Arquivos mensais:junho 2020

PILLOW LAVAS, BLUESCHISTS AND OTHER ANCIENT OCEANIC ROCKS / LAVAS EM ALMOFADA, XISTOS AZUIS E OUTRAS ROCHAS OCEÂNICAS ANTIGAS

Angel Island, San Francisco Bay, is one of the most geologically interesting places, with pilllow basalts, blueschists and serpentinites and wackes. These rocks have been scraped from the subducting plate and represent remnants of a Jurassic oceanic crust, now completely tectonically mixed, in what is called mélange (mixture in French). The Franciscan mélange was formedContinuar lendo “PILLOW LAVAS, BLUESCHISTS AND OTHER ANCIENT OCEANIC ROCKS / LAVAS EM ALMOFADA, XISTOS AZUIS E OUTRAS ROCHAS OCEÂNICAS ANTIGAS”

Microbes influence the formation of iron deposits and can be used in energy fuel cells / Micróbios influenciam na formação de depósitos de ferro e podem ser usados em células de geração de energia

Banded Iron Formations are characteristic iron-rich rocks. The deposition of these rocks occured in specific time intervals in Earth history, such as during the first Great Oxygenation Event (GOE) at ca. 2.4-2.2 billion years ago and after the Neoproterozoic Snowball Earth glaciations (Rapitan-type iron formations). A number of factors seem to have been interconnected inContinuar lendo “Microbes influence the formation of iron deposits and can be used in energy fuel cells / Micróbios influenciam na formação de depósitos de ferro e podem ser usados em células de geração de energia”

THE AGE OF MOUNTAINS AND CONTINENTS FROM TINY MINERALS /A IDADE DAS MONTANHAS E DOS CONTINENTES EM PEQUENOS MINERAIS

Some minerals found in rocks are special in that they accommodate a lot of specific chemical elements in their structures and almost none of other elements. This is the case of zircon (ZrSiO4), which likes Uranium but allow almost no Lead in it’s structure. This turns zircon in an ideal mineral to calculate the ageContinuar lendo “THE AGE OF MOUNTAINS AND CONTINENTS FROM TINY MINERALS /A IDADE DAS MONTANHAS E DOS CONTINENTES EM PEQUENOS MINERAIS”

Stromatolites, the oldest living fossils, part 2: Lagoa Salgada, Rio de Janeiro, Brazil / Estromatólitos, os mais velhos fósseis vivos, parte 2: Lagoa Salgada

Another place where we can find recent stromatolites, Earth’s oldest living fossils (see last post for more info) is at Lagoa Salgada, Rio de Janeiro, Brazil. The pools are for salt evaporation and exploration. Thanks @samyrvq for the very cool pics! Outro local onde podemos encontrar estromatólitos recentes, os fósseis vivos mais antigos da TerraContinuar lendo “Stromatolites, the oldest living fossils, part 2: Lagoa Salgada, Rio de Janeiro, Brazil / Estromatólitos, os mais velhos fósseis vivos, parte 2: Lagoa Salgada”

Stromatolites, the oldest living fossils – part 1: Shark Bay, Australia / Estromatólitos, os mais velhos fósseis vivos, parte 1: Shark Bay

Stromatolites are the oldest known evidence of life, dating back to more than 3.5 billion years ago. They are formed by colonies of cyanobacteria that trap mostly calcareous sediments in column-shaped structures. Nowadays they only occur in places with high salinity where animals that mess up the ocean floor in search of food (the seagrazers)Continuar lendo “Stromatolites, the oldest living fossils – part 1: Shark Bay, Australia / Estromatólitos, os mais velhos fósseis vivos, parte 1: Shark Bay”

Graphite deposits, burial of organic carbon and the first appearance of complex life forms / Depósitos de grafita, soterramento de carbono orgânico e a primeira aparição das formas de vida complexas

Graphite is a natural form of carbon crystallized under lower pressures and temperatures than those needed to stabilize diamond. It is a very important mineral resource with applications in the steel industry, as a lubricant, in refractories, paints, oven and brake linings, brushes, batteries, electrodes, pencils, explosives, magnetic tapes, fertilizers and in the making ofContinuar lendo “Graphite deposits, burial of organic carbon and the first appearance of complex life forms / Depósitos de grafita, soterramento de carbono orgânico e a primeira aparição das formas de vida complexas”

APATITE FISSION TRACKS and mountain denudation / TRAÇOS DE FISSÃO EM APATITA e denudação das montanhas

Those small minerals can help to understand how quickly a mountain belt is eroded. The method is based on the decay of radiogenic elements within the mineral structure, which leaves small tracks due to the damage caused by the nuclear disintegration. By counting the density and length of the tracks, we can estimate the timeContinuar lendo “APATITE FISSION TRACKS and mountain denudation / TRAÇOS DE FISSÃO EM APATITA e denudação das montanhas”

PLAGIOGRANITE – a very important component of the ocean floor!

PLAGIOGRANITO – um componente muito importante do fundo do oceano! Do you know what plagiogranite is? This very special type of granite is composed of plagioclase with small amounts of quartz and ferromagnesian minerals. They were long recognized as very important parts of ophiolitic complexes, rocks that represent ancient pieces of ocean floor that areContinuar lendo “PLAGIOGRANITE – a very important component of the ocean floor!”

Aragonite crystal fans in 3D

Aragonite crystal fans in three dimensional view, with pseudo-hexagonal sections in the surface where the coin is resting and prismatic sections in the side cut. Those beautiful crystals are precipitated directly on the seafloor when the ocean is supersatured in CaCO3. This happened ca. 630-540 million years ago, after a global glaciation created ice capsContinuar lendo “Aragonite crystal fans in 3D”