scholarly journals 3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt—Paleoarchean crust in cold environments

2016 ◽  
Vol 2 (2) ◽  
pp. e1500368 ◽  
Author(s):  
Maarten J. de Wit ◽  
Harald Furnes
Keyword(s):  
South Africa ◽  
Sea Level ◽  
Volcanic Rocks ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Sea Floor ◽  
Cold Environments ◽  
Barberton Greenstone Belt ◽  
Mineral Growth ◽  
Hydrothermal Fields

Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth’s surface temperatures in the early Archean were similar to those in more recent times.

Magmatic-Hydrothermal Fluids

Elements ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 401-406 ◽  
Author(s):  
Andreas Audétat ◽  
Marie Edmonds
Keyword(s):  
Metal Content ◽  
Fluid Phase ◽  
Volcanic Eruptions ◽  
Hydrothermal Systems ◽  
Ore Deposits ◽  
Hydrothermal Fluids ◽  
Geological Processes ◽  
Mineral Growth ◽  
Fluid Saturation ◽  
Fluid Phase Equilibria

Magmatic-hydrothermal fluids play a key role in a variety of geological processes, including volcanic eruptions and the formation of ore deposits whose metal content is derived from magmas and transported to the site of ore deposition by means of hydrothermal fluids. Here, we explain the causes and consequences of fluid saturation in magmas, the corresponding fluid-phase equilibria, and the behavior of metals and ligands during the transition from magma to an exsolved hydrothermal fluid. Much of what we know about magmatic-hydrothermal systems stems from the study of fluid inclusions, which are minute droplets of fluids trapped within minerals during mineral growth.

scholarly journals MORPHOLOGY OF LESVOS' ISLAND COASTS

2018 ◽  
Vol 36 (2) ◽  
pp. 1008
Author(s):  
Γ. Λειβαδίτης ◽  
Α. Αλεξούλη-Λειβαδίτη
Keyword(s):  
Sea Level ◽  
Salt Marshes ◽  
Volcanic Rocks ◽  
Tectonic Activity ◽  
Sea Floor ◽  
Ecological Importance ◽  
Rocky Coast ◽  
Wave Erosion ◽  
Rock Strata ◽  
Sand Flats

The morphology of the coasts of the island of Lesvos is controlled mainly by the erosivity of the volcanic rocks that form >51.2% of the coasts of the island. Thus, the NE, Ν, W and the biggest part of the S coasts consist exclusively of volcanic rocks, with the E coast and the remaining part of the S coast to be formed by metamorphic rocks i.e. schists, phyllites and matbles, being the 31.7% of the coast. Neogene and alluvial formations occupy the coast of the Geras and Kalloni Gulfs and secondarily some other bays representing an area of 15.7%, with the remaining 1.4% of the coast to be consisted of peridotites and serpentinites. The coasts formed by Neogene and Quaternary deposits are rather gentle incorporating small bays where beaches have been formed. Furthermore, in the case of Geras and Kalloni Gulfs lagoons and swamps (permanent and/or seasonal) have been formed due to the low gradients of the coastal zone, the increased sediment fluxes from torrents and the low-energy wave and current regime; these wetlands are of great ecological importance. Beach zone consists of sand and pebbles of varying size, whilst the backshore zone is covered by grass and is traversed by scattered creeps. Beach rocks have been identified below or under the sea level, which are present in coasts of carbonate rocks but they are absent from those of volcanic rocks. The study of beach rocks showed a discontinuous uplifting of the sea level which reaches up to 3m during the last 4000-4500 years. Sloping coasts of various angles (from a few degrees up to 40-60 degrees) with a rather smooth relief deep into the sea; their slope remains the same above and under the sea level. Lithologically, these coasts consist mainly of volcanic rocks. This type of coast does not belong to the category of actively retreating coasts. Cliffs constitute another category of coasts. They vary from cliffs of few meters height (2 - 3 m) to cliffs of bigger size (falaise), being the product of marine erosion. These coasts belong to the category of actively retreating coasts. Along their coastline intensive erosion is observed; whilst in some places blocks of the retreating rocky coast remain offshore. In other places narrow shores, consisting of sand and pebbles, are formed on the foot of the cliff. The most steep coasts are formed primarily in acid volcanic rocks (pyroclastic, ryolitic) and secondarily in other type of volcanic rocks. In the case of intensively broken cracked loose rocky formations, rockfalls are also occurred frequently. In the case of formations that undergone intensive tectonic activity, weathering and eronional processes are amplified resulting to the formation of a thick weathered horizon, which with the underlain broken rock-strata often comes into a fragile equilibrium that results to rockfalls. Finally, along both the gently sloping coasts and the cliffed coasts are formed pocket beaches. The coasts of Lesvos are characterized genetically according to the classification system of Shepard (1963), in primary and secondary coasts. I) Primary coasts. 1) Alluvial plain coasts 2) Wind deposition coasts. 3) a) Dunes. Sand flats form in front of dunes. 4) Landslides coasts. 5) Volcanic coasts. 6) Fault coasts. II) Secondary coasts shaped mainly by marine agencies of erosion or deposition. 1 ) Coasts that were created by the erosion of waves. We distinguish: a) Wave straitened cliffs. They are distinguished from the fault coasts because they bordered by gently inclined sea floor. 2) Made irregular by wave erosion. 3 Beaches. Enough widespread type of coasts covered by sand, gravel etc. 4 Salt Marshes and marsh grass coasts. 5 Swamps and Lagoons.

The geochemistry of gold-bearing chemical sediments, Dickenson Mine, Red Lake, Ontario: a reconnaissance study

1981 ◽  
Vol 18 (3) ◽  
pp. 624-637 ◽  
Author(s):  
R. Kerrich ◽  
B. J. Fryer ◽  
K. J. Milner ◽  
M. G. Peirce
Keyword(s):  
Volcanic Rocks ◽  
Hydrothermal Fluids ◽  
Base Metals ◽  
Sea Floor ◽  
Red Lake ◽  
Reconnaissance Survey ◽  
Rare Elements ◽  
Chemical Sediments ◽  
Mobile Base ◽  
Gold Bearing

Auriferous sedimentary rocks at the Dickenson Mine, Red Lake, are characterized by large enrichments of rare elements (Au, Ag, Pd, As, Sb, B) and metals conventionally considered to be relatively immobile (Ni, W), with negligible concentrations of the abundant and mobile base metals. Based on a reconnaissance survey involving 12 rocks analysed for 42 elements, these sediments can be represented in terms of a mixture of two components―mafic volcaniclastic material and hydrothermal precipitates. The volcaniclastic component has a composition closely comparable to mafic volcanic rocks that conformably envelope the sediments, and contributes all of the Al, Ti, V, Sc, Zr, and F. The hydrothermal component donates Si, Fe, Mn, Mg, Ca, K, Si, and C, together with Au, Ag, Pd, As, Sb, B, W, and Ni. Chromium and nickel are contributed from both sources. Alteration of the mafic volcanic rocks that envelope the auriferous sediments involved fixation of Si, K, and CO2, in contrast to the typical patterns of metasomatism in footwall rocks to base metal massive sulphide deposits, which are characterized by Mg, Fe (Si, S) addition.Quartz isolated from chert within the auriferous sediments and volcanic rocks has a maximum δ18O of 19‰, which is within the range of δ values for marine cherts of ~2.8 Ga, and signifies precipitation in equilibrium with ambient marine water of ~−1‰ at ~70–90 °C. Mafic volcanic wall rocks to the sediments have whole-rock δ18O values of 16–17‰ and Δquartz–chlorite ≤ 2‰. The anomalously heavy whole-rock isotopic composition and small quartz–chlorite fractionation may result from the growth of chlorite from precursors such as zeolites and smectite. Alternatively, chlorite or its precursors may have become enriched in 18O by isotope exchange with metamorphic hydrothermal fluids that become ponded when discharge to the hydrosphere was capped by overlying basalts.Rare earth element (REE) distributions in sediments and mafic volcanic wall rocks are characterized by relatively flat normalized patterns up to Sm–Gd, followed by an abrupt continuous decline in abundance. This implies modification of the primary tholeiitic abundances by hydrothermal solutions capable of mobilizing heavy REE's relative to light REE's. The environment that would satisfy the geological observations and chemical data is one of metamorphic hydrothermal fluids emmanating onto the sea floor during a period of relatively quiescent mafic submarine volcanism, with subsequent capping of the discharge during emplacement of the overlying pillow basalts.

scholarly journals A Systematic Assessment of Stable Sr Isotopic Compositions of Vent Fluids in Arc/Back-Arc Hydrothermal Systems: Effects of Host Rock Type, Phase Separation, and Overlying Sediment

2020 ◽  
Vol 8 ◽  
Author(s):  
Toshihiro Yoshimura ◽  
Shigeyuki Wakaki ◽  
Tsuyoshi Ishikawa ◽  
Toshitaka Gamo ◽  
Daisuke Araoka ◽  
...  
Keyword(s):  
Host Rock ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Hydrothermal Systems ◽  
Systematic Assessment ◽  
Average Value ◽  
Carbonate Sedimentation ◽  
The North ◽  
Back Arc ◽  
Hydrothermal Fields

Variations in the stable isotopic composition of seawater Sr (δ88Sr) is a new tool for estimating the rates of global carbonate sedimentation over geologic time, yet the isotope compositions of the major sources and sinks of Sr to the world oceans are still in need of further constraint. We report δ88Sr values of vent fluids from arc/back-arc seafloor hydrothermal systems in the western Pacific. In the sediment-starved hydrothermal fields of the Manus Basin, Izu-Bonin Arc, and Mariana Trough, the δ88Sr values of end-member fluids for each site showed little variation (0.29–0.30‰) and were close to the average value of oceanic volcanic rocks, reflecting dissolved Sr sourced from host rocks. Chlorine-depleted fluids from phase-separated hydrothermal systems in the North Fiji Basin had the end-member δ88Sr values of 0.26, 0.28, and 0.29‰. Thus, both sediment-starved and phase-separated vent fluids had the end-member δ88Sr values indistinguishable from or very close to the range of oceanic volcanic rocks. Therefore, the δ88Sr compositions in these hydrothermal sites are controlled predominantly by Sr sourced from host rock with a small influence from secondary mineral precipitation/re-dissolution. Fluids from the sediment-hosted hydrothermal fields of the Okinawa Trough, however, were characterized by low δ88Sr values of approximately 0.22‰ and high 87Sr/86Sr ratios, indicating interactions with sedimentary carbonates. As for the modern oceanic δ88Sr budget, the sediment-hosted sites lower the global hydrothermal δ88Sr. Since both sediment-starved and -hosted hydrothermal systems provide a long-term control on the global Sr cycle, the end-member δ88Sr value is an important constraint on the evolution of Sr cycling in past oceans.

scholarly journals Hydrothermal recycling of sedimentary ammonium into oceanic crust and the Archean ocean at 3.24 Ga

Geology ◽  
2021 ◽  
Author(s):  
E.E. Stüeken ◽  
T.J. Boocock ◽  
A. Robinson ◽  
S. Mikhail ◽  
B.W. Johnson
Keyword(s):  
Oceanic Crust ◽  
Hydrothermal Vents ◽  
Nutrient Recycling ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Biological Productivity ◽  
Recycling Process ◽  
Fixed Nitrogen

The Archean ocean supported a diverse microbial ecosystem, yet studies suggest that seawater was largely depleted in many essential nutrients, including fixed nitrogen. This depletion was in part a consequence of inefficient nutrient recycling under anoxic conditions. Here, we show how hydrothermal fluids acted as a recycling mechanism for ammonium (NH4+) in the Archean ocean. We present elemental and stable isotope data for carbon, nitrogen, and sulfur from shales and hydrothermally altered volcanic rocks from the 3.24 Ga Panorama district in Western Australia. This suite documents the transfer of NH4+ from organic-rich sedimentary rocks into underlying sericitized dacite, similar to what is seen in hydrothermal systems today. On modern Earth, hydrothermal fluids that circulate through sediment packages are enriched in NH4+ to millimolar concentrations because they efficiently recycle organic-bound N. Our data show that a similar hydrothermal recycling process dates back to at least 3.24 Ga, and it may have resulted in localized centers of enhanced biological productivity around hydrothermal vents. Last, our data provide evidence that altered oceanic crust at 3.24 Ga was enriched in nitrogen, and, when subducted, it satisfies the elemental and isotopic source requirements for a low-N, but 15N-enriched, deep mantle nitrogen reservoir as sampled by mantle plumes.

scholarly journals Analysis of Hydrothermal Systems Beneath Tayukeng through Long-Term Geochemical Signals of Hydrothermal Fluids in Tatun Volcano Group, Taiwan

2021 ◽  
Vol 18 (14) ◽  
pp. 7411
Author(s):  
Hsin-Fu Yeh ◽  
Hung-Hsiang Hsu
Keyword(s):  
Surface Temperature ◽  
Hydrothermal System ◽  
Hydrothermal Fluid ◽  
Thermal Water ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Geochemical Variations ◽  
Northern Taiwan

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles. The Tayukeng (TYK) area is the most active fumarole site in the TVG. In this study, we analyzed the long-term geochemical variations of hydrothermal fluids and proposed a mechanism responsible for the variation in TYK. There are two different aquifers beneath the TYK area: a shallow SO42−-rich aquifer and a deeper aquifer rich in Cl−. TYK thermal water was mainly supplied by the shallow SO42−-rich aquifer; therefore, the thermal water showed high SO42− concentrations. After 2015, the inflow of deep thermal water increased, causing the Cl− concentrations of the TYK to increase. Notably, the inferred reservoir temperatures based on quartz geothermometry increased; however, the surface temperature of the spring decreased. We inferred that the enthalpy was lost during transportation to the surface. Therefore, the surface temperature of the spring does not increase with an increased inflow of deep hydrothermal fluid. The results can serve as a reference for understanding the complex evolution of the magma-hydrothermal system in the TVG.

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

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