Evaluating the role of fire over a decade in a tropical mountainous forestgrassland mosaic

Forest-grassland mosaics comprise a major component of tropical landscapes,hosting invaluable biodiversity and providing essential ecosystem services to hundreds of millions of people worldwide.While open biomes often benefit from disturbance,forests can particularly be susceptible to structural changes resulting from such disruptions.Here we evaluate the influence of fire on the structure and landscape properties within natural forest islands immersed in a matrix of megadiverse montane grasslands.We conducted this study in 15 forest islands located in southeastern Brazil,assessing its fire frequency,intensity,and post-fire time over an eleven-year period from January 2012 to December 2022.Our results show that fire frequency is linked to soil characteristics and the percentage of herbaceous cover within the forest islands.We also found that the post-fire time is related to the percentage cover of the forest islands’associated herbs and shrubs.However,neither fire frequency,intensity,nor post-fire time was connected to significant changes in plant species richness,abundance,or in the upper vegetation strata(tree species richness and abundance,and canopy cover)in the interior of the forest islands.Furthermore,these fire-related variables did not result in temporal changes in the forest island’s canopy variation or landscape metrics.Our results underscore a low fire frequency and intensity within our study area,potentially explaining the limited fire-associated impact,and primarily on the lower vegetation strata.Despite acknowledging the relative stability of these forest islands under current fire regimes,we suggest further studies that can experimentally manipulate not only fire but also other anthropic disturbances for understanding the temporal dynamics of the forest islands and,consequently,their preservation.This perspective is indispensable for comprehensively understanding the ecological consequences of anthropogenic disturbances in natural forest islands.

Further Information of the Associated Li Deposits in the No.6 Coal Seam at Jungar Coalfield, Inner Mongolia, Northern China

Total 138 coal samples and 14 parting samples were taken from the No. 6 Seam of the Jungar Coalfield, Inner Mongolia. These samples were analysed by optical microscopy, sequential chemical extraction procedure （SCEP）, inductively coupled plasma mass spectrometry （ICP-MS）, X-ray powder diffraction （XRD）, and scanning electron microscope in conjunction with an energy-dispersive X-ray spectrometer （SEM-EDX） analysis. The results indicate that the Li contents have reached the industrial grade of the coal associated Li deposit, and the total Li reserves have reached 2406600 tons, that is, 5157000 tons Li2O in the No. 6 seam in the Jungar Coalfield. The sequential chemical extraction procedure results suggest that the Li concentration is mainly related to inorganic matter. The minerals in the coals consist of kaolinite, boehmite, chlorite-group mineral, quartz, calcite, pyrite, siderite and amorphous clay material. Some Li could be absorbed by clay minerals in the Li-bearing coal seam. The chlorite phase？could be？most likely the host for a part of Li. The Yinshan Oldland should be the most possible source of Li of the coal.

A Method for Environmental Data Management Applied to Megasites in the State of Sao Paulo, Brazil

The management of contaminated areas with multiple sources of contamination (megasites) is among the biggest challenges for the Brazilian environmental agencies, especially because aquifers in big urban areas, like the Sao Paulo Metropolitan Region, are important sources of water for human supply purposes. One of the main reasons that hamper the proper management of urban environmental problems is a lack of a unified system where all information can be easily integrated into regional studies. To address this problem, a method for data integration and management using a Geographic Information System (GIS) was developed. This method was applied to the case of a regional contamination of an aquifer by chlorinated solvents at a former industrial district in Sao Paulo city, named Jurubatuba, but the final product might also be used for data management of contaminated areas for the entire State of Sao Paulo. The main result obtained was that the site-by-site approach for aquifer contamination management is ineffective. Furthermore, there are many other suspected and potential sources of contamination without any information available after more than 10 years since the contamination problem was discovered at the FIZ 131.

Rhyacian and Neoproterozoic magmatic associations of the Gurupi Belt,Brazil: Implications for the tectonic evolution, and regional correlations

The Gurupi Belt,in north-northeastern Brazil,is a mobile belt developed in the south-southwestern margin of the Sao Luis cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover.Field,petrographic,geochemical,geochronological,and Nd isotopic information(new and published)constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed.The Rhyacian was the main period of magmatic activity,which can be grouped into two main stages.(1)~2185-2130 Ma:pre-collisional,juvenile,calc-alkaline magnesian and calcic ferroan granitoid suites,and minor calc-alkaline and tholeiitic mafic plutonism(now amphibolites),formed in intra-oceanic to transitional/continental arcs;and intra-or back-arc volcano-sedimentary basin.(2)~2125-2070 Ma:syn-(two-mica granites)to late-collisional(potassic to shoshonitic granites and quartz-syenite)plutonic suites produced after crustal thickening and melting,with localized migmatization,that intruded during the compressive D1 deformational phase and concomitantly with greenschist to amphibolite metamorphism.There is a zonation of the Rhyacian episodes,with intra-oceanic stages occurring to the northeast,and the continental arc and collisional phases occurring to the southwest,indicating the presence of an active continental margin to the southwest,and subduction from NE to SW(present-day configuration).This magmatic framework is a continuation to the south of what is described for the Sao Luis cratonic fragment to the north,and the orogenic scenario is identical to what is observed for the same period in the West African Craton(Eburnean/Birrimian orogen),which additionally supports previous geological correlations.In the Neoproterozoic,a few magmatic occurrences are recognized.An extensional event allowed the intrusion of an anorogenic,nepheline syenite at ca.730 Ma,which was followed by the intrusion of a crustal,calc-alkaline microtonalite,of uncertain tectonic setting,at 624 Ma.Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 Ma.This metamorphic event is probably related to crustal thickening,which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 Ma.The absence of oceanic and arc-related assemblages,along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic-Early Cambrian evolution of the Gurupi Belt,with rifting and posterior closure of the basin,without oceanization.Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly,respectively,but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events,but,instead,as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time.

Visualizing Fit between Dengue and Climatic Variables on Capitals of the Brazilian Northeast Region by Generalized Additive Models

Recent analysis indicates that the numbers of dengue cases may be as high as 400 million/year in the world. According to the Ministry of Brazilian Health, in 2015, there were 1,621,797 probable cases of dengue in the country including all classifications except discarded, the highest number recorded in the historical series since 1990. Many studies have found associations between climatic conditions and dengue transmission, especially using generalized models. In this study, Generalized Additive Models (GAM) was used associated to visreg package to understand the effect of climatic variables on capitals of Northeast Brazilian, from 2001 to 2012. From 12 climatic variables, it was verified that the relative humidity was the one that obtained the highest correlation to dengue. Afterwards, GAM associated with visreg was applied to understand the effects between them. Relative humidity explains the dengue incidence at an adjusted rate of 78.0% (in São Luis-MA) and 82.3% (in Teresina-PI) delayed in, respectively, -1 and -2 months.

Dynamic Modelling of Dengue Epidemics in Function of Available Enthalpy and Rainfall

In this work, we present results of an investigation of environmental precursors of infectious epidemic of dengue fever in the Metropolitan Area of Rio de Janeiro, RJ, Brazil, obtained by a numerical model with representation of infection and reinfection of the population. The period considered extend between 2000 and 2011, in which it was possible to pair meteorological data and the reporting of dengue patients worsening. These data should also be considered in the numerical model, by assimilation, to obtain simulations of Dengue epidemics. The model contains compartments for the human population, for the vector Aedes aegypti and four virus serotypes. The results provide consistent evidence that worsening infection and disease outbreaks are due to the occurrence of environmental precursors, as the dynamics of the accumulation of water in the breeding and energy availability in the form of metabolic activation enthalpy during pre-epidemic periods.

Farming-Biodiversity Segregation or Integration? Revisiting Land Sparing versus Land Sharing Debate

Land Sparing (LSP) was proposed to spatially segregate biodiversity and production in order to maximize both, while Land Sharing (LSH) defenders posit that farming and nature integration is preferable, through eco-agriculture and low-input systems. Based on a multidisciplinary review on historical land-use data, ecological aspects, agricultural production potential, economic and food security topics, we summarize LSP/LSH major findings and caveats. Although LSH still has to address some issues, LSP relies on a series of assumptions that are not supported by data, particularly regarding the positive effects of intensification on agriculture expansion. Furthermore, we developed conceptual models to theoretically predict the responses of biodiversity and ecosystems services in dynamic landscapes with different natural habitat proportions and different intensification levels on the farmed areas. Agriculture intensification may expand farmland reducing habitat area fostering population declines at the “natural” patches (via habitat reduction and decreasing species intra patch flux through the matrix), as well as at the farm site by direct effect of intensification (heterogeneity reduction and pesticide use), leading to a species extinction and ecosystems services loss. This multiple negative effect of agriculture intensification is worsening in regions where habitat proportion is below 30%, such as in many tropical biodiversity hotspots, making LSH a much safer strategy for conservation and food security.

Metamorphic disturbances of magnetite chemistry and the Sm-Nd isotopic system of reworked Archean iron formations from NE Brazil

Iron formations are valuable archives of sedimentary conditions and post-depositional events.However,geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism and deformation,hampering their use as records of regional geological events.This work focuses on strongly reworked magnetite-quartz-rich rocks from the São Josédo Campestre Massif,one of the oldest fragments of preserved crust in South America.The genetic classification of these magnetite-quartz-rich rocks is not straightforward because primary assemblages and textures were variably modified by granulite facies metamorphism during a regional Paleoproterozoic migmatization event.To address genetic ambiguities,we analyzed their magnetite and pyroxene chemistry,wholerock geochemistry,and Sm-Nd isotopes.Magnetite chemistry indicates that pyroxene-poor iron formations(Type B)are low in trace elements such as Ti,Al,V,and Mn,suggesting a chemical similarity to iron formations elsewhere.In contrast,magnetites from pyroxene-enriched Type A iron formations are rich in trace elements and more akin to magnetite crystallized from higher temperature systems,such as skarn and IOCG.The^(147)Sm/^(144)Nd of these rocks show substantial variation even at the outcrop scale,indicating a locally-controlled,highly heterogeneous mixture of Archean,Paleoproterozoic,and Neoproterozoic sources.Therefore,our geochemical tools point out to heterogenous signatures of these magnetitequartz rocks and proxies compatible with both low and high-temperature conditions and age of deposition spanning sources from the Archean to the Neoproterozoic.We interpret that the studied São Josédo Campestre magnetite-quartz rocks represent Archean iron formations with original magnetite chemistry and isotopic signatures variably modified by metamorphism and by at least one deformation-related hydrothermal event.These results contrast with similar examples from China and Greenland where iron formations either preserved the magnetite chemistry or the primary isotopic signatures.Our study indicates that metamorphism can selectively affect chemical proxies used to study iron formations and undermine the genetic classification of iron ores.Thus,these proxies should be carefully applied in the interpretation of syn-depositional environments of polydeformed belts.

巴西中部元古代Parano和Bambu′i群叠层石的古生态和构造背景(英文)

叠层石的形态和它们与陆源沉积的关系反映了沉积盆地的构造背景。在巴西中部地区 ,叠层石出现在中元古和新元古代的 Paranoa′群、Vazante群和 Bambui′群。根据沉积学和矿物学的研究分析 ,Paranoa′群形成于被动边缘盆地 ,而另外两个群形成于前陆盆地。Vazante群沉积在形成巴西褶皱带的山脉附近 ,然而 Bam bui′群的大部分都形成于克拉通地区。通常远离山脉褶皱带的 Paranoa′群和 Bambui′群内的叠层石建造的形态和规模的改变与环境的变化有关。在柱状生长方向的频繁变化和不规则的丰富陆源物质的夹层进入叠层石 ,表征活跃的构造背景 ,例如在Vazante,Paranoa′群和 Bam

The generation and evolution of the Archean continental crust:The granitoid story in southeastern Brazil

The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inlier related to the Southern S?o Francisco Craton(SSFC),are integrated with geochronological,isotopic and geochemical data on Archean granitoids from the SSFC.The rocks are divided into three main geochemical groups with different ages:(1)TTG(3.02–2.77 Ga);(2)mediumto high-K granitoids(2.85–2.72 Ga);and(3)A-type granites(2.7–2.6 Ga).The juvenile to chondritic(Hf-Nd isotopes)TTG were divided into two sub-groups,TTG 1(low-HREE)and 2(high-HREE),derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts.The compositional diversity within the TTG is attributed to different pressures during partial melting,supported by a positive correlation of Dy/Yb and Sr/Zr,and batch melting calculations.The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs,indicating the presence of subduction processes concomitant with TTG emplacement.From~2.85 Ga to 2.70 Ga,the dominant rocks were K-rich granitoids.These are modeled as crustal melts of TTG,during regional metamorphism indicative of crustal thickening.Their compositional diversity is linked to:(i)differences in source composition;(ii)distinct melt fractions during partial melting;and(iii)different residual mineralogies reflecting varying P–T conditions.Post-collisional(~2.7–2.6 Ga)A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms,and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle.The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening,regional metamorphism and crustal melting,and post-collisional extension,similar to that seen in younger Wilson Cycles.It is compelling evidence that plate tectonics was active in this segment of Brazil from~3 Ga.

Proto-Adamastor ocean crust(920 Ma)described in Brasiliano Orogen from coetaneous zircon and tourmaline

Proto-Adamastor ocean bathed Rodinia and successor continental fragments from 1.0-0.9 Ga up to0.75 Ga,and evolved into world Adamastor Ocean at 0.75-0.60 Ga.Mesoproterozoic oceanic crust is poorly preserved on continents,only indirect evidence registered in Brasiliano Orogen.We report first evidence of ophiolite originated in proto-Adamastor.We use multi-technique U-Pb-Hf zircon andδ^11B tourmaline isotopic and elemental compositions.The host tourmalinite is enclosed in metaserpentinite,both belonging to the Bossoroca ophiolite.Zircon is 920 Ma-old,εHf(920 Ma)=+12,HfTDM=1.0 Ga and has’oceanic’composition(e.g.,U/Yb<0.1).Tourmaline is dravite withδ^11B=+1.8‰(Tur 1),0‰(Tur 2),-8.5‰(Tur 3).These characteristics are a novel contribution to Rodinia and associated world ocean,because a fragment of proto-Adamastor oceanic crust and mantle evolved at the beginning of the Brasiliano Orogen.

U-Pb provenance fingerprints of metavolcanic-sedimentary successions of the Mineiro belt:Proxies for the continuity of plate tectonics through the Paleoproterozoic

We document new U-Pb detrital zircon LA-MC-ICP-MS data for seven metavolcanic-sedimentary successions and metasedimentary sequences and reassess additional dates of five siliciclastic samples toward their tectonic significance in the context of the Mineiro belt,Southern São Francisco Craton.This belt represents a crustal segment of the 2.47–2.00 Ga Minas Orogen,classically known by its Siderian and Rhyacian juvenile rocks with important implications in the Earth’s geodynamics.The new and compiled detrital provenance constraints unravel the long-lived magmatic and sedimentary history of the studied basins,lasting ca.230–220 Myr.The maximum depositional dates around 2.1 Ga reflect the renewed sediment budget with the subsequent metamorphic episode ca.2.0 Ga.Most of the unmixed relative probability diagrams are consistent with sourcing from the Siderian and Rhyacian arcs of the Mineiro belt,determining a detrital provenance change in time and space for the precursor basins.Alternative potential sources could be the youngest rocks of the Mantiqueira and Juiz de Fora terranes that constitute the other segments of the Minas Orogen,given the age match.The overall detrital fingerprints determine the study basins resumed mainly in Rhyacian fore-arc and/or back-arc settings,i.e.,akin to a subductionrelated system that evolved to a collisional(foreland)environment.Few samples show fingerprints of primary extensional settings,determined by major Archean detrital populations sourced from areas outside the Mineiro belt beside the Paleoproterozoic detritus.The working model considers the collage between the Mineiro belt and the ancient foreland around 2.10 Ga and eventual interaction with other crustal segments of the Minas Orogen,generating the ca.2.0 Ga metamorphism over the metasedimentary samples.The more complete isotopic repository in detrital and igneous zircon grains for the studied supracrustal successions and the associated rocks allows new insights into the Rhyacian–Orosirian dynamics of the Minas orogeny.In a broader perspective,the juvenile nature of the Mineiro belt reinforces the paradigm of uninterrupted continental growth during the Paleoproterozoic Earth.

Isotopic and geochemical constraints for a Paleoproterozoic accretionary orogen in the Borborema Province,NE Brazil:Implications for reconstructing Nuna/Columbia

The Alto MoxotóTerrane of the Borborema Province presents a wide exposure of Paleoproterozoic crust,but unlike other continental blocks of South America,its orogenic history is strongly obliterated by late Neoproterozoic deformation.New isotopic and geochemical studies were conducted in mafic-ultramafic(Fazenda Carmo Suite)and granitic-gneissic rocks(Riacho do Navio Suite)within the terrane.The former present zircon U-Pb crystallization ages at ca.2.13 Ga,whereas Sm-Nd data suggests a juvenile origin via melting of early Paleoproterozoic to Archean peridotitic sources.Geochemical data for these rocks are compatible with tholeiitic magmas with some degree of crustal contamination and trace element distribution points to a continental-arc related setting interpreted as remnants of the early stages of subduction.In contrast,the Riacho do Navio Suite was emplaced at ca.2.08 Ga and has highly negativeεNd(t)values indicating crustal reworking.The suite displays calc-alkali to alkali-calcic and ferroan geochemical signatures compatible with Cordilleran magmas.In addition,trace-element distribution as well as discriminant diagrams suggest that the precursor magmas were generated during the later stages of a continental arc or in a syn-collisional setting.Based on our results,we suggest that the studied units might represent missing pieces of a Paleoproterozoic accretionary orogen that formed the crustal framework of the Alto MoxotóTerrane,and that this represents a block associated with assembly of the Nuna/Columbia supercontinent,which is now largely hidden within the Neoproterozoic orogenic belts of West Gondwana.

An exotic Cretaceous kimberlite linked to metasomatized lithospheric mantle beneath the southwestern margin of the S?o Francisco Craton,Brazil

We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals(titanite,calzirtite,anatase,baddeleyite and pyrochlore)of a newly discovered Late Cretaceous kimberlite(U-Pb zircon age 90.0±1.3 Ma;2σ)named Osvaldo Franca 1,located in the Alto Paranaíba Igneous Province(APIP),southeastern Brazil.Pyrope grains are lherzolitic(Lherz-1,Lherz-2 and Lherz-3),harzburgitic(Harz-3)and wehrlitic(Wehr-2).The pyrope xenocrysts cover a wide mantle column in the subcratonic lithosphere(66–143 km;20–43 kbar)at relatively low temperatures(811–875°C).The shallowest part of this mantle is represented by Lherz-1 pyropes(20–32 kbar),which have low-Cr(Cr_(2)O_(3)=1.74–6.89 wt.%)and fractionated middle to heavy rare earth elements(MREE-HREE)pattern.The deepest samples are represented by Lherz-2,Lherz-3,Harz-3,and Wehr-2 pyropes(36–43 kbar).They contain high-Cr contents(Cr_(2)O_(3)=7.36–11.19 wt.%)and are characterized by sinusoidal(Lherz-2 and Wehr-2)and spoon-like(Lherz-3 and Harz-3)REE patterns.According to their REE and trace elements,pyrope xenocrysts have enriched nature(e.g.,Ce and Yb vs.Cr_(2)O_(3)),indicating that the cratonic lithosphere has been affected by a silicate melt with subalkaline/tholeiite composition due to their low Zr,Ti and Y concentrations.Besides minerals with typical kimberlitic signatures,such as ilmenite and zircon,the exotic compositions of phlogopite and ulvöspinel suggest an enriched component in the magma source.The formation of rare mineral phases with strong enrichment of light-REE(LREE)and high field strength elements(HFSE)is attributed to the late-stage kimberlitic melt.We propose a tectonic model where a thermal anomaly,represented by the low-velocity seismic anomaly observed in P-wave seismic tomography images,supplied heat to activate the alkaline magmatism from a metasomatized cratonic mantle source during the late-stages of Gondwana fragmentation and consequent South Atlantic Ocean opening.The metasomatism recorded by mineral phases is a product of long-lived recycling of subducted oceanic plates since the Neoproterozoic(Brasiliano Orogeny)or even older collisional events,contributing to the exotic character of the Osvaldo Fran?a 1 kimberlite,as well as to the cratonic lithospheric mantle.

Timing of Proterozoic magmatism in the Sunsas belt, Bolivian Precambrian Shield, SW Amazonian Craton

We present new U–Pb zircon and monazite ages from the Sunsas belt granitic magmatism in Bolivia, SW Amazonian Craton. The geochronological results revealed four major magmatic events recorded along the Sunsas belt domains. The older igneous event formed a granitic basement coeval to the Rio Apa Terrane(1.95–1.85 Ga) in the southern domain. The second magmatic episode is represented by 1.68 Ga granites associated to the Paraguá Terrane(1.69–1.66 Ga) in the northern domain. The 1.37–1.34 Ga granites related to San Ignacio orogeny represent the third and more pervasive magmatic event, recorded throughout the Sunsas belt. Moreover, magmatic ages of ~1.42 Ga revealed that the granitogenesis associated to the Santa Helena orogeny also affected the Sunsas belt, indicating that it was not restricted to the Jauru Terrane. Lastly, the 1.10–1.04 Ga youngest magmatism was developed during the Sunsas orogeny and represents the final magmatic evolution related to Rodinia assembly. Likewise, the 1.95–1.85 and 1.68 Ga inherited zircon cores obtained in the ~1.3 Ga and 1.0 Ga granite samples suggest strong partial melting of the Paleoproterozoic sources. The 1079 ± 14 Ma and 1018 ± 6 Ma monazite crystallization ages can be correlated to the collisional tectono-thermal event of the Sunsas orogeny, associated to reactions of medium-to high-grade metamorphism. Thus, the Sunsas belt was built by heterogeneous 1.95–1.85 Ga and 1.68 Ga crustal fragments that were reworked at 1.37–1.34 Ga and 1.10–1.04 Ga related to orogenic collages. Furthermore, the 1.01 Ga monazite age suggests that granites previously dated by zircon can bear evidence of a younger thermal history. Therefore, the geochronological evolution of the Sunsas belt may have been more complex than previously thought.

Unraveling one billion years of geological evolution of the southeastern Amazonia Craton from detrital zircon analyses

Despite representing one of the largest cratons on Earth,the early geological evolution of the Amazonia Craton remains poorly known due to relatively poor exposure and because younger metamorphic and tectonic events have obscured initial information.In this study,we investigated the sedimentary archives of the Carajás Basin to unravel the early geological evolution of the southeastern Amazonia Craton.The Carajás Basin contains sedimentary rocks that were deposited throughout a long period spanning more than one billion years from the Mesoarchean to the Paleoproterozoic.The oldest archives preserved in this basin consist of a few ca.3.6 Ga detrital zircon grains showing that the geological roots of the Amazonia Craton were already formed by the Eoarchean.During the Paleoarchean or the early Mesoarchean(<3.1 Ga),the Carajás Basin was large and rigid enough to sustain the formation and preservation of the Rio Novo Group greenstone belt.Later,during the Neoarchean,at ca.2.7 Ga,the southeastern Amazonia Craton witnessed the emplacement of the Parauapebas Large Igneous Province(LIP)that probably covered a large part of the craton and was associated with the deposition of some of the world largest iron formations.The emplacement of this LIP immediately preceded a period of continental extension that formed a rift infilled first by iron formations followed by terrigenous sediments.This major change of sedimentary regime might have been controlled by the regional tectonic evolution of the Amazonia Craton and its emergence above sea-level.During the Paleoproterozoic,at ca.2.1 Ga,the Rio Fresco Group,consisting of terrigenous sediments from the interior of the Amazonia Craton,was deposited in the Carajás Basin.At that time,the Amazonian lithosphere could have either underwent thermal subsidence forming a large intracratonic basin or could have been deformed by long wavelength flexures that induced the formation of basins and swells throughout the craton under the influence of the growing Transamazonian mountain belt.

High-pressure metamorphic rocks in the Borborema Province, Northeast Brazil: Reworking of Archean oceanic crust during proterozoic orogenies

We present the first evidence of Archean oceanic crust submitted to Proterozoic high-pressure(HP)metamorphism in the South American Platform.Sm-Nd and Lu-Hf isotopic data combined with U-Pb geochronological data from the Campo Grande area,Rio Grande do Norte domain,in the Northern Borborema Province,reflect a complex Archean(2.9 Ga and 2.6 Ga)and Paleoproterozoic(2.0 Ga)evolution,culminating in the Neoproterozoic Brasiliano/Pan-African orogeny(ca.600 Ma).The preserved mafic rocks contain massive poikiloblastic garnet and granoblastic amphibole with variable proportions of plagioclase+diopside in symplectitic texture,typical of high-pressure rocks.These clinopyroxene-garnet amphibolites and the more common garnet amphibolites from the Campo Grande area are exposed as rare lenses within an Archean migmatite complex.The amphibolite lenses represent 2.65 Ga juvenile tholeiitic magmatism derived from depleted mantle sources(positive values of+3.81 to+30.66)later enriched by mantle metasomatism(negative εNd(t)values of-7.97).Chondrite and Primitive Mantle-normalized REE of analyzed samples and discriminant diagrams define two different oceanic affinities,with E-MORB and OIB signature.Negative Eu anomalies(Eu/Eu*=0.75-0.95)indicate depletion of plagioclase in the source.Inherited zircon cores of 3.0-2.9 Ga in analyzed samples indicate that the Neoarchean tholeiitic magmatism was emplaced into 2923±14 Ma old Mesoarchean crust(εNd(t)--2.58 and Nd TDM=3.2 Ga)of the Rio Grande do Norte domain.The age of retro-eclogite facies metamorphism is not yet completely understood.We suggest that two high-grade metamorphic events are recognized in the mafic rocks:the first at 2.0 Ga,recorded in some samples,and the second,at ca.600 Ma,stronger and more pervasive and recorded in several of the mafic rock samples.The Neoproterozoic zircon grains are found in symplectite texture as inclusions in the garnet grains and represent the age of HP conditions in the area.These zircon grains show a younger cluster of concordant analyses between 623±3 Ma and 592±5 Ma withεHf(t)values of+0.74 to-65.88.Thus,the Campo Grande rock assemblage is composed of Archean units that were amalgamated to West Gondwana during Neoproterozoic Brasiliano orogeny continent-continent collision and crustal reworking.

Sm-Nd systematics of metaultramafic-mafic rocks from the Arroio Grande Ophiolite(Brazil): Insights on the evolution of the South Adamastor paleo-ocean

In this contribution we present new insights on the evolution of the Dom Feliciano Belt,southernmost Mantiqueira Province,integrating new whole-rock Sm-Nd isotopic data for the Arroio Grande Ophiolite(Punta del Este Terrane,Brazil/Uruguay border)with previously published bulk-rock and isotope geochemistry of the South Adamastor paleo-ocean metamafic rocks located in Uruguay(Paso del Dragon Complex,Punta del Este Terrane)and Namibia(Chameis Subterrane,Marmora Terrane,Gariep Belt).For the regional geology,the new data corroborate previous hypothesis and demonstrate the depleted mantle features of the amphibolites and metagabbros of the studied ophiolite.The Arroio Grande Ophiolite rocks are compared with its Uruguayan and Namibian counterparts,demonstrating their isotopic and geochemical similarities and differences,and the backarc affinity of the South Adamastor paleo-ocean.The MORB-affinity amphibolites from the Arroio Grande Ophiolite-Paso del Dragon Complex are,so far,the most juvenile rocks in the eastern sector of the Dom Feliciano Belt,yielding εNd(640)Ma)between+7.3 and+9,and high 147Sm/144Nd(>0.169)and 143Nd/144Nd(640 Ma)ratios(0.51219-0.51229).The South Adamastor is interpreted in this paper as an internal back-arc ocean,with limited lateral extension,opened at around 750-650 Ma as the result of the closure of the older Charrua-Goianide paleoocean during the Brasiliano/Pan-African orogenic cycle and final configuration of the West Gondwana paleocontinent.

Distinguishing the Regional Atmospheric Controls on Precipitation Isotopic Variability in the Central-Southeast Portion of Brazil

Precipitation isotope ratios(O and H)record the history of water phase transitions and fractionation processes during moisture transport and rainfall formation.Here,we evaluated the isotopic composition of precipitation over the central-southeastern region of Brazil at different timescales.Monthly isotopic compositions were associated with classical effects(rainfall amount,seasonality,and continentality),demonstrating the importance of vapor recirculation processes and different regional atmospheric systems(South American Convergence Zone-SACZ and Cold Fronts-CF).While moisture recycling and regional atmospheric processes may also be observed on a daily timescale,classical effects such as the amount effect were not strongly correlated(δ^(18)O-precipitation rate r≤-0.37).Daily variability revealed specific climatic features,such asδ^(18)O depleted values(~-6‰to-8‰)during the wet season were associated with strong convective activity and large moisture availability.Daily isotopic analysis revealed the role of different moisture sources and transport effects.Isotope ratios combined with d-excess explain how atmospheric recirculation processes interact with convective activity during rainfall formation processes.Our findings provide a new understanding of rainfall sampling timescales and highlight the importance of water isotopes to decipher key hydrometeorological processes in a complex spatial and temporal context in central-southeastern Brazil.

Recycling process and proto-kimberlite melt metasomatism in the lithosphere-asthenosphere boundary beneath the Amazonian Craton recorded by garnet xenocrysts and mantle xenoliths from the Carolina kimberlite

Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is located on the southwestern border of the Amazonian Craton.We also present Sr-Nd isotopic data of garnet xenocrysts and whole-rocks from the Carolina kimberlite.Mantle xenoliths are mainly clinopyroxenites and garnetites.Some of the clinopyroxenites were classified as GPP–PP–PKP(garnet-phlogopite peridotite,phlogopite-peridotite,phlogopite-K-richterite peridotite)suites,and two clinopyroxenites(eclogites)and two garnetites are relicts of an ancient subducted slab.Temperature and pressure estimates yield 855–1102℃ and 3.6–7.0 GPa,respectively.Clinopyroxenes are enriched in light rare earth elements(LREE)(La_(N)/Yb_(N)=5–62;Ce_(N)/Sm_(N)=1–3;where N=primitive mantle normalized values),they have high Ca/Al ratios(10–410),low to medium Ti/Eu ratios(742–2840),and low Zr/Hf ratios(13–26),which suggest they were formed by metasomatic reactions with CO_(2)-rich silicate melts.Phlogopite with high TiO_(2)(>2.0 wt.%),Al_(2)O_(3)(>12.0 wt.%),and FeOt(5.0–13.0 wt.%)resemble those found in the groundmass of kimberlites,lamproites and lamprophyres.Conversely,phlogopite with low TiO_(2)(<1.0 wt.%)and lower Al_(2)O_(3)(<12.0 wt.%)are similar to those present in GPP-PP-PKP,and in MARID(mica-amphibole-rutile-ilmenite-diopside)and PIC(phlogopite-ilmenite-clinopyorxene)xenoliths.The GPP-PP-PKP suite of xenoliths,together with the clinopyroxene and phlogopite major and trace element signatures suggests that an intense proto-kimberlite melt metasomatism occurred in the deep cratonic lithosphere beneath the Amazonian Craton.The Sr-Nd isotopic ratios of pyrope xenocrysts(G3,G9 and G11)from the Carolina kimberlite are characterized by high ^(143)Nd/^(144)Nd(0.51287–0.51371)and eNd(+4.55 to+20.85)accompanied with enriched ^(87)Sr/^(86)Sr(0.70405–0.71098).These results suggest interaction with a proto-kimberlite melt compositionally similar with worldwide kimberlites.Based on Sr-Nd whole-rock compositions,the Carolina kimberlite has affinity with Group 1 kimberlites.The Sm-Nd isochron age calculated with selected eclogitic garnets yielded an age of 291.9±5.4 Ma(2σ),which represents the cooling age after the proto-kimberlite melt metasomatism.Therefore,we propose that the lithospheric mantle beneath the Amazonian Craton records the Paleozoic subduction with the attachment of an eclogitic slab into the cratonic mantle(garnetites and eclogites);with a later metasomatic event caused by proto-kimberlite melts shortly before the Carolina kimberlite erupted.