U-Pb dating of overpressure veins in late Archean shales reveals six episodes of Paleoproterozoic deformation and fluid flow in the Pilbara craton

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 961-965 ◽  
Author(s):  
Birger Rasmussen ◽  
Jian-Wei Zi ◽  
Janet R. Muhling ◽  
Daniel J. Dunkley ◽  
Woodward W. Fischer
Keyword(s):  
Fluid Flow ◽  
Fluid Pressure ◽  
Ore Deposits ◽  
Banded Iron Formations ◽  
Mineral Growth ◽  
History Of ◽  
Iron Formations ◽  
Discrete Populations ◽  
Orogenic Events ◽  
Pilbara Craton

Abstract Fluid flow in the upper crust not only impacts the redistribution of heat and elements, driving the formation of economic ore deposits, but it also exerts control on metamorphism, metasomatism, and deformation. However, reconstructing the history of fluid flow in ancient basins is exceedingly difficult, particularly in Archean sedimentary rocks because of extensive overprinting and recrystallization. Here, we report U-Pb ages for monazite and xenotime that grew in bedding-parallel veins in 2.63–2.5-b.y.-old shales along the southern Pilbara craton, Australia. The U-Pb ages define six discrete populations, at 2.41 Ga, 2.30 Ga, 2.20 Ga, 2.10 Ga, 2.05 Ga, and 1.66 Ga, which formed ≥200 m.y. after deposition. The abundance of bedding-parallel crack-seal and fibrous veins in banded iron formations (BIFs) and underlying shales suggests a history of episodic buildup of fluid pressure followed by microfracturing, fluid expulsion, and mineral growth. Thermometry of vein minerals indicates temperatures between 230 °C and 320 °C, implicating the migration of hydrothermal fluids. The development of bedding-parallel veins at 2.41 Ga, 2.20 Ga, and 1.66 Ga was coeval with regional orogenic events known to have affected the craton, whereas vein growth at 2.30 Ga, 2.10 Ga, and 2.05 Ga reveals new episodes of deformation and fluid flow. Our results show that well-preserved Archean shales devoid of structural fabrics and >150 km inboard of the craton margin preserve a cryptic history of fluid overpressure, crack-seal vein development, and hydrothermal fluid flow between 2.41 and 1.66 b.y. ago.

scholarly journals Rhabdophane Th-Pb ages indicate reactivation of Mesoarchean structures in west Pilbara Craton during breakup of Greater India and Australia-Antarctica

Geology ◽  
2021 ◽  
Author(s):  
Birger Rasmussen ◽  
Jian-Wei Zi ◽  
Janet R. Muhling
Keyword(s):  
Fluid Flow ◽  
Shear Zones ◽  
Drill Hole ◽  
Carbonaceous Shale ◽  
Low Grade ◽  
Early Environment ◽  
Metasedimentary Rocks ◽  
Rift Propagation ◽  
History Of ◽  
Pilbara Craton

Uranium-Th-Pb dating of phosphate minerals in very low-grade metasedimentary rocks from the Archean Pilbara Craton, Western Australia, has revealed a long history of deformation and fluid flow during the Paleoproterozoic. However, this technique has not detected evidence for fluid flow along craton margins during Phanerozoic rifting and breakup. We report the use of in situ Th-Pb geochronology of rhabdophane, a hydrous light rare earth element phosphate, to date fluid flow in shale from the 2.76 Ga Mount Roe Basalt from drill hole number 6 of the Archean Biosphere Drilling Program (ABDP6), northwestern Pilbara Craton. Thorium-Pb dating of rhabdophane in carbonaceous shale yields three main populations with weighted mean 208Pb/232Th ages of 152 ± 6 Ma, 132 ± 4 Ma, and 119 ± 4 Ma, which indicates phosphate growth up to 2.64 b.y. after deposition. The rhabdophane ages are coeval with three major breakup events in eastern Gondwana: separation of Southwest Borneo and Argoland from Australia (ca. 156–152 Ma), breakup of Greater India from Australia (ca. 140–135 Ma), and separation of Greater India/India from Antarctica (ca. 123 Ma). The proximity of drill hole ABDP6 to major Mesoarchean faults and shear zones on the craton margin, which are parallel to rift propagation and basin development, points to episodic reactivation of ancient crustal structures >2.8 b.y. after their formation. Our results also highlight the potential of rhabdophane as a U-Th-Pb geochronometer for dating low-temperature (<200 °C) fluid flow and hydrous alteration. The migration of Mesozoic fluids through Archean shales adds weight to questions about the origin of geochemical signals in ancient altered rocks and how to extract information about the early environment and biosphere.

scholarly journals Genetics and ecology of plant species occurring on the Banded Iron Formations in the Yilgarn, Western Australia

2019 ◽  
Vol 67 (3) ◽  
pp. 165
Author(s):  
Margaret Byrne
Keyword(s):  
Plant Communities ◽  
Western Australia ◽  
Conservation Status ◽  
Conservation Strategies ◽  
Individual Species ◽  
Banded Iron Formations ◽  
Topographic Complexity ◽  
Granite Outcrops ◽  
History Of ◽  
Iron Formations

Banded Iron Formations (BIFs) are a distinctive feature in the Yilgarn craton of southern Western Australia occurring as geographically isolated ranges within a mosaic of alluvial clay soils interspersed with sandplains and occasional granite outcrops. They are prominent features across a flat, highly weathered plateau, forming unique geologically stable components in an unglaciated landscape. The topographic complexity of BIFs provides areas of key environmental heterogeneity in a subdued landscape, offering a mosaic of habitats and abundance of niche microhabitats that support unique plant communities with high species diversity including many narrowly endemic species and those with distributions centred on these banded iron formations. Genetic and ecological studies have been undertaken on several species that are endemic to, or have distributions centred on, the banded iron formations of the Yilgarn. These studies provide a basis for understanding the diversity and evolutionary history of the plant communities that occur in these diverse environments. This Special Issue brings together studies on several these species to complement studies already published, and this overview provides a summary of the genetics and ecology of 21 species that are restricted to, or have distributions centred on, BIFs. Many of these species have conservation status under national and state legislation and understanding of genetics and ecology of these species assists with conservation strategies. A range of genetic patterns was identified among these species making generalisations difficult and indicating analysis of individual species is required in order to provide information for conservation and management decisions.

Bone Resorption Induced by Fluid Flow

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Lars Johansson ◽  
Ulf Edlund ◽  
Anna Fahlgren ◽  
Per Aspenberg
Keyword(s):  
Fluid Flow ◽  
Soft Tissue ◽  
Bone Resorption ◽  
Energy Density ◽  
Fluid Pressure ◽  
Time History ◽  
State Of Stress ◽  
Fluid Flow Velocity ◽  
History Of ◽  
Tissue Interface

A model where bone resorption is driven by stimulus from fluid flow is developed and used as a basis for computer simulations, which are compared with experiments. Models for bone remodeling are usually based on the state of stress, strain, or energy density of the bone tissue as the stimulus for remodeling. We believe that there is experimental support for an additional pathway, where an increase in the amount of osteoclasts, and thus osteolysis, is caused by the time history of fluid flow velocity, fluid pressure, or other parameters related to fluid flow at the bone/soft tissue interface of the porosities in the bone.

The search for protolife

1975 ◽  
Vol 189 (1095) ◽  
pp. 213-230 ◽  
Keyword(s):  
Organic Geochemistry ◽  
Convincing Evidence ◽  
Low Grade ◽  
Banded Iron Formations ◽  
The Earth ◽  
Show Evidence ◽  
History Of ◽  
The Origin Of Life ◽  
Greenstone Belts ◽  
Iron Formations

Convincing evidence for the existence of extraterrestrial protolife has been found in the organic geochemistry and fossil contents of carbonaceous meteorites. The search for prebiological protolife in the early history of the Earth has so far been concentrated on the investigation of low-grade metamorphic areas characterized by greenstone belts. Despite some puzzling isotope data, it seems likely that life had already colonized the areas represented by these low-grade terrains. It is suggested that a more profitable search could be extended to high-grade metamorphic areas, which are likely to include older rocks. Even the oldest rocks known ( ca . 4000 Ma B.P.), however, show evidence (in relics of banded iron formations, and in the presence of marble and disseminated graphite) of biological activity. It seems that carbon isotope ratios have so far provided the most powerful tool towards understanding this situation. Efforts should be directed towards identifying a period in Earth history which postdates the origin of life but antedates the origin of photosynthesis, but from present evidence it would seem that both events occurred before the formation of the oldest rocks known.

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