Geochemical constraints on the Hadean environment from mineral fingerprints of prokaryotes

The environmental conditions on the Earth before 4 billion years ago are highly uncertain, largely because of the lack of a substantial rock record from this period. During this time interval, known as the Hadean, the young planet transformed from an uninhabited world to the one capable of supporting, and inhabited by the first living cells. These cells formed in a fluid environment they could not at first control, with homeostatic mechanisms developing only later. It is therefore possible that present-day organisms retain some record of the primordial fluid in which the first cells formed. Here we present new data on the elemental compositions and mineral fingerprints of both Bacteria and Archaea, using these data to constrain the environment in which life formed. The cradle solution that produced this elemental signature was saturated in barite, sphene, chalcedony, apatite, and clay minerals. The presence of these minerals, as well as other chemical features, suggests that the cradle environment of life may have been a weathering fluid interacting with dry-land silicate rocks. The specific mineral assemblage provides evidence for a moderate Hadean climate with dry and wet seasons and a lower atmospheric abundance of CO2 than is present today.Fil: Novoselov, Alexey A.. Universidad de Concepción; ChileFil: Silva, Dailto. Universidade Estadual de Campinas; BrasilFil: Schneider, Jerusa. Universidade Estadual de Campinas; BrasilFil: Abrevaya, Ximena Celeste. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Chaffin, Michael S.. State University Of Colorado Boulder; Estados UnidosFil: Serrano, Paloma. Alfred Wegener Institute Helmholtz Centre For Polar And Marine Research,; AlemaniaFil: Navarro, Margareth Sugano. Universidade Estadual de Campinas; BrasilFil: Conti, Maria Josiane. André Tosello Institute; BrasilFil: Souza Filho, Carlos Roberto de. Universidade Estadual de Campinas; Brasi

Turmalinitos vulcanogênicos da formação Morro da Pedra Preta do Grupo Serra do Itaberaba (SP): petrografia, composição química da turmalina e implicações metalogenéticas

Tourmalinites associated with amphibolites, metachert, iron formation, metatuffs, metasedimentary, metavolcaniclastic and calc-silicate rocks were found in the Morro da Pedra Preta Formation, basal metavolcano-sedimentary sequence of the Serra do Itaberaba Group (São Paulo State, Brazil). The syn-sedimentary origin of the tourmalinites is attested by the deformation of the alternating tourmaline-rich and quartz-rich layers, the presence of rip-up clasts, and whole-rock chemistry similar to that of surrounding metassedimentary rocks. Microprobe analyses show that the tourmaline compositions are: 1) within the schorl-dravite series, for the examples associated with metatuffs, iron formation, metachert metavolcaniclastic and metasedimentary rocks, and 2) within the dravite-uvite series, for those associated with amphibolites, metatuffs and calc-silicate rocks. The former are characterized by low Ca and high Na and Al contents, with variable Fe and Mg contents (schorl-dravite series), whereas the latter, a F-bearing tourmaline, has low Na and Al and high Mg and Ca contents. The schorl component of the tourmaline of the proximal tourmalinites is indicative of the potential of Morro da Pedra Preta Formation for gold, which contrasts with the conditions required for the formation of volcanic massive sulphide deposits (hypersaline fluids and association with magnesian tourmalinites). The tourmaline of the various tourmalinites of the Morro da Pedra Preta Formation is not typically magnesian and its composition was more strongly influenced by the composition of the neighboring rocks than that of the hydrothermal fluids, especially when the tourmalinite was deposited in an intermediate to distal position in relation to the volcano-exhalative center.Turmalinitos associados a anfibolitos, metachert, formação ferrífera, metatufos, rochas metassedimentares, metavulcanoclásticas e calciossilicáticas são encontrados na Formação Morro da Pedra Preta, seqüência metavulcano-sedimentar basal do Grupo Serra do Itaberaba (SP - Brasil). A deformação da rocha, que é formada por leitos ricos em turmalina alternados com leitos ricos em quartzo, a presença de clastos do tipo rip-up e a química de rocha total semelhante à das rochas metassedimentares comprovam a origem sin-sedimentar dos turmalinitos. Análises químicas da turmalina por microssonda eletrônica mostram que, para a turmalina dos turmalinitos associados a metatufos, formação ferrífera, metachert e rochas metavulcanoclásticas e metassedimentares, as composições são intermediárias à série schorlita-dravita, enquanto para os turmalinitos associados a anfibolitos, metatufos e a rochas calciossilicáticas, as composições são intermediárias à série dravitauvita. As primeiras apresentam conteúdos baixos de Ca e elevados de Al e Na, com variações nos teores de Fe e Mg (série schorlita-dravita), e as últimas são caracterizadas por teores baixos de Na e Al e altos de Mg e Ca, contendo adicionalmente flúor. A componente schorlita da turmalina dos turmalinitos situados em porções proximais aos centros de atividade vulcano-exalativa de fundo oceânico é indicativa do potencial para ouro da Formação Morro da Pedra, o que contrasta com as condições requeridas para a formação de depósitos de sulfetos maciços (fluidos hipersalinos e associação com turmalinitos magnesianos). A turmalina dos vários turmalinitos da Formação Morro da Pedra Preta não é tipicamente magnesiana e sua composição foi mais fortemente influenciada pela composição das rochas circundantes do que por aquela dos fluidos hidrotermais, especialmente no caso em que o turmalinito se depositou em uma posição intermediária a distal em relação ao centro de atividade vulcano-exalativa

Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil

FAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISPetrographic and geochemical data obtained on the Araguainha impact crater (Goias/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact-induced congruent melting of an alkali-granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium-rich granite, similar to postcollisional, A-type granites, also found in terrains outside the Araguainha crater, in the Brasilia orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact-induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact.Petrographic and geochemical data obtained on the Araguainha impact crater (Goias/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact-induced congruent melting of an alkali-granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium-rich granite, similar to postcollisional, A-type granites, also found in terrains outside the Araguainha crater, in the Brasilia orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact-induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact513443467FAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISAPQ 0870/1