Ultramafic-Hosted Hydrothermal Systems at Mid-Ocean Ridges: Chemical and Physical Controls on pH, Redox and Carbon Reduction Reactions

2013 ◽  
pp. 267-284 ◽  
Author(s):  
W. E. Seyfried ◽  
D. I. Foustoukos ◽  
D. E. Allen
Keyword(s):  
Hydrothermal Systems ◽  
Reduction Reactions ◽  
Carbon Reduction ◽  
Ocean Ridges ◽  
Physical Controls

scholarly journals The Geology of the Torlesse Supergroup, Southern Tararua Range, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Thomas O. H. Orr
Keyword(s):  
Active Continental Margin ◽  
Accretionary Prism ◽  
Hydrothermal Systems ◽  
Late Triassic ◽  
Geochemical Data ◽  
Submarine Fan ◽  
Ocean Ridges ◽  
Basement Rocks ◽  
Prism Model ◽  
Feldspathic Sandstone

<p>Basement rocks in the southern Tararua Range are part of the Torlesse Supergroup, possibly Late Triassic to Late Jurassic in age, and form two distinct associations. The sedimentarv association consists mainly of quartzo-feldspathic sandstone and argillite with minor olistostrome, calcareous siltstone and microsparite. The sandstone and argillite were deposited as turbidites in a mid- to outer- submarine fan environment. The sediment was derived from a heavily dissected active continental margin that was shedding sediment of mainly plutonic and metamorphic origin. The volcanic association consists mainly of metabasite and coloured argillite with minor chert and limestone. Geochemical data indicate that the metabasites were erupted in an oceanic intraplate environment. The nature of amygdules in amygdaloidal metabasites suggests eruption in less than 800m of water. Coloured argillites have two distinct origins, namely sediments formed by the degredation of basalt; and also pelagic material modified by metal-rich effluent either from hydrothermal systems associated with mid-ocean ridges or intraplate volcanism. The rocks of the volcanic association indicate formation in an environment similar to present day mid-ocean islands. Nowhere were rocks of the two associations observed to be conformable. Coupled with this, the nature of the two associations suggests that they were formed in separate environments. The following structural history is proposed: 1) Early veining; 2) Isoclinal folding and development of a NNE striking cleavage; 3) Faulting both at low and high angles to bedding, extreme amounts of which have resulted in mélange; 4) NE-SW trending close to open folds; 5) E-W trending open to gentle folds; 6) Recent faulting, predominantly NE trending strike-slip faults. The nature of the two associations and the deformational style and history supports an accretionary prism model for the development of the Torlesse Supergroup. Rocks of the southern Tararua Range show many similarities with, and probably represent a northward continuation of, the Esk Head Mélange of the South Island.</p>

scholarly journals The Geology of the Torlesse Supergroup, Southern Tararua Range, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Thomas O. H. Orr
Keyword(s):  
Active Continental Margin ◽  
Accretionary Prism ◽  
Hydrothermal Systems ◽  
Late Triassic ◽  
Geochemical Data ◽  
Submarine Fan ◽  
Ocean Ridges ◽  
Basement Rocks ◽  
Prism Model ◽  
Feldspathic Sandstone

<p>Basement rocks in the southern Tararua Range are part of the Torlesse Supergroup, possibly Late Triassic to Late Jurassic in age, and form two distinct associations. The sedimentarv association consists mainly of quartzo-feldspathic sandstone and argillite with minor olistostrome, calcareous siltstone and microsparite. The sandstone and argillite were deposited as turbidites in a mid- to outer- submarine fan environment. The sediment was derived from a heavily dissected active continental margin that was shedding sediment of mainly plutonic and metamorphic origin. The volcanic association consists mainly of metabasite and coloured argillite with minor chert and limestone. Geochemical data indicate that the metabasites were erupted in an oceanic intraplate environment. The nature of amygdules in amygdaloidal metabasites suggests eruption in less than 800m of water. Coloured argillites have two distinct origins, namely sediments formed by the degredation of basalt; and also pelagic material modified by metal-rich effluent either from hydrothermal systems associated with mid-ocean ridges or intraplate volcanism. The rocks of the volcanic association indicate formation in an environment similar to present day mid-ocean islands. Nowhere were rocks of the two associations observed to be conformable. Coupled with this, the nature of the two associations suggests that they were formed in separate environments. The following structural history is proposed: 1) Early veining; 2) Isoclinal folding and development of a NNE striking cleavage; 3) Faulting both at low and high angles to bedding, extreme amounts of which have resulted in mélange; 4) NE-SW trending close to open folds; 5) E-W trending open to gentle folds; 6) Recent faulting, predominantly NE trending strike-slip faults. The nature of the two associations and the deformational style and history supports an accretionary prism model for the development of the Torlesse Supergroup. Rocks of the southern Tararua Range show many similarities with, and probably represent a northward continuation of, the Esk Head Mélange of the South Island.</p>

Unveiling the volcanic evolution of the Mohns Ridge

2021 ◽  
Author(s):  
Håvard Stubseid ◽  
Anders Bjerga ◽  
Haflidi Haflidason ◽  
Rolf Birger Pedersen
Keyword(s):  
Autonomous Underwater Vehicles ◽  
Volcanic Eruptions ◽  
Integrated Approach ◽  
Hydrothermal Systems ◽  
Ocean Ridges ◽  
Spreading Ridges ◽  
Geological Evolution ◽  
Fast Spreading ◽  
Slow Spreading ◽  
Resolution Dataset

&lt;p&gt;Volcanic eruptions are far less common along slow-spreading ridges compared to fast-spreading ridges. Consequently, knowledge of the volcanic rejuvenation along close to 1/3 of the global mid-ocean ridges is poorly constrained. To determine the temporal evolution of the rift valley of one of the slowest spreading-ridges in the world, the Mohns Ridge in the Norwegian-Greenland Sea, we have interpreted more than 3000 km of sub-bottom profiles. Sedimentation rates derived from several core locations along the ridge are used to calculate the age of the underlying volcanic crust. Here we present a framework for understanding the geological evolution of rift valleys of slow-spreading ridges using an integrated approach combining geological and geophysical data. The high-resolution dataset acquired using autonomous underwater vehicles, cover more than 50% of the 575 km long Mohns Ridge. The results unravel large variation in sediment thickness inside the central rift area, from exposed basalts to several meters of sediments, within only a few hundreds of meters. Studied sub-bottom profiles reveal active volcanism in the deepest parts of the ridge, areas thought to be inactive, surrounded by significantly older crust covered in meters of sediments. We find that all axial volcanic ridge systems (AVRs) in our area completely renewed their surface within the last 30-50 ka. Detailed volcanological investigation of the central parts of an AVR reveal at least 72 individual eruptions during the last 20 ka ranging in size from 1.2x10&lt;sup&gt;3 &lt;/sup&gt;m&lt;sup&gt;2&lt;/sup&gt; - 2.6 x10&lt;sup&gt;5&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt;. These estimates have been verified with visual observations and sampling using an ROV. Our estimates indicate that more than 230 eruptions are required to renew the surface of an average AVR. Based on the acquired age assessments a volcanic eruption is anticipated to occur approximately every 200 years. Volcanic renewal is a first order control on the lifetime of magmatically driven hydrothermal systems.&lt;/p&gt;

scholarly journals Exploring the Restless Floor of Yellowstone Lake

Eos ◽  
2017 ◽  
Author(s):  
Robert Sohn ◽  
Robert Harris ◽  
Chris Linder ◽  
Karen Luttrell ◽  
David Lovalvo ◽  
...  
Keyword(s):  
Research Team ◽  
Hot Springs ◽  
Hydrothermal Systems ◽  
Yellowstone Lake ◽  
Ocean Ridges

Yellowstone Lake, far from any ocean, hosts underwater hot springs similar to those on mid-ocean ridges. A research team is investigating the processes that drive the lake’s hydrothermal systems.

A magnesium budget for serpentinisation of abyssal peridotite during the Cenozoic

2020 ◽  
Author(s):  
Andrew Merdith ◽  
Muriel Andreani ◽  
Isabelle Daniel ◽  
Thomas Gernon
Keyword(s):  
Isotopic Composition ◽  
Earth Science ◽  
Oceanic Lithosphere ◽  
Relative Magnitude ◽  
Spreading Rate ◽  
Hydrothermal Systems ◽  
Iron Hydroxides ◽  
Geological Time ◽  
Ocean Ridges ◽  
Magnesium Loss

&lt;p&gt;The marked increase in seawater Mg/Ca during the Cenozoic is poorly understood, due to the limited availability of proxy data and uncertainty in elucidating the respective contributions of Mg sources and sinks through geological time&lt;sup&gt;1&lt;/sup&gt;. Though established as a potentially large source of dissolved Mg over twenty years ago, the weathering of abyssal peridotites&lt;sup&gt;2&lt;/sup&gt; is a largely unexplored potential source of Mg to oceanic budgets. The release of magnesium from peridotite weathering can occur in high temperature environments, during serpentinisation near the ridge axis&lt;sup&gt;3&lt;/sup&gt;, as well as low temperature off-axis environments where peridotite and serpentinite are altered to clays, carbonates and silicates&lt;sup&gt;4&lt;/sup&gt;. The relative magnitude of Mg fluxes from these sources are poorly constrained. Recent studies, however, now provide a general method for estimating bulk crustal lithologies of mid-ocean ridges based on spreading rate (i.e. proportion and mass of basalts, gabbros, peridotites and serpentinised peridotite) through time&lt;sup&gt;5&lt;/sup&gt;&amp;#8212;enabling us to quantitatively assess potential Mg contributions from these different environments.&lt;/p&gt;&lt;p&gt;We constructed a model for oceanic crustal weathering (proportional to depth below the seafloor) to develop estimates of the mass and isotopic composition of magnesium loss from peridotite during alteration in both high- and low-T environments. As Mg fractionation occurs predominantly in low-T reactions, the primary serpentinisation reaction in near-ridge environments is unlikely to result in isotopic differentiation. Comparably, the secondary low-T alterations, of both remaining peridotites (to clays and iron hydroxides) and serpentinite (e.g. to talc and dolomite) are likely to result in the fractionation of Mg. We extend our analysis to incorporate the fractionation of these systems&lt;sup&gt;4&lt;/sup&gt; and their release of Mg into the ocean. We completed our analysis by presenting a compilation of fluid data for magnesium concentrations in ultramafic bodies from hydrothermal systems, in order to evaluate our model.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;(1) Staudigel, H. &quot;Chemical fluxes from hydrothermal alteration of the oceanic crust.&quot; (2014): 583-606.&lt;/p&gt;&lt;p&gt;(2) Snow, J.E. and Dick, H.J., 1995. Pervasive magnesium loss by marine weathering of peridotite. Geochimica et Cosmochimica Acta, 59(20), pp.4219-4235.&lt;/p&gt;&lt;p&gt;(3) Seyfried Jr, W.E., Pester, N.J., Ding, K. and Rough, M., 2011. Vent fluid chemistry of the Rainbow hydrothermal system (36 N, MAR): Phase equilibria and in situ pH controls on subseafloor alteration processes.&amp;#160;Geochimica et Cosmochimica Acta,&amp;#160;75(6), pp.1574-1593.&lt;/p&gt;&lt;p&gt;(4) Liu, P.P., Teng, F.Z., Dick, H.J., Zhou, M.F. and Chung, S.L., 2017. Magnesium isotopic composition of the oceanic mantle and oceanic Mg cycling.&amp;#160;Geochimica et Cosmochimica Acta,&amp;#160;206, pp.151-165.&lt;/p&gt;&lt;p&gt;(5) Merdith, A.S., Atkins, S.E. and Tetley, M.G., 2019. Tectonic controls on carbon and serpentinite storage in subducted upper oceanic lithosphere for the past 320 Ma.&amp;#160;Frontiers in Earth Science,&amp;#160;7, p.332.&lt;/p&gt;

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