scholarly journals Steadying Mid-Ocean Ridge Spreading Rates

Eos ◽  
2020 ◽  
Vol 101 ◽  
Author(s):  
Kate Wheeling
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Data Set ◽  
Mid Ocean Ridge ◽  
History Of ◽  
Spreading Rates ◽  
Ocean Ridge

Researchers used an up-to-date global magnetic anomaly data set to track the history of magnetic field reversals and obtain more accurate estimates of tectonic spreading rates.

scholarly journals Rift- and subduction-related crustal sequences in the Jinshajiang ophiolitic mélange, SW China: Insights into the eastern Paleo-Tethys

Lithosphere ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 821-833
Author(s):  
Wen-Jun Hu ◽  
Hong Zhong ◽  
Wei-Guang Zhu ◽  
Zhong-Jie Bai
Keyword(s):  
Mantle Metasomatism ◽  
Spreading Ridge ◽  
Crustal Assimilation ◽  
Ophiolitic Mélange ◽  
Mid Ocean Ridge ◽  
History Of ◽  
T Values ◽  
Ocean Ridge ◽  
Subducting Slab ◽  
Important Branch

Abstract The Paleozoic Jinshajiang ophiolitic mélange in southwest China marks an important branch ocean (i.e., the Jinshajiang Ocean) of the Paleo-Tethys. Basic-intermediate rocks are widespread features in the mélange; their formation age is well known, but the petrogenesis has not been well studied, which means that the evolutionary history of the Jinshajiang Ocean is not well constrained. To understand the nature of the mélange and the ocean, we present a set of elemental and isotopic data from two typical crustal sequences in two areas of the Jinshajiang ophiolitic mélange, Zhiyong and Baimaxueshan. The basalts in the ca. 343 Ma Zhiyong crustal sequence show mid-ocean-ridge basalt–like geochemical compositions with Nb/La ratios of 0.98–1.15 and εNd(t) values of +6.5 to +7.7, indicating that the basalts formed in the spreading ridge of the ocean. In contrast, the 283 Ma Baimaxueshan crustal sequence consists of gabbros and basaltic-andesitic lavas, which have an arc affinity with Nb/La ratios of 0.54–0.67 and εNd(t) values of +5.1 to +6.5. The geochemical differences were not caused by crustal assimilation but reflect mantle metasomatism by fluids dehydrated from the subducting slab. Therefore, we propose that the Zhiyong and Baimaxueshan crustal sequences formed in seafloor spreading and subduction settings, which were related to the opening and closure of the ocean, respectively.

Melvicalathis, a new brachiopod genus (Terebratulida: Chlidonophoridae) fromdeep sea volcanic substrates, and the biogeographic significance of the mid-oceanridge system

Zootaxa ◽  
2008 ◽  
Vol 1866 (1) ◽  
pp. 136 ◽  
Author(s):  
DAPHNE E. LEE ◽  
MURRAY R. GREGORY ◽  
CARSTEN LÜTER ◽  
OLGA N. ZEZINA ◽  
JEFFREY H. ROBINSON ◽  
...  
Keyword(s):  
Deep Sea ◽  
New Genus ◽  
Significant Component ◽  
Ocean Ridges ◽  
Southeast Indian Ridge ◽  
Mid Ocean Ridge ◽  
History Of ◽  
Cryptic Habitats ◽  
Ocean Ridge ◽  
Ridge System

Brachiopods form a small but significant component of the deep-sea benthos in all oceans. Almost half of the 40 brachiopod species so far described from depths greater than 2000 m are small, short-looped terebratulides assigned to two superfamilies, Terebratuloidea and Cancellothyridoidea. In this study we describe Melvicalathis, a new genus of cancellothyridoid brachiopod (Family Chlidonophoridae; Subfamily Eucalathinae) from ocean ridge localities in the south and southeast Pacific Ocean, and cryptic habitats within lava caves in glassy basalt dredged from the Southeast Indian Ridge, Indian Ocean. These small, punctate, strongly-ribbed, highly spiculate brachiopods occur at depths between 2009 m and 4900 m, and appear to be primary colonisers on the inhospitable volcanic rock substrate. The ecology and life-history of Melvicalathis and related deep-sea brachiopods are discussed. Brachiopods are rarely reported from the much-studied but localised hydrothermal vent faunas of the mid ocean ridge systems. They are, however, widespread members of a poorly known deep-sea benthos of attached, suspension-feeding epibionts that live along the rarely sampled basalt substrates associated with mid-ocean ridge systems. We suggest that these basalt rocks of the mid-ocean ridge system act as deep-sea “superhighways” for certain groups of deep-sea animals, including brachiopods, along which they may migrate and disperse. Although the mid-ocean ridges form the most extensive, continuous, essentially uniform habitat on Earth, their biogeographic significance may not have been fully appreciated.

On: “Suppression of sea‐floor‐scattered energy using a dip‐moveout approach—Application to the mid‐ocean ridge environment” by G. M. Kent, I. I. Kim, A. J. Harding, R. S. Detrick, and J. A. Orcutt (May‐June 1996 GEOPHYSICS, 61, 821–834)

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 316-318
Author(s):  
A. J. Calvert
Keyword(s):  
Sea Floor ◽  
Counter Example ◽  
Scattered Energy ◽  
Mid Ocean Ridge ◽  
Out Of Plane ◽  
History Of ◽  
The Common ◽  
Velocity Filtering ◽  
Ocean Ridge ◽  
Water Depths

In their paper, Kent et al. (1996) present an excellent case history of the use of dip moveout (DMO) and velocity‐filtering in the common midpoint (CMP) domain for the suppression of out‐of‐plane arrivals scattered from a deep sea‐floor. However, they imply that as a result of a “small offset approximation” the use of DMO in this way is limited to surveys recorded in water depths of at least a few kilometers with conventional streamer offsets. This is incorrect. I argue here that the application of DMO will reduce to water velocity the stacking velocity of arrivals scattered from the upper surface of the seafloor without any restriction on water depth. Furthermore, I argue that this use of DMO is simply an example of the equivalence between 2-D and 3-D DMO for marine surveys where all source‐receiver azimuths are equal, and that no “small offset approximation” is required. I first present a counter‐example to the claim of Kent et al. (1996) that seafloor scattering cannot be suppressed using DMO in shallow water, and then consider in more detail their argument for the application of DMO to out‐of‐plane scattering. In the discussion that follows, I only consider DMO in the context of a constant velocity medium.

Porphyry intrusions and albitites in the Bardoc–Kalgoorlie area, Western Australia, and their role in Archean epigenetic gold mineralization

1992 ◽  
Vol 29 (8) ◽  
pp. 1609-1622 ◽  
Author(s):  
W. K. Witt
Keyword(s):  
Western Australia ◽  
Gold Mineralization ◽  
Shear Zones ◽  
Rock Composition ◽  
Gold Mines ◽  
Mid Ocean Ridge ◽  
History Of ◽  
Compatible Elements ◽  
Ocean Ridge ◽  
Textural Evidence

Minor intrusions in the Menzies – Kambalda greenstone belt of the Archean Eastern Goldfields Province, Western Australia, range from quartz–feldspar porphyry to plagioclase–hornblende porphyry. The porphyries display enrichment of mobile and incompatible elements (K to Zr) and depletion of relatively compatible elements, with negative Nb, P, and Ti anomalies, on mid-ocean-ridge basalt-normalized spidergrams. The composition and timing of emplacement of the porphyries are consistent with a genetic relationship with spatially related granitoids. Porphyries occur in 30% of gold mines in the Menzies–Kambalda belt. The association appears to be largely structural, since both the intrusions and the mineralizing fluids exploit zones of weaknesses, such as lithological contacts and shear zones. Porphyries have been modified to varying degrees by hydrothermal alteration, especially pervasive albitization. Textural evidence indicates that secondary albite and associated sodic amphibole formed late in the deformation history of the greenstones and were broadly contemporaneous with secondary phyllosilicate, carbonate and sulphide minerals related to gold mineralization. Recent studies in the Alleghany district of California suggest the initial rock composition may critically influence the nature of alteration associated with gold mineralization. Therefore, albitization of porphyries may be caused by the same hydrothermal fluids that deposit gold and produce potassic alteration in mafic rocks.

scholarly journals Global variation of seismic energy release with oceanic lithosphere age

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nicolás Pinzón ◽  
Carlos A. Vargas
Keyword(s):  
Cross Sections ◽  
Thermal Evolution ◽  
Seismic Energy ◽  
Oceanic Lithosphere ◽  
Physical Factors ◽  
Additional Tool ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Spreading Rates ◽  
Ocean Ridge

AbstractVariations in Mid Ocean Ridge seismicity with age provide a new tool to understand the thermal evolution of the oceanic lithosphere. The sum of seismic energy released by earthquakes during a time, and for an area, is proportional to its lithospheric age. Asthenospheric temperatures emerge on ridge centers with new crust resulting in high seismic activity; thus, the energy released sum is highest on the young lithosphere and decreases with age. We propose a general model that relates the systematic variation of seismic energy released with the lithospheric age. Our analysis evaluates the main physical factors involved in the changes of energy released sum with the oceanic lithosphere age in MOR systems of different spreading rates. These observations are substantiated based on three cross-sections of the East Pacific Rise, six sections in the Mid Atlantic Ridge, and three profiles in the Central Indian Ridge. Our global model provides an additional tool for understanding tectonic processes, including the effects of seismicity and mid-plate volcanism, and a better understanding of the thermal evolution for the young oceanic lithosphere.

Movements of thick evaporites on the flanks of a mid-ocean ridge: the central Red Sea Miocene evaporites

2020 ◽  
Author(s):  
Neil Mitchell ◽  
Wen Shi ◽  
Ay Izzeldin ◽  
Ian Stewart
Keyword(s):  
Red Sea ◽  
North Atlantic ◽  
Ocean Basin ◽  
Vertical Movements ◽  
Oceanic Spreading ◽  
Mid Ocean Ridge ◽  
History Of ◽  
Global Sea Level ◽  
Ocean Ridge ◽  
Thermal Subsidence

<p>Thick evaporites ("salt") were deposited in the South and North Atlantic, and Gulf of Mexico basins, in some parts deposited onto the flanks of nascent oceanic spreading centres.  Unfortunately, knowledge of the history of evaporite movements is complicated in such places by their inaccessibility and subsequent diapirism.  This is less of a problem in the Red Sea, a young rift basin that is transitioning to an ocean basin and where the evaporites are less affected by diapirism.  In this study, we explore the vertical movements of the evaporite surface imaged with deep seismic profiling.  The evaporites have moved towards the spreading axis of the basin during and after their deposition, which ended at the 5.3 Ma Miocene-Pliocene boundary.  We quantify the evaporite surface deflation needed to balance the volume of evaporites overflowing oceanic crust of 5.3 Ma age, thermal subsidence of the lithosphere and loss of halite through pore water diffusion, allowing for isostatic effects.  The reconstructed evaporite surface lies within the range of estimated global sea level towards the end of the Miocene.  Therefore, the evaporites appear to have filled the basin almost completely at the end of the Miocene.  Effects of shunting by terrigenous sediments and carbonates near the coast and contributions of hydrothermal salt are too small to be resolved by this reconstruction.</p>

scholarly journals 2D reactive transport simulations of mid-ocean ridge hydrothermal systems

2019 ◽  
Vol 98 ◽  
pp. 05006
Author(s):  
Donald DePaolo ◽  
Eric Sonnenthal ◽  
Nicholas Pester
Keyword(s):  
Reactive Transport ◽  
Hydrothermal Systems ◽  
Maximum Temperature ◽  
Charge Balance ◽  
Seawater Chemistry ◽  
Fluid Chemistry ◽  
Mid Ocean Ridge ◽  
Spreading Rates ◽  
Ocean Ridge ◽  
Model Fluids

Water-rock interactions in mid-ocean ridge hydrothermal systems are a critical part of Earth system evolution. Extensive insights have been developed from vent fluid chemistry and laboratory experiments, but these leave unanswered many questions about the temporal evolution and spatial structure of the hydrothermal systems that can only be addressed with reactive transport simulations. Other issues are the effects of changing spreading rates and seawater chemistry through Earth history. We are addressing this problem using the Toughreact code, starting with 2D static (no seafloor spreading) simulations of the near-axis region where most of the interaction occurs. The simulations use a dual-permeability grid to represent fractured rocks, and also have a formulation for Sr isotope exchange. Vent fluid Ca, Mg, SO4, and Na concentrations and Sr isotopes can be used as a guide to fluid chemical evolution. Initial simulations reproduce modern vent fluid chemistry even with maximum temperature only at 380°C, and suggest that fluids need not be in equilibrium with the rocks at any point in the system. Model fluids continue to evolve chemically even in the upflow zone prior to venting. The effects of different seawater chemical composition, as proposed for the Cretaceous, for example, can be captured with charge-balance models.

A new Tertiary sill complex of mid-ocean ridge basalt type NNE of the Shetland Isles: a preliminary report

1986 ◽  
Vol 77 (3) ◽  
pp. 223-230 ◽  
Author(s):  
F. G. F. Gibb ◽  
R. Kanaris-Sotiriou ◽  
R. Neves
Keyword(s):  
North Atlantic ◽  
Ridge Basalt ◽  
The North ◽  
Tectonic History ◽  
Mid Ocean Ridge ◽  
Intrusive Rocks ◽  
History Of ◽  
Geochemical Analyses ◽  
Ocean Ridge ◽  
Basalt Type

ABSTRACTBasic intrusive rocks recently encountered in wells N and NNE of the Shetland Isles are probably parts of a single large sill complex which extends for over 130 km along the edge of the Faeroe-Shetland Trough. The sills intrude thick Mesozoic sediments which almost certainly overlie continental crust but the complex also appears to underlie, and extend beyond the SE edge of, the Faeroes basaltic lava plateau. Petrographic and geochemical analyses of drill core samples recovered from some of these sills reveal that they are of mid-ocean ridge basalt (MORB) type; an observation which provides evidence regarding the plate tectonic history of this area of the North Atlantic and has major implications for the nature of the continental/oceanic crust transition.

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