transferred stress northwards on pre-existing transtensional fault systems within the Karoo rift basins, causing tectonic inversion and uplift. During the Mesozoic and most of the Cenozoic the basin is characterized by very slow cooling. The second period of fast cooling and denudation during the Pliocene was likely related to the southward propagation of the East African Rift System into Mozambique.

We would like to thank Pereira (2015) for his interest in our work and appreciate the opportunity to clarify some aspects of the Rodrigues et al . (2015) study. Here we dispute several fundamental assertions made in the discussion of our original paper.

U–Pb detrital zircon data from the Baixo Alentejo Flysch Group in the South Portuguese Zone show significant age differences between formations. The Visean Mértola Formation and Serpukhovian to early Bashkirian Mira Formation are dominated by zircons in the 316–388?Ma age range, whereas the late Bashkirian to late Moscovian Brejeira Formation is dominated by zircons with an age range of 498–687?Ma. Detrital zircons spanning an age range of 0.9–1.1?Ga are present in the Brejeira Formation but are absent in the Mértola and Mira formations. Detrital zircon ages of the Mértola and Mira formations indicate provenance from an extra-basinal source (Ossa–Morena Zone) with a minor intra-basinal contribution (South Portuguese Zone). The abundant presence of detrital zircon with age ranges of 500–750 and 0.9–1.1?Ga in the Brejeira Formation suggests a sediment source from the Avalon–Meguma terranes with limited recycling from the SW Portugal Domain. The different inferred source areas for the Baixo Alentejo Flysch Group formations are attributed to the presence of a forebulge that was formed in Mid-Visean times during the foreland phase of the South Portuguese Zone. The forebulge acted as a physical barrier separating sub-basins that accumulated the Mértola–Mira and Brejeira sediments respectively.

This work is focused on the turbiditic sediments from the Carboniferous Baixo Alentejo Flysch Group (BAFG) in the South Portuguese Zone, an external zone of the Iberian Variscides. The aim of this work is to constrain the provenance and tectonic setting of these sediments in a context of a complex evolution of SW Iberian Variscides. For this purpose, we performed a systematic study of petrographical and geochemical signatures of greywackes and shales from the three BAFG formations: Mértola, Mira and Brejeira. Major and trace element composition and ratios suggest heterogeneous source area composition for BAFG shales and greywackes. For the oldest Mértola Formation greywackes, source area is dominated by granitoid rocks with minor mafic input. The latter becomes residual in the Mira Formation. The youngest Brejeira Formation greywackes show clear felsic affiliation associated with an increase in recycled components. The shales of all three BAFG formations denote a granodioritic affiliation. Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values suggest moderate weathering in the source areas of Mértola and Mira formations. These indices, together with A–CN–K relations, point out to steady-state weathering conditions in the source areas of both formations. In contrast, both CIA and PIA values for the Brejeira Formation indicate variable conditions of palaeoweathering, from moderate to intense, as a consequence of non-steady-state conditions probably triggered by tectonic instability in the provenance area. Compared to the greywackes, the shales of all three BAFG formations exhibit higher CIA and PIA values, as well as low K2O/Al2O3 (~0.2) and index of compositional variability (b1), reflecting the cumulative effect of multiple cycles of sedimentary recycling and prolonged chemical weathering history. Major and trace element distribution and upper continental crust-normalized multi-element plots suggest that the sediments of BAFG were derived mainly from a continental arc/active margin with minor contribution from old continental crust. Together, our geochemical data are compatible with BAFG sediments derived mainly from SW border of the Ossa Morena Zone (Gondwanan affinity), with possible contribution from an external (Avalonian) source.

Well-preserved primary textural features were recognized in cherts and jaspers that form one of the manganese ore-hosting units of the Soloviejo Mn deposit, in the Iberian Pyrite Belt. These include (i) spherulitic, (ii) banded and (iii) brecciated. The spherulites (0.04—0.3 mm) consits of a central core of minute grains of hematite or quartz, rimmed by chalcedony or microcrystalline quartz. Banded jaspers show no spherulitic textures. Banded textures are made up by alterations of micro- to meso-bands of silica and hematite. They often show soft-sediment deformation features, such as microslumps, pinch-and-swell, and load cast. Diagenetic brecciation overprints these pristine textures. Breccias consist of jasper fragments (mm to cm), affected by total or partial recrystalization, cemented by different proportions of microcrystalline quartz. Primary textures in siliceous hydrothermal precipitates reflect different stages of formation and diagenetic maturation of its silica gel precursor. Their interpretation helps in constraining the initial conditions assisting the hydrothermal activity at the Soloviejo deposit, and its early evolving stages.

New Re and Os analyses of pyrites from Aljustrel, Lagoa Salgada and Neves-Corvo deposits yield concentrations that are similar to those previously reported for the Rio Tinto and Tharsis deposits, all at the Iberian Pyrite Belt. Osmium contents in IPB pyrites increase from the deeper stockwork zones towards the upper massive sulphides. Pyrite samples from IPB sulphide orebodies plot on a major 187Re/188Os-187Os/188O linear array, yielding an age of 359±26 Ma and an initial 187Os/188O ratio of ca. 0.57. Five samples from Neves-Corvo sulphide-rich stockwork ores yield an age of 358 ±29 Ma and an initial 187Os/188O ratio of 0.49 ±0.07, in accord with palynological and isotopic age constraints for ore formation at the IPB. Pyrites from Neves-Corvo copper-tin ores have Re/Os ratios and osmium concentrations that are similar to those in pyrites from sulphide-rich stockwork ores; however, their highly radiogenic initial 187Os/188O ratios (4.89–7.85, if preserving original isotope system-atics) preclude derivation from the same sources as the remaining IPB sulphides. The overall Re-Os geochemical data conform to previous Sr, Nd and Pb isotopic studies supporting multiple sources for IPB metallogenesis.